Chapter 11 Cenozoic el mamey group of northern hispaniola: a sedimentary record of subduction, collisional and strike-slip events within the north America-Caribbean plate boundary zone

Chapter 11

Cenozoic E1 Mamey Group of Northern Hispaniola: A Sedimentary Record of Subduction, Collisional and Strike-Slip Events within the North America-Caribbean Plate Boundary Zone

RUURDJAN DE ZOETEN and PAUL MANN

Cretaceous and Cenozoic paleogeographic and plate tectonic reconstructions of the Greater Antilles (Hispaniola, Cuba, Jamaica, and Puerto Rico) are complicated by large-offset, Eocene? to Recent strike-slip movements between the North America and Caribbean plates. Moreover, Eocene?-Recent oblique subduction of the Bahama carbonate platform presently affects the Hispaniola region and further complicates the reconstruction of this wide and complex plate boundary zone. This paper describes a detailed sedimentological study of deformed and uplifted Eocene to Lower Pliocene sedimentary rocks (El Mamey Group) between the North America and Caribbean plates in northern Hispaniola (Dominican Republic). Paleocene to Lower Pliocene siliciclastic and carbonate rocks of the E1 Mamey Group, which crop out within a 500 km 2 area of the central Cordillera Septentrional and are well exposed in road and stream cuts, formed the object of this regional tectonic study. On the basis of its compositional, age and facies character, we divide the sedimentary succession of the E1 Mamey Group of the central Cordillera Septentrional into three lithologically distinct, stratigraphic sequences which we relate to three tectonic phases that affected this segment of the North America-Caribbean plate boundary from the Eocene to Recent. Phase 1 (Paleocene to Middle Eocene). Sedimentary and facies characteristics of an approximately 250-m-thick section of Upper Paleocene to Lower Eocene siliciclastic and carbonate rocks (Los Hidalgos ~ormation), suggest that these rocks were deposited in a deep-marine, hemipelagic environment adjacent to an active volcanic arc. Calc-alkaline volcanic flows and sills are interbedded with these deep-marine sedimentary rocks. Termination of deposition and volcanism in Early to Middle Eocene time coincides with a major folding and uplift event, which we believe was caused by the early attempted subduction of the Bahama carbonate platform beneath the arc-related basin. This event terminated arc activity in the Hispaniola volcanic arc and forearc. Phase 2 (Late Eocene to Early Miocene). Sedimentary and facies characteristics of a 4000-m-thick, Upper Eocene to Lower Miocene siliciclastic succession (Altamira and Las Lavas formations of the E1 Mamey Group) suggest that these rocks were deposited as submarine turbidites and other types of mass-flow deposits within a west-northwest-trending, elongate basin. Petrographic analysis of framework grains of sandstones within the section shows two distinct sandstone populations separated by a linear, 100-400-m-wide left-lateral strike-slip fault zone. Petrographic differences across the fault zone are especially prominent in coeval Oligocene sedimentary rocks and suggest that the two basins were juxtaposed by lateral fault movement sometime after Oligocene time. The end of deep-marine siliciclastic deposition in both basins coincides with a gentle Middle Miocene folding event believed to be related to transpressional strike-slip faulting. Phase 3 (Late Miocene to Recent). Sedimentary and facies characteristics of an approximately 250-m-thick section of Upper Miocene to Lower Pliocene carbonate rocks (Villa Trina Formation) suggest that these rocks were deposited as a shallow carbonate bank above slightly folded, Early Miocene siliciclastic rocks. Carbonate deposition was terminated in Early Pliocene time by a folding and uplift event believed to be related to transpression along a restraining bend in the Septentrional fault zone.

INTRODUCTION

Objectives The island of Hispaniola consists of a 250-kmwide tectonic collage of fault-bounded igneous,

metamorphic, and sedimentary basement blocks of Late Cretaceous to Middle Eocene age that formed in an intra-oceanic island-arc setting (cf. Bowin, 1975; Sykes et al., 1982; Mann et al., 1991, for regional reviews; Fig. 1). The basement blocks are overlain by a cover of Upper Eocene to Pliocene

Caribbean Basins. Sedimentary Basins of the World, 4 edited by E Mann (Series Editor: K.J. Hsfi), pp. 247-286. 9 1999 Elsevier Science B.V., Amsterdam. All rights reserved.

248

R. DE ZOETEN and E MANN

Fig. 1. Present-day plate structure of the Caribbean region. Direction and rates of plate motion relative to the Caribbean plate are from DeMets et al. (1990) and Dixon et al. (1998). The island of Hispaniola straddles the active left-lateral strike-slip zone separating the North America and Caribbean plates. The large amount of plate convergence and topographic uplift of Hispaniola is related to transpression between two thick crustal blocks: the Bahama carbonate platform to the north and the Cretaceous Caribbean oceanic plateau (hatched pattern) on the Caribbean plate to the south. Box shows map area shown in Fig. 2. siliciclastic and carbonate sedimentary rocks that post-date island-arc activity and mainly record the initiation of the present period of left-lateral strike-slip motion between the North America and Caribbean plates (Fig. 2). Many previous tectonically oriented studies in northern Hispaniola have focused on the composition and structure of arcrelated basement rocks in order to better understand the origin and tectonic history of the Greater Antilles island-arc system (for example, Nagle, 1979; Palmer, 1979; Pindell and Draper, 1991; Joyce, 1991; Fig. 2). Following the earlier sedimentation and tectonics study of Dolan et al. (1991), the objective of this paper is to reconstruct the depositional history of Paleocene to Lower Pliocene sedimentary rocks of the central Cordillera Septentrional that either post-date or accompany the final stages of island-arc activity in Hispaniola (Fig. 1). The method of this paper is to reconstruct the depositional history and water depth of sedimentary basins overlying arc rocks through the use of: (1) regionally correlated measured sections of continuous stratigraphic sequences; (2) integration of biostratigraphic data as a way to reconstruct sedimentary environments, determine water depths through time, and date sedimentary, tectonic, and eustatic events; (3) integration of paleocurrent and sandstone petrographic data to determine siliciclastic provenance.

Based on the same outcrops discussed in this paper, de Zoeten and Mann (1991) published a Cenozoic structural history of the area using data on major and minor faults and folds observed in the same set of outcrops as described in this paper. Dolan et al. (1991) presented a summary of some of the preliminary results of this study in their discussion of the pattern of regional basin formation during the Cenozoic in Hispaniola and Puerto Rico. Neither of the previous studies presented the primary sedimentological data collected by de Zoeten (1988) that are fundamental to many tectonic interpretations.

Significance of this study The Cordillera Septentrional is a critical area for studies of post-Middle Eocene island-arc tectonics in Hispaniola because the area straddles the Septentrional fault zone, which is presently the main strikeslip fault zone separating the North America and Caribbean plates (Mann et al., 1991, 1998) (Fig. 2). Marine studies have shown that the Septentrional fault zone continues westward as fault zones bounding the Middle Eocene to present Cayman Trough pull-apart basin (Rosencrantz et al., 1988; Calais and Mercier de L6pinay, 1995) and eastward as active fault zones along the southern edge of the Puerto Rico Trench (Grindlay et al., 1997; Dolan et al., 1998; Fig. 1). The Cordillera Septentrional provides the largest sub-

CENOZOIC EL MAMEY GROUP OF NORTHERN HISPANIOLA aerial exposure of this 3600-km-long, interplate fault system outside of Central America (Fig. 1).

249

GEOLOGIC SETTING OF THE CORDILLERA SEPTENTRIONAL Ages and distribution of rock units

TECTONIC SETTING OF THE CORDILLERA SEPTENTRIONAL Plate-scale tectonic setting

The Cordillera Septentrional ('Northern Range') forms an elongate, east-northeast-trending mountain range that rises to a maximum elevation of 1249 m (Fig. 2). The range is partially bounded by seismically active, strike-slip and reverse faults related to left-lateral displacement between the North America and Caribbean plates across Hispaniola (Mann et al., 1991, 1998; Fig. 2B). Transpression across northern Hispaniola is probably a response to highly oblique subduction of the Bahama carbonate platform (Mullins et al., 1992; Mann et al., 1995; Dolan et al., 1998) (Fig. 2A). The relation between the general shape of the unsubducted Bahama Platform and the thrust front north of Hispaniola suggests that as much as 100 km of Bahamanian crust may been subducted beneath Hispaniola (Dolan et al., 1998). Local convergence in Hispaniola may also be related to the location of the island between the Bahama carbonate platform to the north and thicker-thanaverage oceanic plateau seafloor of the Caribbean Sea to the south (Mann et al., 1995; Diebold and Driscoll, Chapter 19; Figs. 1 and 2). Island-scale tectonic setting

A regional, unbalanced cross-section modified from Mann et al. (1991) illustrates several important features about the Cenozoic structural history of Hispaniola (Fig. 2B). (1) A prominent folding and thrusting event in central Hispaniola is Late Miocene and younger in age and verges southward to southwestward. (2) Late Miocene and younger reverse and oblique-slip faulting is responsible for the present pattern of morphotectonic units in central Hispaniola, including the distribution of the three major ramp, or thrust-bound, basins the Cibao, San Juan-Azua, and Enriquillo (Mann et al., 1991; Mann et al., Chapter 12). (3) Cretaceous-Eocene island-arc terranes of the northern and central part of the island are topographically high-standing and deeply eroded; the Cretaceous oceanic plateau terrane of the southern part of the island is relatively low-standing and less deeply eroded. The lower elevation of the oceanic plateau in the south may also reflect its footwall position relative to the higher-standing hanging wall block represented by the island-arc terranes in the north (Fig. 2B).

Basement units Igneous, metamorphic, and sedimentary rocks ranging in age from Cretaceous to Early Pliocene are exposed in the Cordillera Septentrional whereas siliciclastic sedimentary rocks of Mio-Pliocene age are exposed in the adjacent, asymmetric Cibao basin (de Zoeten and Mann, 1991) (Figs. 2B and 3). The oldest, arc-related rocks of the Cordillera Septentrional occur in three basement complexes of the Cordillera Septentrional that include the Samana Peninsula (Joyce, 1991) and Rio San Juan complex to the east of the study area, and the Puerto Plata complex (Pindell and Draper, 1991) to the north of the study area (Fig. 3). Mann et al. (1991) and Mann and Gordon (1996) proposed that all three inliers may have been uplifted by late Neogene restraining bend tectonics along the Septentrional fault zone (Fig. 3). Basement rocks of the Cordillera Septentrional and the Samana Peninsula can be divided into two lithologic provinces: a blueschist-serpentinite-sedimentary complex interpreted as an outer forearctrench assemblage by previous workers (Nagle, 1979; Bowin and Nagle, 1982; Pindell and Draper, 1991; Draper and Nagle, 1991; Joyce, 1991); and a volcanic-plutonic-sedimentary complex interpreted to be a forearc assemblage (Bowin and Nagle, 1982; de Zoeten and Mann, 1991; Calais et al., 1992). Based on a compilation of data, Mann et al. (1991) have classified these two areas as tectonostratigraphic terranes originating as fragments of the forearc or accretionary prism of the arc (Fig. 2B). We follow the block terminology of the central Cordillera Septentrional that was defined by de Zoeten and Mann (1991). This scheme subdivides the basement of our study area into the Altamira block to the west and the La Toca block to the east separated by the left-lateral Rio Grande fault zone (Fig. 4C). Basement of the La Toca block in the eastern part of the study area consists of Upper Cretaceous to Eocene andesitic tuff and tonalite of the Pedro Garcfa Formation (Eberle et al., 1982; Peralta-Villar, 1985) (Fig. 4C). Basement of the Altamira block in the western part of study area consists of Upper Paleocene to Lower Eocene pelagic carbonate rocks of the Los Hidalgos Formation that are crosscut by dikes and sills of the Palma Picada intrusives (Muff and Hernandez, 1986) (Fig. 4C). The Los Hidalgos Formation correlates well with the Paleocene-Eocene E1 Cacheal tufts described by Calais et al. (1992) in the western Cordillera Septentrional.

250

R. DE ZOETEN and E MANN

CENOZOIC EL MAMEY GROUP OF NORTHERN HISPANIOLA

251

Fig. 3. Map of northern Hispaniola showing ages of exposed rocks and the four main physiographic provinces which include the Cordillera Septentrional, Samana Peninsula, Cibao Valley, and Cordillera Septentrional. The area mapped in detail for this study is boxed and lies in the central part of the Cordillera Septentrional (cf. Fig. 4 for detailed maps). Major high-angle faults include: HFZ -- Hispaniola fault zone; SFZ = Septentrional fault zone; CFZ = Camti fault zone. Labelled basement complexes of the Cordillera Septentrional are discussed in the text.

Relation of major structures to outcrop pattern of sedimentary units Younger, s e d i m e n t a r y units above these three b a s e m e n t c o m p l e x e s g e n e r a l l y dip away from the inliers or are b o u n d e d by high-angle faults (Figs. 3 and 4C are based on a 1 : 1 5 0 , 0 0 0 geologic c o m p i l a t i o n map of the Cordillera Septentrional by de Z o e t e n et al., 1991). The ages of E o c e n e through Pliocene sedimentary units in the western Cibao basin and central and eastern Cordillera Septentrional defines a large synclinal structure with the axis of the syncline a p p r o x i m a t e l y parallel to the long axis of the Cibao basin (Fig. 3). The orientation and age of this postPliocene fold is consistent with the regional pattern of n o r t h e a s t - s o u t h w e s t shortening across Hispaniola seen on the cross-section in Fig. 2B. In our study area, ages of rock units indicate two large h a l f - d o m e or anticlinal structures adjacent to the Septentrional and Rio Bajabonico fault zones (Figs. 4C and 5). Tilting related to the Paradero half-

d o m e along the Septentrional fault zone accounts for the northeast dips o b s e r v e d over m u c h of the A l t a m i r a b l o c k (Fig. 5B). F o l d i n g related to the Pedro Garcfa anticline accounts for the northeast dips observed over m u c h of the La Toca block. The A1tamira fault zone abruptly truncates fold axes developed in the central part of the study area (Fig. 5A). Well-dated, U p p e r E o c e n e to L o w e r M i o c e n e d e e p - m a r i n e siliciclastic s e d i m e n t a r y rocks of the A l t a m i r a and Las Lavas formations u n c o n f o r m a b l y overlie arc-related b a s e m e n t of the A l t a m i r a block (Fig. 4B). T h e s e two formations together consist of about 4000 m of thin- to m e d i u m - b e d d e d sandstone i n t e r b e d d e d with c o n g l o m e r a t e . About 1200 m of O l i g o c e n e to L o w e r M i o c e n e siliciclastic sedimentary rocks of the La Toca F o r m a t i o n u n c o n f o r m a b l y overlie, or are locally faulted against, igneous rocks of the Pedro Garcfa F o r m a t i o n (Fig. 5). M i d d l e M i o c e n e to L o w e r Pliocene shallowmarine l i m e s t o n e of the Villa Trina F o r m a t i o n forms

Fig. 2. (A) Map of the northeastern Caribbean plate margin modified from Dolan et al. (1998). Crystalline basement rocks represent the exhumed core of the Caribbean island-arc that became inactive in Eocene to Oligocene time in this area. Rocks of the Bahama carbonate platform on the North America plate north of Hispaniola are part of a passive margin sequence formed following the Mesozoic rifting of North and South America. Rocks of the Caribbean plate and oceanic plateau were mainly formed as part of a large oceanic plateau in Late Cretaceous time. Convergence in Hispaniola is related to the local impedance of the eastward migration of the Caribbean plate by the salient formed by the Bahama Platform. Box shows map of northern Dominican Republic in Fig. 3. Key to abbreviations: OFZ = Oriente fault zone; SDB = Santiago deformed belt; EPGFZ = Enriquillo-Plantain Garden fault zone; SFZ = Septentrional fault zone; NHDB = North Hispaniola deformed belt; PRT = Puerto Rico trench; LMOB = Los Muertos deformed belt. (B) Cross-section across Hispaniola modified from Mann et al. (1991). Convergence between the Bahama Platform and the Caribbean oceanic plateau across the island of Hispaniola has led to extreme topographic uplift and erosion of the extinct arc core and the formation of three, thrust-bound ramp basins of Neogene age: the Enriquillo, San Juan and Cibao. Abbreviations of fault zones from north to south: CFZ = Cam6 fault zone; R G F Z = Rfo Grande fault zone; SFZ = Septentrional fault zone; HFZ - Hispaniola fault zone; GFZ = Guacara fault zone; SJRFZ = San Josd-Restauraci6n fault zone; SJLPFZ San Juan-Los Pozos fault zone; EPGFZ Enriquillo-Plantain Garden fault zone; and BAGFZ = Bahoruco fault zone. See Mann et al. (1991) for detailed descriptions of faults and terranes. - -

=

252

R. DE ZOETEN and E MANN

CENOZOIC EL MAMEY GROUP OF NORTHERN HISPANIOLA the youngest sedimentary unit in the Cordillera Septentrional and is at least 250 m thick (de Zoeten and Mann, 1991; Calais et al., 1992) (Fig. 6). The limestone exhibits both conformable and unconformable contacts with the underlying siliciclastic rocks of the La Toca and Altamira formations, respectively. Dips in the Villa Trina Formation define a large, post-Early Pliocene anticline that coincides with the topographically highest part of the Cordillera Septentrional (Fig. 6A). The angular contact between the Villa Trina Formation and the underlying siliciclastic formations is generally found in the western and central Cordillera Septentrional whereas conformable or disconformable contacts are found in the eastern part of the range (Calais et al., 1992).

PREVIOUS WORK AND STRATIGRAPHIC FRAMEWORK OF THE CENTRAL CORDILLERA SEPTENTRIONAL Previous studies

The stratigraphic nomenclature developed in previous studies of the central Cordillera Septentrional is summarized in Fig. 7. Previous work by Eberle et al. (1982) and Redmond (1982) on the sedimentary rocks of the Cordillera Septentrional has been on a regional scale (1 : 100,000) with little emphasis on detailed mapping of smaller areas. Vaughan et al. (1921) published the first reconnaissance map of the Cordillera Septentrional. Their proposed stratigraphy was based mainly on work done along the southern margin of the Cibao Valley and correlated units exposed in the Cibao Valley. Oil exploration by Dohm (1943) and Beall (1943) assembled a more detailed geologic map at a scale of 1 : 100,000 and used the nomenclature of Vaughan et al. (1921). Bermudez (1949) analyzed 22 samples from the Cordillera Septentrional for planktonic foraminifera to revise formation ages established previously by Dohm (1943); (Fig. 7). Bermudez (1949) found that the oldest sedimentary rocks of the 'Abuillot Formation' (the Los Hidalgos Formation in this paper) consisted of hard, thin-bedded limestone containing Lower Eocene radiolaria and planktonic foraminifera.

253

Eberle et al. (1982) compiled a lithologic and structural map of the central and eastern Cordillera Septentrional, based on reconnaissance mapping and detailed biostratigraphic sampling of calcareous nannofossils. One formation, the E1 Mamey, was established to include all siliciclastic rocks of Eocene to Early Miocene age. The E1 Mamey Formation was divided into two, laterally equivalent 'facies': the Luperon facies north of the Cam6 fault zone, and the Altamira facies to the south (Fig. 7). Eberle et al. (1982) were also the first to recognize the intrusive rocks in the Palma Picada area south of E1 Mamey (Figs. 4C and 7). The study by Redmond (1982) focused on the sedimentology of Cenozoic sedimentary rocks of the central Cordillera Septentrional and their relation to the occurrence of amber deposits in the area. Redmond refers to these turbiditic rocks as the Altamira Formation after the town of Altamira along the SantiagoAltamira highway (Fig. 4A). A Late Eocene age was determined for the Altamira Formation based on the planktonic and benthonic foraminifera from ten samples (E. Robinson, in Redmond, 1982). Calais et al. (1992) carried out stratigraphic and structural mapping in the western Cordillera Septentrional that dated a Lower Paleocene-Eocene fine-grained section equivalent to the Los Hidalgos Formation (El Cacheal tufts) unconformably overlain by a Lower Miocene to Upper Pliocene siliciclastic section (Gran Mangle and Villa Vasquez series). Stratigraphic n o m e n c l a t u r e of this study

We propose a stratigraphic scheme shown in the far right column of Fig. 7 based on data presented in this paper. We measured over 9000 m of stratigraphic sections and integrated these with 199 biostratigraphic analyses. Of these 199 biostratigraphic analyses, 136 were done on samples collected specifically for this study (all biostratigraphic data shown on Fig. 4B are compiled in Appendix 1 of de Zoeten, 1988). Combining biostratigraphic data with detailed lithostratigraphy, we recognized that the Altamira and La Toca blocks were characterized by distinct stratigraphy and sandstone composition (de Zoeten and Mann, 1991) (Fig. 4C). These two blocks are separated by the Rfo Grande fault zone, a

Fig. 4. (A) Map of central Cordillera Septentrional showing major towns, road system and streams with outcrops that are referred to in the text of this paper. Paved roads are shown by heavy lines; unpaved, secondary roads in the mid-1980's are shown as dashed lines. (B) Map of the central Cordillera Septentrional showing the age of exposed rock units based on microfossils from 140 sample localities shown by circles. Patterns indicate ages which and are constrained by both biostratigraphy and stratigraphic relationships. Microfossils used in this compilation include calcareous nannofossils, planktonic foraminifera, and benthonic foraminifera. Appendix 1 in de Zoeten (1988) provides a list of microfossils identified from each sample site. (C) Map showing lithostratigraphy and formations of the central Cordillera Septentrional. The study area is limited to the area between the Septentrional fault zone (SFZ) and the Camfi fault zone (CFZ), and is separated into the Altamira block and the La Toca block by the Rfo Grande fault zone (RGFZ). Key to abbreviations: A F Z = Altamira fault zone; RBFZ = Rio Bajabonico fault zone; CBA = Canada Bonita anticline; LS = Llanos syncline.

254

R. D E Z O E T E N and R M A N N

Fig. 5. (A) Major structural features of the central Cordillera Septentrional modified from de Zoeten and Mann (1991). Note the en echelon arrangement of major anticline and half-domes, which are shaded in gray. Key to numbered folds: 1 = Paradero half-dome; 2 = Canada Bonita syncline; 3 = Llanos syncline; 4 = Ocampo anticline; 5 = Pedro Garcfa anticline; 6 = Sonador anticline. Lines A - A I, B - B I, and C - U indicate cross-sections shown in (B). (B) One-to-one cross-sections of the central Cordillera Septentrional. Key to rock units: KTpg = Pedro Garcfa Formation (shaded); Tlh = Los Hidalgos Formation (shaded); Tp = Palma Picada intrusive rocks (shaded); Ta = Altamira Formation; Tt = La Toca Formation; T1 = Las Lavas Formation; Tvt = Villa Trina Formation. Heavy dot pattern indicates Mio-Pliocene sedimentary rocks of the Cibao basin; wavy lines are unconformities. SFZ -- Septentrional fault zone; R G F Z = Rfo Grande fault zone; CFZ = Camti fault zone. Dip symbols represent the dip of beds measured in outcrop.

CENOZOIC EL MAMEY GROUP OF NORTHERN HISPANIOLA

255

Fig. 6. Map showing the distribution and structure of the Villa Trina Formation in the Cordillera Septentrional. The elevation of the base of the Villa Trina Formation above sea level was determined from 1:50,000 topographic maps.

Fig. 7. Comparison of stratigraphic columns for the central Cordillera Septentrional including the stratigraphy proposed on the basis of data presented in this paper. Most previous work was reconnaissance in nature. This study used systematic biostratigraphy and detailed measured sections to better establish the character and age of lithologic units and correlate them across the central part of the mountain range. 100-400-m-wide, oblique-slip shear zone (de Zoeten and Mann, 1991). The name E1 M a m e y Group was proposed by Dolan et al. (1991) and in this paper to include all the Upper Eocene to Lower Miocene sedimentary rocks in the Cordillera Septentrional. The Altamira block

comprises the Altamira and Las Lavas formations and the La Toca block comprises the La Toca and Luperon formations (Figs. 4C and 7). The Luperon Formation has been described previously by Nagle (1979), Eberle et al. (1982), and Pindell and Draper ( 1991) (Fig. 7).

256

R. DE ZOETEN and R MANN

~

r~

r~ c~

c~

o

m

.~

0

o

~ ~ . ~:~ .,~ . ~

~

~

~

.,.,

.,.,

,.~

~ ,...,

~

;>

_=~.~:~

_

~

~,

~

-~ ..~

9

~

m.o

~

9

~

:~

o ~

~ .,.-, z~

~

~

;>, r~ ,..C:~

o

o

=~ '~ =~

~

~=~

E

0

~

c~

,o

9

~;~

r,.) ~ , . - ,.~

o

=o-~

~o

:~~ ~

m

m

o

o

.~.-~..'~.~.= ~ "~ :~ ~

"~ ~

= .-

o

0

i

i

i

i

b~

b~

o

o

o

.~

o ,"~

"~ .~

.

.~=.~

=o~

~o

~.~

~

~o

.

~

~

9,-.

o

o~

.~'~

~

.,,_.

o=

.,.. ,.r

~

0"~

0

o;~

~

;~.~

~

*"

"c:~ , ' ~

.~

.~

.~-

~ . ~ .~ o~,~ ~'~ .~ ,~ ,~

~

M

..,

~,~E

~

~

.

..~ .~ .~

0

.-,

o

c:= Ei

;~,.

~

.o.~

_

o,.~

o

"~

9 m

.,..~., o

~

,..-~ r~

=,-~

~

o o

=o ~ ~" . - . ~ r~

~,

~

o,..

m

'" 0

o~

~.~

r~l

r~

~s

r~

;

.~ ~= ~"

~

~

=~.~

~

o ~,

~o'~

~a

~

o

0

o

9,-.

i=

o

.,--~

.o

~"=

r./3 ..c:~ i

i

i

;>,

9"

-

, ~ ""

o

="=

.-.=

.~

9

~E

o

= =~'~

o

~'~ o = . ~

~-

~.~ ~ " ~

=.-= o

.~-.-.-~ ~

~"

,~==

-.-

==~i==~

~ ~

O~ 0

=~

-

"~

o ~ =~ ~ ~

~

o

=~

..

" ..

_o~.~ ~..=

~

~ . ~

~,T..

,

0

0

r~

!

~

0

.~ ~ . ~ =

~o

'c~ '-'-

,

~

~~

~

=. == . . . .

0

0

,

.~

.

o ~

c~

.

~

~.~ ~r~

~ 0

.

r~ ~1

.

. ,.._

~

c~ ~

r~ ~ r ""

~

~.,

r~

~o

~

,-~

0

0

.~...,

== ~ . ~

iaa==

==

;=" " - r.~

.

r

,.

0

cn

CENOZOIC EL MAMEY GROUP OF NORTHERN HISPANIOLA Facies classification used in this study

In our stratigraphic and sedimentologic study of the Altamira, Las Lavas and La Toca formations, we used the facies classification for deep-marine siliciclastic rocks that was developed by Pickering et al. (1986). This classification, a modification of Mutti and Ricci Lucchi's (1978) lithofacies classification, facilitates facies descriptions and interpretations in the field. The Pickering et al. (1986) classification is a comprehensive and purely descriptive scheme used to subdivide lithologies into mappable facies. Four of the seven facies classes proposed by Pickering et al. (1986) were recognized in the central Cordillera Septentrional. These commonly seen facies are summarized on Fig. 8. The letter-number code shown in Fig. 8 modified from Pickering et al. (1986) is used for all measured sections and outcrop photographs presented in this paper. Biostratigraphic age determinations used in this study

Ages of stratigraphic units are based on their fossil content (Fig. 4B). Reworked older fauna, however, are an inherent problem associated with resedimented turbidite deposits characteristic of the E1 Mamey Group and so the youngest ages were picked to represent the time of deposition. Location grid used in this study

The Universal Transverse Mercator (UTM) grid location system is used throughout this paper to precisely locate outcrops discussed in the text. This grid is printed on U.S. Defense Mapping Agency 1:50,000 topographic maps which were used as basemaps for our field investigations (see Preface of Mann et al., 1991, for a key to these maps in the Dominican Republic; the grid zone is 19Q).

STRATIGRAPHY OF THE ALTAMIRABLOCK Definition of the Altamira block

The Altamira block is bounded on the north by the Cam~ fault zone (Pindell and Draper, 1991), on the east by the Rio Grande fault zone (de Zoeten and Mann, 1991), and on the south by the Septentrional fault zone (Mann et al., 1998; Fig. 5A). The basement rocks of the Altamira block comprise Upper Paleocene to Lower Eocene, sedimentary and igneous rocks of the Los Hidalgos Formation. The deep-marine siliciclastic rocks of the Altamira Formation sit unconformably over the Los Hidalgos Formation and its intrusive Palma Picada

257

rocks south of E1 Mamey (UTM 847816). The Las Lavas Formation, which conformably overlies the Altamira Formation, consists of calcareous and terrigenous, deep-marine turbidite and other mass-flow deposits. The topographically higher regions of the Altamira block are capped by Upper Miocene to Lower Pliocene, shallow-marine carbonate rocks of the Villa Trina Formation (Fig. 6). Basement of the Altamira block Los Hidalgos Formation The Los Hidalgos Formation is composed of thinly laminated to medium-bedded, dark gray, red and green recrystallized biomicrite interbedded with minor amounts of volcaniclastic calciturbidites and tuffaceous shale (argillite). The base of the Los Hidalgos Formation is not exposed, but the formation is at least 250 m thick in single outcrops. The formation is exposed in three localities in the study area: (1) in an irregular-shaped area 3-12 km south of E1 Mamey (UTM 847816); (2) on a ridge 0.4 km wide, and 5 km long just north of Altamira (UTM 096752); and (3) as a fault-bounded sliver within the Rio Grande fault zone about 3 km north of Santiago (UTM 299594; Fig. 4C). Based on its outcrop distribution at these three localities, the Los Hidalgos Formation appears to underlie most of the Altamira block. Thin parallel laminae in the recrystallized biomicrites are laterally continuous, but locally bioturbated by Skolithos and Planolites. Laminated limestones contain matrix-supported, silt-sized, angular plagioclase grains and ellipsoidal silt-sized grains, interpreted to be calcified radiolarians or recrystallized planktonic globigerinid foraminifera. Acarinina and Morozovella spp. have been identified in thin-sections (E. Robinson, pers. commun., 1988) suggesting that the rocks range in age from Late Paleocene through Early Eocene and that they were deposited in bathyal to abyssal water depths (1506000 m; cf. Appendix 1 of de Zoeten, 1988). These rocks contain stylolites which are crosscut by complex micro- to mesoscopic calcite veins. The structure of the Los Hidalgos Formation is described in more detail by de Zoeten and Mann (1991) and Calais et al. (1992). Thin- to medium-bedded calciturbidites (1-30 cm) with partial Bouma sequences (Tad, Tae) are interbedded with the laminated limestone unit. The coarser fraction consists of poorly graded, fine- to medium-grained plagioclase crystals, volcanic rock fragments and bioclasts. An abrupt grain-size change occurs between the basal sand unit and the overlying recrystallized limestone, which composes the pelagic division (Te) of the sand bed. The limestone unit is commonly bioturbated.

258 Thin parallel laminae and abundant planktonic fossils in the Los Hidalgos Formation indicate slow deposition from suspension in a deep-marine environment. Pelagic to hemipelagic accumulation in the basin was periodically interrupted by low-density turbidity flows or other mass-flow processes introducing the coarser clastic material of the Ta turbidite intervals.

Palma Picada intrusive rocks Porphyritic rocks of the Palma Picada Formation intrude the Los Hidalgos Formation sedimentary rocks near Palma Picada (UTM 922778) (Fig. 4C). These compositionally diverse, porphyritic rocks consist of a series of vertical dikes and horizontal sills, which are approximately 250 m thick (Eberle et al., 1982; Muff and Hernandez, 1986). Stratigraphy of the Altamira Formation Outcrop distribution and general stratigraphy The Altamira Formation extends over a 200 km 2 area from the Rfo Grande fault zone to a poorly defined western limit near E1 Mamey (Fig. 4C). The Altamira Formation consists of thin- to medium-bedded sandstone and siltstone couplets, with minor interbedded conglomerate and thick-bedded sandstone. The Altamira Formation is divided into two members: (1) a 50-m-thick basal conglomerate, the Ranchete Member, which makes up a minor part of the total thickness of the Altamira Formation, and lies unconformably above rocks of the Los Hidalgos Formation, and the Palma Picada intrusions (UTM 906815; Fig. 4C); and (2) the Canada Bonita Member, an approximately 2500-m-thick section of alternating sandstone and siltstone with interbedded conglomerate; this member composes most of the thickness of the Altamira Formation (Fig. 4C). The Ranchete Member of the Altamira Formation is named here after the village of Ranchete, which is located 3.5 km southwest of E1 Mamey (UTM 838824; Fig. 4A). In this area, the Ranchete Member is exposed as a thin (<130-m-wide), 3.5-km-long belt rimming the northern margin of the Los Hidalgos Formation (Fig. 4C). Sedimentary rocks of the Altamira Formation overlie the basal conglomerate of the Ranchete Member in an arcuate belt stretching 40 km across the center of the study area (Fig. 4C). This unit is here named the Canada Bonita Member of the A1tamira Formation, after the village of Canada Bonita, 7 km north of Navarette (UTM 064703; Fig. 4A). The Canada Bonita Member is composed of 80% very thin- to medium-bedded, sandstone and siltstone couplets (facies types: C2.2, C2.3, D2.2), 15% conglomerate (AI.1, A2.1), and 5% thick-bedded sandstone (B2.1, C2.1).

R. DE ZOETEN and E MANN Sandstone and siltstone of the Canada Bonita Member are blue-gray, calcite-cemented, feldspathic litharenite, which weathers to an orange-tan color. The Bouma facies Tde of the sandstone and siltstone couplet of the Altamira Formation typically lack mud-sized particles. These upper divisions consist predominantly of coarse- to fine-grained silt with only minor clay. Clasts in conglomerates of the Canada Bonita Member range in size from granules to boulders, but most commonly range in size from pebbles to cobbles. The clasts are equidimensional or oblate in shape, and subrounded to well rounded. In general, clasts are composed of: (1) recrystallized limestone (~60%), including biomicrite, dark-gray, green, and banded argillite, and carbonaceous silt derived from the underlying Los Hidalgos Formation; (2) plutonic porphyries (~20%); (3) bioclastic limestone (~10%); and (4) sandstone and volcanic fragments (,-10%). The conglomerate matrix is a gray to light brown, fossiliferous volcaniclastic sand.

Age and paleobathymetry Biostratigraphic analysis on 37 samples indicates that the Altamira Formation ranges in age from Middle or Late Eocene to Late Oligocene (Fig. 4B). Ten samples from the lower part of the Altamira Formation exposed near E1 Mamey have been well dated as Middle to Late Eocene using calcareous nannofossils and foraminifera (Appendix 1 in de Zoeten, 1988). These dates constrain the upper age limit of the underlying Ranchete Member as Late Eocene. The lower age limit of the Ranchete Member is constrained by the Early Eocene age of the underlying Los Hidalgos Formation. Several samples from the Canada Bonita Member collected along the Santiago-Puerto Plata highway suggest Late Eocene ages (Appendix 1 in de Zoeten, 1988) (Fig. 4C). However, Bourgois et al. (1982, 1983) and S. Monechi (pers. commun., 1988) determined that three samples from beds stratigraphically below the Upper Eocene sample localities contain distinct Oligocene faunas (Appendix 1 in de Zoeten, 1988). No northwest-striking faults separating the sample localities along the Santiago-Puerto Plata highway were recognized (de Zoeten and Mann, 1991) (Fig. 4C). This suggests that Upper Eocene calcareous nannofossils are reworked and that deposition of the Altamira Formation continued into Late Oligocene time as we show on Fig. 7. Paleoenvironmental studies on the benthonic foraminiferal assemblage indicate upper bathyal water depths (150500 m). Measured sections of the Altamira Formation Seven sections were measured from west to east to better characterize rapid lateral facies changes

259

CENOZOIC EL M A M E Y GROUP OF NORTHERN HISPANIOLA

Plata highway (Fig. 11, inset map). The rocks are gently folded into an anticline-syncline pair whose structure is described in detail by de Zoeten and Mann (1991). These measured sections all describe variations within a 1000-1500-m-thick section of lateral equivalent rocks of the upper Canada Bonita Member of the Altamira Formation (Fig. 7). The Calabaza measured section is separated from the Northern Canada Bonita and Southern Canada Bonita sections by the north-south striking Altamira fault zone (Eberle et al., 1982; Figs. 4C and 5). Despite the structural complexity related to folding and the presence of the Altamira fault zone, there are many similarities between all five sections near the Santiago-Puerto Plata highway that allow the various sections to be correlated. For example, all three section are overlain by the basal conglomerate

within the Altamira Formation. The measured sections are divided into three sets based on geographic location and similar facies patterns. From west to east, the three sets are: (1) E1 Mamey and Guananico, (2) Southern Canada Bonita, Northern Canada Bonita, and Calabaza, and (3) Rio Perez and Llanos syncline (Fig. 4A). The basal conglomerate of the Ranchete Member was only measured in the westernmost E1Mamey section (Fig. 9, inset map; Fig. 10). The Guananico section lies 10 km to the west of Altamira and lies along strike of the E1Mamey section (Fig. 9, inset map). The Guananico and E1 Mamey sections are dominated by a repetitive series of thin- to medium-bedded sandstones and siltstones (C2.2, C2.3, D2.2 facies). Five sections of the Altamira Formation were measured along or adjacent to the Santiago-Puerto A. El M a m e y section" Altamira Fm.

B. Guananico section: Altamira Fm.

90C C2.1

m

TOP

r,, !

2 - 2.3

400

400

\ )2.1 \

r \

3 \

80C

\ \

300

'

l

\

\

r~

\ \ \

\

A1.1 OffsettoB

)G

\

\

\

\ 600

- 2.3 / 1~2.2

(~ F - G \ 600 B2.1 / C2.1 \

TOP

t

\\

u. Eoc

\

\m

1u Eoc \\\

100 ~A~ ~

\

soo

..... ', ~ Breccia (Fig. 10) 1 LOS tt=calg(s IJ~ U P a l l Eoc ForlTl(tion 0 ~ l i " ~ F " "" (Eocene) III .... Grain Size I I Gravel =~o,IMed. Sand

groove cast ripplemark

Mio Miocene Olig Oligocene Eoc Eocene

\

C2..2 2387

\ \ I

)G

C 2 . 2 - 2 . 3 ! D2.2

500t

C2.3

~-"- F

BASE I Gravel Med. Sand

Silt G R

\

100

~ooo

\

A22

' - 2.3 / D2.2

\

200

\

,2..2-2.3 \

700

\

\ \

, ~

\

300

\ 700

200

\ \

~2 2-'23/D22 \

=E,

\

~t

\

800

\

Silt F C

flute cast a-axis clast orientation

u m I

upper middle lower

Very thin to med. bedded Med. to very thick bedded 13;El Covered interval

" - ~

Stratigraphyinferred Fault Facies type

A2.1 2387 Sandstone sample (~ Paleocurrent direction

I

Offset in El Mamey "measured section

IE'MameY]--//~ I

41 J l l " / / " f =

~

0 5 km I

''

I

Guananico]

I ~,Mamo,sec,~on iJ "~ I II Guananico[ ~

I~Y:;," ~

se='~ I

%~

I

- Map trace of measured section

Fig. 9. Measured sections from the E1 Mamey (A) and Guananico (B) localities (cf. inset map for location of sections). The sections summarize facies types, paleocurrent indicators, biostratigraphic samples with age determinations, and sandstone sample localities used for point-count analyses. See Fig. 8 for explanation of letter-number codes of facies types. Note along-strike offset in the E1 Mamey section at 120 m above the base.

260

R. DE ZOETEN and E MANN

Fig. 10. Normally graded, sedimentary breccias from the Middle(?) to Late Eocene Ranchete Member of the Altamira Formation (location of photograph shown on section in Fig. 9). Clasts are composed of grey, recrystallized biomicrites of the underlying Upper Paleocene to Lower Eocene Los Hidalgos Formation. Outcrop is exposed in roadcut just south of Los Hidalgos Pass (UTM 847816). Jacob's staff is divided into 0.5 m increments. Dip to northeast. Color version at http://www.elsevier.nl/locate/caribas/

of the Las Lavas Formation and all three sections consist predominantly of thin- to medium-bedded sandstone and siltstone (C2.2, C2.3, D2.2) and associated conglomerate (AI.1, A2.1). The Calabaza section consists of a higher percentage of conglomerate (~50%) than the Northern Canada Bonita and Southern Canada Bonita sections (12%). The Rfo Perez and Llanos syncline sections are south and southwest of Altamira (Fig. 11, inset map). These sections consist of thick-bedded sandstonesiltstone couplets (B2.1, C2.1 facies), conglomerates (AI.1, A2.1 facies) and thin- to medium-bedded sandstones and siltstones (C2.2, C2.3, D2.2 facies). El Mamey and Guananico measured sections of the Altamira Formation Ranchete Member of the Altamira Formation The E1Mamey section is a composite section based on two traverses (Fig. 9, inset map). The basal 54 m of the section forms the type section of the Ranchete Member, which is exposed along the road near Los Hidalgos Pass (UTM 846817) (Fig. 4A). The overlying section was measured in the Arroyo Berraco Blanco stratigraphic section (UTM 927844; Fig. 4A). The contact between the Ranchete Member and the underlying Los Hidalgos Formation is unconformable, although we found that this contact is locally modified by faulting at two localities (UTM 846817; 871825). The lower part of the Ranchete Member consists of a massive, tightly packed sed-

imentary breccia (AI.1), which is approximately 15 m thick. The breccia grades into thick-bedded, coarse-tail graded conglomerates (A2.3; Fig. 10) and is capped by medium-bedded, parallel-stratified conglomerates (A2.1). Clast rounding increases upward in the section from angular in the A2.3 facies to subrounded clasts in the A2.1 facies. Gravel to cobble size, angular clasts near the base of the Ranchete Member are composed entirely of gray and dark gray, recrystallized limestone, which reflect the lithology of the underlying basement rocks of the Los Hidalgos Formation (Fig. 10). The percentage of recrystallized limestone clasts decreases upward in the section at the expense of marly packstone clasts composed mainly of red algae and larger reefal foraminifera. Lepidocyclina foraminifera in the packstone clasts suggest that they formed in a backreef environment (E. Robinson, Appendix 1 in de Zoeten, 1988). Laterally equivalent conglomerate to the northwest (UTM 906815) contain up to 50% dark purple porphyry clasts of the Palma Picada intrusions. This conglomerate also exhibits an upsection increase in shallow-water carbonate clasts. Canada Bonita Member of the Altamira Formation The overlying Canada Bonita Member in the E1 Mamey and Guananico sections consists mostly of thin- to medium-bedded, alternating sandstones and siltstones, which are mostly facies D2.2, D 1.2, C2.3, with minor C2.2 (Fig. 12). These facies are interbed-

CENOZOIC EL M A M E Y GROUP OF NORTHERN HISPANIOLA

261 O

,.~

O

""'~

O

O

o.~

O

O

.,,~

,,,.o

or,.)

E~

O O

rs~

.,.-~

O,, ~

~Z O ~

~

9

o

-~ r,..) ~

~< 0

~Zo

=~ ~

~,~ .~,.~

NN~

o ~c~

~

~ o

-~

,.~

" ~

~

r~

~ g.~

262

R. DE ZOETEN and R M A N N

9

r,.)

9 .,,,.

9

O

~,,,,~ 9 9

.=. 9

.< 9

N

r,.) .~

~ .,,a

r,,) ~: O

(D

Z

O

<~

r,.)

~

O

,x::

CENOZOIC EL MAMEY GROUP OF NORTHERN HISPANIOLA ded with minor, thick-bedded sandstone and siltstone couplets (C2.1). Conglomeratic facies (AI.1, A2.3) are rare, and mostly found near the base of the Canada Member. Thin-bedded sandstone and siltstone couplets of the Canada Bonita Member have a sand/silt ratio greater than 1 : 1, are tabular, laterally continuous for at least 10 m, exhibit sharp basal contacts, and are overlain by medium- to coarse-grained, structureless or poorly graded sand (Tbd, Tabd). Thin parallel laminae are very common throughout the lower division of beds. These laminae are defined by 0.5-4 mm biogenic carbonate grains composed mostly of red algae and benthonic foraminifera. The silty upper division of C2.2 and C2.3 sandstone and siltstone couplets contain isolated stringers of medium to coarse sand, are locally parallel-laminated, and are commonly bioturbated by Skolithos, Planolites, and Glockeria. The thick-bedded sandstones of the Canada Bonita Member have sand/silt ratios greater than 1:1 and exhibit erosional basal contacts with local load and groove casts. The lower division of beds are massive or coarse-tail graded and capped by parallel laminae which are defined by concentrations of coarser-grained carbonate material (Tbd, Tabd). Siltstones are commonly thin (3-10 cm), mud-poor, parallel-laminated, and occasionally show bioturbation by Skolithos and Glockeria. Beds are tabular and exhibit good lateral continuity at the outcrop scale. No vertical cycles were recognized in the Canada Bonita Member, except for rare, thin (1-3 m) thickening-upward cycles within rhythmically bedded, thin, sand-silt couplets (Fig. 12). Two 2-7-m-thick, thinning-upward intervals of C2.1-C2.3 facies are found 450 and 470 m above the base of the Guananico section (Fig. 9). Both intervals are composed of lithic-rich calcarenites (Tabd). These inferrals include the only calciturbidites found in the Altamira Formation. Their lateral extent or geometry could not be determined. Twenty-eight groove casts measured from the bottom of medium- to thick-bedded sandstones indicate a northwest to southeast (110 ~ mean paleocurrent trend. In the Guananico section, eight unimodal flute casts indicated paleoflow to the southeast (Fig. 9). Northern and Southern Canada Bonita measured sections of the Altamira Formation Canada Bonita Member of the Altamira Formation The Northern and Southern Canada Bonita sections consist mostly of very thin- to medium-bedded sandstone and siltstone couplets (C2.2, C2.3, D2.2), interbedded with minor conglomeratic facies (AI.1, A2.1), and thick-bedded sandstones (C2.1) (Fig. 12A,B). At the base of the Southern Canada Bonita

263

section to the south of the anticlinal axis (Canada Bonita anticline) (Fig. 11, inset), a conglomeratic sequence 40 m thick displays two depositional units. The base of the upper conglomerate unit is scoured at least 1 m into the underlying conglomerate (Fig. 13A). Both conglomerate units grade upwards from predominantly pebble to boulder, clastsupported disorganized conglomerates (AI.1 facies) (Fig. 14A), to pebble to cobble, poorly stratified conglomerate (A2.1, A2.5 facies) (Fig. 14B). Although poorly stratified conglomerate appears massive, the preferred orientation of the a-axis of conglomerate clasts parallel to bedding produces a stratified appearance in the conglomerate (Fig. 14B). Smaller conglomerate bodies (A 1.1, A2.1) form 2-5-m-thick concave-down channel structures within alternating thin-bedded sandstones and siltstones (630 m from the base of the Northern Canada Bonita section, and 170 m from the base af the Southern Canada Bonita section) (Fig. 12A). The lower part of the Northern Canada Bonita section (Fig. 12B) is dominated by thin- to medium-bedded sandstone and siltstone couplets (C2.2, C2.3, D2.2). These couplets have a 1:3 sand/silt ratio. Basal sands are medium- to very coarse-grained and massive to thinly laminated. Basal sands occasionally exhibit normal, inverse, and coarse-tail grading (Tdb). A sharp contact divides the upper and lower divisions of couplets. The upper division of most couplets are silt-rich, but increasing clay-sized fraction causes the beds to be transitional into the D2.2 and D1.2 facies. The siltstone contains parallel laminations, commonly bioturbated by Skolithos and Planulites, and contains lignite fragments with a-axes ranging from 0.5 to 10 cm. The a-axis of lignite fragments are oriented parallel to laminations. In the Td intervals, coarse-grained sand stringers and lenses are oriented parallel to bedding. Locally, outsized carbonate blocks with longest axes ranging from 25 to 160 cm are found isolated in the thin- to medium-bedded couplets (410 and 585 m from the base of the Northern Canada Bonita section, 225 m from the base of the Southern Canada Bonita section). In general, conglomerate displays thinning- and fining-up cycles with increasing internal organization of clasts (Fig. 13A). Thinning- and fining-up cycles are poorly expressed in the thin- to medium-bedded sandstone and siltstone couplets (C2.2, C2.3, D2.2), which range in thickness from 5 to 300 m. Thirty-three paleocurrent indicators were measured using sole marks, tipple marks, and orientation of a-axes of conglomerate clasts. At least fifteen measurements of the a-axes of conglomerate clasts were averaged to a mean direction, which is shown on the section in Fig. 12. The orientations of bimodal paleocurrent measurements were scattered, but generally show either N-S or NNW-SSE bidirectional

264

R. DE ZOETEN and E MANN

Fig. 13. (A) Drawing from photographs of conglomerate exposed in a roadcut along the Santiago-Puerto Plata highway (UTM 062706). Outcrop consists of two vertically stacked, fining-upwards conglomerate bodies within the Upper Oligocene Canada Bonita Member. This outcrop occurs 60 m above the base of the Southern Canada Bonita measured section shown in Fig. 12A. Letter-number codes indicate facies types of Pickering et al. (1986) (see Fig. 8 for explanation). Location of photograph shown in Fig. 14A is indicated by box. (B) Drawing from photographs of a poorly stratified conglomerate (A2.1) which forms the basal unit of the E1 Limon Member of the Las Lavas Formation and crops out in a roadcut along the Santiago-Puerto Plata highway (UTM 072690). Note the sharp contact with thinly bedded sandstones and siltstones (C2.3). paleoflow. Three unimodal measurements indicate paleocurrent flow both to the south and north.

Calabaza measured section of the Altamira Formation Canada Bonita Member of the Altamira Formation The base of the section starts at a 350-mthick, faulted conglomerate ridge (AI.1, A2.1) and is capped by a 400-m-thick section of thinto medium-bedded sandstone and siltstone couplets (Fig. 12C). This conglomerate is predominantly massive, disorganized, clast-supported, and decreases in thickness upward in the section. The few basal contacts observed are erosive. Thin- to medium-bedded sandstone and siltstone (C2.1, C2.2, D2.2) is tabular and laterally continuous for 5 m or more. These beds consist of silt to coarse-grained sand, and exhibit a graded or structureless lower division and an upper division characterized by parallel laminae (Tabd, Tbd). Rare

30-90-cm-thick beds (C2.1) are interbedded with the thin- to medium-bedded sand and silt couplets. These thicker beds are graded, and commonly contain groove marks (Tabd). The Calabaza section shows a distinct 1400 m thinning- and fining-up cycle, in which conglomerate decreases in thickness and abundance upward (Fig. 12C). Only one 10-m-thick thinning- and fining-up cycle was recognized. Eleven bidirectional paleocurrent indicators suggest northeast-southwest (70 ~ paleoflow (Fig. 12C). Well-preserved flute casts measured within 10 m of the base of the Las Lavas Formation indicate a paleoflow towards the northwest (285~

Rio Perez measured section of the Altamira Formation Canada Bonita Member of the Altamira Formation The R/o Perez section (Fig. l lA) is laterally equivalent to the Northern Canada Bonita, Southern

CENOZOIC EL MAMEY GROUP OF NORTHERN HISPANIOLA

265

Fig. 14. (A) Disorganized, clast-supported conglomerate (type A I.1) observed in the Upper Oligocene Canada Bonita Member. Location of photo is shown in drawing of Fig. 13A. Bar scale on card is 15 cm long. (B) Poorly stratified, clast-supported conglomerate of the Upper Oligocene Canada Bonita Member. Note absence of stratal boundaries and well-developed, parallel orientation of oblate clasts. Bar scale on card is 15 cm long. Color version at http://www.elsevier.nl/locate/caribas/ Canada Bonita, and Calabaza sections (Fig. 12). It is composed of 60% alternating, thin- to medium-bedded sandstone and siltstone (C2.2, C2.2, D2.2), 20% thick-bedded sandstone and siltstone couplets (B2.1, C2.1), and 20% conglomeratic facies (AI.1, A2.1). Characteristics of the thin- to medium-bedded facies are identical to those described for the Northern Canada Bonita and Southern Canada Bonita sections. Thick-bedded sandstones (B2.1, C2.1) are tabular and laterally continuous over distances of 10 m

and have a sandstone to siltstone ratio much greater than 1:1 (average 4 : 1 ) (Fig. l l A ) . Bouma intervals include Tbd and Tabd. The lower Ta intervals are medium- to coarse-grained, massive, coarsetail graded, or amalgamated. Tb intervals are very common. Higher concentrations of red algae, larger reefal foraminifera, and plant fragments define parallel laminae and rare cross-bedding. The overlying siltstone of the Td interval also contains abundant plant and lignite debris. The siltstone is parallel-lam-

266 inated, bioturbated, and rarely exhibit ripple marks. Conglomerate of the Rio Perez section consist of massive, clast-supported, disorganized facies (AI.1), and thick-bedded, clast-supported, stratified and poorly graded facies (A2.1, A2.3) (Fig. l lA). Conglomerate horizons range in thickness from 1 to 50 m. Basal contacts are scoured. Lateral geometry is difficult to discern on outcrop scale, but some smaller-scale beds are discontinuous over distances of 5-20 m and exhibit convex-downward channel cross-sections (e.g., 80 m from the base of Rio Perez section; Fig. 11). A total of 32 groove marks and flute clasts were measured from the bottom of C2.1 sandstone beds in the Rio Perez section (Fig. l lA). Twenty-five bidirectional measurements indicate a northwestsoutheast (~120 ~ paleocurrent trend, and seven unimodal current indicators suggest flow to the southeast. There are five coarsening- and thickening-upward sequences (5-20 m thick) capped by conglomerates (A1.1, A2.1). This coarsening- and thickening-upwards trend appears to reverse to a fining- and thinning-upwards trend toward the top of the section (400 m from the base), where beds define three, 10-50-m-thick, thinning- and fining-up cycles. Llanos syncline measured section of the Altamira Formation Canada Bonita Member of the Altamira Formation The Llanos syncline section is composed of about 70% thick-bedded sandstone and siltstone couplets (C2.1, B2.1), 25% thin- and medium-bedded facies (C2.2, C2.3, D2.2) and 5% conglomeratic facies (AI.1, A2.1) (Fig. llB). The basal contact of the Canada Bonita Member with the Los Hidalgos Formation is obscured by vegetation. Thick-bedded sandstone is predominantly C2.1 facies type, tabular-shaped, and laterally continuous. However, a few sandstone beds form discontinuous, broad convex-down channels (450 m above the base of the section). Although facies assemblages are quite different between the Llanos syncline and the Rio Perez sections, individual facies characteristics are similar. In the Llanos syncline section alternating sandstone and siltstone beds (B2.1, C2.1, C2.2, C2.3) form packages of 3-20-m-thick, thickening- and coarsening-upwards cycles. These cycles are rarely capped by conglomerate-filled (AI.1), concave-down scours which range from 1 to 5 m in thickness (Fig. 11B). B imodal paleocurrent indicators, based on 27 groove casts, suggest an east-west to northwestsoutheast (90-120 ~ flow direction (Fig. l lB). Unimodal measurements from flute casts and tipple marks indicate that the paleocurrents flowed towards the southeast (135~

R. DE ZOETEN and R MANN Facies analysis of the Altamira Formation Facies of the Ranchete Member The basal Ranchete Member breccia suggests local erosion and limited transport of the underlying Los Hidalgos Formation (Fig. 9A). The lithologically homogeneous, angular clasts suggest that the breccia was deposited as a rock fall (Fig. 10). It is unclear if the rockfall was subaerial or submarine. The graded nature of the overlying A2.3 conglomerates indicates a transition from a disorganized deposition to a more organized deposition from submarine, high-concentration turbidity or other mass-flow currents (Fig. 9A). The upward increase in clast rounding may reflect increased grain-to-grain contacts during transport or increasing distance from source area, or a combination of both factors. Facies of the Canada Bonita Member Several sedimentary features displayed by rocks of the Canada Bonita Member rocks support Redmond's (1982) interpretation that these rocks are deep-marine turbidity deposits. These features include graded beds, poor to well developed Bouma sequences (Taba, Tba), bathyal depths based on benthic foraminifera (Appendix 1 in de Zoeten, 1988), and lateral and vertical facies relationships. The absence of organization and the very coarse nature of A1.1 and A2.1 conglomerate horizons indicates rapid deposition from high-concentration turbidity currents or debris flows; AI.1 facies suggests rapid sedimentation by frictional freezing processes, and A2.1 facies implies deposition from traction bedload processes (Picketing et al., 1986). Smaller, convex-down conglomerate beds (1-7 m thick; A I.1, A2.1) suggest that the coarsest-grained material moved as channelized flows. Internal stratal features of thick-bedded sandstone (B2.1, C2.1 facies) suggest deposition from high-concentration turbidity currents. The B2.1 sandstone facies indicate more rapid deposition than the C2.1 sandstones (Pickering et al., 1986). Deposition of the repetitive, thin- to medium-bedded sandstones and siltstones resulted from low-concentration turbidity currents. The predominance of parallel-laminated and the structureless lower division of these beds suggests rapid deposition from high-velocity flows. Three distinct facies assemblages are recognized in the Canada Bonita Member of the Altamira Formation. The first is characterized by conglomerates (AI.1, A2.1) interbedded with alternating thin- to medium-bedded sandstone and siltstone (C2.2, C2.3, D2.2) found in the Northern Canada Bonita, Southern Canada Bonita, and Calabaza sections (Fig. 12). Facies D2.2, C2.3, and C2.2 appear to be organized into a few poorly developed, thinning- and

CENOZOIC EL MAMEY GROUP OF NORTHERN HISPANIOLA fining-upward sequences, which are about 100 m thick. Individual conglomeratic units average about 5 m in thickness and exhibit greater internal organization and fining-upwards trends. We infer that the thin-bedded sandstone and siltstone turbidite couplets represent channel/overbank or interchannel deposits (Mutti and Normark, 1987). In this interpretation, the conglomerate-filled channels serve as conduits for sediment transport from the slope. The coarse nature of the overbank sediment and channel deposits requires either very competent flows or a nearby source. The Rio Perez and the Llanos syncline sections (Fig. 11) illustrate the second major facies assemblage in the Canada Bonita Member, which consists of coarsening- and thickening-up packages of tabular-shaped, thick-bedded sand (B2.1, C2.1). This facies assemblage is interpreted as representing prograding depositional lobes in a submarine fan system (Mutti and Normark, 1987). Channel-fill conglomerates capping the coarsening- and thickening-up packages suggest that lobes were prograding (Shanmugan and Moiola, 1988). Fan lobe progradation is further supported by the reversal in vertical cycles at the top of the Rio Perez section, which suggests a transition from lobe facies assemblage to more proximal channel/overbank deposits (Fig. 11). The final facies assemblage consists chiefly of thin- to medium-bedded, sandstone and siltstone couplets (C2.2, C2.3, D2.2) which characterize the E1 Mamey and Guananico sections. Lithologically and sedimentologically these deposits resemble the overbank deposits described in the first facies assemblage, although the absence of conglomerates or thick-bedded sandstone beds argues against a direct correlation. These rocks are more likely basinal deposits at the distal regions of the fan or distal interchannel deposits. Sedimentary rocks of the Las Lavas Formation Outcrop distribution and general stratigraphy of the Las Lavas Formation The Las Lavas Formation crops out over 800 km 2 in the Cordillera Septentrional in a belt extending from Monte Cristi in the west to northeast of Santiago (Figs. 3, 4C). This study focused on the best-exposed sections along the south-central flank of the Cordillera Septentrional. Approximately 450 m of section is exposed in isolated outcrops along the Santiago-Puerto Plata highway, and more than 1600 m is exposed in the type section along the Arroyo Las Lavas (UTM 087645) (Fig. 4A). The Las Lavas Formation consists of lithic and carbonate conglomerate, lithic-rich calcarenite and thin- to medium-bedded sandstone and siltstone couplets. The Las Lavas Formation is divided into two

267

members: the E1 Limon and the overlying La Pocilguita Member (Fig. 7). The E1 Limon Member forms a resistant hogback which strikes 110~ for approximately 6 km. The ridge-forming E1 Limon Member is offset by north-south striking faults (Fig. 4C). The type section is found in the Arroyo Las Lavas near the village of E1 Limon (UTM 094689), 7 km to the northeast of Navarette (Fig. 4A). The E1 Limon Member disconformably overlies the Altamira Formation near the village of E1 Limon (UTM 097688) (Fig. 4A). The E1 Limon Member is approximately 260 m thick and consists of a basal conglomerate (A1.1, A2.1 facies comprising 40% of the members), thin- to medium-bedded couplets (C2.2, C2.3, D facies comprising 30% of the members), capped by interbedded lithic-rich calcarenites (AI.1, A2.3, C2.1, C2.2 facies comprising 30% of the members). The La Pocilguita Member conformably overlies the E1 Limon Member and is named after the village La Pocilguita del Limon, 1 km south of E1 Limon (UTM 088678) (Fig. 4A). The La Pocilguita Member is 1300 m thick with more than half the section consisting of alternating thin- to medium-bedded siliciclastic sandstone and siltstone (C2.2, C2.3, D facies) and the remainder consisting of lithic-rich calcarenite (AI.1, A2.3, A2.7, C2.1, C2.2 facies) and minor lithic conglomerate (A1.1). West-northwest striking shear zones increase in number southward in the Las Lavas Formation toward the Septentrional fault zone (de Zoeten and Mann, 1991). The regional effect on these shear zones on the stratigraphy of the Las Lavas Formation appears minor, because biostratigraphic dating is consistent with southward younging in the southdipping section (Fig. 4B). Age and paleobathymetry of the Las Lavas Formation Biostratigraphic analysis of four samples indicate that deposition of the E1 Limon Member occurred during Late Oligocene time (Appendix 1, in de Zoeten, 1988). Fourteen samples from the La Pocilguita Member indicate a Late Oligocene to Early Miocene age (Appendix 1, in de Zoeten, 1988). Very few depth-distinctive benthic foraminifera were recognized. One sample suggests deposition at bathyal depths. Measured sections of the Las Lavas Formation Three sections were measured from the Las Lavas Formation. From west to east, these sections include the Navarette, Las Lavas, and Rio Jacagua (Fig. 15). The Navarette section was measured along the Santiago-Puerto Plata highway south of the Southern Canada Bonita section (Fig. 11). The Las Lavas measured section is the type section for the Las Lavas Formation (Fig. 15A). The Las Lavas sec-

268

R. DE ZOETEN and E MANN

A:Z ~9

o . O,...,

o~ r.gZ

g~

Z

o~

,..z.

z~0~ r

,.q

o

..~

~

o

9

,.tzZ

,x:Z

9 ,.,,~

O

CENOZOIC EL MAMEY GROUP OF NORTHERN HISPANIOLA

269

Fig. 16. Measured section of the Lower Oligocene to Lower Miocene La Toca Formation. Inset map shows location of the measured section near Pedro Garcfa and location of the three along-strike offsets in this composite section (A, B, C). Also shown is the location of the Rfo Jacagua measured section that appears in Fig. 15C.

tion overlies the Calabaza section measured of the Altamira Formation in the Arroyo Las Lavas (Fig. 11, inset map). The Rfo Jacagua section is bounded on the north by the Rio Grande fault zone and on the south by the Septentrional fault zone (Fig. 16, inset map).

Las Lavas measured section: type locality of the Las Lavas Formation El Limon Member of the Las Lavas Formation The basal conglomerate of the E1 Limon M e m b e r exposed in Arroyo Las Lavas thickens westwardly

270 from 50 to at least 150 m before being truncated by the north-south striking Altamira fault zone (Fig. 4C). The contact between the basal conglomerate and the underlying Altamira Formation is inferred to be an erosional disconformity based on lateral alongstrike variations in thickness and distinct lithologic differences across the conglomerate. The conglomerate is massive to thick-bedded (Fig. 15A). Conglomerate beds of the E1 Limon Member are disorganized, clast-supported (AI.1), with some A2.3 beds showing marked scouting and poor grading, and some A2.1 beds showing tangential cross-stratification. Conglomerate clasts in the E1 Limon Member range in size from pebbles to cobbles. Clasts are equidimensional or oblate, subrounded to well rounded, and have a poorly defined a-axis orientation. Near E1 Limon (UTM 094689), clasts are composed predominantly of recrystallized limestone (>60%) (which include gray, black, green, and banded argillite derived from the Los Hidalgos Formation) and minor amounts of volcanic (15%), plutonic (5%), sandstone (5%), and packstone (5%) clasts. Some conglomerate beds contain higher concentrations of igneous clasts (e.g., andesite 32%, tonalite 12%). The basal conglomerate of the E1 Limon Member is overlain by about 80 m of monotonous thinto medium-bedded sandstones and siltstones (C2.2, C2.3, D2.2) (Fig. 15A). The beds are tabular and laterally continuous. The basal division of beds are massive or poorly graded, and the upper parts are mud-rich siltstones exhibiting parallel laminae and more rare bioturbation by Planolites and Skolithos. The thin-bedded facies of the E1 Limon Member is overlain by about 60 m of medium-bedded to massive lithic-rich carbonates. Lithic-rich carbonate conglomerate is clast-supported and exhibits both disorganized (AI.1) and organized (A2.3) internal character (Fig. 15A). Clasts are predominantly lithic to carbonate clasts. The texture and lithology of the lithic component resembles that of the basal conglomerate. The lithic fragments decrease upward in the graded beds. Larger carbonate clasts (760 cm) are irregularly shaped and are composed of coral heads, branching corals, and fossiliferous wackestone and mdstone, while the smaller grains are mainly red algae, larger reefal foraminifera, and coral fragments. Calciturbidites and calcarenite interbedded with the carbonate conglomerates are medium- to very thick-bedded, and contain abundant (5-40%) sandto pebble-sized lithic fragments. Medium- to thick-bedded, clastic limestone is tabular, laterally continuous, and has a sharp basal contact. Clastic limestone is commonly massive, exhibits coarse-tail grading and lacks sole marks. Calciturbidites and calcarenite are predominantly composed of biogenic material, including red algae, larger

R. DE ZOETEN and R MANN reefal foraminifera, coral and shell fragments with lesser lithic fragments. A few foraminiferal rudstones, found as outsized boulders (1-5 m), are composed entirely of large shallow-marine Eulepadina foraminifera which are diagnostic of Oligocene reef, forereef, or shelf environments (Appendix 1 in de Zoeten, 1988). La Pocilguita Member of the Las Lavas Formation Very thin- to medium-bedded siliciclastic facies (C2.2, C2.3, D2.2) conformably overlie the E1 Limon Member and make up more than half of the La Pocilguita Member (Fig. 15). Bed geometry and internal organization of these facies are identical to those previously described in the Altamira Formation. Thin-bedded facies are interbedded with individual and stacked lithic-rich clastic limestone beds, which increase toward the south. Calcarenites range in grain size from silt to small cobbles, and are organized into conglomerate (A2.3, A2.7) and sandstone and siltstone couplets (C2.1, C2.2, B2.1). Thinner-bedded (0.5-2 m) conglomeratic facies (A2.3, A2.5, A2.7) define 1-4-m-thick finingupward cycles, which begin at 420 m above the base of the section. The basal contact of conglomerate beds are erosional, but on the scale of the outcrop appear to be tabular and laterally continuous. Carbonate-rich, lithic pebble conglomerate grades up into structureless coralline gravel beds, parallel-laminated calcarenite, silty calcilutite, and back into thin-bedded siliciclastic rocks. The thicker and coarser conglomerate is mostly organized into A I.1 and A2.1 facies and consist of very few carbonate clasts. Gravel- to silt-sized calcarenite in the La Pocilguita Member commonly shows well developed Bouma sequences (Tabd, Tabcd). Beds are tabular and laterally continuous. Calcarenite beds have sharp stratal boundaries and display few sole marks. Lithic fragments are typically concentrated in the lower portion of the bed (Ta) and decrease in abundance upward. Basal sands of the Ta interval are coarse-tail graded or structureless, and grade into parallel laminae, tipple marks, and laminated calcilutite. Compositionally, the calcarenite is identical to that found in the E1 Limon Member. Calcarenite is composed mainly of red algae, larger reefal foraminifera, coral fragments, and fossiliferous packstone. It is difficult to discern any large-scale vertical organization in the Las Lavas Formation (Fig. 15). However, on a smaller scale, calcarenite beds increase in frequency upsection and are organized into small (1-5 m thick) thinning- and fining-up cycles with conglomeratic bases. The only matrixsupported, disorganized conglomerate (A1.4) recognized in the Altamira or Las Lavas formations is

CENOZOIC EL MAMEY GROUP OF NORTHERN HISPANIOLA present near the top of the Las Lavas measured section (Fig. 15A). Conglomerate clasts are composed of cobble-sized coral heads with a minor amount of lithic pebbles supported in a calcareous shale matrix. Paleocurrent indicators were measured on a few medium- and thick-bedded calcarenite and siliciclastic strata. Measurements on 24 bimodal current features, including groove casts and a-axis clast alignment of conglomerate indicate bidirectional, northwest-southeast (~ 130 ~ trending flow. Twentythree unimodal paleocurrent structures indicate that currents flowed predominantly to the northwest. Navarette measured section of the Las Lavas Formation El Limon Member of the Las Lavas Formation Along the Santiago-Puerto Plata highway, the basal conglomerate of the E1 Limon Member is approximately 50 m thick (Fig. 15). The conglomerate is massive to poorly bedded, clast-supported, and disorganized to organized (A2.1, AI.1) (Fig. 13B). Poor stratification is defined by oblate clasts preferentially oriented parallel to bedding (Fig. 14B). The basal contact with the underlying Altamira Formation is faulted south of Canada Bonita (UTM 071692). The lateral geometry of the conglomerate horizon is difficult to discern in the field (e.g. Fig. 14B). The conglomerate body appears to pinch out over a lateral distance of 10 m, and is replaced by pebble stringers, which are found interbedded with very thin- to thin-bedded sandstone-siltstone couplets. Conglomerate clasts have similar characteristics to those described in the Las Lavas section. Approximately 40 m of facies D siltstone and shale and minor amounts of C2.3 sandstone and siltstone overlie the basal conglomerate of the E1 Limon Member (Fig. 15). These siltstones and shales are pervasively sheared, which results in a distinctive blocky weathering pattern. There does not appear to be any vertical organization in this thin-bedded sequence. Along the Santiago-Puerto Plata highway, the relationship between the calcarenite and siliciclastic units is less clear. Carbonate conglomerate, foraminiferal rudstone and lithic-rich calcarenite (20 m thick) are found in the Arroyo Guanabano (UTM 073687), east of the highway (Fig. 4A). West of the highway (UTM 068687), limestones of the Late Miocene-Pliocene Villa Trina Formation caps the surrounding hilltops and occur as talus blocks at the level of the road. La Pocilguita Member of the Las Lavas Formation In the Navarette section (Fig. 15B) the following four units comprise the La Pocilguita Member over-

271

lying calcarenite of the E1 Limon Member: (1) thinto medium-bedded sandstone and siltstone (C2.2, C2.3, D2.2 comprising 75% of the La Pocilguita Member); (2) interbedded medium to very thick calcareous sandstone beds (C2.1 comprising 10% of the member); (3) 5-15-m-thick calcarenite packages comprising 10% of the member; and (4) pebblecobble lithic conglomerate comprising 5% of the member. The thin-bedded rocks (C2.2, C2.3, D2.2) have sharp basal contacts and are overlain by parallel-laminated to massive, medium- to coarse-grained sand. The thick sand beds (C2.1) are laterally continuous, although some are lenticular-shaped. The thick sandstone is composed of poorly graded to massive, coarse-grained carbonate-rich sand (Tabd, Tdb). Thick (5-15 m) packages of lithic-rich calcarenite and pebble conglomerate are found 240 m and 430 m above the base of the section (Fig. 16). At 240 m above the base, a 15-m-thick clastic limestone unit is in fault contact with underlying thin-bedded siliciclastic rocks. Stratal boundaries are poorly developed in the calcarenite, which is predominantly massive and contains few lithic fragments. Carbonate material consists predominantly of red algae, larger reefal foraminifera, coral fragments and carbonate rock fragments. The 20-m-thick conglomerate exposed 310 m above the base of the section is poorly stratified (A2.1 facies). Clasts are composed of similar lithologies as those of the basal conglomerate of this section. Secondary gypsum fills some fractures in the clasts and in the surrounding thin-bedded siliciclastic rocks. Vertical organization is not apparent in this section, although exposures are limited. Poorly defined a-axis clast orientations in the basal E1 Limon conglomerate suggests varied north-south to northwestsoutheast paleocurrent trends. Rio Jacagua measured section of the Las Lavas Formation

Beds of the Las Lavas Formation (Fig. 15) could not be directly correlated between the Arroyo Las Lavas and the Rio Jacagua sections (location maps in insets of Figs. 11 and 16). The thick lithic conglomerate that characterized the base of the Las Lavas and Navarette sections was not observed in the Rfo Jacagua section. For this reason, the medium-bedded to massive, lithic-rich calcarenite and carbonate conglomerate was inferred to form the base of the Las Lavas Formation in the Rio Jacagua section. These clastic limestones are about 15 m thick and exhibit similar characteristics to those in the E1 Limon Member in the Lavas and Navarette sections. The Rio Jacagua section is dominated by small-scale (110 m) thinning- and fining-up cycles composed of

272 carbonate-rich conglomerates (AI.1, A2.3), calciturbidites (C2.1, C2.2, C2.3) and siliciclastic turbidites (C2.1, C2.2, C2.3, D2.2) (Fig. 15C). Over 70 bidirectional paleocurrent structures indicate a uniform northwest-southeast (130 ~ mean trend to paleoflow direction. The five unidirectional indicators suggest a paleoflow towards the southeast. Facies analysis of the Las Lavas Formation

Vertical facies assemblages and lateral facies relationships in the Las Lavas Formation are not clearly developed and appear to be more heterogeneous than those described above from the Altamira Formation. The stratigraphy and lithology in the E1 Limon Member indicate rapid deposition of coarse terrigenous and intrabasinal clastic sediment from highconcentration turbidity currents and debris flows. The facies of the La Pocilguita Member are similar to those found in the Altamira Formation. The two formations differ mainly in their lithologic composition, with the Las Lavas Formation containing abundant calciturbidites and the Altamira Formation containing siliciclastic turbidites. The influx of intrabasinal, carbonate biogenic material in the Las Lavas Formation suggests an actively prograding carbonate platform at the basin edge. Deposition by deep-marine turbidity currents in the Las Lavas Formation is supported by the occurrence of graded bedding, good lateral continuity of beds in larger outcrops, development of partial to complete Bouma sequences, vertical facies cycles, and diverse facies associations. Calciturbidites of the Las Lavas Formation were deposited by gravity-driven processes similar to those which deposited the siliciclastic turbidites because the two rock types share the same sedimentary structures.

R. DE ZOETEN and E MANN because tectonic uplift has been less on the La Toca block (Fig. 6A).

STRATIGRAPHY OF THE LA TOCA BLOCK Definition of the La Toca block

The basement rocks and sedimentary cover of the La Toca block is abruptly separated from the basement rocks and sedimentary cover of the Altamira block by the Rio Grande fault zone (Fig. 4C). The La Toca block is bounded on the north by the Camt~ fault zone, on the southwest by the Rio Grande fault zone, and on the south by the Septentrional fault zone. The basement rocks and sedimentary cover of the La Toca block extend to the Rio San Juan area of the eastern Cordillera Septentrional (Draper and Nagle, 1991). The basement of the La Toca block consists of two types of Upper Cretaceous to lower Tertiary rocks: (1) volcanic rocks of the Pedro Garcfa Formation in the central Cordillera Septentrional (Eberle et al., 1982; Peralta-Villar, 1985); and (2) a heterogeneous assemblage of igneous and metamorphic rocks of the Rio San Juan complex in the eastern Cordillera Septentrional (Draper and Nagle, 1991). The basal section of the La Toca Formation consists of interbedded sandstone, siltstone and conglomerate and is faulted against both basement assemblages. The contact between the basement rocks and sedimentary cover of the La Toca Formation is inferred to be a fault-modified unconformity, because the compositions of the Upper Eocene to middle Oligocene basal conglomerates directly reflect the lithologies of the underlying Upper Cretaceous to lower Tertiary basement rocks. Basement complex of the La Toca block

Carbonate rocks of the Villa Trina Formation

Siliciclastic rocks of the Altamira block are capped by a widespread, little studied, --~250-m-thick Upper Miocene to Lower Pliocene shallow-water carbonate unit, the Villa Trina Formation (Fig. 6). The Villa Trina Formation is composed of a lower unit of medium-bedded to massive, marly limestones with few isolated deposits of reefal material. The Villa Trina Formation is capped by well-indurated, medium- to thick-bedded wackestones and packstones, which are interbedded with massive reefal deposits, and reefal talus deposits. This upper unit exhibits a karst topography. Similar lithologies of the Villa Trina Formation cap the La Toca block to the east of the Rio Grande fault zone (Fig. 7). The Villa Trina Formation is more extensive on the La Toca block than the Altamira block probably

Pedro Garcia Formation In the central Cordillera Septentrional, basement rocks of the La Toca block consist of the Pedro Garcfa Formation, which is exposed in a 45 km 2 inlier west of the village of Pedro Garcfa (UTM 266670) (Fig. 4A). The fault-bounded igneous rocks are composed mostly of volcanic rocks (aphanitic andesite, amygdaloidal andesite, tuff, and pyroclastic) with a minor amount of intrusive rocks (tonalite, basaltic dikes, and porphyritic volcanic rocks) (Eberle et al., 1982; Peralta-Villar, 1985). A single K-Ar radiometric date indicates that this igneous complex is at least 72 4- 6 Ma (Bowin and Nagle, 1982). Rio San Juan complex The modal distribution of sandstone grains studied in thin-section and the composition of clasts

CENOZOIC EL MAMEY GROUP OF NORTHERN HISPANIOLA within conglomerates of the La Toca block exposed in the central Cordillera Septentrional suggests a metamorphic and igneous source area. Likely siliciclastic source areas include the Rfo San Juan complex to the east (Draper and Nagle, 1991) and/or the Puerto Plata basement complex to the north (Pindell and Draper, 1991). Both complexes consist of serpentinite, gabbro, and mafic and felsic schist. Based on similar lithologic assemblages and some similar rock types, Draper and Nagle (1991) believe that the Rfo San Juan and the Puerto Plata basement complexes formed in the Upper Cretaceous to lower Tertiary forearc-trench environment and were offset by the Camfi fault zone in Neogene time. Because of their lithologic similarities and the possibility of lateral fault offset, Mann et al. (1991) included both basement complexes as part of the Rfo San JuanPuerto Plata-Pedro Garcfa disrupted terrane.

Stratigraphy of the La Toca Formation Outcrop distribution and general stratigraphy of the La Toca Formation The La Toca Formation crops out over an area of 100 km 2 in the central Cordillera Septentrional. The La Toca Formation is bounded on the south and west by the Rfo Grande fault zone, and on the north by the Cam6 fault zone (Fig. 4C). The base of the La Toca Formation is faulted against the Upper Cretaceous igneous rocks of the Pedro Garcfa Formation (UTM 233663) (Fig. 4C). The La Toca Formation consists of an approximately 300-m-thick basal conglomerate (AI.1, A1.4, A2.3, A2.5 facies), which crops out as hogback ridges, up to 4 km in length (Fig. 16). Sedimentary rocks overlying the basal conglomerate (and possibly laterally equivalent to the conglomerates) are about 500-m-thick and composed mostly of alternating, very thin- to medium-bedded, sandstone and shale couplets (C2.2, C2.3, D 1.2, D2.2) (Fig. 16). These couplets are capped by a 300-m-thick package of thick- to very thick-bedded, sandstones (B2.1, C2.1). These thick-bedded sandstones are exposed in a faulted synclinal ridge (La Cumbre Ridge), striking northwest, which separates north- and south-flowing streams in the central Cordillera Septentrional (Fig. 4A). High-angle faulting north of the Rio Grande fault zone has complicated the stratigraphy of the La Toca Formation (Fig. 5B). To the north of the Rio Grande fault zone, strata generally strike north- to northwesterly and dip to the east. In this area, sedimentary rocks of the La Toca Formation are deformed by high-angle faults. Of the three siliciclastic formations of the E1 Mamey Group described in this chapter, the La Toca Formation received the least amount of study, and the following descriptions should be considered as a preliminary report.

273

Age and paleobathymetry of the La Toca Formation Thirty-six biostratigraphic analyses were performed on twenty samples collected from the La Toca Formation (Appendix 1 in de Zoeten, 1988) (Fig. 16). No microfossils from the basal conglomerate were identified. The overlying sediments range in age from Early Oligocene to early-Middle Miocene. Sedimentary rocks of the La Toca Formation could be as old as Late Eocene, if they correlate with compositionally similar rocks described by Draper and Nagle (1991) that overlie the Rfo San Juan complex. Studies of benthic foraminifera in the La Toca Formation indicate deposition in middle to upper bathyal water depths (150-1500 m; Appendix 1 in de Zoeten, 1988). Measured sections of the La Toca Formation One composite section was measured for the La Toca Formation. Because of structural complexities, this section consists of three parts (Fig. 16, inset map). The base of the section (part A) lies northeast of the village of Altamira, where the Rfo Grande cuts through a steeply dipping basal conglomerate ridge (Fig. 4A). The majority of the section (parts B and C) was measured to the east in outcrops along the Rfo Yaroa (Fig. 4A). The base of the La Toca section consists mostly of a 300-m-thick package of amalgamated conglomeratic facies (A 1.4, A1. l, A2.3, A2.7) with minor interbedded sandstones (B2.1; Fig. 16). Disorganized, matrix-supported facies (A1.4) and a minor clastsupported facies (A1.1) comprise the lower 200 m of the conglomerate. Most conglomeratic beds are tabular, medium-bedded to massive, with planar basal contacts which rarely drape over clasts protruding from the underlying bed. Internal organization of the conglomerate appears to increase upward in the section. Locally, upsection, inversely graded facies (A2.3, A2.7) are interbedded with clast-supported, parallel-stratified conglomerates. Conglomerate hogbacks, extending for 5 km along strike, are separated by laterally equivalent, alternating, thin- to medium-bedded sandstones and shales (C2.2, C2.3, D2.2, D 1.2). Clasts in the base of the La Toca Formation range from granule to boulder in size. They are equidimensional to oblate in shape, and are subangular to rounded. The composition of clasts directly reflects the heterogeneous lithologies in the underlying Pedro Garcfa Formation (Eberle et al., 1982). Clasts in outcrops near the village of Pedro Garcfa (Fig. 16, inset) are composed of approximately 70% volcanic rocks, including tuff, andesite and amygdaloidal lava, 20% tonalite, and 10% sandstone, argillite (recrystallized limestone), vein quartz, serpentinite, and coralline rudstone. This indicates that the Pedro Gar-

274 cfa Formation was the major sediment source of the La Toca Formation. Above the basal conglomerate, the measured section continues in the east up the R/o Yaroa (Fig. 16). 350 m above the base of the section is a sedimentary package, 500 m thick, dominated by very thin- to medium-bedded sandstones and shales (D1.2, D2.2, C2.3 facies). Beds are tabular, laterally continuous, and exhibit sharp basal contacts. Basal sands are relatively coarse-grained, graded or structureless, and have mud-rich, massive, and bioturbated upper divisions (Tabd, Tbd). A few thin- to medium-bedded, lens-shaped calcareous sandstone beds are interbedded with the sandstone and shale couplets. Higher in the section lithic-rich calciturbidites and lithic conglomerate are interspersed between thin-bedded siliciclastic couplets (Fig. 16). Calciturbidites are organized into C2.1 and C2.2 facies (Tabd, Tbcd), but are less abundant than in the Las Lavas Formation (e.g. Fig. 15). Together with the conglomerate (1-2-m-thick AI.1 facies), the calciturbidites form small (1-5 m thick) coarsening- and thickening-up cycles. Thick-bedded sandstones (B2.1, C2.1, C2.2) and lesser amounts of conglomerate beds (AI.1, A2.7) form the upper 300 m of the La Toca Formation (Fig. 16). Sandstone beds have high sand to silt ratios ( 2 : 1 - 1 0 : 1), are commonly tabular, laterally continuous, and thick- to very thick-bedded (ranging from 0.5 to 3.5 m thick). Basal sands range from gravel to medium sand in grain size. Lower division of beds are coarse-tail graded, or massive, and grade up into parallel-laminated sands, rarely containing tipple marks (Tabd, Tbd). Load casts are the dominant type of sole marks. The upper division in many beds contain concentrations of lignite and amber fragments that define parallel laminae in the siltstones. The finer fraction of beds is mud-poor and parallel-laminated or massive. Locally interbedded with the sandstone beds are 1-10-m-thick pebble to small cobble conglomerate beds (AI.1, A2.7 facies) (Fig. 16). Clast-supported, disorganized conglomerates are dominant. Clasts are composed of a wide assortment of lithologies, which include volcanic, plutonic, metamorphic, and sedimentary rock fragments. Vein quartz and serpentinite fragments are present. In the 800-m-thick section above the basal conglomerate, increasingly coarse sand and conglomerate beds define a thickening- and coarsening-up cycle (>400 m) that is capped by almost 300 m of thick-bedded sandstones. Thin (1-5 m) isolated sandstone packets also reflect thickening-upward trends. The thick-bedded sandstone at the top of the section shows no large-scale thickening- or thinningupward trend, but locally there are both thinningand thickening-up cycles (Fig. 16).

R. DE ZOETEN and E MANN Few paleocurrent indicators were found in the La Toca Formation. Nine measurements of groove marks indicate a northwest-southeast mean paleocurrent trend. Another twelve paleocurrent structures were measured between anastomosing high-angle faults in the Rfo Grande fault zone and therefore are possibly subject to tectonic rotation. They suggest both northwest-southeast and northeast-southwest mean paleocurrent trend (Fig. 16). Facies analysis of the La Toca F o r m a t i o n

The internal organization of the basal conglomerate of the La Toca Formation is distinct from conglomerate described in both the Altamira and Las Lavas formations. Matrix-supported, basal conglomerate of the La Toca Formation indicates rapid deposition from cohesive debris flows (Middleton and Hampton, 1976). Whether deposition occurred from broad, unconfined sheets or from channelized flows is not clear. Very thin- to medium-bedded sandstones and siltstones (C2.2, C2.3, D2.2, D2.1) in the lower part of the La Toca Formation suggest deposition from lowconcentration turbidity currents and from high-concentration silt-dominated turbidity currents (Fig. 16). Coarsening and thickening of sandstone upsection suggests progradation of a marine depositional system. Thick-bedded sandstone capping the La Toca Formation section was deposited by high-concentration turbidity currents. Because vertical organization is lacking in these thick, tabular sandstone beds, it is unclear if they were deposited as lobes, channel-lobe transitional facies, or as delta frontal sands.

PALEOCURRENTS FROM THE EL MAMEY GROUP

More than 280 bidirectional and unidirectional paleocurrent indicators were recorded from the Upper Eocene to Lower Miocene siliciclastic rocks in the E1 Mamey Group (Fig. 17). For completeness another 90 measurements from work by Dolan et al. (1991) were added to the measurements collected during this study. Measurements taken from structurally tilted beds have been rotated around horizontal axes. Sole marks are generally scarce in the study area, but occur mostly in facies C2.1 and C2.2. (Fig. 8). Unimodal measurements are based on flute casts and ripple marks. Groove casts, channel axes and a-axis clast orientation provided bimodal current indicators. Rose plots of bidirectional measurements shown in Fig. 17 indicate a uniform northwest-southeast trend in paleocurrents continued from the Late Eocene through the Early Miocene. Unimodal paleocurrent indicators, however, suggest that the paleoslope reversed during latest Oligocene time. Uni-

C E N O Z O I C EL M A M E Y G R O U P OF N O R T H E R N H I S P A N I O L A

275

Fig. 17. Paleocurrent data from siliciclastic marine rocks from the Upper Eocene to Lower Miocene Altamira, Las Lavas, and La Toca formations in the central and western Cordillera Septentrional (modified from Dolan et al., 1991). Rose diagrams differentiate between unidirectional (shown in white) and bidirectional (shown in black) paleocurrent indicators. Unidirectional paleocurrent indicators from the Lower Miocene Las Lavas Formation near Monte Cristi and the Lower Miocene La Toca Formation from near Moca show a mean northwesterly paleoflow.

modal indicators found in the Altamira Formation (Upper Eocene to Upper Oligocene) show paleoflow towards the southeast (Fig. 17). Paleocurrents measured in the Las Lavas and La Toca formations (middle Oligocene to Lower Miocene) suggest paleoflow to the northwest (Fig. 17). A significant number (8%) of paleocurrent indicators are oriented at high angle (N-S) to the predominant current orientation, and suggest the possibility of lateral (north or south) sediment source areas. Alternatively, anomalous north-south oriented paleoflow structures may simply have formed from interchannel deposits. Dolan et al. (1991) compiled paleocurrent data from four Late Cretaceous to Miocene basins in both Hispaniola and Puerto Rico and included some of these data from the E1 Mamey Group. Dolan et al. (1991) showed that all four basins are characterized by elongate shapes with most paleocurrents oriented in a basin-parallel orientation. The elongate basins in Puerto Rico appear to have formed as intra-arc basins which accompanied volcanic activity in the arc. The elongate basins of Hispaniola have largely post-dated magmatic activity of the Hispaniola arc.

SANDSTONE PETROGRAPHY OF THE EL MAMEY GROUP

Methodology Thirty-six medium- to coarse-grained sandstone samples were selected for point-counting to determine the petrographic mode (Dickinson, 1970; Graham et al., 1976). Samples are representative of the 5-km-thick siliciclastic section of the Altamira, Las Lavas, La Toca formations, and range from Upper Eocene to Lower Miocene (location of petrographic samples shown on all measured sections). Samples were collected over a 500 k m 2 geographic area. The Gazzi-Dickinson point-count method described by Ingersoll et al. (1984) was followed. Using this method, a point is counted as a rock fragment if the cross-hairs fall on the aphanitic part of a rock fragment. A point is counted as a mineral grain if the cross-hair falls on a phenocryst greater than 0.0625 mm. For each thin-section, 300-350 points were identified. Thin-sections were stained with sodium cobaltinitrite to facilitate recognition of orthoclase. Because of the inherent difficulty of recognizing chert from felsic volcanic rock fragments,

276

R. D E Z O E T E N and E M A N N

Table 1 Point-count data based on 300-350 point counts per thin section following the conventions of the Gazzi-Dickinson method (Ingersoll, 1984) No.

Sample no. Age

Quartz

Feldspar Lithicfragments

Qm F

Lt

Qp Lvm Lsm Lv

1 1 2 18 1 0 1 0 0

19 3 22 50 14 14 9 13 46

80 96 76 32 85 86 90 87 54

1 0 1 13 1 0 0 0 0

19 3 22 50 14 14 9 13 46

80 97 77 37 85 86 91 87 54

0 1 1 15 0 0 1 0 0

100 99 85 57 93 82 70 92 100

0 0 14 28 7 18 29 8 0

100 100 85 70 93 82 70 92 100

0 0 0 0 0 0 0 0 0

0 0 15 30 7 18 30 8 0

Las Lavas Formation Eocene? 10 10187 Oligocene 11 6687 Early Oligocene 12 7 Early Oligocene 13 6187 Early Oligocene 14 6087 Early Oligocene-Early Miocene 15 12387A Early Oligocene-Early Miocene 16 5787 Early Miocene 17 6887 Early Miocene 18 1B Early Miocene 19 10987 Early Miocene 20 10887 Early Miocene 21 8387 Early Miocene 22 7387 Oligocene? 23 1787 Oligocene? 24 1887 Oligocene? 25 -521 Oligocene? 26 14287

3 1 1 2 8 2 1 15 18 27 0 0 34 18 27 3 1

33 58 24 20 10 17 10 37 42 25 30 39 56 20 38 23 39

64 41 75 78 82 81 89 48 40 48 70 61 10 62 35 74 60

2 0 1 2 2 1 1 10 16 13 0 0 14 7 13 1 1

33 58 24 20 10 17 9 37 42 25 30 39 56 20 38 23 39

65 2 42 1 75 0 78 1 88 7 82 1 90 1 53 9 42 6 62 24 70 0 61 0 30 64 73 16 49 29 76 3 60 0

97 98 98 98 89 98 99 89 92 75 100 100 4 84 71 86 99

1 1 2 1 4 1 0 2 2 1 0 0 32 0 0 8 1

99 99 98 98 96 99 100 98 99 93 100 100 89 100 100 90 99

0 0 0 0 1 0 0 0 0 5 0 0 0 0 0 0 0

1 1 2 1 3 1 0 2 1 2 0 0 11 0 0 10 1

La Toca Formation 27 9487 Oligocene 28 7887 middle Oligocene 29 8687 middle Oligocene 30 13987 Late Oligocene 31 8887 Late Oligocene 32 13187 Late Oligocene 33 10587 Early Miocene 34 8287 Early Miocene 35 9587 Early Miocene

5 40 33 51 30 41 74 29 28

16 21 46 41 60 39 12 60 54

79 39 21 8 10 20 14 11 18

4 9 26 9 21 20 15 7 18

16 21 46 41 60 38 11 60 54

80 70 28 50 19 42 74 33 28

97 46 70 8 51 50 1 29 56

1 1 5 0 0 0 6 2 9

99 0 70 28 90 1 100 0 100 0 100 0 28 41 96 0 91 1

1 1 9 0 0 0 31 4 8

Altamira Formation Early 1 15387 Early 2 2387 Early 3 1687 Early 4 4908 Early 5 -746 Early 6 -745 Early 7 -744 Early 8 4687 Early 9 15687

Eocene Eocene Oligocene Oligocene Oligocene Oligocene Oligocene Oligocene Oligocene

2 53 25 92 49 50 93 69 35

Lm Ls

Percentages are recalculated to 100%. Data indicate that sands from the La Toca Formation consist of much more quartz than coeval sandstones from the Altamira Formation. The quartz grains from the La Toca Formation are predominantly polycrystalline. Key to abbreviations: Q -- quartz, F = feldspars, L = lithic fragments, Qm = monocrystalline quartz, Lt = total lithic fragments and polycrystalline quartz, Qp = polycrystalline quartz, Lvm -- total volcanic and metavolcanic lithic fragments, Lsm -- total sedimentary and metasedimentary lithic fragments, Lv = total volcanic lithic fragments, Lm = total metamorphic lithic fragments, Ls = total sedimentary lithic fragments.

the former was grouped with the felsic fragments. Recalculating framework modes by assigning the questionable polycrystalline grains to chert showed no significant (<5%) change in their ternary distribution. Recalculated point-count data are shown in Table 1.

Results Altamira Formation Framework modal data indicate that the siliciclastic rocks in the central Cordillera Septentrional range in composition from volcanic arenite to quartz-rich,

lithic arkose (Fig. 18). Sandstone of the Late Eocene to Late Oligocene age Altamira Formation are characterized by: (1) abundant volcanic lithic fragments; (2) feldspars; (3) biogenic fragments; and (4) the absence of quartz (Fig. 19A). Las Lavas Formation The composition of Las Lavas Formation sandstone changed from Late Oligocene to Early Miocene time (Fig. 18A). Quartz and plagioclase grains gradually increase in abundance upsection, whereas the concentration of volcanic lithic fragments remains constant. Similar to the Altamira For-

CENOZOIC EL MAMEY GROUP OF NORTHERN HISPANIOLA

277

Fig. 18. (A) Ternary plots of quartz, feldspar, and lithic fragments (QFL) which illustrate change in composition with time for the (1) Altamira Formation, (2) La Toca Formation, and (3) Las Lavas Formation. From Late Eocene to Early Miocene the underlying arc and forearc crust of the area is subjected to progressively deeper levels of erosion related mainly to tectonic events. (B) QFL ternary diagram of sandstone framework grains from all three formations. Tectonic provenance fields from Dickinson et al. (1983) are shown. mation, sandstone of the Las Lavas Formation (Upper Oligocene) is volcanic arenite. Lower Miocene sandstone from the Las Lavas Formation, on the other hand, is feldspathic litharenite (Fig. 19B). Detrital serpentine was found in three samples near the top of the Lavas section (two samples of Late Oligocene age; one sample of Early Miocene age). In these three samples, serpentinite fragments make up almost 30-+- 10% of the framework grains in each sample. Several Miocene sandstones from the Las Lavas Formation contain albite-rich plagioclase, which contain parallel-oriented needle-shaped microlites, along with zoisite and epidote inclusions. These types of plagioclase grains are also commonly found in plagioclase grains from the La Toca Formation sandstone.

La Toca Formation Sandstone from the La Toca Formation has a much lower volcanic lithic component (24-1-3%), and a significantly higher quartz concentration (37 :i: 3%), than sandstone from the Altamira and Las Lavas Formations (Figs. 18A and 19C). Polycrystalline quartz is the most abundant and is probably metamorphic in origin. Plutonic quartz makes up most of the inclusion-rich monocrystalline quartz.

Detrital mineral grains such as hornblende, serpentinite, epidote, zoisite, and several types of mica make up a significant proportion (5-30%) of the framework grains.

Comparison of all formations of the El Mamey Group Sandstone from the Altamira, Las Lavas, La Toca formations exhibit several similar characteristics. They contain abundant intrabasinal biogenic material, such as red algae, larger reefal foraminifera, and lesser amounts of coral and shell fragments. The lithic fragments are predominantly volcanic, although, significant quantities of sedimentary rock fragments are recognized in sandstones from the Altamira Formation. Terrestrial organic debris (lignite and amber) is a minor constituent in all the sandstones. The majority of the lignite and amber deposits are concentrated in the thick-bedded sandstone at the top of the La Toca Formation (Redmond, 1982; Iturralde-Vinent and MacPhee, 1996) (Fig. 16). Overall, the sandstone of the E1 Mamey Group are well compacted, contain very little clayor mud-sized fraction (<5%), and are moderately well cemented with sparry calcite and much lesser amounts of laumonite and analcite. All sands have

278

R. DE ZOETEN and R MANN

CENOZOIC EL MAMEY GROUP OF NORTHERN HISPANIOLA very low porosities (<3%). Chloritization, epidotization, and clay alteration of volcanic rock fragments are likely to be pre-depositional, because alteration either appears to be localized within grain boundaries, or slightly affecting the matrix (Fig. 19A,B). Some plagioclase grains show partial calcite replacement and/or seritization.

Provenance of the Altamira Formation The Altamira Formation sandstones are characterized by very low quartz contents, high plagioclase/orthoclase values, and a volcanic-rich lithic component. These grain parameter values all point to a volcanic provenance (Fig. 18B). The volcanic rock fragments are composed predominantly of lathwork and felsitic (65-97%) grains with a lesser amount of microlitic grains. These grains suggest a diverse volcanic source with a composition that ranges from silicic to basaltic lavas (Dickinson, 1970). Framework grains of sandstones plotted on a QFL diagram fall within the provenance field of a magmatic arc setting as described by Dickinson and Suczek (1979) and Dickinson et al. (1983) (Fig. 18B). Plotting the modal distribution of sandstone from the Las Lavas Formation on a QFL ternary diagram (Fig. 18B) indicates that Miocene sandstone is derived from a transitional magmatic arc setting. The composition of Altamira Formation and Las Lavas Formation sandstone of Late Oligocene age suggests an undissected arc source (Dickinson et al., 1983).

Provenance of the La Toca Formation La Toca Formation sandstone is more heterogeneous and their framework modes plot in the feldspar and quartz realms of the QFL diagram, which correlates to the dissected magmatic arc field (Dickinson et al., 1983) (Fig. 18B). The presence of volcanic lithic fragments and the high plagioclase/orthoclase ratio suggests that the sedimentary source for the La Toca Formation continued to be a volcanic arc. The increase in compositional complexity in the La Toca Formation implies breaching of the shallow levels of the arc with exposure of plutonic-metamorphic rocks (Fig. 18B).

279

DISCUSSION

Three-phase tectonic and sedimentary history of northern Hispaniola Based on sedimentary data presented in this paper, the tectonic and basin evolution of northern Hispaniola can be divided into three phases, each of which is marked by distinct depositional facies (Fig. 20): (1) Paleocene to Middle Eocene phase records the termination of arc activity and uplift of arc basement rocks probably as the result of early interaction between the Hispaniola arc and the Bahama carbonate platform; (2) Late Eocene to Early Miocene phase marks the first major deposition of deep-marine siliciclastic rocks; and (3) Late Miocene to Early Pliocene phase records tectonic uplift of northern Hispaniola to near sea level and subsequent deposition of shallow-marine limestones of the Villa Trina Formation (Fig. 6). Data from this study of the central Cordillera Septentrional has refined the timing and extent of these phases and, therefore, the tectonic history of plate interactions in this part of the North AmericaCaribbean plate boundary zone

Phase 1: Paleocene to Middle Eocene Tectonics Coeval igneous and metamorphic rocks in northern Hispaniola are interpreted to have formed in an intra-oceanic island-arc environment at the leading edge of the Caribbean plate (Bowin, 1975; Nagle, 1979; Draper and Nagle, 1991; Pindell and Draper, 1991; Dolan et al., 1991; Calais and Mercier de Ldpinay, 1995) (Fig. 20A). Isotopic ages for northern Hispaniola suggest that island-arc development was continuous from a mid-Cretaceous orogenic event (Draper et al., 1996) to the Late Eocene or Early Oligocene (Kesler et al., 1991). Near the end of the arc phase, initial opening of the Cayman Trough marks a change from northeast to eastward Caribbean plate motion and the transition from a convergent to the present east-west strike-slip margin (e.g., Sykes et al., 1982; Mann et al., 1995). Several authors believe that the collision of the Caribbean plate with the buoyant Bahama Platform

Fig. 19. (A) Thin-section photomicrograph with crossed-polars of an Upper Eocene to Upper Oligocene Altamira sandstone consisting of felsitic and microlitic volcanic rock fragments, plagioclase, and carbonate rock fragments. The width of the photo is approximately 1.65 mm (sample no. 7-46). (B) Thin-section photomicrograph with crossed-polars of a typical Lower Miocene sandstone of the Las Lavas Formation which consists of polycrystalline quartz, plagioclase, felsite and lathwork type volcanic rock fragments, and bioclasts. The width of the photo is approximately 3.3 mm (sample no. 10887). (C) Thin-section photomicrograph with crossed-polars of a Lower Oligocene to Lower Miocene sandstone from the La Toca Formation. This photomicrograph shows polycrystalline and monocrystalline quartz, plagioclase, volcanic rock fragments, and zoisite. The large, twined plagioclase grain near the center of the photomicrograph contains unidentified, needle-shaped microlites which exhibit a preferred parallel orientation. The width of the photo is about 1.65 mm (sample no. 10587). Color version at http://www.elsevier.nl/locate/caribas/

280

R. DE Z O E T E N and R M A N N

Fig. 20. Block diagrams summarizing three main tectonic phases in the evolution of the North America-Caribbean plate boundary zone in northern Hispaniola. (A) Phase 1 is marked by Paleogene to Early Eocene deposition of hemipelagic, fine-grained turbidites (Los Hidalgos Formation = number 5) which are interbedded with arc-related dikes and sills of intermediate composition. Similar deep-marine sedimentary rocks are found to the north (Imbert Formation = number 4) and to the south (Magua Formation = number 6) of the study area and suggest a regionally extensive basin at least 40 km wide. The substrate of the Imbert Formation is a heterogeneous basement consisting of serpentinite, gabbros, volcanic rocks and blueschists (Puerto Plata basement and Rio San Juan complexes = number 3), whereas the substrate of the Magua Formation is greenschist metamorphic rocks intruded by granodiorite plutons (Duarte complex = number 7). Tuffaceous horizons are common in the Imbert, Los Hidalgos, and Magua formations and suggest an active arc environment probably to the south along the Hispaniola segment of the volcanic arc. We interpret these geologic relationships in terms of a forearc basin developed above a south- to southwest-dipping slab of subducted Atlantic ocean floor (number 2). Large-scale, Middle Eocene folding and uplift will terminate Phase 1 deposition. This compressive event is related to attempted subduction of the Bahama Platform (number 1) beneath the forearc area. (B) Phase 2 is marked by Upper Eocene to Lower Miocene deposition of several kilometers of siliciclastic turbidites (El Mamey Group = number 8; Tabera Group -- number 9) in west-northwesterly striking, elongate basins. Arrows indicate paleoflow directions based on paleocurrent studies in turbiditic rocks (cf. Fig. 17). Source areas for the Tabera Group include Lower Cretaceous metasedimentary rocks (Amina schists = number 10) and volcanic arc rocks exposed to the east. Source area for the E1 Mamey Group include folded, hemipelagic rocks of the Los Hidalgos Formation to the south (number 5), the Puerto Plata basement and

CENOZOIC EL MAMEY GROUP OF NORTHERN HISPANIOLA terminated subduction and arc-related volcanism and initiated east-west movement (Pindell and Draper, 1991; Dolan et al., 1991; Mann et al., 1995). Calais and Mercier de L6pinay (1995) have correlated the Late Eocene deformation seen in northern Hispaniola with a convergent event of the same age in southern Cuba and northern Haiti.

281

ship was recognized by us in the central Cordillera Septentrional between the tightly folded Upper Paleocene to Lower Eocene Los Hidalgos Formation and less folded overlying Upper Eocene Altamira Formation. In the western Cordillera Septentrional, Calais et al. (1992) recognized this same unconformity separating the Paleocene-Eocene E1 Cacheal tufts from the overlying Lower Miocene series.

Paleocene-Eocene rock record The oldest sedimentary rocks in northern Hispaniola are mainly turbidites and hemipelagic sedimentary rocks of Paleocene to Middle Eocene age. These rocks were deposited in a deep-marine environment above igneous and metamorphic arc basement rocks (Fig. 20A). This deep-marine depositional phase seems to have affected all components of the arc system, including: (1) deposition of the Imbert Formation in the 'outer forearc-trench setting' (Nagle, 1979; Pindell and Draper, 1991); (2) deposition of the Los Hidalgos Formation in the 'inner arc setting'; and (3) deposition of the Magua Formation on the volcanic arc (Palmer, 1979). Unlike the Los Hidalgos Formation, the Imbert and Magua formations contain a significant amount (10-60%) of siliciclastic rocks. Igneous activity during deposition of the Imbert and the Los Hidalgos formations is shown by interbedded calcareous tuffaceous rocks in the Imbert Formation and Palma Picada porphyritic rocks intruded into the Los Hidalgos Formation (Fig. 20A). Although no radiometric ages have been determined for these igneous rocks, pelagic foraminifera from the tuffaceous rocks of the Imbert Formation indicate a Paleocene-Early Eocene age (Nagle, 1979). The Palma Picada igneous rocks intruded the calcareous sediments of the Los Hidalgos Formation either during or after their deposition and must be Late Paleocene to Middle Eocene in age. Pindell and Draper (1991) report that the Irabert Formation is overlain unconformably by Upper Eocene sedimentary rocks of the Luperon Formation. The stratigraphic relationship between shallowmarine, Lower to Middle Eocene limestone of the La Isla Formation and the Imbert Formation is unclear, but the La Isla Formation limestone is believed to post-date Imbert deposition and pre-date Upper Eocene rocks above the unconformity (Pindell and Draper, 1991). A similar, unconformable relation-

Interpretation of phase 1 tectonic and sedimentary events Unconformable contacts between the basement and overlying sedimentary rocks indicate that basement blocks were locally uplifted and exposed by Late Eocene time, and possibly as early as the Late Paleocene. Lithologies of the Imbert and Magua formations indicate that arc-derived sediments were deposited on the edges of the deep-marine forearc basin (Fig. 20A). The composition of the Los Hidalgos Formation indicates that very little terrigenous sediment reached its position in the deep basin. Three reasons may be responsible for the absence of terrigenous sediment in the Los Hidalgos Formation: (1) the basin was effectively isolated from a siliciclastic source, possibly because of an irregular bottom topography; (2) the basin was a great distance from the source of siliciclastic material; or (3) because only a small area of arc rocks were subaerially exposed during this time. The deep-marine origin and present proximity of the Imbert and Los Hidalgos formations suggest that these formations may be laterally equivalent. Lessfolded shallow-marine limestone deposits of the La Isla Formation overlie folded rocks of the Imbert Formation and suggest that the Imbert Formation was uplifted with an outer 'arc-trench' assemblage to near sea level during Late Paleocene to Middle Eocene time (Pindell and Draper, 1991). A similar uplift history for the Los Hidalgos Formation is suggested based on the Middle Eocene angular unconformity separating the folded Los Hidalgos Formation and the less-folded Altamira Formation. The mixture of shallow-marine carbonate clasts and clasts derived from the Los Hidalgos Formation at the top of the basal conglomerate (Ranchete Member) of the Altamira Formation further suggests that the Los Hidalgos Formation had been uplifted to near sea level by Late Eocene time. Thus, the fore-

Rfo San Juan complexes and Pedro Garcfa Formation to the north (number 3). Regional uplift in Middle Eocene time is attributed to the initial attempted subduction of the Bahama Platform (number 1) beneath the Hispaniola arc and Oligocene to Miocene left-lateral, strike-slip faulting along the Rio Grande fault zone (RGFZ) and the Septentrional fault zone (SFZ). (C) Phase 3 is marked by Upper Miocene to Lower Pliocene deposition of shallow-watercarbonate rocks (Villa Trina Formation -- number 11). This limestone appears to have covered most of northern Hispaniola as shown by the wide distribution of its remnants (cf. map in Fig. 6). Late Pliocene to Present uplift of the Cordillera Septentrional along the transpressional Septentrional fault zone has folded the Villa Trina Formation and uplifted it to an elevation of 1250 m. Uplift of the Cordillera Septentrional has accompanied subsidence of coeval rocks in the Cibao basin to depths greater than 3500 m below sea level (Yaque Group = number 12).

282 arc may have uplifted as a single block during this time period. This folding and uplift event coincides with the cessation of most subduction-related processes and probably resulted from the early oblique collision of the Caribbean plate with the Bahama Platform (Pindell and Draper, 1991). Phase 2: Late Eocene to Early Miocene Tectonics Phase 2 covers the depositional period from the Late Eocene to the Early Miocene (that is, the period of deposition of the Altamira, Las Lavas, and La Toca formations; Fig. 7). The tectonic regime during this period has been interpreted by Sykes et al. (1982) and Mann et al. (1995) as transitional: collision with the Bahama Platform was ending, and the Caribbean plate was moving along strike-slip faults in a more easterly direction. In the western Cordillera Septentrional, Calais et al. (1992) provided important structural confirmation of this transition period. They mapped an older set of collision-related folds affecting Paleocene and Eocene rocks equivalent to the Los Hidalgos Formation with folds having north- to east-northeast-trending axial traces and a younger, strike-slip set of folds affecting Miocene rocks that have northwest-trending axial traces and sub-vertical fold axes. Late Eocene to Early Miocene rock record Systematic lateral facies and facies assemblage changes which commonly characterize submarine fans (e.g., Walker, 1984) are not well expressed in the siliciclastic deposits exposed in the central Cordillera Septentrional. The best documentation of lateral facies relationships is recorded in the measured sections from the Altamira Formation (Figs. 9, 11 and 12). The channel (AI.1, A2.1) and overbank deposits (C2.2, C2.3, D2.2) in the Northern Canada Bonita, Southern Canada Bonita, and Calabaza sections resemble middle submarine fan deposits (Mutti and Ricci Lucchi, 1978; Nilsen and Abbot, 1981). The stacked tabular sandstones (B2.1, C2.1) seen in the Rio Perez and Llanos syncline sections are similar to deposits interpreted as outer fan lobes or as large crevasse-splay lobes in the middle fan environment (Mutti and Ricci Lucchi, 1978; Shanmugan and Moiola, 1988). Thin- to medium-bedded sandstone and siltstone facies (C2.2, C2.3, D2.2) seen in the E1 Mamey and Guananico sections may represent basin plain or distal overbank deposits. The Rio Perez, Llanos Syncline, Southern Canada Bonita, Northern Canada Bonita, and Calabaza sections are all laterally equivalent. Their areal distribution in the E1 Mamey Group suggests north to northeast fan progradation from the Northern Canada Bonita to the Rio Perez section. Such progradation

R. DE ZOETEN and E MANN would require paleocurrents flowing from the south and southwest. This prediction, however, conflicts with the mean paleocurrent trend (125 ~ measured from 170 structures, 40 of which indicate that the current flowed to the southeast (Fig. 17). High concentrations of calcareous biogenic material in the turbidite rocks of the E1 Mamey Group indicate shallow-water carbonate production near the shelf margin. Limestone turbidites and debris sheets recognized in slope and basinal settings have commonly been reported in both ancient rocks (Cook and Mullins, 1983) and modem environments (Schlager and Chermak, 1979). Deep-marine fossiliferous limestones, like those from the Las Lavas Formation, commonly emanate from a line source dissected by several small channels and are rarely associated with submarine fans (Cook and Mullins, 1983). Vertical facies relationships show that the Oligocene section exposed along the SantiagoPuerto Plata highway is more conglomeratic than the Upper Eocene section near E1 Mamey. A gradual, upsection transition from lobe to channel/overbank deposition suggests that southeasterly prograding submarine fan systems developed during Late Oligocene time. Vertical relationships in the La Toca Formation point to a prograding submarine fan or delta during Early Miocene time. A major, Late Oligocene depositional event is marked by sudden appearance of limestone conglomerate and calciturbidite in the E1 Limon Member at the base of the Las Lavas Formation (Fig. 15). Intrabasinal, clastic limestone beds increase upward in the section. The section is overlain by platform carbonate of the Villa Trina Formation (Fig. 6). Sandstone petrography from the Altamira, Las Lavas and La Toca formations on the QFL diagram indicates that these sediments came from an arc environment (cf. Dickinson and Suczek, 1979) (Fig. 18B). Modal distribution of framework grains suggest two compositional trends: (1) sandstone from the Altamira and Las Lavas formations have a different sand grain composition from coeval sandstone from the La Toca Formation; and (2) quartz content increases upsection from the Altamira through the Las Lavas Formation. Compositional differences in the sandstones from the La Toca and Altamira formations imply two distinct source areas, with apparently no mixing between the two. This interpretation is further supported by the absence of serpentinite grains in the Altamira Formation sandstones. In contrast, serpentinite clasts are found in the La Toca Formation as well as in the Lower to Middle Eocene sedimentary rocks to the north of the Camfi fault zone. Only the very youngest sandstone (Lower Miocene) in the Las Lavas Formation have similar modal distributions as the sandstone from the La Toca Formation. Superimposed on this trend

CENOZOIC EL MAMEY GROUP OF NORTHERN HISPANIOLA is a time-dependent unroofing sequence from Upper Eocene undissected magmatic arc provenance to a Lower Miocene dissected arc provenance (Fig. 18B). Calais and Mercier de L6pinay (1995) have correlated Upper Eocene to Lower Miocene sedimentary formations in northern Hispaniola (Altamira Formation) with similar rocks in northern Haiti and southern Cuba. They interpret this period as a time of tectonic quiescence when topographic relief generated by the Late Eocene uplift event was eroding to sea level. The Late Eocene uplift and folding event may explain why there is little or no Oligocene preserved in the western part of the Cordillera Septentrional (Calais et el., 1992).

Interpretation of phase 2 tectonic and sedimentary events Sandstone petrography and facies relationships suggest that the La Toca Formation was probably deposited in a separate basin from the basin in which the Altamira and Las Lavas formations were deposited (Fig. 20B). However, it is also possible that these formations may have been deposited in different localities within a larger basin with a wide range of source areas. The La Toca Formation is separated from the coeval Altamira and Las Lavas formations by the 100-400-m-wide, left-lateral Rfo Grande fault zone (de Zoeten and Mann, 1991). The composition of sandstone and conglomerate changes abruptly across the Rfo Grande fault zone. Quartz-rich, La Toca Formation sandstone lie north of the Rfo Grande fault zone, whereas lithic-rich Altamira Formation sandstone occur to the south of the fault. Distinct Upper Cretaceous to lower Tertiary basement complexes underlying sedimentary rocks are likewise separated by the Rfo Grande fault zone. Differences in basement rock lithologies, composition of overlying sandstone, and sedimentary facies profiles suggest distinct origins for the sedimentary rocks now juxtaposed along the Rfo Grande fault zone. Left-lateral oblique-slip motion on the Rfo Grande fault zone appears to have juxtaposed the Altamira and La Toca blocks which Mann et al. (1991) have interpreted as part of much larger terranes (Fig. 20B). Similar relationships, in which blocks with distinctly different geologic histories are in fault contact, are documented for several of the ten other terranes proposed by Mann et al. (1991) in Hispaniola. Movement of blocks along multiple high-angle faults is consistent with large-offsets documented further west in the Cayman Trough (Rosencrantz et al., 1988) (Fig. 1). The time of 'docking' or present juxtaposition of the La Toca and Altamira blocks is not well constrained. The La Toca and Altamira blocks were possibly juxtaposed by Miocene time for two reasons: (1) similar detrital compositions of Lower

283

Miocene sandstones from both the La Toca and Las Laves formations (Fig. 18A); and (2) the widespread cover of Upper Miocene to Lower Pliocene Villa Trine Formation limestones over the siliciclastic formations (Fig. 6). The consistent northwest-southeast trend of paleocurrents measured in Upper Eocene to the Lower Miocene indicates a long-lived, elongate basin as proposed by Dolan et el. (1991) for the E1 Mamey and three other coeval deformed basin complexes in Hispaniola and Puerto Rico. Deposition of the E1Mamey Group rocks within an elongate depositional basin is further supported by: (1) complex lateral facies patterns, which do not form classical deep-sea fan morphologies (Link, 1982); and (2) regional stratigraphy which suggests that the 'outer forearc-trench' assemblage was bathymetrically shallow to the north of the basin from Early Eocene time to the Present (Pindell and Draper, 1991), and that the area of the Los Hidalgos Formation to the south of the basin also formed a bathymetric high during at least Late Eocene time and possibly into the Oligocene (Fig. 20B). The mechanism that produced the complex basins of the E1 Mamey Group is unclear. Although the basin is situated in the forearc region of Hispaniola, siliciclastic deposition began during the waning stages of arc activity in Late Eocene time (Fig. 20B). The basin may have formed by down-warping between the uplifted 'outer forearc-trench' assemblage (Imbert Formation) and the 'inner forearc' (Los Hidalgos Formation)' during the final stages of the collisional event with the Bahama Platform. Folding and uplift of these arc environments would provide igneous and metamorphic source areas that seem to be absent prior to the Middle Eocene folding and uplift event. Calais et el. (1992) show that an older set of folds affecting the Eocene Los Hidalgos equivalent rocks in the area (El Cacheal tufts) of the western Cordillera Septentrional has north to east-northeast axial trends while a younger set of folds with northwest-trending axial traces affecting post-Eocene rocks. They interpreted the older set of folds as related to the Bahama collision and the younger set as related to post-collisional strike-slip movement. Alternatively, the highs flanking the basin may have been formed by strike-slip faults roughly parallel to the axis of the basin (Fig. 20B). Whether the basin formed in a convergent or strike-slip setting is not clear from the sedimentary results of this study, but it is likely that both processes may have affected early basin formation and sedimentation given the transition from arc to strike-slip tectonics at the time of deposition of most of the sediments. Based on regional plate reconstructions and the presence of the Eocene to Recent Cayman Trough west of the area, strike-slip faulting may have played an impor-

284

R. DE ZOETEN and R MANN

tant role in the development of Upper Eocene source areas and basins (Fig. 1).

stones are found throughout the Cordillera Septentrional and Samana Peninsula (Fig. 6).

Eustatic controls on deposition in the El Mamey Group Coarse-grained, channel/overbank deposits in the Altamira Formation correlate with a global sea level lowstand in the Late Oligocene (Haq et al., 1987) and may represent a 'lowstand fan'. The introduction of calciturbidites of the Las Lavas Formation into the basin may indicate that the drop in sea level forced carbonate progradation on to the slope environment. An unstable slope environment would provide a source area for carbonate-rich gravity flows. Another possibility is that rising sea level, following the lowstand, produced a quiescent period inhibiting siliciclastic transport into the basin and increasing carbonate production on the shelf. Carbonate produced on the shelf could be mobilized by localized tectonic activity and moved into the deeper basins. Although Oligocene sedimentation patterns appear to coincide with a Late Oligocene fall in sea level, tectonic influences on sedimentation may have also been important. Upper Oligocene olistostromes containing outsized platform carbonate blocks have been documented in the Tavera Group (Palmer, 1979; Groetsch, 1983) and in the Ocoa Group (Heubeck et al., 1990) south of the study area (Fig. 2).

Interpretation of phase 3 tectonic and sedimentary events De Zoeten and Mann (1991) divided the Neogene uplift history of Hispaniola into two major events: (1) Middle Miocene uplift event, and (2) a post-Early Pliocene uplift event. The Middle Miocene uplift is recorded by a ubiquitous change from deep-marine deposition (Las Lavas and La Toca formations) in Early Miocene time to shallow-marine deposition (Villa Trina Formation) in Late Miocene and Early Pliocene time. Post-Early Pliocene restraining bend tectonics continues to uplift the Cordillera Septentrional to its present position at 1250 m above sea level (Fig. 6).

Phase 3: Late Miocene to Recent Tectonics Miocene strike-slip faulting and related deformation is documented in several areas of northern Hispaniola (de Zoeten and Mann, 1991). Gentle folding of the siliciclastic units of the E1 Mamey Group, which is not recognized in the overlying shallowwater carbonate rocks, indicates Middle Miocene folding, probably associated with transpressional strike-slip faulting. Calais et al. (1992) report the same folding event affecting rocks of the western Cordillera Septentrional. During post-Early Pliocene time, northern Hispaniola underwent transpression associated with the strike-slip 'restraining bend' in the plate boundary zone near Hispaniola (Mann et al., 1991). Obliqueslip movement on the Septentrional fault zone uplifted Upper Miocene to Lower Pliocene limestones to 1200 m above sea level (de Zoeten and Mann, 1991). Late Miocene to Pliocene rock record Few Middle Miocene rocks are found in northern Hispaniola (Figs. 4B, 7). This time period marks a change from Lower Miocene deep-marine sedimentation to Upper Miocene shallow-marine carbonate deposition. Upper Miocene to Lower Pliocene lime-

CONCLUSIONS

Detailed studies of several Paleocene through Miocene sedimentary formations exposed in the central Cordillera Septentrional, Dominican Republic, indicate at least three, distinct tectonic phases in the Cenozoic evolution of the North America-Caribbean plate boundary zone. Each tectonic phase is characterized by deposition of characteristic sedimentary facies and is punctuated by a short-lived folding event. The three phases include: (1) Paleocene to Early Eocene deposition of at least a 250-m-thick section of hemipelagic, finegrained turbidites (Los Hidalgos Formation) interbedded with arc-related dikes and sills of intermediate composition (Palma Picada intrusive rocks). Sedimentation was terminated by a folding and uplift event, which is thought to be related to early attempted subduction of the Bahama Platform beneath the Hispaniola arc (Fig. 20A). (2) Late Eocene to Early Miocene deposition of approximately 4000 m of deep-marine, siliciclastic turbidites (Altamira, Las Lavas, and La Toca formations) into at least two elongate basins subsequently juxtaposed by strike-slip faulting. We interpret sandstone compositions suggesting two distinct source areas during Late Eocene and Oligocene time as evidence that the basins were isolated from one another and later juxtaposed by a 400-m-wide, linear, strike-slip fault (Rfo Grande fault zone). Similarities in sandstone composition indicate that the two basins were juxtaposed in Miocene time. Siliciclastic sedimentation was terminated by a folding and uplift event, which is thought to be associated with transpressional strike-slip faulting related to North America-Caribbean plate motion (Fig. 20B). (3) Late Miocene to Early Pliocene deposition of more than 250 m of shallow-marine limestones

C E N O Z O I C EL M A M E Y G R O U P OF N O R T H E R N H I S P A N I O L A

(Villa Trina Formation). Carbonate sedimentation was terminated by a folding and uplift event related to the current pattern of restraining bend tectonics and active collisional underthrusting of the Bahama Platform. Maximum uplift of the limestone is associated with a large fold in the convex, uplifted side of the restraining bend (Fig. 20C).

ACKNOWLEDGEMENTS

This work formed part of a master's thesis by R. de Zoeten that was supervised by E Mann, E. McBride and M. Cloos at the University of Texas at Austin (de Zoeten, 1988). M. Perez, L. Pena, J. Guzman and G. Draper provided assistance in the field and W. Eberle, E Cepek, S. Monechi, B. Redmond, and E. Robinson generously provided us with unpublished map and biostratigraphic data. We thank J. Dolan, G. Draper, E. McBride, C. Heubeck, J. Lewis, M. Cloos and J. Pindell for useful discussions and J. Dolan, G. Draper, and E. Calais for their careful reviews of this paper. This work was supported by Grant 17068-AC2 from the Donors of the Petroleum Research Fund of the American Chemical Society to E Mann. University of Texas Institute for Geophysics contribution 1423.

REFERENCES

Beall, R., 1943. Geologic map of the eastern portion of the Cibao Basin, Dominican Republic. Scale 1 : 100,000. Dominican Seaboard Oil Co., New York Office, Santo Domingo (unpubl.). Bermudez, EJ., 1949. Tertiary smaller foraminifera of the Dominican Republic. Cushman Lab. Foraminiferal Res. Spec. Publ. 25, 322 pp. Bourgois, J., Vila, J.-M. and Tavares, I., 1982. Datos geol6gicos nuevos acerca de la regi6n de Puerto Plata (Republica Dominicana). 9th Caribbean Geological Conference, Santo Domingo, Dominican Republic, Vol. 2, pp. 633-635. Bourgois, J., Blondeau, A., Feinberg, H., Glaqon, G. and Vila, J., 1983. The northern Caribbean plate boundary in Hispaniola: tectonics and stratigraphy of the Dominican Cordillera Septentrional (Greater Antilles). Soc. G6ol. Fr. Bull., 25 (1): 83-89. Bowin, C.O., 1975. The geology of Hispaniola. In: A.E.M. Nairn and EG. Stehli (Editors), The Gulf of Mexico and the Caribbean. The Ocean Basins and Margins, Vol. 3, Plenum, New York, pp. 501-552. Bowin, C.O. and Nagle, F., 1982. Igneous and metamorphic rocks of the northern Dominican Republic: an uplifted subduction zone complex. 9th Caribbean Geological Conference, Santo Domingo, Dominican Republic, Vol. 1, pp. 39-50. Calais, E. and Mercier de L6pinay, B., 1995. Strike-slip tectonic processes in the northern Caribbean between Cuba and Hispaniola (Windward Passage). Mar. Geophys. Res., 17: 63-95. Calais, E., Mercier de L6pinay, B., Saint-Marc, E, Butterlin, J. and Schaaf, A., 1992. La limite de plaques d6crochante nord cara'fbe en Hispaniola: 6volution pal6og6ographique et structural c6nozoYque. Bull. Geol. Soc. Fr., 163: 309-324.

285

Cook, H.E. and Mullins, H.T., 1983. Basin margin. In: EA. Scholle, D.G. Bebout and C.H. Moore (Editors), Carbonate Depositional Environments. Am. Assoc. Pet. Geol. Mem., 33: 539-618. DeMets, C., Gordon, R.G., Argus, D.F. and Stein, S., 1990. Current plate motions. Geophys. J. Int., 101: 425-478. De Zoeten, R., 1988. Structure and Stratigraphy of the Central Cordillera Septentrional, Dominican Republic. MA thesis, University of Texas at Austin, 168 pp. (unpubl.). De Zoeten, R. and Mann, E, 1991. Structural geology and Cenozoic tectonic history of the central Cordillera Septentrional, Dominican Republic. In: E Mann, G. Draper and J. Lewis (Editors), Geologic and Tectonic Development of the North America-Caribbean Plate Boundary Zone in Hispaniola. Geol. Soc. Am. Spec. Pap., 262: 265-279. De Zoeten, R., Draper, G. and Mann, E, 1991. Geologic map of the northern Dominican Republic (scale 1:150,000). In: E Mann, G. Draper and J. Lewis (Editors), Geologic and Tectonic Development of the North America-Caribbean Plate Boundary Zone in Hispaniola. Geol. Soc. Am. Spec. Pap., 262: Plate 1. Dickinson, W.R., 1970. Interpreting detrital modes of greywacke and arkose. J. Sediment. Petrol., 40: 695-707. Dickinson, W.R. and Suczek, C.A., 1979. Plate tectonics and sandstone composition. Am. Assoc. Pet. Geol., 63: 2164-2182. Dickinson, W.R., Beard, L.S., Brakenridge, G.R., Erjavec, J.L., Ferguson, R.C., Inman, K.F., Knepp, R.A., Lindberg, EA. and Ryberg, ET., 1983. Provenance of North American Phanerozoic sandstones in relation to tectonic setting. Geol. Soc. Am. Bull., 94: 222-235. Dixon, T., Farina, E, DeMets, C., Jansma, E, Mann, E and Calais, E., 1998. Relative motion between the Caribbean and North American plates and related plate boundary zone deformation based on a decade of GPS measurements. J. Geophys. Res., 103: 15,157-15,182. Dohm, C.F., 1943. Geologic map of and report on the western portion of the Cibao Basin, Dominican Republic. Scale 1 : 100,000. Dominican Seaboard Oil Co., New York Office, Santo Domingo (unpubl.). Dolan, J.E, Mann, E, de Zoeten, R., Heubeck, C., Shiroma, J. and Monechi, S., 1991. Sedimentologic, stratigraphic, and tectonic synthesis of Eocene-Miocene sedimentary basins, Hispaniola and Puerto Rico. In: E Mann, G. Draper and J. Lewis (Editors), Geologic and Tectonic Development of the North America-Caribbean Plate Boundary Zone in Hispaniola. Geol. Soc. Am. Spec. Pap., 262:217-263. Dolan, J., Mullins, H. and Wald, D., 1998. Active tectonics of the north-central Caribbean region: oblique collision, strain partitioning and opposing slabs. In: J. Dolan and E Mann (Editors), Active Strike-Slip and Collisional Tectonics of the Northern Caribbean Plate Boundary Zone. Geol. Soc. Am. Spec. Pap., 326: 1-61. Draper, G. and Nagle, E, 1991. Geology, structure and tectonic development of the Rfo San Juan complex, northern Dominican Republic. In: E Mann, G. Draper and J. Lewis (Editors), Geologic and Tectonic Development of the North America-Caribbean Plate Boundary Zone in Hispaniola. Geol. Soc. Am. Spec. Pap., 262: 77-95. Draper, G., Guti6rrez, G. and Lewis, J.F., 1996. Thrust emplacement of the Hispaniola peridotite belt: orogenic expression of the mid-Cretaceous Caribbean arc polarity reversal? Geology, 24:1143-1146. Eberle, W., Hirdes, W., Muff, R. and Pelaez, M., 1982. The geology of the Cordillera Septentrional (Dominican Republic). 9th Caribbean Geological Conference, Santo Domingo, Dominican Republic, Vol. 2, pp. 619-632. Graham, S.A., Ingersoll, R.V. and Dickinson, W.R., 1976.

286 Common provenance for lithic grains in Carboniferous sandstones from Ouachita Mountains and Black Warrior Basin. J. Sediment. Petrol., 46: 620-632. Grindlay, N., Mann, E and Dolan, J., 1997. Researchers investigate submarine faults north of Puerto Rico. EOS, 78: 404. Groetsch, G.J., 1983. Resedimented Conglomerates and Turbidites of the Represa and Janico Formations, North-Central Dominican Republic. M.S. Thesis, George Washington University, Washington DC, 108 pp. Haq, B.U., Hardenbol, J. and Vail, ER., 1987. Chronology of fluctuating sea levels since the Triassic. Science, 235: 1156-1167. Heubeck, C.E., Mann, E, Dolan, J. and Monechi, S., 1990. Diachronous uplift and recycling of sedimentary basins during Cenozoic tectonic transpression, northeastern Caribbean plate margin. Sediment. Geol., 70: 1-32. Ingersoll, R.V., Bullard, T.E, Ford, R.L., Grimm, J.E and Sares, S.W., 1984. The effect of grain size on detrital modes: a test of the Gazzi-Dickinson point-counting method. J. Sediment. Petrol., 54:103-116. Iturralde-Vinent, M.A. and MacPhee, R.D.E., 1996. Age and paleogeographical origin of Dominican amber. Science, 273: 1850-1852. Joyce, J., 1991. Blueschist metamorphism and deformation on the Samana Peninsula: a record of subduction and collision in the Greater Antilles. In: E Mann, G. Draper and J. Lewis (Editors), Geologic and Tectonic Development of the North America-Caribbean Plate Boundary Zone in Hispaniola. Geol. Soc. Am. Spec. Pap., 262: 47-76. Kesler, S., Sutter, J., Barton, J. and Speck, R., 1991. Age of intrusive rocks in Hispaniola. In: E Mann, G. Draper and J. Lewis (Editors), Geologic and Tectonic Development of the North America-Caribbean Plate Boundary Zone in Hispaniola. Geol. Soc. Am. Spec. Pap., 262: 165-172. Link, M.H., 1982. Slope and turbidite facies of the Miocene Castaic Formation and the lower part of the Marple Canyon Sandstone Member, Ridge Route Formation, Ridge Basin, southern California. In: J.L. Crowell and M.H. Link (Editors), Geologic History of Ridge Basin, Southern California. Pacific Section of the Society of Economic Paleontologists and Mineralogists, Los Angeles, CA, pp. 79-88. Mann, E and Gordon, M., 1996. Tectonic uplift and exhumation of blueschist belts along transpressional strike-slip fault zones. In: G. Bebout, D. Scholl, S. Kirby and J. Platt (Editors), Dynamics of Subduction Zones. Am. Geophys. Union Monogr., 96: 143-154. Mann, E, Draper, G. and Lewis, J., 1991. An overview of the geologic and tectonic development of Hispaniola. In: E Mann, G. Draper and J. Lewis (Editors), Geologic and Tectonic Development of the North America-Caribbean Plate Boundary Zone in Hispaniola. Geol. Soc. Am. Spec. Pap., 262: 1-28. Mann, E, Taylor, E, Edwards, L. and Ku, T., 1995. Actively evolving microplate formation by oblique collision and sideways motion along strike-slip faults: an example from the northern Caribbean plate margin. Tectonophysics, 246: 1-69. Mann, E, Prentice, C., Burr, G., Pena, L. and Taylor, E, 1998. Tectonic geomorphology and paleoseismology of the Septentrional fault system, Dominican Republic. In: J. Dolan and E Mann (Editors), Active Strike-Slip and Collisional Tectonics of the Northern Caribbean Plate Boundary Zone. Geol. Soc. Am. Spec. Pap., 326: 63-123. Middleton, G.V. and Hampton, M.A., 1976. Subaqueous sediment transport and deposition by sediment gravity flows. In: D.J. Stanley and D.J.E Swift (Editors), Marine Sediment Transport and Environmental Management. Wiley, New York, pp. 197-218. Muff, R. and Hernandez, M., 1986. The hydrothermal alteration and pyrite-galena-sphalerite mineralization of a porphyrite

R. DE Z O E T E N and E M A N N intrusion at Palma Picada in the Cordillera Septentrional, Dominican Republic. Natural Resources and Development (Ttibingen, West Germany), Vol. 26, pp. 83-94. Mullins, H. and nine others, 1992. Carbonate platforms along the southeast Bahamas-Hispaniola collision zone. Mar. Geol., 105: 169-209. Mutti, E. and Normark, W.R., 1987. Comparing examples of modern and ancient turbidite systems: problems and concepts. In: J.K. Leggett and G.G. Zuffa (Editors), Marine Clastic Sedimentology: Concepts and Case Studies. Graham and Trotman, London, pp. 1-37. Mutti, E. and Ricci Lucchi, E, 1978. Turbidites of the northern Apennines: introduction to facies analysis (translation by T.H. Nilsen). Int. Geol. Rev., 20: 125-166. Nagle, E, 1979. Geology of the Puerto Plata area, Dominican Republic. In: B. Lidz and E Nagle (Editors), Hispaniola: Tectonic Focal Point of the Northern Caribbean, Three Tectonic Studies in the Dominican Republic. Miami Geological Society, Miami, FL, pp. 1-28. Nilsen, T.H. and EL. Abbot, 1981. Paleogeography and sedimentology of Upper Cretaceous turbidites, San Diego, California. Am. Assoc. Pet. Geol., 65 (7): 1256-1284. Palmer, H.C., 1979. Geology of the Moncion-Jarabacoa area, Dominican Republic. In: B. Lidz and E Nagle (Editors), Hispaniola: Tectonic Focal Point of the Northern Caribbean, Three Tectonic Studies in the Dominican Republic. Miami Geological Society, Miami, FL, pp. 29-68. Peralta-Villar, J., 1985. Geologie und Erzffihrung in der Umgebung des Intrusionsbrekzienkorpers von Los Jobos/Pedro Garcia. Dominikanische Republik. M.S. Thesis, Institut der Universit~it Heidelberg, 111 pp. Pickering, K., Stow, D., Watson, M. and Hiscott, R., 1986. Deep-water facies, processes and models: a review and classification scheme for modern and ancient sediments. Earth-Sci. Rev., 23: 75-174. Pindell, J.L. and Draper, G., 1991. Stratigraphy and geological history of the Puerto Plata area, northern Dominican Republic. In: P. Mann, G. Draper and J. Lewis (Editors), Geologic and Tectonic Development of the North America-Caribbean Plate Boundary Zone in Hispaniola. Geol. Soc. Am. Spec. Pap., 262:97-114. Redmond, B.T., 1982. Sedimentary Processes and Products: an Amber-Beating Turbidite Complex in the Northern Dominican Republic. Ph.D. Dissertation, Rensselaer Polytechnic Institute, New York, 495 pp. Rosencrantz, E., Ross, M.I. and Sclater, J.G., 1988. Age and spreading history of the Cayman Trough as determined from depth, heat flow, and magnetic anomalies. J. Geophys. Res., 93: 2141-2157. Schlager, W. and Chermak, A., 1979. Sediment facies of platform-basin transition, Tongue of the Ocean, Bahamas. In: L.L. Doyle and O.H. Pilkey (Editors), Geology of Continental Slopes. Soc. Econ. Paleontol. Mineral. Spec. Publ., 27: 193-208. Shanmugan, G. and Moiola, R.J., 1988. Submarine fans: characteristics, models, classification, and reservoir potential. Earth-Sci. Rev., 24: 383-428. Sykes, L.R., McCann, W.R. and Kafka, A.L., 1982. Motion of Caribbean plate during last 7 million years and implications for earlier Cenozoic movements. J. Geophys. Res., 87: 10,656-10,676. Vaughan, T.W., Cooke, W., Condit, D.D., Ross, C.E, Woodring, W.E and Calkins, E C., 1921. A Geological Reconnaissance of the Dominican Republic. Gibson Brothers, Inc., Washington, 268 pp. Walker, R.G., 1984. Turbidites and associated coarse clastic deposits. In: R.G. Walker (Editor), Facies Models (2nd Ed.). Geological Association of Canada, Toronto, ON, pp. 171-188.