Carbonate platform depositional sequences, Upper Cretaceous, south-central Pyrenees (Spain)

Tectonophysics, 129 (1986) 205-231 Elsevier Science Publishers

CARBONATE

B.V., Amsterdam

PLATFORM

CRETACEOUS,

ANTONIO

205 - Printed

DEPOSITIONAL

SOUTH-CENTRAL

SIM6

in The Netherlands

SEQUENCES,

PYRENEES

UPPER

(SPAIN)

*

Departament de petrologia, Facultat de Geologia, Universitat de Barcelona, Gran Via 585, 08007 Barcelona (Spain) (Received

June 10, 1985; revised version

accepted

October

1, 1985)

ABSTRACT

Simb, A., 1986. Carbonate (Spain).

platform

In: E. .Banda

and

depositional

S.M. Wickham

sequences, (Editors),

Upper

Cretaceous,

The Geological

south-central

Evolution

Pyrenees

of the Pyrenees.

Tectonophysics, 129: 205-231.

The

Upper

carbonate

Cretaceous

platform

and inherited

(Cenomanian-Maastrichtian)

sequences

depositional

of the depositional

where the major

profile.

Depositional

Five depositional

sequences

have

been

a ramp to a skeletal rimmed

is an angular

unconformity

was determined

platform. distal

Cessation (Upper

slope.

sequence

of platform

boundary platform

platform

is an angular

and

areas:

address:

Pyrenees

relative

analysis

The platform

slope increased by

sea-level

permit

shows

five

fluctuations

an understanding

to the Mesozoic

Department Sciences,

margin

normal

of Geology

margin

produced (4)

sea-level

by an abrupt

The

marine expansion.

0 1986 Elsevier Science Publishers

morphology. sequence margin,

by 24 km of the previous

Vallcarga

ramp, erosional

University

St., Madison,

basin

ramp with upright

relative

prograding

B.V.

sea-level

rise and

sequence

(Upper

and turbidite

fault created carbonate

of Wisconsin-Madison,

WI 53706 (U.S.A.).

and

rise. The upper

escarpment

A listric normal

block with a north-northwest

and Geophysics,

ramp with erosional

more or less at the same position,

continuous

skeletal homoclinal

1215 W. Dayton

homoclinal

of the

the former

(3) The Sant Corneli

the backstepping

faulting.

maximum

steepened

drop.

location

rise drowned

by pre-existing

sea-level

(Middle-Upper

The lower boundary

The platform

sea-level

a distally

remained

indicating

margin.

drop.

controlled

from

Fe sequence

bypass

a sea-level

Coniacian),

at the platform

listric

Santa

(2) An abrupt

was largely

a more or less flat footwall

Weeks for Geological

0040-1951/86/$03.50

fault.

a mixed terrigenous-skeletal

a distal-steepened

basin, which corresponds

* Present

tilting.

one records

normal

The slope results

unconformity

drowning,

Santonian-Campanian), depositional

basin. and

(1) The

was due to a relative

Santonian),

and gentle basin between

recognized:

model

development

Coniacian-Lower

margin

and basin

(Turonian-Lower

The depositional

deep slope and dysaerobic relief

geometries

shelf with an escarpment

and the upper by a listric

The Congost

deep

south-central

are tectonism,

history.

Cenomanian), margin

of the

parameters

two ramp

Lewis G.

206 over shales. and a tilted and faulted and Campos)

laterally

The beginning

of compressional

4ren sequence

(Maastrichtian),

tary

thrust

and

The

main

compressional (3) inherited sea-level

movements; depositional

fluctuations

The

in terms

profile.

tirowth

of each sequence

sequence

platform

of abrupt

abrupt

the escarpment ended. (foreland

svatems (La Pobla

in mass-flow

and basm

evolutmn

in

deduced

subsidence of platform

were less important

the

deposits.

collapse.

(5) The

of synsedimen-

studied

area.

with

a

basin). events.

sea-level risesin accordance

potential

turbidttic resulted

shelf and basin with development

and basin inversion

of the carbonate (2) relative

about

nearshore

anticlines.

(1) tectonism

block where siliciclastic of the fault escarpment

brought

a siliciclastic

thrust-ramp

parameters

are:

Erosion

tectonism

associated

Maastrichtian-Paleocene Cretaceous

hanging-wall

filled the basin.

from

the

flexurc.

and

Pyrenenn

w-ith subsidence

and rim. \ilictclastic

Upper

extenstonal events:

progradation.

and and and

factors.

INTRODUCTION

Carbonate platforms abound throughout geological history and cover large areas. In the past, investigation was on recognition of ancient carbonate platform facies associations and depositional profiles which were compared with present-day platforms (e.g., Wilson, 1975; Bathurst, 1975; and Sellwood. 1978, amongst others). Recently, thanks to the new tool of seismic stratigraphy. the geometric relationships between sedimentary bodies as well as their evolution have been reinterpreted in terms of their response to sea-level variations, sedimentary processes and structural history. Reviews of carbonate platform margin models have been given by Mcllreath and James (1978) Read (1982, and 1985), James and Mountjoy (1983). and Cook and Mullins (1983). Concepts on carbonate platform response to relative sea-level fluctuations were dealt with by Kendall and Schlager (1981). Schlager also pointed out some problems in platform drowning (Schlager, 1982). The geotectonic context plays an important role with carbonate platforms; for Lstance, subsidence due to faulting or flexure appears to have controlled the location of many margins (James and Mountjoy, tional

setting

recent (Mullins Jansa,

1983); it also influences

and orientation and Neuman,

1981) carbonate

platform

the carbonate

of the shoreline 1979; Mullins, margins

(Tucker,

sedimentation,

1985). Seismic

1983) and ancient

help in the understanding

deposiprofiles

of

(Schlee et al., 1979: of the geometric

relationships. Read (1982, 1985) described different models of carbonate platform evolution using three dimensional features. Some fossil examples were described by Aitken (1978), Playford (1981) and Cook and Taylor (1983, in Cook, 1983). Cretaceous and Tertiary sediments of the south-central Pyrenees (Fig. 1) are exceptionally well exposed. The moderate structural deformation and quality of the exposure makes the study of a cross section possible and comparable to that of a seismic section. Carbonate and siliciclastic depositional environments can be followed in space and time. In this report, the Upper Cretaceous platform evolution is described from the Nogueres area in the south-central Pyrenees (Fig. 1). Tectonics and sea-level fluctuations influence depositional cyclicity. Also there is a special

20 Km

Orp

\

I

Upper Thrust sheets

/TJj

HadIeThat

sheets

Ezzl _--__

Lower Thrust sheets

oo.00

Eocene

nnn

Oliq3cene Mwcene

Fig. 1. Structural sketch of the Pyrenees (A) showing the major thrusts and faults (numbers refer to the text) and structural map of the south-central Pyrenees (based on Muiioz. 1985) with localities and rivers aforementioned in the text (B).

emphasis on the platform geometries and depositional facies as well as the features that control this evolution.

GEOLOGICAL

SETTING

The Pyrenees are a Late Cretaceous to Oligocene E-W elongated mountain belt about 300 km long and 140 km wide (Fig. 1). The main structural elements are: (1) the North Pyrenean fault (NPF, of Fig. l), interpreted as a plate-to-piate boundary, seems to continue down to the Moho, with a down-throw to the south of 15 km in the central Pyrenees. Low-grade metamorphism and lherzolite emplacement occurred during Albian times along this line; (2) the North Pyrenean zone consisting mostly of Mesozoic and Tertiary sediments thrust toward the north; and (3 and 4) the South Pyrenean zone consisting of several south-verging thrusts of Paleozoic (3), Mesozoic and Tertiary rocks (4). Three thrust sheets have been differentiated

(Mufioz,

1985): (a) upper thrust sheets, consisting

and complete incomplete thrust

Mesozoic and reduced

sheets, formed

On

the basis

anomaly

sequence;

(b) middle

Mesozoic

sequence

of pre-Hercynian

of paleomagnetic

identification

and an Eocene

of basement,

flysch:

an

and (c) lower

basement. data

and structural

of cover thrust sheets with a thick

thrust sheets, formed

on continental

considerations

rocks,

oceanic

magnetic

(Van der Voo, 1969: Le Pichon

and Sibuet, 1971; Choukroune et al., 1973a. b; Souquet et al., 1977: Choukroune and Mattauer, 1978; Kristoffersen, 1978; Vandenberg, 1980; Grimaud et al., 1982: Masson and Miles. 1984) it seems to be generally accepted that a Mesozoic distension and opening led to continental margin sedimentation along the Iberian and European plates, followed by a compressional stage during Maastrichtian Paleogene times that ended with the formation of the Pyrenees. Puigdefabregas Souquet (1985) defined six major megacycles in base of Pyrenean basin and the tectonic movements. They considered that a small wrenching

and and

evolution occurred

during the Upper Cretaceous. The study area is located in the upper thrust sheets of the South Pyrenean zone (Fig. 1). This unit forms a large syncline with gently dipping Mesozoic limestones cropping out on the south flank, and shales and limestones on the north flank. The central part was filled with nearly horizontal Tertiary sediments. Continuous outcrops different

on the north flank between Orgafia and Sopeira allow observations of the platform margins which can easily be correlated with the platform interior

of the Montsec UPPER

area (Fig. 1).

CRETACEOUS

STRATIGRAPHY

The early studies of Mey et al. (1968) established of this area. Later work on the St. Corneli

r%iziCciiO 1

1

MAASTRICHTIAN

1

1

85

Fig. 2. Upper

Cretaceous

STRATIGRAPHIC

the main lithostratigraphic

area (Gallemi

UNITS--

/MEY et d,i968(

ARE

1

CONGOST

stratigraphic

Sq

CDNGOST1s r

units and depositlonal

et al., 1983) divided

sequences

GALLEMI et d,1983

units the

209

units and

into more members Rios

regional

(1972)

and

stratigraphy

sedimentology Nagtegaal Llompart

(Fig. 2). Rose11 (1967)

Garrido-Mejias and

tectonics.

of the Upper

(1972), Liebau (1982)

Gallemi

(1973) More

Cretaceous

(1973)

Souquet

have

already

detailed

papers

have

been

Von Moeri (1977)

(1967), Garrido-Mejias studied

the Mesozoic

on paleontology

published

and

by Rose11 (1970)

Caus et al. (1981)

Rose11 and

et al. (1983), and Caus et al. (1983). Souquet

(1984) and

Sirno, Puigdefabregas and Gili (1985) recognized the main depositional sequences and sedimentary character of each one. Detailed sequential and facies maps can be found in Lopez-Lopez (1982) and Simo (1983, 1984). The stratigraphic units in this paper are based on the geological map correlation of the different lithostratigraphic units. Formations and members are integrated into a simplified stratigraphic framework with a depositional sequential character (Fig. 2). UPPER

CRETACEOUS

DEPOSITIONAL

SEQUENCES

The sequential character of the Upper Cretaceous deposits has been shown Garrido-Mejias (1973), who was the first to recognize the tectonic control

by on

sedimentation. He divided the sedimentary record into tecto-sedimentary sequences. Souquet et al. (1977) synthesized the main Pyrenean Mesozoic cycles relating them to global tectonism. Caus et al. (1983) and Rose11 and Llompart (1984) recognized sea-level changes as sequence boundaries, and Souquet (1984) took tectonism and relative sea-level changes as sequence boundaries to give a generalized depositional model.

Simo et al. (1985) defined

the major

area. Five major genetic sequences (third-order nized (Fig. 3) in the second order Upper Maastrichtian). is an angular depositional

depositional

sequences

in the Tremp

cycles of Vail et al., 1977) are recogCretaceous sequence (Cenomanian to

(1) The Santa Fe sequence (upper Cenomanian); its lower boundary unconformity and the upper boundary records a sea-level drop. The pattern

shows a thickening

basin marls. (2) The Congost sequence prograding distally steepened carbonate

outward

carbonate

shelf, slope breccias

and

(Turonian to Lower Coniacian): has a NW ramp, with an upper boundary produced by

non deposition and erosion. (3) The St. Corneli sequence (Upper Coniacian, Lower Santonian): an upright carbonate platform margin, slope marls and dysaerobic basin. It was terminated by a sea-level rise. (4) The Vallcarga sequence (Upper Santonian-Campanian), where its lower limit represents the major marine expansion and extensive growth fault development, and its upper limit is the basin collapse that resulted from the beginning of the tectonic compressive stage. (5) The Aren sequence (Maastrichtian) siliciclastic nearshore, shelf bars and slope shales developed during compressional tectonism. The upper limit is an angular unconformity in red beds. These sequences chain.

can also be recognized

all along

the Pyrenean

Turbiditer

Fig. 3. Depositional sequences and geometries. Numbers i to 5 refer to depositional sequences (see Fig.

Santa Fe sequence (Upper Cenomanian)

The Santa Fe sequence corresponds to the Santa Fe limestone (or Prealueolina limestones), Sopeira marls and Santa Fe Breccias. It rests with angular unconformity on earlier Mesozoic and Paleozoic rocks. The platform carbonate sequence is made of tabular (average 40 m thick and 50 km long) planar bedded limestones that become

thicker basinward

(150 m thick over 5 km long} and progrades

water marls. The escarpment from the escarpment erosion.

between

limestones

over deeper

and marls was filled by breccias

Depositional facies are: (a) platform jacies-mainly wackestone and lime mudstone, commonly showing

pelletal wackestone, bioturbation, planar

miliolid bedding

and a fining and tinning up sedimentary sequence; (bf ~~~~je~~e”f~~je,~ of massive and coarse skeletal grainstone and coral-rudist reefs; (c) marginnf-slope ,ftlc’m---cmresponds to a coarsening and thickening up sedimentary sequence of mud flows and debris flows. The number and volume of boulders increases upwards (maximum 140 m’). They consist of cemented skeletal grainstones or fragments of coral-rudist reefs, in a matrix of clasts. marls and patchily distributed non-cemented skeletal grainstones (Figs. 4 and 5). There is no evidence of an original submarine fan or even coalescing fans. Therefore, deposition appears to have occurred along the platform margin in an apron environment. Mass flows and submarine sliding were

Fig. 4. Aerial

photograph

sequence

slope

erosional

unconformity

the dominant to the basin

facies

of the Ribagorqa

downlap,

river

the Congost

of the Vallcarga

area

sequence

sequence

near deep

Sopeira slope

village;

breccias

showing onlap

the Santa

(arrows).

and

Fe the

lower boundary.

mass transport processes. The estimated depositional dip with respect facies is loo. (d) Basin facies are shales and glauconitic marls with

slump scars. The depositional model of this sequence (see Fig. 13) was mostly controlled by the pre-existing basin morphology. Growth faulting in Lower Cenomanian produced tilting (up and downthrown blocks) and localized basins (downward pocenter). The interior platform lagoonal limestones overlie these tilted blocks, truncate older deposits. escarpment. Prograding

deand

Carbonate shelf edge facies developed around the fault peri-platform talus facies overly the lower slope-basin

marls. The thickening outward geometry results from: (a) basin morphology (tabular platform and steep shelf margin); and (b) shelf edge rapid upbuilding due to a slight relative sea-level rise. The cessation of platform development was due to a short sea-level drop and karstification of the margin. A rapid relative sea-level rise and a slight basin tilting drowned the platform. Drowning of the platform resulted in deposition of a glauconite bed or ferruginous hardground, Pithonella lime mudstone (pelagic condensed mudstones) commonly covers the platform facies. Congost sequence (Turonian-Lower

Coniacian)

The Congost sequence, a distally steepened ramp, occurs above the drowned rimmed shelf of Santa Fe sequence (Congost limestone and Reguard marls) and

Fig.

5. Santa

grainstone, supported

Fe sequence

in (B) a matrix texture (Sopeira

marginal formed village).

slope hy clast,

facies. rudists.

A. Boulders corals

and

(white

C&XX) nf cemented

flat pebble

conglomerates

skeletal in a mud

Fig. 6. Congost depositional sequence. A. Carbonate shallow ramp facies, prograding coral-rudist reefs (r), fore-reef (fr) and rudist beds (b) (Congest Fm., Flamiqell river). B. Marly deeper ramp to carbonate shallow ramp facies, coarsening and thickening upward sedimentary sequence. (f) Santa Fe sequence interior platform (Flamic;ell river). C. Deep slope facies onlap of Congest sequence. breccias beds (arrows) over (1) Santa Fe sequence marginal slope facies (Ribagorqa river). D. Polish sample of deep slope boulder showing karst cavities with dissolution boundary (d). cement (c), “terra rossa” (t ) and glauconitic shales of the Lower Coniacian (,q). The boulder is eroded from the Santa Fe sequence platform margin (Ribagorqa river, scale in centimeters).

Y w

714

begins

at the base of the Pithunellu

limestone.

from few to 400 m in 22 km. thinning margin

(8 km farther).

Erosion

at the toe of escarpment The sedimentary Depositional (thickness

again

Its thickness toward

of the earlier shelf margin

of carbonate

breccias,

increases

the Santa resulted

interbedded

basinward

Fe sequence

shelf

in sedimentation

with slumped

shales.

sequence is shallowing and coarsening upward overall (see Fig. 13). facies are: (a) carbonate shutlou, rump facies with a lower member

25-100

m) of bioclastic

ing up cycles (Fig. 6). Grain

wackestone-packstone

in coarsening

size is very fine to fine. It grades upward

and thickento coarse-very

coarse oolitic-skeletal grainstone with large scale cross bedding. Abundance framestones with reef talus increases basinward (Fig. 13). Thickness

of coral of these

buildups do not exceed 35 m (Fig. 6). These sediments are covered with miliolid grainstones, stromatoporoid and rudist beds toward the basin. The sequence is shallo~ng up and shows the characteristics of a homocl~nal ramp (see Read, 1982). (b) Mu+ deeper rump facies consist mostly of alternation nodular lime mudstones and shales. Planktonic foraminifera and bioturbation are common. Intraformational structures and breccias have not been observed (Fig. 6). (c) Deep slope or escarpment, the escarpment and talus of Santa Fe sequences act as the deep slope of

Fig. 7. Congest platform syncline).

(f)

depositional

overlain

sequence:

by marls

(m)

carbonate and large-scale

platform foresets

progradation.

Santa

of the prograding

Fe sequence carbonates

interior

(Santa

Fe

215

the Congost slightly

sequence.

silicified

slumped Commonly equant

rudist

shales and breccias

well rounded, radiaxial

Shelf break and slope sediments

(mostly

cemented

and

sandstone crust

pelagic wackestone,

dull luminescent

cherts).

of the Santa Fe sequence

are

Above

are

(Figs. 4 and 6). Breccia boulders

skeletal

they have a ferruginous cement,

nodular

cement

(silicified)

show dissolution

pink in colour

sediments

(up to 1 m3) are fairly

or coral-rudist and

these

marine

holes

framestone. filled

shale and locally,

(Fig. 6). Breccias and shales onlap

with late

the depositional

profile (Figs. 4 and 6). Locally in the Tremp and Montsech area this unit is eroded by a fourth-order cycle, the Collada Gasso sequence (Sirno et al., 1985) which are shelf and restricted Chara limestone and shale facies. The depositional model was largely controlled by pre-existing basin morphology and basin subsidence. Basin subsidence can be observed by: (1) thickening outward of the deep slope breccias, and (2) basinward flexure of the depositional profile. Thus a tabular body can be distinguished with horizontal progradation (130 m thick and 15 km long) (Fig. 7) that changes gradually with time towards a gentle offlap where the substrate dip increases due to flexure. However, the upper surface is represented by very continuous planar bed with fauna1 assemblage indicating deposition near sea-level. These beds are covered by a hardground. Cessation of platform siliclastic

development was due to a basin tilting influx in the platform and megabreccias

and a relative sea-level drop with in the European slope margin (see

Lagier, 1985; Simo, 1985). A relative sea-level rise drowned St. Corneli sequence (Upper Coniacian-Lower

the platform

(Fig. 13).

Santonian)

The Sant Corneli sequence corresponds to a shallow carbonate platform (Aramunt and Montagut), slope marls (Anserola) and basin ribbon limestones (Aguas Salenz). Its geometry shows a carbonate body of 100 m (inner platform) to nearly 350 m (outer platform). The platform margin is vertical, and slope shale becomes thicker, from

100 to 600 m, basinward

(thickness

reduction

from

platform

margin

to

marginal-slope facies is abrupt, Fig. 13). Depositional facies are: (a) Platform fucies (20 km wide), (1) of white-gray skeletal wackestone to grainstone, coral patch reefs and rudist beds, and (2) red cross-bedded calcarenites with some quartz and rudist reefs. The inner platform shows bioturbated shales, rudist beds and lime mudstone-wackestone. The outer platform, consists of skeletal packstone-grainstone, with isolated large rudists and coral patch-reefs, and calcarenites which have a bar geometry with coarsening up sequences and 3-5 m long foresets (Fig. 8). Paleocurrents are toward NNW and NE. Prograding rudist reefs may develop between platform bars and marginal-slope facies. (b) Marginal-slope facies (3 km wide) are well-bedded lime mudstones and shales, with a few sand sheets and knoll coral reefs (10 m thick and 120 m large). (c) Slope facies (nearly 30 km wide) are nodular marls and shales with slump scars and

Fig. X. St. Corneli Corneli

north

depositional

sequence.

flank, west of Aramunt

A. Cross-bedded

calcarenites

of the shoal platform

village). B. Deep slope slump scars (Ribagoqa

margin

river area).

(St

217

glauconite

beds. The sequence

8). Basinward, becomes

thin

dominant.

thins up and the shale content

bedded

and

ppm-Garrido-Mejias, abrupt

silty-shale

(d) Basin facies are thin-bedded

and sponge spicules (thickness An

bioturbated

increases with

many

lime mudstone

upward

(Fig.

slump

scars

with radiolaria

450 to 3000 m), with a high proportion

of boron

(500

1973).

backstepping

preceding sequence. geomorphic position

of the platform

occurs

after

the

drowning

of the

The shelf-slope break remains more or less in the same (upright margin of Playford, 1981, stationary margin of James

and Mountjoy, 1983, or upbuilding margin of Cook, 1983). The carbonate platform accreted at the same rate as the sea-level rise. With time, the platform thickness increased and relief between platform and slope increased becoming gullied, indicating rapid sea-level rise. Pre-existing basin morphology resulting from the tilting and drowning of two successive carbonate platforms, created a deep basin with a longer slope.

and backstepping

of the margin

The upper boundary of this sequence is marked by a very rapid sea-level rise and growth faulting. No sea-level drop has been recorded. The rapid relative sea-level rise is indicated by (1) 160 km coastal onlap; (2) backstepping of the next carbonate platform sequence; (3) deposition of deep shales over the platform surface; and (4) retrograding geometry of the shelf margin top. Shelf break shoal retreat gave rise to an inclined surface, later covered unconformably sequence. The growth faults are curved from E-W the relative sea-level there formation of the Pyrenees.

was an acceleration

by deep shales of the Vallcarga to NE (Fig. 14). Associated with of the subsidence

related

to the

Vaifcarga sequence (Upper Santonian-Campanian) This sequence represents the maximum extension of the Upper deposits. It corresponds to slope-basin turbidites (Mascarell Member), (Herbasavina facies

Member)

(Montsec

and rudist reefs (Colladas

limestones).

The depositional

Member), geometry

and carbonate shows:

Cretaceous shelf shales platform

(a) a south

flat

surface deepening northwards, where shelf shales and shallow water limestones were deposited, and (b) a northwestern basin filled with turbidites which eroded the previously deposited sequences. Between shelf and basin a listric normal fault forms a slope (Figs. 3 and 13) on which deposits of previous sequence were resedimented as olistoliths, debris flows and mudflows. Depositional facies: (a) Carbonate ramp, near tabular calcareous body (thickness up to 759 m) with large-scale cross bedding prograding north and northwest. The lower contact is gradual but rapid over open marine shales (Fig. 9) the upper boundary is made of sandstones. The overall sedimentary sequence is coarsening and shallowing up. Massive skeletal sandstones are the dominant lithology. Some rudist and red algal patch-reefs occur at the top of the sequence. (b) Open marine shelf shales; they are located south of slope escarpment and cover the St. Corneli

Fig. 9. Vallcarga depositional sequence interior C’ongost

((‘I)

and the

sequence. A. Carbonate

(c’) (Montsec).B. Erosive Santa Fe ( f’) sequences. Lower

platform

ramp

(r)

and inner shelf facies

lower boundary Cretaceoua

( /c)

(s) over St. Comeli

cutting off the slope facies of the (Rihagorqa

river).

219

sequence

and other Mesozoic

(on the St. Corneli

sequence

shelf facies are nodular ammonites upward.

foraminifera.

shales

Frequency

with some thin

outward.

(c) Slope fucies

turbiditic

basin

and

The lower boundary

marls and shales with isolated

and planktonic Massive

deposits.

is sharp, locally angular

shelf edge), and the upper contact

were

absent

shelf shale indicates

silty beds and

is gradational.

corals and rudists

of skeletal and

sand sheets increases

scarce

the geometric

an escarpment

Inner

mixed with

slump

relationship (may

scars occur between

be 100-200

m of

relief). This slope is an erosional escarpment (shelf shale by-pass). (d) Slope-basin turbidites, formed in an elongate E-W basin bounded to the south by an escarpment (Fig. 14). Throughout the sequence, escarpment instability resulted in mass movement. Turbidites were deposited on an irregular substrate, and erode underlying sequences. Evidence of irregular and tilted substrate are: variability of current indications in the same sandstone bed (NW, SW), abundance of mass movement with SW transport direction, and slumped turbidite beds. Nagtegaal (1972) clearly pointed out the presence, at the base of the sequence, of mass movement toward the southwest

and suggested

the presence

of temporary

tectonically

induced

slopes. The

turbiditic basin shows (1) one major direction toward the NW and W (“La Palla system”), and (2) one minor direction toward the NE and E in the Esera and Turbon area, cropping out near the canyon feeder (Camp0 breccia), “Camp0 system”. In the area between Isabena and Turbon both paleocurrents directions are recorded (Van Hoorn, 1970). Petrological analysis (Van Hoorn, 1970) shows that the “Campos system” has different types of polycrystalline quartz compared to the “La Pobla system” groups

turbidites.

(Van Hoorn,

The petrology

1970; Nagtegaal,

of the turbidite

beds shows two dominant

1972): (a) carbonate

grains (algal, bryozoan,

echinoderm, bivalve fragments showing micritic rims and algal borings, and shallow and planktonic foraminifers); and (b) quartz is the predominant extrabasinal constituent, and quartzite, phyllite, chert and feldspars are the secondary constituents. Plants and wood fragments are very abundant. These data show a complex source area: (a) a siliciclastic and (b) a neritic area. The neritic source may be the carbonate

platform

located

south

of the escarpment

(Montsec),

and

the main

siliciclastic source may be related to the far-east of the Pyrenees (below the Mediterranean Sea) where already compression (Tapponnier, 1977) and a minor source coming from the south (“Campo” system) started. Siliciclastic sources are igneous and metamorphic rocks (Van Hoorn, 1970). The geometry resulting (Figs. 3 and 13) from the depositional facies shows a southern distally steepened ramp prograding NNW, an erosional escarpment, and a turbiditic basin. The Vallcarga sequence was deposited during a rapid relative sea-level rise and later still-stand. The coarsening upward sequence in the basin suggests growth of the siliciclastic source area and/or increase of the tectonic activity.

220

Shelf basin collapse The change and

from extension

is evidenced

nodular

lime-mudstone,

able throughout

to compression

by the collapse

took place at the end of Campanian,

of the shelf edge and

conglomerates

deposition

and debris flow deposits.

the basin (80 km) and wedge towards

of slumped

They are recogniz-

the northwest.

Collapse of the Vallcarga edge (fault escarpment) can be observed on the south side of St. Corneli anticline (Fig. 10). Open marine shales (Herbasavina shales) are overlain by white lime mudstone (related to the Montsec limestones). The lower contact to the east is gradational but rapid, and to the northwest is erosive. To the east, parallel bedding is well preserved, but to the northwest beds are truncated and folded by growth faults. A water reservoir covers the continuation of the margin, but a bypass down to the escarpment

toe can be inferred

(Fig. 10).

The olistostrome at the toe of the escarpment has a multistory evolution, with mixed deposits from the siliciclastic and neritic source area. There is a lower unit of conglomerates which are in sharp contact on the turbidites, prograding and wedging toward the northwest (Simo et al.. 1985). Most of this material comes from a south siliciclastic source area and the escarpment. Listric normal faults developed and started the collapse of the carbonate source area (upper unit) (Fig. 10). Lime-mudstone olistoliths and matrix-supported conglomerates are cut into earlier deposits. Resedimentation ceased after emplacement of stratified olistoliths. A great thickness of sediment (230 m) accumulated at the toe of escarpment.

Fig. 10. Vallcarga fossilized photograph.

sequence

by Aren sequence

shelf edge collapse. sandstones

Notice

(St. Corneli

the growth

faults affecting

south flank anticline

white mudstones

near Montesquiu

and

village). Serial

221

Olistostrome neritic

development

can be summarized

source areas were quickly

displaced

as follows:

over the platform;

offlapped

into the basin,

with mass-flow

to fluid-flow

faulting;

and (4) collapse

of the southern

platform

Aren depositional

(1) Siliciclastic

and

(2) coarse siliciclastic

sequences;

(3) listric normal

shelf edge (Simb et al., 1985).

sequence (Maastrichtian)

The Aren sequence

represents

the final stage of the Upper

It has a predominant siliciclastic lithology, the influence of tidal and wave currents.

Cretaceous

a shallowing up tendency A general northwestward

basin

fill.

and it shows progradation

(Ghibaudo et al., 1973, 1974) is well demonstrated by both facies mapping and paleontological data (Nagtegaal et al., 1983). It corresponds to the Aren Sandstone formation and Salas Marls member. Detailed study of the Aren Sandstone formation comes from Ghibaudo et al. (1973, 1974) who gave a well documented description of the nearshore sedimentation in the Aren area (Ghibaudo Maier-Harth (1982) is a later paper on the same area and describes

et al., 1974). the offshore

facies. In the Tremp area, Nagtegaal et al. (1983) defined the main facies and environments and recognized successive erosive surfaces as the effect of the movement of the St. Corneli anticline. Sgavetti et al. (1984) recognized eighteen depositional sequences related to both uplift of the anticline and sea-level fluctuations. Simo et al. (1985) defined and extensively described the Aren depositional sequence. The depositional sequences above occurred during extensional tectonism. Change from extension to compression took place during the Campanian-Maastrichtian boundary and the siliciclastic Maastrichtian strata (Aren depositional sequence) were deposited during compression. Inversion from listric normal fault to listric thrust fault induced anticline growth south of the shelf break (St. Corneli anticline). Evidence of synsedimentary folding (Fig. 11) are: (1) basal angular unconformity, onlap and reduction of thickness of Aren presence of progressive unconformities, and

sequence against the anticline; (2) (3) change in source area. Another

synsedimentary contemporaneous

anticline

anticline is the Turbon-Egea erosion (Papon, 1969).

The Aren depositional

sequence

with evidence

has two major cycles in the Tremp

of faults

and

area: Cycle I

(lower cycle) with three shallowing up sequences of siliciclastic nearshore facies to the south, prograding north to shelf sand bars (3 km wide, 7 km long and 40 m thick). To the north, they onlap the limb of the anticline. Shelf sedimentation around the anticline shows a cyclicity given by: (a) tilting, drowning of shelf bars, shale onlap and channel incision on bar tops; (b) stabilization, shelf bar progradation onlapping the anticline. Vertical superposition of different cycles results in a progressive basal unconformity. Top of Cycle I is characterized by a general shallowing, local karstification and coarse conglomerate influx from the south. Between place.

Cycle

I and

II, paleogeographic

changes

and

regional

shallowing

took

.

.

I

Sandstone bars b) Sandyshelf

Fig. Il. Aren depositional map around olistostrome St. Corneli

Neat-shore

sandstones

sequence:

fossilization

the Tremp-Orcau and associated

of the synsediment~r~

area. The lower boundary sediments.

St. Corneli

of the sequence

Notice the nnlap and wedging

anticline,

corresponds

geometry

Geological

to the top of the

of the sequence

over the

pericline.

Cycle II (upper cycle) is characterized by (a) non-marine depositi(~n on the former nearshore-shelf area (Fig. 12), (b) marine deposition and northwest progradation around the anticline, and (c) change of source area from south to north. Five minor cycles can be distinguished in the area around the anticline (Fig. 11 )_ directly

controlled

by: (a) Iistric normal

faulting,

(b) westward

lateral

migration

of

sedimentary wedges (Cycles B, C and D), and (c). relative sea-IeveI changes. Listric normal faults were triggered by episodic movements of the anticline. Slope gradient increases westward. so that shelf sandstone bodies occur exclusively near the anticline. Away from it, sediments consist mostly of shales and thin-bedded turbidi tes (P~igdef~bregas and Simri. 1984). The Turbon was another synsedimentary anticline developed at the basin and always submergent. The sedimentary processes were sliding of the vergent anticline flank material, resulting in a chaotic mass of breccias and shales. Both cycles can also be distinguished: (1) a lower cycle corresponds to the anticline growing, and (2)

223

Fig.

12. Aren

shallowing (Orcau

depositional

up sequences

village).

conglomerates

B. Cycle (Santa

sequence.

A, Panoramic

(1 and 2) of prograding II beach

Engracia

village).

progradation,

view of the Cycle

I with

two coarsening

shelf bars (sb), and the Cycle II sandstone planar

stratas

at

the background

channel

and (ch)

are Oligocene

224

an upper

cycle corresponds

movement

to beach

progradation

without

evidence

of anticline

(Sirno, 1984).

DEPOSITIONAL

HISTORY

The Upper depositional

Cretaceous sequences.

(Cenomanian-Maastrichtian) In the south-central

the sequences are as follows: (1) Skeletal rimmed shelf

with

of the Pyrenees

Pyrenees,

escarpment

the evolution

bypass

margin

shows five

and geometry

of

(Middle-Upper

Cenomanian, Santa Fe sequence): it has a very extended (50 km wide) thin (40 m thick) interior platform and a narrow (5 km wide) thick (150 m thick) platform margin,

also a chaotic

Fig. 13. Platform Figs. 2 and 3).

evolution

and massive

and depositional

marginal

foreslope

models. Numbers

1-4

(3 km wide) adjacent

refer to depositional

to the

sequences

(see

225

platform caused

margin

(Fig. 4), and shallow

by extensive

tectonism

basin

and a listric

(Fig. 13). The platform normal

faulting

geometry

(Cenomanian)

was which

changed the basin configuration. The interior platform covers the highest part of the footwall; the platform margin is on the fault escarpment, and the basin is at the foot of this

escarpment

and

over

caught up a slight relative sea-level

the hanging-wall

sea-level

rise (Lower Turonian),

block.

rise resulting

Carbonate

in vertical

after a short sea-level

sedimentation

accretion.

drop, drowned

An abrupt the platform

and hardgrounds, glauconite and pelagic sediments were deposited. (2) Distally-steepened ramp with erosional distal deep slope (Turonian-Lower Coniacian, Congost sequence) has (Fig. 13) a northnorthwest prograding nature (Fig. 7) and its thickness increases basinward from few to 400 m in 22 km, thinning against the Santa Fe sequence shelf margin (8 km farther along). The erosion of the Santa Fe margin results in an onlap of resedimented breccias and shales (Figs. 6 and 13). Its geometry is mainly controlled by the pre-existing basin configuration and basin flexuring. The top surface of the Santa Fe sequence is nearly flat in the inner zone and on the margin a depositional escarpment existed. Between the inner zone and margin, flexuring took place, due to basin tilting (Fig. 13). A relative sea-level still-stand together with an initial high rate of carbonate sedimentation and low rate of basinal accumulation brought about a high rate of lateral accretion. Through time, depth increased (due to flexure) leading to gentle offlap of basinal sediments. Resedimentation on the deep slope occurred during this stage. A sea-level drop caused the cessation of carbonate sedimentation, siliclastic sedimentation in the inner

platform,

Coniacian)

(3) Homoclinal Lower Santonian, platform

and erosion

submerged

in the slope. An abrupt

the platform

and caused

relative

the margin

sea-level

to retreat

rise (Upper 6 km.

ramp with upright margin and deep slope (Upper ConiacianSt. Corneli sequence) has (Fig. 13) a mixed terrigenous-carbonate

(12 km wide) thicker at the margin,

a narrow (3 km wide) marginal

slope, a

very large (30 km) and thin (100-200 m thick) slope, and also a deep basin. The most prominent attribute of the depositional geometry is the wide slope that results from the margin

backstepping

(24 km) of the previous

facies become thicker basinward indicating a flexuring The platform shows a siliciclastic influx that suggests The coarse materiai was stored on the platform and basinward. A continuous relative rise of sea level is margin and marginal-slope geometries (Fig. 13). A third drowned the platform and faults affected the slope.

sequences

(Fig. 3). The slope

and onlap over the slope. the beginning of tectonism. only fine sediment moved inferred from the platform abrupt relative sea-level rise

(4) Distal steepened skeletal homoclinal ramp, erosional escarpment and turbiditic basin (Upper Santonian-Campanian, Vallcarga sequence). The beginning of tectonism brought about a landward migration, of almost 160 km, of the hinge zone (region of zero subsidence) and a normal fault created two depositional areas (Figs. 13 and 14): (a) on the south (footwall block) a skeletal homoclinal ramp prograding northward; and (b) on the north (hanging-wall block) a turbiditic basin developed

St. Fe sq. platform ----

Congast

54. platform

St. Corneli

marg,n

-

margin

sq. platform

va11carga

00.0

margin

--c Current $D

Fig. 14. Paleogeographic various

platform

sketch map with the synsedimentary

rq. escar~nt

Vallcsrga

Arm

rq. platfom

margin

direction

rg cynsedimmtary

faults and folds and the last position

fold5

of the

margins.

over irregular, faulted and tilted blocks. A lateral Between both areas there is an erosional escarpment

filling is assumed in which sediments

(Fig. 14). of the St.

Corneli slope facies (Tremp area) and Cretaceous-Triassic (on the Campos area) crop out. There is no evidence of a sea-level fall on the carbonate platform suggesting that the turbidites are probably not low-stand turbidites (see Shanmugam and

Moiola,

Progradation

1982). The sea level stood of the terrigenous

up of the turbidite

sequence.

controlled

system

channel

still and the platform

system is inferred The Campo

(Van

Hoorn,

breccia

accreted

due to coarsening

has been interpreted

1970) with

boulders

coming from the erosional escarpment. (5) Siliciclastic nearshore, shelf and basiri with development

and

laterally.

and thickening as a fault

conglomerates

of synsedimentary

thrusts and associated anticlines (Maast~chtian, Aren sequence). The change from extension to compression caused the collapse of the shelf edge and escarpment of the Vallcarga sequence. The compression started first in the east and moved westward along the Pyrenees. However, in the south-central Pyrenees it began at the same time, but in the east (Tremp area, Fig. 1) the thrust reached the surface resulting in basin inversion and uplift of the area (Simb et al., 1986). The Aren sequence shows two cycles which correspond to the main tectonic stages: (a) lower cycle with tectonic activity (e.g., development of Boixols thrust, St. Corneli and Turbon anticlines, progressives unconformities, uplift of Montsec-St. Corneii area,. . . ) and (b) upper cycle with tectonic stability (karstification of the Montsec

227

(M. Soler, pers. ~~mmun., deposits sponds

(being

affected

with another

and basin inversion Figures

1985) and

St. Corneli),

by the anticline

compressive in the studied

growing).

tectonic

and the depositional

sedimentation

of coastal

pulse (Cretaceous-Paleocene

corre-

boundary)

area.

3, 13 and 14 show schematically

superposition,

and

The end of the sequence

the depositional

history.

Figure

sequence

14 represent

geometry

and

a paleogeographic

sketch with the last position of the different piatform margins and the synsedimentary faults and folds. The sea level dropped two times (Lower Turonian, Upper Coniacian) and rose abruptly three times (Lower Turonian. Upper Coniacian and Lower

Santonian).

The carbonate

production

caught

up with sea level and

thus

progradation of the shelf margin took place. Notice the geometry of the Vallcarga sequence escarpment which cuts off the Upper Cretaceous margins and Mesozoic sediments to the west. CONCLUSiONS

AND DISCUSSION

The five Upper Cretaceous depositional sequences of the Pyrenees are controlled by tectonism and relative sea-level changes. Unconformities or sequence boundaries correspond to rapid sea-level rises (“condensed sections”, in the sense of Vail et al., 1984) and erosional truncations (subaerial or submarine) induced by tectonism. Subsidence, faulting and thrusting are important factors of the depositional history of the Upper Cretaceous. Van Hoorn (1970) suggested migration of the underlying evaporitic Keuper (Upper Triassic) in the basin center and diapirism on the basin margin to explain the great subsidence. Souquet (1984, his fig. 1) pointed out subsidence of the platform margin and shifting of the depocenters (Upper Senonian-Paleocene) from northeast to southwest suggesting an initial thrusting; wrenching (Puigdefhbregas and Souquet, 198.5), evaporite migration, thrusting or normal faults causing subsidence being the main arguments. Listric normal faulting (Lower Santonian~ affected the former

sequences

and

coincided with major basin expansion, associated with subsidence. To the west the fault cuts off older strata, and to the east it is bounded by a transfer fault (in the sense of Gibbs, 1984). On the basin and escarpment. submarine erosion occurred; the Campo

breccia originated

by erosion

erosion (see Van Hoorn, 1971, discussion). before the faulting (Figs. 13, 14).

of a fault escarpment Flexuring

and not by subaerial

of the margin

was continuous

Tectonic style changed from extension to compression at the CampanianMaastrichtian boundary. During the Maastrichtian, thrusting and folding changed the basin configuration, and caused uplift and subaerial unconformities (Fig. 3). The sea level rose (relatively) through the sequences with m~imum transgression in the Upper Santonian-Lower Campanian. Generalized shallowing occurred during compressional tectonism. Vail et al.‘s (1977) global cycles of sea-level changes chart also shows a relative sea-level rise from the Middle Cenomanian to the top of

the Maastrichtian.

The relative

former

platform,

carbonate

Drowning

of the previous

shallow-water controlled sequence,

carbonate

sea level rose abruptly

making

major

platforms facies and

changes

resulted

each in the

in rapid

the preservation

time

drowning

platform

landward

retreat

of topographic

the

geometry. of the

relief which

the facies distribution of the next sequence. During deposition the sea level would have stayed stable (Upper Turonian-Lower

of each Conia-

cian, Campanian) or rose slightly (Upper Cenomanian. Upper ConiacianLower Santonian). Drowning occurred where rate of relative sea-level rise exceeded vertical accumulation rate, and the platform was submerged below the euphotic zone (see Kendall and Schlager. 1981). causing a major landward shift of shallow-platform facies (see Read, 1982, 1985). The problem of the drowning of a carbonate platform is that the carbonate production potential is generally greater than the tectonic-subsidence or sea-level rises (see discussion Schlager. 19Sl). Schlager (1981) concluded abrupt

subsidence

resident

to drown

communities

Steinmetz drowning

the carbonate

by environmental

(1984) described a Holocene resulted from high-frequency

in Schlager. 1981: and Kendall and that tectonism induced the necessary platform,

when evidence

or climatic

changes

of stress on the

is absent.

partially drowned carbonate sea-level changes (fourth;

Hine

and

platform, where fifth- and sixth-

order submergence events). These retarded the vertical growth of the platform. In conclusion, in the Pyrenees Upper Cretaceous. abrupt relative sea-level rises caused the major changes in basin history, platform geometry and facies distribution. The cessation of carbonate production was due to both sea-level fall and rise. Late Cretaceous tectonism was responsible for basin tilting, listric normal and inverse faults and induced gradual subsidence as well as sporadic acceleration. The Upper Cretaceous evolutionary trend (rimmed shelf --t distally steepened ramp ---)homoclinal ramp with large slope --) distally steepened homoclinal and turbiditic basin --) and tectonically controlled siliciclastic nearshore-shelf

ramp com-

plex) of the south-central Pyrenees was controlled by abrupt sea-level rises, tectonics and inherited depositional profile (Figs. 3. 13). The growth potential of platform and rim, siliciclastic second-order

progradation.

and sea-level

fluctuations

of each sequence

were

factors.

.ACKNOWLEDGMENTS

This study summarizes the results obtained during the mapping of the Cretaceoua supported by the “Servei Geologic de Catalunya (Departament de Politica Territorial i Obres Publiques de la Generalitat de Catalunya)“. The author would like to express his thanks for permission to publish this paper. The manuscript greatly benefited from critical reviews by Fred Read and Maurice Tucker. KEFERENCES

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