Revision of the biostratigraphy of the Chatham Group (Upper Triassic), Deep River basin, North Carolina, USA

Review of Palaeobotany and Palynology, 77 (1993): 75-95 Elsevier Science Publishers B.V., Amsterdam

75

Revision of the biostratigraphy of the Chatham Group (Upper Triassic), Deep River basin, North Carolina, USA Ronald J. Litwin a and Sidney R. A s h b aUS Geological Survey, MS 970, Reston, VA 22092, USA bDepartment of Geology, Weber State University, Ogden, UT 84408, USA (Received August 12, 1991; revised and accepted October 29, 1992)

ABSTRACT Litwin, R.J. and Ash, S.R., 1993. Revision of the biostratigraphy of the Chatham Group (Upper Triassic). Deep River basin. North Carolina, USA. Rev. Palaeobot. Palynol., 77:75 95. Paleontological evidence from the Upper Triassic Chatham Group in the three subbasins of the Deep River basin (North Carolina, USA) supports a significant revision of the ages assigned to most of this non-marine continental sedimentary sequence. This study confirms an early(?) or mid-Carnian age in the Sanford subbasin for the base of the Pekin Formation, the lowest unit of the Chatham Group. However, diagnostic late Carnian palynomorphs have been recovered from coals in the lower part of the Cumnock Formation in the Sanford subbasin, and from a sample of the Cumnock Formation equivalent in the Wadesboro subbasin. Plant megafossils and fossil vertebrates from rocks in the Sanford subbasin also support a late Carnian age for the Cumnock Formation and its equivalents. The overlying Sanford Formation, which has not yet been dated paleontologically, probably includes beds of Norian age, as over 1000 m of strata may be present between the Cumnock Formation coals (dated here as late Carnian) and the top of the Sanford Formation. This chronostratigraphic interval appears similar to, but slightly longer than, that preserved in the Dan River Danville and Davie County basins 100 km to the northwest. Our evidence, therefore, indicates that the Chatham Group was deposited over a much longer time interval [early(?) to midCarnian through early Norian] than previously was believed.

Introduction Conflicting p a l e o n t o l o g i c a l l y - b a s e d ages, ranging from P e r m i a n ( E m m o n s , 1856) to latest Triassic (Schultz a n d H o p e , 1973), have been assigned to the C h a t h a m G r o u p o f the D e e p River basin. M o r e recently, the G r o u p has been r e g a r d e d as m i d - C a r n i a n or older, and was p r o p o s e d to represent some o f the earliest Triassic d e p o s i t i o n in the US p o r t i o n o f the N e w a r k S u p e r g r o u p (Cornet, 1977). The a b u n d a n c e o f conflicting age assignments (Table I) is s o m e w h a t suprising, because the lower p o r t i o n o f the C h a t h a m G r o u p (the Pekin a n d the C u m n o c k F o r m a t i o n s ) c o n t a i n s some o f

Correspondence to: Dr. R.J. Litwin, US Geological Survey, Paleontology and Stratigraphy Branch, MS 970, National Center, Reston, VA 22092, USA. 0034-6667/93/S06.00

the m o s t diverse and a b u n d a n t assemblages o f p a l y n o m o r p h s , p l a n t megafossils, fossil vertebrates, a n d fossil invertebrates f o u n d in the N e w a r k S u p e r g r o u p (see Olsen, 1989; Olsen et al., 1991). Litwin et al. (1991) recently re-assigned the ages o f the u p p e r p o r t i o n o f the Pekin F o r m a t i o n a n d the C u m n o c k F o r m a t i o n (both o f which had been d a t e d previously as m i d - C a r n i a n ) , on the basis o f specific p a l y n o m o r p h a n d p l a n t megafossil assemblages k n o w n m o r e c o m m o n l y from late C a r n i a n p o r t i o n s o f the Chinle F o r m a t i o n a n d lower D o c k u m G r o u p in the US Western Interior. The diversity and a b u n d a n c e o f the fossil record o f the C h a t h a m G r o u p w a r r a n t s a m o r e c o m p r e hensive e v a l u a t i o n o f this p a l e o n t o l o g i c a l evidence and its age a s s i g n m e n t (Table I). Therefore, the goals o f this study were: (1) to reevaluate the b i o s t r a t i g r a p h i c a l evidence from the C h a t h a m

~. 1993 - - Elsevier Science Publishers B.V. All rights reserved.

76

R.J LITWIN A N D S,R. ASH

TABLE I Evaluation of paleontological evidence and age assignment Sample

(Sub)basin

Formation

State

Reference

I*

Sanford

Pekin (lower)

NC

2a*

Sanford

Pekin (middle)

NC

2b 3**

Sanford Wadesboro

Pekin (middle) probable Cummock equivalent

NC NC

4"*

Sanford

Cumnock

NC

5**

Sanford

Cumnock

NC

6a*

Sanford

Cumnock

NC

6b*

Sanford

Cumnock

NC

7 8 9 I0

Dan River Danville Davie County

Stoneville Cow Branch ("lower") none Chinle

NC VA NC UT

PK 1 of Cornet (1977), Traverse (1986), Olsen et al. (1991); this study (R4392) PK2 of Cornet (1977), Traverse (1986), Olsen el al. (1991): this study (R4362) This study (R4393) PK3 of Cornet (1977), Traverse (1986), Olsen et al. (1991): this study CM 1 of Cornet (1977), Traverse (1986), Olsen et al. (I991): this study No. 827 of Robbins and Textoris (1986, 1988): this study Bethany Church of Traverse (1986); this study (R4366) Bethany Church of Traverse (I986); this study (R4365) This study (R405I) This study (R4367) This study (R4052) Litwin el al. (1991) (R4331)

*Sample recollected from same locality as previous studies. **Sample from previous study, reexamined for this report.

G r o u p , (2) to propose ages for C h a t h a m G r o u p strata that are consistent with the greatest a m o u n t of available fossil evidence, and (3) to c o m p a r e these revised ages for C h a t h a m G r o u p strata to the overall kate Triassic biochronology in the eastern and southwestern US.

dual name reflects a nomenclatural change at the N o r t h Carolina-Virginia border. The Davie C o u n t y basin occurs along strike with the D a n River Danville basin, and may be an eroded southerly outlier o f it.

Lithostratigraphy of the Chatham Group Structural J'ramework The Deep River basin, the most southerly o f the exposed Early Mesozoic basins o f eastern N o r t h America (Froelich and Olsen, 1984), comprises, from north to south, the D u r h a m , Sanford, and Wadesboro subbasins (Fig. IA). The separation of the D u r h a m and Sanford subbasins is based partly on the presence o f a complex faulted uplift and partly on sedimentological differences; that o f the Sanford and Wadesboro subbasins has developed mainly because o f overlap o f upper Mesozoic and Tertiary coastal plain sediments across this area (A.J. Froelich, pers. commun., 1991). Equivalent strata occur in other early Mesozoic basins in N o r t h Carolina. The D a n River Danville basin is a single depositional and structural basin, but its

Strata in the Deep River basin were assigned to the C h a t h a m G r o u p by E m m o n s (1856). Campbell and Kimball (1923) later subdivided the g r o u p into (in ascending order) the Pekin, C u m n o c k , and Sanford F o r m a t i o n s (Fig. 2), with the type-localities for the C u m n o c k and Sanford F o r m a t i o n s in the Sanford subbasin, and the type-locality for the Pekin F o r m a t i o n in the Wadesboro subbasin. In the Sanford subbasin the three formations are conformable. Brown et al. (1985) retained formations only in the Sanford subbasin, and referred the strata in the D u r h a m and Wadesboro subbasins to "undivided C h a t h a m G r o u p " . We retain the use o f the Pekin F o r m a t i o n in the Wadesboro subbasin because it contains the type-area of that formation (Campbell and Kimball, 1923). The geology o f the

RI~VISIONOF THE BIOS'IRAII(;RAPHYOF THE CHATHAMGROUP,DEEP RIVERBASIN(NC, USA)

77

DANVILLE ,-

BASIN

. . . . . .

/:'

DABNA~~

D u r h a m ~ DURHAM-IE COUNTY BA

• Asheville

^_ See. Charlotte•

(-~ ~

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SANFORD SUBBASIN

DEEP - RIVER BASIN

[

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0 --~

40 M 0 Miles '40 " 80 Kilometers

20

~ Wilmingtonf

~,r'~

~ 00,'~"£' ,a£~\01~,~~'"

~, ~/~

~ju

]

Fig. 1. (A) Map of North Carolina, showing the Deep River basin with its component subbasins, the Dan River-Danville basin, and the Davie Counly basin. (B) Map enlargement of the Deep River coalfield, showing localities of samples 2. 4, 5, and 6. PreQuaternary geological base after Reinemund (1955).

Deep River basin has been documented by Campbell and Kimball (1923), Reinemund (1955), Patterson (1969), Randazzo et al. (1970), Randazzo and Copeland (1976), Bain and Harvey (1977), Brown et al. (1985), Hoffman and Gallagher (1988), Gore et al. (1989), and Olsen et al. (1991). The stratigraphic nomenclature of the Chatham Group was

summarized in Luttrell (1989), together with a correlation of all the Newark Supergroup formations, many of which are referred to in this paper. The age assignments for the Chatham Group and Dan River Group presented in Luttrell (1989, plate 1) were based primarily on our information presented below.

7~

R.J

J ) Z 0 i I-- I <

Red to brown ciaystone, siltstone and fine-grained sandstone, with interposed lenticular beds of grey, coarse-grained arkosic sandstone and conglomerate

cc I o

I

cr

Meters

o

(.3

L,L Z <

Feet - - 1200

300 - -

u)

(29

--

200

GO

<

Cl"

II

800

--

100 - -

- - 400

cc

W

--?--

Grey siltstone

D..

0

0

Black and grey shale CUMNOCK COAL~ Sam les

~ Sample 3 (probable horizon)

Grey bsiltstone ,.~ley lllb and fine-grained sandstone

LITWIN

AND SR. ASH

prises 150 240 m of grey carbonaceous claystones, siltstones, and fine-grained sandstones. This formation contains some of the thickest coal deposits in the Newark Supergroup; these are present only in the eastern part of the Sanford subbasin (the "Deep River coalfield"). Two widespread and extensively mined coals, the lower (Gulf coal) approximately 1 m thick, and the upper (Cumnock coal) approximately 3 m thick, occur in the lower part of the formation (Robbins and Textoris, 1986). The mines are now abandoned, but some of the historically more productive sites are indicated on Fig. lB. The Sanford Formation, the uppermost Chatham Group formation, is predominantly reddish brown and coarse-grained sandstones, with interbedded siltstones and thick conglomerates at its top, and ranges from 150 to 910 m in thickness (Reinemund, 1955; Hoffman and Gallagher, 1988).

Previous palynological studies and age assignments

Z

O F--

Red to brown claystone and siltstone

r't" O IJ_ Z ~ "x-" LU

~

Pomona Pipe and Clay Products Pit (Sample 2b) Boren Clay Products Pit (Sample 2a) Grey, coarse-grained sandstone

D_ i

I!

-

Lockville (Sample 1) "Millstone grit"

Fig. 2. Lithostratigraphy of the Sanford subbasin succession, after Reinemund (1955), with approximate horizons of palynological samples examined in this study.

The Chatham Group has a maximum thickness of approximately 3048 m in the Deep River basin (Reinemund, 1955). The lowest unit, the Pekin Formation, is composed of local basal conglomerates and red, brown, and purple fine-grained claystones to medium-grained sandstones. In the Sanford subbasin the formation ranges from 550 to 1220 m in thickness, with medium- to coarsegrained arkosic sandstone and conglomerate present locally in the lower part (Reinemund, 1955). The conglomerates have been used for fabrication of grindstones, and clays and deeply weathered siltstones and sandstones in the middle part of the formation have been mined (as in the Boren and Pomona pits; Fig. IB) for use in the terra cotta industry. The overlying Cumnock Formation corn-

The pioneer palynological work in the Deep River basin was carried out on material from the clay and coal deposits of the Sanford subbasin. Fossil palynomorphs were first reported from these rocks by Berry (1940), who had examined a "Triassic coal from near G u l f " (Cumnock Formation). Berry noted only that the assemblage consisted of a dozen morphotypes, was dominated by fern spores, and lacked cycadophytic taxa. Koob (1961) provided the first description of palynological assemblages from the basin, from the Cumnock Formation in the Deep River coal field. Both Berry's and Koob's samples were from approximately the same stratigraphic interval as samples 4 6 of the present study (Table I). Koob concluded, from the presence of Ephedra (Equisetosporites) chinleana and Paraconcavisporites lunzensis, that the Cumnock Formation was Keuper-equivalent or younger (Middle to Late Triassic in age). Schultz and Hope (1973) reported the first palynomorph assemblages from the middle Pekin Formation (sample locality 2, Table I) and assigned a latest Triassic (Rhaetian) age to that formation, predominantly on the basis of the occurrence of pollen they identified as Classopollis (Corollina) reclusus. Schultz and Hope (1973) speci-

R E V I S I ON O F q H E B I O S T R A T I G R A P H Y O F T H E C H A T H A M G R O U P , D E E P R I V E R BASIN (NC, USA}

fically compared the Pekin Formation palynomorph assemblage with assemblages described from the Rh/it of Germany by M/idler (1963, 1964). Other taxa identified from the Pekin Formation by Schultz and Hope included Uvaesporites

argent~formis, Dictyophyllidites mortonii, Cyclogranisporites oppressus, Duplexisporites cf. D. probh, maticus, Camarozonosporites rudis, Guthoerlisporites cancellosus, Trilites klausii, and Trizonites cerebralis. Palynomorphs were documented from the Gulf coal (same locality as CM1, Table I) by Dunay and Fisher (1974), who noted the occurrence of Pseudenzonalasporites summus, Vallasporites ignacii, Camerosporites secatus, and Ovalipollis ovalis in the sample. They made no age determination on the basis of palynomorphs, but accepted Gregory's (1957) biostratigraphic correlation (on vertebrate evidence) of the Cumnock Formation with the upper Bunte Mergel or lower Stubensandstein in the Germanic Triassic, thus endorsing an older (approximately early mid-Norian boundary) age for these strata than that proposed by Schultz and Hope (1973). Palynomorphs were first obtained from the Wadesboro subbasin (sample locality 3, Table I) and from the lower part of the Pekin Formation in the Sanford subbasin (sample locality 1, Table I) by Cornet (1977), who also restudied palynomorphs from the middle Pekin and the Cumnock formations in the Sanford subbasin (sample localities 2a and 4, Table l). Cornet confirmed the presence of many of the taxa previously identified by Koob, Schultz and Hope, and Dunay and Fisher, and identified others, including "~Qvcadopites sp. 103" (i.e. Cycadopites stonei of Helby et al., 1987), Patinasporites densus, Camerosporites pseudoverrucatus, and Lagenella martinii in samples from the Pekin and Cumnock formations of the Sanford subbasin. He re-identified Classopollis (Corollina) reclusus, first recorded 1¥om the Pekin Formation by Schultz and Hope (1973), as Corollina meyeriana. Cornet (1977, p. 71) concluded that deposition of the Chatham Group was rapid, spanning approximately 1 Ma, and placed it at the mid late Carnian boundary, but indicated that the Group was almost entirely mid-Carnian. A mid-Carnian age would be ~ 15 Ma older than that suggested by Schultz and Hope, and ~6 10 Ma older than that indicated

79

by Dunay and Fisher (1974), on the basis of time scales proposed by Harland et al. (1982), Forster and Warrington (1985), Harland et al. (1989), Odin and L~tolle (1982), Palmer (1983), and Cowie and Bassett (1989). Robbins (1985) re-examined the Cumnock coal seam (sample 5, Table 1) for palynomorphs and suggested that the assemblage could be either midor late Carnian. Traverse (1986) re-evaluated palynomorph data from the Wadesboro and Sanford subbasins, and reported that the lowest portion of the Pekin Formation was early Carnian, the middle of the formation was mid-Carnian, and the Cumnock coals (Gulf and Cumnock seams) were late mid-Carnian. He also concluded, because of the dominance of Patinasporites, that the Wadesboro subbasin sample 3 (Table I) contained a late Carnian palynomorph assemblage. He questioned Cornet's assignment of sample 3 to the Pekin Formation, and implied a possible correlation with the lower part of the Sanford Formation in the Sanford subbasin. Later, Traverse (1987) assigned the lowest Pekin Formation sample to the Ladinian (Middle Triassic), on the basis of Ediger's (1986) palynological age determination for strata of the Richmond basin ("Productive Coal Measures") of eastern Virginia, which Ediger proposed to be correlative to the Lettenkohle of the Germanic Trias. Traverse also suggested that deposition in the southerly Early Mesozoic basins terminated at the end o f the Carnian. Robbins and Textoris (1986, 1988) restudied the Cumnock Formation palynomorphs (samples 5 and 6, Table I) and proposed a mid-Carnian age on the basis of similarity of the palynomorph assemblages to those studied by Cornet (1977) from sample 4 (CM1, Table I) from the Gulf coal mine. Gore et al. (1989) accepted a late Carnian age for sample 3 from the Pekin Formation, whereas Olsen et al. (1991) most recently re-interpreted the same sample as mid-Carnian.

Palynological data (this study) Eight palynological samples of the Chatham Group were re-examined (and re-sampled where necessary) for this study (Table I). Seven are from known palyniferous intervals in the Sanford sub-

~0

RJ

DANVILLE

DAVIE COUNTY

COW BRANCH ("LOWER")

NONE

DEEP

DAN RIVER

RIVER

I

CHINLE

PEKIN

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BASIN

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STONEVILLE

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Camarozonosporites rudis Kraeuselisporites cooksonae Gordonispora fossulata Neoraistrickia americana Uvaesporites gadensis Dictyophyllidites harris# Paracirculina quadruplicis Praecirculina granifer Calamospora tener Placopollis koobi Monocrinopollis cf. M. mulleri Dictyophyllidites morton/ Alisporites opii Colpectopollis ellipsoideus Cycadopites sp. indet. Trilites klausii Cordaitina minor Cycadopites fragilis Guthoerlisporites cancellosus Patinasporites densus Pityosporites devolvens Vallasporites ignacii Verrucosisporites morulae Lycopodiacidites kokeni Converrucosisporites cameronfi Cycadopites stonei Granulatisporites infirmus Foveosporites sp. indet. Pityosporites chinleanus IAlisporites gottesfeldii Camerosporites pseudoverrucatus Brachysaccus neomundanus Lagenella martini/ Minutosaccus crenulatus Ovalipollis ovalis Platysaccus triassicus Pseudenzonalasporites summus Alisporites parvus

o

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Pityosporites oldhamensis Camerosporites secatus Pretricolpipollenites bharadwajii Microcachrydites doubmgeri Cometipollis reticulata Plicatisaccus badius Enzonalasporites vigens Infernopollenites sulcatus New Genus A sp. A

Equisetosporites chinleanus Aratrisporites satumi Samaropollenites speciosus Brodispora striata Sulcatisporites kraeusefi ?Araucariacites sp.indet. Pyramidosporites traversei Camerosporites verrucosus

Fig. 3. Composite palynological assemblage chart showing the occurrence of taxa from the Chatham Group, other Newark Supergroup strata discussed in this report, and a correlative sample from the lower part of the Chinle Formation (Utah). Black circles indicatc taxa which provide the most important biostratigraphic information, shaded circles indicate confirmed identifications, and question marks indicate identifications hampered by pyrite damage, thermal alteration, or other degradation.

REVISION OF THE BIOSTRATIGRAPHYOF THE CHATHAM GROUP, DEEP RIVER BASIN (NC. USA)

basin (Fig. 2). Three of the seven (samples 1, 2a, and 2b) are from the lower and middle portions of the Pekin Formation, and four (samples 4, 5, 6a, and 6b) are from the lower part of the Cumnock Formation. Cornet's (1977) solitary assemblage from the "type Pekin" in the northern end of the Wadesboro subbasin (sample 3, Table I) also was re-examined. This sample probably was collected from the Cumnock Formation equivalent in the Wadesboro subbasin (Joseph P. Smoot, pers. commun., 1991). The eight samples, described below, were grouped into four successively younger diverse palynomorph assemblages, which provided us a solid basis for age determination of the upper portion of the Chatham Group. We also examined assemblages from samples of four other lithologic units: the Stoneville Formation and Cow Branch Formation of the Dan River Danville basin (Virginia and North Carolina), an unnamed unit from the Davie County basin (North Carolina), and the Shinarump Member of the Chinle Formation (Utah) (Fig. 3). These four samples were examined for comparison with the Chatham Group samples, which form the basis of this study. Illustrated specimens from this study and the England Finder coordinates for them are reposited at the US Geological Survey, National Center (Reston, Virginia). The slides for samples PK3 and CM1 are reposited at the Pennsylvania State University (University Park, Pennsylvania). England Finder coordinates for specimens illustrated from these two samples, however, are reposited at the US Geological Survey. Discussion

Sample l, from the lower part of the Pekin Formation in the Sanford subbasin, is from the same site as sample PK1 of Cornet (1977), Traverse (1986) and the stratigraphically lowest pollen sample of Olsen et al. (1991) (Table I). It comprised matrix removed from the type-specimen of Ctenophyllum braunianum (Emmons, 1857), a plant megafossil collected near Lockville and now housed in the US National Museum of Natural History (USNM 8218). The palynomorph assemblage from this sample (Fig. 3) shows the least similarity in composition to any of the Deep River basin Chat-

~]

ham Group assemblages, to those from the Davie County or Dan River Danville basins, or to those from the Late Triassic of the US Western Interior. The overall standard of preservation of the palynomorphs is poor. Gymnosperm pollen is neither abundant nor diverse and the assemblage is dominated by pteridophytic spores. Selected components of the assemblage are shown in Fig. 3. The sample contains scarce Camarozonosporites rudis (Plate I, 1) and questionable Patinasporites densus, which originate in the early Carnian (Visscher and Brugman, 1981; Brugman, 1983: Van der Eem, 1983), and several taxa not previously reported from the Triassic of the United States, including Kraeuseli~porites cooksoniae (Plate I, 2) and Gordonisporafossulata (Plate II, 4, 5). The assemblage is indicative only of an early(?) to mid-Carnian (Cordevolian Julian) age. A mid-Carnian (Julian) age is favored on the basis of stratigraphic position, but an early Carnian (Cordevolian) age cannot be excluded on the basis of the available palynomorph evidence. The assemblage confirms, however, that the Chatham Group includes some of the oldest strata in the Newark Supergroup, as suggested by Cornet (1977). The next samples, in ascending stratigraphic order, are from the middle of the Pekin Formation, in the Boren and Pomona Clay Pits (samples 2a and 2b, Table I). The Boren sample (2a) is from a block containing unidentified plant megafossils, that was obtained from the plant-bearing interval at the Boren pit by W. DiMichelle. Sample 2b is from the same stratigraphic level, but from the Pomona Clay Pit, site of the vertebrate locality of Baird and Patterson (1968), and was also removed from plant megafossil specimens housed at the U S N M N H ( U S N M N H A c c . N o . 367828). Palynomorph taxa recovered from these samples include Minutosaccus crenulatus, Lagenella martinii (Plate Ill, 1),

?Patinasporites densus, Alisporites opii, Camerosporites secatus, Camerosporites pseudoverrucatus, Klausipollenites gouldii, Ovalipollis ovalis, and Alisporites gottesfeldii (Fig. 3). Also present are Neoraistickia americana (Plate I, 11), Uvaesporites gadensis (Plate I, 6), Lycopodiacidites kokeni (Plate I, 3), and possible Cycadopites stonei, a taxon which presently appears to be restricted to the upper Carnian in the Chinle Formation of the US

R.J LITWIN A N D S,R. ASH

~2 PLATE

10

1

REVISION OF THE BIOSTRATIGRAPHYOF THE CHATHAMGROUP, DEEP RIVER BASIN(NC. USA)

Western Interior. These assemblages are more similar to each other and to younger assemblages from the Newark Supergroup and from the Western Interior, than they are to the lower Pekin Formation assemblage (sample 1) from Lockville. Although they lack several diagnostic taxa common to the other western US late Carnian assemblages (Chinle Formation and Dockum Group), we tentatively assign them a late Carnian age. On the basis of palynological evidence alone, the age could be as old as the mid-Carnian-late Carnian boundary; assignment of a late Carnian age is, however, supported by associated fossil vertebrates and plant megafossils (discussed below). Samples 2a and 2b are from the middle of the Pekin Formation, but are probably the highest palynological samples presently known from that formation in any of the subbasins. Shultz and Hope (1973), Cornet (1977), and Cornet and Olsen (1985) reported Corollina meyeriana from the 2a and 2b sample horizons. We cannot confirm its presence, but we note that other circumpolloid taxa, such as Praecirculina granifer (Plate I, 4), are present. Confirmation of the presence of Corollina meyeriana would support a postmid-Carnian age, as the first appearance of Corollina meyeriana has been documented as a Norian event (sensu Visscher and Brugman, 1981; Brugman, 1983; Helby et al., 1987). We believe, however, that occurrences of Corollina (Classopollis) reported from the Pekin Formation pertain to specimens of Gordonispora fossulata, which was first described from European strata by Van der Eem (1983). This taxon occurs in the Pekin Formation and is of similar size and shape to Corollina meyeriana (Plate II, 4, 5); we also have recorded it

in Carnian samples from Arizona (Chinle Formation, unpubl, data). One sample re-examined for this study (sample 3) originally was attributed to the upper part of the Pekin Formation by Cornet (1977), and was reported to have been from the type-locality of the formation in the Wadesboro subbasin. Cornet suggested a late Carnian age for the palynomorph assemblage, but did not include it in his zonation. Traverse (1986) noted the questionable stratigraphic assignment, but recognized the sample as the first of late Carnian age reported from the Chatham Group. Gore et al. (1989) also accepted it as late Carnian, but Olsen et al. (1991) assigned it to the mid-Carnian without discussion. The stratigraphic setting of sample 3 is debateable because the stratigraphy of the Wadesboro subbasin is complex and relatively poorly known (A.J. Froelich and J.P. Smoot, pers. commun., 1991). Our examination of Cornet's assemblage confirms a dominance of Patinasporites densus, in addition to the presence of Minutosaccus crenulatus (Plate IV, 4), Cordaitina minor, Klausipollenites

gouldii, Microcachrydites fastidoides, Microcachrvdites doubingeri, Enzonalasporites vigens (Plate II, 7), Vallasporites ignacii, Plicatisaccus badius, Todisporites rotundiformis, Dictyophyllidites mortonii, Cycadopites fragilis, ?Lagenella martinii, and Cornetipollis reticulata (Plate III, 4; Fig. 3). The last taxon has a highest occurrence in the late Carnian in the US Western Interior, and is present in the Shinarump Member to lower part of the Petrified Forest Member succession in the Chinle Formation, and in the Tecovas Formation in the Dockum Group. The lower parts of the Dockum Group and the Chinle Formation contain the

PLATEI I. 2. 3. 4. 5. 6. 7. 8. 9. 10. I I.

83

Camarozonosporites rudis. Pekin Formation (lower), sample 1. Kraeuselisporites cooksoniae. Pekin Formation (lower), sample 1. Lycopodiacidites kokeni. Pekin Formation (middle), sample 2a. Praecirculina gran~fer. Pekin Formation (middle), sample 2a. Uvaesporites gadensis. Pekin Formation (lower), sample 1. Uvaesporites gadensis Pekin Formation (middle), sample 2a. Praecirculina granifer. Cumnock Formation (lower), sample 4. Pretricolpipollenites bhardwajii. Cumnock Formation (lower), sample 5. Brmtispora striata. Cumnock Formation (lower), sample 6b. Pseudenzonalasporites summus. Cumnock Formation (lower), sample 5. Neoraistrickia americana. Pekin Formation (middle), sample 2b.

~4

RJ

PLATE

II .......iiiiii~2i~iiiiiiiill

............

2

4

lO~m

5

h

8

I. Camerosporites secatus. Cumnock Formation (lower), sample 6b. 2, 3. Camero~sporites verrucosus. Stoneville Formation (upper), sample 7. 4, 5. Gordonisporajbssulata. Pekin Formation (lower), sample 1. 6. Cycadopites stonei. Cumnock Formation (lower), sample 5. 7. Enzonalasporites vigens. Cumnock Formation (equivalent), sample 3. 8. Patinasporites densus. Cumnock Formation (lower), sample 5.

ii

L I I W I N A N D S.R. A S H

REVISION OF THE BIOSTRA[IGRAPHY OF THE CHATHAM GROUP. DEEP RIVER BASIN (NC, USA}

~5

highest occurrences of Brodispora striata and Camerosporites secatus, neither of which range into

Carnian age. They contain Klausipollenites gouldii, Camerosporites secatus (Plate 2, 1), Alisporites sp.,

post-Carnian strata (Geiger and Hopping, 1968; Litwin, 1986). A late Carnian age assignment for sample 3 also is supported by the abundance of Patinasporites densus and Minutosaccus crenulatus, which are common in late Carnian assemblages (Dolby and Balme, 1976; Visscher and Krystyn, 1978: Visscher and Brugman, 1981). Therefore, if Cornet's sample PK3 (Table I) in the Wadesboro subbasin is not from the upper Pekin Formation, but, as we believe, from the Cumnock Formation equivalent or from the Sanford equivalent (Traverse, 1986), suggestions that the Pekin Formation is diachronous in the Wadesboro and Sanford subbasins are not supported by the palynological evidence. If the sample is from the type Pekin Formation, the upper part of that formation in the Wadesboro subbasin is clearly late Carnian and any evidence for diachroneity rests upon the age of the top of the Pekin Formation in the Sanford subbasin. To date no palynological samples from this subbasin have been reported from above the horizon sampled in the Boren or Pomona Clay Pits (middle Pekin Formation). The next higher samples (4 6, Table I) in the Sanford subbasin are from the Gulf and Cumnock coal beds in the lower part of the overlying Cumnock Formation (Fig. 2), and these are late Carnian in age. The four Cumnock Formation samples (Table I, 4 6b) yielded palynomorph assemblages that are most similar in composition to that from the Wadesboro subbasin (sample 3), to which Traverse (1986) assigned a late Carnian age. Of these, sample 5 (Carolina Mine No. 1 sample No. 827) of Robbins and Textoris (1986) contains the most diverse late Carnian palynological assemblage (Fig. 3). In re-examining this sample we have noted Cycadopites stonei (Plate II, 6), Brodispora striata, Pseudenzonalasporites summus (Plate I, 10), Equisetosporites chinleanus (Plate III, 2, 5), Minuto-

Pityosporites devolvens, Vallasporites ignacii, Cordaitina minor, Cycadopites sp., ?Lagenella martinii, Trilites klausii, Todisporites rotund!l'ormis, Dictyophyllidites harrisii, Dictyophyllidites mortonii, Verrucosisporites morulae, Converrucosisporites cameronii, Praecirculina granOCer (Plate I, 7), Monocrinopollis cf. M. mulleri, and Brodispora striata (Plate I, 9), which are characteristic of the

saccus crenulatus, Klausipollenites gouldii, Samaropollenites speciosus, Patinasporites densus (Plate II, 8), Alisporites opii, and a form we refer

Palynology of the Dan River-Danville basin

to as "'New Genus A new species A" (Plate IV, 1, 2; Fig. 3). Samples 4, 6a, and 6b are less diverse than sample 5, but are consistent with a late

late Carnian zone II of Litwin et al. (1991). Comparison of the sample 5 assemblage with those from late Carnian samples from the US Western Interior shows a correlation with an assemblage from the Shinarump Member of the Chinle Formation at Capitol Reef National Park, Utah (Litwin et al., 1991; Fig. 3, sample 10). Sample 5 also compares closely with assemblages from the Monitor Butte and lower Petrified Forest Members of the Chinle Formation, suggesting that the lower part of the Cumnock Formation correlates best with the lower part of the Chinle Formation. The species lists of age diagnostic taxa for samples 5 and 10 are shown in Fig. 3. As noted above, a morphotype used by us only as a regional index taxon in the lower part of the Chinle Formation (i.e. "New Genus A new species A") also occurs in the Cumnock Formation, suggesting a greater biostratigraphic value and geographic range for this morphotype than was previously realized. The Sanford Formation, which overlies the Cumnock Formation, has not yet yielded palynomorphs, but Reinemund (1955) estimates that it comprises over 900 m of strata. The stratigraphically highest palynological sample we have examined (late Carnian) is from the lower Cumnock Formation, approximately 1000 m below the top of the Sanford Formation (Reinemund, 1955). Accordingly, we suggest that the Sanford Formation probably extends at least into the lower Norian.

The Stoneville Formation of the Dan RiverDanville basin (Fig. 1A) occupies the same stratigraphic position as the Sanford Formation in the Deep River basin (Fig. 4). Although these are

R . J LITWIN A N D S.R. A S H

86

PLATE III

ii

2

!

4

i!!!!!~iii!ii!ill ¸ ~i¸¸¸

!

REVISION O F T H E B I O S T R A T I G R A P H Y O F T H E C H A T H A M G R O U P , DEEP R I V E R BASIN

(NC, USA)

87

o~

x3 (D

3 2. 3 4 5

Extension of the Sanford Formation into the Norian on the basis of stratigraphic thickness and palynomorph data supplied by Litwin (1989, oral communication) from the partly correlative Stoneville Formation of the Dan River- Danville basin. (See footnote 2) Extension of the Sanford Formation into the Norian on the basis of palynornorph data obtained from the Stoneville Formation of the Dan River Danville basin (See footnote 5) Physical stratigraphy from Thayer (t970) LCB= lower beds of the Cow Branch Formation Extension of the Stoneville Formation into the Norian on the basis of palynological data supplied by Litwin (1989 oral communication) Physical stratigraphy taken from Thayer (1970), Henika and Thayef (1983), and Smoot and Weems (oral communication) Smoot and Weems suggest, on the basis of their recent field observations that the tower part of the Cow Branch Formation exposed in the vicinity of Walnut Cove is an artifact of fault duplication of a portion of the Pine Hall and Cow Branch Formations The age of the Stoneville Formation is based on palynological data presented elsewhere in this paper (sample 7)

Fig. 4. Stratigraphic ages assigned to the Chatham Group and the Dan River Group in previous palynological studies and this study, with correlation to the zonation of Cornet and Olsen (1985). Circled numbers I through 8 correspond to sample numbers in Fig. 3, and represent the same sample, or samples from the same outcrop interval. stratigraphically the youngest Triassic formations in their respective basins, the Stoneville F o r m a t i o n differs from the Sanford F o r m a t i o n in that it is largely lacustrine in origin and has produced datable p a l y n o m o r p h assemblages. Samples collected by R.E. Weems, from cores taken by the Marline U r a n i u m C o r p o r a t i o n from the upper part of the formation, have produced a p a l y n o m o r p h assemblage which Litwin et al. (1991) (sample 8, Table

I; Fig. 3) assigned to the early Norian. Assignment o f the Stoneville F o r m a t i o n assemblage to the early N o r i a n is made on the basis o f the presence of C a m e r o s p o r i t e s v e r r u c o s u s (Plate II, 2, 3). The last appearance of its precursor, C a m e r o s p o r i t e s s e c a t u s , appears to be late Carnian (Litwin e t a l . , 1989; Litwin and Skog, 1991). P a l y n o m o r p h assemblages from the upper part o f the Cow Branch F o r m a t i o n immediately under-

PLATE II1 I. 2. 3. 4. 5.

Lagenella martinii. Pekin Formation (middle), sample 2a. Equisetosporites chinleanus. Cumnock Formation (lower), sample 5. Striae are broken, but adherent to the central body. Monocrinopollis cf. M. mulleri. Pekin Formation (middle), sample 2a. Cornetipollis reticulata. Cumnock Formation (equivalent), sample 3. Equisetosporites chinleanus. Cumnock Formation (lower), sample 5. This species does not possess the tectate columellate striae present in C. reticulata.

88

RJ

LITWIN A N D S.R. ASH

PLATE IV

a

4~

!1i

i

3

lO~m

4

\

_

6

I

REVISIONOF THE BIOSTRATIGRAPHYOF [HE CHATHAM GROUP. DEEP RIVER BASIN(NC, tSA)

lying the Stoneville Formation have been dated as late Carnian (Robbins and Traverse, 1980; Robbins, 1982). We have examined assemblages from this interval, and concur with this age assignment. We have also examined a sample (sample 8, Table I) from the Cow Branch Formation outcrop near Walnut Cove. These beds were considered to be distinguishable from the main outcrops of the formation, and were designated as "lower Cow Branch" by Thayer (1970), but palynomorphs recovered from them are not significantly different from those reported by Robbins and Traverse (1980) and others we have examined from more northerly outcrops of the formation. On the basis of this similarity (Fig. 3) and recent field observations by J.P. Smoot and R.E. Weems, the "lower Cow Branch" beds are assessed here as faultrepeated section, and the Cow Branch Formation is not, therefore, differentiated into upper and lower units (Fig. 4).

Palynology ~?['the Davie County basin The Newark Supergroup is exposed in a small outlier basin in Davie County, North Carolina, but the section there has not been subdivided into formations. A single productive palynological sample, collected from this basin by R.E. Weems (sample 9), yielded a low diversity and only moderately well preserved assemblage which is dominated by an unknown inaperturate palynomorph, perhaps Graminoides cernes. Palynomorphs identified more confidently from this sample are Vallasporites

~¢nacii, Alisporites opii(?), Klausipollenites gouldii, PiO,osporites devolvens, Sulcatisporites kraeuselii, Praecirculina gran(l'er, and Dictyophyllidites harrisii. Camerosporites secatus and Camerosporites

89

pseudoverrucatus are also present, and the assemblage indicates that the strata are no younger than late Carnian, nor older than early Carnian; a finer age resolution is not possible.

Plant megajossil data The plant megafossil assemblage from the lower part of the Pekin Formation is not very similar to those plant megafossil assemblages currently known from the Upper Triassic, either the older Eogink¢oites or the younger Dinophyton assemblage zones of Ash (1978, 1980) in the Chinle Formation. The Lockville site in the Sanford subbasin has yielded a floral assemblage including Acrostichites tenu(folius and Acrostichites rhombijblius, Pseudodaneopsis obliqua and Pseudoda-

neopsis plana, Laccopteris lanceolata, Cvcadites acutus, Podozamites long(/blius, and Pterophyllum pect#tatum. These taxa have not yet been reported in higher Newark Supergroup strata or from the Triassic of the US Western Interior. The Lockville assemblage lacks Zamites powellii, a cycadeoid which is common in other strata assigned to the Eoginkgoites and Dinophyton zones, and its unique composition suggests that it may predate the Eoginkgoites zone. However, its relationship to the oldest plant megafossils in the Chinle Formation (Temple Mountain Member) remains uncertain, and this topic is still under study. A larger number of well-preserved plant megafossils have been recovered from about the middle of the Pekin Formation, in the Boren Clay Products and Pomona Pipe Products clay pits of the Sanford subbasin. Hope and Patterson (1969, 1970), Delevoryas and Hope (1971, 1975, 1976), Hope (1975), and Gensel (1986) described some of

PLATE IV

1, 2. "New Genus A new species A". Cumnock Formation (lower), sample 5. I. 2.

3. 4. 5.

Lateral view. Distal view.

Klausipollenites gouldii. Cumnock Formation (lower), sample 5. Minutosaccus crenulatus. Cumnock Formation (equivalent), sample 3. Placopollis koobii. Cumnock Formation (lower), sample 5. This taxon was first noted by Koob (1961) and was described by Cornet (1989) as a dispersed tetrad. It has superficial resemblance to "'New Genus A new species A", a robust bisaccate (1, 2) with a rugulate corpus and heavily thickened sacci from the Chinle Formation; Placopollis koobi is, however, trichotomosulcate. 6, 7. l~/ernopollenites .s'ulcatus. Cumnock Formation (lower), sample 5.

90

this material, but many components of the flora remain unpublished. Ash (1980) placed this assemblage in his mid-Carnian Eoginkoites Zone, on the basis of the presence of Eoginkgoites sp., Danaeopsis plana, Neocalamites knowltonii, and other taxa. Eoginkgoites and Dinophyton may cooccur in several formations in the Newark Supergroup. Specimens referred to Eoginkgoites, collected from the Boren pit by R.C. Hope (pers. commun., 1991), are under study at the University of Texas (Austin) but have not yet been formally described. Gensel (1986) identified a specimen of Dinophyton sp. indet, in the Boren assemblage, and assigned it a mid-Carnian age on the basis of the palynological review of Traverse (1986). We have examined Gensel's Dinophyton specimen, which has preserved cuticle, but not the spinose cuticle characteristic of the type-species. It represents a new (and perhaps ancestral) species or an ecotypic variant of D. spinosus. The latter seems less likely because nothing similar has yet been recognized among the many Dinophyton specimens collected from numerous plant-bearing localities in both fluvial and lacustrine deposits of the Chinle Formation. The presence of Eoginkgoites in the middle Pekin Formation does not, however, preclude a late Carnian age assignment. Eoginkgoites has been collected from upper Carnian strata in the Chinle Formation. Eoginkgoites and Dinophyton may co-occur in the upper part of the Stockton Formation of the Newark basin. The type-locality of Eoginkoites is in the uppermost part of the Stockton Formation at Carversville, Pennsylvania (Bock. 1952). A Dinophyton specimen similar to the Pekin Formation specimen was recovered at Phoenixville, Pennsylvania, by Axsmith and Kroehler (1989), but its identification is impeded by tack of diagnostic cuticle. The Phoenixville section has also been mapped as the upper part of the Stockton Formation (Miles et al., 1980; Smoot et al., in press). Palynomorphs recovered from the upper Stockton Formation beds in which the Dinophyton specimen occurred were dated as late Carnian by Cornet (Axsmith and Kroehler, 1989). We have examined palynomorphs recovered from a sample from the Phoenixville site (Stockton Formation) provided to one of us (SRA) by Axsmith, and confirm a late Carnian age. This palynomorph

RJ. EI1WIN AND S.R. ASH

data, and the late Carnian occurrences of Eoginkgoites in the Chinle Formation, provide circumstantial evidence in support of a late Carnian age for the middle Pekin Formation. The Boren Pit also has produced Cladophlebis daugherO,i, Phleb-

opteris smithii, Wingatea plumosa, Clathropteris walkeri, Cynepteris lasiophora, Zamites powellii, and Pelourdea sp., which are all common in the younger Dinophyton zone of Ash (1980). Hope and Patterson (1969) initially correlated the middle Pekin Formation assemblages with the flora from the late Carnian Monitor Butte Member of the Chinle Formation. The co-occurrence of Eoginkgoites and Dinophyton in the Pekin Formation, and perhaps the Stockton Formation, may be interpreted in several ways. Assemblages from the Boren and Pomona pits may represent Dinophyton zonal assemblages that contain relict Eoginkgoites occurrences, suggesting stratigraphic overlap of the two taxa at the generic level, with a potential biostratigraphic separation of these taxa at the species level. If the eastern Dinophyton occurrences are of a separate species, these may predate Dinophyton spinosus in the US Western Interior. An alternative currently under study is that the Eoginkoites zone may everywhere be of late Carnian age, which may enable us to resolve two megafossil zones within the late Carnian.

Fossil vertebrate data Fossil vertebrates from the Chatham Group show close relationships to those of late Carnian age from the US Western Interior. Gregory (1957) correlated the Cumnock Formation with the Stockton and Lockatong formations of the Newark basin, and with the Chinle Formation of the US Western Interior, on the basis of large herbivorous tetrapods (Placerias and Typothorax), parasuchians (Rutiodon), and fishes (Redfieldius and Diplurus). He also noted the presence of a mammal-like reptile (Microconodon) in the Cumnock Formation. Baird and Patterson (1968) used parasuchians (Rutiodon), aetosaurs (Typothorax), and dicynodonts (Placerias) to correlate vertebrate assemblages from the middle Pekin Formation at the Pomona pit to western US assemblages

REVISION OF THE BIOSTRATIGRAPHY OF THE CHATHAM GROUP, DEEP RIVER BASIN (NC, USA)

from beds in the lower part of the Chinle Formation that were later assigned by Stewart et al. (1972) to the Monitor Butte Member and lower part of the Petrified Forest Member. [These western US assemblages included the abundant vertebrate material that Camp and Welles (1956) recovered near St. Johns, Arizona.] Baird and Patterson also correlated the Pekin Formation assemblage with those of the Stockton Formation of New Jersey and the New Oxford Formation of Pennsylvania; these formations have yielded palynological assemblages that Cornet recognized as late Carnian (Cornet, 1977; Axsmith and Kroehler, 1989). However, Olsen (1988) assigned a mid-Carnian age to an ichnological assemblage from the middle Pekin Formation in the Pomona Clay pit on the basis of one undescribed taxon, Brachychirotherium sp., which has not been found in younger strata. Olsen et al. (1982) noted that fossil fish from lacustrine strata in the Durham subbasin of the Deep River basin were probably late Carnian in age, on the basis of the presence of Diplurus newarki, Turseodus sp., and "Semionotus brauni", and correlated these assemblages with those from the lower part of the Chinle Formation. Olsen et al. (1982) also assigned a late Carnian age to the Cumnock Formation fish assemblages of the Sanford subbasin but subsequently (Olsen et al., 1991) revised this to mid-Carnian, proposing that the Cumnock Formation in the Sanford subbasin and the Cumnock Formation equivalent in the Wadesboro subbasin predated the lacustrine interval in the Durham subbasin. The palynological evidence presented and reviewed here demonstrates, however, that the Cumnock Formation of the Sanford subbasin and its equivalent in the Wadesboro subbasin are late Carnian in age and equivalent to the lacustrine facies with fossil fish in the Durham subbasin. Palynological data have not yet been obtained from the Durham subbasin, but Gore et al. (1989) has concurred with the late Carnian age for the Durham fish assemblages. Conclusions

Strata assigned to the lower part of the Pekin Formation of the Chatham Group near Lockville,

91

North Carolina, are clearly some of the oldest rocks in the US portion of the Newark Supergroup, having yielded palynomorphs of early(?) to midCarnian age. Palynomorph evidence indicates that the Chatham Group is not wholly (or even largely) mid-Carnian as suggested by Cornet (1977) and Cornet and Olsen (1985) but ranges from the early(?) or mid-Carnian into the early Norian, Many previous age assignments of Chatham Group strata in the three subbasins of the Deep River basin appear to be too old, and present evidence now indicates a much closer correlation of palynomorph, plant megafossil, and fossil vertebrate biochronology between Triassic strata in the US Western Interior, the eastern Early Mesozoic basins and western Europe than previously was recognized. Diachroneity of correlative lithostratigraphic units (formations) in the three subbasins of the Deep River basin was suggested by Gore et al. (1989) and Olsen et al. (1991) but is regarded as doubtful because: (1) the oldest palynomorph assemblages from the Cumnock Formation in the Sanford subbasin have been shown here to be late Carnian, not mid-Carnian as previously thought, and lithostratigraphic correlatives in the Durham subbasin contain late Carnian fish assemblages; (2) late Carnian palynomorphs have been recovered from the probable Cumnock Formation equivalent in the Wadesboro subbasin, and the middle Pekin Formation of the Sanford subbasin has yielded mid- to late Carnian palynomorphs. (The upper part of the Pekin Formation in the Sanford subbasin is as yet undated, but also should prove to be late Carnian.) An abrupt late Carnian termination for deposition in the southern suite of Early Mesozoic basins, as suggested by Traverse (1987), no longer seems plausible. Evidence indicates that deposition continued into Norian times in the Dan River Danville basin and probably the Deep River basin, but an unknown thickness has been removed from sequences there by erosion. Currently, it is difficult or impossible to assess how much post-Carnian strata has since been stripped away. Low thermal maturity of palynomorphs in the Chatham Group cannot be used as evidence for minimal Triassic loading above the present top erosional surface in

92

these basins, because palynomorphs from the Chinle Formation in the Capitol Reef area of Utah (sample 10), from the San Juan basin of New Mexico, and from elsewhere on the Colorado Plateau, have consistent low thermal alteration indices (TAI 2 3) despite having been buried under substantial thicknesses (thousands of meters) of post-Triassic strata. The use of thermal alteration of Triassic palynomorphs as indicators of relative depth of burial of the Newark Supergroup is further complicated by effects of igneous intrusions, diagenetic processes, fluid flow, and mineralization. The palynological zonation of Cornet and Olsen (1985) for the Newark Supergroup of the eastern United States appears to be internally inconsistent and, in a critical part, too old. Their oldest zone (the "'Chatham Richmond-Taylorsville Zone") was defined as mid-Carnian in its entirety. However, the Sanford and Cumnock Formations, and probably the upper part of the Pekin Formation of the Chatham Group are demonstrably younger than mid-Carnian on the basis of palynological, plant megafossil, and fossil vertebrate evidence. The Chatham Group alone probably spans three of the four Upper Triassic palynofloral zones of Cornet and Olsen (1985) (Fig. 4). We recommend that the present informal zonal scheme used for the Newark Supergroup, which is based on a combination of lithostratigraphic, geographic, and biologic nomenclature, should be replaced with a formal zonation based strictly upon biological criteria [see: North Anwrican Stratigraphic Code IOriel, 1983) and the International Stratigraphic Guide (Hedburg, 1976)]. This would avoid problems such as that outlined above, and would facilitate future refinement or emendation of these zones, and aid their correlation with Late Triassic sequences and biozonations elsewhere.

Acknowledgements We are most grateful to the following people for their assistance: Norman O. Frederiksen (USGS, Reston) for providing Cumnock coal samples 6a and 6b (Bethany Church locality), Francis M. Hueber and William DiMichelle (USNM, Department of Paleobiology) for permitting us to subsam-

R.I I_IrWIN AND S.R. ASH

ple rock matrix of paleobotanical type-specimens from Chatham Group collections, Robert E. Weems (USGS, Reston) for samples from the Dan River basin and Davie County basin and helpful discussion, Brian Axsmith (Franklin and Marshall College) for matrix sample from his Stockton Dinophyton site, and Albert J. Froelich (USGS, Reston) and Joseph P. Smoot (USGS, Denver) for helpful discussion and critical manuscript review. We are also most grateful to Robert A. Fensome (Geological Survey of Canada), W. Punt (Rijksuniversiteit Utrecht), and an anonymous reviewer for helpful manuscript review and comments. In addition, we thank Robert C. Hope (Sampson County Community College, Clinton, North Carolina) for helpful discussions regarding the Boren plant assemblage, Patricia Gensel (University of North Carolina, Chapel Hill) for loan of the Dinophyton material from the Pekin Formation, Alfred Traverse (The Pennsylvania State University) for loan of and permission to reexamine Cornet's samples PK3 (sample 3) and CMI (sample 4), Eleanora I. Robbins (USGS, Reston) for loan of Chatham Group specimens, especially sample No. 827 (sample 5), and to Nancy Goodwin and Vicky Andrle (USGS, Reston) for technical support. This research was funded by the eastern Mesozoic basins Project ORG 9590-03752 (to RJL), and NSF Grant EAR-88-04130 (to SRA).

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