EARLY OSTREIDS FROM THE ADJUNTAS FORMATION, DIFUNTA GROUP, NORTHEASTERN MEXICO MARIA DEL CARMEN PERRILLIAT and FRANCISCO J. VEGA INSTITUTO DE GEOLOGiA UNIVERSIDAD NACION AL AUTONOMA DE MEXICO MEXICO , D.F. , MEXICO

I. ABSTRACT Eocene beds of the Mesogean region a nd Four ostreid species from the Lower Eo­ the southern United States (Raulin and cene Adjuntas Formation are reported, Delbos, 1855; Gardner, 1927; Vyalov, 1936, two of them described herein. The stratig­ 1948). A wide distribution of ostreid taxa is raphic range and paleoenvironmental in­ proposed to be the result of island-hop­ terpretation of the material reinforces pre­ ping, when explaining interoceanic distri­ vious conclusions on deltaic plain deposits butions (Stenzel, 1971). Ostreid beds of the of Lower Eocene age for the Adjuntas For­ Adjuntas Formation are included in a del­ mation. taic plain sequence, chiefly of red and green beds. The Adjuntas comprises II. INTRODUCTION mudstones, siltstones, and sandstones, with a thickness of 260 meters. Some gray The Adjuntas Formation has proved to beds at the base and the top of the forma­ be the youngest and one of the most fos­ tion include Venericardia (Venericor) siliferous formations of the Difunta Group. planicosta and Turritella mortoni postmor­ Previous works have been devoted to the toni, indicative of a Lower E ocene age. description of new molluscan taxa, found These gray beds have been in terpreted as in the deltaic plain and inner shelf deposits inner shelf deposits (Vega and Perrilliat, of this formation (Vega and Perrilliat, 1989b). The green beds of this formation 1989a; 1989b; 1992). The first formal stratig­ contain a great abundance of freshwater raphic report on the Difunta Group consi­ gastropods, interpreted as inhabitants of dered the Adjuntas Formation to be of deltaic plain deposits, below the phreatic Maastrichtian age, based on the presence level (Vega and Perrilliat, 1992). of Exogyra costata Say (McBride et al., The lithology of the Adjuntas Formation 197 4). Subsequently, Vega and Perrilliat varies laterally and between the synclines (1989a) reported in the Adjuntas Forma­ where it outcrops. L ithology at localities tion the presence of Venericardia (Ven­ IGM 1973 and IGM 2645 is more sandy than ericor) planicosta Lamarck and Turritella at the type section (McBride et al., 197 4), mortoni postmortoni Conrad, index with almost no green beds, and the os­ for the of the Gulf Coastal Plain treids are distributed in well-defined strata (Shimer and Shrock, 1944). Without de­ of 1 to 2 meters thickness. Some sandstone tailed morphological examination, the os­ beds between the ostreid banks contain treid species here reported superficially tree-trunks in vertical position, replaced resemble Exogyra costata. It is probable by light brown sandstone. Some red beds that previous authors confused this Creta­ include leaf remains. The ostreid banks ceous grypheid with the Tertiary ostreids seem to be monospecifi c and the valves, al­ present in the Adjuntas Formation out­ though very near one to each other, rarely crops (McBride et al., 1974; Wolleben, are found to be cemented. A coarse sand­ 1977). stone matrix of brown color includes all the The Adjuntas Formation has its most ex­ ostreid remains. In other parts of the locali­ tensive outcrop areas in the synclines of ty 2645, the left valves of the ostreids were the La Popa basin (Text-figure 1). The os­ found still attached to bored limestone treids here described were collected at fragments. This could represent an es­ three localities in the Escondida and Del­ tuary , near the distrib~tary channel~, at gado synclines (Text-figure 2). whose ed ges the ostre1d banks prolifer­ ated. A subsidence period in the La Popa III. STRATIGRAPHY AND basin generated conditions for the deposi­ PALEO ENVIRONMENT tation of the Adjuntas Formation sedi­ The ostreid subgenus Turkostrea has ments, forming marshes, swamps, and es­ been reported in the Lower and Middle tuaries, in which a diverse molluscan 15 16 Tulane Studies in Geology and Paleontology Vol. 26 fauna developed during Lower Eocene Suborder OSTREINA Ferussac, 1822 time. Superfamily OSTREACEA Rafinesque, 1815 IV. ACKNOWLEDGMENTS Family OSTREIDAE Rafinesque, 1815 We are grateful to M. en C. Zoila Graciela Castillo R. of the Instituto de Genus OSTREA Linnaeus, 1758 Ciencias del Mary Limnologia, UN AM, for Ostrea Linnaeus, 1758, Systema naturae per tria her kind help in comparison of the regna naturae, p. 696. material with collections of Recent ostreids Type species: Ostrea edulis Linnaeus; Re­ at her laboratory. Mr. Luis Burgos P. cent, England; by subsequent designation, Chil­ cheerfully helped in doing the figures. Dr. dren, 1823. E.H. Vokes (Tulane University) made val­ uable comments and critically reviewed Subgenus TURKOSTREA Vyalov, 1936 the manuscript. Turkostrea Vyalov, 1936, Acad. Sci. USSR, Comptes Rendus (Doklady), new ser., v. 4 V. SYSTEMATIC DESCRIPTIONS (13), no. 1, p. 18. Order PTERIOIDA Newell, 1965 Type species: Ostrea turkestanensis Roma-

0 30Km TEXAS San Antonio 0 I •• Eagle Pass CHIHUAHUA/ Piedras Negras za•N . \. COAHUILA \. Monclovao . -·\ .,r.. ./ .)

Z6°N ._,..._rownsvi Ile Torreon .! PARRAs ~ f B4s1N ~ \ ../., ___. .Saltillrr '· DURANGO \... -v· {\\ "----... j' . ~ / ·-~ . ../ . /'. TAMAULIPAS ./. ./ ZACATECAS ./ \ ~ / ./ I02°W /·..JS.L.P. \ 100°w\ Cd. Victoria

Text-figure 1. Generalized location map of Difunta Group in northeastern Mexico, showing distribution of Parras and La Popa basins in Coahuila and Nuevo Leon states. Enclosed area in center is shown in text-figure 2. No. 1 Adjuntas Formation Ostreids 17

novsky Ostrea strictiplicata Raulin and De­ gauche ornee d'environ 60 plis fins; surface lbos; Central Asia (USSR, Uzbekistan); Mon­ d'adherence petite; crochet, 116 ; canal assez tagne-Noire (Aude), France; Middle Eocene; by profond, 1/2; bourrelets saillants; sillons pro­ original designation. fonds se continuant clans la valve par des points; expansions bien developpees. Valve droite un peu convexe. Impression musculaire grande au 0STREA (TURKOSTREA) STRICTIPLICATA centre de la moitie posterieure." (Raulin a nd Raulin and Delbos, 1855 Delbos, 1855) Plate 1, figures 2, 5; Type locality: Terrain a Nummulites de la Plate 2, figures 2, 3 Montagne Noire (Aude), France. Ostrea strictiplicata RAULIN and DELBOS, Occurrence: Lutetian, Paris Basin; Lower Eo­ 1855, Bull. Soc. Geol. France, ser. 2, v. 12, p. 1158. cene, between Moussolens and Montolieu (Aude); Lutetian, Egypt, Transylvania Basin, Ostrea (Ostrea) moussoulensis ASTRE, 1922, Perse and Turkestan. Bull. Soc. Hist. Nat. Toulouse , v. 50, p. 161 , Figured specimens: Plate 1, figs. 2, 5, IGM pls. 1-6. 6312 ; length 24.9 mm, height 38.4 mm, diameter Ostrea multicostata Deshayes. KIEH, 1930, Bull. (both valves) 22.8 mm. Plate 2, figs. 2, 3, IGM Soc. Geol. France, ser. 4, v. 30, p. 89. 6311; length 75.4 mm, height 91.2 mm, diameter "Test epais. Coquille arrondie-ovalaire. Valve (both valves) 60. 7 mm; locality IGM 1973.

0 5 10 Km t::=::=::::t:=:===~

1 26° 15

FOSSIL LOCAL ITIES ··t- IGM -1973 ( 1 ) +IGM-2645 ( 2 ) -tlGM-2647

Text-figure 2. Location ma p of the three ostreid localities in the Escondida and Del­ gado synclines, La Popa basin, Nuevo Leon , Mexico. Tulcrne Studies in Geology and Paleontology Vol. 26

Other occin-rences. IGM locality nos. 1973, right valve finely pitted, the pitting persistent in 2G47. some individuals around the entire inner mar­ Discnssicm: The complete synonymy gm. Adductor scars rather small. crescentic, not deeply excavated. posterior and below the me­ of this specir·s 1s in Kieh (1930, p. 89), who dian horizontal." (Gardner, 1927) made a revision of the subspecies and var­ ieties that have been assigned to this spe­ Description: Shell of large size, inequivalve cies. and which need not to be repeated and inequilateral, ovate-trigonal. The left valve has 20 lo 25 radial ribs, some of them bifurcated here. Within the Mexican specimens from in the ventral region. In the attachment area the locality IGiv1 1973, we have smaller speci­ surface of the shell is smooth. The ligament area mens than those called by Kieh as ex­ is broad, the catachomata are present in almost ogyroidals. We also have the gryphaeiform all the margin of the shell. The adductor muscle type; the Asiatic specimens show this fea­ is reniform. The right valve has an ornamenta­ ture also. while those from the meridional tion of concentric lamellae. The anachomata are region of France and northern Africa have present all around the margin of the shell. The this feature only partially. Kieh (1930, p. adductor muscle is big and deep. The Quenstedt 87) mentioned that this species lived in lit­ muscle is present. toral zones or shores during the Middle Eo­ Type material. USNM 369239. Right valve; al­ cene, having numerous varieties, following titude 10.6 mm, latitude 6.1 mm, semi-diameter various living conditions. 2.4 mm. Left valve of another individual; al­ titude 10.5 mm, latitude 6.95 mm, semi-diameter :3.45 mm. OsTRr:A (TuHKOSTH.I<:A) DUVALI Type locality: Austin-Elgin Ferry road, 1 mile Gardner, 1927 north of Austin-Bastrop Highway, Bastrop Plate I, figures 1, 6; County, Texas. Plate 2, figures 1, 6 Occurrence: , probably the Ostren d11l•al1 GARDNER. 1927. Jour. Washing­ Indio Formation, Eocene. ton Acad. Sci.. v. 17, no. 14, µ. 366. rigs. 1-4. Figured specimens: Plate 1, figs. 1, 6, IGM 6314; length 80.1 mm, height 78.3 mm, diameter "Shell of moderate dimensions for the genus, (left valve) 34.0 mm. Plate 2, figs. 1, 6, IGM 6315; ineqwv

PLATE I Figures 1, 6. 0. trea (Turkostrea) duvali Gardner. 1927 (x 1 ). IGM 6314: length 80.1 mm, height 78.3 mm. diameter (left valve) 34.0 mm. LocCllity: IGM 2645. Adjuntas Formabon, Nuevo Leon. Mexico. 2, 5. Ostrea (Turkostrea) strictiplicata Raulin and Delbos. 1855 (x l). IGM 6312; length 2-L9 rnm; height 38.4 mm. diameter (both valves) 22.8 mm. Locality: IGM 1973, Adjuntas Formation, Nuevo Leon, Mexico. 3. 4. Oslrea rTurkostrea) escoHdidn Perrilliat and Vega. n. sp. (x 1 l. IGM 6317 (holotypel: 1Ength 48.9 mm, height 56.9 mrn, diameter (both valves) 36.0 nnn. Locality: IGM 264:), Adjuntas Formation. Nuevo L 'On, Mexico. No. 1 Adjuntas Formation Ostreids 19

4

6

PLATE 1 20 Tulane Studies in Geology and Paleontology Vol. 26

0STREA (TURKOSTREA) ESCONDIDA lapping lamellae in both valves, being Perrilliat and Vega, n. sp. more foliaceous in the left valve. The sub­ Plate 1, figures 3, 4; margins are strongly punctate in the left Plate 2, figures 4, 5; valve and weak in the right valve. Plate 4, figures 1, 2, 4, 6 Ostrea cynthiae Maury (1912, p . 37, pl. 6, Description: Shell small for the genus, in­ fig. 5) from the Midway (Eocene) of Sol­ equivalve and inequilateral. The left valve is dado Rock, Gulf of Faria, has a very con­ convex, ovate-trigonal in outline. The sculpture vex left valve, not plicated, with irregular is of numerous, thin radial ribs, some of them concentric lamellae, and the right valve bifurcated in the ventral region. The umbo is has no sculpture. The main feature of the opisthogyrous and the ligament area is narrow right valve of the Nuevo Leon specimens is and trigonal, the catachomata are visible. The the numerous, low concentric imbrica­ adductor muscle scar is reniform. The right tions, each one of these with thin radial valve has the same outline as the left one, the sculpture is of numerous, low concentric lamel­ threads with narrow interspaces. lae on the whole surface of the shell. Each lamella presents slender radial threads with 0STREA (Subgenus?) POPAENSIS narrow interspaces. The umbo is opisthogyrous Perrilliat and Vega, n. sp. and the ligament area is narrow. The Plate 3, figures 1-6; anachomata are clear and the adductor muscle scar is reniform. Plate 4, figures 3, 5 Holotype: IGM 6317, length 48.9 mm, height Description: Shell of medium size, trigonal, 56.9 mm, diameter 36.0 mm. sometimes the posterior margin is elongated, in­ Paratype: IGM 6318, length 36.6 mm, height equilateral, inequivalve and thick. The right 42. 7 mm, diameter 13.0 mm. valve has an ornamentation of numerous radial Type locality: IGM 2645. Southwest margin of ribs, bifurcated in the ventral margin, and co­ the La Escondida syncline, approximately 20 km vered by concentric lamellae. In some valves northwest of the town of San Jose de la Popa, the ribs have disappeared and only thick con­ and 15 km southeast of Espinazo village, Nuevo centric lamellae are present. The umbo is pro­ Leon, Mexico. sogyrous. The anachomata and/or relict Occurrence: Adjuntas Formation, Mexico; anachomata are present. In a few specimens the Lower Eocene. Quenstedt muscle scar is preserved. The ad­ Etymology: The name of the species is dedi­ ductor muscle is in the posterior region, re­ cated to the Escondida syncline, where outcrops niform and big. In a few specimens the mantle of Tertiary rocks have yielded a diverse mac­ muscle scars are present. The margin is smooth. roinvertebrate fauna, with a great number of The left valve is concave and the attachment oyster banks. area is small. It has the same sculpture as the Discussion: The Mexican specimens are right valve, but the ribs are less pronounced. The interior of the valve is smooth and presents not like any other species described from the Quenstedt muscle scar, mantle muscle scars, the Eocene. The most similar species is and the reniform adductor muscle. The umbo is Ostrea kochae Gardner (1933, p. 140, pl. 8, prosogyrous. The catachomata are present in al­ figs. 1-5) from the Tehuacana Member, most three-quarters of the margin. Kincaid Formation (Paleocene), from 7 1/2 Holotype: IGM 6321; length 70. 7 mm, height miles southeast of D'Hanis, Medina 76.2 mm, diameter 30.0 mm. County, Texas, but this species has over- Paratype: IGM 6322; length 57.3 mm, height

PLATE 2 Figures 1, 6. Ostrea (Turkostrea) duvali Gardner 1927 (x 1). IGM 6315; length 78.4 mm, height 93. 7 mm, diameter (right valve) 24.6 mm. Locality: IGM 2645, Adjuntas Formation, Nuevo Leon, Mexico. 2, 3. Ostrea (Turkostrea) strictiplicata Raulin and Delbos, 1855 (x 0.5). IGM 6311; length 75.4 mm, height 91.2 mm, diameter (both valves) 60. 7 mm. Locality: IGM 1973, Adjuntas Formation, Nuevo Leon, Mexico. 4, 5. Ostrea (Turkostrea) escondida Perrilliat and Vega, n. sp. (x 1). IGM 6318 (paratype); length 36.6 mm; height 42. 7 mm, diameter (right valve) 13.0 mm. Locality: IGM 2645, Adjuntas Formation, Nuevo Leon, Mexico. No. 1 Adjuntas Formation Ostreids 21

PLATE 2 22 Tulane Studies in Geology and Paleontology Vol. 26

67.0 mm, diameter 18.0 mm. VI. LITERATURE CITED Type locality: IGM 2645. Southwest margin of the La Escondida syncline, approximately 20 km ASTRE, GASTON, 1922, Recherches critiques northwest of town of San Jose de La Popa, and sur l'Ostrea,

PLATE 3 Figures 1, 4. Ostrea (Subgenus?) popaensis Perrilliat and Vega, n. sp. (x 1). IGM 6321 (holotype); length 70. 7 mm, height 76.2 mm, diameter (right valve) 30.0 mm. Locality: IGM 2645, Adjuntas Formation, Nuevo Leon, Mexico. 2, 3. Ostrea (Subgenus?) popaensis Perrilliat and Vega, n. sp. (x 1). IGM 6323 (paratype); length 41.1 mm, height 46.0 mm, diameter (left valve) 18.2 mm. Locality: IGM 2645, Adjuntas Formation, Nuevo Leon, Mexico. 5, 6. Ostrea (Subgenus?) popaensis Perrilliat and Vega, n. sp. (x 1). IGM 6322 (paratype); length 57.3 mm, height 67.0 mm, diameter (right valve) 18.0 mm. Locality: IGM 2645, Adjuntas Formation, Nuevo Leon, Mexico. No. 1 Adjuntas Formation Ostreids 23

PLATE3 24 Tulane Studies in Geology and Paleontology Vol. 26

RAFINESQUE, C. S. , 1815, Analyse de la na­ VEGA, F. J., and M. C. PERRILLIAT, 1989b, ture ou tableau de l'univers et des corps or­ On a new species of Venericardia from the ganises. Palermo, 224 p. Lower Eocene in northeastern Mexico (Di­ RAULIN, V., and J. DELBOS, 1855, Extrait funta Group): Tulane Studies in Geology and d 'une monographie des Ostrea des terrains Paleontology, v. 22, no. 3, p . 101-106. tertiaires de l' Aquitaine: Bulletin de la VEGA, F. J., and M. C. PERRILLIAT, 1992, Societe Geologique de France, ser. 2, v. 12, Freshwater gastropods from early Eocene p. 1144-1164. Difunta Group, northeastern Mexico: Jour­ SHIMER, H. W. , and R . R . SHROCK, 1944, nal of Paleontology, v. 66, no. 4, p. 603-609. Index fossils of North America. JohnWiley VYALOV, 0. S., 1936, Sur la classification des and Sons, London, 837 p. huitres: Academie des Sciences de la USSR, STENZEL, H. B ., 1971, Bivalvia, p. N954- Comptes Rendus (Doklady), new ser., v. 4 N1224, in Treatise on Invertebrate Paleon­ (13), no. 1, p. 17-20. tology, Part N6(3) (R. C. Moore, ed.), Geolog­ VYALOV, 0. S., 1948, Printsiply klassifikatsii ical Society of America and University of semeystva Ostreide: Lvovskiye geologiches­ Kansas Press, Lawrence, 1224 p. kiye obshestvenniye trudy pri gosudarstven­ VEGA, F. J. , and M. C. PERRILLIAT, 1989a, nom, Universitete imeny Ivan Franko, La presencia de! Eoceno marino en la Paleontologicheskaya seria, no. 1, p. 30-40. cuenca de La Popa (Grupo Difunta), Nuevo WOLLEBEN, J. A., 1977, Paleontology of the Leon; orogenia postypresiana: Universidad Difunta Group (Upper -Tertiary) N acional Aut6noma de Mexico, Instituto de in Northern Mexico: Journal of Paleontolo­ Geologia, Revista, v. 8, no. 1, p. 67-70. gy, v. 51 , no. 2, p. 373-398.

December 29, 1993

PLATE 4 Figures 1, 2. Ostrea (Turkostrea) escondida Perrilliat and Vega, n. sp. (xl). IGM 6319 (paratype); length 44.4 mm, height 49. 7 mm, diameter (right valve) 16.5 mm. Locality: IGM 2645, Adjuntas Formation, Nuevo Leon, Mexico. 3, 5. Ostrea (Subgenus?) popaensis Perrilliat and Vega, n. sp. (x 1). IGM 6324 (paratype); length 73.3 mm, height 90.2 mm, diameter (right valve) 23.3 mm. Locality: IGM 2645, Adjuntas Formation, Nuevo Leon, Mexico. 4, 6. Ostrea (Turkostrea) escondida Perrilliat and Vega, n. sp. (x 1). IGM 6320 (paratype); length 48.6 mm, height 58.0 mm, diameter (left valve) 16.2 mm. Locality: IGM 2645, Adjuntas Formation, Nuevo Leon, Mexico. No. 1 Adjuntas Formation Ostreids 25 .

PLATE 4