Lower Tithonian microconchiate simoceratins from eastern Mexico: Taxonomy, biostratigraphy, and palaeobiogeography ANA B. VILLASEÑOR, FEDERICO OLÓRIZ, and CELESTINA GONZÁLEZ−ARREOLA Villaseñor, A.B., Olóriz, F., and González−Arreola, C. 2011. Lower Tithonian microconchiate simoceratins from eastern Mexico: Taxonomy, biostratigraphy, and palaeobiogeography. Acta Palaeontologica Polonica 56 (1): 133–158. The precise record of simoceratins sampled bed−by−bed is first reported from Mexico (Mazatepec area in Puebla, cen− tral−eastern Mexico), as well as the existence of lappeted peristomes in these ammonites. Both Pseudovolanoceras aesinense and the subspecies Pseudovolanoceras aesinense chignahuapense are shown to occur among Mexican simoceratins. The European species and the Mexican subspecies share the same stratigraphic range in the studied sec− tions, yet they differ in ephebic sculpture. Ecological adaptation to neritic seas corresponding to eastern Mexico areas is interpreted, forcing phenotypic deviation with geographic significance, i.e., subspeciation. The new subspecies would in− dicate stratigraphic horizons within the Semiformiceras semiforme/Haploceras verruciferum Chronozone in the Mediter− ranean Tethys. A revision of contemporaneous simoceratins in the Americas is founded on a comparative analysis with respect to the European species P. aesinense. Key words: Ammonitina, Pseudovolanoceras, Tithonian, Upper Jurassic, Mexico. Ana Bertha Villaseñor [[email protected]] and Celestina González−Arreola [[email protected]], Departamento de Paleontología, Instituto de Geología, UNAM. C. P. 04510, México, DF Mexico; Federico Olóriz [[email protected]], Departamento de Estratigrafía y Paleontología, Facultad de Ciencias, Universidad de Granada, Campus Universitario de Fuente Nueva, 18002, Granada, Spain. Received 22 March 2010, accepted 26 July 2010, available online 16 August 2010. Introduction Servizio Geologico d’Italia, Roma, Italy; GPIBO, Goldfuss− Museum und Paläontologisches Institut der Universität Bonn, Upper Jurassic deposits from East−Central Mexico have long Germany; IGM, National Paleontological Collection (Museo been investigated due to their importance for oil exploration. Maria Carmen Perrilliat Montoya), Institute of Geology, Mex− Cantú−Chapa (1967) gave valuable preliminary information ico City, Mexico; NS3Col, Museo di Paleontologia dell’Uni− about Middle Tithonian to Berriasian ammonites gathered versità di Roma, Italy; Rin, Collection housed in the Comune from outcrops in the Mazatepec area, Puebla, Mexico. Cantú− di Piobicco, Pesaro, Italy; SMNS, Staatlisches Museum für Chapa (1989) proposed a type−section for the Tithonian– Naturkunde, Stuttgart, Germany; UNAM, Universidad Nacio− Berriasian boundary in the Mazatepec area, and Adatte et al. nal Autónoma de México, Mexico; USNM, United States (1992) provided a precise biostratigraphy for calpionellids, in− Natural Museum, New York, USA. dicating the Jurassic–Cretaceous boundary in the area. On the Other abbreviations.—Ac, A; Cantú−Chapa collection; C, basis of calpionellid and ammonite biostratigraphy, Stinnes− number of constrictions; CT, Colle Tordina (Monti della beck et al. (1993) questioned the previous proposal for the Rossa, Appennino Marchigiano), Italy; Dm, measured shell Jurassic/Cretaceous boundary type−section made by Cantú− diameter; M, macroconchs; m, microconchs; FAD, first oc− Chapa (1989). A further approach to sedimentology and dia− currence datum; MTQ, Mazatepec Quesos section in the genesis in Kimmeridgian deposits of the “San Andrés” For− Apulco River area in Fig. 2; PS, periumbilical sculpture; mation at Jonotla (Puebla) and Tlacolula (Veracruz), a region PS/2, number of periumbilical sculptural elements, ribs, bul− which includes the Mazatepec area, was made by Hernández lae or tubercles, per half−a−whorl; U, umbilical size; U/D, De La Fuente (1996). size ratio between the umbilicus and shell diameter; Wh, Institutional abbreviation.—BSPG, Bayerische Staatssamm− whorl height; Wh/D, size ratio between whorl height and lung für Paläontologie und Geologie, Munich, Germany; shell diameter; specimen number a, b, letters refer to mould CCS, Material housed in the Museo di Paleontologia del and cast of the same specimen. Acta Palaeontol. Pol. 56 (1): 133–158, 2011 doi:10.4202/app.2010.0030 134 ACTA PALAEONTOLOGICA POLONICA 56 (1), 2011 20o 01' 32'' Mazatepec town MEXICO * Mazatepec area Apulco sections Hydroelectric MT-2 Puebla station MTQ Apulco river 1km 20o 00' 00'' 97o 25' 21" 97o 24' 39" Fig. 1. Location of the studied sections. A. Regional location for Puebla state. B. Inlet for the precise location of the sections investigated on the banks of the Apulco River in the Mazatepec area. (Figs. 1, 2) and shows a 22 m thick succession made of Geological setting brownish, more or less calcareous siltstones and silty lime− stones (Tamán Formation) containing decimetre to metre The geological locality Apulco River section MT−2 lies within size concretions in the lower and middle part of the section. the Apulco Valley, Sierra Norte de Puebla, near the village of Mazatepec, Puebla (Figs. 1, 2). This mountainous region be− longs to the geologic subprovince of Eastern Sierra Madre Historical background (López Ramos 1979a: 291, figs. 6−1, 6−8) and the Mexican Fold−and−Thrust Belt (Suter 1990; a geologic province ac− An overview of Upper Jurassic rocks and palaeoenvironments cording to Ortega−Gutiérrez et al. 1992) where NNW–SSE in the Apulco Valley, located in Sierra Norte de Puebla be− trending folds are interrupted southward by rocks of the Trans− tween Jonotla (Puebla) and Tlacolula (Veracruz), was given mexican Volcanic Axis or Belt. by Hernández De La Fuente (1996). In studying fossiliferous Upper Jurassic outcrops above the Apulco River banks are sections of the area, this author included some outcrops men− difficult to access due to dense forest coverage in the area near tioned by Cantú−Chapa (1971: fig. 1). In his geological local− Mazatepec. The Upper Jurassic section shows a lower, coarse ity Apulco River, Hernández De La Fuente (1996) collected bedded part containing mid−shelf to lower−ramp carbonates Idoceras sp., Mazapilites sp., and Uhligites sp. (without illus− (San Andres Formation; Hernández De La Fuente 1996). tration), and mentioned the common occurrence of ammonites Overlying it are thinner bedded, brownish to grey−black silt− within the Tamán Formation. stones with silty interbeds and occasional calcareous horizons Over the past ten years, two of us (ABV and FO) have showing common, mainly parallel, fine cross lamination (up− studied outcrops around the Apulco River as part of a research per Lower Kimmeridgian and Tithonian Tamán Formation; programme focusing on sections of the San Andrés, Tamán, see Cantú−Chapa 1971 for regional biostratigraphy and corre− and Pimienta Formations, to provide a precise biostratigraphy lation). Regional deepening is 108° to 308° NE, and common based on bed−by−bed sampling (e.g., Villaseñor et al. 2000a, faulting impedes precise lateral observation and correla− 2003; Villaseñor and Olóriz 2001, 2009; López−Caballero tion among outcrops. Evidence of synsedimentary sliding 2006; López−Caballero et al. 2007). (slumps) and horizons containing more calcareous concre− This paper presents the palaeontological analysis carried tions are common in the Lower Tithonian succession. Cover− out on the first specimens of simoceratins collected bed−by− age by alluvium (severe flooding during 1999) affects the bed in Mexico from Lower Tithonian siltstones of the Tamán Tithonian deposits. Cherty intercalations in grayish to darkish Formation cropping out along the Apulco River, Mazatepec, and more calcareous clayey limestones characterise the Puebla (Figs. 1, 2). The studied material was collected from Pimienta Formation (López Ramos 1979b: 315). Apulco section MT−2 (Villaseñor et al. 2003; López−Cabal− The new Apulco section MTQ crops out along the west lero et al. 2007; Villaseñor and Olóriz 2009) and the new bank of the Apulco River, close to the hydroelectric station MTQ section. VILLASEÑOR ET AL.—TITHONIAN SIMOCERATID AMMONOIDS FROM MEXICO 135 Apulco section (MT-2) Apulco section (MTQ) [covered] 40 39 38 37 PIMIENTA FM. 36 UPPER TITHONIAN 35 34a 34b 34c 33 32 31 30 29 28 -MT-Q14 -MT-Q13 27a -MT-Q12 27b -MT-Q11 27c 26 LOWER TITHONIAN TAMAN FORMATION LOWER TITHONIAN TAMAN FORMATION -MT-Q10 25 24 2m 23 2m 22b 22 21b 0m -MT-Q9 0m 21a [submerged] Pseudovolanoceras aesinense chignahuapense (Cantú-Chapa, 1990) Pseudovolanoceras aesinense limestone with fine (Meneghini, 1885) parallel lamination cherty horizon Pseudhimalayites steinmanni (Haupt, 1907) concretional silty limestone limestone siltstone calcareous siltstone Housaites butti ()Imlay, 1942 siltstone with small calcareous concretions perisphinctids Fig. 2. Stratigraphic sections with indication of precise records of Pseudovolanoceras aesinense (Meneghini, 1885) and Pseudovolanoceras aesinense chignahuapense (Cantú−Chapa, 1990) in the Apulco sections MT−2 and MTQ. Note the occurrence of other ammonites significant for biostratigraphy and correlation. Records of simoceratins from the Americas.—Precise in− have been reported with illustration, aside from some text cita− formation about the record of Lower Tithonian simoceratins tions. Krantz (1928) identified the southernmost record, from from the Americas is rare, and to date only four specimens Argentina, while the other three records were reported by doi:10.4202/app.2010.0030 136 ACTA PALAEONTOLOGICA