Boletín de la Sociedad Geológica Mexicana / 2019 / 691 Mid–late Cenomanian larger benthic foraminifers from the El Abra Formation W Valles-San Luis Potosi Platform, central–eastern Mexico: Taxonomy, biostratigraphy and paleoenvironmental implications Lourdes Omaña, Rubén López-Doncel, José Ramón Torres, Gloria Alencaster, Iriliana López-Caballero ABSTRACT Lourdes Omaña ABSTRACT RESUMEN Gloria Alencaster lomanya@geología.unam.mx The Valles–San Luis Potosí Platform is La Plataforma Valles–San Luis Potosí es parte de Departamento de Paleontologia, Instituto de part of an extensive carbonate platform un sistema de plataformas extenso que se encon- Geologia, Universidad Nacional Autonoma system that rimmed the ancestral Gulf traba bordeando el antiguo Golfo de México en el de Mexico, Ciudad Universitaria, Coyoacan, of Mexico during the middle (Albian) Albiano hasta el Cretácico Superior. La caliza El 04510, CDMX, Mexico. through Upper Cretaceous. The El Abra Abra es un depósito de aguas poco profundas; ésta Formation consists of a shallow-water contiene un conjunto de foraminíferos bentónicos Rubén López-Doncel deposit; it contains a benthic foramin- que incluye 18 especies, que se describen e ilustran José Ramón Torres iferal assemblage that includes 18 species, en este documento. Las sucesiones estudiadas de Instituto de Geologia, Universidad Autonoma which are described and illustrated in this la parte superior de la Formación de El Abra de San Luis Potosi, Av. Dr. Nava # 5, San Luis paper. The studied successions from the fueron datadas como del Cenomaniano medio– Potosi, Mexico. upper part of the El Abra Formation were tardío; se proponen dos zonas (Zona de Conjunto dated as mid–late Cenomanian. On the Pseudolituonella reicheli y Zona de Intervalo Iriliana López-Caballero basis of these findings, two zones are pro- Nezzazatinella picardi). La primera Zona de Facultad de Ciencias, Universidad Nacional posed Pseudolituonella reicheli Assemblage Conjunto se caracteriza por una asociación abun- Autonoma de Mexico, Ciudad Universitaria, Zone and Nezzazatinella picardi Interval dante de foraminíferos bentónicos. Está sobreya- Coyoacan, 04510, CDMX, Mexico. Zone. The first Assemblage Zone is cida por la Zona de Intervalo Nezzazatinella characterized by an abundant benthic picardi donde se reduce la riqueza de especies de foraminiferal association. It is overlain las asociaciones de foraminíferos y luego desapa- by the Nezzazatinella picardi Interval Zone rece. La desaparición de foraminíferos bentónicos where the species richness of the fora- es coincidente con grandes cambios de nivel del miniferal assemblage is reduced and later mar y un aumento en el aporte de sedimentos desde disappears. The benthic foraminiferal el depósito hemipelágico de la Formación Soyatal demise is coincident with major sea-level que contiene abundantes pithonélidos y foraminí- changes and an increase in siliciclastic feros planctónicos de estrategía r y r-k (Zona de input from the hemipelagic deposit of the Alcance Parcial (Whiteinella archaeocretacea)). Soyatal Formation, which contains abun- Dos facies estratigráficamente correlacionables dant pithonellids and r and r-k strategist han sidoreconocidas en la Formación El Abra: la planktic foraminifera (Whiteinella archaeo- Facies Taninul y la Facies El Abra. Se infiere cretacea Partial Range Zone). Two strati- un depósito de plataforma marina abierta de graphically correlative facies have been aguas cálidas someras (Facies Taninul). Ésta recognized in the El Abra Formation: the incluye un packstone peloidal con foraminíferos, Taninul and the El Abra Facies. A warm, packstone y packstone-wackestone. Un ambiente shallow-water, open marine platform restringido (Facies El Abra) puede deducirse deposit (Taninul Facies) is inferred. It por los abundantes miliólidos y ostreídos. La includes peloidal-foraminiferal packstone, textura de la roca es un wackestone-packstone. packstone–grainstone, and packstone– Otra microfacies consiste de un wackestone- wackestone. A restricted environment (El packstone con un auge de pithonélidos y la pre- Abra Facies) can be deduced from the sencia de foraminíferos de estrategia r y r-k depo- abundant miliolids and ostreids. The tex- sitados durante la inundación de la plataforma ture is a wackestone–packstone. Another (Formación Soyatal). microfacies (Soyatal Formation) consists of wackestone–packstone with an acme Palabras clave: Cenomaniano, of pithonellids and the occurrence of r foraminíferos bentónicos, and r-k strategist planktic foraminifers Formación El Abra, San Luis deposited during the platform drowning. Potosí, México. BOL. SOC. GEOL. MEX. 2019 VOL. 71 NO. 3 Keywords: Cenomanian, ben- P. 691 ‒ 725 thic foraminifers, El Abra http://dx.doi.org/10.18268/BSGM2019v71n3a5 Formation, San Luis Potosí, Mexico. Manuscript received: April 5, 2018. Corrected manuscript received: May 7, 2018. Manuscript accepted: May 11, 2018. late Cenomanian larger benthic foraminifers from the El Abra Formation – Mid 692 / Boletín de la Sociedad Geológica Mexicana / 2019 1. Introduction and pelagic wackestone bearing planktic foramini- fers and pithonellids (Soyatal Formation). During the mid–Cretaceous, particularly in the The drowned episode in the Cenomanian/Turo- Albian through Cenomanian, widespread carbon- nian (C/T) interval at the global level is linked ate platform development took place throughout INTRODUCTION with rising sea level (Haq et al., 1987; Haq, 2014; the tropical–subtropical shallow-water environ- Hallam, 1992; Miller et al., 2005; Gale et al., 2008), ments of the Tethys (Schroeder and Neumann, and widespread flooding of Mediterranean plat- 1985, p. 5). Benthic foraminifers and algae are the forms (Drzewiecki and Simó, 1977; Caus et al., most important groups that inhabited this milieu. 1997; Hart et al., 2005; El-Sabbagh et al., 2011; In Mexico, during the Albian/Cenomanian, the Korbar et al., 2012). Valles–San Luis Potosí Platform (VSLPP) was part The start of the demise of the carbonate platforms of a wide carbonate platform system that bordered occurred during the latest Cenomanian (Whitei- the ancestral Gulf of Mexico (Salvador, 1991). nella archaeocretacea Zone), with a major biological This platform experienced the evolution of a rich change that affected benthic organisms such as and diverse benthic foraminiferal assemblage now rudists and larger benthic foraminifera. contained in the El Abra Limestone. Philip and Airaud-Crumière (1991, p. 117) docu- In this study, we analyzed calcareous samples mented that the benthic foraminifera were affected derived from the Cenomanian El Abra Formation in two steps; the genera Praealveolina, Chrysalidina, containing an abundant and well-preserved ben- Pseudocyclammina, and Pseudolituonella disappeared thic foraminiferal assemblage that also includes at the top of Geslinianum Zone. During the late algae, corals, echinoderms, and annelids. Cenomanian (Juddii Zone) the benthic forami The El Abra Formation is renowned for its inverte- nifera were scarce and poorly diversified miliolids, brate fossils, primarily Albian rudists, which have been analyzed by numerous authors (e.g. Adkins, textularids, and trochamminids. At second step 1930; Coogan; 1973; Alencáster, 1998; Alencáster occurs when a major extinction affected the ben- and García-Barrera, 2008). thic foraminifera at the C/T boundary. The Albian benthic foraminifers from the El Abra Parente et al. (2008) also reported a two-step pa Formation were documented by Bonet (1956), and ttern of extinction of larger foraminifers in the Tavitas and Solano (1984) from the eastern part upper Cenomanian in shallow-water carbonates VSLPP. They reported an assemblage composed of the southern Apennines (Italy). They stated that of Orbitolina (Mesorbitolina) texana, Dictyoconus wal- “the first step eliminated the alveolinids, the most nutensis (Carsey), Coskinolina sunnilandensis (Maync), extreme k strategists, reducing the diversity of the Pseudonummoloculina heimi (Bonet), and Dicyclina larger foraminifera to less complex forms such as schlumbergeri (Munier-Chalmas). Chrysalidina, Pseudolituonella and Pseudoraphydionina; We studied the benthic foraminiferal community when the high productivity persisted only r–oppor- from the western part of the VSLPP. This associ- tunist planktic foraminifers predominated while ation has been dated as middle-late Cenomanian the rise of the mesotrophic threshold triggered the and is very different from the well-known foramin- second step extinction of larger foraminifera.” iferal association of the eastern part composed However, in the present study, the C/T boundary mostly of orbitolinids (Omaña et al., 2016). interval is characterized by the disappearance The upper part of the El Abra Formation in the first of larger forms such as Pseudolituonella, Daxia, area of study represents the last shallow-water Merlingina, Hemicyclammina, Dicyclina, and Cuneolina. deposit preceding the VSLPP, which was drown- Later, only forms such as Nezzazatinella picardi, Prae- ing at the Cenomanian/Turonian boundary inter- chrysalidina, rotalids, miliolids, and algae remained, val (Basañez et al., 1993; Omaña et al., 2012). It this interval is overlain by a deposit with abundant late Cenomanian larger benthic foraminifers from the El Abra Formation is overlain by a succession of bioclastic packstone pithonellids, and r and r-k strategist planktic fora- – Mid Boletín de la Sociedad Geológica Mexicana / 2019 / 693 INTRODUCTION / GEOLOGICAL SETTING Figure 1 Map with locations