Mid-late Cenomanian larger benthic foraminifers from the El Abra Formation, Valles-San Luis Potosí Platform, central-eastern Mexico: Taxonomy, biostratigraphy and paleoenvironmental implications

Abstract

espanolThe Valles-San Luis Potosi Platform is part of an extensive carbonate platform system that rimmed the ancestral Gulf of Mexico during the middle (Albian) through Upper Cretaceous. The El Abra Formation consists of a shallow-water deposit; it contains a benthic foraminiferal assemblage that includes 18 species, which are described and illustrated in this paper. The studied successions from the upper part of the El Abra Formation were dated as mid-late Cenomanian. On the basis of these findings, two zones are proposed Pseudolituonella reicheli Assemblage Zone and Nezzazatinella picardi Interval Zone. The first Assemblage Zone is characterized by an abundant benthic foraminiferal association. It is overlain by the Nezzazatinella picardi Interval Zone where the species richness of the fora-miniferal assemblage is reduced and later disappears. The benthic foraminiferal demise is coincident with major sea-level changes and an increase in siliciclastic input from the hemipelagic deposit of the Soyatal Formation, which contains abundant pithonellids and r and r-k strategist planktic foraminifera (Whiteinella archaeo-cretacea Partial Range Zone). Two stratigraphically correlative facies have been recognized in the El Abra Formation: the Taninul and the El Abra Facies. A warm, shallow-water, open marine platform deposit (Taninul Facies) is inferred. It includes peloidal-foraminiferal packstone, packstone-grainstone, and packstone- wackestone. A restricted environment (El Abra Facies) can be deduced from the abundant miliolids and ostreids. The texture is a wackestone-packstone. Another microfacies (Soyatal Formation) consists of wackestone-packstone with an acme of pithonellids and the occurrence of r and r-k strategist planktic foraminifers deposited during the platform drowning. EnglishLa Plataforma Valles-San Luis Potosi es parte de un sistema de plataformas extenso que se encontraba bordeando el antiguo Golfo de Mexico en el Albiano hasta el Cretacico Superior. La caliza El Abra es un deposito de aguas poco profundas; esta contiene un conjunto de foraminiferos bentonicos que incluye 18 especies, que se describen e ilustran en este documento. Las sucesiones estudiadas de la parte superior de la Formacion de El Abra fueron datadas como del Cenomaniano medio- tardio; se proponen dos zonas (Zona de Conjunto Pseudolituonella reicheli y Zona de Intervalo Nezzazatinella picardi). La primera Zona de Conjunto se caracteriza por una asociacion abundante de foraminiferos bentonicos. Esta sobreyacida por la Zona de Intervalo Nezzazatinella picardi donde se reduce la riqueza de especies de las asociaciones de foraminiferos y luego desaparece. La desaparicion de foraminiferos bentonicos es coincidente con grandes cambios de nivel del mar y un aumento en el aporte de sedimentos desde el deposito hemipelagico de la Formacion Soyatal que contiene abundantes pithonelidos y foraminiferos planctonicos de estrategia r y r-k (Zona de Alcance Parcial (Whiteinella archaeocretacea)). Dos facies estratigraficamente correlacionables han sidoreconocidas en la Formacion El Abra: la Facies Taninul y la Facies El Abra. Se infiere un deposito de plataforma marina abierta de aguas calidas someras (Facies Taninul). Esta incluye un packstone peloidal con foraminiferos, packstone y packstone-wackestone. Un ambiente restringido (Facies El Abra) puede deducirse por los abundantes miliolidos y ostreidos. La textura de la roca es un wackestone-packstone. Otra microfacies consiste de un wackestone-packstone con un auge de pithonelidos y la presencia de foraminiferos de estrategia r y r-k depositados durante la inundacion de la plataforma (Formacion Soyatal).