Abstract

OMANA, Lourdes et al. 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. Bol. Soc. Geol. Mex [online]. 2019, vol.71, n.3, pp.691-725.  Epub Dec 06, 2019. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2019v71n3a5.

The Valles-San Luis Potosí 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.

Keywords : Cenomanian; benthic foraminifers; El Abra Formation; San Luis Potosí; Mexico.

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