RECORD OF EARLY APTIAN-EARLY ALBIAN OCEANIC ANOXIC EVENTS IN CENTRAL-EASTERN MEXICO (TAMPICO-MISANTLA BASIN)

The Early Cretaceous Oceanic Anoxic Events (OAEs ) represent major perturbations in the climate system and in the carbon cycle, identified by pronounced carbon isotopic excursions (CIE), and widespread burial of organic carbon. These episodes of environmental global change also occur with significant effects in marine biota. Present study uses biostratigraphy, microfacies analysis, and geochemistry data to characterize paleoceanographic conditions and biotic responses to oceanic anoxic events throughout an interval deposited during Early Aptian to Late Albian (Globigerinelloides blowi to Ticinella praeticinensis planktic foraminifera zones) in central-eastern Mexico.

The herein studied 92 m-thick Linderos section, located in the Tampico-Misnatla Basin, is mainly constituted by a continuous carbonate marine succession of the Tamaulipas Formation, deposited in open marine conditions below the storm wave base. Record of the carbon isotope curve presents levels in which negative excursions are followed by abrupt positive trends. The most evident occurred in the Early Aptian across Globigerinelloides blowi and Leupoldina cabri zones, interval through which δ¹³C values drop to 1.47‰ followed by a sharp positive excursion that reaches 2.57‰, in addition to a total organic carbon (TOC) that slightly increased from 0.9 to 1.3%. In the Early Albian, throughout the transition between Ticinella madecassiana and Ticinella primula zones, δ¹³C values decline from 3.73 to 2.44‰, with a subsequent increase of 0.4‰, along with an increment in TOC content that reaches a maximum of 4.40%. In both intervals, the negative CIE is accompanied by a declining pattern in planktic foraminifera abundance, contrasting with an increase trend in radiolarians and colomiellids, characteristic that points out to eutrophic water conditions. Moreover, prevailing U/Th index values >0.75 suggest oxygen deficient conditions.

Eutrophic conditions, high productivity regime and an oxygen depleted setting recorded on the Linderos section, relate to the emplacement of the OAE 1a in the Early Aptian and, OAE 1b in the Early Albian. Biotic and geochemistry features show strong similitudes with deep water Tethyan Realm sections.