Chemostratigraphy of Albian deposits in Northern Tunisia: Inferred Early and Late Albian Oceanic anoxic events (OAE1b and OAE1d) occurrence in the southern Tethys

Abstract

An integrated study of multiple geochemical proxies (δ13Corg, TOC, ChemGr, trace elements) and a biostratigraphic calibration of the Albian oceanic anoxic events OAE1b and OAE1d Performed respectively in the Ain Asker and El Djehaf sections. A comparison of the newly collected isotopic data with the records from Europe (France and Italy), China and Mexico provided a reliable and precise identification of both prominent black shale levels (Paquier and Breistroffer) that characterize the OAE 1b and OAE1d, respectively. The studied record shows an increase in the marine organic carbon accumulation rate, in particular in the levels recording the anoxic events. The F2 unit of the Ain Asker section (OAE1b) shows TOC values of 2.3%, with evidence of degraded marine organic matter. Completely anoxic conditions were never established during the sediment deposition, although evidence of oxygen depletion at the bottom of the basin is clearly documented by the distribution pattern of redox-sensitive trace metals. The results suggest an increase in organic carbon burial rates during the OAE 1b due to the effect of enhanced surface productivity, The F3 unit of the El Djehaf section develop a higher rate of TOC rate (around 9%) and a markable positive organic carbon excursion explaining the planktic biomass enrichment and anoxic redox conditions.