Environmental conditions during the Toarcian Oceanic Anoxic Event (T-OAE) in the westernmost Tethys: influence of the regional context on a global phenomenon

摘要

A geochemical analysis has been conducted in the Fuente de la Vidriera section of the External Subbetic (Betic Cordillera, southern Spain) in order to interpret the incidence of the Toarcian Oceanic Anoxic Event (T-OAE) in the westernmost end of the Tethys. The obtained values of detrital, redox and palaeoproductivity proxies throughout the succession show minor fluctuations, but only punctual significant changes. Detrital input is nearly constant during the studied interval, except punctually in the lower part of serpentinum Zone, characterized by an increase in both fluvial and eolian detrital transport. Associated to this local higher fluvial and eolian activity, a comparatively higher concentration of organic matter is punctually registered, as revealed by the comparatively highest total organic carbon (TOC) value (0.99 wt.%). The remaining part of the section shows TOC values in the lower range of those registered in the Tethyan Toarcian sections (< 0.4 wt.%). The obtained ratios of redox-sensitive trace metals lead to the interpretation of oxic to dysoxic bottom-waters, with a singular sharp decrease in oxygenation corresponding to a short interval within the serpentinum Zone (sample FV-18) correlated to the T-OAE. The minor incidence of the T-OAE registered in this westernmost end of the Tethys, in which punctual dysoxic conditions are restricted only to a decimetre-scale interval reveals the importance of regional context and local oceanic-atmosphere dynamics on the local record of this phenomenon.