Coupling of trace elements in brachiopod shells and biotic signals from the Lower Jurassic South-Iberian Palaeomargin (SE Spain): Implications for the environmental perturbations around the early Toarcian Mass Extinction Event

In the westernmostTethys, the Early Jurassic involved critical environmental changes affecting marine ecosystems. Brachiopods were particularly affected in the South-Iberian Palaeomargin. A late Sinemurian-early Pliensbachian tectonic event led to the collapse of shallow platforms related to the Atlantic Ocean opening. Subsequently, the early Toarcian Extinction Event occurred during a carbon cycle perturbation and the development of oxygen-depleted conditions, mainly affecting benthic communities. In the Subbetic Domain, brachiopod dynamics concur with these major environmental perturbation events. Geochemical imprint of brachiopod shells from this area has been analyzed revealing a clear synchrony between oscillations of trace elements content, global trends in the C and O cycling, and faunal diversity dynamics around critical bioevents, allowing to validate global and regional models related to the platform collapse and the early Toarcian biotic crisis. In the Sinemurian-Pliensbachian turnover and the Toarcian crisis, the redox-sensitive trace metals, REEs, and Fe content in the brachiopod shells show positive excursions. Nevertheless, their trend together with brachiopod diversity patterns, the lower TOC values, and the sedimentary data, support that oxygen depletion must have played a secondary role as environmental stress factor for the benthic fauna. Instead, an increasing temperature gradient is invoked to have played a decisive role, as demonstrated by the main faunal turnover and replacement events correlating with the palaeotemperatures from the peri-Iberian platforms. Shifts on palaeoproductivity, continental influx, and hydrothermal input are also deduced by the increasing concentrations of several trace elements, interpreted as complementary triggering factors of these Early Jurassic bioevents in the westernmost Tethys Ocean.

Automated summary

The Early Jurassic in the westernmost Tethys Ocean saw critical environmental changes affecting marine ecosystems, particularly impacting brachiopods in the South-Iberian Palaeomargin. Geochemical analysis of brachiopod shells revealed clear synchrony between trace element oscillations, global trends in the C and O cycling, and faunal diversity dynamics, validating global and regional models related to platform collapse and the early Toarcian biotic crisis. Oxygen depletion played a secondary role as an environmental stress factor for benthic fauna, with increasing temperature gradient and other triggering factors like shifts in palaeoproductivity and hydrothermal input being more significant in the major environmental perturbation events during the Sinemurian-Pliensbachian turnover and the Toarcian crisis.