Expression of an oceanic anoxic event in a neritic setting: lower Aptian coral rubble deposits from the western Maestrat Basin (Iberian Chain, Spain)

A singular lower Aptian lithofacies from the western Maestrat Basin (Iberian Chain) highlights the reaction of carbonate platform paleocommunities to natural disturbances of regional to global significance. It is composed mainly of sand- to cobble-sized coral rubble rigidly bound by Lithocodium aggregatum and is coeval with the early Aptian Oceanic Anoxic Event (OAE1a) and the intensified greenhouse conditions connected with this event. Severe storms induced by high atmospheric concentrations of CO₂ had a recurrent catastrophic impact on coral populations, giving rise to sub-basin—wide coral rubble levels. Physical responses to elevated atmospheric CO₂ levels, such as increased nutrient fluxes, together with low sedimentation rates, and the presence of a hard substratum, favored the mass occurrence of Lithocodium crusts, large flattened Palorbitolina lenticularis, and bioeroders such as lithophagid bivalves and endolithic sponges. These encrusted coral rubble deposits are here interpreted as records of chemical and physical disturbances linked to the OAE1a. Due to significant extension and normal faulting recorded in the lower Aptian of the western Maestrat Basin, however, earthquake-induced natural stresses might also have played a part in the generation and reworking of these coral rubble deposits.