Ichnofabric evidence for the lack of bottom anoxia during the lower Toarcian Oceanic Anoxic event in the Fuente de la Vidriera section, Betic Cordillera, Spain

The early Toarcian (Early Jurassic) global marine mass extinction is usually related to the development of organic-rich sediments preserved as black shales and interpreted as a global oceanic anoxic event—the Toarcian Oceanic Anoxic Event (T-OAE). In the Betic Cordillera, southern Spain, the deep-marine Fuente de la Vidriera section contains the T-OAE as recorded at the westernmost part of the European Tethys. Ichnological analysis of the section indicates a relatively abundant and moderately diverse trace-fossil assemblage composed of Alcyonidiopsis isp., Chondrites isp., Nereites isp., Palaeophycus herberti, Planolites isp., Teichichnus isp., Thalassinoides isp., and Trichichnus linearis. A welldeveloped endobenthic multi-tiered community is characterized by an upper tier represented by homogenized sediment—individual burrows difficult to discern, a middle tier with a relatively diverse trace-fossil assemblage of mainly vagile deposit feeders, and a lower tier with activities of semisessile deposit feeders. The ichnoassemblage indicates oxic or slightly dysoxic bottom waters that were relatively favorable for benthic organisms. The absence of anoxia is confirmed by previously published geochemical and isotopie data. The T-OAE did not induce extreme conditions for macrobenthic organisms inhabiting the seafloor in this area of the westernmost Tethys. Local factors probably limited the influence of the anoxic event in bottom waters but may have induced oxygen deficiency in upper water masses, producing unfavorable living conditions for pelagic biota and, consequently, a sudden decrease in ammonite abundance.