Taphonomy, ichnology, and palaeoecology to distinguish event beds in varied shallow-water settings (Betic Cordillera, SE Spain)

Abstract

The recognition of event beds is of paramount importance to reconstruct palaeoenvironments and to determine palaeoecological parameters. Tortonian and Tyrrhenian deposits have been studied in the Cabo de la Huerta section (Alicante, Southeastern Spain), where both open-platform and coastal deposits crop out. In the absence of sedimentary structures, we carried out ichnological, taphonomic, and palaeoecological analyses to determine the main processes involved in the material’s sedimentation. The Tortonian beds are made up of interbedded fine-grained and coarse-grained calcarenites. Event beds are mainly signalled by the presence of Ophiomorpha nodosa in coarse-grained calcarenites, typically produced by opportunistic crustaceans just after sedimentation. Background sedimentation is represented by fine-grained calcarenites without well-preserved burrows due to the soupy consistency of the substrate. The alternance of burrow-rich and burrow-poor beds reveals a decreasing-upward frequency of storm events pointing out a deepening-upward trend. The Tyrrhenian material records a regression from a sandy beach environment to a continental backshore. A thick skeletal concentration of resedimented shells from different habitats and with different residence times on the substrate was found between the beach and backshore deposits. Its features make it recognizable as a major storm deposit where a census assemblage is mixed together with a time-averaged one. Integrated palaeontological analysis is shown to be an excellent tool in diverse environmental settings in order to differentiate event beds, in particular where clear sedimentological criteria are not available.