Echinoid assemblages as a tool for palaeoenvironmental reconstruction – an example from the Early Miocene of Egypt

Andreas Kroh, James H Nebelsick
2003 Palaeogeography, Palaeoclimatology, Palaeoecology  
A rich Lower Miocene echinoid fauna has been investigated from Gebel Gharra, NW of Suez, Egypt. The ca 140 m long section consists of a siliciclastic lower part and a carbonate-dominated upper part. This corresponds to a general transgression/regression cycle. In all, 27 different echinoid taxa were recognised. The level of taxonomic identification varies depending on test completeness and preservation of specific morphological characters. The palaeoecology of the echinoids was inferred using a
more » ... functional morphological approach and actualistic comparisons. A wide variety of ecological habitats are represented with the presence of regular as well as irregular sea urchins; epibenthic as well as endobenthic forms, as well as a wide range of interpreted burrowing depths for different irregular echinoids. Seven different echinoid assemblages were distinguished, which differ with respect to the species diversity, skeletal taphonomy and sedimentary environment: (1) the Parascutella Assemblage displays spectacular mass accumulations of sand dollars accumulated by proximal storm deposits and winnowing; (2) the Cidaroid^Echinacea Assemblage represents a slightly deeper, moderate-energy environment with a highly structured habitat and corresponding variety of regular and irregular sea urchins; (3) a Spatangoid Assemblage with a diverse fauna of burrowing echinoids; (4) the Transported Assemblage represents an allochthonous collection of echinoids from shallow-water, coarse sandy substrates; (5) the Mixed Assemblage representing a slightly shallower, low-to moderateenergy environment with reduced sedimentation rates; (6) a Clypeaster martini Assemblage characterising a shallow, higher-energy environment; (7) finally, the poorly diverse Phyllacanthus Assemblage from shallow-water carbonates. Diversity variations within the assemblages are correlated primarily to substrate variation, burrowing depths as well as taphonomic factors. The transgression/regression cycle is well reflected by the echinoid assemblages, which show a general deepening of depositional environment followed by shallowing upward tendencies. ß
doi:10.1016/s0031-0182(03)00610-2 fatcat:pg3t4eknt5hkjelv7ddvsgfmje