Macrobenthic ecology, paleoecology and taphonomy of high-productivity systems: Upper Cretaceous Mishash Formation (Israel) and the modern Benguela system

Factors governing the deposition of sediments rich in silica, organic carbon, and phosphorite in high-productivity (upwelling) marine settings are complex, and the high degree of organic rain to the seafloor and associated anoxia has resulted in these regions being regarded as “benthic dead zones”. However, contrary to this stereotype, the Upper Campanian Mishash Formation of Israel, which is one of the most intensive and geographically extensive high-productivity regions in the geologic record, contains abundant and diverse benthic macrofauna. I examined both this ancient record and macrobenthos death assemblages from the modern Benguela system (SW Africa) to explore gradients in community structure and taphonomic conditions across upwelling seafloors, and to use these features to infer seafloor conditions, especially bottom oxygen levels.; Five sections of the Mishash Formation from southern Israel were described. The lower Phosphatic-Carbonate unit of the Formation contains a series of 1–9 meters thick cycles composed of micritic organic-rich carbonates, cherts and porcelanites and diagenetically obliterated carbonate layers; each cycle is capped by a phosphate-bearing shell bed. An upward trend of overall coarsening grain size, increasing fossil abundance and shell packing in each cycle is interpreted as reflecting an increase in bottom oxygen and water energy levels, from quasi-aerobic (below storm wave base) to fully aerobic (above fair-weather wave base). Faunal analysis indicate decreasing species richness, body size and abundance of deposit-feeding bivalves along an inferred increasing oxygen gradient, associated to closer proximity to upwelling center.; For Benguelan death assemblages, an increase in species richness, epifaunal-infaunal ratio, disarticulation of shells, and decrease deposit-feeding bivalve abundance and in body size of chemosymbiotic bivalves is observed with increasing distance from the upwelling center, from opal and organic-rich oozes towards phosphate-rich sands. This corresponds to an onshore-offshore gradient of increasing oxygen reported for northern Benguela waters by others.; This study demonstrates the local abundance and diversity of macrobenthos in upwelling systems, as well as their sensitivity to seafloor conditions. Modern Benguela and Cretaceous Mishash systems are both characterized by highly dynamic and patchy seafloors, including the co-occurrence of anaerobic to fully aerobic conditions even within the upwelling center.