Cyclic upwelling facies along the Late Cretaceous southern Tethys (Israel): taphonomic and ichnofacies evidence of a high-productivity mosaic

The factors governing deposition of silica, organic carbon, and phosphate-rich sediments in high-productivity marine settings are complex. Many fundamental questions regarding seafloor oxygen levels at the time of deposition remain unclear for both modern and ancient examples. This study explores the macrobenthic paleontologic evidence for bottom-water conditions, especially seafloor oxygen levels, across a Cretaceous high-productivity tract in Israel. The lithologic composition, bed thicknesses, macrofaunal content, ichnofabric and bioclastic fabric of a paleohigh, paleolow, and three paleointermediate sections of the Upper Campanian Mishash Formation of southern Israel were described and sampled to establish a regional paleoecologic-paleoceanographic reconstruction.Both fine- and coarse-scaled (order of magnitude larger) cyclicity was recognized. Fossil-rich beds (often capped by or containing coarse phosphorites) are stratigraphically positioned at the top boundaries of the fine-scale cycles, which have a thickness of between 1–9 m and contain, in addition, organic-rich carbonates, porcelanites and cherts. Going up-cycle, there is an increase in both grain size and intensity of shell packing, consistent with an increase in bottom water energies or a relative shallowing-up cycle. The up-cycle trend of increasing bioturbation and faunal diversity and abundance observed within the Mishash small cycles reflects an increase in bottom oxygen levels or increase in the duration of individual aerated events associated with variations in upwelling intensity, or both.The geographic proximity to the center of the high productivity cell, as well as the nature of the topographic barriers, is represented in two end member basins. The fossiliferous Qazra sub-basin demonstrates the variability of the system moving from laminated barren layers to densely packed ones, whereas the Zin sub-basin (albeit laminated layers) is burrowed and bioturbated, making for the only solid evidence of past macrobenthic life in this setting that lacks shelly intervals.The macrofaunal analysis indicates a higher degree and longer duration of seafloor oxygen and energy events than previously recognized from sedimentology/geochemistry alone. Specifically, the macrofaunal remains suggest that seafloor oxygen levels were dysaerobic to fully aerobic. Also, water-energy levels were higher than previously recognized, showing an intensity of seafloor disturbance similar to that of the above storm wave base.This new, detailed examination of high-productivity deposits thus reveals the highly dynamic and spatially heterogeneous nature of the Mishash upwelling system. Contrary to thinking of such settings as “dead zones”, there is abundant body and trace fossil evidence throughout the record for variable oxygen and variable water energy levels.Both the ecologic and the taphonomic utility of macrobenthos are displayed as paleo-seafloor indicators of upwelling regions. Combining all the biogenic constituents observed along the facies tract with taphonomic and the more typical sedimentologic information provides a better tool for reconstruction of the past environment in high-productivity settings.