ANCIENT-MODERN COMPARISON OF MACROBENTHIC COMMUNITY STRUCTURE ALONG OXYGENATION GRADIENTS IN CRETACEOUS AND MODERN UPWELLING SYSTEMS

This study is a first attempt to investigate the (paleo)ecological and taphonomic significance of macrobenthic invertebrate assemblages from sedimentary records rich in biogenic silica, organic matter and phosphate, using both a modern (SW Africa) and ancient (Upper Cretaceous, Israel) upwelling example to identify robust patterns.

Benthic communities are present but highly variable across these high-productivity tracts. These communities are characterized by distinctive community structures and taphonomic signatures. Both ancient Mishash and modern Benguela systems document a decrease in body size of chemosymbiotic bivalves (lucinids) and % of chemosymbionts and deposit-feeders, and an overall increase in species richness, epifaunal-infaunal ratio, and disarticulation of shells, corresponding with increasing distance from the upwelling center, parallel to inferred gradients of increasing oxygen levels.

The similarity between the community structures of macrobenthos in the ancient and modern upwelling examples of this study is quite remarkable, especially given that oceanic configurations and global climate were so different between the Upper Cretaceous and the present. The similarities are also impressive because they have few genera in common.

The ecological picture of upwelling seafloors provided by this integration of Cretaceous Mishash and modern Benguela evidence constitutes an improved model for the temporal and spatial complexity of conditions within upwelling systems in general, especially those of the late Mesozoic to Recent, and a valuable basis for inferring and refining their paleoenvironmental conditions.