FORAMINIFERA OF THE LATEST CRETACEOUS OIL SHALE SEQUENCE, NEGEV ISRAEL: A CASE STUDY OF THE SOUTHERN TETHYAN UPWELLING SYSTEM

The late Cretaceous succession in Israel is part of an extensive high productivity upwelling regime that persisted over ~20 m.y. in the southern margins of the Tethys. Such systems, characterized by high nutrient levels, are often associated with oxygen deficient bottom water and by accumulation of phosphates, porcelanites, cherts and “oil shales” (=organic rich carbonates). The deposition of a ~40 m thick oil shale sequence in the Negev, Israel, indicates a major change in the evolution of the high-productivity regime and reorganization of the marine ecosystem.

Here we propose to reconstruct the paleobiological developments of the Late Cretaceous upwelling system, Negev region, by using high-resolution records of planktic and benthic foraminifera. We focus on the time interval from top Phosphate Member (PM) throughout the Oil Shale (OSM) and up to the base of the Marl (MM) members.

Our new planktic foraminiferal biostratigraphy indicates that the oil shale sequence spans only ~1m.y. from ~71-70 Ma, and reveals unusually high sedimentation rate of ~4 cm/1ky. This very high accumulation rate will allow us to identify and characterize in great detail the last phase in the dynamic of this long lasted upwelling system.

Both, planktic and benthic foraminiferal assemblages record major changes at the transitions between the top PM and the overlying OSM and between the OSM and the MM. The PM is characterized by the dominance of specializing buliminids, known to be associated with dysoxic to nearly anoxic conditions at the sea floor. Planktic foraminifera are rarely present in this interval, but abruptly appear in great quantities and high diversity at the base of the OSM. At the same time, the buliminds are replaced by rotaliids, suggesting an increase in bottom water aeration. The intermediate water dwellers, keeled globotruncanids, start to appear shortly above the base of the OSM, supporting our notion that this transition involves a probable deepening and increasing ventilation of the intermediate water. The OSM to MM transition marks another important paleoenvironmental change as indicated by changes in assemblage composition and further increase in planktic foraminiferal abundance and diversity. These changes represent a further increase in bottom water aeration, water column deepening and the probable ending of the enhanced upwelling activity in this region.