Late Cretaceous upwelling system along the Southern Tethys Margin (Israel): Interrelationship between productivity, bottom water environments, and organic matter preservation

Abstract

Organic‐rich Upper Cretaceous sequences in Israel were deposited in an extensive, highly productive upwelling‐linked system which prevailed along the southern Tethys margin, and lasted for ∼19 m.y. (Santonian to late Maastrichtian). An understanding of the spatial and temporal characteristics of this system was gained through detailed paleontological and geochemical analyses of subsurface sequences in two basins in Israel, representing an outer (Shefela) and an inner (Zin) facies belt. The nature of the upwelling system, and its effect on the sedimentary record, is related to two basic environmental parameters, namely paleoproductivity intensity and oxygen levels at the bottom. The assessment of these parameters and their interrelationship has been performed through the development of paleontological (foraminiferal) criteria, which are independent of the organic matter content. Following the establishment of these criteria, it is concluded that the productivity reached its maximum intensity during the late Campanian, which was also the time of most notable differentiation between the center of the upwelling system in the inner belt and the less intense conditions in the outer basin. This distribution is expressed in varied lithology (organic‐rich carbonates, phosphorites, and siliceous rocks) at the core of upwelling and a uniform lithology (organic‐rich carbonates) at the margin of this system. The uniform lithology of the Maastrichtian in both basins, composed of organic‐rich carbonates, is ascribed to a gradual weakening of productivity. The bottom conditions in the inner belt during the late Campanian (the time of maximum surface productivity) were near anoxic, changing to more aerated (dysaerobic) conditions during the early Maastrichtian. In the outer belt a more aerated bottom (dysaerobic) prevailed throughout the late Campanian to late Maastrichtian. The elevated organic matter content in both basins reflects the overall environment of high productivity; its actual variations, however, seem to be unrelated to changes in surface productivity and bottom oxygen levels.

Analysis of Selected Oil Shale Samples from El-Lajjun, Central Jordan

“…During the formation of oil shale, Jordan was located in an epicontinental sea [11]. Bioproductivity was enhanced by deep cold water rich in nutritants brought to the surface by upwelling currents [12] [13]. The deposition was influenced by syn-sedimentary tectonics [14] resulted in the formation of internal shelf basins structured by shallow swells [15].…”

“…This is related to the formational factors that control their formation during upper cretaceous [8] [24]. Rocks are rich in productivity derived material that is related to deep cold upwelling water currents at the time of OS formation [12].…”

Calcareous nannofossils as paleoproductivity indicators in Upper Cretaceous organic-rich sequences in Israel

“…1) is based on planktic foraminifera (Almogi-Labin et al, 1993) and calcareous nannofossils (Eshet and Moshkovitz, 1995). The nannofossil zonation used in the present paper is based on the NC zonation scheme of Roth (1978) because it suits the Israeli nannofossil assemblages better than the CC zonation of Sissingh (1977) as shown by Eshet and Moshkovitz (1995).…”

“…Paleogeographic reconstructions suggest that the shoreline during this period was about 100 km to the southeast during the Campanian, and even further to the east in the Maastrichtian (Bender, 1974;Germann et al, 1987;Glenn, 1990). The accumulation of organic-rich carbonates, cherts and phosphorites, as well as the microfossil assemblage composition, indicates highly productive paleoenvironments, associated with a large-scale upwelling system that existed along the southern margins of the Tethys (Reiss, 1988;Almogi-Labin et al, 1993;Eshet et al, 1994).…”

“…Reiss (1988) and Shemesh and Kolodny (1988) suggested that these sequences were accumulated in an upwelling regime. A recent series of geochemical and paleontological studies that focused on the Coniacian-Maastrichtian organic-rich sequences in Israel have enabled detailed reconstruction of the productivity history in these sequences (Bein et al, 1990;Almogi-Labin et al, 1993;Eshet et al, 1994).…”