From Phytoplankton Turnovers to Oil Shale Plays - Source Rock Potential of a High Productivity Sequence

Abstract

The complexity of organic matter (OM) formation, its source to sink propagation and preservational process through geological time, has been the focus of extensive and interdisciplinary studies. In this study we address this issue by examining the Upper Cretaceous organic-rich succession in the Levant. A multi-proxy approach, integrating elemental, isotopic, Rock-Eval and faunal analysis, is amalgamated into a holistic model through which the properties of presently prospected OM could be elucidated. A turnover in primary producer assemblages, and reorganization of bottom-water bacterial consortium, enforced sedimentological and faunal changes. The siliceous and phosphatic lithologies of the Campanian gave way to the Maastrichtian uniform organic-rich deposits; a six-fold increase in sedimentation rates has facilitated both the increase in the amount of OM and its excellent preservation; and, the ratio of the elemental compounds in the OM has shifted in favor of carbon. While the entire Upper Cretaceous organic-rich sequence is considered as an excellent source rock, these oceanographic modifications resulted in a marked interval, with the highest OM content and generation potential levels, which stands out as the potentially preferred target layer for HC production. Consequently, we propose that biological shifts promote a change both in the amount and type of OM.