--> --> The Manara Barremian-Albian Sequence: A Potential Onshore Analog to Levant Basin Source Rock Systems

AAPG Geoscience Technology Workshop

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The Manara Barremian-Albian Sequence: A Potential Onshore Analog to Levant Basin Source Rock Systems

Abstract

The sedimentary succession of the Barremian-Albian along the Levant margin is marked by a transition from a siliciclastic to a carbonate-dominated marine environment. Previous studies described these margins as a low-relief shelf or platform formed as a consequence of continuous regional subsidence. New insights from a long (360 m) core from northern Israel challenges this model and offers a new model for the slope in the region during the Oceanic Anoxic Event 1 (OAE-1) event in this region. Results from high-resolution elemental, mineralogical, sedimentological and petrophysical analyses revealed the emplacement of abundant mass-transport deposits (MTDs) during the Late Barremian and Aptian. These episodes are accompanied by high total organic matter (TOC) content. This organic matter is comprised of types II-III and III kerogens with up to 32% TOC in the Barremian and type III and IV with up to 2% TOC in the Aptian. Notably, some of this organic matter is reworked down slope and co-occurs with reworked pyrite and iron oxides. The scarcity or absence of bioturbation in both the background sediment and the disturbed sequences hints that the sediment/water interface was deposited in suboxic conditions. However, a decrease in S and Fe is observed at the contact between the shales and some MTDs. This is explained by increased oxic conditions at the sediment-water interface as a result of turbulence and mixing, associated with the descending sediment masses. The observed evidence of recurrent ventilation events of the low-energy basinal environment during the Late Barremian and Aptian, predate the wide-scale establishment of OAE-1 in the northern Arabian margin. This event, also identified in southern France, suggests a period of high productivity in the western Tethyan and allowed for the accumulation of significant amount of organic carbonate off shelf – a potential source rock in the Levant basin today. Moreover, the presence of coarse-grained MTDs within deep-water calcareous sediments indicates a much steeper gradient of the northern Arabian margin than previously considered. These steep slopes would allow the formation of canyons into the basin and opens the possibility of these organic rich units to be related to low stand wedges and lobes in the deep Levant Basin.