Abstract
The main source rock (SR) of the Aquitaine Basin, the most important oil province in France, corresponds to organic-rich marine limestones of Upper Kimmeridgian age (Lons Formation in the Béarn area and Parnac Formation in the Quercy area). In order to better characterize their depositional environment, in particular the conditions of accumulation and preservation of organic-matter, a sedimentological, micropaleontological and geochemical study of the Crayssac section (Quercy) has been performed. Organic-rich sediments are argillaceous limestones (65 to 99% CaCO3) organized in repetitive beds of up to 1-m thickness. Their total organic matter content reaches up to 15 wt.%, and in this SR kerogen is type of II and immature. Microfauna content, the lack of barrier facies and the control of the wave action base over the depositional environments reflect deposition in an open marine type homoclinal ramp. Strong similarities with Kimmeridgian organic-rich limestones of the Middle East (Hanifa Formation) suggest that the Parnac Formation could act as an analogue of this prolific SR.
Highlights
In the context of increasing unconventional oil and gas exploration, carbonate petroleum source rock (SR) (SR) are of special interest for the oil industry due to their commonly high prolific character (Murris, 1980; Droste, 1990)
The studied rocks correspond to argillaceous limestones and limestones
Our results show that the Parnac Formation is composed of a succession of limestones, argillaceous limestones and organic-matter-rich argillaceous limestones, which can petrographically defined as mudstones and wackestones
Summary
In the context of increasing unconventional oil and gas exploration, carbonate petroleum SR (SR) are of special interest for the oil industry due to their commonly high prolific character (Murris, 1980; Droste, 1990). One of the best-known examples of carbonate SR is the Upper Jurassic Hanifa Formation (Fm) (Upper Oxfordian/Lower Kimmeridgian, Gulf of Arabia), which is one of the most prolific SR in the world (Alsharhan and Magara, 1994; Poppelreiter et al, 2012). This Formation comprises organic-rich argillaceous limestone beds (Gotnia Basin) which pass laterally into calcareous shales (Qatar Arch) (Poppelreiter et al, 2012). The depositional conditions and geochemistry of the Hanifa Fm remain to be investigated in detail, due in particular to the scarcity of wells crossing this SR (e.g., Harris and Katz, 2005; Myers, 2009)
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