--> Abstract: Sedimentological and Biological Signature of the Permian / Triassic Boundary, Southern Rub’ Al-Khali Basin, Saudi Arabia: Role of the Microbial Activity, by Aurelien Virgone, Jeremie Gaillot, Olivier Ridet, and Alain Jourdan; #90077 (2008)

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Sedimentological and Biological Signature of the Permian / Triassic Boundary, Southern Rub’ Al-Khali Basin, Saudi Arabia: Role of the Microbial Activity

Aurelien Virgone1*, Jeremie Gaillot2, Olivier Ridet1, and Alain Jourdan3
1Total, France
2Lille University, France
3SRAK, Saudi Arabia
*[email protected]

The palaeoecological and sedimentological events associated with the Permian/Triassic transition are described for the eastern part of the Rub’ Al-Khali Basin. A sequential architecture within a reliable chronostratigraphic framework was assessed from cores and cutting samples, and general facies distribution. Some environmental breaks are better understood at a small-scale with the help of a high-resolution sequence-stratigraphic framework. The Permian/Triassic transition occurred during a major flooding event on an extensive flat platform, associated with a drastic palaeoecological crisis and favourable development of microbial activity. In low-energy environments, microbialites exhibit different growth strategies from laminated stromatolites to thrombolites at different stratigraphic levels. Some features of the thrombolitic facies suggest large variations in salinity. This schizohaline effect can take place at a regional scale within isolated intra-shelf lows (subtidal setting), where freshwater and marine flooding can quickly alternate. At a larger scale, it seems that the paleohighs were drowned, connecting different palaeogeographical domains that were isolated during the Late Permian. In this context, a drastic change in the global oceanic circulation pattern may have occurred. In a high-energy context, the microbial activity was also intense but susceptible to erosion and generated coated grains and/or oncoïdal flat pebbles associated with oolites. In this case, microbial activity favoured early cementation processes. To conclude, several microbial events occurred during the maximum flooding events of the Late Permian-Early Triassic sequences. This Permian/Triassic extinction is not viewed as a unique event but interpreted as a multiple-steps crisis inducing progressive environmental deterioration.

 

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain