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AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain

A Permian-Triassic Boundary in the Middle East: A Review

Oliver Weidlich1; Aymon Previous HitBaudTop2; Michaela Bernecker3; Leopold Krystyn4; Sylvain Richoz4

(1) Wintershall Holding AG, Kassel, Germany.

(2) Geological Museum, UNIL_BFSH2, Lausanne, Switzerland.

(3) Department of Applied Geosciences, Geosciences, Muscat, Oman.

(4) Institute for Paleontology, Vienna University, Althanstrasse, Austria.

The Middle Permian - Early Triassic Khuff Formation occurs throughout the subsurface in the Middle East and is believed to contain the biggest gas reserves in the region. Along the epeiric Arabian platform shallow-water carbonates and evaporites prevail in the northern and central part and pass southward in argillaceous carbonates and siliciclastics. In eastern direction shallow-water carbonates pass in deep marine deposits of the Neo-Tethys. Outcrops in Saudi Arabia, Iran, UAE and Oman provide important analogue data for subsurface geologic models.

The Permian-Triassic Boundary (PTB) event, about 251 million years ago, was the time of the most severe mass extinction during the Phanerozoic that heavily affected marine and terrestrial ecosystems. Sedimentary rocks of the Khuff Formation and equivalent formations in the Middle East yield abrupt litho- and biofacies changes which are believed to be the result of events associated with Permian-Triassic Boundary (also called end-Permian mass extinction in the literature) and the Early Triassic recovery interval.

During the last decade numerous data of Permian/Triassic rocks in the Middle East have been published which make a compilation of the state-of-the-art knowledge of the PTB necessary. Possible phenomena associated with PTB and the Early Triassic recovery are: (i) Hardground ontop Permian strata, (ii) Clay and high gamma ray readings at the PTB, (iii) negative Uranium excursion, (iv) negative stable carbon isotope shift(s), (v) microbialite horizon(s), (vi) anoxic oceanic conditions and so-called anachronistic sediments, (vii) seafloor cements, (viii) organisms with small body size.

The following key observations have been made:

 

Saudi Arabia outcrops

Subsurface Saudi, Qatar, UAE

N Oman subsurface

S Oman subsurface

Oman Mts Arab PF

Oman Mts Tethys

Iran Zagros

Iran Subsurface

Seafloor cement

not observed

not observed

not observed

not observed

observed

observed

not observed

not observed

Anoxic conditions

not observed

not observed

not observed

not observed

observed

observed

observed

observed

Microbialites

observed

not observed

not observed

not observed

observed

observed

observed

observed

Negative δ13C excurs.

not observed

not observed

not observed

not observed

observed

observed

observed

observed

Negative U excurs.

not observed

not observed

not observed

not observed

not observed

observed

observed

observed

PTB clay & GR peak

not observed

not observed

observed

observed

not observed

observed

not observed

not observed

PTB hardground

not observed

not observed

not observed

not observed

observed

observed

not observed

not observed


Generally, the PTB data collected by numerous researches in the Middle East are in good correspondence with observations from locations around the world. A more detailed comparison of Middle East data suggests that duration and severity changed across the Arabian platform. Depending on the depositional setting and ecosystem, recovery was either rapid or could encompass as much as the Lower and Middle Triassic. Possible scenarios explaining the differential response of carbonate-producing organisms to environmental changes will be discussed in more detail.