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The Jurassic Mafraq Formation: Facies, Stratigraphy and Reservoir Potential in an Outcrop Analog Section (Wadi Sahtan, Oman Mountains, Sultanate of Oman)

Bendias, Daniel *1; Aigner, Thomas 1
(1) Department of Geosciences, Sedimentary Geology, University of Tuebingen, Tuebingen, Germany.

The lower to middle Jurassic Mafraq Formation is well exposed throughout the Oman Mountains. In the type section of Wadi Sahtan, the Mafraq Formation is 160 m thick and unconformably overlies the Triassic Jilh Formation. Detailed field logging, outcrop Gamma-ray spectroscopy as well as thinsection analyses were carried out, which is currently being followed by a regional study on the Mafraq of the entire Oman Mountains.

The section in Wadi Sahtan consists of a complex alternation and mixing of fluvial to estuarine channel sandstones, rooted paleosoils and marine carbonates. Siliciclastics dominate the lower and uppermost part of the section, while the central portion consists mainly of carbonates with oolitic intervals and typical Jurassic fauna like "Lithiotis" shells.

This complexity results in some 30 facies types and 10 lithofacies associations which represent different depositional environments ranging from fluvial to shallow-marine. Facies types and associations were calibrated with core data in order to link surface observations to subsurface data.

In outcrops the Mafraq represents one large-scale transgressive- regressive cycle which can be further subdivided into medium- and smaller-scale cycles. Fluvial and possibly estuarine channel sandstones in the lower part and oolitic grainstones in the upper part form potential reservoir facies that show different lateral reservoir geometries. Shale intervals and thick paleosoils in the lower and uppermost part of the Mafraq have good seal potential.


AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain