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Gharif Formation
Geologic formation in Oman From Wikipedia, the free encyclopedia
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The Gharif Formation is a geologic formation in Oman. It preserves fossils dating back to the Permian period. The Gharif clastic reservoirs are an important hydrocarbon production unit, and the formation is a major producing oil and gas reservoir in Oman.[1][2][3]
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Stratigraphy
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The subsurface Gharif Formation has been informally divided into 3 members (Lower, Middle and Upper) by geologists from Petroleum Development Oman. Though these members may be difficult to distinguish in certain localities due to rapid lateral facies changes, differential incision, salt movement or erosion, multiple studies have shown that these 3 members can be correlated on a regional scale.[1][3][4]
Lower Gharif Member
The lower member is about 65 m (214.5 ft) thick in north and central Oman. It has been split into 3 submembers:[1][3][4]
- Lower Gharif submember-1 unconformably overlies the Al Khlata Formation and is made up mostly of cross-bedded quartz sandstone. Locally, crinoid and brachiopod remains can be found. Though its thickness varies across central Oman, it is generally about 25 meter thick and does not exceed 30 meters.[1]
- Lower Gharif submember-2 (or the Maximum Flooding Shale) contains bioturbated lime-mudstones and is under 10 meters thick.[1][3]
- Lower Gharif submember-3 (also known as the Haushi Limestone) is about 35 meters thick and occurs in much of central and north Oman. It is a cross-bedded oolitic packstone and grainstone, and stromatolitic mudstone.[1]
Middle Gharif Member
The middle member is about 85 m (280.5 ft) thick in north and Central Oman. It contains the following 3 informal units (from the base up):[1][3]
- Middle Gharif unit 1 is less than 10 meters thick and represents shoreface, tidal flat, lagoonal and mixed paralic environments.[1]
- Middle Gharif unit 2 is under 40 meters thick. Deposited after the demise of the 'Haushi Sea' in an episodically dry environment, it exhibits interlocking marine and non-marine conditions, representing major progradation and coastal advance.[1]
- Middle Gharif unit 3 (occasionally inappropriately referred to as the Playa Shale) is made up of a red-brown Shale and is over 40 meters thick. Though suggested to represent an extensive intracratonic ephemeral lake system, it has been reinterpreted to be laid down during a long dry period which caused significant pedified palaeosol horizon development.[1][3]
Upper Gharif Member
The upper member is about 90 m (295 ft) thick in north and central Oman. Informally, it has been split into the ‘Upper Gharif Sandstone’ and ‘Upper Gharif Red Beds’.[1][3]
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Fossil content
Amphibians
Fish
Acanthodians
Bony fish
Cartilaginous fish
Invertebrates
Plants
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References
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