Late Cretaceous Conglomerates of the Qahlah Formation, north Oman
Published:January 01, 2014
Iftikhar A. Abbasi, O. Salad Hersi, A. Al-Harthy, 2014. "Late Cretaceous Conglomerates of the Qahlah Formation, north Oman", Tectonic Evolution of the Oman Mountains, H. R. Rollinson, M. P. Searle, I. A. Abbasi, A. I. Al-Lazki, M. H. Al Kindi
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Conglomerate sequences over 700 m thick were deposited subsequent to ophiolite emplacement during Late Cretaceous time in north Oman. The conglomerates were deposited by streams draining the allochthonous ophiolite and Hawasina complex after their obduction onto autochthonous Mesozoic and older Oman shelf sequences and subsequent uplift. The conglomerates belong to the Qahlah Formation of Late Cretaceous age, which is sandwiched between the Semail Ophiolite/Hawasina complex and Maastrichtian–Palaeogene carbonate rocks. The siliciclastics of the Qahlah Formation are the first sediments deposited over the obducted oceanic crust sequence of ophiolite and Hawasina lithologies. In five locations studied in north Oman, the thickness of the formation varies from 140 m to over 700 m and comprises interbedded conglomerate, sandstone and siltstone. The sediments were deposited in isolated segmented depressions each characterized by its source terrain depending on lithologies exposed in the source area. Lithofacies associations, clast sorting and grain roundness suggest deposition in stream-dominated alluvial fans. Clasts in the conglomerates range from subangular to subrounded pebbles to boulders with both grain and matrix (sandstone) support. Cross-bedded fining-upwards sequences in channelized conglomerate and sandstone suggest deposition by high-energy flows in the proximal to distal reaches of alluvial fans. High proportions of chert and ophiolite fragments in the conglomerates suggest rapid erosion of obducted oceanic crust. The presence of Loftusia-bearing carbonate beds and bivalve-bearing conglomerate beds in different sections indicates occasional interruption of alluvial deposition by marine transgressions.
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Tectonic Evolution of the Oman Mountains
The Oman Mountains contain one of the world's best- exposed and best-understood fold–thrust belts and the largest, best-exposed and most intensively studied ophiolite complex on Earth. This volume presents new international research from authors currently active in the field focusing on the geology of the Oman Mountains, the foreland region, the carbonate platforms of Northern and Central Oman and the underlying basement complex. In addition there is a particular focus on geoconservation in the region. The volume is divided into three main sections that discuss the tectonics of the Arabian plate using insights from geophysics, petrology, structural geology, geochronology and palaeontology; the petrology and geochemistry of the Oman Ophiolite and the sedimentary and hydrocarbon systems of Oman, drawing on the geophysics, structure and sedimentology of these systems. The volume is enhanced by numerous colour images provided courtesy of Petroleum Development Oman.