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ABSTRACT

Along the western flank of the Haushi-Huqf Upift in Oman, the upper Palaeozoic succession consists of (from oldest to youngest): (1) glaciogenic Upper Carboniferous-Lower Permian Al Khlata Formation; (2) marine Lower Permian Saiwan Formation (= Lower Gharif Member of subsurface Oman); (3) continental Lower and Middle Permian redefined Gharif Formation (= Middle and Upper Gharif members of subsurface Oman); and (4) lower part of the Middle Permian marine Khuff Formation. The succession overlies lower Palaeozoic-Proterozoic rocks, and the Khuff Formation is truncated by Triassic and younger unconformities. The Al Khlata Formation is about 100 m (328 ft) thick, and consists of a succession of diamictite, sandstone enclosing pebbles to boulders of sandstone, dolomite, black chert and pink granite clasts (ranging in diametre from a few centimetres to a metre). The overlying Saiwan Formation comprises two bioclastic units: lower ‘Bellerophon Limestone’ (10-18 m, 33-59 ft thick) and the upper ‘Metalegoceras Limestone’ (35-40 m, 115-131 ft thick). A basal Pachycyrtella Bed of the Saiwan Formation yielded Pachycyrtella omanensis associated with subordinate specimens of the genus Strophalosia indicating a mid-Sakmarian age. Brachiopod, ammonoid and bivalve assemblages in the main part of the Saiwan indicate a late Sakmarian age. The Saiwan Formation contains (5 metres above its base in the type section) Arabian Plate Maximum Flooding Surface MFS P10 of late Sakmarian age, and based on the latest Permian time scale is recalibrated at about 284 Ma (previously 272 Ma).The redefined Gharif Formation (70-100 m; 230-328 ft) lies unconformably above the Saiwan Formation, and consists of shale and sandstone deposited in floodplain and ephemeral shallow-lake environments. Uppermost Gharif ‘estuarine’ subunit B lies conformably below the first marine Khuff deposits, and contains a rich macroflora that is not diagnostic of a precise age, but is considered ?Roadian-?early Wordian. The incomplete Khuff Formation (30 m, 98 ft) consists of three informal members (1-3 from base up). The transition from Gharif subunit B to lowermost Khuff member 1 represents an environmental change from a distal fluviatile/estuarine system bordering a coastal plain, to a clastic transgressive shoal/barrier environment. Khuff members 2 and 3 reflect a carbonate shelf environment. The lower sequence boundary of the Khuff transgression is interpreted to be at the base of Gharif subunit B. Marine fauna in the Khuff Formation includes cephalopods, brachiopods, conodonts, ostracods and bivalves, which indicate a Middle Permian Wordian age. Conodont fauna from the uppermost levels of Khuff member 3 suggests a late Wordian age. The foraminifera indicate a Middle Permian age (Wordian and Capitanian).

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