The glaciogenic permo-carboniferous Al Khlata Formation, Oman : sedimentary facies and origin of its glaciation, with comparisons to the Hoya Formation, Canning Basin, Australia
Al Khlata Formation is an oil-bearing reservoir in Oman. Its origin during the Late Palaeozoic Gondwanan glaciation in the southern part of the Arabian Peninsula is demonstrated by its glaciogenic deposits. Outcrops of the AI Khlata Formation occur in a belt parallel to the Huqf fold axis, the best outcrops being found in the two wadis Al Khlata North and South. In the southern wadi, glacial deposits rest directly on dolomites of the Pre-Cambrian Khufai Formation, which have NE-SW trending glacial striations. One of the key aspects of this study was a detailed investigation of the outcrops which allowed the identification of the different facies units. Measured wadi-wall sections and lateral facies mapping allowed a better understanding of the complex nature of the depositional processes. This has further been integrated with the result of shallow boreholes cores to refine the correlation between the outcrops of Wadis AI Khlata North and South, and also the AI Khlata sequence in five oil wells between the Rahab and AI Huwaisah fields. Furthermore, a brief visit was made to Iceland to see a small active ice sheet and its marginal glacio-fluvial sediments, and also to W. Australia to see cores of the Permo-Carboniferous Hoya Formation from the Canning Basin for comparison with the Al Khlata Formation sequences. The AI Khlata Formation comprises four fades associations, which are further subdivided into facies. These are: (1) Diamictite Facies Association, which has been divided into a Massive Diarnictite Facies and a Stratified Diarnictite Facies, (2) Conglomerate Facies Association including Cross-stratified Sandy Conglomerate, Gravel Lag and Massive Gravel, (3) Sandstone Facies Association divided into Crossbedded Sandstone and Pebbly Sandstone and Rippled Sandstone, and (4) Fine-grained Facies Association which, in turn, has been divided into a Deformed SiltiMudstone, Laminated SiltstonelMudstone, Black ShalelMudstone, and Graded Rhythmite. These facies have been recognised in both outcrop and cores. Earlier workers proposed that the direction of ice flow was from the SW to NE. This is not accepted in this paper, where evidence is presented to support an ice-flow direction from NE to SW. Later fluvial flow towards the NE possibly resulted from the collapse of the continental margin towards a new Proto-Arabian Sea. The thesis presents a new hypothesis for the origin of the AI Khlata Formation. It is proposed that the Early Permian glaciation in Oman resulted from crustal uplift just prior to the calving of a microcontinent along the NE Arabia margin of Gondwana and the creation of Neo-Tethys. It is suggested that the triple-junction area, where Neo-Tethys and the Proto-Arabian Sea were later to meet, was a site of sufficient thermal uplift to become a centre of mountain glaciation.