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Geological Society, London, Special Publications; 1990; v. 49; p. 109-125;
DOI: 10.1144/GSL.SP.1992.049.01.08
© 1990 Geological Society of London

Evolution of the Oman Tethyan Continental Margin

The Lower Kahmah Group of Oman: the carbonate fill of a marginal shelf basin

E. A. Haan1, S. G. Corbin2, M. W. Hughes Clarke1 & J. E. Mabillard3

1 Petroleum Development Oman LLC, XXG/3, P.O. Box 81, Muscat, Sultanate of Oman
2 I LASMO Cy. Ltd., Bastion House, 140 London Wall, London EC2Y 5DN, UK
3 Koninklijke Shell Exploratie en Productie Laboratorium, EPX/36, Volmerlaan 6, 2288 GD Rijswijk, The Netherlands

Following the rifting and spreading related to the opening of the Tethys Ocean during the Triassic and Early Jurassic, relaxation and subsidence affected its passive margins. In Iran and Oman, such subsidence of the continental margins gave rise to deeper marine, marginal shelf basins, that initially were filled with pelagic sediments, but were progressively infilled by prograding shallow shelf-derived sediments. In Oman the fill sequence is well displayed for study in surface outcrops in the Oman Mountains as well as in subsurface geological and geophysical data. This paper provides an integrated picture of the geometry and facies distribution of the sediments, which filled this marginal shelf basin. The pelagic facies comprises the Rayda Formation and the basin, therefore, is named the Rayda Basin. The prograding, shelf-derived, fill facies comprises the Salil Formation. Surface-type sections of these two formations are described from outcrops in the Oman Mountains. The last stage of the basin fill is represented by a diversified shallow marine facies, referred to as the Habshan Formation, which is defined in Abu Dhabi. This unit prograded over the entire sag basin and almost levelled the pre-existing basin topography in such a way that overlying deposits hardly reflect the original Rayda Basin outline. The Habshan shoal facies is therefore in part coeval with the Rayda and Salil and exhibits a complex interdigitation with those two formations towards the basin margin. The seismostratigraphic expression of the Habshan, Salil and Rayda Formations provides a valuable tool for defining basin outline and mode of infill. A number of seismic lines are presented in relation to well log correlation panels to highlight the complexity of the sedimentary processes affecting these units. The fill of the basin was completed by the Valanginian and the ovelying Lekhwair Formation of Hauterivian to Barremian age represents a renewed marine transgression.