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Development of Incisions on a Periodically Emergent Carbonate Platform (Natih Formation, Late Cretaceous, Oman)

¹ JVR Centre for Carbonate Studies, Sultan Qaboos University, P.O. Box 36 PC 123 Al Khod, Oman; EGID Institute, Bordeaux3 University, France; carinegrelaud{at}yahoo.fr
² EGID Institute, Bordeaux3 University, France
³ JVR Centre for Carbonate Studies, Sultan Qaboos University, P.O. Box 36 PC 123 Al Khod, Oman; present address: Oman Geo-Consultants, Shatti Al Qurm, Oman
⁴ Department of Geology and Petroleum Geology, University of Aberdeen, Scotland, U.K.

Subaerial exposure of carbonate platforms is generally recorded by karstification and pedogenesis, whereas erosion features such as incisions along emersion surfaces have seldom been observed and studied. However, the recognition of incisions and the characterization of their fill may facilitate definition and hierarchy of sequence boundaries, especially along exposure surfaces that do not otherwise present clear petrographic evidence for emersion. In the Natih Formation (Late Albian–Early Turonian, Oman), two successive incision surfaces are present in the upper part of the first third-order depositional sequence. Seismic interpretation of regional subsurface data has allowed the quantification of progradational geometries within the Natih sequence I carbonate platform and the correlation of incision surfaces with forced regressive prograding wedges on the margins of the intrashelf basin. Detailed geological sections and correlations have been made from three outcrop localities, allowing a precise description of geometries and facies of incision fills. Morphology, orientation, and extent of these incisions have been assessed from detailed seismic interpretation coupled with forward seismic modeling. The integration of outcrop and seismic data sets at the regional and local scales allows the interpretation and discussion of the origin and factors controlling the development of these incisions and a refinement of the stratigraphic model. These two incisions record rapid sea-level variations (500 ky) with a magnitude of approximately 20 and 30 m that occurred during the early Cenomanian. This is probably not a unique case, since for the same time interval, incisions have been observed in siliciclastic systems in western Canada and India and in carbonate systems on the Arabian plate.