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Abstract

The mid-Cretaceous is an informal term that, in the Middle East, includes the Cretaceous stages of Hauterivian through Cenomanian. During this 37 to 45 million years time interval twenty cycles of relative change of coastal onlap were proposed by Haq et al. (1988), and since that time, some of these cycles have been subdivided further. The average duration of these so-called second-order cycles is 1.8 to 2.2 million years, depending upon which time scale is used.

The challenge is to identify accurately depositional cycles in the stratigraphic record of the Middle East platform and to correlate them precisely with a reference section of cycles. The quantitative stratigraphic technique of graphic correlation achieves this goal. Graphic correlation is a numerical correlation technique that is simple to apply and gives precise and reproducible correlations. Graphic correlation is based on an integrated database of fossil tops and bases and other geologic events. The technique creates hypotheses of correlation that make no assumptions about the completeness of each fossil range.

A composite standard database from the Aptian through the Turonian has been constructed using 42 geologic sections in the Tethyan Realm. More than 1000 bioevents of ammonites, inoceramids, planktic foraminifers, selected rudists, benthic foraminifers, nannofossils, and dinoflagellates have been integrated with nearly 100 depositional and geochemical events. Among these fossils are many of the zonal indicators. The stage boundaries are defined by key taxa in generally accepted reference sections in France, Tunisia, and Texas. The scale is calibrated to the Harland time scale.

Platform exposures of the middle Cretaceous in Oman record six or more global cycle boundaries at the Habshan/Lekhwair contact, at the Shuaiba/Nahr Umr contact, several within the Nahr Umr, possibly at the base and top of the Natih “F” Member, at the top of the “E” Member, and at the contact between the “C” and “B” Members. Other cycles may be recognized as more detailed stratigraphic information is collected.

Sediment accumulation rates progressively increased during deposition of the Albian-Cenomariian carbonate platform. Depositional rate of the Nahr Umr was approximately 1.00 cm/1000 years. Depositional rate of the Natih was about 5.00 cm/1000 years. Clearly, many submarine hiatuses developed during deposition of the Nahr Umr.

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