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ABSTRACT

The biostratigraphic zonation of Barremian – Aptian shallow-water carbonate systems has a low resolution due to the slow evolutionary rate of most species living in these environments. A notable exception to this are the orbitolinid foraminifers, which show relatively rapid evolutionary trends mainly in the embryonic structures, and can thus be used for high-resolution dating of these strata. Here a revised orbitolinid biostratigraphic zonation scheme is presented for the eastern Arabian Plate.

This zonation is based on published work and new research on orbitolinid-rich successions in shallow-water carbonate platform environments and intra-shelf basin margins. A subdivision into six zones and three subzones is proposed for the Barremian and Aptian, using the evolutionary lineages Montseciella (= ex-Dictyoconus) arabicaRectodictyoconus giganteus, Eopalorbitolina – Palorbitolina and PraeorbitolinaMesorbitolina. In this paper we also introduce a new species, Palorbitolina ultima, which represents the advanced development of Palorbitolina lenticularis.

This revised zonation was derived from a unique database covering the eastern Arabian and northeastern African plates including offshore Abu Dhabi, Ethiopia, southwest Iran, Oman, Somalia and Yemen. As a result, a revision of the age assignment of the Dariyan Formation in southwest Iran is proposed. In addition, examples of biostratigraphic zonations, which constrain regional (sequence) stratigraphic correlations are: (1) the regional appearance of the short range, Late Barremian species Montseciella arabica, that allows to correlate a third-order sequence in a low-angle, carbonate ramp system over a distance of 4,000 km; (2) the assemblage of Palorbitolina and Praeorbitolina species that characterise the late Early Aptian maximum flooding event; and (3) the subsequent appearance of different Mesorbitolina species that characterise the regressive Upper Aptian deposits.

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