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 ) arabica – Rectodictyoconus giganteus, Eopalorbitolina – Palorbitolina and Praeorbitolina – Mesorbitolina . 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.

Abstract Post-Turonian (Late Cretaceous) rudist-bearing limestones of the Nurra region in northwestern Sardinia (northern Tethyan margin) and in the central-southern Apennines and Apulia (central Tethyan domain) have recorded relevant changes in the characteristics of the carbonate platforms following the “middle” Cretaceous crisis events which affected the peri-Tethyan region as well as other regions worldwide. Rudist bivalves became the dominant lithogenetic taxon owing to their proliferation in shallow-water environments and strong dominance of Late Cretaceous carbonate factories. Their inception, evolution, and demise were seemingly controlled by a complex interplay of environmental processes that, acting on a global scale, profoundly modified the Early Cretaceous hydrosphere-atmosphere system and forced Tethyan depositional systems to change their organization, internal architecture, and facies patterns. As a result, wide, open shelves developed where the almost ubiquitous mode of carbonate fixation was that of foramol factories. In this paper, evidence of the remarkable regional variability in the rudist-bearing carbonate platforms of the Mediterranean Tethys is presented. The analysis of the resulting shallow-water facies has demonstrated that, in spite of several stratigraphic similarities and common sedimentological features, some remarkable differences occurred between the northern Tethyan margin and the central Tethyan banks as regards the areal partitioning of the main paleoecologic controlling factors. This resulted in the deposition of rhodalgal successions in Sardinia (northern Tethyan margin) and rudist-rich foramol facies in the Apennine-Apulia (central Tethys) regions, respectively. Such Late Cretaceous carbonate systems can be viewed as geological products which have closely and coherently recorded the globally changing environmental conditions of the oceanic realm. In spite of this, the difference of the facies partitioning in different Tethyan regions according to a latitudinal gradient is interpreted as derived mainly from local variable paleoceanographic and paleoclimatic conditions.