Late Aptian to Turonian stratigraphy of the eastern Arabian Plate – depositional sequences and lithostratigraphic nomenclature

This stratigraphic article summarizes a number of observations on the mid-Cretaceous stratigraphy of Arabia made during the 2nd Arabian Plate Geology Workshop held in Abu Dhabi in January 2010. These observations pertain to the lithostratigraphic nomenclature applied on the eastern Arabian Plate and its relationship to mid-Cretaceous (Late Aptian–Turonian) depositional systems and sequences recognized plate-wide. It appears that several of the commonly applied lithostratigraphic terms are diachronous as a result of (i) plate-wide migration of carbonate and siliciclastic facies belts; (ii) the occurrence of intra-shelf basins at different times and locations; (iii) differential preservation beneath erosional unconformities; and (iv) simple differences in usage across political boundaries. A plate-wide sequence stratigraphic scheme is thus a powerful tool for regional correlation and mapping, and for reconciling lithostratigraphic differences.

The studied interval can be subdivided into two primary sedimentary systems that differ in lithology, depositional geometries and dominant faunal assemblages. First, latest Aptian- and Albian-aged systems, which are characterized by volumetrically significant Arabian Shield-derived siliciclastics (both sandstones and claystones) that alternate with carbonate beds. The carbonate beds thicken up-section and have generally very low-angle, muddy ramp depositional geometries. Organic-rich basinal facies are found only in the Kazhdumi Basin in SW Iran at this time. The faunal composition of the carbonates is dominated by benthic foraminifera (notably orbitolinids). Within this succession three third-order depositional sequences are distinguished (MFS K90, K100 and K110). Secondly, Cenomanian–early Turonian-aged sedimentary systems are characterized by a marked reduction in siliciclastic influx, the development of carbonate platform to intra-shelf basin topography and deposition of basinal source rocks. Rudists are the dominant component of grainy, high-energy platform margin/barrier facies, and are also present in the platform top sediments. Within this succession three Cenomanian sequences can be correlated clearly at the scale of the plate (MFS K120, K130 and K140), whereas the number of sequences in the Turonian interval is less well known owing to significant local erosion and/or non-deposition during a period of tectonic instability.

Applying this robust sequence stratigraphic framework in combination with a synthesis of biostratigraphic age calibration demonstrates the diachronous character of the Mauddud, Safaniya, Ahmadi and Mishrif formations and equivalents from the southern to the northern part of the Arabian Plate.