Sedimentological and Biostratigraphic study of the Al-Thawrah & Starbeh Formations in the Al-Haffah Sheet

Abstract

The Thawrah and Starbeh formations are exposed in the central part of the Al-Haffah Sheet at a scale of 1:50000, extending from north to south. Some stratigraphic levels of these formations are partially or entirely absent. The formations were investigated from biostratigraphic, petrographic, and sedimentological perspectives, based on field data collected from four geological sections across the study Sheet. These sections, from north to south, are: North Saqiyat Aramo NSA, Jabalaya Sheikh Hassan Jsh, Ain Lilon LL, and Qalaat Al-Mahalba QH. A total of 91 samples were collected for detailed petrographic analysis under the microscope.

Biostratigraphic studies enabled the specific refinement of the ages of the studied rock units and the delineation of boundaries between stratigraphic stages. They also revealed a stratigraphic gap represented by the absence of the Globotruncanita elevata zone, which characterizes the base of the Campanian.

Petrographic analysis showed that the formations consist of repetitive alternations of marly, calcareous-clayey, calcareous-phosphatic, and calcareous-dolomitized rocks. These include (clayey biopelmicrite, biosparite, partially dolomitized biopelmicrite, and phosphatic-glauconitic biopelmicrosparite). Lithostratigraphic correlation clarified the facies variability and allowed for the reconstruction of spatial and temporal distribution patterns.

Sediment logical interpretation indicates that these formations were deposited in environments ranging from upper sub tidal settings at the base of the Thawrah Formation to calm, deeper open-marine conditions towards the top of the Starbeh Formation. These deposits represent regressive–transgressive sedimentary sequences within a basin subject to cyclic fluctuations in sea level.