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Middle and Upper Jurassic Foraminifera and Their Applications in Biostratigraphy and Lithostratigraphy of Saudi Arabia

Al-Dhubaib, Abdullah J.*1
(1) ETSD, Saudi Aramco, Dhahran, Saudi Arabia.

Semi-quantitative micropaleontological analysis of thin sections has provided considerable insight into biocomponent composition, as well as providing definition of various biozones within the interval of the Middle Dhruma to uppermost Hanifa formations in both outcrop and subsurface localities. Subsequently a local biozonation scheme was created that provides the basis for both local correlations among studied sections in outcrop, and regional correlations between the outcrop area and subsurface well sections in the eastern parts of Saudi Arabia. These biozones also provide a significant contribution towards understanding the biostratigraphy and lithostratigraphy of the studied formations in the whole region.

In biostratigraphic terms, the Bathonian-Kimmeridgian foraminifera in the Tethyan region, show significant generic and specific faunal change, at the Callovian-Oxfordian boundary, with subordinate changes at Bathonian-Callovian and Oxfordian-Kimmeridgian boundaries. In lithostratigraphic terms, the variety of the foraminiferal fauna in different units has also provided important tools to the recognition of studied formations in subsufrace localities. Some species are considered markers for formational boundaries, such as the last appearance of Paleopfenderina trochoidea, one of the criteria to characterize the Callovian/Oxfordian boundary in the Tethyan region. In Saudi Arabia, this is also a specific marker for the Tuwaiq/Hanifa formational contact. Some species are considered markers for the studied members and units. These include all high trochoid coiled species of Andersenolina, including Andersenolina elongata, A. cherchiae and A. altispira, disappear in the Upper Hanifa Formation. The absence of these species and the presence of Paleopfenderina salernitana along with the constant occurrence of Alveosepta jaccardi, could be a regional marker for the Upper Hanifa Formation (the Ulayyah Member) and the Late Oxfordian age as well.

In conclusion, the interpreted biozones have increased our understanding of regional lateral heterogeneities, and are of value to regional correlation studies between the subsurface and outcrop areas. They also have improved our understanding of the lithostratigraphy and biostratigraphy of the studied carbonates.

