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Post-evaporitic carbonates of the Saudi Arabian Late Jurassic

Hughes G., Naji N., Al-Khaled M., Harland T., Bacchus D.

Volumina Jurassica

2006

Vol. 4, no. 1

91-91

The Hith Formation forms the latest lithostratigraphic unit of the Jurassic Shaqra Group, and was deposited during the Tithonian. The Formation outcrops in central Saudi Arabia, but has been studied in detail in subsurface eastern Saudi Arabia where the upper carbonate member hosts an important hydrocarbon reservoir called the Manifa reservoir. Chronostratigraphic control is absent, and the Tithonian age is based on stratigraphic position between the underlying Kimmeridgian Arab Formation, and the overlying Sulaiy Formation, of Berriasian age. The lower anhydrite-dominated member is un-named, and considered to represent subaqueous deposition representing the transgressive systems tract of the Manifa sequence. A transitional unit, consisting of interbedded anhydrites and carbonates, approximates with the maximum flooding zone, and the overlying carbonates are considered to represent the results of a prograding shallow marine succession related to the highstand systems tract. The carbonates of the Manifa reservoir consist of five parasequences, each of which represents a shoaling-upwards cycle that commences with a stromatolitic, microfaunally-barren unit that is followed by fine-grained grainstones with a monospecific but abundant ostracod biofacies. A succession of coarse pelloidal grainstones with rare Foraminifera, including Redmondoides lugeoni, Trocholina alpina and miliolids, then follows, that passes vertically into coarse ooid grainstones that form the uppermost part of each parasequence. The Hith Formation represents the culmination of a succession of hypersaline and euryhaline cycles that characterise the Late Jurassic of Saudi Arabia, and provides an insight to the palaeoenvironmental conditions that existed across the Arabian Plate at the end of the Jurassic.