Facies Analysis, Regional Stratigraphy, and Diagenetic History of the Late Jurassic Arab Formation in the UAE

Abstract

Despite numerous studies that have been conducted on the stratigraphy of the Arab Formation, the regional chronostratigraphic correlation between the fields and countries is still poorly defined. Several discrepancies are also observed related to the paleogeographic evolution of the Arab Formation. Some paleogeographic reconstruction models proposed the oolitic grainstone shoal developed synchronously under rapid progradation, while others suggested asynchronous deposition. This study reconstructed the regional stratigraphic architecture of the Arab formation by utilizing subsurface data from several onshore and offshore oilfields in Abu Dhabi, including a recently acquired seismic survey, well log, and core analysis. The precipitation of anhydrite, dolomitization, and limestone host rocks was defined within the 2nd, 3rd, and 4th ordersrelative sea-level cycles. Good connectivity between the inner ramp and open sea during 2nd-order transgressive cycles accounts for limestone-dominated lithology with limited anhydrite formation. In contrast, periodic restriction of the inner platform during 2nd-order early regressive cycles caused the precipitation of scattered to pervasive anhydrite cement in the dolostones. In the late regressive cycle, the most laterally extensive dolomitization was observed with nodular and chickenwire anhydrite, indicating the formation by both evaporative sabkha pumping and the seepage reflux of lagoon brines.
Sequence stratigraphy interpretation of the Arab Formation indicated four second-order sequences from mud-dominated basinal limestones, grain-supported oolitic and skeletal shoals, and lagoonal to supratidal anhydrite-rich deposits. General east-southeast progradation trends were observed in the seismic with the toplap of the Hith Formation and possibly this formation is truncated in the east. An angular unconformity was observed in the easternmost part of Abu Dhabi, which could be associated with the Upper Jurassic uplift and erosion of the east Arabian Plate. LA-ICP-MS U-Pb dating result of the ooids in the lower Arab C interval shows the age range of 144.9 ± 2.3 Ma, which is consistent with the age results from Sr isotope analysis of least or un-altered skeletons in the sample located at 26.5 m deeper, 147.3 ± 3.6 Ma. This indicates that the lower interval of the Arab Formation might have been deposited in the Tithonian, which is slightly younger than what has been previously accepted.

Date of Award	26 May 2025
Original language	American English
Supervisor	Mohammad Alsuwaidi (Supervisor)