The Euphrates Graben is one of the most important petroliferous basins in Syria. One known source rock is the marine Upper Cretaceous Shiranish Formation, but no detailed information exists about its source rock potential. The aim of the investigation is to: (1) identify the variations in source rock characteristics due to changes in paleoceanography, and (2) to correlate these variations with their effect on the timing of petroleum generation. Two organic facies with different characteristics of petroleum generation were identified: Type II facies with hydrogen index (HI) values of > 350 mg HC/g TOC, and a Type II/III facies with HI values of < 350 mg HC/g TOC. Both organic facies are considered likely sources of paraffinic-naphthenic-aromatic petroleum with variable<br>amounts of gas based on the pyrolysis gas chromatography scheme of Horsfield (1989). Bulk kinetic experiments have shown that predicted petroleum formation temperatures are closely similar within each of the facies, but different between the facies, with onset (TR 10%) temperatures of 136°C for the Type II facies and 144°C for the Type II/III facies. This corresponds to approximately 600 m difference in burial depth or delayed onset of petroleum generation by 5.75 million years for a 3.3 K/my heating rate. Facies analysis of well logs indicated that Type II/III facies of the lower Shiranish Fm. was influenced by terrestrial input of different intensity. During the Upper Shiranish Formation. a progressive deepening of the depositional environment was probably coupled to an enhanced marine paleoproductivity leading to Type II facies.


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