Source rock potential and organic facies properties of the oligo-miocene deposits in the Pasinler-Horasan, Tercan-Aşkale Basins (East Anatolia)

Tekin, Tansel
The study involves the investigations of source rock potential and their organic facies characteristics and the depositional conditions of the Oligo-Miocene deposits in the Tercan-Aşkale and Pasinler-Horasan Basins (Eastern Anatolia). For this purpose, seven stratigraphic sections from each basin are studied. Organic geochemical and organic petrographic (microscopy based organic facies study) analyses are carried out by using a total of 102 surface samples. The studied sections are composed dominantly of clastic lithologies and interfingering tuffaceous volcanics particularly in the Pasinler-Horasan Basin. The lithologies of the collected rock specimens are mostly marl, shale and clayey limestones. The source rocks have mostly "excellent" potential, however all of them are thermally immature. The source rocks are composed predominantly of oil-prone amorphous kerogen. The detailed microscopic investigation of the amorphous kerogen is shown that the discrimination of the marine vs. non-marine environments mcan be possible in the studied basins : The amorphous kerogen in the non-marine (or in the remnant sea environments having dominant lacustrine characteristics) source rocks is generally yellow to dirty yellow or translucent, mostly irregular, spongy, fibrous or reticular in appearance. The grain margins of the amorphous kerogen are generally fringed, scattered or disseminated. Under the fluorescence light, it has bright and stronger yellow-orange colors. The other type of amorphous kerogen present in the marine (or highly marine influenced environments) source rocks is dark yellow to orange, even reddish brown in color. The appearance of this amorphous kerogen is mostly granular, and their grain margins are generally clear and sharp. Under the fluorescence light examination, marine originated amorphous matter has relatively darker and dull yellow-orange color at the same maturity level. During the Oligo-Miocene time in the Tercan-Aşkale and Pasinler-Horasan basins, the lagoonal/marine, remnant sea and lacustrine environments are formed. During the Late Oligocene-Early Miocene time, in the Tercan-Aşkale Basin, lagoonal, transitional and marine (influenced) environmental conditions are determined for the source rock deposition. After then, in the Early(?)-Middle Miocene time, the remnant sea environments are formed, most probably by the regression of the sea at the end of Early Miocene or at the beginning of the Middle Miocene, and source rock deposition is occurred in these environments. In the Pasinler-Horasan Basin, source rocks are formed in lacustrine environments during Late Miocene-Pliocene. These lacustrine environments are brackish-saline(?) and probably alkali dominated. The organic facies studies also indicate the fresh water influenced phases in these lakes and remnant seas, during the source rock deposition. The seven different organic facies are distinguished in the source rock levels depending on the physico-chemical conditions of the depositional environment and the possible precursor organism of the amorphous kerogen.


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Citation Formats
T. Tekin, “Source rock potential and organic facies properties of the oligo-miocene deposits in the Pasinler-Horasan, Tercan-Aşkale Basins (East Anatolia),” Ph.D. - Doctoral Program, Middle East Technical University, 2002.