Palynological and petroleum geochemical assessment of the Lower Oligocene Mezardere Formation, Thrace Basin, NW Turkey

Authors : Kadir GÜRGEY, Zühtü BATI

Pages : 349-383

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Publication Date : 0000-00-00

Article Type : Research Paper

Abstract :  The Oligocene clastic sequence of the Mezardere Formation insert ignore into journalissuearticles values(MF); with laterally variable organic richness has long been known as a proven source of gas with minor oil accumulations across the Thrace Basin of northwest Turkey. However, based on well data for the thick MF, neither detailed work in relation to age dating and stratigraphy nor a close linkage between the depositional facies/ environments, organic richness/organic proxies, and cyclicity has been established yet. In the present study, the MF was informally subdivided into Lower MF insert ignore into journalissuearticles values(LMF); and Upper MF insert ignore into journalissuearticles values(UMF); based on the distinct differences in palynological and geochemical data. Based on the common occurrences of Glaphyrocysta cf. semitecta and absence of Wetzeliella gochtii , the LMF is considered to be deposited during the earliest Oligocene insert ignore into journalissuearticles values(?Pshekian); under the prevailing marine conditions. The UMF is characterized by a very rich and diverse dinocyst assemblage having abundant occurrences of age-diagnostic Wetzeliella gochtii and a Solenovian age is assigned. Common Pediastrum occurrences in the UMF may suggest fresh water input as is the case for many source rocks of the Central and Eastern Paratethys. The UMF shows the geochemical characteristics of a typical transgressive sequence such as higher TOC, hydrogen index insert ignore into journalissuearticles values(HI);, and relative hydrocarbon potential insert ignore into journalissuearticles values(RHP); values than those for the regressive LMF. On the RHP basis, three short-term transgressive to regressive cycles are recognized in the entire MF in the wells studied. The early mature UMF samples showed a fair to good source rock potential insert ignore into journalissuearticles values(average TOC = 1.14 wt. %; HI = 283 mg oil/g TOC); and low to moderate genetic petroleum potential insert ignore into journalissuearticles values(GP = 3.65 mg oil/g rock); and source potential index insert ignore into journalissuearticles values(SPI = 1.44 t oil/m 2 );. The LMF samples were not evaluated due to their apparently low TOC, HI, and S2 values. Better understanding of the MF will eventually aid a better understanding of the paleoenvironment of the Eastern Paratethys.
Keywords : Thrace Basin, Lower Oligocene, Wetzeliella gochtii, transgression, regression, source rock