Nature of a regional dogleg pattern in maturity profiles from Thrace basin, northwestern Turkey: A newly discovered unconformity or a thermal anomaly?

摘要

Vitrinite reflectance (%R_o) profiles of the Thrace basin are characterized by a regional dogleg pattern corresponding to the depths of Ceylan and Hamitabat formations. We investigated the nature of this dogleg pattern using a one-dimensional thermal-maturity model by simulating three possible geological scenarios: (1) two possible newly discovered unconformities, one between the Hamitabat and Soucak or Hamitabat and Ceylan formations and the other within the Hamitabat Formation; (2) an abnormal paleoheat-flow regime (paleothermal kick) that developed in the Oligocene and extended until the end of the early Miocene; and (3) a sharp thermal-conductivity contrast in the stratigraphic column caused by thermally low conductive deposits of the Ceylan Formation, which act as a regional thermal blanket. The sensitivity of each suggested scenario within the model and their effect on the observed dogleg pattern have been examined. A comparison of the measured and calculated (modeled) %R_o profiles from the proposed scenarios shows that the dogleg pattern can be best explained by a combination of the second (paleoheat flow) and third scenarios (thermal conductivity) instead of the unconformity scenario. However, the discovery of these two newly defined discordance surfaces with the help of well and seismic data requires a significant modification to the chronostratigraphy of the Thrace basin. The Hamitabat, Karaaaç, Fçtepe, and Gaziköy formations and the lower sections of the Kean Formation are suggested to be time-correlative counterparts in a newly constructed chronostratigraphy. Thus, the Hamitabat Formation can be evaluated as a part of the early–middle Eocene sequence similar to the Gaziköy Formation. In this article, we suggest that the Hamitabat Formation be classified as a group instead of a formation.