AKSOY, M. ZIHNI, Turkish Petroleum Corp., Ankara, Turkey

ABSTRACT: Stratigraphic Traps in Oligocene Delta of the Thrace Basin, Northwest Turkey

Two main depositional environments are recognized in the Tertiary sedimantary Thrace Basin which is located in northwest Turkey. The lower sequence of sediments were deposited in deep marine environments by turbidity currents as submarine fans (app. 3500 m thick) until the end of Eocene. At this time, the rate of subsidance was higher than the rate of sedimentation. The upper sequence of sediments were deposited in various subenvironments of a deltaic complex (app. 2600 m thick) throughout the Oligocene. This study has focused on the upper sequence of sediments.

Deltaic deposition started in the beginning of Oligocene when the

environment of deposition became shallow as a result of the higher rate of sedimentation than subsidance. Deltaic sequence has been divided into 13 coarsening upward depositional cycles by using the method of "well log sequence stratigraphy". These cycles have been correlated in 7 stratigraphic sections flattened at a tuff level as marker datum observed in GR-SONIC logs of 37 wells located in the northwestern part of the Thrace Basin. These correlations show that progradation of the delta is from north-northwest and west, to south-southeast and east. Using mainly GR-SONIC and composite logs as well as other data (logs, cores) obtained from 37 wells studied, lithological separations and sand ratios of each cycle have been determined. Based on these determinations and thickness distribu ions of each cycle in the deltaic sequence, many exploration areas are delineated in the study area in which stratigraphic traps may have the most potential.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.