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The distribution of organic matter in the Eocene-Oligocene sequence of the Thrace basin, Turkey, may be used to help identify depositional cycles and environments. Four types of organic matter (amorphous, herbaceous, woody, coaly) were microscopically recognized and organic matter profiles were prepared for the Ceylan-1, Osmancik-1, and Abalar-1 wells.

Deposition of Tertiary sediments in the Thrace basin commenced with a middle Eocene transgression, resulting in the Sogucak and Ceylan formations. This transgression was followed by a regression and the Mezardere Formation (lower middle Oligocene) lagoonal sediments were deposited. A subsequent minor transgression is represented by the lower Osmancik Formation. The Oligocene ended with deposition of Danismen lagoonal-deltaic sediments. The organic matter profiles from the above mentioned wells correspond to the depositional cycles.

Amorphous organic matter is common in the Eocene sediments in the examined wells. The lower Oligocene regression was indicated by an increase in herbaceous and woody organic types. The Mezardere Formation shows differences in organic types in the examined wells. Abundance of amorphous organic matter in the Abalar-1 well instead of abundant terrestrial organic matter in the others indicates that marine influences were far greater at Abalar-1. The regressive and the transgression phases correspond to increases in the relative abundances of terrestrial and amorphous organic matter respectively. The increase in the abundance of amorphous type indicates a marine transgression at the base of Osmancik Formation. This was followed by a regressive period, which is indicated by abundant terrest ial matter with little or no amorphous organic matter.

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