ALLUVIAL FAN AND LACUSTRINE FAN-DELTA COMPLEXES (EARLY-MIDDLE MIOCENE) IN SEDIMENT BALANCED AND SEDIMENT OVERFILLED RIFT BASIN IN WESTERN ANATOLIA, TURKEY

Alaattin Sayili, Zuhtu Bati and Y. Haluk Iztan 
Turkish Petroleum Corporation (TPAO), Ankara, Turkey

The Western Anatolia is an extensional province where several grabens developed in different directions and episodes since Neogene. One of the most attractive grabens for oil exploration is the Alasehir Graben in where 2500 meters thick Neogene deposits were superimposed. The Northeast-Southwest trending asymmetric grabens formed in Early Miocene episode and received coarse clastics from the uplift controlled by NE-SW trending normal graben fault in the eastern boundary. The NE-SW trending asymmetric graben is characterized by coarse clastics in footwall developed on basin-bounding master fault zone during initial stage of rifting. These grain-supported coarse clastics of alluvial fan deposits reflect rapid erosion and deposition from uplifted metamorphic basement during synrifting. The fault-controlled alluvial fan deposits grade into fines of lacustrine-delta complexes in hanging wall of tilted fault block. The deeper lake shales and silts were deposited in the central part of the graben and widens southeastward. The rift climax stage is characterized by mud blanketing due to rapid deepening and submerging in basin floor and backstepping the marginal lacustrine deltas prior to post rifting. The subbasin-bounding faults activated and metamorphic basement exposed in the western boundary of NW-SE trending asymmetric graben in Early (?) to Mid Miocene time. The hanging wall received coarse clastics when subbasin-bounding master fault and/or antithetic faults in the west of the graben activated and the tilted fault blocks emerged and underwent subaerial truncational regime. The overall upward fining sequence occured in rift climax, followed by aggradational parasequence sets of lacustrine delta complexes in sediment balanced and sediment overfilled postrift phase prior to Late Miocene uplifting. The lake deposits with moderate to high TOC content are the source rocks and basin margin delta clastics are the reservoir rocks in Alaşehir Graben. The deeply burried lacustrine shales underwent maturation in superimposed graben coupled with high heat flow due to crustal thinning in extentional graben basin. Hydrocarbon was generated from the lacustrine shales and migrated to stratigraphic traps of the basin margin lacustrine fan-delta clastics.