GILMSUR, N. R., and GERARD MAKEL, SIPM, Hague, Netherlands

ABSTRACT: Structure and Prospects of Alpine Basins or Exploration in Mature Areas

Since the first discovery of relatively small and complex oil fields in the Foothill Belt of the Taurus Mountains in southeast Turkey, the area has been the subject of extensive geological and geophysical surveys. Although a variety of tools were used to identify additional structures, an exact understanding of the relationship between individual structures has remained elusive. Recently acquired three-dimensional seismic data within the NV Turkse Shell lease areas has enabled substantial advances in the understanding of the detailed subsurface structure, deformational history, and relationship between fields and structures.

The historical view of the genesis of the southeast Turkey Foothill Belt is that the terranes presently incorporated in the imbricated zone formed a positive (forebulge) area at the Arabian platform edge in the Cretaceous. Coeval with Upper Mardin and Kastel Formation deposition in the Late Cretaceous, the platform edge was significantly deformed, ultimately leading to imbrication. The location of the eventual breakthrough of the basal thrust plane coincided with the forebulge area.

The resulting structures are typical examples of imbricate structures in a foreland setting. Individual thrust sheets are relatively thin, comprising a layered sedimentary sequence, and have a length that is several times greater than their thickness. The basal decollement plane formed in argillaceous units within the Silurian Dadas Formation. In the west, thrust imbricates are relatively thin, and thrusting involved gentle folding. In the east, the imbricates are much thicker and larger amplitude folding led to higher dips. This difference is caused by the presence, in the east, of a clastic sequence that overlies the argillaceous units of the Dadas Formation. This clastic sequence is progressively cut out to the west such that in the Beykan area, the Cretaceous carbonate sequence li s almost directly on top of the basal shales.

In the area occupied by the Kurkan, Kayakoy, and Kayakoy West structures, deformation resulted in a stack of smaller imbricates. This is in contrast with the Beykan area where, although the sequence is similar in a mechanical sense, the deformation resulted in one large imbricate structure. Because differences in thickness are not apparent, it is argued that friction along the basal slip plane must have been higher here than that along the basal slip plane beneath the Beykan structure.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.