Gravity Tectonics in Foothills Structure Belt of Southeast Turkey

Abstract

The article deals with the geology of the foothills structure belt of the Taurus Mountains in Southeast Turkey. This area includes three main geological provinces from the south northward: (a) the foreland area, (b) the foothills structure belt, which grades into (c) the Taurus orogenic ridge. (a) The foreland area is characterized by a thick Mesozoic-Tertiary carbonate section with subordinate clastics, resting on predominantly shaly-sandy Paleozoic sediments, and is generally affected by gentle folding with normal or high-angle reverse faulting. (b) In the foothills structure belt a stratigraphic record including Paleozoic to Upper Tertiary sediments is present. This belt was affected by intense tectonism, which originated faulted imbricated structures and disharmonic folding. Moreover, extensive gravity gliding tectonics occurred in the area during late Cretaceous time. As proved by regional geologic studies and wildcat drilling carried out by Turkish Gulf Oil Company, a 10,000-foot thick gravity slide, composed of allochthonous sheets of eugeosynclinal sediments and basic igneous rocks, was found intercalated in an Upper Cretaceous shaly-sandy sequence. The allochthonous formations are considered as the indirect evidence of the existence of a Mesozoic geosynclinal trough in the north. The sedimentary filling of this trough as uplifted and tectonized during the Alpine diastrophism in an early cordillera phase. Subsequently it was displaced southward, near the northern edge of the shelf, by gravity tectonics. These large-scale gravity slides had remarkable effects on the evolution of the Southeast Turkey sedimentary basin. (c) The Taurus orogenic ridge is mainly composed of a partly metamorphosed rock sequence, very tectonized and affected by southward thrusting and long-distance gravity gliding. The rock sequence, referred to as Anatolian is considerably different from the Southeast Turkey facies, as it is largely composed of metamorphosed remnants of the Taurus eugeosyncline deposits and of flysch-type sediments intercalated with igneous rocks. The Anatolian facies sequence, herein interpreted as corresponding with a backland area, occurred during the late Alpine orogeny. After a general description of the stratigraphic units in the area, emphasis is given to the geology of the allochthonous slide complex. A general hypothesis on the origin and emplacement of these regional gravity slides is outlined. The article ends with some considerations on problems of oil exploration in areas affected by gravity slides.