Interpretation of Fault-Controlled Ramp Structures in Sedimentary Basins--Example from Caspian Sea Using Landsat TM Data

Assad Iranpanah

Lineaments on a series of edge-enhanced images (TM data) from a region around the Caspian Sea form a geomorphically significant linear trend along the major Caucasus-Kopeh Dagh fault line. This fault represents the line of collision between the Cimmerian continents and the Turan plate on the south and north, respectively. The lineament zone manifests a ramp structure that forms a relatively narrow topographic high in the Caspian Sea.

Paleogeographic studies of the Caspian Sea suggest that the basin is part of the eastern Paratethys, which began to develop in the early Paleogene during the Alpine-Himalayan uplift. On the basis of the lineaments and associated geomorphic features, the Caspian Sea can be divided into southern, central, and the northern Caspian subbasins. The Caucasus-Kopeh Dagh fault line trends N80°W and separates the southern Caspian from the central subbasin, approximately along 40°N latitude. The boundary between the central and the northern subbasins is also a linear topographic high which trends N70°E and lies approximately at 44 °N latitude. The southern and central subbasins have subequal areal extension covering 35.64% and the 36.63% of the whole sea, whereas the northern subbasin occupies only 27.73% of the basin.

The Caucasus-Kopeh Dagh linear feature is a dip-slip reverse fault (Ashkhabad fault) with an apparent dextral horizontal component. Stress analysis utilizing a deformation model of the active tectonism in the area suggests a mean principal horizontal stress orientation that makes an angle of approximately 80° with the Caucasus-Kopeh Dagh lineament trend. This lineament delineates the zone of colliding continental plates between the Turan (Eurasia) and the Cimmerian microcontinents on the north and south, respectively. The initial direction of movement of the Cimmerian-Arabian plates was northeast, a counterclockwise rotation. The rotation is reflected by dextral strike-slip movements along the Ashkhabad fault, with a sharp change of the strike frequency diagrams of the major line ments in the northern part of the Cimmerian microcontinents.

The Ashkhabad fault line marks the late Paleozoic collision zone along the southern boundary of the Hercynian orogenic belt of the Turan plate. The Hercynian belt is not present to the south of the fault line, but its easterly continuation can be traced east of the Germab-Baghan fault line and in the Hindu Kush Mountains in northern Afghanistan. Additional paleogeographic, paleomagnetic, geochronologic, and geologic studies are required to ascertain the nature of the boundary of the Hercynian orogenic belt in this region.

The results of this investigation demonstrate that TM data are very useful in unravelling the tectonic history of intracontinental basins.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.