Gravity Modeling and Its Implications to the Tectonics of the South Caspian Basin
James W. Granath, K. A. Soofi, O. W. Baganz, E. Bagirov, 2007. "Gravity Modeling and Its Implications to the Tectonics of the South Caspian Basin", Oil and Gas of the Greater Caspian Area, Pinar O. Yilmaz, Gary H. Isaksen
Download citation file:
The large isostatic anomaly dominating the northwestern part of the South Caspian Basin is best modeled as a root of South Caspian crust that has displaced the normal lithospheric mantle. In the eastern South Caspian, gravity modeling suggests that continental crust does not extend seaward as far as previously presumed, and that the Turkmen platform is composed of a thickened sedimentary section overlying Caspian Sea-type crust.
Satellite-derived free air gravity data (Sandwell and Smith, 1997) for the South Caspian Basin, combined with low-order onshore free air gravity, show a steep 120-mgal decrease from the Alborz Mountains along the south coast of the Caspian Sea (Figure 1). The negative gravity gradient continues to —150 mgal at the Apsheron sill, on the northern margin of the basin. This negative anomaly is not surprising in light of the 900-m (2952-ft) water depth for most of the southern Caspian Sea, the 20-km (12-mi)-thick sedimentary section, and the anomalous oceanic character of the crust. However, the negative gravity anomaly persists under the Apsheron and northward into the southwestern part of the central Caspian Sea, in an area of low topography and shallow sea bottom. It adjoinsthe negative Bouguer anomaly of the Greater Caucasus Mountains, but in the Caspian Basin, it constitutes a pronounced isostatic anomaly.
In contrast to the western Apsheron area, the eastern South Caspian Basin contains a 40-mgal gravity high that extends 200 km (124 mi) seaward from the coast of Turkmenistan. It is separated fromthe onshore by a small gravity low. Seismic data show no significant changes in thickness of the Tertiary section between onshore and offshore Turkmenistan.