FLEXURAL PLATE SUBSIDENCE, SEDIMENTATION-RATES, AND STRUCTURAL DEVELOPMENT OF THE SUPERDEEP SOUTH CASPIAN BASIN

On a 270-km long seismic line across the west central and central part s of the South Caspian Basin an inverse flexural plate method is used to recover original unloaded plate parameters. The original plate show s remarkable consistency of parameters determined from the 12-second d eep seismic line, with average rigidity D=10(23.6) Nm; bending moment M=10(16) N, dip angle Theta = -0.14 degrees, and in-line compressive s tress of 10(12.3) N m(-1). By sequentially adding the sedimentary unit s to the average 'bare' basement, it is shown that the geometry of the basin at Jurassic time had a major downward warp, a nd high sedimenta ry fill to the west, leaving the eastern section open to possible eros ion during Early and Middle Cretaceous time. The deep western part of the basin was then filled by sediments during late Tertiary/Quaternary time, and a new depocenter created across the central and western par ts of the basin. This newer depocenter was then filled during Pliocene /Quaternary time. The combined flexure of the basement plate, and corr esponding sediment fill behaviors with time, are indicative of corresp onding lithologic variations across the basin and with suspected organ ic-rich sediments. The integrated description of basement, sediments, and depocenter behavior points to the utility of the inverse procedure for improving our understanding of basinal evolution. The value of ri gidity is comparable to estimated oceanic crust values, in line with t he suspected Tethys oceanic fragment of an island are below the sedime nts. The shift in depositional behavior with time, from west to more n ortherly across the line of section, is tied to the orogenic rise of t he Caucasus mountains to the north of the section, and to the continue d subduction of the Talysh-Vandam plate fragment northward today. The transpressional nature of the basin, and the resolution of the in-line compressive stress into components perpendicular to the Great Caucasu s ( similar to 70%) and also perpendicular to the West Caspian deep-la id fault (25-30%), are both in accord with the 25-30 km of present day sedimentary cover, including the variations of thicknesses of seismic stratigraphic units along the section from Azerbaijan in the west to nearly the Turkmenian border in the east. (C) 1997 Elsevier Science Lt d.