STRATIGRAPHY AND STRUCTURE OF EASTERN SYRIA ACROSS THE EUPHRATES DEPRESSION

A N-S crustal-scale geotransect across the northern Arabian platform i n eastern Syria reveals an alternating series of basement uplifts and basins separated by predominantly transpressional fault zones above an effectively uniform crust. Four major tectonic provinces are crossed along a 325 x 100 km corridor that extends from the Iraqi border in th e south to the Turkish border in the north: the Rutbah uplift, the Eup hrates depression, the Abd el Aziz structural zone, and the Qamichli u plift. These features are the manifestations of reactivated pre-Cenozo ic structures that responded to forces acting along nearby Arabian pla te boundaries, particularly Cenozoic convergence and collision along t he margins of the northern Arabian platform, i.e., the Bitlis suture a nd the East Anatolian fault in southern Turkey and the Zagros suture i n Iran and Iraq. The database for this study consists of 3000 km of in dustry seismic reflection data, 28 exploratory wells, and geologic and Bouguer gravity maps. The deep crustal structure and, in part, the ba sement geometry along this transect are inferred from two-dimensional modeling of Bouguer gravity, whereas the shallow (about 8 km) structur e is constrained primarily by well and seismic data. Features of the g eotransect reveal: (1) A relatively uniform crustal column approximate ly 37 km thick with only minor crustal thinning beneath the Euphrates. Crustal thinning may be slightly more pronounced beneath the Euphrate s (about 35 km) to the southeast of the transect where the Bouguer gra vity anomaly is slightly higher. (2) Along the Eupbrates depression, o ngoing subsidence, which began during the Late Cretaceous, resulted in the deposition of at least 3 km of Late Cretaceous and Cenozoic rocks . The structural complexity of the Paleozoic and most of the Mesozoic sedimentary sections along the transect contrasts markedly with a rela tively simple, flat-lying Cenozoic section along most of the transect. A notable exception is the Abd el Aziz uplift, where Cenozoic rocks a re strongly deformed. (3) While Euphrates subsidence continued through out the Cenozoic, the inversion of the E-W-trending Abd el Aziz struct ure into a fault-bounded tilted block began in the Miocene, perhaps as a response to the last episode of intense Miocene collision along the nearby Bitlis and Zagros suture zones.