Mesozoic and Cenozoic deformation inferred from seismic stratigraphy in the southwestern intracontinental Palmyride fold-thrust belt, Syria

摘要

The Palmyride fold-thrust belt in central Syria is an intracontinental, northeast-trending, 400- by 100-km transpressive belt embedded in the northern Arabian platform. During the late Paleozoic and most of the Mesozoic eras, the region of the present-day mountains was a rift-like trough that collected >5 km of sediments, for a total Phanerozoic thickness of >10 km. The southwestern sector of the fold-thrust belt is bounded in the north by the Jhar fault and in the south by the south-vergent frontal thrust faults of the Palmyrides, with the broad AI-Daww depression in between. Structural features that characterize the southern and southwestern region of the Palmyrides include a short-wavelength (typically 5-10 km) fold style controlled by a regional low-angle décollement within Triassic beds, and small Jurassic and Early Cretaceous normal faults whose displacement was reversed mainly during the Cenozoic. Small intermontane basins (about 10 x 30 km), whose strata can be used to infer the history of Palmyride deformation, flank growth fault-bend folds and are mainly a product of Cenozoic shortening in the belt. These structures are elucidated by about 2,000 km of newly available seismic reflection data in the Palmyrides. Synthetic seismic traces generated solely from forward modeling of outcrop information permit age determination of seismic stratigraphic picks in two small basins about 100 km northeast of Damascus. There, minor Late Cretaceous uplift caused local onlap that marks the first inversion phase of the Palmyride trough. Tectonic quiescence throughout the Paleogene epoch, interrupted only in the middle Eocene by minor tectonism, resulted in monotonous deposition of about 2,500 m of mostly limestone. Marked onlap and probable downlap of early Miocene strata onto an Oligocene angular unconformity indicate accelerated tectonism by late Oligocene to early Miocene time. This marks the beginning of the major phase of uplift of the Palmyrides. Recent seismicity indicates that transpression continues today. Despite its relative remoteness from convergent plate boundaries (the nearest, the Bitlis suture in southern Turkey, is about 300 km distant), the Late Cretaceous, middle Eocene, and Neogene phases of deformation in the intraplate setting of the Palmyrides have a direct temporal relationship with major regional tectonism that occurred along the surrounding Arabian plate boundaries. The Palmyride trough was inverted from a trough to a fold-thrust belt in Late Cretaceous time and, subsequently, developed into a transpressive zone throughout Neogene and Quaternary times. Thus, the initiation of inversion in the Palmyrides, an integral part of the Syrian Arc, which extends from central Syria southward to central Sinai, apparently predates development of the Red Sea/Dead Sea plate boundary. In contrast, the intense Neogene through Quaternary deformational episode is clearly related to development of the Red Sea/Dead Sea fault system and to convergence along the northern boundary of the Arabian plate in southern Turkey.