Lower Paleogene Tectonostratigraphy of Balochistan: Evidence for Time-Transgressive Late Paleocene-Early Eocene Uplift

摘要

Analysis of lithofacies, paleoflow directions, and sandstone petrography of upper Paleocene-lower Eocene paralic and continental sediments exposed along the transpressional suture zone of the western margin of the Indian plate indicate that the process of deformation and uplift of the carbonate shelf in this area had started by late Paleocene time. This tectonic uplift and deformation is documented by: (1) an overall shallowing upward synorogenic sequence of sediments, (2) proximal conglomerate facies (consisting of lower Paleocene and Mesozoic clasts) dominating in the western part of the study area and distal facies of sandstone and shale dominating in the eastern part of the study area, (3) the existence of an unconformity of late Paleocene-early Eocene age in the Quetta and Kalat regions, (4) paleocurrent directions in deltaic and fluvial deposits indicating southeastward flowing sediment dispersal paths during late Paleocene-early Eocene time, which is opposite to that found in the late Cretaceous, suggesting a reversal in the depositional slope of the Cretaceous shelf, and (5) petrographic study of sandstones indicating a collision suture/fold thrust belt provenance. This episode of uplift and deformation could be the result of India-Arabian transpression with associated ophiolite obduction or, more likely, to represent the local response to initial India-Asia contact. The unroofing pattern and uplift geometry of the western Indian shelf suggests that this tectonism first started in the southern part of the study area (Kalat-Khuzdar area) during the late Paleocene-early Eocene and proceeded northward in a time-transgressive fashion.