LITHOFACIES AND GEOCHEMICAL ANALYSIS OF THE LATE PALEOZOIC TOBRA FORMATION, SALT RANGE, PAKISTAN: IMPLICATIONS FOR THE PROVENANCE AND PALEOENVIRONMENT RECONSTRUCTION

The late Paleozoic Tobra Formation is an exclusive rock unit of the Salt Range which marks the end of a long period of nondeposition within the Gondwana domain of the Indian Plate. In this study, the lithofacies, petrographic, and geochemical properties of the Tobra Formation are presented to get a comprehensive understanding of the depositional environment, provenance, and paleoclimatic conditions. Three outcrop sections of Western to Eastern Salt Range were selected. Field studies show that the Tobra Formation is composed of six lithofacies that are broadly classified into three facies associations representing alluvial-plain depositional settings characterized by the following distinct depositional elements: (a) alluvial-fan debris-flow deposits, (b) alluvial-fan stream-flow deposits, and (c) overbank-flow deposits. These depositional elements formed as a result of local glaciation in paleogeographically close proximity with a general trend from southwest to northeast and affected the region up to the Eastern Salt Range. Furthermore, the petrographic and geochemical data indicate that lithologic units of the Tobra Formation show a submature to mature nature with characteristic lithic arenite and feldspathic litharenite to the sublitharenite petrofacies. Moreover, in the paleogeographic reconstruction of the Indian Plate during the late Paleozoic, the Tobra Formation was deposited during active tectonics with recycled orogenic phases influenced by glacial to glaciofluvial conditions. The sources of these sediments were igneous rocks, metasediments, and sandstones, more probably derived from the basement-related shield rocks. The majority of glaciofluvial signatures evidence that the Salt Range, Pakistan, occupied the paleogeographic position a little away from the maximum glacial extent during the late Permian as compared with the time-equivalent glacial units, such as the Al-Khalata Formation of Oman and the Talchir Boulder Beds of India.