Stratigraphic and palaeoenvironmental framework of the Early Permian sequence in the Salt Range, Pakistan

Abstract

The Early Permian Gondwana regime succession of the Nilawahan Group is exposed only in the Salt Range of Pakistan. After a prolonged episode of non-deposition that spanned much of the Palaeozoic, the 350 m thick predominantly clastic sequence of the Nilawahan Group records a late glacial and post-glacial episode in which a range of glacio-fluvial, marine and fluvial environments evolved and accumulated. The Early Permian succession of the Salt Range has been classified into four formations, which together indicates a changing climatic regime during the Early Permian in the Salt Range region. The lower-most, Tobra Formation unconformably overlies a Cambrian sequence and is composed of tillite, diamictite and fresh water facies, which contain a floral assemblage (Gangamopteris and Glossopteris) that confirms an Asselian age. The Tobra Formation is overlain by marginal marine deposits of the Dandot Formation (Sakmarian), which contain an abundant brachiopods assemblage (Eurydesma and Conularia). Accumulation of the Dandot Formation was terminated by a regional sea-level fall and a change to the deposition of the fluvial deposits of the Warchha Sandstone (Artinskian). The Warchha Sandstone was deposited by high sinuosity meandering, avulsion prone river with well developed floodplains. This episode of fluvial sedimentation was terminated by a widespread marine transgression, as represented by the abrupt upward transition to the overlying shallow marine Sardhai Formation (Kungurian). The Early Permian Gondwana sequence represented by the Nilawahan Group is capped by predominantly shallow shelf carbonate deposits of the Tethyan realm. The sedimentologic and stratigraphic relationship of these four lithostratigraphic units in the Salt Range reveals a complex stratigraphic history for the Early Permian, which is mainly controlled by eustatic sea-level change due to climatic variation associated with climatic amelioration at the end of the major Gondwana glacial episode, and the gradual regional northward drift to a lower latitude of the Indian plate.

Probable existence of a Gondwana transcontinental rift system in western India: Implications in hydrocarbon exploration in Kutch and Saurashtra offshore: A GIS-based approach

“…In the Nilwahan Group, the oldest deposit is represented by the Early Permian Tobra Formation, glacio-fluvial (Ghazi et al 2012) in origin consisting of conglomerates, sandstones, siltstones and shales that is considered equivalent to the middle part of the Al Khlata Formation of south Oman (Jan and Stephenson 2011). This is followed upward by Early Permian deposits of Dandot Formation of a marginal marine environment (Ghazi et al 2012), Warchha Formation of a meandering fluvial origin (Ghazi and Mountney 2010) and Sardhai Formations of a dominantly fluvial origin with lagoonal and marine influences.…”

“…The Chhidru Formation shows a continuous terrigenous input and freshwater inflow (Ezaki 2006) to the basin represented by grey calcareous sandstones, along with in-frequent limestones and shale beds and is considered to be near shore to a sublittoral environment (Khan and Afzal 2005). This is followed upward by the Triassic Musa Khel Group consisting of Mianwali, Tredian and Khan et al 1986;Ghazi et al 2012). (b) Map depicting layout of Permo-Triassic Gondwana formations as outcrops and subcrops in Indus Basin, Pakistan along with structural layout of relevant faults (after Kusky et al 2005;Raza et al 2008;Aadil and Sohail 2011;Ghazi et al 2012;Hasany et al 2012).…”

Structural model of the Balkassar area, Potwar Plateau, Pakistan

“…It is overlain by the Cambrian Jhelum Group that consists of Khewra Sandstone, Kussak Formation (sandstones and shale), Jutana Formation (dolomite) and Baghanwala Formation (sandstone, siltstone and shale). The group is unconformably overlain by the Lower Permian continental Nilawahan Group (Ghazi et al 2012) and Upper Permian marine carbonates of the Zaluch Group (Shah 2009). The Mesozoic sediments are eroded/ Baker et al 1988;Pennock et al 1989).…”

Lower Permian fluvial cyclicity and stratigraphic evolution of the northern margin of Gondwanaland: Warchha Sandstone, Salt Range, Pakistan

“…Description: These cycles are > 20 m thick ( and marginal-marine environments, notably directly beneath the contact with the 498 overlying the Sardhai Formation (Ghazi, 2009;Ghazi and Mountney, 2012a). The 499 great thickness of these cycles, the dominance of sandstone assemblages and the 500 comparatively thin development of overbank mudstone facies likely reflects a rapid 501 avulsion process (Smith et al, 1989;Mountney, 2011, 2012b).…”

“…Against a background of on-going basin subsidence, development of individual 504 cycles was probably controlled principally by autogenic channel migration and 505 avulsion (Casshyap, 1970;1975;Ghazi et al, 2012a). Even after accounting for the 506 removal of the uppermost part of the Warchha Sandstone by the major unconformity 507 that separates the Permian from the Palaeocene succession in the eastern part of 508 the Salt Range, the number of preserved cycles present in the Warchha Sandstone 509 succession can be shown to systematically increase from east to west (Fig.…”