SANDSTONE PETROLOGY OF THE OLIGOCENE-EARLY MIOCENE PANJGOOR ABYSSAL PLAIN TURBIDITES IN TURBAT-ISPIKAN AREA OF THE MAKRAN ACCRETIONARY WEDGE, SOUTHEAST PAKISTAN

A vast area of the Makran accretionary wedge in southwest Pakistan, mapped as the Oligocene-Early Miocene Panjgoor Formation, comprises mostly the abyssal plain turbidites with isolated thin slivers of the mafic volcanic rocks, agglomerate, purple colored shales, cherts and polymict conglomerate exposed along major thrust zones. Sandstones of the Panjgoor abyssal plain turbidites are lithic arenites composed of a variety of igneous, sedimentary and metamorphic fragments. The igneous fragments include granites, rhyolites, volcanic glasses of acidic to mafic compositions, andesites, basalts and serpentine. The metamorphic fragments include schists, quartzites, gneisses, phyllites, slates and marbles, whereas, the sedimentary fragments include a variety of limestones, calcareous fossil fragments, sandstone, siltstone and radiolarian chert. These lithic fragments, along with the characteristics of associated minerals such as quartz, feldspar, mica and heavy minerals indicate a source terrain that is similar to the Himalayan collision zone. The polymict conglomerate, locally called the Ispikan Conglomerate, is composed of pebbles of a variety of igneous, sedimentary and metamorphic rocks. The sandstone interbedded with the polymict conglomerate has characteristics and provenance similar to those of the Oligocene-Early Miocene Panjgoor abyssal plain turbidites. The mafic volcanic rocks of basaltic composition, along with agglomerate, purple colored shale and chert, as thin slivers (thin wedge-shaped isolated outcrops) or crushed material within the major thrust zones, may represent ophiolitic mélanges, which have been proposed to have formed in response to the accretion of the oceanic floor of the Gulf of Oman during its northward subduction beneath the southern margin of the Eurasian Plate.