GEOCHEMISTRY, MINERALOGY AND PROVENANCE OF UPPER MIOCENE PARKINI MUDSTONE, MAKRAN COASTAL RANGE, PAKISTAN

Upper Miocene Parkini Mudstone of Coastal Makran Range is extensively exposed along the Makran coast of Pakistan and Iran. The geochemistry and detrital mineralogy of Parkini Mudstone have been studied for its geochemical characterization and to interpret its provenance and depositional environment. Parkini Mudstone is an assemblage of 1200-1500m thick sequence of predominantly blue-grey to pale-gray calcareous mudstones, interbedded with centimetre-scaled laminated and occasionally cross bedded fine-grained sandstone. The sedimentary structures suggest the deposition of Parkini detritus in a mid- to upper- slope environment.

The geochemical and mineralogical studies of Parkini Mudstone from four locations revealed that on average these mudstones are composed of 57% SiO₂, 0.8% TiO₂, 17% Al₂O₃, 7% Fe₂O_3, 0.08 MnO, 4% MgO, 2.1% CaO, 2.4% Na₂O, 2.8% K₂O, 0.2% P₂O₅ and upto 11% Ca-free CaCO₃. The mudstone also contain, 60±11 ppm Ni, 295±65 ppm Ba, 190±34 ppm Cr, 95±23 ppm Rb, 155±45 ppm Zr, and 147±49 ppm V as average amounts of trace elements. Quartz is the most dominant mineral followed by Calcite and clay minerals whereas trace amounts of potassium feldspar, chlorite, and mica are also present.

The Parkini Mudstone is moderately enriched in silica. The quartz and clay minerals are positively correlated indicating conversion of feldspar and other less stable minerals into clays during moderate to intense weathering conditions. The positive and generally linear correlation between CaO and CO₂, and between CO₂ and CaO+MgO, indicate biologically active depositional environment. The geochemical results of major oxides do not show much variation indicating the homogeneous nature of provenance and weathering conditions. Similarly the concentration of trace elements in the studied samples do not indicate a volcanic origin. This is interpreted here as the derivation of Parkini detritus from reworked sediments. Deposition of thick sequences of sediments in a short span of time further indicate that a calm depositional environment prevailed along the Makran continental slope during Upper Miocene.