Newly proposed Cretaceous-Palaeocene lithostratigraphy of the Ispikan-Wakai area, southwestern Makran, Pakistan
Abstract
Thrust-bound inliers comprising Cretaceous-Palaeocene succession of varied lithological characters are present around the villages of Ispikan and Wakai of the southwestern Makran, Pakistan and their lithostratigrphy is hereby first time described. We have classified them into two distinct groups named them as the Wakai and Ispikan groups.
The Wakai group, exposed 7-10 km to the southwest of the Wakai village, comprises undifferentiated succession of cream coloured biomicritic limestone interbedded with purple, blue and cream coloured shale and isolated outcrops of basic and ultrabasic rocks. They occur as a few meters to tens of meters thick thrust-bound successions of Cretaceous age cropping out within the domain of the Oligocene-Miocene Panjgur Formation.
The Ispikan group, exposed 3 km to the north east of Ispikan village is divisible into two lithostratigraphic units, the Late Cretaceous Ispikan Formation in lower part and Palaeocene Ispikan Conglomerate in upper part. The Ispikan Formation comprises about 50 m thick succession of cream, purple and varicoloured shale interbedded with very thin bedded fine grained sandstones and siltstones. Its lower contact is thrust with the Oligocene-Miocene Panjgur Formation and upper contact with the overlying Ispikan Conglomerate is transitional and conformable. The Ispikan Conglomerate comprises up to about 250 m thick succession of very coarse grained pebbly sandstone, conglomerate and very minor proportion of medium to fine grained sandstone. Its upper contact is also thrust with the Oligocene-Miocene Panjgur Formation.
It is proposed that these thrust-bound inliers, comprising the Ispikan and Wakai groups, 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 Afghan Block of the Eurasian Plate.
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