Regional significance and biostratigraphy of Cretaceous radiolaria from Pakistan
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In spite of the reported occurrences, this is the first detailed documentation on Cretaceous radiolarian assemblages from Pakistan. Samples from the Murree Brewery section, near Quetta, and Gwal section, southwest of the Muslim Bagh Ophiolite, are analyzed for their taxonomy, geological distribution and biostratigraphic implications for regional correlation. Radiolaria from the Murree Brewery section are mostly recovered from the Goru Formation and partly from the Parh Limestone, while the Sembar Formation was found to be barren of radiolarian assemblages. On the basis of their initial appearance of radiolarian species, four zones are established, in ascending order: the Holocryptocanium barbui and the Pseudodictyomitra pseudomacrocephala Zones in the Goru Formation, the Thanarla veneta Zone in the lower most part of the Parh Limestone, and a new zone, the Patulibracchium californensis Zone, in the upper part of the Parh Limestone. In the Gwal section, most of the samples from the interlaminated radiolarian chert bands of the Sembar Formation yielded abundant and diversified radiolarian assemblages. However, only two samples from the Goru Formation yielded radiolarians of any significant abundance. Four radiolarian zones are recognized from the section, in ascending order: the Sethocapsa trachyostraca and the Thanarla conica Zones are recognized in the lower part of the Sembar Formation, the Holocryptocanium barbui and the Pseudodictyomitra pseudomacrocephala Zones in the upper part of the Sembar Formation and lower Goru Formation. Based on the correlation of radiolarian zonation with those reported from submarine sediments and the land based sections of the world, a Cenomanian - Campanian age is assigned for the Parh Limestone and late Albian age to the Goru Formation of the Murree Brewery section. Although Sembar Formation of the Murree Brewery section was found barren of radiolarians, an Albian age can be assigned on the basis of planktonic foraminiferal assemblage. In the Gwal section, Valanginian to Aptian age is considered to the lower part of the Sembar Formation, and early to late Albian age to the middle and upper part of the Sembar Formation.