Abstract
The newly proposed Middle Cretaceous “Bibai Group”, named after the Bibai peak, is exposed in Kach-Ziarat, Spera Ragha-Chingun areas of the Western Sulaiman Fold-Thrust Belt, Pakistan. It comprises thick succession of the mafic volcanic rocks, volcanic conglomerate, mudstone and sandstone. The stratigraphic nomenclature proposed by previous workers was not clear enough, as they used different names for the succession, such as “Kahan Conglomerate Member” of the Mughal Kot Formation, “Parh-related volcanics” by considering it as part of the “Parh Group, “Bibai Formation” and “Bela Volcanic Group”, which were confusing and misleading. Also previous workers did not realize that the succession may be further classified into distinct mappable lithostratigraphic units and deserved the status of a “Group”. Therefore, we carefully examined and mapped the area and hereby propose the name “Bibai Group” for the overall volcanic and volcaniclastic succession of the Middle Cretaceous age. Based on distinct lithostratigraphic characters we further subdivided the “Group” into two lithostratigraphic units of formation rank, for which we propose the names “Chinjun Volcanics” and “Bibai Formation”. Also based on distinct lithostratigraphic characters we further propose to subdivide our “Babai Formation” into three lithostratigraphic units of member rank, which we named as the “Kahan Conglomerate Member”, “Ahmadun Member” and “Kach Mudstone Member”. In this paper we have defined and briefly described the Bibai Group, its constituent formations and their members. Also we examined and discussed the validity and status of the proposed subdivisions; e.g. formations and members, of the Bibai Group, and are fully satisfied that the proposed subdivisions are appropriate and comply with the Article 24 and 25 of the North American Stratigraphic Codes (2005) and that the previous nomenclatures are inconsistent, confusing and do not comply with the International Stratigraphic Codes.
Highlights
The proposed Middle Cretaceous “Bibai Group”, named after the Bibai peak, is exposed in Kach-Ziarat and Spera Ragha-Chingun valleys of the Western Sulaiman Fold-Thrust Belt (WSFTB, Bender and Raza, 1995), Pakistan (Fig. 1)
In the Kach-Ziarat valley it is dominantly composed of volcaniclastic sediments and infrequently lava flows in lower part, whereas, in the Spera Ragha-Chinjun valley dominantly the in-situ basaltic volcanic rocks (Khan, 1986; McCormick, 1985)
In the Kach-Ziarat valley it is dominantly composed of volcaniclastic sediments and infrequently lava flows in lower part, whereas, in the Spera RaghaChinjun valley dominantly the in-situ basaltic volcanic rocks (McCormick, 1985; Khan, 1986; Siddiqui et al, 1994; Siddiqui et al, 1996)
Summary
The proposed Middle Cretaceous “Bibai Group”, named after the Bibai peak, is exposed in Kach-Ziarat and Spera Ragha-Chingun valleys of the Western Sulaiman Fold-Thrust Belt (WSFTB, Bender and Raza, 1995), Pakistan (Fig. 1). It comprises mafic volcanic rocks, volcanic conglomerate, mudstone, sandstone and ash beds. 2009), did not realize that the succession may be classified into distinct and mappable lithostratigraphic units and deserves the status of a “Group” They used different terminologies, such as the “Kahan Conglomerate Member of the Mughal Kot Formation”, “Parh-related Volcanics”, “Bibai Formation”, “Bibai Volcanics”, and “Bela Volcanic Group”, for the same Middle Cretaceous volcanic and volcaniclastic succession of the WSFTB.
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