Late Cretaceous and Early Tertiary Benthic Foraminiferal Biostratigraphy in Khuzdar District, Balochistan, Pakistan, with Special Reference to the Influence of Tethyan Sea Closure

BROHI Imdad Ali

Journal of science of the Hiroshima University. Series C, Earth and planetary sciences

The paleontological study of benthic foraminifera in relation to the Indian-Asian boundary in Khuzdar District, Balochistan, Pakistan, have been carried in three sections of the Cretaceous-Paleogene: named as 1) PAK-section, 2) MG-section and 3) HR-section (Abbr.) of Hinar. Strata of the three sections contain typical Cretaceous-lower Tertiary benthic foraminifers such as Bolivinoides draco, Coryphostoma incrassata, C. midwayensis, Gavelinella monterelensis, Globorotalites micheliniana, Stensioina beccariiformis, S. excolata, Neoflabellina rugosa, Nuttallides truempyi and Vulvulina spinosa. Fifteen benthic foraminiferal assemblages have been recognized from the PAK-section (seven assemblages) and MG-section (eight assemblages).
The Cretaceous-Paleogene strata are defined into three lithostratigraphic units consisting of the Mughal Kot Formation, the Pab Sandstone and the Jamburo Group in the ascending order. The age of the redefined Jamburo Group ranges from the Maastrichtian to the Middle Oligocene. The Cretaceous bearing strata of the Jamburo Group below the Pab Sandstone are correlated to the Mughal Kot Formation.
The Cretaceous-Tertiary boundary is determined above the Pab Sandstone and the base of the Jamburo Group in the PAK-section and below coarse grained brecciated limestone in the MG-section. Whereas in the Hinar section, it is located between limestone and shale of the Jamburo Group, by the disappearance of such planktonic foraminifers as Globotruncana stuartiformis, G. falsostuarti, Gl. spp., Pseudoguembelina elegans and Recemiguembelina fructicosa and the appearance of the Danian Globorotalia pseudobulloides.
The Cretaceous specimens occurring in the lower parts of the MG-section and PAK-section indicate Maastrichtian that is the age of the above mentioned Mughal Kot Formation and Pab Sandstone. Overall the redefined Jamburo Group consists of various kinds of shale, limestone, shelly limestone and marlstone. The late Cretaceous Mughal Kot Formation reveals more distinct alternation of limestone and shale, with two to three meter thick sandstone separated as a different unit equivalent to the Maastrichtian Pab Sandstone.
Benthic foraminifers change their tests from calcareous to agglutinated across the Cretaceous-Tertiary boundary. The change is most obvious in the PAK-section. However, the frequency of agglutinated taxa shows fluctuation in the Paleogene of the HR-section, and in the MG-section the agglutinated ratio does not largely change at the K/T boundary and gradually decreases afterwards. This decreasing tendency may be associated with restriction of the bottom water circulation of deeper water which may be caused by closure of the Tethyan Sea, and supports the hypothesis of collision of Eurasian and Indian Plates near the end of the Cretaceous and the Early Paleocene to Eocene.

英語

Hiroshima University

[ISSN] 0075-4374

[NCID] AA11095875