Khunamuh Fm

[Original Publication: Kapoor, H.M. and Tokuoka, T. 1985. Sedimentary Facies of the Permian and Triassic of the Himalaya, p. 23-58. In: “The Tethys”The Paleogeography and Paleobiogegraphy (Eds. Nakazava, K. and Dickins, J.m.), Tokai University Press]

Clayey limestone. The Khunamuh Formation is made up of alternation of limestone and black shale and is divisible in six members. The basal E1 Unit and fauna of part Member D of the Zewan Fm are more or less similar.

The sediments o_f the Khunamuh Formation lack bioturbation, possibly due to oxygen restriction. The Khunamuh Formation contains cephalopods, bivalves, and conodonts. It has been subdivided into several zones (Nakazawa et al., 1975). Unit E1 is characterized by Claraia bioni and Etheropecten haydeni, rare occurrence of Hindeodus minuta, Gondolella carinata and Ellsonia trassica. Unit E2 contains Otoceras woodwardi, Glyptophoceras lissarenum, G. himalayanum, Pustula sp., Wartha hisakatsui, Etheropecten haydeni, Claraia bioni, C. dieneri, Anchignathus typicalis, Neogondolella carinata and Hindeodus parvus and has been referred to the lower Otoceran or lower Griesbachian. Unit E3 is represented by Ephemeras subdemissum, O. tibeticum, O. serpentinum, Claraia aff. C. griesbachi, and Eumorphotis venetiana, Neogondolella carinata and Neospathodus critgalli and can be correlated with upper Otoceratan to lower Gyronitan or upper Griesbachian to lowermost Dienerian. The younger units enclose younger ammonoids.

The laminated sediments of the Guryul Ravine section were deposited under low-oxygen conditions (Wignall and Twitchett, 2002, p. 407) in deeper parts of the shelf with anoxia. There is convincing evidence of sea-level rise through the lower part of the Khunamuh Formation (Units E1 and E2), shown by a decrease in thickness and abundance of storm beds up in the section and a general decrease in grain size. The disappearance of the abundant and diverse Permian benthos and the appearance of Hindeodus parvus, nektonic ammonoids and oth_er Triassic taxa took place during this transgression.