Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

S. K. Shah ¹, Ashok Kumar ², C. S. Sudan ¹

Affiliations
1 Department of Geology, University of Jammu, Jammu, IN
2 Wadia Institute of Himalayan Geology, Dehra Dun, IN

Abstract

Spiti - Zanskar Basin of Himalaya exposes rocks ranging in age from Proterozoic to Early Cenozoic. Cambrian trilobites, brachiopods and trace fossils are known from the Kurgiakh area of the basin. The present paper concerns with Early Cambrian trace fossils reported from the same stratigraphic section in which trilobite body fossils are known. The assemblage of trace fossils include: Chondrites sp., Cruziana sp., Rusophycus sp., Phycodes palmatum, sp., Didymaulichnus sp., Protichnites sp., Monomorphicnus monolinearis, Diplichnites sp. associated with scratch marks indicating trilobite movements. The finding of trace fossils far below the definite brachiopod and trilobite body fossil horizons in the Lower Cambrian sequence of Kurgiakh area of Zanskar is of significance.

Keywords

Palaeontology, Trace Fossils, Cambrian, Ladakh, Himalaya.

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Ashok Kumar ¹

Affiliations
1 Wadia Institute of Himalayan Geology - Dehradun, IN

Abstract

Trilobites are important fossils ranging from Cambrian to Permian in age while they are stratigraphically significant in the Lower Palaeozoic. Well preserved trilobites discovered from the Kurgiakh area of the Kunzam La Formation of Zanskar Basin including Ptychoparia consocialis, P. pervulgata, Ptychoparia sp., Lyriaspis spitiensis, Lyriaspis sp., Anomocarella resseri, Anomocaraspis hundwarense. Anomocare sp., Hundwarella transversa, Hundwarella cf. convexa, Hundwarella personata, Hundwarella sp., Elrathia cf. chuwansis, Eymekops hermias. Lisania sp., Damesella sp., Lorenzella sp. Yuehsienszella sp. are reported.

Keywords

Palaeontology, Trilobites, Cambrian, Zanskar.

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Ashok Kumar ¹, Nand Lal ², A. K. Jain ³, R. B. Sorkhabi ⁴

Affiliations
1 Department of Physics, Kurushetra University, Kurukshetra - 132 119, IN
2 Department of Geophysics, Kurukshetrauniversity, Kurukshetra - 132 119, IN
3 Department of Earth Sciences, University of Roorkee, Roorkee - 247 667, IN
4 Department of Geology, ArizonaState University, Tempe, Arizona 85287-1404, US

Abstract

Fission Track (m) ages of apatite and zircon from the Higher Himalayan Crystalline (HHC), SE - Jammu and Kashmiralong Chenab-Suru-Dodarivers and their tributaries provide constraints on the cooling (<250°C) and exhumation history of these rocks. FT ages of apatite/zircon versus the topographic elevations of the host samples from different traverses provide linear relationships, indicating differential and secular nature of exhumation in the Himalaya. The HHC belt is exhumedat a rate of about 0.27 mm/a during Middle to Late Miocene. However, regional exhumation rate near the base along the Main Central Thrust and in central parts of the HHC from FT apatite ages is faster upto 0.35 mm/a since Late Miocene. Exhumation has considerably slowed down to 0.11 mm/a along its northern boundary and 0.02 mm/a along the Zanskar Shear Zone. No apparent faster exhurnationis discernible either along thee MCT or the Zanskar ShearZone (ZSZ). On the other hand, three large fold structures namely the Suru Dome, the Chisoti Dome and the Kishtwaranti formal window have indicated very young and fast exhumation of 0.33 mm/a, 1.1 mm/a and 3.6 mm/a respectively during the last 1 to 5 Ma.

Keywords

Fission Track Ages, Geochronology, Crystallines, NW Himalaya.

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B. S. Venkatachala ¹, Ashok Kumar ¹

Affiliations
1 Wadia Institute of Himalayan Geology, Dehradun - 248 001, IN

Abstract

Vaishnodevi Limestone is a distinctive landmark succession in the Jammu Himalaya. Significant biotas have been identified from a well exposed chert outcrop near Bidda and shale near Muttal. The chert biota is dominated by mat forming crustose, coccoid, chroococcacean cyanobacteria that include Eoentophysalis belcherensisand Palaeopleurocapsa wopfnerii. The other coccoid taxa are Myxococcoides grandis, Gloeodiniopsis lamillosa, Eogloeocapsa avzyanica, Sphaerophycus cf., S. medium, Eosynechococccus moorei, E. grantiis, Siphonophycus kestron, S. robustum, Oscillatoriopsis sp., Circumvaginalis elongatus, Archaeoellipsoides major, and A. minor. Stratigraphically this is the oldest biota thus far known from the Vaishnodevi Limestone and is assigned a palaeoproterozoic-Mesoproterozoic age.

The Muttal biota is composed of Siphonophycus kestron, S. robustum, Oscillatoriopsis sp., Calyptothrix spp., Eosynechococcus medius, Archaeotrichion contortum, Archaeollipsoides bactriformis, A. grandis, A. obesus, Arctacellularia ellipsoidea, Nostochomorpha prisca, Paleonostocalia irregularia, Leiosphaeridia laminariala, Leiosphaeridia sp., Lophosphaeridum spp., Micrhystridium spp., Sphaerocongregus sp., Obruchevella sp., Chuaria sp., Kildinosphaera sp., Spiromorpha indet. and vase shaped microfossils (VSMs). The Muttal biota is from the topmost shale unit of Vaishnodevi Limestone and is assigned a Neoproterozoic age.

It is concluded that the age of the Vaishnodevi Limestone spans the entire Proterozoic and deposited in a supratidal to intertidal and subtidal environment within a shallow shelf regime.

Keywords

Palaeontology, Palaeoenvironment, Vaishnodevi Limestone, Jammu, Himalaya.

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