A Study of the Palaeoclimate and Tectonic Setting of Bhuban Sandstone of Surma Basin in the Indo-Burmese Tectonic Collision Zone of Mizoram
Benjamin L. Chhangte* Jimmy Lalnunmawia** C. Zoramthara*** Zairemmawii**** Christopher Lalthazuala*****
C. Lalremruatfela****** Lawmsangzuali Kawilam*******
Abstract
The Bhuban sandstones of the Surma Group in Kolasib District of Mizoram constitute an important sedimentary unit within the Indo-Burmese Ranges. This study integrates detailed petrographic observations with major and trace element geochemical data to reconstruct the provenance, paleoredox conditions, paleosalinity and tectonic setting of the Bhuban sandstones of Surma Group. Major oxide geochemistry was employed to calculate the C-value which ranges from 0.24 to 1.15, indicating deposition under semi-arid to warm humid climatic conditions with moderate to intense chemical weathering of the felsic source rocks. Paleosalinity conditions was determined using Sr/Ba ratios (0.22-0.59) and the Sr-Ba discrimination diagram suggesting a transitional brackish to freshwater environment with dominant continental influence, consistent with a near-shore fluvio deltaic depositional system. Redox-sensitive trace element ratios such as V/Ni (1.0-2.21), V/Cr, U/Th (0.05-0.29) and Ni/Co versus V/Ni discrimination plots, indicate predominantly oxic- to sub-oxic depositional conditions, reflecting well-oxygenated shallow-water environments. Tectonic discrimination diagrams based on major and immobile trace elements, including QFL and QmFL plots, La-Th-Sc ternary diagrams, La/Sc versus Ti/Zr bivariate plots indicated that the Bhuban sandstones were primarily derived from Active Continental Margin. The petrographic characteristic predominated by quartz along with fewer presence of feldspars and rock fragments inferred recycled orogenic provenance.
Keywords: Bhuban sandstone, Mizoram, Surma group, palaeoclimate, palaeodepositional environment, tectonic setting
