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Biomarker and Carbon Isotopic Evidence of Marine Incursions in the Himalayan Foreland Basin During Its Overfilled Stage
Author(s) -
Roy Biswajit,
Roy Sohom,
Goyal Kanva,
Ghosh Sambit,
Sanyal Prasanta
Publication year - 2021
Publication title -
paleoceanography and paleoclimatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.927
H-Index - 127
eISSN - 2572-4525
pISSN - 2572-4517
DOI - 10.1029/2020pa004083
Subject(s) - sterane , geology , foreland basin , hopanoids , phytane , paleontology , sedimentary depositional environment , source rock , geochemistry , structural basin
The final stages of evolution of the Himalayan foreland basin (HFB) are preserved in the Siwalik Group of rocks deposited by meandering and/or braided rivers in the western and central regions of HFB. However, the time‐equivalent deposits in the eastern part of the foreland provide contradictory evidence of both terrestrial and marine environments. To address the ambiguity, molecular level characterization and stable isotopic composition of organic matter (OM) have been employed in the late Miocene‐Pliocene sequence of the eastern HFB. The n ‐alkane distribution, carbon isotopic (δ 13 C) signature of n ‐alkanes and distribution of hopane and sterane isomers suggest OM contributions from both marine and terrestrial sources during the late Miocene period. Increase in short‐chain n ‐alkane abundance and gammacerane index, low pristane/phytane ratio, higher δ 13 C values, higher regular sterane/17α‐hopane, C 31 R/C 30 ‐hopane and C 27 /C 29 steranes ratios and presence of C 30 sterane provides substantial evidence of stratified anoxic conditions and marine influences at specific stratigraphic intervals. During the late Miocene period, mixing of marine OM sources with terrestrial sources argue for marginal marine depositional conditions amid fluvial‐dominating environments. The entry of marine waters in the eastern HFB through the pre‐existing cratonic troughs possibly resulted from eustatic or relative sea‐level rise. No further evidence of marine incursions is observed in the younger Pliocene sediments. The higher detrital influx from the rising Himalayas, the onset of Northern Hemisphere Glaciation and evolution of physical barriers such as Shillong Massifs and Barind Tracts altogether led to the cessation of marine incursions into the HFB.