Palaeoenvironmental reconstruction for the Permian(lower Gondwana)succession of the Godavari Valley Coalfield in southern India based on a combined palynofacies,carbon isotope,and biomarker study

• 作者: Neha Aggarwal Runcie Paul Mathews Arif Husain Ansari Biswajeet Thakur Shailesh Agrawal
• 来源期刊: 古地理学报（英文版）
• 年，卷（期）: 2022,（1）
• 所属期刊栏目: Palaeoclimatology
• 页码范围: 123-144
• 页数: 22页
• 语种: 英文

摘要

The study presents integrated palynofacies,organic carbon isotope,and biomarker data to reconstruct palaeoenviromental setting for the Permian sediments(borehole MGK-6)of the Kachinapalli block of the Godavari Valley Coalfield,southern India.The palynofacies data reveal three distinct palynofacies(A-C)as follows.Palynofacies A is dominated by abundant arborescent vegetation(glossopterids and conifers)along with structured organic matter,suggesting freshwater forest swamps in proximal settings.Palynofacies B is dominated by abundant degraded organic matter and amorphous organic matter,suggesting lakeshore/flooded palaeomires in slightly dismal settings.It has a high water level in the hinterland,which enables bacterial degradation of organic matter and establishes low-oxygenation conditions within the water column.These conditions would have provided grounds for the accumulation of either degraded or amorphous organic matter.Palynofacies C is dominated by the abundance of charcoal/opaque phytoclasts,indicating prolonged transportation or post-depositional alteration,suggesting a highly-oxidizing condition in distal settings.The bulk organic δ13C range(-25.1‰ to-20.9‰)in the borehole MGK-6 is in close agreement with the global Permian records.This study also shows a weak but statistically significant correlation with the major forms of palynofacies A and C.The inter-linked behaviour of bulk organic δ13C and palynofacies suggests that the changes in palaeobiogeography/palaeodepositional settings were most likely driven by the change in mean annual precipitation.The biomarker study shows the presence of n-alkane from C15 to C31 with unimodal and bimodal distribution patterns,revealing the source materials as vascular plants and microbially-altered organic matter.The combined palynofacies,organic carbon isotope,and biomarker data provide vital clue to salient findings for the development of envi-ronmental conditions of Godavari Valley Coalfield during lower Gondwana sedimentation.