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ABSTRACT Deccan volcanism likely triggered environmental stress that controlled biotic transformations and Cretaceous/Paleogene (K/Pg) boundary mass extinction in the Indian subcontinent, but these revelations still remain inconclusive. Thus, we conducted high-resolution organo-molecular studies on a marine Um-Sohryngkew River K/Pg boundary succession. The results were used as standard reference for comparison with biotic attributes of the brackish water (Jhilmili) to freshwater (Anjar) intertrappean sediments and bole beds of the Deccan Traps. Organo-molecular compounds of the former section show strong correlation with the global stratotype section and point. High amounts of short-chain n- fatty acids and n -alkanes derived from autochthonous marine algal remains were observed in this section. However, the dominance of mid- and long-chain n -alkanes over short-chain n -alkanes in the Jhilmili intertrappean and intravolcanic bole beds of the eastern Deccan volcanic province suggested a terrestrial origin from higher plants under semiarid climatic conditions. The prolific abundance of n -alkanes in the Um-Sohryngkew River succession implies a mixture of terrestrial input from emergent and submerged/floating aquatic macrophytes. Low-molecular-weight aromatic hydrocarbon markers peak in biozone CF2 of the Um-Sohryngkew River succession. Possibly, this corresponds to greenhouse effects linked to the second phase of Deccan volcanism in the latest Maastrichtian, chron 29r. Abundant n -fatty acids found in the eastern Deccan bole beds suggest an origin from bacteria developed in a terrestrial environment. Depleted δ 13 C bulk values recorded from Jhilmili intertrappean and eastern Deccan bole beds are indicative of low primary productivity and burning of terrestrial biomass. Total organic carbon (TOC) maxima observed in the lowermost Danian P1a foraminiferal biozone of the Um-Sohryngkew River succession are also linked to late Deccan phase-two eruptions. The presence of three low-molecular-weight aromatic hydrocarbon markers in the eastern Deccan bole bed implies incomplete combustion of organic compounds in a terrestrial environment. Moreover, the dominance of high-molecular-weight aromatic hydrocarbon markers in biozone CF3 of the Um-Sohryngkew River succession is akin to that reported from other well-established K/Pg boundary successions, suggestive of their possible derivation from regional fire induced by the heat supplied by Deccan volcanism, which has been linked to the K/Pg boundary transition. Thus, regional wildfire played a significant role and affected the ecosystem, which perhaps accounts for the mass extinction.

During the last two decades, extensive paleontological research in the main Deccan volcanic province has led to a better understanding of biodiversity close to the Cretaceous-Paleogene boundary. Several infratrappean localities exposed in Jabalpur, Kheda, Balasinor, Rahioli, Dohad, and Bagh in the Narmada Valley (India) preserve one of the most geographically widespread dinosaur nesting sites known in the world. The well-studied intertrappean beds, such as those of Naskal on the southern margin, Asifabad and Nagpur on the eastern margin, Kisalpuri and Mohgaon Kalan on the northeastern margin, and Anjar on the northwestern margin of the main Deccan volcanic province, have yielded Maastrichtian fish ( Igdabatis ) and dinosaur remains and palynofossils ( Aquilapollenites - Gabonisporites - Ariadnaesporites ), either separately or in association, that suggest a Maastrichtian age for these beds. Only two intertrappean sections, Papro on the northern margin and Jhilmili on the northeastern margin of the main Deccan volcanic province, have produced Paleocene fossils. The fossil record from the infratrappean and intertrappean beds demonstrates that the dinosaurs survived the early phase of volcanism, though there was an apparent decline in their diversity, and that freshwater vertebrate fauna was least affected by the initial volcanic activity. The episodic nature of Deccan volcanism may possibly explain the survival of many freshwater and terrestrial communities during the periods of quiescence. In addition, as in the case of the late Maastrichtian sections in eastern Montana, North America, detritus-feeding freshwater vertebrate communities possibly had greater potential for survival than the terrestrial communities dependent on primary productivity. A close examination of the vertebrate faunal distribution across the two stratigraphic intervals (infratrappean and intertrappean) suggests that sampling bias in the infratrappean beds may have also masked the actual diversity of these beds.

Abstract The Deccan Trap flood basalt volcanism has commonly been considered to have initiated the break-up of India from the Seychelles ( c. 62.5 Ma). In Kachchh, Gujarat, western India, the sedimentary succession in the Paleocene Matanomadh Formation was deposited on highly weathered Deccan Trap basalts that were altered to kaolinite before basin formation. This contrasts with the weathering pattern on flat-topped hills of the Deccan Traps outside the Cenozoic rift basins in the Kachchh region and other parts of India, where basalt is dominantly altered to smectitic minerals. As basalts that are altered to smectite and kaolinite occur just across the faults that bound the Matanomadh Basin, the differential weathering cannot be attributed to climate. Geochemical modelling shows that kaolinite stabilizes in preference to smectite if CO 2 - and O 2 -buffered rainwater interacts with well-drained basaltic rock at high water:rock ratios. Such conditions can be accomplished by rainfall on a slope created by Cenozoic rifting that exposes the graben flank and basin floor basalts to continuously flowing water, the composition of which is buffered by equilibration with the atmosphere. As the rift post-dates both the eruption of the basalts and subsequent smectite formation, the associated extensional tectonics must be unrelated to flood basalt volcanism, and is most likely to correspond to the India–Seychelles break-up.

Abstract The Kachchh Basin, located in Gujarat (India) at the western trailing edge of the Indian plate, comprises several east–west trending seismically active faults. The Kachchh Basin evolved in two major stages. The first is the rift stage, which correlates with the break-up and separation of the Indian plate in the Late Triassic–Early Cretaceous and synrift sedimentation. The second is the post-Deccan Trap inversion stage, when the basin was periodically uplifted along the existing east–west trending intrabasinal master faults: the Katrol Hill Fault, the Kachchh Mainland Fault, the South Wagad Fault, the Gedi Fault and the Island Belt Fault. The inversion of basin was initiated by the onset of a compressive stress regime in response to the collision of the Indian plate with the Eurasian plate in the far north during the Early Eocene. This is shown by the tilting of the Deccan Trap lava flows along with the underlying Mesozoic sequence and the associated intrusive bodies that occupy the core portions of domal and anticlinal flexures bounded by major fault lines. Seismotectonic data on the prolonged aftershock sequence after the 2001 Bhuj earthquake (M w 7.7) reveal continuous low-to-moderate seismic activity along multiple faults covering a large area, now identified as the Kachchh Seismic Zone. This article reviews the neotectonic perspective of the active faults with the prime objective of delineating the post-Deccan Trap inversion phase of the Kachchh Basin, with an emphasis on neotectonism with regard to modern seismic activity. The datasets presented are primarily field-based neotectonic data from active fault zones that cover aspects of the tectonic geomorphology, Quaternary stratigraphy, near-surface fault traces and the nature of the fault in the shallow subsurface based on ground-penetrating radar studies. We also attempt a comparative neotectonic evaluation of each active fault in the Kachchh Basin and discuss the constraints for evolving a viable neotectonic model of the basin.