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.

Abstract: Organic compounds are ubiquitous in the Earth’s surface, sediments and many rocks, and preserve records of geological, geochemical and biological history; they are also critical natural resources and major environmental pollutants. The naturally occurring stable isotopes of volatile elements (D, 13 C, 15 N, 17,18 O, 33,34,36 S) provide one way of studying the origin, evolution and migration of geological organic compounds. The study of bulk stable isotope compositions (i.e. averaged across all possible molecular isotopic forms) is well established and widely practised, but frequently results in non-unique interpretations. Increasingly, researchers are reading the organic isotopic record with greater depth and specificity by characterizing stable isotope ‘structures’ – the proportions of site-specific and multiply substituted isotopologues that contribute to the total rare-isotope inventory of each compound. Most of the technologies for measuring stable isotope structures of organic molecules have been only recently developed and to date have been applied only in an exploratory way. Nevertheless, recent advances have demonstrated that molecular isotopic structures provide distinctive records of biosynthetic origins, conditions and mechanisms of chemical transformation during burial, and forensic fingerprints of exceptional specificity. This paper provides a review of this young field, which is organized to follow the evolution of molecular isotopic structure from biosynthesis, through diagenesis, catagenesis and metamorphism.

Abstract The Middle Devonian Geneseo Formation and its lateral equivalents in the Northern Appalachian Basin are regarded as crucial secondary targets to the extensively explored Marcellus subgroup. High-resolution sedimentology, stratigraphy, and petrography have yielded differentiation of genetically related packages, comprised of distinct lithofacies with characteristic physical, biological, and chemical attributes. In addition, argon ion milling and nanoscale scanning electron microscopy of shale sections has shown that the pore structure of the Geneseo derives from pores defined by phyllosilicate frameworks, carbonate dissolution, and within organic matter. Intervals of silt-rich mudstones and muddy siltstones occur in multiple facies types and “interrupt” facies, reflecting background sedimentation. These deposits and their sedimentary features are interpreted as products of high-density fluvial discharge events. Pore morphology and distribution correlates with distinct mudstone lithofacies as a result of small-scale compositional and textural characteristics. Phyllosilicate framework pores are small triangular openings (100-1500 nm wide) and are the dominant pore type observed in hyperpycnites. Organic matter porosity is common (10-500 nm pore size) and dominates the organic-rich facies that represents “background” sedimentation with high organic content. Carbonate dissolution pores (50-500 nm wide) are observed in calcareous intervals and reflect partial dissolution of carbonate grains during catagenetic formation of carboxylic/phenolic acids.