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- Title
Decrypting paleomire conditions of superhigh-organic-sulfur coals from Meghalaya, India.
- Authors
Adsul, Tushar; Ghosh, Santanu; O'Beirne, Molly D.; Werne, Josef P.; Gilhooly III, William P.; Houghton, Jennifer; Fike, David; Hackley, Paul C.; Hatcherian, Javin J.; Varma, Atul Kumar
- Abstract
The present investigation decrypts the paleomire conditions of the Paleogene superhighorganic-sulfur (SHOS) coals from Meghalaya, India, using δ34SV-CDT values of the total sulfur (δ34STS-V-CDT) and pyritic sulfur (δ34Spy-V-CDT) along with the micropetrography and trace element ratios. Thirty coal samples were collected from the Jaintia Hills in the east, Khasi Hills in the middle, and Garo Hills in the west. From the Jaintia to Garo Hills, the δ34STS-V-CDT ranges from -21.2%o to +1.7%o (Δδ34STS-V-CDT -- 22.9%o), -10.0%o to +18.0%o (Δδ34STS-V-CDT = 28.0%o), and -8.9%o to -4.5%o (Δδ34STS-V-CDT = 4.4%o), respectively. Similarly, the δ34Spy-V-CDT varies from -29.3%o to +6.2%o (Δδ34SPY -V-CDT -- 35.5%o), -21.7%o to +27.1%o (Δδ34Spy-V-CDT -- 48.8%o), and -12.1 %o to -3.7%o (Δδ34Spy-V-CDT = 8.4%o), respectively, in these three hills. The isotopic signatures of the Garo coals suggest sulfur contribution mainly from the parent paleobiota and possibly from sulfides derived from primary sulfate within oxic conditions in a freshwater environment. Sr/Ba values averaging 0.5 and Th/U values > 2.0 further complement the freshwater peat deposition in the Garo Hills. Meanwhile, isotope variations in the Jaintia and Khasi coals indicate bacterial sulfate reduction of sourced seawater sulfate under reducing conditions. Moreover, isotopically depleted pyritic sulfur in the Jaintia coals possibly formed in the water column/near the sediment-water interface (open system). However, mixed 534Spy. V-CDT values in the Khasi coals imply pyrite formation near the sediment-water interface and deeper in the sediments (open and close hybrid system). Additionally, the presence of microscopic framboidal pyrite (FP) and polyframboids, Sr/Ba values > 0.5, and average Th/U ratios close to 2.0 in the Jaintia samples indicate the marine-influenced euxinic-anoxic depositional environment. Nevertheless, the presence of euhedral pyrites with the alleviated FP in the Khasi coals and then complete absence in the Garo coals may suggest dysoxic-suboxic and suboxic-oxic depositional conditions, respectively. Moroever, an amplified inertinite content (Immf= 9.77-33.16 vol.%), possibly induced by atmospheric peat exposure, supplements the suboxic-oxic paleomire in the Garo Hills. Besides, gradually depleting mineral matter content from the Jaintia (13.60 vol.%) to Garo coals (7.36 vol.%) additionally projects a transition from mesotrophic (marginal marine) to raised bog environment (terrestrial), complementing the shift in the paleomire condition of Paleogene coals from eastern (Jaintia) to western (Garo) Meghalayan Hills.
- Subjects
URANIUM; MINERALIZATION; CHLORITE minerals; PETROLOGY; BITUMEN
- Publication
Bulletin of the Geological Society of Greece, 2023, p44
- ISSN
0438-9557
- Publication type
Article