Sulfur stable isotopes in Paleogene coals of Northeast India

Sulfur stable isotope signatures are instrumental in tracing the sources and tracking the movement of sulfur in different environmental compartments, besides providing vital insights into the origin and transport dynamics. Sulfur stable isotope composition in coal can give valuable information regarding sulfur sources and the process of sulfur incorporation in coal. The present study was conducted to determine the total sulfur content and sulfur isotopic composition for bulk sulfur (bulk S δ³⁴S) in Oligocene and Eocene coal samples from coal mines and a few coal stockings in northeast India. The results revealed that the total sulfur content in coal samples varied between 1.03 and 4.80 (wt%) with an average value of 2.64 wt%. The bulk S δ³⁴S in coal samples exhibited a wide range between −4.66 ‰ to 14.78 ‰ (VCDT). Oligocene coal samples from mines in Arunachal Pradesh, Assam, and Nagaland were enriched with heavier sulfur isotopes relative to Eocene coal samples from the Jaintia Hills region of Meghalaya. A moderate positive correlation was observed in the Oligocene coal samples, in contrast to the moderate negative correlation found in the Eocene coal samples. The bulk S δ³⁴S values and sulfur content in coal samples from coal stockings matched closely with Assam and Meghalaya mine samples. The findings of this study can be used to track the sources and movement of coal sulfur in various environmental compartments, besides providing valuable information about sulfur sources, the process of sulfur incorporation in coal, and the depositional environment.