Depositional palaeoenvironment and economic potential of Khadsaliya lignite deposits (Saurashtra Basin), western India: Based on petrographic, palynofacies and geochemical characteristics

The huminite reflectance values (0.30-0.38%, av. 0.34% Rr) suggest that lignites are less mature and have reached up to lignitic stage (low rank B) of coalification. The geochemical (proximate + ultimate) analyses reveal that the lignites are characterized by high moisture content (av. 18%) and relatively low ash yield (av. 27%). The volatile matter yields and carbon contents are moderately high, whereas fixed carbon, sulphur and oxygen contents are average and hydrogen and nitrogen contents are relatively low. Rock-Eval pyrolysis data indicate that the hydrogen index values of the samples vary between 23 and 477 mg HC/g TOC (av. 188 mg HC/g TOC). The Tmax values of the lignites range between 377 and 433 °C (av. 418 °C), along with the presence of ββ hopanes suggesting the immature nature of the deposits. HI vs. Tmax, S2 vs. TOC, HI vs. OI and H/C vs. O/C plots of the studied samples indicate that the organic matters are a mix of type II/III kerogens. The types of kerogen along with high TOC contents (av. 33 wt.%) indicate the ability of lignite-bearing sequence of Khadsaliya to generate mix of oil/gaseous hydrocarbons upon maturation.