Coal petrographic characteristics and depositional conditions of the subsurface Barakar Formation (Early Permian) in Belampalli Coalfield, Godavari Valley, Telangana

Abstract

The coal analytical studies have been taken up, to ascertain the rank on the basis of maceral composition and depositional environment of different seams namely Index, Index below top, Index below bottom, IA, I and the lowermost II (top section) intersected in Bore–hole No. SBS–182, from Sravanapalli area. The random vitrinite reflectance (Ro mean %) study of coal from Index and Index below bottom seams ranges between 0.61% and 0.63%, whereas IA and Seam I have shown lower reflectance which ranges between 0.52% and 0.54%. Thus, all these seams have attained high volatile bituminous C stage of rank. However, III (top section) seam has shown low reflectance (0.45%–0.46%), which indicates attainment of Sub–bituminous B stage. The coal maceral study has revealed that the Index, Index below Top, Index below Bottom seams contain vitric type of coal, whereas IA seam has vitric, fusic and mixed type of coal constitution. The lowermost III top and I seam, however, are represented by both vitric and fusic coal types. The facies study suggests that the vegetal resource of the Index, Index below top and Index below bottom seam has been accumulated during wet moor with intermittent moderate to high flooding. The resource for IA and III Top seam has been deposited during the prevalence of alternate oxic and anoxic moor conditions, which in due course of time changed to wet moor with intermittent moderate to high flooding whereas, I seam has witnessed wet moor with intermittent moderate to high flooding with shift to oxic (dry) moor with sudden high flooding. It has also been noticed that coal quality of III seam has shown deterioration towards the south–western direction of the Belampalli Township.