Analysis of sedimentary facies and depositional environments of the Permian Gondwana sequence in borehole GDH-45, Khalaspir Basin, Bangladesh

• Published in: Geosciences journal (Seoul, Korea) 2002, 6(3), , pp.227-236
• Main Authors: H.M. Zakir Hossain, M. Sultan-Ul-Islam, Syed Samsuddin Ahmed, Ismail Hossain
• Format: Article
• Language: Korean
• Subjects: 지질학
• ISSN: 1226-4806; 1598-7477

Lithofacies analysis of the Permian Gondwana sequencein borehole GDH-45 of the Khalaspir Basin was performed with aview to deduce the nature of depositional environments. On thebasis of dominant lithofacies association, the sequence is dividedinto six lithostratigraphic units (units A to F). Five lithofacies (con-glomerate, sandstone, siltstone, mudstone/shale and coal) are iden-tified within these units. Several sub-lithofacies, such as masive,crudely stratified, cross-stratified, ripple and parallel laminatedsandstones are also identified within these lithofacies. The sequenceforms a fining-upward trend with a rare coarsening-upward unit.The generalised Gondwana sequence is characterised mainly bychannel lags, pebbly massive to crudely cross-stratified sandstone,trough and planar cross-stratified sandstone, ripple laminatedsandstone/siltstone, massive to parallel laminated siltstone, mud-stone/shale and coal in ascending order. The facies associationsrepresent several repeated fining-upward units and cycles, indi-cating various sub-environments (channel, floodplain, flood basin/backswamp) in fluvial regime. The conglomerates might have bendeposited as debris flow or channel lag deposits. The sandstoneswere deposited mainly as multistoried channel and lateral bars inmoderately braided and sinuous streams. The siltstone and mud-stone lithofacies indicate bar top, natural levee or floodplain toflood basin environments. The coal lithofacies suggests depositionin low-lying, short to long persistent, moderately to well drainedand sparse to densely vegetated backswamps in fluvial channel-flood-plain complex. The overall succession of the Gondwana borehole sed-iments sugests that the depositional basin became, with time, gentlerin slope gradient, resulting in a more sinuous stream setting. KCI Citation Count: 0