Facies architecture and depositional dynamics of the Upper Permian Rangal Coal Measures, Bowen Basin, Australia

The Upper Permian Rangal Coal Measures in the northern Bowen Basin, Austral ia, accumulated during rapid basinal aggradation in a retroarc foreland bas in setting. They reflect peatland deposition towards the close of a long-li ved climatic regime that came to an abrupt termination at the Permian-Trias sic boundary, which is well developed in the Newlands mine highwall and adj oining borefield, Six Lithofacies are represented in the Newlands district: (1) erosionally based, vertically stacked, ribbon and sheet-like sandstone bodies (up to 30 m thick and 1000 m wide); (2) heterolithic lobes and wedg es; (3) interbedded siltstone and sandstone sheets; (4) interlaminated clay stone and coal stringers; (5) laterally extensive bituminous coal sheets; a nd (6) laterally extensive laminated carbonaceous siltstone sheets. This fa cies assemblage is interpreted to correspond to six alluvial, cold-climate depositional environments: (1) trunk river channels and crevasse feeder cha nnels; (2) levee bank-proximal crevasse splay; (3) distal splay-overbank; ( 4) marsh; (5) peat mire and (6) floodbasin lake, respectively. The sequence architecture at Newlands reveals that a prolonged period of peat depositio n was progressively terminated by northward-stepping lobes of fluvial sedim ent in the south and by lacustrine drowning in the north, Exceptionally wel l developed, composite, elongate crevasse splay microdeltas, up to 26 m thi ck and >3000 m long, indicate that crevassing was responsible for the Local ized emplacement of thick sediment packages on the proximal floodplain, In the absence of active siliciclastic sedimentation, peat mire environments e xpanded from the distal floodplain, extending across abandoned depositional lobes, The geometry of these deposits reflects in large part accommodation space developed by the compaction of the peat precursor of the thick and l aterally extensive Upper Newlands Seam. Seqnential compaction of peat by el astic overburden controlled the nucleation and location of succeeding elast ic packages. The behavior of the peat under compactional load largely contr olled the lateral facies mosaic and stacking pattern of depositional units on a district scale.