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Facies architecture of alluvial floodbasin deposits: three‐dimensional data from the Upper Triassic Callide Coal Measures of east‐central Queensland, Australia
Author(s) -
JORGENSEN P. J.,
FIELDING C. R.
Publication year - 1996
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1046/j.1365-3091.1996.d01-25.x
Subject(s) - geology , facies , clastic rock , alluvium , alluvial fan , paleontology , sinuosity , geomorphology , bedding , alluvial plain , geochemistry , sedimentary rock , structural basin , horticulture , biology
A detailed investigation of floodbasin facies architecture was undertaken in the Upper Triassic (Carnian‐Rhaetian) Callide Coal Measures in east‐central Queensland, Australia, using extensive highwall and exploration borehole data from ongoing mining activities. The composite Callide Seam Member varies up to 23 m in thickness and is locally split by a number of clastic partings up to several metres thick, ranging from claystone to coarse sandstone. A subset of the nine lithofacies recognized in surface exposures was identified from geologists' logs of cored and uncored drillholes through the Callide Seam Member. Facies mapping of each clastic parting (split) was then undertaken using all available highwall and drilling data. Sequential maps of facies and interval thickness for each coal body and clastic parting over the mine area (6000 × 2500 m) record sediment accumulation in alluvial channel and floodbasin environments (including levees, splays and splay complexes, and mires). The maps indicate that the numerous splays have dominantly elongate plan geometry (up to 4 km long), with lesser irregular and rare lobate shapes. Small, elongate splays were evidently formed during single flood events, whereas larger, elongate bodies and more irregularly shaped complexes were the product of longer‐term splay construction over several flood cycles. Quantitative summaries of splay dimensions indicate a wide variety of shape and size. The distribution of splay orientations is similar to the palaeocurrent distribution in major alluvial channel deposits as established from cross‐bedding. Alluvial channels that sourced the splays and other clastic sediments within seam splits were of low sinuosity, braided planform, constructed sediment bodies up to 2800 m wide and were dominantly loaded rather than incised into underlying peat‐rich substrates.