Sedimentology and palynostratigraphy of Permian rocks exposed at Fairbairn Dam, central Queensland

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Abstract
Sedimentological and palynological studies have been undertaken on a sequence of Permian rocks exposed in the vicinity of Fairbairn Dam, near the town of Emerald in central Queensland. The rocks represent part of the fill of the northern Denison Trough, a north‐south elongate feature on the western margin of the Bowen Basin. The present investigation sheds new light on the depositional environment and stratigraphic context of the exposed sequence. The section is interpreted as the product of coastal environments of deposition. Five lithofacies are recognized and interpreted as: (1) major distributary channel fill: thick, erosively based, cross‐bedded sandstone; (2) interdistributary bay deposits: thinly interbedded sandstone, siltstone and claystone with carbonaceous shale; (3) tidal inlet and tidal delta deposits: erosively based, bimodally cross‐bedded sandstones; (4) beach ridge deposits: massive, quartzose sandstone beds; and (5) middle‐upper shoreface (i.e. inner marine shelf) facies: amalgamated units of hummocky cross‐stratified sandstones. Evidence for tidal flux and the importance of wave‐generated structures suggests that the coastal complex was of mixed‐influence, affected by a balance between fluvial outflow, waves and tides. Regional correlations suggest that the exposed section represents an eastward‐prograding coastal plain without any pronounced deltaic depocentres. Palynological assemblages from four samples support an interdistributary bay interpretation for the thin‐bedded facies, and indicate a Late Permian age for the exposed sequence. Palynofloras, which are dominated by pterophyte spores and disaccate gymnosperm pollen in three samples, and algae and acritarchs in the fourth, are characteristic of the upper stage 5 palynozone of Price (1983). The age and lithostratigraphic correlation suggest that the rocks exposed in the vicinity of the dam spillway are part of the Freitag Formation.