Middle to Late Devonian distal braidplain deposition in the northeast sector of the Darling Basin Conjugate Fault System, near White Cliffs settlement, western New South Wales

Abstract

Sandstone-rich, 6 km-thick, Eifelian–Frasnian strata of the northeast sector of the Darling Basin Conjugate Fault System, lie north of the Darling River Lineament, east of the Koonenberry Fault, and south of the Olepeloko Fault. Fossils are very rare in the study area: exceptions are in the Skolithos-rich beds of the Paroo National Park, and the early Eifelian fish-fragment horizon near Mt Jack Station. Four marker horizons are known southeast of the Paroo National Park: (i) the Mt Jack fish-fragment horizon; (ii) a Skolithos-rich belt at Momba Station; (iii) the mid-Givetian Keginni Conglomerate Member; and (iv) a ∼20 m-thick vein quartz clast-rich unit that crops out near the base of the Frasnian strata. Four braidplains are mapped: (i) White Cliffs (largest); (ii) Mt Jack; (iii) Bullocky Bore; and (iv) the distal part of the Keginni Conglomerate Member. Sediment derivation was from west of the Koonenberry Fault (White Cliffs Braidplain) from the northwest (Mt Jack Braidplain), from the north (Bullocky Bore Braidplain) and from the southeast (Keginni Conglomerate Braidplain). The braided streams/rivers depositing the sheet braidplains were very shallow, and sheet-flood deposition on the braidplains was widespread.

Key Words:

• braided streams
• braidplains
• Devonian
• Mulga Downs Group
• sheet-flood deposition
• Skolithos

Acknowledgements

Barry Angel and John Sutton, then of Mt Jack and Talalara Stations, respectively, and Bill Pick and Alan Harbour of the Paroo National Park, are thanked for hospitality and assistance: the award of a Scientific Licence by the National Parks & Wildlife was essential for the purposes of this study. Alex Ritchie kindly identified the fossil fish fragments collected by the author. Kevin Morgans, Jack O'Toole, Jeff Vaughan and Jack Willoughby provided field assistance, and Peter Rickwood kindly reviewed the manuscript. The critiques of journal reviewers, Kingsley Mills and one anonymous reviewer, much improved the manuscript.