Cambrian paleosols and landscapes of South Australia*

Abstract

Cambrian marine, grey shales are widespread, and so are Cambrian intertidal, redbeds with weakly developed marine-influenced paleosols. A broader view of Cambrian landscapes and soilscapes now comes from paleosols of alluvial coastal plains of the Cambrian (to Ordovician?) Parachilna, Billy Creek, Moodlatana, Balcoracana, Pantapinna and Grindstone Range Formations in the central Flinders Ranges of South Australia. Paleosols are recognised by soil structures such as calcareous nodules (caliche) and cracked ridges (mukkara). They also show gradational changes down-profile in minerals, grainsize and chemical composition comparable with soils. Some of these Cambrian paleosols are thick (>1 m) and well developed (large caliche nodules). They indicate stable alluvial and coastal landscapes of quartzo-feldspathic and locally tuffaceous sediments. Paleoclimates were generally semiarid, although several intervals of subhumid paleoclimate coincide with local marine transgression. Drab-haloed filaments in red claystones, and elephant-skin and carpet textures in sandstones of some of the paleosols may be evidence of biological soil crusts, and some waterlogged marginal marine and lacustrine paleosols had animal burrows. Cambrian paleosols of the Flinders Ranges are assignable to the modern soil orders Vertisol, Aridisol, Inceptisol and Entisol. Modern soils of the Flinders Ranges and central Australia are within the same orders as the Cambrian paleosols, supporting evidence from paleogeomorphology that some Australian landscapes and soilscapes are very ancient indeed.