Holocene climate history of coastal southwestern Australia using calcrete as an indicator
Sheets of groundwater calcrete in the stratigraphic sequences of beach/dune units deposited in the interval mid Holocene-present, record a history of variable Holocene climate. Studies of Holocene coastal-plain areas of the Perth Basin spanning a gradient of climate from humid to semi-arid show that calcrete today is clearly forming as a sheet just above the water table in the zone of capillary rise in humid environments, as thin, isolated lenses under distinct outliers of vegetation zones in subhumid environments, and not at all in semi-arid zones. However, such calcrete sheets are not widespread earlier in the Holocene at levels where former water table positions can be inferred at the various localities. Evidently, apart from small isolated lenses, calcrete sheets did not develop at most localities earlier in the Holocene. The very distinct sealevel history, and the corollary, a distinct water table history, of Holocene coastal plain sequences enable a reconstruction of calcrete history because each water table level should have a distinct calcrete sheet if it was developed. The evidence shows a mid to late Holocene period of relatively more arid conditions and an extension of more humid climates only in the past 2800 14C yrs.