Groundwater calcrete deposits in Australia some observations from Western Australia

TLDR

Groundwater calcretes are non‑pedogenic limestone bodies up to 10 m thick that form in arid Australian basins north of 30° S, where periodic groundwater recharge and high evaporation produce linear, surface‑mounding deposits ranging up to 100 km × 10 km and include both fossil and active formations. The study proposes a carbonate‑precipitation model below the water table to explain the morphology, textures, and apparent inverted stratigraphy of these calcretes. The model posits continuous phreatic‑zone precipitation that drives upward growth, producing small anticlines with shear‑ and concentric‑folding structures.

Abstract

Abstract Groundwater calcretes are a non‐pedogenic form of calcrete occurring in broad fossil drainage systems. In Australia, they only occur north of about latitude 30°S and their formation requires arid conditions with very high potential evaporation as well as the periodic recharge of groundwater systems. They are linear, tabular limestone bodies, averaging about 10 m thick, occurring at or close to the surface and forming gentle mounds. The most extensive are located in the centre of the zone of distribution, where the climatic conditions are optimal, and are of the order of 100 km by 10 km. Some groundwater calcretes are fossil and strongly dissected, others are modern and still in process of formation. A model of carbonate precepitation below the water table, i.e. in the phreatic zone, resulting in continuous calcrete growth, accounts for their morphology, their textures and the apparently inverted stratigraphy suggested by carbon‐14 dating. In areas of maximum growth, small anticlines develop which have structures engendered by both shear and concentric folding due to upward growth pressure.