The geomorphological context of calcrete deposition in the Dalmore Downs area, Northern Territory, Australia

This work describes and provides tentative dates for a previously briefly recorded calcrete suite from semi-arid north-central Australia. The aim is to provide further insight into the nature of carbonate deposition in this area and thereby promote further research. The calcrete deposit occupies 3750 km2and appears to have once served as a conduit for groundwater flow towards the Barkly Tablelands playa system. Two major phases of calcrete precipitation are distinguished tentatively as occurring during the Mid- and Late Pleistocene. Geomorphological and SEM evidence suggest that an earlier phase culminated in the direct calcium carbonate precipitation of travertine mounds. These resulted from effusive groundwater flow, possibly along spring lines. This phase was succeeded by a period of longitudinal dune formation. During a later phase, non-pedogenic calcrete was precipitated between and beyond the mounds, apparently replacing former dunes. The presence of salts within the calcrete infers strong evaporative conditions suggesting that this later precipitation took place in the proximity of a saline lake, possibly palaeo-lake Barkly. Later stage aeolian activity appears to have reworked dune surfaces since the second stage of carbonate deposition