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Groundwater dolocrete occurring within the Fortescue Marsh, a large inland wetland in the Pilbara region of northwest Australia, has been investigated to provide paleoenvironmental and paleohydrological records and further the understanding of low temperature dolomite formation in terrestrial settings over the Quaternary Period. Two major phases of groundwater dolocrete formation are apparent from the presence of two distinct units of dolocrete, based on differences in depth, delta O-18 values and mineral composition. Group 1 (G1) occurs at depth 20-65 m b.g.l. (below ground level) and contains stoichiometric dolomite with delta O-18 values of -4.02-0.71 parts per thousand. Group 2 (G2) is shallower (0-23 m b.g.l.), occurring close to the current groundwater level, and contains Ca-rich dolomite secondary calcite with a comparatively lower range of delta O-18 values (-7.74 and -6.03 parts per thousand). Modelled delta O-18 values of paleoground-water from which older G1 dolomite +/- precipitated indicated highly saline source water, which had similar stable oxygen isotope compositions to relatively old brine groundwater within the Marsh, developed under a different hydroclimatic regime. The higher delta O-18 values suggest highly evaporitic conditions occurred at the Marsh, which may have been a playa lake to saline mud flat environment. In contrast, G2 dolomite precipitated from comparatively fresher water, and modelled delta O-18 values suggested formation from mixing between inflowing fresher groundwater with saline-brine groundwater within the Marsh. The delta O-18 values of the calcite indicates formation from brackish to saline groundwater, which suggests this process may be associated with coeval gypsum dissolution. In contrast to the modern hydrology of the Marsh, which is surface water dependent and driven by a flood and drought regime, past conditions conducive to dolomite precipitation suggest a groundwater dependent system, where shallow ground waters were influenced by intensive evaporation. (C) 2018 Elsevier Ltd. All rights reserved.