Are current models of tufa sedimentary environments applicable to tropical systems? A case study from the Gregory River

Tufa formation in the Gregory River, tropical northern Australia, is strongly influenced by high evaporation rates, perennially warm water temperatures, construction behaviour of aquatic insect larvae, and regular high magnitude floods. These conditions contrast with those of the cool temperate tufa-depositing streams for which sedimentary models have already been developed. Gregory River tufas occur as multiple series of dams separated by waterholes, indicating that under all climatic conditions there is a persistence of hydraulic factors in controlling the dam-pool sequence in fluvial tufa systems. However, at the scale of individual tufa deposits and facies, the Gregory River system displays a deviation away from current models. Tufa domes, upstream-dipping ramps, calcite rafts and larval facies are all common and important features in both modern and fossil tufas of the Gregory River, but they are not included in current tufa models. Thus, specific sedimentary models need to be developed for seasonally humid tropical tufa systems to understand their formation and interpret them correctly in the rock record.