The role of physicochemical and biochemical processes on carbonate precipitation within the Laguna Timone maar in the Pali Aike Volcanic Field, southernmost extra-Andean Patagonia

Abstract

Carbonate deposits and sedimentary records from lakes in southern Patagonia provides an excellent contribution in the regional environmental register. The Laguna Timone is situated within a maar of the Pali Aike Volcanic Field, a Quaternary volcano-tectonic complex in southernmost South America and represents one of hundreds of “pools” of brines developed after explosive volcanic eruptions in a periglacial environment. The lake constitutes an endorheic hydrological system where processes leading to carbonate precipitation took place under extreme physicochemical conditions and biological influences that can be explored. Laguna Timone is recharged by groundwater and sporadic episodes of precipitation (ca. 200 mm/year) and high evaporation rates are controlled by regimes of strong wind (westerlies) and seasonal solar radiation. Carbonate precipitation was studied in microbialite fragments of tufa deposits and carbonate crust located in the edge of the lake, and the mineralogy of all samples is calcite. The clay fraction of the sediment underlying the carbonates was characterized and HRTEM analysis shows that authigenic smectites have influence on calcite crystal precipitation. The positive δ18O values (2.28 ‰) in thin crust layers are associated with evaporation processes. In contrast, the negative δ18O values (−6.52 ‰) in the microbialites show meteoric and/or groundwater influences. The δ13C (−0.43 ‰ to 2.50 ‰) values indicate physico-chemical and biochemical processes controlling the precipitation. The carbonate precipitation involves the interrelations of hydrogeological properties, climate and biological influences. Laguna Timone provides a natural laboratory for understanding mineral precipitation processes that register continuous climatic and environmental archives.