DISTRIBUTION AND 3D MODELING OF QUATERNARY FRESHWATER TUFA FACIES, CALAMA BASIN, ATACAMA DESERT, CHILE

Field mapping, description, and sampling in 2012, 2014, and 2019 show that in the Calama Basin (Atacama Desert) freshwater precipitated carbonate in a shallow lacustrine and palustrine system during the Miocene-Pliocene (Opache Formation) but as localized tufa deposits in the Quaternary (Chiu Chiu Formation). Mapping in 2019, with georeferenced coordinates, shows individual Chiu Chiu limestone deposits scattered across the Basin west of the town of Calama.

Three locations were photographed in detail in order to generate 3D models of the tufa deposits using SfM technology. These models are being integrated into a GIS database that includes observations at numerous other locations west of Calama. The overall distribution of the tufa deposits have been preliminarily mapped based on field observations, aerial photography and multispectral satellite data, and combined with a DEM dataset to understand the spatial and temporal distribution of the tufas.

Detailed stratigraphic sections were measured at sites along dry stream gullies, along the present Loa River, and at point of groundwater sapping and headwall collapse just west of Calama (Ojo de Opache near the San Salvador River). At this latter location, an active but small seep of saline water is precipitating halite, among other minerals, on the headwall, and a small spring discharges fresher groundwater. These features appear to be the last vestige of a more widespread spring and seep system that produced tufas episodically through the Quaternary. Preliminary U-Th dates of tufa carbonate range from 10’s of years where they are adjacent to the modern river, to 2.3 ka, with a cluster of ages ~1.5 ka. Mio-Pliocene carbonates formed between 8-3 My ago, indicating a major reduction if not cessation in carbonate deposition between the Opache and Chiu Chiu formations, with climatic and/or tectonic implications.