Coexisting active travertines and tufas in the southeastern border of the Puna plateau

Abstract

The Terma Los Hornos is an active hydrothermal system located in the southeastern border of the Andean Puna plateau in Catamarca province, northwest Argentina. It exhibits a complete range from high- to low-temperature Quaternary carbonate products still actively forming. Travertines and tufas can be considered lithological end members within the depositional system, but the lack of clear boundaries has generated confusion when trying to distinguish them in the fossil record. In the Terma Los Hornos a continuum between both extremes is recorded, through a transition of different morphologies and dominant but non-diagnostic fabrics, among which we recognize a variety of crystalline crusts, shrubs, spheroidal particles, encrusted bubbles and reeds, lithoclastic, grumulous micritic and silty-sandy carbonates. These were grouped in the following depositional subsystems: 1) vents and pinnacles, 2) mound-apron, 3) terraced-slope, 4) steep slopes and 5) flooding areas and palustrine. Hydrochemistry results show substantial variabilities ranging from 65 °C, pH = 6.41, 1029 ppm alkalinity and 37 ppm calcium concentrations at the vents site to 21 °C, pH = 8.13 and 800 ppm alkalinity and 14 ppm calcium concentrations at ~1 km downstream, were carbonate precipitation is no longer visible. The set of linked subenvironments tend to merge into a larger scale geobody that defines the travertine system, with a proximal area dominated by physicochemical processes and a distal extent with pervasive microbial and common macrophyte features. The travertine system should not be understood as a fixed model, and its limits as well as the existing subenvironments, their extents and degree of overlapping, will depend mainly on three factors: 1) hydrothermal input, 2) climate, and 3) landscape. Perched past travertine deposits together with internal architectures and extent of the presently active travertine system allows thinking about constructive and destructive stages, respectively thought as dominantly expanding and erosional periods. Alternation of these two evolutionary stages and their balance will dictate the volume of primary facies and potential reworking products. A better understanding of these stages and their litho-stratigraphic products, will allow developing predictive stratigraphic and correlation models based on a sequence stratigraphic approach.