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Spatial Distribution of Large-Scale Carbonate Buildups in a Closed Lake System, Lago Strobel, Santa Cruz, Argentina

Abstract

Lago Strobel, located in the Patagonian region of Argentina, has substantial carbonate buildups (precipitates) paralleling its shoreline. These deposits were investigated using satellite imagery (ASTER and Quickbird) and Digital Elevation Models (DEM). Quickbird (0.6 m pan-sharpened) imagery offers the ability to recognize and quantify buildup morphology. Such buildups are white to light tan in color and distinctly different compared with the surrounding dark brown to black basal. This color contrast enables spectral analyses of the Quickbird data to characterize and map well exposed (coalesced buildups) to marginally exposed (separate buildups) carbonate deposits. ASTER thermal IR data has large 90 m pixels and is used to identify zones of large-scale carbonate deposits along the shore of Lago Strobel and in peripheral lakes. Lago Strobel is a large (97.6 km2) isolated water body situated within a Miocene alkaline basalt plateau with little riverine flow into or out of the lake. Carbonate buildups are situated around the entire perimeter of the lake (47.4 km); however, their distributions are not homogeneous and can be characterized into distinct physical morphologies. Such shoreline deposits have an average width of 141 m, cover a total of 6.7 km2, and most commonly form a bulbous morphology that accretes into columnar structures. Thin coatings on basalt boulders are less common and are found in isolation from other the thicker deposits. Bulbous buildups commonly coalesce to form pustular sheets that extend 10 – 500 m. These larger buildups accrete into the lake to form large promontories and small islands. These analyses when combined with ground truthing can provide valuable insights into the controls governing the occurrences of carbonate precipitation in alkaline lakes. Lago Strobel has a substantial carbonate deposit rimming its shore that varies in thickness, width, and morphology. Coalescing domal buildups dominate much of the shoreline and are volumetrically the most significant carbonate deposit. New perspectives on alkaline lake systems such as Lago Strobel can help gain a better understanding of climate history, regional tectonics, and in better characterizing subsurface hydrocarbon reservoirs, particularly those in pre-salt regions along the South Atlantic conjugate margins.