Friday Field Photo #167: Holocene microbialites at Lago Sarmiento

If you’ve ever been to Torres del Paine National Park in Chilean Patagonia you’ve probably seen the curious white ‘bathtub ring’ of rock rimming Lago Sarmiento. These rocks are made of calcium carbonate (limestone) that formed as a result of microbial activity. Such deposits, called microbialites (or stromatolites, thrombolites, etc. depending on their character), develop when a microbial community on the bottom of a body of water traps and binds detrital sediment, some of which becomes the nucleus for sediment that precipitates out of solution. Over time, the precipitated carbonate and trapped sediment grow into a complex of layered mats or, in this case, bulbous ‘lumps’.

The microbialites that you can see exposed around the edge of the lake are fossils, they were formed when the lake level was higher several thousand years ago. There is still microbial activity in the lake at present forming similar features on the lake bottom several meters below the water surface. Modern microbialites such as these at Lago Sarmiento are important analogs for better understanding early Earth history and for addressing questions about life in general.

There is, obviously, a lot more to know about the Lago Sarmiento microbialites. If you want to learn more about the chemistry, biology, and history of these features, check out this paper from the journal Paleogeography, Paleoclimatolgy, Paleoecology.