Geobiology of a crater lake: microbialites and their sediments

Studied microbialites were collected inside the Quaternary Rincon de Parangeo maar located near the city of Valle de Santigao, in the north-central part of the Trans Mexican Volcanic Belt. The Trans Mexican Volcanic Belt is an... [ view full abstract ]

Studied microbialites were collected inside the Quaternary Rincon de Parangeo maar located near the city of Valle de Santigao, in the north-central part of the Trans Mexican Volcanic Belt. The Trans Mexican Volcanic Belt is an active volcanic arc related to the subduction along the Mesoamerican trench of the Rivera and Cocos plates under the North American plate. This volcanic arc crosses central Mexico between latitudes 18 º– 20º N. The volcanoes around Valle de Santiago are part of the Michoacán-Guanajuato volcanic field, which is a vast region (<40, 000 km2) with more than 1000 monogenetic volcanoes, mainly cinder cones. Nearly 22 maar-type volcanoes have been identified in the Michoacán – Guanajuato volcanic field.

A discontinuous ring of well-developed modern microbialites characterized by a thrombolitic matrix and a stromatolitic crust, surround a former crater lake that extends for more than 200 m long toward the northwest and for more than 35 m to the southeast of the crater. The distribution, size and form of these recent microbialites vary along the external facies of a former paleolake. Microbialites occur as irregular multigrouping bioherms forming megascopic lithoherms at 1730 m above sea level. Each individual thrombolite´macrostructure exhibits a characteristic radial concentric layers, and a stromatolitic microstructure with microbial sediments associated to EPS and to bacterial populations. An active tectonic deformation and sinking have promoted extreme environmental conditions in pH, alkalinity, composition and erosional patterns, that in turn, promotes a rapid turnover of microbial life and adaptation strategies with a great astrobiological potential.