Astrobiological implications of rock varnish in tibet

David Krinsley, Ronald Dorn, Barry Digregorio

Research output: Contribution to journalArticlepeer-review

52 Scopus citations


The study of terrestrial geomicrobiology and its relationship to rock weathering processes is an essential tool in developing analogues for similar processes that may have occurred on Mars. Most studies of manganese-enhanced rock varnish have focused on samples taken from warm arid desert regions. Here, we examine samples obtained from eolian-abraded lava flows of the 4700-4800 m high Ashikule Basin in Tibet. Because it receives approximately 300mm of precipitation annually, this site is nowhere near as dry as Atacama Desert locales. However, the dusty, sulfate-rich, high-altitude and high-UV flux environment of the Tibetan locale offers new insight into rock varnish formation processes in a terrestrial environment that displays some attributes similar to those expected on early Mars. Microprobe measurements reveal that Mn enhancements in varnish are two orders of magnitude above the dust source, but Fe is only enhanced by a factor of three. Manganese-enhancing bacterial forms are not abundant but are still approximately 3 times more common than in Mojave and Sonoran Desert varnishes. In addition to its occurrence in subaerial positions, Tibetan varnish also occurs in micron-scale "pods" enveloped by silica glaze and as remobilized constituents that have migrated into the underlying weathering rind. A lack of surficial Mn-rich varnish, therefore, might not imply the absence of varnish. In contrast to suggestions that silica glaze might be a good source of microbial fossils and a key to varnish formation, we did not observe any clear microfossil forms entombed in silica glaze; further, there is no gradation between varnish and silica glaze but only distinct contacts.

Original languageEnglish (US)
Pages (from-to)551-562
Number of pages12
Issue number6
StatePublished - Aug 1 2009


  • Analogue
  • Astrobiology
  • Bacteria
  • Biomineralization
  • Desert varnish
  • Geomicrobiology
  • Life on Mars
  • Manganese enhancement
  • Microstromatolite
  • Rock coating
  • Rock varnish
  • Tibet-Weathering

ASJC Scopus subject areas

  • Agricultural and Biological Sciences (miscellaneous)
  • Space and Planetary Science


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