A comparative study of endolithic microborings in basaltic lavas from a transitional subglacial – marine environment
Subglacially erupted Neogene basaltic hyaloclastites in lava-fed deltas in Antarctica were
found to contain putative endolithic microborings preserved in fresh glass along hydrous alteration
boundaries. The location and existence over the past 6 Ma of these lava deltas has exposed them to
successive interglacials and subsequent percolation of the hyaloclastite with marine water. A statistical
study of the hyaloclastites has found that endolithic microborings are distinctly more abundant within
samples that show evidence for marine alteration, compared with those that have remained in a strictly
freshwater (glacial) environment. Additionally, correlation between elevation and the abundance of
microborings shows endolithic activity to be more prolific within lower elevation samples, where the
hyaloclastites were influenced by marine fluids. Our study strongly suggests that endolithic microborings
form more readily in marine-influenced, rather than freshwater environments. Indeed, marine fluids may
be a necessary precondition for the microbial activity responsible. Thus, we suggest that the chemistry
and origin of alteration fluids are controlling factors on the formation of endolithic microborings in
basaltic glass. The study also contributes to the understanding of how endolithic microborings could be
used as a biosignature on Mars, where basaltic lavas and aqueous alteration are known to have existed
in the past.
Authors: Cousins, Claire R., Smellie, John L., Jones, Adrian P., Crawford, Ian A.
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