Abstract:
In the early 1980's the first evidence of biological alteration of basalt glass
(sideromelane) was published. Since that time additional evidence, including DNA
staining, isotopic abundance and chemical mapping, has come to light suggesting that
this unique alteration of glass can be attributed to microbial activity. Microbial
alteration textures have been seen in a wide variety of samples from around the globe.
The goal of our study was to examine a global selection of basalt glass samples and
develop a systematic description of the alteration textures. One-hundred and twenty-nine
petrographic thin sections from DSDP and ODP drill cores from the Pacific,
Atlantic, and Indian Oceans as well as the Mediterranean Sea were used to create a
catalog of images and a naming classification system of microbial alteration textures.
In total forty unique textures were identified and described. Eighteen textures occurred
in more than 10% of the samples. These more common textures may be a result of
similar microbes or similar environmental parameters. Thirteen samples were selected
for an eleven-element composition analysis via electron microprobe. For three of the
eleven elements the biotic clays are compositionally distinct from the abiotic clays
(Na20, MgO, CaO). Peridotite is another seafloor rock that is also common throughout
the solar system. To determine whether microbial growth might stimulate microbial
dissolution of olivine a series of enrichment cultures were initiated on-board ship with
peridotite drilled on ODP Leg 209 Dissolution was estimated by changes in dissolved
Li and Si in the media through time (up to 709 days). The results suggest that there
was no significant difference between the concentrations of dissolved Li and Si in the
inoculated microbial cultures as compared to the control cultures.
