Paper No. 6
Presentation Time: 9:20 AM
TUBULAR STRUCTURES AND THE INTERPLAY BETWEEN MICROBIAL AND PRESERVATIONAL PROCESSES IN ARCHEAN FENESTRATE MICROBIALITES
JUAREZ RIVERA, Marisol, Geology, University of California-Davis, One Shields Avenue, Davis, CA 95616, SUMNER, Dawn Y., Geology, University of California, Davis, One Shields Avenue, Davis, CA 95616 and MACKEY, Tyler J., Earth and Planetary Sciences, University of California-Davis, One Shields Ave, Davis, CA 95616, mjuarezrivera@ucdavis.edu
Microbially influenced rocks provide insights into the organization of ancient microbial mats. 2521±3 Ma fenestrate microbialites from South Africa contain fossil remnants of ancient microbial communities. They are made of herringbone calcite with traces of organic matter preserved as inclusions. These inclusions define surfaces that are interpreted as remains of ancient microbial mats. To delineate the 3D geometry of these surfaces, specimens were serial sectioned after Stevens et al. (2011); sequential slices were polished in 130µm increments and scanned to yield an image stack, which was rendered into a 3D representation of the microbialite and explored with KeckCAVES software (
http://keckcaves.org). The resulting virtual representation allowed for visualization and characterization of microbial growth surface geometries that were not visible from 2D surfaces. Similar visualizations can be performed on computed tomography and confocal laser scans.
Using this data set, we documented the first record of tube-like structures that connect 3.5 to 5.4mm-thick surfaces defined by organic inclusions. The length of tubes range from 2-10mm, and diameters vary from 0.7 to 2.3mm. The density of organic inclusions vary throughout the tubes and main organic surfaces. Tubes commonly contain a core of well-defined organic inclusions surrounded by a concentric layer of herringbone calcite. This cement is circumscribed by an additional layer of variably dense organic inclusions, which indicate differing degrees of mat preservation during calcite precipitation. Thus, these microbialite features preserve an interplay of microbial and preservational processes associated with calcite precipitation. In addition, tube structures may have played a role in the migration of microbial communities throughout the 3D structures. Comparison of other 3D microbialite surfaces with CT scans of analogous microbial mat growth forms from Antarctic lakes provide a starting point for evaluation of microbial processes associated with specific mat surface geometries.
