The Proceedings of the Eighth International Conference on Creationism (2018)

the confusion associated with abiotic versus biotic processes. A microbialite is technically the umbrella term used for three basic morphologies: stromatolites, thrombolites and dendrolites. Although Burne andMoore’s definition precludes abiotic processes, it is elsewhere assumed. Consider this definition of a stromatolite by Semikhatov et al. (1978, p. 992), “Stromatolites are laminated, lithified, sedimentary growth structures that accrete away from a point or limited surface of attachment. They are commonly, but not necessarily, of microbial origin and calcareous composition.” Note that although a microbial origin is thought most likely, it isn’t a requirement. This is also true for thrombolites and dendrolites. 4. Microbialite Growth Processes Microbialites accrete at a sub-laminar to laminar level using three general processes. 1. There is a purely mechanical interaction between benthic, microbial communities and detrital grains of sediment. Here, the sticky EPS sheaths of microbes trap and bind sediment grains. 2. Precipitation of calcite by purely biological factors due to chemical changes associated with photosynthesis. 3. Precipitation of calcite by purely inorganic factors due to changes in the environment. 5. Growth rates The rate of microbialite growth has been calculated at between 5 mm a year for microbialites at Shark Bay, Western Australia (Playford 1980) to as high as 36.5 cm a year for modern forms growing in Bermuda (Gebelein 1969) and an equally high rate of 36.5 cm a year for forms found in Bahamian tidal channels (Reid et al. 2000). Many factors, however, can influence this rate of growth, and so a growth rate in and of itself should not be characteristic of growth rates in general. For example, the Shark Bay microbialites seem to represent an exhausted ecosystem (Playford 1980, p. 73). Proximal sea level has been dropping consistently for quite some time, and many microbialites now sit within the supratidal zone, completely stranded from a prior, sub-aqueous existence. Since no real opportunity for further growth exists at Shark Bay, the very low rate of growth for these forms should not be used as a proxy for microbialites in a more favorable environment. The modern forms growing in sand-laden channels in the Bahamas, can accrete at 1 lamination per day (365 a year at approximately 1 mm per lamination = approximately 36.5 cm per year), but never actually maintain this rate due to factors such as matt type, burial, lithification, and scouring by sand (Reid et al. 2000). More recently, Berelson et al. (2011) conducted an experiment on silicon microbialites growing in a pond at Yellowstone National Park. They were able to grow a microbialite from scratch and were therefore able to verify a high growth rate of 5.7 cm a year. Eagan and Liddell (1997, p. 302) predicted an extremely high rate of growth for ancient microbialites of between 37 cm to 60 cm a year. These varying rates, although quite diverse, seem to reflect the environment in which the microbialites grew or are growing. Supratidal forms predictably do not really grow at all; sub-tidal forms that are subject to constant erosion and burial, although growing rapidly at times, tend to lose their newly acquired width and height to the erosive activity of sand. On the other hand, the forms found in Cambrian rocks by Eagan and Liddell (1997) seem to have been growing in a favorable environment—hence the high growth rates. The microbialites studied in this paper are temporally and geographically very close to those studied by Eagan and Liddell (1997), and thus serve as an environmental proxy that suggests high rates of microbialite growth. From a creationist perspective, given extremely favorable conditions of growth, it is not implausible to consider growth rates on the order of several meters per year for the Hellnmaria microbialites. METHODS Seven sections of the Hellnmaria Member were measured, described and analyzed (Fig. 2). Samples were collected by hand, but many were drilled from microbialite-rich surfaces. Two microbialite beds, correlative over the entire seven sections, were specifically chosen for high-resolution research and subject to techniques in microscopy, Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and Energy Dispersive X-ray Spectroscopy (EDS). Literature research was also adopted for the purpose of correlating the Hellnmaria forms with others throughout North America, as well as globally. RESULTS 1. Hellnmaria Microbialites Hintze et al. (1988) bundle all of the Hellnmaria microbialites into a single package of strata that spans the upper 154 m of the Hellnmaria Member. We re-measured this segment of the type section being especially attentive to specific microbialite beds, bed thicknesses and general microbialite characteristics. We found eleven distinct microbialite-bearing beds separated by intervening wackestone-grainstone intervals that span the upper 154 m of the Hellnmaria Member (Fig. 1). Due to uplifting, all of the blocks within the study area have a general dip of about 10° towards the southeast. As a result, we could only trace these beds over a geographic area of approximately 20 km 2 before they dipped down into the subsurface. Brand et al. (2012) were able to trace some of these upper Hellnmaria microbialites to the Drum Mountains in the North and the Wah Wah mountains in the south, providing a total areal distribution of over 2600 km 2 . Based on the work of others, it is likely that the total distribution for the Notch Peak microbialites as a whole reaches to several tens of thousands of square km (Hintze et al. 1988; Miller et al. 2003). Bed 9 (Fig. 1) is a 5 – 14 meter-thick microbialite-bearing unit that exhibits a change in morphology as seen in vertical cross- section (Fig. 2). Microbialites change from round at the bottom of the bed to elongate in the middle of the bed and then back to round again at the top of the bed (Fig. 3). Remarkably, each of these changing morphologies can be distinguished at all seven outcrop locations (Fig. 2), with the microbialites in the elongate layer exhibiting a consistent 140°/320° bearing (Fig. 3C). At most of the outcrop locations, coalescing round microbialites are found both beneath and above the strongly elongate layer (Fig. 3A and B). These observations led us to hypothesize the existence of a bi- directional hydrodynamic system that was chiefly at work during the deposition of the elongate layer (Coulson et al. 2016). This interpretation is reinforced by the sedimentological data; micrite found in the interspaces of the lower, round microbialites, as well as in the round forms at the top of the bed indicate the absence Coulson ◀ Stromatolites ▶ 2018 ICC 375