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

of environmental turbulence. Packstones and grainstones in the interspaces of the elongate forms indicate a more aggressive flow- regime. In our model, tightly packed round microbialites began to coalesce with their neighbors at the introduction of a bi-directional flow regime (Coulson et al. 2016). As a result, coalescence occurred parallel to flow constructing linear groups of laterally linked forms (Fig. 3B). Strongly elongate structures naturally followed (Fig. 3C). The round forms at the top of the bed resulted from the removal of this bi-directional hydrodynamic system (Fig. 3D and E). This process of coalescence has a modern analogue in the microbialites at Shark Bay in Western Australia where the same process occurs and for the same reasons (Logan 1961; Coulson et al. 2016). Bed 11 (Fig. 1) is a 1 to 3 m thick microbialite-bearing unit that contains a tightly packed field of round to sub-round microbialites (Fig. 4). Microbialite meso-scale fabric is best described as stromatolitic, but many forms have a large central thrombolitic core composed of mini-stromatolites (Fig. 4B and C). Diameters vary from about 40 – 70 cm, and due to the fissile nature of the overlying strata, are very well exposed in plan-view at multiple locations (Fig. 5A). Heights vary from 20 cm to about 70 cm and in cross-section widen slightly towards the top (Fig. 4B and D; Fig. 5B). As with bed 9, we could only trace this bed over a geographic area of approximately 20 km 2 , although its areal extent is much greater (Brand et al. 2012). All of the microbialites we saw (over five hundred) are upright and in growth position when exposed in cross-section (Fig. 5). This particular bed was so distinctive that even after travailing a valley to get to the next bed several km away, its location within the member could be accurately predicted to within a few vertical meters. Within many of these microbialites were found what we interpreted to be sponge-spicule networks (Fig. 6). These networks represent the remains of siliceous sponges that calcified before postmortem decay, leaving the isolated spicules ‘floating’ in what may have originally been a fleshy matrix (Coulson and Brand 2016). Networks typically do not exceed a few cm in size, with many not exceeding 1 cm, and appear in growth position over micritic bands (Fig. 7). Together, the micritic bands and sponge-spicule networks produce the familiar concave-down laminations that typically define protozoan microbialites (Fig. 4B and D; Fig. 5). Based on the presence of well-washed, inter-columnar grainstones deposited between the microbialites of bed 11 (Fig. 4F), we suggested that these forms grew in a shallow, sub-tidal environment (Coulson and Brand 2016). Microbial biofilms first colonized and stabilized the underlying substrate. As a result of continued microbial trapping and binding of lime mud and/or precipitation of micrite, the meso-fabric took on a stromatolitic texture. This initial rigid microbialite served as a suitable substrate for early sponge attachment. The microbial communities and the sponges then competed for space by encrusting each other. This regular organization eventually led to the construction of a columnar ‘stromatolite.’ Beds 9 and 11 exhibit many factors consistent with an energetic, shallow, sub-tidal marine environment brimming with aquatic life. The grainstones found intercalated between the microbialite beds, as well as those found in the spaces that separate individual microbialites are filled with trilobite hash (Fig. 4F). Other invertebrate fossils such as gastropods, sponges and mollusks, can also be found throughout the entire upper 154 m of the Hellnmaria Member. 2. Upper Cambrian Microbialites in North America Lee et al. (2015) constructed a table of all known upper Cambrian microbialites from around the world. They described a total of 31 geographically distinct sites in North America where upper Cambrian microbialites can be found. Each of the papers referenced by Lee et al. (2015) were perused in order to differentiate in situ microbialites from those of allochthonous origin. Of those 31 sites, 24 were interpreted by the authors to represent areas of in situ growth, conclusions with which I agree. Data for the other 7 sites was either limited or represented allochthonous deposits (Fig. 8). In many of these locations, microbialites were found at multiple stratigraphic horizons. For example, in the Canadian Rockies, microbialites can be found at 8 different horizons (Aitken 1967). In northern Utah, microbialites can be found at 6 different horizons (Saltzman et al. 2004). In Maryland, microbialites can be found at 12 different horizons (Demicco 1985). In Nevada, microbialites can be found at 3 different horizons (Osleger and Montañez 1996). Many of these microbialite beds are also quite extensive, covering several tens of square km in area (Srinivasan and Walker 1993), and many have bed thicknesses of multiple meters (Pratt 1984; Kennard and James 1986). Interestingly, almost all of these locations seem to span the southern United States, from New York to the region around Utah, California and Nevada, and then continue the trail northward through Idaho, Alberta and into the Northwest Territories of Canada. Of these locations, almost all of them are stratigraphically located above Cambrian sandstones that themselves are thought representative of erosional processes related to the Great Unconformity. 3. Upper Cambrian Microbialites globally Although North America boasts some of the best Cambrian microbialites in the world, it is not the only place where abundant Cambrian microbialites can be found. Russia and China also boast plentiful microbialite beds, with lessor distributions found in Australia, Iran, Korea, Argentina, Kyrgyzstan and even Antarctica (Lee et al. 2015) (Fig. 9). 4. Location of the Great Unconformity in Utah The location of the Great Unconformity is best delineated by the presence of the detrital sandstones that unconformably overlie the erosive surface itself (Fig. 8). The Tapeats Sandstone in the Grand Canyon is perhaps the go-to place for creationists seeking to describe, understand and showcase this underlying erosive surface. The Tapeats Sandstone and its related formations are regional in scope, extending over much of present day North America (Peters and Gaines 2012). The correlative formations for the Tapeats Sandstone in and around Utah are known as the Tintic Quartzite in central Utah, the Geertsen Canyon Quartzite in northern Utah, and the Prospect Mountain Quartzite in southern Utah (Yonkee et al. 2014). This latter Formation underlies the Notch Peak Formation, with many exposures showing a clear contact between the Prospect Mountain Quartzite and overlying limestones (Miller and Evans 2012). If we are to use the Cambrian sandstone deposits associated with the Great Unconformity as indicative of the Great Unconformity itself, then the Notch Peak Formation, along with its Coulson ◀ Stromatolites ▶ 2018 ICC 377