ENVIRONMENTAL CONTROLS ON UPPER CAMBRIAN MICROBIALITE MORPHOLOGIES
Four microbialite bearing sections of the Upper Cambrian Notch Peak Formation, covering an area of approximately 2.5 square kilometers, were measured and described so as to record a vertical change in microbialite morphologies. Outcrop thicknesses were all approximately 20 meters. Microbialites at the bottom of all four sections start out round to sub-round with diameters of between 10-50cm and display a laminar, stromatolitic texture. Moving up section, all four outcrops subsequently record a radical change in morphology from round to elongate, with some microbialites over 7 meters long. Throughout this change, microbialite interspaces remain relatively consistent at about 3-7cm, keeping the entire field of forms tightly packed and orderly. Orientation data for elongate long axis on all measured samples exhibits a remarkably consistent bearing of 330° over the entire area. Traveling further up section, there is a sudden reversal to the rounded forms having diameters of between 30-70cm. At three of the four locations, rounded forms just below this horizon and just above that of the elongate forms are fused, thus inferring their being derived from the elongate morphology. In three of the four locations, these large rounded shapes become smaller, ending up very irregular in form and having diameters of around 5cm. Unconformities are absent throughout the study area. This 20 meter package seems to morph in a continuous, conformable fashion from one shape to the next.
At this stage, we have only observed, collected and described the relevant data. Further research will be required before we put forward a paleo-environmental interpretation.