Paleoecology of Upper Harkless archaeocythan reefs in Esmeralda County, Nevada.

摘要

Four previously unstudied reef localities occur in the upper Lower Cambrian (Bonnia-Olenellus Zone) in the Upper Harkless Formation in Esmeralda County, Nevada. These patch reefs were constructed on a shallow, carbonate platform in the subtidal zone by a consortium of archaeocyaths and calcimicrobes (Renalcis). A high diversity of dwelling organisms is found in varying quantities within and surrounding the reefs. Comparisons to the same age reefs in the Forteau Formation in Labrador, Canada preliminarily correlate these two localities. A comparison between modern sponges in Belize and archaeocyaths reveal similarities.; Four phases of diagenesis occur showing synsedimentary, mixing zone, shallow and deep burial cementation. Stratigraphic analyses reveal a shallowing upward sequence from packstone, which encases the reefs, to calcareous sandstone. Data indicates that the shoreline prograded across the carbonate platform. This progradation is theorized to be a result of (1) climate change, (2) a prolonged standstill, or (3) sea level lowering.