QUANTITATIVE MICROSTRUCTURAL AND DIAGENETIC COMPARISON OF CLOUDINA FROM NAMIBIA AND WESTERN NORTH AMERICA: INSIGHT FOR THE EDIACARAN BIOMINERALIZATION EVENT

As one of the first putative mineralizers, Cloudina provides information about the physical and ecological factors that led to widespread biomineralization during the Ediacaran Period. Here we present a quantitative comparison of the skeletal material of Namibian Cloudina specimens with those from another well-known locality, Mount Dunfee, Nevada. Electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS) are utilized in tandem to obtain in situ phase identification and crystallographic data from the skeletal material and its surrounding matrix on a micron-scale. Traditional light miscroscope petrography is also used to identify textural interrelationships of crystal grains in specimens and matrix. Specimens from Mount Dunfee, Nevada were chosen because they appear much less altered in comparison to specimens from most other localities in southwestern North America and compared to samples from Namibia. Well-preserved specimens show more evidence of primary wall crystallites or relic ‘ghosts’ of such crystals, and contain greater trace element (Sr) concentrations, which can be suggestive of primary aragonite cement or skeletal material. The results of this study indicate a strong diagenetic variation between the Namibian thrombolite-bound Cloudina specimens and those from Mount Dunfee, which are preserved in lag deposits. This variation has at times led to the systematic interpretation of these specimens as distinct species. The high resolution quantitative data from EBSD and EDS help clarify such interpretations by allowing us to move beyond apparent morphological similarities and providing greater insight towards the primary mineralogy and microstructural character of these Ediacaran metazoans despite their long digenetic histories.