THE MID-CAMBRIAN MARJUM SOFT-BODIED BIOTA – A FOSSIL TREASURE TROVE IN THE WEST DESERT OF UTAH

Burgess Shale-type (BST) biotas preserve soft-bodied fossils that critically inform current understanding of the biodiversity and ecological complexity of the Cambrian Explosion. In North America, the Canadian Burgess Shale has essentially shaped our understanding of this major evolutionary event. Although the United States also contains several BST biotas, they typically feature much lower preservation quality and species richness. New investigations on the Drumian Marjum biota in Utah reveal that it fundamentally complements our perspective on the emergence of animal life in Laurentia. Totalling 149 species – 57% of which are soft-bodied – the Marjum Formation hosts the second most diverse of the 20+ Cambrian BST biotas of the continent. Assemblages from the main sites – Sponge Gully, Red Wash, and the newly opened Gray Marjum quarry – are fundamentally similar in composition, with strong dominance of panarthropods and sponges in both species richness and fossil abundance. The high quality of fossil preservation in the Marjum strata is evidenced by the common fossilization of internal organs and the presence of animal clades with scarce Cambrian fossil records. The Marjum Formation shares broadly comparable depositional and paleogeographic contexts with the Burgess Shale, both representing quiet, deep-water, recurrently oxygen-depleted environments at the offshore margin of a carbonate platform in Laurentia's subequatorial northern region. The comparison of their remarkable biotas results in a much more vivid picture of the evolutionary and ecological events that unfolded during the Cambrian period in this region of the world. A brief description of our group’s activities, including the recent collection of c. 2000 new fossils, and highlights from some of our most recent studies will be presented to illustrate the multi-faceted scientific significance of the Marjum Konservat-Lagerstaette.