Ichnology, Sedimentology and Paleoenvironmental Reconstruction of the Lower Cambrian Addy Quartzite, northeastern Washington State, U.S.A.

Abstract

The Addy Quartzite is a tide-dominated shallow-marine unit of heterolithic nature found in northeast Washington State. The Addy is Early Cambrian in age and reflects sedimentation during a global transgression along the paleocoast of the North American Craton. Due to a lack of previous integrated ichnologic, sedimentologic and paleoenvironmental data, an evaluation of all ecological aspects during deposition of the Addy Quartzite has not been provided until now. Twelve sedimentary facies, grouped into five facies associations were found within the Addy Quartzite. The sedimentary data clearly shows the establishment of a compound-dunefield. Eleven trace fossils, grouped into six trace fossil assemblages, linked with a sedimentary facies association, were found within the Addy Quartzite. The ichnologic data indicates a diverse and well-established climax community inhabited both the compound-dune bottomsets and interdune areas, and an opportunistic community consisting dominantly of trace fossils reflecting suspension-feeding organisms is favoured in the 2D and 3D dunes of the compound-dune field. The ichnologic data also adds information on the evolutionary paleoecology during the time of Addy deposition, allowing for a more clear designation of the importance of tide-dominated shallow-marine settings and their role in hosting the benthic fauna of the Cambrian agronomic revolution. The Addy Quartzite provides new insight into the evolution of benthic communities along the paleocoast of the North American Craton during the Early Cambrian.