Terminal Ediacaran–Terreneuvian revolutions in Siberia

Abstract

The global reorganizations of marine ecosystems in the terminal Ediacaran and Terreneuvian include two breakthroughs (Cambrian Information Revolution and Agronomic Revolution) followed by the Cambrian Substrate Revolution in the Cambrian Series 2–Furongian. The first two attribute to colonization of new ecological niches by burrowing bilaterians and their gradual expansion within the marine realm. The ichnological record of siliciclastic sequences shows that these processes were most intense in the offshore zone, as compared to more proximal and distal shelf successions. For carbonate basins, the spatial and temporal dynamics of these two revolutions are still poorly understood. The Siberian Platform around the Precambrian–Cambrian transition shows a wide distribution of the marine carbonate facies and hence has high potential for studying the associated endobenthic ecosystem transformations. This study summarizes the results of paleoichnological studies in the terminal Ediacaran and Terreneuvian strata (∼550–521 Ma) in nine regions of the Siberian Platform periphery. The ichnoassemblages are grouped in three stratigraphic intervals (terminal Ediacaran, Fortunian Stage, Cambrian Stage 2) and attributed to sedimentary environments within the models of siliciclastic shelf and/or carbonate ramp. The evolution of the ichnoassemblage structure is evaluated applying the ecosystem engineering and ecospace occupation analyses. The study reveals that the terminal Ediacaran fossil record of the Siberian Platform lacks undisputed trace fossils. In the Terreneuvian, the general patterns of spatiotemporal development of endobenthic communities in the carbonate-associated marine environments generally coincided with those in the siliciclastic basins. The study shows that the greatest innovations in the organism-sediment interactions attributed to the first two Cambrian revolutions happened near the beginning of the Fortunian Stage and Cambrian Stage 2, respectively. However, some important interactions typical for the Agronomic Revolution (e.g., deep infaunal tiering, spreiten burrows) first appeared during the Fortunian.