LATE EDIACARAN COMMUNITIES ACROSS BALTICA WERE SEVERELY IMPACTED BY ENVIRONMENTAL CHANGES PRIOR TO THE CAMBRIAN PERIOD

The late Ediacaran sedimentary successions preserve fossils of the earliest known macroscopic multicellular organisms, known as the Ediacaran biota, during an important transitionary period in the evolution of complex life leading to the Precambrian-Cambrian boundary. The late Ediacaran interval in Baltica is divided into two regional stages, comprising the older Redkino Stage and the younger Kotlin Stage. Although nutrient limitation gave rise to widespread oligotrophic conditions, which persisted through both stages and into the Early Cambrian^1,2,3, a sharp decline in diversity and abundance of the Ediacaran biota has been observed across the boundary between the Redkino and Kotlin horizons⁴. We have compiled detailed chemo-stratigraphic records of lipid biomarkers and stable isotope (δ¹³C_{org, δ}¹⁵N_total) proxies from multiple drill cores located in Russia, Ukraine, Moldova, and Estonia. These records strongly suggest that an abrupt environmental shift between the Redkino and Kotlin stages was at least partially responsible for this decrease in faunal diversity. In particular, an environmental change beginning near the Redkino-Kotlin boundary and persisting through the Kotlin Stage was associated with the development of brackish conditions in marginal marine settings in epicontinental basins across the breadth of Baltica. This was likely a response to sea level, tectonic, and climatic changes during the late Ediacaran time on Baltica. We propose that a significant change in salinity would have perturbed organismic osmoregulation and exerted environmental selection pressure that could have played a major role in reorganization of the ecosystem on Baltica during the Kotlin Stage.

References:

1) Pehr, K. et. al, 2018, Nat. Commun. 2) Goryl, M. et al. 2018, Precam. Res. 3) Duda, J., et al., 2020, Geobiology 4) Grazhdankin, D., 2014, J. Paleontol.