A Late Silurian extinction event and anachronistic period

Abstract

Resurgence of microbialites and anachronistic facies in the aftermath of Phanerozoic extinction events has hitherto only been documented among the major five. Based on the classical Silurian carbonate platform strata of Gotland, Sweden, a biotic event is herein for the first time related to a substantial increase in anachronistic facies. Strata deposited during and shortly after the Lau Event in the Baltic paleobasin (Eke and Burgsvik Formations) include evidence for reduced grazing and infaunal activity in contemporaneous shallow low-latitude seas, e.g., flat-pebble conglomerates, normal-marine stromatolites, mass occurrence of oncoids, and subtidal wrinkle structures (e.g., Kinneyia and microripples). The latter structures have recently been suggested to be restricted to Proterozoic-Cambrian and Early Triassic time and therefore are regarded as anomalous for the Phanerozoic. The co-occurrence of these facies and global extinctions among pentamerid brachiopods and conodonts suggests that minor extinction events also resulted in anachronistic periods, less devastating but fully comparable to those in the aftermath of the end-Ordovician and end-Permian mass extinctions. A global positive stable carbon isotope excursion and the last appearance datum of the conodont Polygnathoides siluricus may facilitate identification of the Late Silurian anachronistic period elsewhere.