Precambrian–Cambrian Transition at the Igarka Uplift (Northwestern Siberian Platform)

Abstract

—The Precambrian–Cambrian transition is one of the most fundamental evolutionary turnovers in the Earth’s history. However, in many cases precise identification and correlation of this crucial boundary in lithologically contrasting sections is complicated, even if the whole spectrum of biostratigraphic and chemostratigraphic methods is applied. The Precambrian–Cambrian transitional strata of the Igarka Uplift (Sukharikha Formation) perfectly illustrate this problem. This unit has arguably one of the most detailed carbonate carbon isotope curves for this time interval (at least within the Siberian Platform). However, an extremely poor paleontological record previously reported from the Sukharikha Formation makes identification of major stratigraphic boundaries highly debatable. We present a detailed study of the Sukharikha and overlying Krasnyi Porog formations in three sections (Sukharikha River, Kulyumbe River, and Khantaisko-Sukhotungusskaya-1 well). Our chemostratigraphic and biostratigraphic data provide a correlation basis for these sections and identify the Cambrian boundary in terms of both the International Chronostratigraphic Chart and General Stratigraphic Scale of Russia. We show that lithologic boundaries and levels of the local first appearance of Tommotian small skeletal fossils are diachronous within the Igarka paleobasin. The latter is putatively caused by paleoecology of the early Cambrian biota and by taphonomic factors. Our data specify the location of the Tommotian Stage (sensu lato)/Cambrian Stage 2 boundary in other key Precambrian–Cambrian transitional sections of the Siberian Platform.