High-resolution carbon isotope chemostratigraphy of the middle Cambrian to lowermost Ordovician in southern Scandinavia: Implications for global correlation

Abstract

Continuous and biostratigraphically well-constrained carbon isotope (δ13Corg) profiles through the upper Miaolingian (middle Cambrian) to Tremadocian (Lower Ordovician) part of the Alum Shale Formation in four drill cores from southernmost Scandinavia are described. The sections record seven Furongian (upper Cambrian) excursions/spikes, of which three appear valuable as auxiliary markers for identifying global stage boundaries. The Steptoean Positive Carbon Isotope Excursion (SPICE) event with a magnitude of up to 2.8‰ is located mainly within the Olenus Superzone. The onset, as specified here, coincides with the end-Marjuman extinction and is marked by a minor negative excursion (up to −1.6‰) right below the Miaolingian–Furongian boundary. The end of the SPICE event approximates the upper boundary of the Olenus Superzone and has potential for correlation of the Paibian–Jiangshanian boundary. The Top of Cambrian Excursion (TOCE) with a magnitude of about −1.6‰ straddles the Parabolina lobata–Parabolina heres megalops zonal boundary in Baltoscandia. This chemostratigraphic excursion, considered as a synonym of the Hellnmaria-Red Tops Boundary excursion (HERB), represents a secondary marker for correlating the base of Stage 10, if defined by the FAD of Eoconodontus notchpeakensis. A positive spike at the Cambrian–Ordovician boundary, here named COBS, recognized in the stratotype section at Green Point (Canada; δ13Ccarb magnitude +5.3‰), Scandinavia (δ13Corg magnitude up to +2.2‰) and elsewhere, appears as a valuable supplementary marker for recognizing this important boundary. The described δ13Corg profile from the Albjära-1 core provides a standard reference for Furongian carbon isotope chemostratigraphy in Baltica, refines the correlation between Baltica and other palaeocontinents, and indicates new possibilities for pinpointing international stage boundaries within the Furongian based on carbon isotope records.