Lower–Middle Ordovician δ13C chemostratigraphy of western Baltica (Jämtland, Sweden)

Abstract

The province of Jämtland, central Sweden, records a well-preserved but very thin suite of the Lower–Middle Ordovician cool-water carbonates. In this study we present the first carbon isotope profile for these strata on the basis of whole-rock samples from the Brunflo 2 core. The studied succession is 41.55m thick and includes, in ascending order, the Bjørkåsholmen Formation, Latorp Limestone, Tøyen Shale, and the Lanna, Holen, and Segerstad limestones. We identify two distinct positive δ13C excursions that can be used for intra- as well as inter-continental correlations. A positive excursion in the Tøyen Shale probably correlates to the mid-late Floian and the Oepikodus evae Zone in Baltica and Precordillera, and the Reutterodus andinus Zone in North America. A continuous increase in δ13C values through the upper Holen Limestone and the preserved part of the overlying Segerstad Limestone is interpreted as the rising limb of the Middle Darriwilian Isotope Carbon Excursion (MDICE), an important tie-point for the global correlation of the Jämtland strata. Negative δ13C values associated with the Latorp Limestone may correlate with similar low values in the late Tremadocian and early Floian of the Argentine Precordillera and the Shingle Pass and Ibex sections in North America.