Abstract
The largely covered Middle Ordovician succession in the classic geological Rostanga area in northwestern Scania has not been studied for some 80 years. A new drill core through a succession ranging from the lower–middle Darriwilian to the lower Sandbian has provided a unique opportunity to investigate the graptolite biostratigraphy and the δ13Corg chemostratigraphy, and clarify their stratigraphic relations, through this ~90 m thick interval, which is developed within a black shale facies. The lithology, biostratigraphy and chemostratigraphy are closely similar to those of the coeval strata in the Fagelsang area, southcentral Scania, including the presence of the Fagelsang Phosphorite, which was previously unrecorded in the Rostanga area. The new data are particularly important in providing evidence of the relations between graptolite biostratigraphy and δ13Corg chemostratigraphy. The Fagelsang3 and Rostanga2 drill core successions are currently the only Darriwilian sequences in the world where these relations have been well established. (Less)
Highlights
An important area for the study of Darriwilian graptolite biostratigraphy in Scania (Skåne), southern Sweden, but in the entire Baltoscandia is at the village of Röstånga, which is located approximately 35 km north of the city of Lund (Fig. 1)
The core interval from 111.10–116.91 m, that is, roughly the stratigraphically lowermost 5 m of the study succession, is light to mediumgrey mudstone. Both graptolite biostratigraphy and chemostratigraphy suggest that this interval may represent a transition to the early Darriwilian carbonate unit known as the Komstad Limestone that is rather widely distributed in Scania
This negative trend would correspond to a similar trend in the lower Holmograptus lentus Zone around a core depth of 45 m in the Fågelsång3 succession
Summary
An important area for the study of Darriwilian graptolite biostratigraphy in Scania (Skåne), southern Sweden, but in the entire Baltoscandia is at the village of Röstånga, which is located approximately 35 km north of the city of Lund (Fig. 1). The core interval from 111.10–116.91 m, that is, roughly the stratigraphically lowermost 5 m of the study succession, is light to mediumgrey mudstone Both graptolite biostratigraphy and chemostratigraphy suggest that this interval may represent a transition to the early Darriwilian carbonate unit known as the Komstad Limestone that is rather widely distributed in Scania (see Bergström et al 2018 for a comparison with the cor responding interval in the Fågelsång area). Its top is marked by a few centimetres thick phosphorite bed (Fig. 3) that appears to have the same stratigraphic position as the prominent Fågelsång Phosphorite in the Fågelsång succession (cf Bergström et al 2000) This partly con glomeratic bed has not been identified with certainty in northwestern Scania, but Tullberg (1883) recorded a lithologically similar bed in a drill core from Stabbarp, which is approximately halfway between Röstånga and Fågelsång (Fig. 1A). The index fossil of the RÖSTÅNGA-2 DRILL CORE m 1.49
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