Environmental fluctuations in the Olenus Zone (Upper Cambrian), southern Scandinavia: A geochemical approach

Niels H. Schovsbo
2000 Bulletin of the Geological Society of Denmark  
The Scandinavian Alum Shale Formation (Middle Cambrian to Lower Ordovician) was deposited under generally low bottom water oxygen levels. In the formation there is a covariance between faunal composition and the level of trace element enrichment caused by their mutual dependence upon changes in the bottom water oxygen levels. A detailed profile of the V/(V+Ni) ratio through the Upper Cambrian Olenus Zone in the Gislövshammar-2 core, Scania, Sweden, is described. Environmental information from
more » ... is zone is particularly relevant since the Olenus species in the zone apparently undergo iterative changes in morphology that may be linked to environmental changes. Moreover, the occurrences of Olenus species and Homagnostus obesus are almost mutually exclusive. The results indicate that the trilobitic intervals coincide with increases in oxygen levels as monitored by the V/(V+Ni) ratio. Peak oxygen levels do not appear at the base of each interval, suggesting that colonisation of the sea-floor took place when the oxygenation level reached a certain threshold but before maximum oxygen levels were reached. The distribution patterns of Olenus and Homagnostus are interpreted as reflecting differences in substrate preference since samples containing Homagnostus have statistically significantly higher TOC levels. The V/(V+Ni) variations in the Olenus bearing intervals suggest that oxygen levels fluctuated more than would be expected from morphological changes apparent in the Olenusspecies.
doi:10.37570/bgsd-2000-47-03 fatcat:evooru3ig5d2fj7nlfyp7srmei