Hydrogen sulphide release to surface waters at the Precambrian/Cambrian boundary.
Animal-like multicellular fossils appeared towards the end of the Precambrian, followed by a rapid increase in the abundance and diversity of fossils during the Early Cambrian period, an event also known as the 'Cambrian explosion'. Changes in the environmental conditions at the Precambrian/Cambrian transition (about 542 Myr ago) have been suggested as a possible explanation for this event, but are still a matter of debate. Here we report molybdenum isotope signatures of black shales from two stratigraphically correlated sample sets with a depositional age of around 542 Myr. We find a transient molybdenum isotope signal immediately after the Precambrian/Cambrian transition. Using a box model of the oceanic molybdenum cycle, we find that intense upwelling of hydrogen sulphide-rich deep ocean water best explains the observed Early Cambrian molybdenum isotope signal. Our findings suggest that the Early Cambrian animal radiation may have been triggered by a major change in ocean circulation, terminating a long period during which the Proterozoic ocean was stratified, with sulphidic deep water.
Institute of Geological Sciences, University of Bern, Baltzerstrasse 3, 3012 Bern, Switzerland. martin.wille@anu.edu.au
Martin
M
Wille
Thomas F
TF
Nägler
Bernd
B
Lehmann
Stefan
S
Schröder
Jan D
JD
Kramers
D000818:Animals; D044822:Biodiversity; D005580:Fossils; D019015:Geologic Sediments / Q000737:chemistry; D049690:History, Ancient; D006862:Hydrogen Sulfide / Q000378:metabolism*; D007554:Isotopes; D008982:Molybdenum / Q000032:analysis; D009792:Oceans and Seas; D012623:Seawater / Q000737:chemistry*
D007554:Isotopes; D008982:Molybdenum; D006862:Hydrogen Sulfide