The Oxfordian-Kimmeridgian transition in the Boulonnais (France) and the onset of organic-rich marine deposits in NWEurope: a climatic control?

We characterised the organic matter content of marine deposits at the Oxfordian-Kimmeridgian transition in the Boulonnais (France). Organic rich deposits in platform environments are evidenced in the uppermost Cymodoce and lowermost Mutabilis Zone (early late Kimmeridgian), associated with enhanced planktonic palaeoproductivity and/or developing dysoxia/anoxia. Similar organic rich intervals in early late Kimmeridgian are also evidenced in platformdeposits in Normandy and Charentes in France, and in basinal deposits from Yorkshire and Dorset in UK. This refined onset of the organic rich bands (ORB), as described in NW Europe during the late Jurassic, is coeval with seawater warming. We propose that this seawater warming was an important trigger of the onset of the late Jurassic ORB deposition system in NW Europe, which began at the Cymodoce-Mutabilis boundary during the early late Kimmeridgian and lasted until the middle part of the Tithonian, over a time span of 6.8Myr.

Automated summary

This study characterized the organic matter content of marine deposits at the Oxfordian-Kimmeridgian transition in the Boulonnais region of France. The results showed that there were organic-rich deposits in platform environments during the early late Kimmeridgian period, which were associated with enhanced planktonic productivity and/or developing dysoxia/anoxia. Similar organic-rich intervals were also observed in platform deposits in Normandy and Charentes in France, as well as in basinal deposits from Yorkshire and Dorset in the UK. The study suggested that the onset of the late Jurassic organic-rich bands (ORB) in NW Europe was triggered by seawater warming.