Oxygen‐restricted facies of the basal Jurassic of North West Europe

Abstract

Events across the Triassic‐Jurassic boundary are a matter of great interest because this marks the time of one of the five biggest marine mass extinctions in the Phanerozoic. Some of the best sections across the boundary are in north west Europe; attention here is focussed on the basal Jurassic. Sedimentological and palaeoecological study has been undertaken of a number of sections in England and Germany, most of them borehole cores, and indicate a range of oxygen‐restricted facies, signifying episodic fluctuations between anoxic and dysoxic conditions. Analysis of the Th/U ratio in the coastal outcrop of St. Audrie's, Somerset, confirms this interpretation. The Triassic‐Jurassic boundary in north west Europe is characterised by a regression‐transgression couplet, with the corresponding sea‐level change being quite possibly of short duration.

Key words:

• Oxygen‐restricted facies
• Jurassic
• Europe