S2: The Jet Project

Integrated Early Jurassic Earth System and Timescale from legacy cores and a new stratigraphic borehole at Prees, UK

Stephen Hesselbo,
University of Exeter, UK

Web Lecture on January 12,  2021 at 3:00 PM (Paris Time)

The JET project is an international team-effort to produce a step change in the quality of the timescale for the Early Jurassic and to use this to understand the forcing factors for environmental changes during this key chapter in the development of the modern Earth system.  The project stems from the realisation that hemi-pelagic mudrock successions in and around the British Isles provide the basis for constructing a continuous astrochronology, biostratigraphy, magnetostratigraphy, chemostratigraphy, and even radioisotopic geochronology, all from the same strata.  The potential of these successions is partly historical, in that much of the pioneering work on Early Jurassic stratigraphy was carried out from the nineteenth century onwards on the coastal exposures of marine strata such as those at Lyme Regis, Watchet, and Robin Hood’s Bay, which has led to boundary stratotypes and biostratigraphic zonations being defined in such locations.  In addition, deep cored boreholes drilled in the in the 1960’s and 1970’s provide access to continuous unweathered samples ranging through most of this interval of time.  These legacy cores and outcrops, however, also have to be supplemented by recovery of new core, and a continuously cored borehole was drilled at Prees, Cheshire Basin, UK, during November and December 2020 supported financially by the International Continental Scientific Drilling Programme (ICDP), the UK Natural Environment Research Council (NERC), the Deutsche Forschungsgemeinschaft (DFG) and the Leibniz Institute for Applied Geophysics (LIAG).  In this talk I will summarise the progress made to date, highlighting recent results from work on the Llanbedr (Mochras Farm), Burton Row, and other legacy cores, and outlining the initial outcomes of new coring at Prees.  One of the emerging themes is the necessity to integrate sedimentological and biostratigraphic analysis to construct a stable astrochronological age model.