by Stephen Peter Hesselbo

The Early Jurassic Epoch was a time of extreme environmental change. Through this period there are well-documented examples of rapid transitions from cold, or even glacial climates, through to super-greenhouse events, the latter characterized worldwide by hugely enhanced organic carbon burial, multiple large-magnitude isotopic anomalies, global sea-level changes, and mass extinctions. These events not only reflect changes in the global climate system but are also thought to have had significant influence on the evolution of Jurassic marine and terrestrial biota. Furthermore, the events may serve as comparators for present-day and future environmental transitions. Although our knowledge of specific global change events within the Early Jurassic is rapidly improving, a prime case-in-point being the Toarcian Oceanic Anoxic Event (or T-OAE), we have neither documented all the events, nor do we have a comprehensive understanding of their timing, pacing, or triggers. A key factor in our fragmentary knowledge is the discontinuous nature of the existing datasets. The major goal for this proposed ICDP project is therefore to produce a new global standard for these key 27 million years of Earth history by re-drilling a 45 year old borehole at Mochras Farm on the edge of Cardigan Bay, Wales, and developing an integrated timescale and stratigraphy for the cored material. The new datasets will be applied to understand fundamental questions about the long- and short-term evolution of the Earth System. ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ 04-2015 Full Proposal – Addendum November 2018 Executive summary In this addendum we propose a drill site at Prees, in Shropshire, England, as an alternative Mochras, which for logistical and financial reasons has become unviable. The site at Prees lies within the Cheshire Basin in a tectonic and depositional setting that is very similar to Mochras. The Early Jurassic strata at Prees occur between 20 and 615 m below surface, and recovery of the succession will be logistically simpler and less costly than was the case at Mochras. Analysis of a downhole gamma-ray log and cuttings from an oil and gas exploration well drilled at Prees in 1972 indicates that the succession was deposited at comparable sedimentation rates to Mochras and has a similar thermal history. The prospects for astrochronology, microfossil and macrofossil biostratigraphy, chemostratigraphy and magnetostratigrapy are all shown to be good to excellent. Lack of a Toarcian section at Prees is compensated for by the opportunity to core through the Triassic–Jurassic boundary and recover Rhaetian and Norian strata, thus allowing direct linkage to the ICDP supported Colorado Plateau Coring Project. It is anticipated that drilling operations could commence in autumn 2019.

• The principal scientific objectives are as follows:
• To construct the first biostratigraphically-calibrated magnetostratigraphy for the entire 27 Myr-long Early Jurassic based on a single section To generate a high-resolution continuous cyclostratigraphy for the Early Jurassic and associated astronomical time scale allowing insights into Solar System resonance, length-of-day and tidal dissipation To construct a multi-proxy chemostratigraphy to track supercontinent break-up influence on the global Earth system.
• To provide a new record of the Triassic/Jurassic mass extinction and subsequent recovery of the carbon cycle, biosphere and ocean, and effects from CO2 and other volatile releases from the Central Atlantic Magmatic Province.
• To provide insights in to Early Jurassic sea-level change and the greenhouse-icehouse-greenhouse transitions through the Pliensbachian–Toarcian interval.
• To understanding of interdependencies among primary productivity, microbial metabolism, nutrient fluxes and ocean redox state.
• To provide an integrated record of changes in atmospheric and marine composition understood in the context of quantitative whole-Earth system models.
• To provide an order of magnitude improvement in knowledge of Early Jurassic geological time scale through full synthesis of radio-isotopic and chonostratigraphical scales.
• A greatly enhanced knowledge of regional tectonic processes

Earth System, England, Europe, JET, Jurassic, Mochras, PREES, Timescale

Latitude: 52.90000, Longitude: -2.65000