Integrated Understanding of the Early Jurassic Earth System and Timescale (JET)

点击翻译按钮获取中文摘要

We propose a large-scale, multi-faceted, international programme of research on the functioning of the Earth system at a key juncture in its history - the Early Jurassic. At that time the planet was subject to distinctive tectonic, magmatic, and solar system orbital forcing, and fundamental aspects of the modern biosphere were becoming established in the aftermath of the end-Permian and end-Triassic mass extinctions. Breakup of the supercontinent Pangaea was accompanied by creation of seaways, emplacement of large igneous provinces, and occurrence of biogeochemical disturbances, including the largest magnitude perturbation of the carbon-cycle in the last 200 Myr, at the same time as oceans became oxygen deficient. Continued environmental perturbation played a role in the recovery from the end-Triassic mass extinction, in the rise of modern phytoplankton, in preventing recovery of the pre-existing marine fauna, and in catalysing a 'Mesozoic Marine Revolution'. However, existing knowledge is based on scattered and discontinuous stratigraphic datasets, meaning that correlation errors (i.e. mismatch between datasets from different locations) confound attempts to infer temporal trends and causal relationships, leaving us without a quantitative process-based understanding of Early Jurassic Earth system dynamics.This proposal aims to address this fundamental gap in knowledge via a combined observational and modelling approach, based on a stratigraphic 'master record' accurately pinned to a robust geological timescale, integrated with an accurate palaeoclimatic, palaeoceanographic and biogeochemical modelling framework. The project has already received $1.5M from the International Continental Drilling Programme towards drilling a deep borehole at Mochras, West Wales, to recover a new 1.3-km-long core, representing an exceptionally expanded and complete 27 My sedimentary archive of Early Jurassic Earth history. This core will allow investigation of the Earth system at a scale and resolution hitherto only attempted for the last 65 million years (i.e. archive sedimentation rate = 5 cm/ky or 20 y/mm). We will use the new record together with existing data and an integrative modelling approach to produce a step-change in understanding of Jurassic time scale and Earth system dynamics.In addition to order of magnitude improvements in timescale precision, we will: distinguish astronomically forced from non-astronomically forced changes in the palaeoenvironment; use coupled atmosphere-ocean general circulation models to understand controls on the climate system and ocean circulation regime; understand the history of relationships between astronomically forced cyclic variation in environmental parameters at timescales ranging from 20 kyr to 8 Myr, and link to specific aspects of forcing relating to solar energy received; use estimated rates and timing of environmental change to test postulated forcing mechanisms, especially from known geological events; constrain the sequence of triggers and feedbacks that control the initiation, evolution, and recovery from the carbon cycle perturbation events, and; use Earth system models to test hypotheses for the origins 'icehouse' conditions. Thirty six project partners from 13 countries substantially augment and extend the UK-based research