Integrated sediment transport and provenance in Mesozoic environments: evidence from the Lower Jurassic, UK

Mesozoic OAEs, which are well evidenced by the significant occurrence of black shale, multiple large isotopic anomalies, and global sea-level change, have been extensively studied in sedimentary successions in Europe that were laid down in shallow marine environments. Very good chemostratigraphic and biostratigraphic control for this region allows for high resolution, super-regional, correlation of successions and assessing potential causes and expressions of OAEs in these environments. However, the understanding of the sedimentary structures, lithologies, depositional processes and provenance has barely improved since these events were first identified on the basis of their organic carbon rich nature. For the purposes of the study of sediment provenance and transportation mechanisms during the Early Jurassic - which may also put constraints on the palaeogeography, hydrological cycle, and consequently weathering and runoff conditions - an integrated stratigraphic analysis of mudrock is being carried out on a major Early Jurassic succession, the Mochras borehole (Cardigan Bay Basin, UK). To obtain a comprehensive understanding of sediment provenance and how these different processes interacted to produce the various rocks, it is important to interrogate sedimentary features from the macro-scale (e.g. color, bed and lamina thickness, depositional structures) to the micro-scale (e.g. mineral composition, grain-size variability, diagenetic textures) which requires accurate and more detailed description of mudrock. Based on sequence stratigraphy, with the constraints of magnetostratigraphy, and combined with complementary geochemical data (e.g. XRF, C, O, Sr isotopes), a comprehensive dataset is currently being generated. In addition, data from a planned new borehole from the Cheshire Basin, at Prees, UK, recovering the lower part of the Jurassic, will provide a complementary sediment record. The detailed geochemical analysis of mineralogy and petrology of mudrocks from Pliensbachian will be presented.