EARLY JURASSIC EARTH SYSTEM AND TIMESCALE (JET): MOCHRAS (WALES) COREHOLE

The Mochras Hole A core (1967-1969) recovered 1.3 km of Lower Jurassic marine mudstones at Llanbedr (Mochras Farm) on the margin of Cardigan Bay, Wales. Sediments in the Mochras Farm core were deposited in the newly evolving Atlantic Ocean when the world was experiencing changes between greenhouse and icehouse conditions leading to sea level rise and fall, and punctuated by global carbon cycle perturbations and oceanic anoxia. Hole A is biostratigraphically complete but has been heavily sampled and the core has degraded over time. We see an opportunity to study the sequence stratigraphy of these sediments and to develop a high resolution water depth curve. We have been funded by ICDP and NERC to drill a new core designated Hole B that will be used to analyze Early Jurassic sea-level change and understand its relationship to icehouse-greenhouse transitions. Preliminary results from Hole A are encouraging: 1) sedimentation was rapid (5-8 cm/kyr), apparently continuous, and displays a cyclicity that can be used for orbital time control; 2) values of δ¹³C_org and ^δ13C_carb show distinct minima in the H. falciferum Zone associated with the Toarcian Ocean Anoxic Event (TOA); 3) benthic foraminiferal biofacies show that the TOA was a maximum flooding event, with biofacies shallowing upward in the remaining Toarcian; 4) sequence boundaries are subdued in these mudrocks, but can be correlated with those inferred from shallower sections in the Cleveland Basin and confirmed with benthic foraminiferal biofacies in Hole A. Future work on Hole B will included detailed benthic foraminiferal, ostracod, and sortable silt studies to elucidate paleowater trends, sequences, and flooding surfaces.