Abstract This study focuses on a condensed sequence of alternating carbonate–clastic sediments of the Barrington Member, Beacon Limestone Formation (latest Pliensbachian to early Toarcian) from Somerset (SW England). Abundant ammonites confirm (apart from the absence of the Clevelandicum and Tenuicostatum ammonite subchronozones) the presence of Hawskerense Subchronozone to Fallaciosum–Bingmanni subchronozones. Well-preserved, sometimes diverse assemblages of ostracods, foraminifera, nannofossils and low-diversity dinoflagellate assemblages support the chronostratigraphic framework. Stable-isotope analyses demonstrate the presence of a carbon isotope excursion, relating to the Toarcian Oceanic Anoxic Event, within the early Toarcian. Faunal, geochemical and sedimentological evidence suggest that deposition largely took place in a relatively deep-water (subwave base), mid-outer shelf environment under a well-mixed water column. However, reduced benthic diversity, the presence of weakly laminated sediments and changes in microplankton assemblage composition within the Toarcian Oceanic Anoxic Event indicates dysoxic, but probably never anoxic, bottom-water conditions during this event. The onset of the carbon isotope excursion coincides with extinction in the nannofossils and benthos, including the disappearance of the ostracod suborder Metacopina. Faunal evidence indicates connectivity with the Mediterranean region, not previously recorded for the UK during the early Toarcian.

Abstract A large submarine-slide deposit from the western Scotian Slope off eastern Canada was imaged on a 3D seismic reflection dataset in the Barrington exploration block. The mass-transport deposit (MTD) forms a tongue-shaped body that is 25 km long and 8 km wide, with a run-out distance from the headscarp of 41.5 km and a total volume of 12.5 km 3 . In profile, it consists of a chaotic seismic facies. This facies forms a highly rugose top surface morphology, suggesting that the flow consisted of an abundance of intact angular blocks. Its base reveals evidence of erosion typical of submarine MTDs, with linear downslope-trending gouges and excavation of a pit 50-m-deep. The source area and headscarp of the Barrington MTD are somewhat obscured by postdepositional erosion. Additionally, high-resolution seismic profiles show that the deposit is draped by approximately 30 m of late Pleistocene and Holocene sediment, providing an age estimate of 30 ka for the failure. Despite this drape, the modern seafloor above the MTD still has a highly rugose morphology, echoing the top surface of the deposit. Seismic profile data show a series of stacked MTDs underlying the Barrington MTD, suggesting that mass-failure recurrence is common on geologic time scales. Although it is difficult to attribute mass-failure triggering mechanisms, high sedimentation rates due to proximal shelf glaciers and intense erosion causing oversteepening, and likely established preconditions for instability. Local seismicity, possibly a result of glacial rebound, is the most probable initiating factor.