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 We report new ichthyosaur material excavated in lower Toarcian levels of the LafargeHolcim Val d'Azergues quarry in Beaujolais, SE France. A partially articulated skull and a smaller, unprepared but likely subcomplete skeleton preserved in a carbonate concretion are identified as stenopterygiids, a family of wide European distribution during the Early Jurassic. These specimens are among the finest preserved Toarcian exemplars known from Europe and, in one of them, soft tissue preservation is suspected. Their state of preservation is attributed to the combination of prolonged anoxic conditions near the water–sediment interface and early carbonate cementation resulting from the activity of sulfate-reducing bacteria. We also present carbon and strontium isotope values obtained from the study site that allow detailed temporal comparisons with other Toarcian vertebrate-yielding sites and environmental perturbations associated with the Toarcian Oceanic Anoxic Event (T-OAE). These comparisons suggest that the relatively high abundance and good preservation state of Toarcian vertebrates was favoured by a prolonged period of low bottom water oxygenation and accumulation rates. The environmental conditions that prevailed during the T-OAE were probably responsible for the extensive nature of Lagerstätte-type deposits with exceptional preservation of marine organisms. Testing whether the T-OAE had a biological impact on marine vertebrates requires a precise chemostratigraphic context of the fossil record spanning the Pliensbachian–Toarcian interval.

Abstract The Triassic–Middle Jurassic (early Mesozoic) stratigraphy of the Arabian Plate is briefly reviewed with reference to updating the relevant portions of the regional sequence stratigraphic model first published in 2001— Arabian Plate Sequence Stratigraphy . Sedimentary cyclicity is evident within early Mesozoic carbonate, evaporitic, and siliciclastic rocks on the Arabian Plate and permits the recognition of plate-wide, third-order sequences, especially constituent maximum flooding surfaces. These sequences can be constrained by biostratigraphy and other age calibration tools where available, with outcrop and well log correlations permitting the sequences to be interpolated between biostratigraphic control points. New data and concepts published since 2001 enable the regional sequence stratigraphic model to be updated; certain surfaces can be recalibrated in terms of age because of better biostratigraphic constraint or new insight into the sedimentary response to sea-level change. This sequence model enables inter-regional correlation that is difficult using lithostratigraphy alone. Eustasy is considered as an important control on sequence development for the early Mesozoic of Arabia, but the interplay of this with tectonics and climate change is also fundamental to the development of the sedimentary cyclicity observed.