Abstract Geochemical and palaeontological methods are used to determine the oxygenation histories of Jurassic sequences at Ravenscar, North Yorkshire, and Lyme Regis, Dorset. The ichnology of these sequences is compared with interpreted oxygen levels, allowing current models of oxygen-related trace fossil occurrence to be tested. These case studies support pre-existing models of trace fossil occurrence in demonstrating that burrow diversity, diameters and depth of infaunal tiering increase with increasing oxygen levels. The case studies suggest that trace fossil ethologies may not always be a reliable indicator of palaeo-oxygenation: in some cases, substrate consistency may have a greater influence over ethology than oxygen levels. Chondrites is confirmed as a common constituent of dysoxic settings; however, other trace types may also be indicative of such settings.

Abstract During the early Toarcian, black-shale deposition was widespread, and several different models have been proposed to explain environmental conditions and controlling factors. Multidisciplinary investigations combining microfacies analysis, geochemical parameters, and paleoecological data reveal that sea-level variation was the main forcing factor for facies distribution within the Central European Basin. This interpretation is supported by the comparison of several Lower Toarcian sections from Europe. The results show that a Pliensbachian to early Toarcian regression caused the enclosure of the SW German basin, inducing stagnant conditions. Deposition of organic-matter-rich sediments started in the central part of the basin while contemporaneous sediments in basin-margin areas were affected by reworking. The subsequent slow transgression was of minor extent and led to long-term stagnation, which led to anoxic conditions in the benthic environment. Maximum oxygen depletion existed during the exaratum Subzone times and is indicated by largest fecal pellet sizes, a distinct type of lamination, highest content of organic carbon and sulfur, and a lack of paleocurrents and benthic macrofauna. Enhanced water circulation and improved living conditions in the benthic environment could not have been established until a further sea-level rise. Consequently, the bituminous mudstones of the European Epicontinental Sea were not deposited during a Liassic sea-level maximum.

Abstract The Hispanic Corridor is a postulated marine seaway linking the eastern Pacific and western Tethyan oceans as early as Early Jurassic times. Two existing hypotheses relate the Pliensbachian-Toarcian bivalve extinction and recovery to immigration of bivalve species through the Hispanic Corridor. The extinction hypothesis implies that, in South America, the Pliensbachian-Toarcian extinction can be partly explained by the immigration of bivalves through the Hispanic Corridor and subsequent competitive replacement. The recovery hypothesis states that, in NW Europe, the renewed rise in diversity in the late Toarcian/Aalenian was largely a consequence of immigration of taxa from Andean South America via the Hispanic Corridor. To test these hypotheses, I calculated immigration and origination rates of bivalves per million years. In both regions, early Pliensbachian to Aalenian immigration rates remained at low levels, thus disproving both hypotheses. By comparison, the origination of new species generally played a much more important role than immigration in controlling overall diversity of both regions. Future research should investigate if this is a more general pattern in the recovery of post-extinction biotas. The apparently global Pliensbachian-Toarcian diversity crisis may be best explained by a combination of physicochemical factors, invoking intense volcanism, sea-level highstand and widespread anoxia, as well as biological factors. Recovery from this mass extinction commenced when origination rates increased again, which, in the Andean basins, was in the Aalenian and in NW Europe, the late Toarcian.