Abstract This contribution is an overview of the Early Jurassic dinoflagellate cysts of the Lusitanian Basin in Portugal, with particular emphasis on the effects of the Jenkyns Event (Toarcian Oceanic Anoxic Event) on the evolution of this planktonic group. We review and discuss data from 214 samples from six Lower Jurassic successions (upper Sinemurian to upper Toarcian) in the Lusitanian Basin. The late Pliensbachian radiation of dinoflagellate cysts was well recognized in this basin. The pre-Jenkyns Event interval is highly productive, with maximum abundance and species richness values. However, this palaeoenvironmental perturbation severely affected the evolution of this group for the remainder of the Early Jurassic. The prolonged recovery of the dinoflagellates in the Toarcian following the Jenkyns Event is not typical of the northern regions (Arctic and Boreal realms), where new species began to evolve earlier compared with southern European basins.

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 At the beginning of the Jurassic period, southern European areas formed a single continental mass open to the east (western Tethys), and the Iberian plate lay between latitude 25°N and 35°N. It was separated from the larger European plate to the north by a narrow trough corresponding to the early rifting of the Bay of Biscay. To the NW it was separated from the Laurentia–Greenland Plate by an epicontinental sea showing a typical horst and graben structure, which would eventually become the palaeogeographical connection between the northern and central Atlantic. The opening of the Bay of Biscay took place between latest Jurassic and early Campanian times, giving rise to SE-directed movement and anti-clockwise rotation of the Iberian plate (e.g. Ziegler 1988 b ; Osete et al . 2000 ). Jurassic palaeogeography was characterized by a large part of the central and western Iberian plate forming an emergent massif (the so-called Iberian Massif), whilst the surrounding areas were occupied by intracratonic basins that formed shallow epicontinental seas, predominantly filled with marine carbonate deposits (Fig. 11.1 ). Those areas, located to the north and NE of the Iberian Massif, correspond from west to east to Asturias, the Basque-Cantabrian basin, and the South Pyrenean basin. To the east extended the Iberian basin, whereas the southern margin of the Iberian Massif was occupied by a wide carbonate platform parallel to a narrow oceanic trough connecting Tethys with the central Atlantic Ocean. These areas together comprised the south Iberian margin basin, whose proximal