Abstract Quantitative analysis performed on latest Pliensbachian–early Toarcian calcareous nannofossil assemblages from the Camino section (Basque Cantabrian Basin) allowed their response to the environmental changes recorded during this time interval to be deciphered, characterized by an extinction event. The results were introduced within a principal component analysis and compared with the stable isotope and total organic carbon curves. During the latest Pliensbachian, the Mirabile and the lowermost part of the Semicelatum Ammonite Subzones, Schizosphaerella , Bussonius prinsii , Biscutum finchii , Calcivascularis jansae and Similiscutum avitum , taxa that probably thrived in rather cold waters, dominated the calcareous nannofossil assemblages. Coinciding with warmer and wetter conditions, which probably led to an increase in surface water fertility, recorded slightly below the extinction boundary, the mesotrophic taxa B. novum , L. hauffii and Calyculus spp. were dominant. Nevertheless, T. patulus and C. jansae , which became extinct just below the extinction boundary, show preferences for oligotrophic conditions. Salinities similar to those of modern oceans have been inferred around the extinction boundary, considering the coupling between the abundances of Calyculus spp. and the species richness together with the absence of black shales. After the extinction boundary, nannofossil assemblages were dominated by the deep-dwelling C. crassus and the shallow-dwelling Lotharingius species, interpreted as opportunistic taxa. This work confirms that calcareous nannofossils are a really useful tool for palaeoceanographic and palaeoenvironmental reconstructions, especially in terms of climatic changes.

Abstract In this paper, we present a detailed review of upper Pliensbachian–lower Toarcian kerogen assemblages from the southern areas of the West Tethys shelf (between Morocco and northern Spain) and demonstrate the use of the Phytoclast Group as a tracer of palaeoenvironmental changes in the early Toarcian. The kerogen assemblages in the studied sections from the southern areas of the West Tethys shelf are dominated by the Phytoclast Group and terrestrial palynomorphs, although punctual increases in amorphous organic matter, freshwater ( Botryococcus ) and marine microplankton (dinoflagellate cysts, acritarchs and prasinophyte algae) were observed at specific stratigraphic intervals. The opaque/non-opaque phytoclasts ratio was used to trace changes in palaeoclimate and other palaeoenvironmental parameters and reflect climate gradients associated with water availability during early Toarcian. During the Pliensbachian–Toarcian and Jenkyns events, changes in kerogen assemblages in the southern areas of the West Tethys shelf correlated with changes in the northern Tethys and Panthalassa shelf. The acceleration of the hydrological cycle associated with the aforementioned events was less intense in the northern Gondwana, southern and western Iberian basins, a reflection of the palaeogeographic position of these basins within the semi-arid climate belt when compared with the northern Iberian region and other northern areas of the West Tethys and Panthalassa shelf, inserted in winter-wet and warm temperate climate belts. Amorphous organic matter enrichment associated with the Pliensbachian–Toarcian and Jenkyns events reflects an increase in primary productivity linked with increased continental weathering, fluvial runoff and riverine organic matter, and nutrient input into marine areas, inducing water column stratification and promoting the preservation of organic matter.

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