No abstract

The causes and duration of the early Toarcian anoxic event are controversial. Integration of data from calcareous and organic phytoplankton provides a biochronological framework that allows precise correlations across the western Tethys. In particular, the Carinolithus superbus nannofossil Zone can be used to correlate the levels enriched in organic matter and the related δ 13 C negative excursion. Although a variable duration is given in the literature for this negative excursion, it is likely that it lasted between 520 and 650 ka. Increased atmospheric p CO 2 , related to excess volcanic emissions (magmatic activity in the Karoo and Ferrar Provinces), had an impact on climate and ocean chemistry, and marked the inception of a biotic crisis affecting many organisms. The beginning of the crisis within shallow carbonate platforms, documented at southern latitudes, predates the levels enriched in organic matter. Dinoflagellate cysts experienced a decrease in abundance in the C. superbus Zone, until they temporarily disappeared. The nannoplankton crisis was twofold: a decrease in size and low calcified specimens are observed in addition to a drastic decrease in absolute abundance. The increased atmospheric p CO 2 , as a result of the magmatic activity and temporarily amplified by transient methane release, could have been the trigger for the biocalcification crisis, which first affected the probably more reactive neritic system, and eventually the nannoplankton community.

The Upper Permian and Triassic sequences of the NW Caucasus present a good record of the Cimmerian events, rather undisturbed by the subsequent Alpine deformations. Original field work with new fossil identifications, microfacies analysis, and sandstone petrography were carried out. During the late Permian, active strike-slip basins were filled by continental clastics successions. Marine ingressions during the latest Permian, led to the formation of sponge reefs and skeletal carbonate ramps. During the Triassic, several siliciclastic wedges were intercalated within the marine carbonate succession. Most important is a conglomerate body made up of serpentinite pebbles of Spathian age (early Triassic), recording the exhumation and erosion of schistose antigorite serpentinites. By the late Anisian a severe deformation affected the Peredovoy (= Fore) Range of the NW Caucasus. Lower Triassic to Anisian sediments deformed also in chevron folds were overlaid with angular unconformity by a siliciclastic, and also volcaniclastic, conglomeratic and arenitic body, up to several hundred meters thick. By the late Ladinian-earliest Carnian, marine sedimentation resumed locally, forming a carbonate ramp during part of the Norian. Towards the end of the Norian, the entire area emerged and was again mildly tilted. The subsequent post-Cimmerian transgression occurred largely during the Middle Jurassic. Consequently, the most important Cimmerian deformations appear to be of early and middle Triassic age.

SUMMARY A palynological investigation of the Lower and lowermost Middle Jurassic (Sinemurian to Aalenian) strata of North Yorkshire has been undertaken which incorporates material from the BGS Brown Moor Borehole, near Acklam and the coastal outcrops between Staithes and Robin Hood’s Bay. The resulting dataset is an additional contribution to the Jurassic dinoflagellate cyst biostratigraphy of northern England. Two distinctive variants of Liasidium variabile appear to have biostratigraphical significance in the Upper Sinemurian of North Yorkshire. Specimens of L. variabile from the Caenisites turneri Ammonite Zone, the Eparietites denotatus Ammonite Subzone and the Oxynoticeras simpsoni Ammonite Subzone have short apical and antapical horns. Forms from the overlying uppermost Oxynoticeras oxynotum Ammonite Zone, however, are characterized by elongate apical horns and rounded hypocysts. The regional dinoflagellate cyst diversity increase in the late Pliensbachian and the disappearance of many dinoflagellate cysts in the Lower Toarcian are both interpreted as being related to eustatic fluctuations. The paucity of dinoflagellate cysts close to the Dactylioceras tenuicostatum-Harpoceras falciferum Ammonite zonal transition in the Lower Toarcian was caused by the spread of widespread marine anoxia during the Lower Toarcian maximum flooding event. A new species of dinoflagellate cyst, Nannoceratopsis symmetrica , is described.

~ The recent description of Umhriudiniurn rnediterraneense Bucefalo Palliani & Riding 1997 from the Early Jurassic of central Italy and Greece has provided new information on the phylogeny of the dinoflagellate cyst Family Suessiaceae. On the basis of the morphology of the five suessiacean genera, a subdivision of the family into two new subfamilies is proposed. These are the Late Triassic Suessioideae and the Early Jurassic Umbriadinoideae. The evolution of the Family Suessiaceae is related to the evolution of scleractinian corals, largely on the basis of the similarity of their evolutionary patterns and geographical palaeodistributions.