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The uppermost Triassic to Lower Jurassic interval has not been extensively studied across the island of Ireland. This paper seeks to redress that situation and presents a synthesis of records of the uppermost Triassic and Lower Jurassic from both onshore and offshore basins as well as describing the sedimentological characteristics of the main lithostratigraphical units encountered. Existing data have been supplemented with a re-examination and logging of some outcrops and the integration of data from recent hydrocarbon exploration wells and boreholes. The Late Triassic Penarth Group and Early Jurassic Lias Group can be recognised across the Republic of Ireland and Northern Ireland. In some onshore basins, almost 600 m of strata are recorded, however in offshore basins thicknesses in excess of two kilometres for the Lower Jurassic have now been recognised, although little detailed information is currently available. The transition from the Triassic to the Jurassic was a period of marked global sea-level rise and climatic change (warming) and this is reflected in the lithostratigraphical record of these sediments in the basins of Northern Ireland and offshore basins of the Republic of Ireland. In general, the sediments of this interval are thicker than those in Great Britain and have potential for detailed study of climatic and sea-level fluctuation.

The Tonian-Cryogenian System boundary is to be defined at a GSSP (Global Boundary Stratigraphic Section and Point) beneath the first evidence of widespread glaciation. A candidate lies within the Dalradian Supergroup of Scotland and Ireland, which is least deformed and metamorphosed in Argyll, western Scotland. We present new stratigraphic profiles and interpretations from the Isle of Islay and the Garvellach Islands, update the chemostratigraphy of the Appin Group Tonian carbonates underlying the thick (ca. 1 km) glacigenic Port Askaig Formation (PAF) and demonstrate an environmental transition at the contact. The Appin Group forms a regionally extensive, >4 km-thick, succession of limestones, shales and sandstones deposited on a marine shelf. On Islay, the upper part of the lithostratigraphy has been clarified by measuring and correlating two sections containing distinctive stratigraphic levels including molar tooth structure, oolite, stromatolitic dolomite and intraclastic microbial mounds. Significantly deeper erosion at the unconformity at the base of the overlying PAF is demonstrated in the southern section. Carbonate facies show a gradual decline in δ 13 C VPDB from +5 to +2‰ upwards. In NE Garbh Eileach (Garvellach Islands), a continuously exposed section of Appin Group carbonates, 70 m thick, here designated the Garbh Eileach Formation (GEF), lies conformably beneath the PAF. The GEF and the GEF-PAF boundary relationships are re-described with new sedimentological logs, petrological and stable isotope data. Interstratified limestone and dolomicrosparite with δ 13 C of −4 to −7‰ (a feature named the Garvellach anomaly , replacing the term Islay anomaly ) are overlain by dolomite in which the isotope signature becomes weakly positive (up to +1‰) upwards. Shallow subtidal conditions become peritidal upwards, with evidence of wave and storm activity. Gypsum pseudomorphs and subaerial exposure surfaces are common near the top of the GEF. The basal diamictite (D1) of the PAF is rich in carbonate clasts similar to slightly deeper-water parts of the underlying succession. D1 is typically several metres thick with interstratified sandstone and conglomerate, but dies out laterally. Scattered siliciclastic coarse sandstone to pebble conglomerate with dropstones associated with soft-sediment deformation is interbedded with carbonate below and above D1. Dolomite beds with derived intraclasts and gypsum pseudomorphs are found above D1 (or equivalent position, where D1 is absent). Published and new Sr isotope studies, including successive leach data, demonstrate primary Tonian 87 Sr/ 86 Sr values of 0.7066–0.7069 on Islay, decreasing to 0.7064–0.7066 in the younger GEF limestones on the Garvellachs, with 1700–2700 ppm Sr. Other typically Tonian characteristics of the carbonates are the Sr-rich nature of limestones, molar tooth structure, and dolomitized peritidal facies with evidence of aridity. Seabed surveys suggesting uniformly-dipping strata and shallow borehole core material illustrate the potential for extending the Tonian record offshore of the Garvellachs. A candidate Tonian-Cryogenian GSSP is proposed on Garbh Eileach within the smooth δ 13 C profile at the cross-over to positive δ 13 C signatures, 4 m below the first occurrence of ice-rafted sediment and 9 m below the first diamictite. Although lacking radiometric constraints or stratigraphically significant biotas or biomarkers, the Scottish succession has a thick and relatively complete sedimentary record of glaciation, coherent carbon and strontium chemostratigraphy, lateral continuity of outcrops and 100% exposure at the proposed boundary interval.

The late Quaternary to Recent Ostracoda of the Ponto-Caspian region, defined here as the Aral, Caspian and Black seas, play a fundamental role in our understanding of the geological and hydrological evolution of these three large water bodies. Together with sedimentological and geochemical records, the ostracods provide evidence for both natural (climate-influenced) and man-made environmental change. All three seas possess ostracod faunas that are closely related, the Caspian and Black Sea elements are probably isolated remnants of the late Neogene Paratethys fauna while the Aral Sea comprises a much younger fauna introduced from the basins to the east.

We review the utility of ostracods for palaeoclimatic reconstruction at different taxonomic levels. Ostracods can provide palaeoenvironmental information based on several approaches. The chemical and isotopic composition of their mineral shells as well as the relatively minor organic component trapped within the carbonate lattice may give direct quantitative evidence of conditions in their natural habitat. Morphological observations and detailed morphometric records of valve size, shape and outline within a species may provide subtle clues to environmental changes between different habitats or adjacent stratigraphic intervals. Uniformitarian approaches can be applied to species, genera and supra-generic classifications but with decreasing resolution and increasing uncertainty in palaeoenvironmental significance (1) the higher the taxonomic unit and (2) the older the material geologically. The classical methodology of combining the habitat and environmental preferences of individual species to infer palaeoclimatic conditions remains as valid today as when such observations were first made in the nineteenth century.