We present a high-resolution analysis of planktonic foraminifers, calcareous nannofossils, ostracods, dinoflagellate cysts and pollen grains in four sequences from DSDP-ODP holes in the southwestern Mediterranean Alboran and Balearic basins (976B, 977A, 978A and 134B) encompassing the previously defined Messinian-Zanclean boundary.The study focuses on (1) the marine reflooding, which closed the Messinian Salinity Crisis prior to the Zanclean GSSP; (2) the nature of the Lago Mare in the deep basins (indicated by Paratethyan dinoflagellate cysts), which appears to comprise several Paratethyan influxes without climatic control; and (3) the depositional context of the youngest Messinian evaporites which accumulated in a marine environment relatively close to the palaeoshoreline. Isolation of the Aegean Basin during the paroxysmic second step of the crisis is considered to have stored Paratethyan waters, which may then have poured into the Mediterranean central basins after deposition of the evaporitic sequence.

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Oligo-Miocene (‘Maikopian’) deposits are considered the main source rocks in the Black Sea area, although only a few source-rock data are available. Geochemical logs from nine wells are used together with age constraints provided by calcareous nannoplankton, well and seismic data to determine vertical and lateral changes of the source potential. Oligocene rocks overlie Eocene deposits with a major unconformity on the western Black Sea shelf in Bulgaria. A west–east-trending erosional structure (the Kaliakra canyon) developed during Lower Oligocene time and was filled with Oligo-Miocene deposits. Potential source rocks are present in different stratigraphic units, but the most prolific intervals accumulated during time intervals when the isolation of the Paratethys resulted in oxygen-depleted, brackish environments with high bioproductivity. These include Lower Solenovian rocks related to blooms of calcareous nannoplankton, which form an extensive layer outside the Kaliakra canyon. This unit hosts a good potential to generate oil and gas. Diatom-rich, very good oil-prone source rocks accumulated during a second isolation event in the Kozakhurian. Thick sections of these diatom-rich rocks occur within the canyon and are present in thin layers outside of it. High productivity of siliceous organisms is attributed to upwelling within the canyon. All studied units are thermally immature on the shelf.

Permo-Triassic basins, both onshore and offshore UK, typically have good reservoir rocks and frequently good seals, but their continental depositional environment requires that source beds of a different age must be invoked if they are to be prospective. In the Dorset-English Channel Basin, the overlying Liassic shales provide an oil prone source, while in the Southern Gas Basin of the North Sea and the East Irish Sea, the underlying Carboniferous has generated large volumes of gas and some oil. Other Permo-Triassic basins, onshore, are generally devoid of hydrocarbons and this can in large part be explained by an absence of an adequate source rock. The Cheshire Basin lies adjacent to the East Irish Sea Basin and contains a similar, thick Permo-Triassic sequence. The presence of outcropping Coal Measures on three sides of the Basin gives encouragement as to sourcing potential. However, the six exploration wells drilled in the Basin to date (four during the last ten years) have proved dry. Review of recent seismic data, particularly mid-late 1980s vibroseis surveys, suggests that the Basin developed as a Permo-Triassic half-graben over a Hercynian inversion. Therefore, as one moves from the western edge towards the basin centre progressive erosion of Westphalian strata below the base Permian event may be observed, culminating in a likely Lower Palaeozoic subcrop in the southeastern part of the Basin. A large, faulted high in the centre of the Basin, in many ways similar to the Morecambe Field structure, was proven dry by the Burford-1 well, apparently due to an absence of an underlying source. Nevertheless, seismic data in the northern part of the Basin, supported by the Knutsford-1 penetration, suggest the presence of underlying Coal Measures. However, regional projections suggest that the thick, Dinantian-Namurian bituminous shales which appear to have sourced the East Irish Sea fields, are absent from much of the Basin. A further difference between the Cheshire and East Irish Sea Basins is the presence, in the former, of the Tarporley ‘Siltstone’ Formation above the main reservoir objective of the Helsby Sandstone Formation. The former may be regarded as a likely non-sealing waste zone over much of the central and eastern parts of the Basin, but in the SW where the coarser Malpas Sandstone facies is developed, and in the north, it becomes a viable reservoir target in its own right, sealed by the Bollin Mudstone Formation and, ultimately, by the Northwich Halite. It is therefore proposed that the successful exploration for hydrocarbons in the Basin is likely to depend on finding a combination of sub-cropping Coal Measures and reservoir-grade Tarporley Siltstone, sufficiently deeply buried to retain an effective Mercia Mudstone and preferably halite seal. These conditions appear to prevail in the NW part of the Basin, where the search for suitably large, closed structures is currently in progress.

Compared with the prolific success of the Triassic play in the East Irish Sea Basin (EISB) the lack of hydrocarbon discovery in neighbouring Permo-Triassic basins of the Irish Sea has been an enigma. However, recent exploration of the Peel, Solway and Central Irish Sea basins has provided new insights into the geology of these basins and the controls upon hydrocarbon prospectivity in the Irish Sea area. Regional seismic interpretation suggests that 12 of the 15 exploration wells drilled in the basins adjacent to the EISB tested valid structural closures at top Triassic reservoir level. Re-evaluation of the Irish Sea petrolemn system reveals that, although effective reservoirs occur in the Lower-Middle Triassic Ormskirk Sandstone Formation, and evaporites in the Middle-Upper Triassic Mercia Mudstone Group provide a regional top seal, the major factor controlling hydrocarbon prospectivity is the limited presence of effective source rocks in the underlying Carboniferous section. A further control upon prospectivity is the timing of hydrocarbon migration, from those areas where Carboniferous source rocks were deposited and preserved. The Namurian basinal marine oil-and gas-prone shales, which form the principal source of hydrocarbons for the Triassic play in the EISB, are restricted to an east-west fairway extending from the EISB into the Kish Bank Basin. Rocks of this age are absent from the Peel and Solway basins as a result of Variscan uplift and erosion. However, palaeogeographical reconstructions based on well and outcrop data suggest that, even if preserved, the depositional environment was not conducive to the formation of marine oiland gas-prone source rocks. Well and seismic data suggest that rocks of Namurian age were not deposited in the Central