Abstract Detailed logging ofkey outcrops and boreholes in the mainly nearshore and marginalmarine sediments of the Colwell Bay Member has enabled regional correlations to be established. The Colwell Bay Member comprises a single depositional sequence, based by a combined sequence boundary and transgressive surface and terminated by a second sequence boundary. Regionally developed omission surfaces delimit five parasequences within the Colwell Bay Member. Environmentally controlled mollusc assemblages indicate progressive SW-to-NE progradation of marginal-marine environments within each parasequence. Previous interpretations of the Solent Group as deposited in a narrow embayment of the proto-English Channel are evaluated and rejected. It is interpreted as a remnant of a wide area of coastal and near-coastal sediments, deposited in a wide embayment of the southern North Sea Basin, now largely removed by mid-Tertiary uplift and erosion.

The dominantly nonmarine Solent Group of the Hampshire Basin, southern England, spans the Late Eocene and earliest Oligocene. It contains a rich biota, including mammals and charophytes, but contains few fully marine, time-diagnostic intervals. Correlation with standard marine successions is provided here using bio-stratigraphically significant mammals and charophytes via interdigitation of strata with those containing marine zonal indicators or via magnetostratigraphy in other parts of Europe. This allows the re-identification of recently described normal polarity intervals in the Solent Group to magnetochrons C16n, 15n, 13r1n, and 13n, and improved calibration of the Solent Group to the geomagnetic polarity time scale (GPTS). Consistent with this calibration, interpreted Solent Group sea-level changes can be related to those recognized to be global in deep-marine successions in central Italy. The major sea-level fall associated with polar ice buildup at the Oligocene isotope event Oi-1 near the beginning of the Oligocene is shown to be represented in the Hamstead Member of the Bouldnor Formation by the falling stage systems tract followed by a major hiatus before the next maximum flooding surface. This hiatus encompasses the large European mammalian faunal turnover known as the “Grande Coupure.” Improved calibration to the GPTS allows better dating of climate proxies, such that recently described summer freshwater temperatures can be shown to track global fluctuations across the Eocene-Oligocene transition.

Four different types of paleosols are recognized in the late Eocene–earliest Oligocene Solent Group (Isle of Wight, UK), representing a patchwork of ecosystems. Weakly developed marsh paleosols (Entisol-like; histic Inceptisol-like) are the most common, and there are relatively fewer, slightly elevated Inceptisol-like and Alfisol-like paleosols present as well. The more developed paleosols allow for a quantitative paleoclimatic reconstruction. The Eocene-Oligocene transition is associated globally with the Oi-1 glaciation event. Some nonmarine sequences show long-term cooling and aridification associated with the glaciation. Reconstructed paleoclimatic conditions using Solent Group paleosols do not; instead, they reflect steady mean annual temperatures and gradually increasing mean annual precipitation. This result is consistent with previous evaluations of floral assemblages, which indicate consistent vegetative covering and niche floral elements spanning the Eocene-Oligocene transition. In contrast, there is a significant change in the mammalian faunas found throughout western Europe (Grande Coupure). The evidence for relatively static climatic conditions is not consistent with the scenario of a climatically driven turnover event for the Grande Coupure, although the impact of increased seasonality cannot be ignored.

Abstract The northwest-southeast oriented Hampshire DieppeBasin, approximately 280 km long (Hamblin etal., 1992), is a structural basin formed by Miocene inversion of the underlying Mesozoic Hampshire-DieppeHigh and the adjacent Jurassic-Lower Cretaceous extensional sedimentary basins (Chadwick, 1993; Hibschet al., 1993). The onshore portion in southern England, the Hampshire Basin (Figure 1)/ covers much of the county of Hampshire and extends into the adjacent counties of the Isle of Wight, Dorset, and West Sussex. Its southern boundary is formed by east-west, north youngingmonoclinal folds involving Upper Cretaceousand Paleogene strata, draped over reversed normal faults in Jurassic-Lower Cretaceous strata(Chadwick, 1993). The other boundaries correspond to the Paleogene-Upper Cretaceous (Chalk) junction andwere exposed as a result of post-Miocene erosion. The Paleogene succession (Daley, 1999) was depositedunconformably on weakly folded and eroded Upper Cretaceous (Campanian) Chalk (Melville and Freshney,1982) and subsequently uplifted and deformed duringmid-Paleocene (Laramide) crustal compression (Hamblinet al., 1992). The Paleogene strata dip steeply in the vicinity of the monocline, whereas to the north, dips are shallow in low-amplitude folds. At the beginning of Paleogene time, the British area was some 12 south of its present position (Irving,1967) and considerably warmer than at present (Reidand Chandler, 1933; Daley, 1972). Britain lay on the western margins of what has been called the Northwest European Tertiary Basin (Vinken et al., 1988). At the western end of this basin, the Tertiary North. Sea Basin extended northward between the British and Scandinavian land masses. The present Hampshire(tectonic) Basin was at the southeastern end of this369sedimentary basin. The Paleogene succession here is up to 652m thick (Edwards and Freshney, 1987a) (Figure 2).It begins with upper Paleocene coastal plain sediments and continues with lower to mid-Eocene (Ypresian-Bartonian,NP10-NP17), cyclically alternating marine, nearshore, and coastal plain sediments. Extreme shallowing and possibly subaerial exposure(Edwards and Freshney, 1987b) at the mid-upper Eocene (NP17-NP18) boundary preceded the onset ofpredominantly argillaceous, strongly river-influenced, shallow-marine, laguno-Iacustrine and lacustrine sedimentation(represented by the Solent Group), which continued at least into the early Oligocene (Rupelian,NP23). This major change in sedimentary style signifies the establishment of a better-defined sedimentary basin of unknown extent. The change coincided with gradual uplift of the Weald-Artois axis (coincidentwith the major Midi basement fault), linking extreme southeastern England to northeastern France (Hamblinet al., 1992). As a result of post-Miocene erosion, the middle and upper formations of the three comprising the Solent Group are now confined to the Isle of Wight.