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.

The greenhouse-icehouse change across the Eocene-Oligocene transition and associated Oi-1 glaciation event is the most profound climatic change in Earth’s recent geological history. Marine reconstructions of the Oi-1 glaciation using foraminiferal δ 18 O isotopic compositions suggest that much of the change was associated with Antarctic ice growth rather than climatic change. Nonetheless, some cooling is expected to have occurred on land in addition to drier conditions associated with water tied up in the polar ice caps, and some recent results based on stable isotope analyses of bones support this viewpoint. Nonmarine paleoclimatic conditions (mean annual temperature, mean annual precipitation) may be quantitatively reconstructed using paleosols preserved in continental successions to test this general model. Results from Oregon and Nebraska suggest moderate drying and cooling, not as a stepwise change at the time of the Oi-1 glaciation, but as part of a long-term aridification and cooling event associated in part with emplacement of the Cascade Range. In contrast, intermontane Montana’s paleoprecipitation and paleotemperatures fluctuated on short-term (i.e., Milankovitch) time scales but on balance were both essentially unchanged by the Oi-1 glaciation. Results from Europe (UK, Spain) suggest a different pattern characterized by stable (i.e., unchanging) paleotemperatures in both localities and increasingly wet conditions in the UK. Taken together, these results indicate that (1) strongly regionalized climatic change was associated with the Oi-1 glaciation, (2) physiographic position with respect to orographic features played a key role in determining those regional climatic responses to the global event, and (3) there was little or no cooling on land associated with the Oi-1 glaciation.

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.