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Original Article |
1 1Department of Earth and Environmental Sciences, University of Greenwich, Medway Campus, Chatham Maritime ME4 4TB, UK
2 2Department of Palaeontology, Natural History Museum, Cromwell Road, London SW7 5BD, UK (e-mail: asg@nhm.ac.uk)
3 3Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
4 4Department of Geology and Geochemistry, Stockholm University, S-10691, Stockholm, Sweden
5 5Core Magnetics, The Green, Sedbergh LA10 5JS, UK
6 6GSC Inc., 826 Plainwood Drive, Houston, TX 77079, USA
The magnetostratigraphy, clay mineralogy, cyclostratigraphy and sequence stratigraphy of the estuarine and continental Solent Group (Isle of Wight, Hampshire Basin, UK), which is of Late EoceneEarly Oligocene age, were investigated. A new magnetostratigraphy for the Solent Group is correlated to the chronostratigraphic standard using limited biostratigraphical data, and it is concluded that the base of the Oligocene falls close to the base of the Bembridge Limestone Formation. A long time-series of clay mineral XRD data was generated, which shows striking variation in illitic clay abundance. Illite is interpreted to have formed in gley palaeosols through repeated wetting and drying in response to high seasonality. High illitic clay values are tuned to c. 400 ka eccentricity maxima to develop an age model. In addition to a very strong c. 400 ka signal in the data, spectral analysis of the clay data also confirms the influence of short eccentricity (c. 100 ka) and obliquity (c. 40 ka) cycles. The succession displays seven conspicuous 1020 m thick sequences, which represent transitions from transgressive estuarine environments through highstand floodplains to freshwater lakes. The sequences correspond exactly to the long eccentricity (c. 400 ka) cycles. A sea-level curve is derived using the amount of incision as a minimum measure of eustatic fall, but there is no evidence of a major eustatic drop of 3090 m corresponding to the early Oligocene glaciation of Antarctica. It is likely that incision was suppressed by rapid rates of subsidence.
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