Correlation of Eocene-Oligocene marine and continental records: orbital cyclicity, magnetostratigraphy and sequence stratigraphy of the Solent Group, Isle of Wight, UK

Abstract

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 Eocene–Early 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 10–20 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 30–90 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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