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Decoding Quaternary sea levels

Raised beaches and estuarine sediments tell us about past sea levels. They are key evidence in Quaternary science, the branch of geology that investigates the ice ages, and can often be associated with floral, faunal, and human remains. Geologists Charles Lyell (1838) and Joseph Prestwich (1859) were among the first to correctly recognize the remains of these ancient strandlines and their observations were built on in the 20th century by researchers such as Fredrick Zeuner (1959). Today we recognize such features in many locations including Australia, New Zealand, Papua New Guinea, and the west coast of the United States (Murray-Wallace & Woodroffe 2014).

In northwest Europe the evidence falls into two types of sequences:
• Former strandline and intertidal–subtidal deposits
• Estuarine sediments

Strandline deposits are well preserved on the Sussex and Hampshire coastal corridor where at least four chronologically discrete sequences are recognized (Bates et al. 2010). The best-known of these are the marine sediments preserved 40 m above sea level at Boxgrove in West Sussex. Here a beach and marine sand sequence is preserved and sealed by a regressive facies of sands and silts and an overlying land surface. The site also demonstrates the close relationship between Palaeolithic archaeology and Quaternary science because extensive evidence for human activity around 0.5 million years ago — in the form of flint knapping scatters, butchered animals, and even the remains of the humans themselves — lies on the preserved land surface (Roberts & Parfitt 1999). Similar, although probably younger, sequences occur on the south side of the English Channel at places such as Sangatte, France.

Marine sands overlain by cold climate solifluction deposits, Boxgrove, West Sussex.

Marine sands overlain by cold climate solifluction deposits, Boxgrove, West Sussex.

In contrast to the coarse sand and gravel sequences of former strandlines further inland we often see sediments belonging to the estuaries of rivers such as the Thames, Somme, or Seine, and river systems such as the Solent that no longer exist. Estuarine deposits can be extensive, for example those at Stone Point in Hampshire in the estuary of the former Solent River, or restricted, such as small tidal channels like those preserved around Selsey Bill. Significantly, these channels may contain a wide range of palaeoenvironmental indicators including large and small mammal remains, molluscs, foraminifera, ostracods, pollen, plant remains, and insects. These biological remains allow us to reconstruct the local environment and climate history and also let us apply biostratigraphy to the dating or correlation of such sites.

The importance of these sequences is in preserving a record of land and sea interaction during periods of high sea level and consequently they provide a yardstick for change in the Quaternary, comparable to river terrace records. The preservation of these sequences is, however, dependent on their topographic and tectonic setting. For example, preservation of sequences will only occur where emerging shorelines dominate as a result of tectonic or isostatic uplift. Here uplift elevates the sequences beyond the likely envelope of marine erosion during subsequent high sea-level events. Today the challenge for Quaternary scientists is to apply a robust chronological framework to these deposits in order for us to fully understand the interaction between climate change, sea-level history, and the way in which our species has adapted to such changes in the past.


References

Bates, M R, R Briant, E Rhodes, J Schwenninger, and J Whittaker (2010). A new chronological framework for Middle and Upper Pleistocene landscape evolution in the Sussex/Hampshire Coastal Corridor. Proceedings of the Geologists’ Association 121, 369–392.

Lyell, C (1838). Address delivered at the anniversary meeting of the Geological Society of London, on the 17th February 1837. American Journal of Science and Arts 33, 76–117.

Murray-Wallace, C V and C Woodroffe (2014). Quaternary Sea-Level Changes. A global perspective. Cambridge University Press, Cambridge.

Prestwich, J (1859). On the westward extension of the old raised beach of Brighton and on the extent of the sea-bed of the same period. Quarterly Journal of the Geological Society of London 15, 215–221.

Roberts, M B and S Parfitt (1999). Boxgrove: A Middle Pleistocene hominid site at Eartham Quarry, Boxgrove, West Sussex. English Heritage Archaeological Report 17. English Heritage, London.

Zeuner, F E (1959). The Pleistocene Period. Its Climate, Chronology and Faunal Successions. Hutchinson Scientific and Technical, London. 447 p.

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