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An 8000-year record of sea-level change from grain-size parameters: data from beach ridges in DenmarkGeology Department B-160, Florida State University, Tallahassee, Florida 32306, USA The low-energy beach ridge system near the town of Jerup, in the extreme north of Denmark, was sampled at 154 sites, on a pattern of one per ridge (intervals of 50-51 years, starting about 7800 BP). None of these ridges was built by storm waves or by wind. They are not like high-energy ridges to the north, which differ in size, morphology, bedding and granulometry. In the low-energy system, sand grain-size kurtosis (inverted) is a reliable index of wave energy density in the surf zone, and also indicates an important component of settling. Kurtosis tends to be more-or-less constant in sets of 5-20 ridges, then to change abruptly at set boundaries, which therefore represent sea- level changes (1-5 m), centuries apart. The sixth moment measure (grain size) and ridge spacing also indicate sea-level change. Glacio-isostatic rebound has averaged 2 to 2.1 mm yr-1 for this system; the history of this rebound plots best on a semi-log diagram showing a decrease from about 4 mm yr-1 (at 6000 BP) to about 1.3 mm yr-1 (at 1000 BP). The Jerup sea-level curve matches the Gulf of Mexico curve as far back as the latter goes. Each provides sea level history in the 'Little Ice Age' (most recent millennium), and other changes since 3000 BP; the Jerup curve shows earlier fluctuations. The largest changes were in the range 3-5 m; maximum rates were about 1 cm yr-1 .
Key Words: sea level • grain size • kurtosis • beach ridges • wave energy • isostatic rebound • climate change • Denmark.
The Holocene, Vol. 3, No. 3,
220-231 (1993) This article has been cited by other articles:
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