Abstract
THE Anglo–Welsh outcrop of the Lower Old Red Sandstone (Siluro–Devonian) reaches approximately 2,000 m in thickness and is largely alluvial1, consisting of long sequences of fining upwards cyclothems2. The fine grade (floodplain) members of the cyclothems commonly include one or more pedogenic carbonate units which are evident in the vertical profile3–6. The carbonates seem to represent episodes of soil formation, each of which lasted for about 104 yr. Well horizonated palaeosols indicate periods of prolonged weathering, which implies that the alluvial plains on which they were formed remained unflooded for long periods. This could have arisen either because rivers shifted about on the plains, or because of a cyclical river dissection–aggradation coupled with lateral movements. The distribution of Quaternary calcretes7 suggests that the climate was hot (mean annual temperature 16–20° C) with a low seasonal rainfall (mean annual precipitation 100–500 mm). This is supported by palaeomagnetic results, which indicate a low (southerly) latitude for the Anglo–Welsh area8.
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ALLEN, J. Geomorphology of Siluro-Devonian alluvial plains. Nature 249, 644–645 (1974). https://doi.org/10.1038/249644a0
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DOI: https://doi.org/10.1038/249644a0
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