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A NOTE ON A. S. WATT’S GRASS HEATH AND SOIL TYPES OF LAKENHEATH WARREN, BRECKLAND, SUFFOLK, AND THEIR GEOLOGICAL INTEREST A. S. Watt in two classic papers described the results of detailed investigations of the relation between vegetation, flora and soil on Lakenheath Warren in the western part of Breckland, adjacent to Fenland (Watt, 1936, 1940). One of the four major vegetation types he described was grass heath. He identified seven soil types associated with grass heath, corresponding to stages in the development of a podsol and bearing different types of grass heath. They were called grasslands A to G, using the same letters for the related soil types, with A the youngest and G the most mature soil profile. In the earlier paper, Watt described the geology of the study area, basing his description on Boswell’s (1931) account of glaciation in East Anglia, with a lower Chalky-Jurassic boulder clay, an upper Chalky boulder clay, with sand, brickearth and gravel intervening between the two. Watt suggested that the sands of Breckland resulted from decalcification of the boulder clays and from the interglacial sand between the two, itself derived from decalcification of the underlying Chalky-Jurassic boulder clay. Watt used the term ‘interglacial’ in a purely stratigraphic sense, with no climatic connotation. The origin of the sands of the Breckland has been a matter of debate since the time of Watt’s papers. Recently, a study of the sands in the Little Ouse and Waveney valleys has indicated that the sands derive from sediments of a lake ponded in the Little Ouse and Waveney valleys by ice in the Fenland during the Wolstonian Cold Stage (West, 2007, 2009; Gibbard et al., 2009). This glaciation is to be distinguished from the earlier and much more extensive glaciation of the Anglian Cold Stage, which deposited the widespread chalky boulder clay of East Anglia. Between the two are temperate Hoxnian Stage lake sediments and the ‘interglacial’ sediments described by Watt. Sections of the sands in the Little Ouse valley show stratified sands up to several metres in depth, with occasional strings of small flints, underlying the heaths which border the present valley. These sands have been included in a sediment unit named the Lopham Sands, with a type area in the valley at South Lopham. Lakenheath Warren, the area of Watt’s studies, lies in an extensive dry valley (c. 15–25 m O.D), extending east from Fenland and 5 km south of the Little Ouse valley. Three of his profile types, of grasslands E, F and G, are described in detail in his 1940 paper, and show, under the A and B1 horizons, depths of laminated, bedded (stratified) sand, with strings of flints parallel to the bedding. He labelled these sands ‘interglacial sand’ in Figure 1 of his 1940 paper, since they were thought to represent a time between the two glaciations. The descriptions show their similarity with the Lopham Sands. The similarity suggests that these sands at Lakenheath Warren are also sediments of a water body ponded by Fenland ice in the Lakenheath valley against the rising Chalk to the east, part of the extensive sweep of sand found against the Chalk escarpment on the eastern side of Fenland. Thus, where grasslands E, F and G are found in Lakenheath Warren, the thick sand body underlying them has resulted in the development of a mature podsol, a geological control differentiating their origin from the less mature soils of Trans. Suffolk Nat. Soc. 46 (2010)
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grasslands A to D. So it is possible that the distribution of grasslands E, F and G may indicate the presence of underlying stratified sand, of the same age as the Lopham Sands and related to the same time of ponding of water. Furthermore, Watt (1936) noted that the most heavily podsolised soils appear to be confined to the low ground under 50 ft (c. 15 m) O.D., a distribution which is understandable in relation to the ponded lake. References Boswell, P. G. H. (1931). The stratigraphy of the glacial deposits of East Anglia in relation to early man. Proceedings of the Geologists’ Association, 42: 87–109. Gibbard, P. L., Pasanen, A. H., West, R. G., Lunkka, J. P., Boreham, S., Cohen, K. M & Rolfe, C. (2009). Late Middle Pleistocene glaciation in East Anglia, England. Boreas, 38: 504–528. Watt, A. S. (1936). Studies in the ecology of Breckland. I. Climate, soil and vegetation. Journal of Ecology, 24: 117–138. Watt, A. S. (1940). Studies in the ecology of Breckland. IV. The Grass-heath. Journal of Ecology: 28: 42–70. West, R. (2007). The Little Ouse River, the Waveney River and the Breckland: a joint history. Trans Suffolk Nat. Soc., 43: 35–48. West, R. (2009). From Brandon to Bungay. An exploration of the landscape history and geology of the Little Ouse and Waveney Rivers. Ipswich, Suffolk Naturalists’ Society. Richard West
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