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Marine molluscan assemblages in the Early Pleistocene of Sidestrand, Bramerton and the Royal Society borehole at Ludham, Norfolk

1967; Royal Society; Volume: 253; Issue: 784 Linguagem: Inglês

10.1098/rstb.1967.0034

2054-0280

P. E. P. Norton,

Marine Biology and Ecology Research

An account of a quantitative study of Mollusca from three East Anglian sites is given and from this work the author defines a series of molluscan Assemblage Zones and attempts to interpret the ecological and depositional environment in which they accumulated. The interpretations are thought to have local rather than regional significance. In the basal assemblage zone at Ludham (L.M. 1) and in zone L.M. 2 next above, the death-assemblages contain many Red Crag and Coralline Crag species, not recorded from Harmer’s ‘Icenian Stage’ to which by his definition the Crag in the Ludham Borehole belongs. The L.M. 1 assemblage suggests deposition in sublittoral marine waters shallower than 50 m; the L.M. 2 assemblage suggests deposition at approximately 15 m. In zone L.M. 3 an association of mud-inhabiting bivalves dominated by Abra alba may have been in situ . Zone L.M. 4 is very poor in molluscs and the sediments are very silty. The zone L.M. 5 assemblage indicates deposition in less than 8 m of water; here the trend to shallower-water deposition of the assemblages culminates (the situation in zones L.M. 4 and L.M. 6 remaining obscure). The L.M. 5 and L.M. 6 assemblages, as regards their extant, intertidal species, resemble those of zones B.M. 1 and B.M. 2 (respectively) of the Bramerton Common sequence. This may indicate similar depositional conditions; yet each Ludham assemblage has proportionally more individuals of extant sublittoral species, which may indicate diachronism or changes of facies. At Sidestrand, the impoverished assemblage is interpreted as littorally deposited; it permits no analogy with the Bramerton and Ludham assemblages.