Middle and Late Pleistocene environmental history of the Marsworth area, south-central England

To elucidate the Middle and Late Pleistocene environmental history of south-central England, we report the stratigraphy, sedimentology, palaeoecology and geochronology of some deposits near the foot of the Chiltern Hills scarp at Marsworth, Buckinghamshire. The Marsworth site is important because its sedimentary sequences contain a rich record of warm stages and cold stages, and it lies close to the Anglian glacial limit. Critical to its history are the origin and age of a brown pebbly silty clay (diamicton) previously interpreted as weathered till. The deposits described infill a river channel incised into chalk bedrock. They comprise clayey, silty and gravelly sediments, many containing locally derived chalk and some with molluscan, ostracod and vertebrate remains. Most of the deposits are readily attributed to periglacial and fluvial processes, and some are dated by optically stimulated luminescence to Marine Isotope Stage (MIS) 6. Although our sedimentological data do not discriminate between a glacial or periglacial interpretation of the diamicton, amino-acid dating of three molluscan taxa from beneath it indicates that it is younger than MIS 9 and older than MIS 5e. This makes a glacial interpretation unlikely, and we interpret the diamicton as a periglacial slope deposit. The Pleistocene history reconstructed for Marsworth identifies four key elements: (1) Anglian glaciation during MIS 12 closely approached Marsworth, introducing far-travelled pebbles such as Rhaxella chert and possibly some fine sand minerals into the area. (2) Interglacial environments inferred from fluvial sediments during MIS 7 varied from fully interglacial conditions during sub-stages 7e and 7c, cool temperate conditions during sub-stage 7b or 7a, temperate conditions similar to those today in central England towards the end of the interglacial, and cool temperate conditions during sub-stage 7a. (3) Periglacial activity during MIS 6 involved thermal contraction cracking, permafrost development, fracturing of chalk bedrock, fluvial activity, slopewash, mass movement and deposition of loess and coversand. (4) Fully interglacial conditions during sub-stage 5e led to renewed fluvial activity, soil formation and acidic weathering

Rapid method for the determination of cation-exchange capacity of calcareous and non-calcareous soils

Abstract ?Compulsive? exchange takes place between a barium-soil and magnesium sulphate solution because Ba2+ ions are removed from solution by precipitation of barium sulphate. This phenomenon provides a basis for the very convenient routine method for cation-exchange capacity determination in soils described here. An EDTA titration is used to measure the amount of magnesium exchanged from a standard solution by a Ba-soil, which enables the cation-exchange capacity to be calculated. Advantages of the method are its speed and that the sample does not have to be washed exhaustively, so avoiding possible hydrolysis. It compares favourably with standard A.O.A.C. procedure and is much more widely applicable. Soils rich in organic matter, e.g., peats, or with much calcium carbonate, can be handled without difficulty

A new apparatus for recording particle size distribution

A manometer and sensitive capacitance transducer follow the drop in hydrostatic pressure at a point near the bottom of a column of soil suspension during sedimentation. Current from the transducer is fed to a recorder which traces an accumulation curve. The first derivative (slope of the curve) gives a summation curve of the particle size distributions. Results on four soils with different particle size distributions agree with those obtained by a standard pipette-sampling/sieving procedure over the range 20-200 microns effective settling diameter

Distribution of pyrophosphate-extractable iron and organic carbon in soils of various groups

Summary Potassium pyrophosphate (0.1m) removes very little Fe from crystalline Fe oxides at pH 10, but peptizes finely divided hydrous amorphous oxides and organic matter in soils. Fe and C contents of extracts from each horizon of twenty-six British soil profiles show distinctive patterns, independent of the residual dithionite-soluble Fe. Thus extracts of humus Fe podzols have maximum Fe and C in the B horizon, peaty gley podzol has maximum Fe in the B horizon but maximum C in the surface. These groups are differentiated from non-podzols which have maximum pyrophosphate extractable Fe and C in the surface horizon, decreasing with depth. Intermediate patterns help to quantify differences in soils of classes having properties of more than one soil group