Summary
The Holderness tills are described, and grouped into two series: the Basement Series below, and the Drab-Purple-Hessle Series above. The Basement Till is shown to underlie (and not overlie as was formerly supposed) the Sewerby raised beach, which is considered to belong to the Last Interglacial. The Basement Till was therefore deposited during the Saale Glaciation or earlier, and the Bridlington Crag (which has been rediscovered after being hidden for sixty years) may thus be of Holstein (Great Interglacial) age or earlier. The Drab-Purple-Hessle Series is considered to have been deposited from one composite ice sheet of Würm age, probably Main Würm, and the “moss silts” which underlie it at Dimlington are placed in a Würm interstadial. The Early Würm may be represented by the solifluction bed at Sewerby. The Kelsey Hill Gravels, the Kirmington silts and the Speeton Shell Bed are reassessed, and their position in the chronology is discussed.
Macrofabric (stone orientation) and microfabric studies of the four tills exposed in the coastal areas of East Yorkshire indicate that the regional direction of ice movement during both the Saale and Weichsel Glaciations was from north-east to south-west. The Saale (Basement) Till was considerably modified by the advance of ice during the Weichsel Glaciation; in particular, the stones in the Basement were reorientated so that their long axes now lie at right angles to the direction of movement of the Weichsel ice sheet. The fabrics of the three Weichsel tills (Drab, Purple and Hessle) are alike, and it is suggested that all three were deposited from one composite ice sheet. The relationship of vertical joints in the Basement and Drab Tills to directions of ice movement is discussed; those in the Basement possibly originated as ac tension joints inherited from the parent ice, whereas some of those in the Drab are probably conjugate shear joints formed during post-depositional deformation of the till.
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