Silver Pit
The
Silver Pit is a long valley in the bed of the
North Sea, 45
km = 27 miles east of
Spurn Head in
England. (chart) In origin, it is probably a
tunnel valley (Benn & Evans fig.9.27) which was kept free of
periglacial deposits by the
Wash River when the sea level was lower, towards the end of the
Devensian glaciation. However, it may date partially or largely, from the
Wolstonian glaciation.
The
Outer Silver Pit is a west-to-east valley in the bed of the
North Sea. Its widest part is 125 to 175 km (75 to 105 miles) east of
Flamborough Head in
England. It lies between the
Dogger Bank and the ridge dividing the northern from the southern North Sea basins, which runs between
Norfolk and
Friesland.
There are several theories as to how the Outer Silver Pit came to exist. It may have been formed by an
asteroidal impact or more prosaically, by the
dissolution of a thick bed of
salt which permitted the upper strata to collapse. See the external link
Silver Pit Theories. The
Silverpit Formation is salt and other deposits laid down in a desert lake (like the
Great Salt Lake or the
Dead Sea) during the early
Permian, before the influx of the
Zechstein Sea. (Cameron
et.al. p.42)
The
Urstrom, was the great river of the
Polish and north
German plain, which drained the melt-waters from the northern part of the
alpine and southern part of the
Scandinavian ice during the Devensian. The older theory that it flowed by way of the Outer Silver Pit is not a likely explanation as before it got that far west, the
Urstrom would have found an outlet southwards overland to the valley at the
Strait of Dover, or northwards under the sea ice. There is no reason to think that it flowed along the top of
this ridge, even with a retaining ice sheet to the north. That would have required the ice to be grounded in the middle of the North Sea basin but not at the western edge, near the source of its British component.
In the
Cromerian interglacial, before glaciation had much influenced the area, a ridge of high ground joined the
Upper Cretaceous chalk in
Kent,
England to that of the
Boulonnais at
Cap Blanc Nez, in the
Pas de Calais in
France. It is possible that in the Cromerian, the Outer Silver Pit was the bed of the combined
Maas,
Rhine,
Scheldt and
Thames. Since at that stage, the Strait of Dover had probably not been breached, the southern North Sea basin was a lake impounded by the Kent-
Calais ridge and by the Norfolk-Friesland ridge. Whether the lake spilled through the Outer Silver Pit would depend on the extent to which the modern sea bed to the north is formed by later marine and glacial sediment. The eastern end of the Outer Silver Pit is aligned with the lowest part of the Norfolk-Friesland ridge. However, the outlet at the western end of the pit appears to be blocked by somewhat higher ground.
Whatever the facts concerning the course of the southern North Sea rivers, the Outer Silver Pit will not have been initiated by the rivers. One of the other theories must be looked to for that.
*Benn, D.I. & Evans, D.J.A.
Glaciers and Glaciation (1998) ISBN 0-340-58431-9
*Cameron, Crosby, Balson, Jeffery, Lott, Bulat & Harrison.
The Geology of the Southern North Sea (1992) ISBN 0-11-884492-X
*Glennie, K.W.
Lower Permian - Rotliegend in ed. Glennie
Introduction to the Petroleum Geology of the North Sea. (1990) ISBN 0-632-02711-8
*Imray, Laurie, Norie & Wilson pub.
East Coast of England: Orfordness to Blythe marine chart (1980)
*
Silverpit crater*
Timeline of glaciation*
Silver Pit theories*
Silver Pit chart The Outer Silver Pit is further to the north-east, at the eastern end of the Skate Hole..
*
Outer Silver Pit chart It lies between the
Dogger Bank and the
Norfolk to
Friesland ridge.
