By Felix Whitham, Mike Horne and Terry Rockett.

A report on the field trip to Dimlington

by members of the Hull Geological Society on Sunday 7th May 2000.

Members met at the Caravan Park Easington at 10 a.m. on a fine sunny morning before moving off to the cliff top at the northern edge of the huge B.P. gas installation, where permission was obtained to park cars and descend the cliff close to their gas pipeline and Dimlington High Cliff thus saving a walk of nearly 3 km from Easington. The tide was still fairly high on the beach so time was spent examining sections of the very wet and slumped cliffs but it proved impossible to identify any of the bedding sequence- Few fossils were found but a large number of erratic rocks were recorded. It had been intended to auger the beach at low tide to prove the existence of the Basement Beds but after lunch this proved to be unnecessary. Recent rough seas had swept a broad platform of the shore close to low tide level clear of sand exposing an area of Basement deposits for several hundred metres including a number of large erratic boulders, some over one metre in diameter. The previous exposure on this scale was last seen in 1964 (see figure). Unfortunately on the present visit no trace of the blue clay patches recorded previously could be found.

Large quantities of Larvikite boulders have been deposited at the base of part of the cliff to protect the gas terminal from coastal erosion. This was landed on the beach at high tide from barges and then moved into place at low tides. Numerous pieces of this fresh Larvikite could be seen on the beach, and may in future years be confused with glacially deposited Larvikite. At present the Larvikite glacial erratics can be distinguished by their roundness and lighter colour; they might also have ice scratch marks on them.

Much research work has been carried out by previous workers in the past and the following information was compiled as a field handout and given to members attending the meeting:-

The sequence of cliff and beach exposures from Easington (map ref TA400193) to Dimlington High Cliff (map ref TA390220) on the Holderness Coast of East Yorkshire extends for approximately 3 km exhibiting an excellent section of glacial deposits, which include in ascending order the Basement Beds with erratic inclusions of blue clays and yellowish compacted sands [Bridlington Crag], overlain by Drab Till [now Skipsea Till], capped by Purple and Hessle Tills [now Withernsea Till] (see Madgett and Catt 1978).

Following a study and extensive analysis of the tills of East Yorkshire, Lincolnshire and North Norfolk including vertical and lateral variations in particle size, distribution, mineralogy and other petrographic features by Madgett and Catt showed that the Devensian glacial succession in Eastern England contains only two tills, i.e. Skipsea Till and Withernsea Till. The Hessle Till is now considered to be a post-Flandrian weathering profile, lying on whichever of these two tills occurs on the surface.

The cliffs at Dimlington High rise to about 30.5 metres O.D., the Basement Bed about 2.5m, Skipsea Till 6.5m and the Withernsea Till approximately 21.5m. The unusually high cliffs and the height of the Basement Till at Dimlington compared to the rest of the coastal sequence up to Skipsea is considered by some researchers to be due to ice pushing relatively soft Basement Till until a build up occurs and the height of the Till becomes too high for the ice to move it further. It would then be over-ridden and left as a ridge rising above the old marine platform, forming the crest of a push moraine (Catt and Penny 1968).

In 1964 following gales and sweeping tides, large areas of the Basement Beds with patches of Bridlington Crag were exposed on the foreshore about 300m south of the highest part of the cliff (map ref. TA393216). The blue clays containing numerous well-preserved bivalves, with abundant and large ostracods and foraminifera (see list and fig.) were seen by Felix Whitham. and many examples of some of the species were collected by him at that time. A large variety of glacial erratic rocks are scattered along the foreshore mostly derived from the continuous erosion of the boulder clay cliffs including some from the Pennines, Lake District, Scotland, the Scottish Borders and Scandinavia (see list below).

In the past little attention has been paid to the origin of Carboniferous, Jurassic and Cretaceous fossils along with the occurrence of black flints found in the Withernsea and Skipsea Tills and seen loose in pebble beds on the beach. Examination of the Cretaceous echinoids which include Echinocorys, Micraster, and Galerites usually preserved in black flint, along with the belemnite Belelmnitella mucronata, suggest a Late Campanian/Early Maastrichtian age for these species, which including the black flint are not present in the land based Chalk of north-east England. However, they do occur in higher chalk exposed in the eastern part of Norfolk with similar preservation and in beds known to exist below the North Sea off the Holderness Coast. Some rarer examples of Lower Cretaceous fossils also occur, including the belemnites Hibolites and Acroteuthis, fragments of the ammonite Aegocrioceras and the oyster Exogyra.

Fossils from the Lower Jurassic include the ammonites Dactylioceras commune, Hildoceras bifrons, Arnioceras and Peronoceras. Common examples of the oyster Gryphaea, with rarer specimens of the bivalve Cardinia, along with belemnites and occasional crinoids are also to be found. The Carboniferous brachiopod Productus and coral Lithostrotion are well exposed in some of the very large limestone boulders found on the beach at low tide.

Previous researchers have suggested that ice movements from the north, moving across the Whitby area, Speeton and Flamborough Head, were responsible for the masses of Lower Jurassic rocks and fossils, also for the Cretaceous fossils and blocks of chalk found in the tills of Holderness. Whilst this may be true regarding the Jurassic material which does occur north and south of Whitby it is difficult to justify in respect of the Cretaceous Chalk fossils which come from much higher levels of chalk than that exposed on land. The most probable explanation is that ice moving in from the east scraped higher chalk beds of Upper Campanian-Lower Maastrichtian age associated with black flints, from the bed of the North Sea where they are known to be present. Occasionally thick extended bands of fragmented chalk are exposed in the cliffs at Skipsea containing fossils from these two stages, particularly Belemnitella mucronata.

Catt J.A. & Penny L.F. 1968. The Pleistocene Deposits of Holderness, East Yorkshire. Proceedings of the Yorkshire Geological Society 35, 375-420.

Madgett P.A. & Catt J.A., 1978. Petrography, Stratigraphy and Weathering of Late Pleistocene tills in East Yorkshire, Lincolnshire and North Norfolk. Proceeding of the Yorkshire Geological Society 42, 55-108.