The Flamborough Quaternary Research Group

 "So...... how many “Bridlington Crags” are there? Ongoing work with the Penny Collection" by Rodger Connell, Stuart Jones, Derek Gobbett and Mike Horne. (abstract of a talk given to Hull Geological Society on 10th December 2013).

 Masses of shell rich marine clays (and associated glauconitic sands) within, what is now termed, the Basement Till of Holderness were first documented by the eminent geologists Sedgwick, Phillips and Lyell in the 1820s and 1830s at Bridlington. At the time it was thought the deposit might be of similar age to the Pliocene/Early Pleistocene Crags (shelly sands and gravels) of East Anglia – hence the name Bridlington Crag. Lamplugh was fortunate to observe the deposit first hand in the 1880s when Bridlington north shore was stripped of sand after storms. Three to four tons of the clay was collected by a Mr Headley at the time and an extensive macro and micro fauna was recovered. Lamplugh also noted a mass of clay with a “peaty seam” which he believed was a terrestrial deposit. Whilst some of the material had a range of small clasts within it Lamplugh only recorded small phosphatic “lumps” from the main clay masses which he considered to be derived from the Speeton Clay. He interpreted the masses of marine clay to have been deposited in an arctic environment which were ripped from the sea floor by the ice sheet that deposited the Basement Till. Much later Catt and Penny (1966) considered the rafts to date from the late Hoxnian, with the enclosing Basement Till believed to be of “Wolstonian” age, the glaciation preceding the Ipswichian (Sewerby) interglacial. A number of masses of Bridlington Crag were again exposed on the north shore in 1964 after storms. Palynological and microfossil (coccoliths) analyses from samples collected then were published in the 1970s. The coccolith assemblage indicated derivation from restricted Kimmeridge Clay to Chalk bedrock sources and the palynology an Early Pleistocene date. As yet unpublished in detail amino acid analyses from shells from the same exposures also suggest an Early or Early Middle Pleistocene date for the sediment. Bulk samples of the material collected from the Bridlington exposures in 1964 are curated in the Penny Collection at Hull University and in the Hull and East Riding Museum. Recent work has confirmed the very limited clast assemblage in the Bridlington material and new palynological analyses are being undertaken to help clarify the age and provenance of the deposit.

Similar erratic masses (rafts) of shelly clay are also known from within the Basement Till at Dimlington, south Holderness. Erratic clasts and shells collected from a large raft exposed in the 1950s and 60s are curated in the Penny Collection, University of Hull. The macro and micro fauna is generally considered to be similar to that recovered from the Bridlington material, but in contrast the collection contains a rich and varied set of erratic pebbles and cobbles. Igneous, metamorphic and sedimentary lithologies are present, with some igneous rocks definitely from the Oslo Graben in southern Norway. The shells in the extant collection contain some species that may have required different environmental conditions suggesting that material from varying environments may be incorporated into the rafts. Work is ongoing to further identify the sources of the erratic rocks from Dimlington and sediment enclosed by some of the shells will be used for palynological analyses. It is possible that the material from the two sites either have a different provenance or a different age.

 Lamplugh recorded a third site in 1890 with an arctic macrofauna and apparently enclosed within the Basement Till in the eastern cliffs at South Landing on Flamborough Head. Recently collected samples from this poorly exposed material suggest it does resemble Bridlington Crag lithologies from the other two sites. Interestingly the few clasts recovered from the sediment are dominated by greywackes possibly from southern Scotland. Again palynological analyses are being undertaken to help clarify the age and provenance of the fine grained sediment. At this site the sediment is apparently associated with till that resembles Skipsea Till at sites to the south. The FQRG has obtained a preliminary OSL age estimate of ~55.7 ka from sands beneath the deposit suggesting that the South Landing site is within an assemblage that dates to the last, Devensian, glaciation rather than one that preceded the Ipswichian interglacial.

All three sites considered to belong to the “Bridlington Crag” appear to have significantly different clast assemblages. Does this indicate different provenance or age? Whilst at two of the sites (Bridlington and Dimlington) the erratic rafts are within the Basement Till at the third site (South Landing) the material is within a Devensian context. Palynological analyses are being undertaken to determine if there are similar age diagnostic taxa at the three sites. Unfortunately we have so far failed to discover the mollusc species required for modern amino acid geochronology in the collections, though work on the microfauna (foraminifers or ostracods) may be possible in the future. Work continues on the clast assemblages, macro and microfaunas and floras in an attempt to clarify the palaeoenvironment, age and provenance of the material termed the “Bridlington Crag”.'

Copyright - Hull Geological Society 2025

HOME

Copyright Hull Geological Society.

Registered Educational Charity No. 229147