Discover Somerset and Explore the Fossils and Geodiversity of Bleadon Hill
- Wayne Munday
- Jul 8
- 3 min read
Updated: Sep 11
Sip back and discover Somerset and explore the fossils and geodiversity of Bleadon Hill designated an Site of Special Scientific Interest (SSSI) and a Geological Conservation Review (GCR) located on the southern edge of the Mendip Hills clearly signposted off the A370 near Weston-super-Mare. Bleadon Hill mainly comprises of two down-faulted sections of Carboniferous Limestone from the Black Rock Limestone subgroup though to the south there is an interesting low ridge of calcite-cemented sand and gravel whose origin is ambiguous and uncertain. Laying at over 80 meters above sea level and traditional Pleistocene shorelines this ridge is separated from the main hillslope by a dry valley. Known as the Bleadon Member it yields rare single celled Lower Jurassic foraminifera likely from the Sinemurian Stage between 199.5 -192.9 million years ago. The ridge has a mix of Carboniferous Limestone and the sands whose layered and rippled features suggest a former waterlain environment. Dating possibly from the Jurassic or Pleistocene it has been proposed that this ridge is either a Mesozoic sea beach deposit, Pleistocene shoreline, glaciofluvial gravel or a proglacial lake-shore sediment. Though the clues do not add up, the geodiversity provides an interesting conundrum of inconsistent, incomplete or contradictory evidence and unresolved questions and debate still surround the hill’s glacial history.
The fossils found in the sands at the base of the ridge on Bleadon Hill’s are obviously too old to be Pleistocene in age. It is thought that these fossils have been reworked meaning that they have been transported from older Jurassic rocks and incorporated into the younger sediment rather than indicating the ridge is Early Jurassic in age.
The relatively light calcite cementation of the Bleadon Member challenges a proposed Jurassic origin as over 145 million years old would typically show much heavier, tightly bound and extensively cemented sediments due to the prolonged time of diagenesis from the physical, chemical and biochemical changes that transform loose sediments into solid sedimentary rocks by compaction, cementation, dissolution and recrystallisation.
By contrast the Bleadon Member deposit have only light, point-contact cementation where grains are minimally bonded at their edges. This is a a feature more typical of younger and less consolidated sediments from the Pleistocene Epoch where sediments would not have yet undergone the full diagenetic transformation seen in much older rock formations.
The possible explanation that the ridge is glacial is also confusing because the sediments have an absence of glacially transported erratic material. However, it is thought that the ridge was formed during the Quaternary Era when an ice sheet may have rested against Bleadon Hill. Meltwater from the ice sheet is believed to have deposited the sand and gravel across the area and the remnants now make up the exposed ridge.
If a glacier is the correct explanation this would mean that an ice sheet did reach as far south as the Sedgemoor Basin and would represent the southernmost limits of Pleistocene glaciation in South-West of England.
Bleadon Hill offers a captivating geological puzzle shaped by faults, fossils and sedimentary complexity. While the presence of rare reworked Jurassic foraminifera, ripple-marked sands, and light calcite cementation complicates efforts to pinpoint the precise origin of the Bleadon Member these very inconsistencies make the site scientifically valuable. Whether the ridge represents a Mesozoic beach, a Pleistocene shoreline, or a glaciofluvial deposit from a far-reaching ice sheet the ambiguity underlays the importance of continued study. As a designated Site of Special Scientific Interest (SSSI) and Geological Conservation Review (GCR) sit, Bleadon Hill invites the visitor to explore the evolving story of Somerset’s ancient landscape.
