Discover Bristol and Explore the Fossils and Geodiversity of Barnhill Quarry near Chipping Sodbury
- Wayne Munday
- Jun 26
- 4 min read
Updated: Jun 30
Sip back and discover Bristol and explore the fossils and geodiversity of Barnhill Quarry near Chipping Sodbury a site rich in Triassic bone beds, coral reefs and ancient marine life. Known locally as Arnold’s Quarry this disused limestone quarry may appear unassuming at first glance but it tells a story dating back 300 million years. Designated a Site of Special Scientific Interest (SSSI) Barnhill Quarry exposes layers where Triassic Rhaetic Clay sitting on top of Carboniferous Limestone. Erosion has revealed a limestone wave-cut platform featuring karstic grikes and a fossil-rich base yielding vertebrate remains, while overlying shales preserve bivalves and fish fossils. This was once former shallow tropical sea with coral reefs and ancient tidal flats.
Barnhill Quarry has been a site of curiosity and scientific research for nearly two centuries though it is the works and drawings of Professor Sidney H. Reynolds published in the 1930's that still today serve as a key reference for fieldwork. His work mapped out the exact locations of fossils, the bone bed and the quarry’s distinctive geological features.
Interestingly, Professor Sidney H. Reynolds was the longest-serving Head of Geology at the University of Bristol and played a key role in developing the department’s teaching, research, and collections. Educated at Cambridge, Reynolds contributed significantly to Palaeozoic and Carboniferous geology and received the Lyell Medal in 1928 a prestigious annual scientific medal given by the Geological Society of London for contributions to “soft rock” studies.
The limestone laid down at Barnhill Quarry happened during the Arundian and Holkerian sub-stages of the Visean Series between 344.5 - 337 million years ago - a series whose name derives from the town of Visé in northeastern Belgium.
The limestone exhibits ripple marks commonly known as wave-formed or oscillation ripples a wave-like sedimentary structure created by the back-and-forth motion of water in a shallow marine environment. These ripples are a type of geological bedform or a surface feature formed on sediment or sand by the fluid movement of moving water on a sediment surface and deposited into distinct patterns by the flow.
Within the limestone is a fossil rich coral beds and rare stromatolite formations whose microbial mats record the rhythmic rise and fall of ancient seas. These features make Barnhill Quarry one the best exposed sections showing shallow marine cyclic sedimentation from this time period in southern England.
At the top of these limestone rocks lies a dramatic limestone pavement that has been eroded by an advancing Triassic Sea. This natural pavement features include deep and narrow fissures known as karstic grikes. Overlying this pavement is the Rhaetic succession of the Penarth Group marking the very end of the Triassic. This six-metre-thick section includes layers of Westbury Formation and Cotham Member capped by early Jurassic deposits.
Barnhill Quarry is particularly known for its “bone bed” of Late Triassic or Rhaetian Age vertebrate assemblages. Fossils are sparse and are often unfortunately fragmentary and weathered. The predominant species are from two major vertebrate groups of cartilaginous fish (chondrichthyans) and bony fish (osteichthyans).
Among the majority of fossil remains of teeth found at Barnhill Quarry from chondrichthyan specimens is the Hybodus cloacinus a Hybodontiformes and Rhomphaiodon minor a Synechodontiformes - both are ancient orders of now extinct shark.
The Hybodontiformes were a long-lived and globally successful group of cartilaginous fish closely related to modern sharks and rays. Originating around 400 million years ago in the Devonian, they thrived in both marine and freshwater environments.
Other chondrichthyan fossil remains include a collection of specialised scales called placoid scales or dermal denticles that cover the skin cartilaginous fish like sharks and rays. Structurally similar to teeth these tiny V-shaped scales are embedded in the skin and project outward giving the shark skin its distinctive rough and sandpaper-like texture.
Placoid scales serve several key functions like reducing drag when swimming and protecting against predators, parasites and physical abrasion. Their unique structure and function make them a defining characteristic of cartilaginous fish.
Other fossil remains of chondrichthyan's are their dorsal fin spines that are typically fixed and not movable. These spines are an important anatomical and functional feature also unique to many cartilaginous fish. The dorsal fin spines in chondrichthyans are rigid, cartilage-based structures located at the leading edge of the dorsal fins. Unlike the bony spines of bony fish, these spines are composed of calcified cartilage and are not shed. Their primary function is defence though they may also have helped stabilise the shark during swimming.
The osteichthyan fossil record from Barnhill Quarry reveals a small but diverse assemblage of bony fish from the Rhaetian period comprising of both ray-finned species of actinopterygians and a lobe-finned species of a sarcopterygian. Both Severnichthys acuminatus and Sargodon tomicus are present along with Ceratodus sp., a sarcopterygian. Additionally, scattered throughout the Rhaetian Aged shales are also well preserved bivalves and saltwater clams.
Barnhill Quarry provides a continuous vertical record of the transition from the marine-rich Carboniferous to the terrestrial-influenced Triassic Period and offers a snapshot into an ecosystem just before the end-Triassic mass extinction that would reshaped life on Earth. Designated a Site of Special Scientific Interest (SSSI), it reveals a transition from Carboniferous shallow seas to Triassic environments through its fossil-rich limestone layers along with ripple-marked pavements and karstic features. Among these fossils is the Late Triassic “bone bed” containing fossils of both cartilaginous and bony fish. These include teeth, scales, and spines from extinct shark relatives like Hybodontiformes and Synechodontiformes, as well as rare specimens of ray-finned and lobe-finned fish such as Severnichthys acuminatus, Sargodon tomicus, and Ceratodus. The site’s scientific importance is largely built on early 20th-century work by Professor Sidney H. Reynolds, whose research remains foundational. Barnhill Quarry continues to be a vital location for understanding southern England’s ancient marine ecosystems and the evolutionary story preserved in its rocks.
