Discover Somerset and Explore the Fossils and Geodiversity of Barns Batch Spinney on Dundry Hill
- Wayne Munday
- Jun 27
- 3 min read
Sip back and discover Bristol and explore the Jurassic Period fossils and geodiversity of Barns Batch Spinney known for ammonites and exposures of Inferior Oolite limestone. Located just southwest of Bristol, Barns Batch Spinney is located on Dundry Hill a place designated as an SSSI and internationally recognised for its exposures of the Inferior Oolite Group a fossil-rich Middle Jurassic limestone sequence from the Aalenian and Bajocian Stages dated to approximately between 178 - 166 million years ago. Dundry Hill was historically cited by the famous French naturalist Alcide Charles Victor Marie Dessalines d'Orbigny in 1850 as the English type section for the rocks of the Inferior Oolite in England and still remains a reference point for global stratigraphy and fossils for this time period. Further extensive studies during the early 19th century led to the meticulous documentation of ammonite biostratigraphy and laid the groundwork for modern interpretations of the Middle Jurassic sequence as we understand it today.
During the Early Jurassic Britain was submerged beneath a shallow shelf sea, but by the end of the epoch, falling sea levels, crustal uplift, and volcanic activity in the North Sea Basin led to dramatic landscape changes. This transition ushered in the Middle Jurassic, a period defined by diverse depositional environments including shallow seas, rivers, deltas, lagoons, and saltmarshes. The resulting sedimentary deposits included limestone and a variety of clastic rocks such as mudstone, siltstone and sandstone.
The Middle Jurassic is important for its rich and varied marine fossil record across the United Kingdom and especially for Ammonoids an extinct and recognisable coiled-shelled cephalopod comprising the subclass Ammonoidea.
Ammonites are considered "zone fossils" because their characteristics of rapid evolution, widespread distribution, abundant preservation and distinctive shell shapes that make them ideal for identifying and correlating specific intervals of geological time. These characteristics allow geologists to define biostratigraphic zones known as "ammonite zones" which help divide and correlate rock layers across different regions with relative precision.
Fossil evidence of the Middle Jurassic reveals a vibrant marine ecosystem with abundant invertebrates such as corals, sponges, bryozoa, brachiopods, molluscs, echinoderms, and microscopic organisms like foraminifera and phytoplankton. Trace fossils from burrowing crustaceans are also common. Marine reptiles, including ichthyosaurs, plesiosaurs, pliosaurs, crocodiles, and turtles, thrived alongside diverse fish species while belemnites were widespread and central to the marine food chain. On land both dinosaurs were well-established and early mammals had now appeared. Plant life was dominated by gymnosperms such as conifers and cycads along with ferns and horsetails.
Dundry Hill is renowned for its well-preserved Jurassic stratigraphy and The Barns Batch Spinney exposes the lowest part of the Inferior Oolite Group lying beneath the Middle and Upper Inferior Oolite rock seen at the adjacent South Main Road Quarry where recent studies of the South Main Road Quarry has led to a revised ammonite biostratigraphy based on detailed bed-by-bed fossil collection including the identification of a new ammonite horizon yielding Sonninia micracanthica.
The exposure at The Barns Batch Spinney is significant because they represent one of the most complete sections of the Discites Zone a biostratigraphic unit within the early Bajocian Stage of the Middle Jurassic Period, dating to approximately 170–168 million years ago. Named after the index ammonite Hyperlioceras discites this zone fossil is key for precise dating and correlation of Jurassic rock layers across several geographic regions extending across mainland Europe. Prominent exposures of the Discites Zone occur in the Inferior Oolite Group particularly at Dundry Hill where it is among the among the thickest in Britain.
Barns Batch Spinney is protected as Sites of Special Scientific Interest (SSSIs) and responsible access and observation are encouraged. The surrounding countryside offers accessible public footpaths and bridleways, making the area suitable for to visit to observe fossil-bearing horizons.
