The Lower Ordovician Lickey Quartzite is well-known for its lack of fossils. It is interpreted as a near-shore sand flat facies: as such it would have suffered bioturbation, wave agitation and twice-daily scouring by tidal currents. These processes, combined with predation and scavenging would quickly remove any potential fossils. It is worth remembering that, ‘absence of evidence is not evidence of absence’, and in many cases biologically active environments frequently have a very low potential for preserving fossil remains. However, it would be mere speculation to suggest that the environment in which the sands of the Lickey Quartzite were deposited supported any kind of biota without some tangible evidence.
On a recent Geo-Champions ‘research walk’ I identified a single bedding plane that preserves the paired burrow openings of Diplocraterion. While no cross-sections of the U-shaped burrows have been observed, the more or less consistent spacing of the pairs of openings supports this interpretation.
(Lickey Diplocraterion) – The paired burrow openings on a bedding surface in the Lickey Quartzite.
To date, these trace fossils constitute the only evidence we have of the life that inhabited the Ordovician environment of the Lickey area. Their absence from other beds suggests that in this instance they were preserved by an unusual event, in which a sudden inundation of sediment preserved the burrows without disrupting them.
When I was first shown the Lickey Quartzite at the summit of Bilberry Hill, it seemed incongruous. Unlike the other exposures in this formation, much of the rock at this location was a poorly sorted monomict breccia of quartzite fragments strongly bonded by a silica cement. There was debate as to whether the rocks were truly outcrop or displaced boulders, and speculation about the origin of the breccia. As it was assumed that this exposure must be close to the supposed hinge of the ‘Lickey Anticline’, it was suggested that the fragmentation could be associated with folding of the rock. However, more intense folding is seen in the Barnt Green Road Quarry, without the development of this type of brecciation. If the origin was structural, it was more likely to be fault-related. The other possibility was a sedimentary origin.
The outcrop on Bilberry Hill: the yellow-handled mattock is on the fallen slab in the centre of the picture.
When the group recently undertook a ‘research walk’ along the length of the Lickey Ridge, I was struck by the fact that the unconformity seen at the Rubery Cutting rises southwards towards Bilberry Hill. It occurred to me that if the unconformable surface preserved a Silurian landscape with significant relief, the only source of sediment on the high points would be the Lickey Quartzite itself, and that the Bilberry Hill breccia might be sitting on the same unconformity as the Silurian Rubery Sandstone.
On the 26 May, a group of Lickey Hills Geo-Champions undertook a clearance of the site. Malcolm Coghill, David Green, Ken Lewis, Julie Schroder, Adrian Wyatt and I spent a fruitful three hours excavating, cleaning and discussing. We noted many contacts between breccia and unbrecciated Lickey Quartzite, in a variety of orientations, but most significantly, we unearthed a clear easterly-dipping unconformity between the two units. It is seen in outcrop, and its continuation can be traced in a detached slab that has fallen without any horizontal displacement.
We therefore conclude that the breccia is of Silurian age, more or less contemporaneous with the Rubery Sandstone, and reflects deposition of weathered fragments of Lickey Quartzite on a topographical high spot, beyond the reach of the encroaching Silurian sea. This would suggest that the Lickey Ridge may have had an earlier existence in the Lower Palaeozoic. The fact that the breccia lacks the extensive jointing that characterises the Lickey Quartzite may suggest that folding of the quartzite took place in the Ordovician, prior to the development of the unconformity.
The Bilberry Hill Unconformity in outcrop, with the Silurian breccia resting on the Lickey Quartzite.
Beneath the surrounding thin soil layer lies a white deposit of very fine sand and silt, which contains occasional well-rounded frosted grains, and embedded fragments of quartzite and breccia. This unsorted detritus is clearly derived from the outcrop, and may be the consequence of weathering under periglacial conditions.
The unconformity in the fallen slab.
As a footnote, the clearance was greatly enhanced by the use of a portable pressure washer – the WORX Hydroshot. A forty litre Aquaroll was used to take water to the site, and two freshly recharged batteries in the Hydroshot proved more than adequate to exhaust the water supply.
By Alan Richardson
