Ground Investigation in South West Wales Discovers Marine Fossils

While undertaking a project within a commercial retail park in South West Wales, one of our geological engineers uncovered a number of marine fossils which included Brachiopods and Gastropods.

The historical mapping, which was analysed as part of the Phase 1 Desk Study highlighted that a large section of the retail park and the northern area of the site had been a Limestone Quarry from approximately the late 1800’s until the 1980’s. Environmental search results suggested that the quarry had been infilled and thus become a landfill during the 1980’s.

On the basis of the desk study information and discussions with the client, it was decided that the ground investigation should consist of boreholes in order to assess the depth to the top of the rock head, both within the area previously shown as the Limestone Quarry and within the southern section of the site, which was believed to be outside of the quarry. Additionally, contamination testing and ground gas monitoring were undertaken within the standpipes installed in the boreholes.

The site investigation, which was carried out in the car park of a commercial premises, involved a series of shallow (dynamic) windowless sampler boreholes, hand dug inspection pits to assess the existing foundations and deep boreholes. All the site works were undertaken while still allowing both the car park and the commercial property to remain open, as well as keeping the public safe without compromising on site security.

The boreholes were drilled using standard cable percussive drilling techniques until refusal on the bedrock (Pembroke Limestone). A Rotary Coring rig was mobilised to site in order to prove a significant depth of rock. The Brachiopod and Gastropod fossils were identified, first by our lead driller then confirmed by the on-site engineer, within the rock cores recovered from one of the boreholes.

The Pembroke Limestone, in which the marine fossils were discovered, is a sedimentary bedrock which was formed approximately 326-359 million years ago in the Carboniferous Period, when the local environment was dominated by shallow carbonate seas, similar to the modern day Caribbean. The fossils appear to have undergone recrystallisation during diagenesis.

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