Kidwelly, our beautiful village with its estuary, tidal flats and beyond, looking north to the high
ground towards Mynyddygarreg and Pontantwn. How often do we wonder as to exactly what it is that we are walking on, what is the history of the rock beneath our feet?
514 Ma (million years ago) ‘Wales’ was part of a tiny Arc shaped microcontinent (approx. the size of modern day Indonesia) located South of the Equator, under marine waters. Due to sea floor spreading and plate tectonics, ‘Wales’ drifted Northwards and migrated through varying climates which included the Southern Desert, Equatorial Rainforest, Northern Desert and finally into the Northern Hemisphere.
We may wonder why this information is important, what does this have to do with the rocks beneath our feet? At this point I need to explain that rocks fall into three main categories. Sedimentary, Metamorphic and Igneous. Sedimentary form from either detrital grains or by precipitation from solution in water. Metamorphic rocks form when heat and or pressure causes pre-existing rocks to recrystalise (without melting). Igneous rocks form from molten material as it cools and are associated with volcanic activity.
The fact that Wales, especially South Wales, spent a vast period of time under Marine waters 550-400 ma gives us a good clue as to the type of Geology expected. By the Silurian period (443.8(+/- 1.5) to 419.2(+/- 3.2)) Ma, the Iapetus ocean is closing and two continents collide producing the Caledonian Orogeny. The collision brings together Wales, Scotland and England.
This uplift brings Britain above sea level and terrestrial sediments shed from the Caledonian Mountains. Due to the climate at the time (southern Desert Belt) the arid conditions and sediments created Sandstone (Old Red Sandstone).
Within Pembrokeshire volcanic activity once ruled the day and the remnants of magma which had cooled and crystallised at depth have since been eroded and can now be seen at Whitesands Bay (Carn Llidi and Penbiri) and Garn Fawr on the Strumble Peninsula. But what about here in Kidwelly?
The bedrock is almost exclusively sedimentary in nature. Sediment includes sand, silt, mud and clay. North of Kidwelly, (Llansaint) the bedrock (known as the Senni Formation) is sedimentary sandstone aged 410.8-393.8 Ma, formed during the Devonian Period. This formation is characterised by the green colour of the sandstone, which is due to the presence of chloritized Micas. (Chlorite is a green mineral, and Mica a Silicate mineral).
Red Brown Siltstone and Mudstone. It is well known for early vascular plant remains inc. Gosslingia breconensis, Hostinella heardii, Krithodeophyton croftii, amongst others. Fossilised fish have been recorded including Pteraspis dixoni and Cephalaspis Sp. which can be found at Pen-y-Gau Ferryside.
The fossil record supports that at the time, environmental conditions could have seen a wetter climate and high water table. This type of rock is the same as that of the famous Pen-y-fan and Brecon Beacons escarpment. This formation and sediment was brought about by river and floodplain deposits carried from eroding mountains.
Moving to Kidwelly and the immediate surrounding area, sedimentary rocks are again found, including tidal deposits, sand, silt and clays. The Bishopston Mudstone formation is the dominant feature, the rock consisting of Mudstone and Sandstone are commonly fossiliferous. Trace coal is also a feature. The Bishopston Mudstone underlies the coal measures group and were therefore set down during the Carboniferous Period 329-319 ma. The Carboniferous period is central to Wales and its economic evolution as during the early Carboniferous period marine transgression produced warm shallow tropical seas rich in coral and shelly fauna.
By the mid part of this period, marine transgression left extensive deltas and coastal plains which supported forests. By the late Carboniferous period, accumulations of peat formed the now famous coal seams of the coal measures.
When contemplating fossil hunting, most think of the ‘Jurassic Coastline’ of Southern England. However, south west Wales and in particular our beautiful village of Kidwelly doesn’t lack far behind we have many varying species of fossiliferous flora and fauna.
Indeed, just beyond Kidwelly is MynyddyGarreg and Smarts Quarry, which is a SSSI. Here research into a Bivalve (Mollusk) within the Namurian Quartizite (Carboniferous period 326-313 ma) is continuing. This particular site is researched for the fossil and sediment type which was deposited via estuarine rather than shoreline activity.
So the next time you are sat enjoying the beautiful view, raise your cup of tea (or glass of wine) to the past 500 million years, to the creation of new land, the creation of mountains and to now extinct species, knowing that the land you tread is made up of tiny grains that have existed for millions of years having travelled thousands of miles, having seen the Southern Desert, Equatorial Rainforest, Northern Desert, warm tropical seas, floodplains and deltas.
Knowing that this made Kidwelly.
