Cardiff east where there is smaller bays

Cardiff   Cowbridge   Bridgend   Ogmore   Ogmore-by-Sea lies on the western edgeof the Glamorgan Heritage Coast.

It is 8 miles west from my home area, 4 milessouth of Bridgend and about 20 miles west of Cardiff (Figure 1). The main beachis two miles long stretching from the mouth of River Ogmore and the MerthyrMawr sand dunes in the west to the rocky shoreline in the east where there issmaller bays and inlets such as Hardy’s Bay and Horseshoe Bay with caves andsecluded coves. At the low tides of 0 metres you can see Tusker Rock, around 2miles off-shore, which was a notorious hazard for ships. At high tides of 10metres the sand is completely covered and just sharp rocks are exposed.

         All therocks you see along the Ogmore coast are sedimentary rocks that were depositedbetween 340 and 195 million years ago between the Carboniferous and Jurassic.The oldest rocks seen are grey Carboniferous Limestones. These were depositednear the equator in a warm, shallow, subtropical environment. There is a vastarray of fossils, especially corals such as Syringopora, Zaphrentis andCaninia, Gastropods, Brachiopods and Crinoids. Around 300 million years ago, therocks got deformed and folded and as a result deposits such as Millstone Gritand the Coal Measures of the later Carboniferous Period, that can be found tothe north, are missing as well as the sandstones, shales and red marls foundbetween Lavernock Point and Penarth which would have been deposited between thePermian and Triassic. On top of the Carboniferous Limestone, Triassic Brecciashave now been deposited (Figure 3). The Triassic Breccias consists of angularLimestone fragments held in red cement.

These are most likely to have beendeposited by a flash flood as the angular and poorly sorted clasts suggeststhat they have been transported under high energy but that they had nottravelled far. The red colour shows that the Breccia contains iron that hasbeen oxidised and it suggests that it came from desert environment. At thebeginning of the Jurassic Period, around 205 million years ago, sea levelsstarted to rise causing the land to form islands before being fully submerged.This drowning event was made up of a series of marine transgressions followedby still stands, which carved out several wave cut platforms in the CarboniferousLimestones.  Rocks deposited on the shoreline of these islands are nowknown as Sutton stone which consist of white, conglomeratic limestones withpebbles of black chert and Carboniferous limestones. After this, there is noevidence of any further geological events at Ogmore being preserved until theend of the last Ice Age around 10,000 years ago.

Looking at past climate datacollected by the British Geological Survey, the Geology of Ogmore was greatlyaffected by the position of South Wales at the time. During the Carboniferousperiod, South Wales was on the edge of a mountain chain present on the eastern boundaryof a continent that included North America. To the south, large parts of Gondwanawere covered by a vast ice-cap which lead to low global sea levels.

Thissuggests that South Wales was mainly covered by tropical swamps, rivers andshallow seas. This can be seen in the Limestones, found at Ogmore, that containboth land and freshwater species. During the Triassic period, South Wales occupied a tropical position 16-34° north ofthe equator, within the northern part of the supercontinent of Pangaea, and aremainly above sea level with an arid climate.

This means the Triassicenvironment was hot and arid with rivers and temporary lakes. Wind would havecreated the sand dunes, sand and gravel wouldhave been deposited along channels by the rivers and salt pans would haveformed by the evaporation of water. Evidence of this environment at Ogmore isthe Breccias with a rusty red colour. These two climates are very different topresent day South Wales where it is on the eastern Atlantic margin, affected by14 glacial-interglacial fluctuations and currently in the Holocene warm stage.

Waleshas a maritime climate with weather that is often cloudy, wet and windy but mild.Ogmore attractsa vast range of wildlife throughout the year. The Ogmore Angling Association(OAA) manages the waters of River Ogmore (Figure 4) as a game fishery, with an emphasison the healthy population of salmon and sea trout that run up stream, as wellas brown trout.

The lower tidal reaches are also fished for mullet, flounderand bass. The Merthyr Mawr sand dunes, across the River Ogmore, are managed byNatural Resources Wales (NRW), and are designated as a Site of SpecialScientific Interest (SSSI) due to its wealth of important plant life and insectspecies. There are colonies of Prickly Saltwort, Sea Sandwort andBabington’s Orache. Further inland the dunes have become stabilised withspecies such as Marram Grass and Sand Couch. The dune slacks are also home tosome wild orchid species. One of these species is Marsh Helleborine (Figure 5) andit only grows in the slacks because they are submerged during in winter.

The past environment in Ogmore hasheavily influenced how the current environment has formed. The cliffs along thecoast are almost entirely formed of Carboniferous Limestone from a pasttropical marine environment and Triassic Breccias from a desert environment.Due to the resistant nature of these rocks, the cliff has exhibited low ratesof erosion in recent centuries (0.02 to 0.1 metre per year according toWilliams & Davies, 1987) producing the beautiful coastline present today.The change in climate has dramatically altered the species which live inOgmore. As its location has drifted northwards, the climate has becomecolder/more temperate and with this, many tropical plants and animals cannotsurvive anymore.

This shows how the geology, geography, climate and ecologyhave interacted to produce the present environment seen in Ogmore.