Cardiff east where there is smaller bays

Cardiff

 

Cowbridge

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Bridgend

 

Ogmore

 

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

 

 

 

 

 

 

 

 

 

All the
rocks you see along the Ogmore coast are sedimentary rocks that were deposited
between 340 and 195 million years ago between the Carboniferous and Jurassic.
The oldest rocks seen are grey Carboniferous Limestones. These were deposited
near the equator in a warm, shallow, subtropical environment. There is a vast
array of fossils, especially corals such as Syringopora, Zaphrentis and
Caninia, Gastropods, Brachiopods and Crinoids. Around 300 million years ago, the
rocks got deformed and folded and as a result deposits such as Millstone Grit
and the Coal Measures of the later Carboniferous Period, that can be found to
the north, are missing as well as the sandstones, shales and red marls found
between Lavernock Point and Penarth which would have been deposited between the
Permian and Triassic. On top of the Carboniferous Limestone, Triassic Breccias
have now been deposited (Figure 3). The Triassic Breccias consists of angular
Limestone fragments held in red cement. These are most likely to have been
deposited by a flash flood as the angular and poorly sorted clasts suggests
that they have been transported under high energy but that they had not
travelled far. The red colour shows that the Breccia contains iron that has
been oxidised and it suggests that it came from desert environment. At the
beginning of the Jurassic Period, around 205 million years ago, sea levels
started to rise causing the land to form islands before being fully submerged.
This drowning event was made up of a series of marine transgressions followed
by still stands, which carved out several wave cut platforms in the Carboniferous
Limestones.  Rocks deposited on the shoreline of these islands are now
known as Sutton stone which consist of white, conglomeratic limestones with
pebbles of black chert and Carboniferous limestones. After this, there is no
evidence of any further geological events at Ogmore being preserved until the
end of the last Ice Age around 10,000 years ago.

Looking at past climate data
collected by the British Geological Survey, the Geology of Ogmore was greatly
affected by the position of South Wales at the time. During the Carboniferous
period, South Wales was on the edge of a mountain chain present on the eastern boundary
of a continent that included North America. To the south, large parts of Gondwana
were covered by a vast ice-cap which lead to low global sea levels. This
suggests that South Wales was mainly covered by tropical swamps, rivers and
shallow seas. This can be seen in the Limestones, found at Ogmore, that contain
both land and freshwater species. During the Triassic period, South Wales occupied a tropical position 16-34° north of
the equator, within the northern part of the supercontinent of Pangaea, and are
mainly above sea level with an arid climate. This means the Triassic
environment was hot and arid with rivers and temporary lakes. Wind would have
created the sand dunes, sand and gravel would
have been deposited along channels by the rivers and salt pans would have
formed by the evaporation of water. Evidence of this environment at Ogmore is
the Breccias with a rusty red colour. These two climates are very different to
present day South Wales where it is on the eastern Atlantic margin, affected by
14 glacial-interglacial fluctuations and currently in the Holocene warm stage. Wales
has a maritime climate with weather that is often cloudy, wet and windy but mild.

Ogmore attracts
a 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 emphasis
on the healthy population of salmon and sea trout that run up stream, as well
as brown trout. The lower tidal reaches are also fished for mullet, flounder
and bass. The Merthyr Mawr sand dunes, across the River Ogmore, are managed by
Natural Resources Wales (NRW), and are designated as a Site of Special
Scientific Interest (SSSI) due to its wealth of important plant life and insect
species. There are colonies of Prickly Saltwort, Sea Sandwort and
Babington’s Orache. Further inland the dunes have become stabilised with
species such as Marram Grass and Sand Couch. The dune slacks are also home to
some wild orchid species. One of these species is Marsh Helleborine (Figure 5) and
it only grows in the slacks because they are submerged during in winter.

The past environment in Ogmore has
heavily influenced how the current environment has formed. The cliffs along the
coast are almost entirely formed of Carboniferous Limestone from a past
tropical marine environment and Triassic Breccias from a desert environment.
Due to the resistant nature of these rocks, the cliff has exhibited low rates
of erosion in recent centuries (0.02 to 0.1 metre per year according to
Williams & Davies, 1987) producing the beautiful coastline present today.
The change in climate has dramatically altered the species which live in
Ogmore. As its location has drifted northwards, the climate has become
colder/more temperate and with this, many tropical plants and animals cannot
survive anymore. This shows how the geology, geography, climate and ecology
have interacted to produce the present environment seen in Ogmore.