Geology Field Report
The coastline of Pembrokeshire displays greater scenery and rocks than any similar area in Britain with an exposure of over 250 miles. The underlying rocks, making the landscape, are ancient since they were built before the end of the carboniferous period of about 290 million years ago (Dorset Geologist Association Group, 2013). There are rocks that were formed back to a period of around 600 million years ago that have been found on the coast of the treginnis peninsula (Downes, 2011). Rocks younger than 290 million years have been lost, mainly because of marine erosion and weathering (Howells, 2007).
In terms of geological structure, the county can be divided into two parts that are the north and the south. The rocks in the north are of the lower Palaeozoic age and the Precambrian age (Howells, 2007). Most of the rocks are made from sea floor deposits with some igneous rock. These stones are said to have been laid down before the Caledonian mountain formation period that ended at around 400 million years ago (Howells, 2007). The rocks show southwest to north-east grains. As the result of this event and process, the faults and folds seen in the rocks at ceibwr bay were created (Dorset Geologist Association Group, 2013). The rocks to the south are younger, with the majority belonging to the upper Paleozoic age. The most common stone is the carboniferous limestone formations and the old red sandstone, as well as the coal measures of the south Pembrokeshire coalfield (Howells, 2007).
Majority of the rocks are the sedimentary rocks with traces of volcanic rocks along the southern shore of St. Bride’s bay (Downes, 2011). The faults and folds in the rocks of the south, for instance, the cobbler’s hole at St. Ann’s Head, were formed. As a result, during the hercynian orogeny of mountain formation, the general grain structure is almost the east-west nature (Dorset Geologist Association Group, 2013). The diversity of the coastal landscape seen today is a result of the geological actions and processes, such as river weathering, glaciations and marine erosion on these rocks (Howells, 2007).
On the Saundersfoot, on the south of the harbor, there are disclosures of ancient events of the late Carboniferous. The rocks contained mainly of the mudstone and sandstone that had traces of coal seams (Dorset Geologist Association Group, 2013). The Saunderfoot formed the major coalfield of the Pembrokeshine. A number of folds that appear to be cut by the thrust fold are also seen to the southern part of the area (Howells, 2007). In addition, tearing and shearing seem to take place, and it is associated with the seams of coal, as based that coal has the low level of competence than fireclay units and sandstone. There was asymmetrical fold structure with a worn base, where the shale was weaker, which had crushed during the tectonic measure (Downes, 2011). This fold has a steeper limb to the north because of the high amount of force from the south, which is a good example of angular folds.
In addition, a corresponding syncline can also be seen towards the north of the Saundersfoot, although highly eroded away, and the center is filled with beach sediments (Howells, 2007). In another 200 meters down to the south, there is another major over fold in massive sandstones thrust over a series of coal-bearing units, and shales that have the freshwater mussel carbonicola. At the Tenby areas, there are visible cliffs that are about 50 meters high that are folded in the carboniferous limestone (Dorset Geologist Association Group, 2013). Spectacular coastal features like stacks and arch l formations within the rock and forms are also found at the Tenby.
On the southern part of little Fervent red mudstone are bare with well-developed calcrete horizons in moher cliffs formation (Dorset Geologist Association Group, 2013). When one moves south at the Freshwater West, red mud can be observed, as well as sandstone made up of ferric that was formed by an oxidizing atmosphere. The sediments were deposited by a winding river and the show fining up units from the conglomerate (Bird, 2011). At the Armoth, the main observable features are list of fold and fault structures that are thrust due to crustal softening period of the Variscan orogeny (Howells, 2007).
Another standard bay is the Whitesands bay which comprises of a wide range of geological feature. To the north of the car park at the St. David’s, there is an indication of the Lingula flag formation that was formed during the upper Cambrian. They are made up of sandstone, mudstone and flagstones (Dorset Geologist Association Group, 2013). Due to sweating out quartz crystals are common in the sandstone units. Sedimentary structures are also observed. Such structures include the cross bedding, load casts and the graded bedding (Bird, 2011).
At south of the parking, Menevian cluster beds are bare and roofed by the periglacial head and elevated beach material. It is also observable that these beds are cut by a 10 meter wide dolerite dyke to the north of a few steps. The Solva bed is also exposed to the south and contains fine-grained sandstone and siltstone with perceptive cleavage, and that is the evidence of micro-folding (Bird, 2011). Far south of the Whitesands bay, at Ogofgolcha, the basal conglomerate of the carfax group is seen. This basal conglomerate suggests that a faulting and folding (Howells, 2007).
The Wiseman’s bridge lies between the Saundersfoot and the Amroth (Dorset Geologist Association Group, 2013). It mainly contains many different kinds of geological structures that were both formed during the ancient period and the current age’s end. It was observed that there are many stony channel stacks with possible tidal influence at the Wiseman’s bridge. There are also great cafes that were developed as a result of coal mining (Dorset Geologist Association Group, 2013). The coal was mined directly from cliffs. There was an interesting rock structure and a cut fold on the beach (Bird, 2011). The Pembrokeshire is the only county in Britain with a wide range of geological structures and landforms. It is, indeed, a complete source of geological data, as it contains all types of rocks. These rocks include the sedimentary, the igneous and the metamorphic rock (Howells, 2007).
Sedimentary rocks, being an example of the rocks that are found in the Pembrokeshire, are affected by water in various ways. The first way is that the formation of the sedimentary rocks is dependent on the weathering that is dependent on water (Bird, 2011). A major function of water is to assist in deposition of the weathered material that later accumulate forming the sedimentary rocks. The process of accumulating the sedimentary rocks by water is called denudation. Water transports the weathered materials from the weathering site to the areas where the sediments are precipitated out (Dorset Geologist Association Group, 2013).
The cambium started with a widespread rise in the ocean level (Howells, 2007). This folded features the Precambrian land surface, hence forming an extensive continental shelf that is evident at the St Non’s bay and the Whitesands bay on the St David’s peninsula. The transgressions were favored by the displacement of water by melting of the Precambrian ice. Expansion of sea water, as a result of warming up of the earth, that caused water to take up more volumes (Bird, 2011). Further, the marine transgression that took place on the flat land surface that was succeeded by erosion after the Caledonian orogeny, with deposition of shale. The little erosion produced madly sediments only that quickly moved to the marine carboniferous (Howells, 2007).
The coastline shape is determined by erosion from water and ice, which caused the accumulation of high masses of sandy and gravelly sediment in the area along the Irish Sea region. Additionally, the melted water from the glacier-carved broad valley in the landscape moves through and out of the Wales (Bird, 2011). The lower reaches of these valleys were filled with water, as sea level rose, consequently, allowing erosion that occurred deep into the coastline. Water waves from the Atlantic Ocean have resulted in the formation of various landforms. These include caves, arches, stacks and stumps. On the other hand, deposition from water waves is also evident at the Pebbly beaches and sandy beaches and bays that line the coast (Bird, 2011).
Rising temperatures cause the sea level to increase, hence submerging the coastline (Dorset Geologist Association Group, 2013). This submerging made the water wearing away activities to reach the inland and even erode shallow bare rocks.
At the coastal border, the structures of the Carboniferous Limestone are shortened not only by the cliffs, but also by this active erosion surface (Dorset Geologist Association Group, 2013). The dip of the Carboniferous, limestone that is bare in the cliffs varies as of landwards, to the west of the Devil’s Cauldron, to seawards, east of Flimston Bay. There are vertical and almost-vertical cliff structures that infrequently protrude, where the landward dip is replaced by cliffs that are greatly gentler in shape. Much of the cliff foot is noticeable by a jumble of boulders from equally recent and older rock falls (Dorset Geologist Association Group, 2013).
It was observed that the failure of sand, soil and granular rocks under physical conditions involved a range of micromechanical processes that produced kinematically, geometrically and texturally diverse natural structures. The typical structure is made up of two sub-parallel surfaces. Joints are the major categories (Bird, 2011). Shear fractures or faults are often idealized by relative sliding of two surfaces in the frictional contact are symbolized by stretchy crack model. Another group of structures resulting from the breakdown in porous-granular rock is the narrow-tabular zone of restricted to a small area strain referred to like a band (Howells, 2007). The most widespread type in this category is shear bands, largely characterized by shearing mechanism with either minor compaction or small dilation. Shearing without or with very little volume change and pure dilation or compaction without macroscopic shearing exist and represent the essential end members (Bird, 2011).
Deformation bands occur with mostly volume change. Another category of structures resulting from the collapse of the porous-granular rocks is a slender-tabular zone of controlled strain (Bird, 2011). The latter group can be sub-grouped into compaction bands that are characterized by a size diminish in the parent rocks and dilation bands characterized by volume increase. Shear bands may have either dilatants or compacted volumetric deformation (Downes, 2011). Without being particular regarding the relative magnitudes of shear plus the volumetric components within a band, the presence of a noticeable shear displacement slope across the band classify the shear groups. The nature of deformation inside individual layers is prescribed by textural properties of the parent rock (Howells, 2007).
Distinctive granular rocks are made up of granules, holes, and cement (Dorset Geologist Association Group, 2013). Deformation of these rocks engages in the change of size, as well as the shape of one or more of these constitutive rudiments. The investigative feature of shear bands is a macroscopic cut off offset across a tabular zone of finite small width with reverence to the other two dimensions. Previously continuous markers, for example, beds or older shear bands can determine the shear offset (Downes, 2011). Shear bands in grainy rocks have limited offsets in millimeters to centimeters. The standard shear strain calculated from these extents is on the order of unity.
The distance end to end dimension of unique shear bands is restricted to less than 100 meters. Consequently, it is necessary to form new shear bands in order to expand or lengthen a shear band formation (Bird, 2011). Deformation bands lack proof of macroscopic shear offset from predominantly by volumetric bend and are for that reason called volumetric deformation bands. Deformation bands with raised porosity occur in the undeformed state and no macroscopic shear counterbalance, as accounted by Downes (2011). In the case of deformation, the lacking of a shear offset was resolute based on crosscutting dealings of deformation bands with depositional marker and with other interweave bands that were formed earlier.
