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CYNGOR CEFN GWLAD CYMRU COUNTRYSIDE COUNCIL FOR WALES SITE OF SPECIAL SCIENTIFIC INTEREST CITATION ANGLESEY TRWYN DWLBAN Date of notification: 1957, 1985 National Grid Reference: SH532817 O.S. Maps: 1:50000 Sheet number: 114 1:25000 Sheet number: SH58 Site Area: 17.3 ha Description: This site is selected for its geological interest. The rock platform, cliffs and quarry faces of Trwyn Dwlban and Castell-mawr provide important exposures of Carboniferous Limestone strata. The rocks consist of limestone and sandstone layers, part of the Benllech Limestone, formed during the Brigantian Stage of the Lower Carboniferous Period. This is the type or reference locality for several members of the Benllech Limestone. Sedimentary structures of outstanding interest are displayed, including sandstone- filled pipes cutting the limestone layers, assumed to have formed by the collapse of wet sand into fissures opened by earth movements. These are associated with large cylindrical pits, also filled with sandstone, which are amongst the largest of their kind in Britain. They are thought to have formed by palaeokarstic processes, i.e. removal of the limestone in solution. This is a nationally important Carboniferous Limestone site with considerable potential for future research. The Carboniferous Limestone at Trwyn Dwlban is overlain by late Pleistocene deposits of great importance in unravelling the glacial/interglacial history of North Wales. A well-developed raised shore platform is underlain by a mixture of cemented angular limestone head and raised beach sediments which pass upwards into a pure limestone head. Irish Sea till overlies the head deposits and sometimes rests directly on the shore platform which exhibits excellent striations. This is one of only two sites known in North Wales where raised beach sediments of undisputed origin occur. It also records the clearest evidence from any section in North Wales for a sequence of environmental changes ranging from interglacial conditions with high sea-levels, through a period of severe periglacial climate, to full glacial conditions and a major incursion of ice from the Irish Sea. The site is unique in North Wales and provides a crucial link with South Wales, where raised beaches are a common element of the Pleistocene succession. Trwyn Dwlban is therefore a site of exceptional significance in developing a Late Pleistocene chronology for North Wales. This document is NOT a definitive legal version and has been formatted, updated and partially edited for use on the CCW Web site. This document should not be used in any legal proceedings, public enquiry or any other hearing or appeal. If you require a full legal copy of the document please contact CCW in writing. .

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Wales Regional Geology RWM | Wales Regional Geology
Wales regional geology RWM | Wales Regional Geology Contents 1 Introduction Subregions Wales: summary of the regional geology Available information for this region 2 Rock type Younger sedimentary rocks Older sedimentary rocks 3 Basement rocks Rock structure 4 Groundwater 5 Resources 6 Natural processes Further information 7 - 21 Figures 22 - 24 Glossary Clicking on words in green, such as sedimentary or lava will take the reader to a brief non-technical explanation of that word in the Glossary section. By clicking on the highlighted word in the Glossary, the reader will be taken back to the page they were on. Clicking on words in blue, such as Higher Strength Rock or groundwater will take the reader to a brief talking head video or animation providing a non-technical explanation. For the purposes of this work the BGS only used data which was publicly available at the end of February 2016. The one exception to this was the extent of Oil and Gas Authority licensing which was updated to include data to the end of June 2018. 1 RWM | Wales Regional Geology Introduction This region comprises Wales and includes the adjacent inshore area which extends to 20km from the coast. Subregions To present the conclusions of our work in a concise and accessible way, we have divided Wales into 6 subregions (see Figure 1 below). We have selected subregions with broadly similar geological attributes relevant to the safety of a GDF, although there is still considerable variability in each subregion. The boundaries between subregions may locally coincide with the extent of a particular Rock Type of Interest, or may correspond to discrete features such as faults.
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