North Wales) Thematic Geological Mapping S 14 G Campbell and B a Hains Contributors M G Culshaw, J a Crummy and M a Lewis
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TECHNICAL REPORT WA/88/2 Deeside (North Wales) thematic geological mapping S 14 G Campbell and B A Hains Contributors M G Culshaw, J A Crummy and M A Lewis BRITISH GEOLOGICAL SURVEY TECHNICAL REPORT WA/88/2 Onshore Geology Series Cover pcover Well-bedded limestone of the Cefn Mawr Limestoneis ex- posed in Waen Brodlas quarry, now disused. The main face[SJ 1875 73151 is here seen fromthe south- west. The unusualnature of the bedding at this stratigraphic hor- izon is particularlywell displayed, with several prominent low-angle discordant bedding-plane contacts. Deeside (North Wales) thematic Back cover 1 To the south of Waen Brodlas quarry [SJ 186 7321 the moundytopography comprises geologicalmapping deposits of made ground associated with the numerous shafts and trial pits that characterise muchof Halkyn Mountain. Most weresunk during the nineteenthcentury in S D G Campbell and B A Hains the search for lead andcopper veins. 2 Beautifullypreserved fossil cri- Contributors noids are exposed in a disused quarry [SJ 188 7251 on Halkyn M G Culshaw and J A Crummy engineering geology Mountain. The rock-type was main- ly usedly for ornamental purposes. M A Lewis hydrogeology 3 A spectacularly well-preserved trace-fossil burrow system(Zoophy- cos) exposed in PantQuarry [SJ 201 7021, in which limestone isworked. 4 Sand and gravel is worked in the Rhosemor pit [SJ 216 6701, here seen fromthe north. 5 The Loggerheads CountryPark is a Siteof Special Scientific Interest. Large-scale bedding typicalof the Loggerheads Limestone dips gently to the east in the west-facing scarp. 6 Well-bedded and fmely laminated chertsare exposed in the disused Pen yr Henblas quarries [SJ 191 7273. Geographic index United Kingdom, North Wales, Clwyd Subject index Thematic maps, resources, geo- technics, hydrogeology, minerals, coal, aggregate, ground stability This report was produced under contract to the Department of the Environment on behalf of the Welsh Office, but the views expressed in it arenot necessarily those of the Department nor of the Offke. Bibliographic reference Campbell, S D G, and Hains, B A. 1988. Deeside (North Wales) thematic geological mapping. British Geological Survey Technical Report WAl88i2. 0 Crowncopyright 1988 Keyworth,Nottingham British Geological Survey 1988 BRITISH GEOLOGICAL SURVEY The full range of Survey publications is available through the Keyworth, Nottingham NG12 5GG Sales Desks at Keyworth and Murchison House, Edinburgh. s Plumtree (06077) 6111 Telex 378173 BGSKEY G Selected items can be bought at theBGS London Information Fax e 060 77-6602 Office, and orders are accepted here for all publications. The adjacent Geological Museum bookshop stocksthe more popular Murchison House, West Mains Road, Edinburgh EH93LA books for sale over the counter. Most BGS books and reports . .. 031-6671000Telex727343 SEISED G . .. - are listed in HMSO’s Sectional List 45, and can be bought from e Fax e 031-668 2683 HMSO and through HMSO agents and retailers. Maps are listed in theBGS Map Catalogue and the Ordnance Survey’s London Information Office at theGeological Museum, Trade Catalogue, and can be bought from Ordnance Survey Exhibition Road, South Kensington, LondonSW7 2DE agents as well as from BGS. e 01-5894090 Telex8812180 GEOSCI G The BritishGeological Survey carries out the geological survey 01-9389056157 Fax 3 01-584 8270 of Great Britain and Northern Ireland (the latter as an agency service for the government of Northern Ireland), and of the surrounding continental shelfi as well as its basic research 64 Gray’s Inn Road, London WClX 8NG projects. It also undertakes programmes of British technical aid e 01-242 4531 in geology in developing countries as arranged by the Overseas Development Administration. 19 Grange Terrace, Edinburgh EH9 2LF e 031-6671000Telex727343 SEISED G The British Geological Survey is a component body of the Natural Environment Research Council. St Just, 30 Pennsylvania Road, Exeter EX4 6BX s Exeter (0392) 78312 Maps and diagrams in thisbook use topography based on Ordnance Survey mapping Bryn Eithyn Hall, Llanfarian, Aberystwyth, Dyfed SY23 4BY 3 Aberystwyth (0970) 611038 Windsor Court, Windsor Terrace, Newcastle upon Tyne NE2 4HB CS 091-2817088 Fax e 091-2819016 Geological Survey of Northern Ireland, 20 College Gardens, Belfast BT9 6BS e Belfast (0232) 666595and 666752 Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB e Wallingford(0491) 38800 Telex 849365 HYDRO G Fax 3 0491-32256 Parent Body Natural Environment Research Council Polaris House, North Star Avenue, Swindon, Wiltshire SN2 1EU e Swindon(0793) 40101 Telex 444293 ENVRE G Fax e 0793441652 CONTENTS Appendices A. List of British Geological Surveyopen-file ExecutiveSummary 1 reports, 1: 10 OOO/lO 560 geological maps and Notes to the userand limitations 4 palaeontological reports produced as part of the 99 Introduction 7 project B. Geotechnical tests quoted in the database,and Objectives7 their applications 10 1 The use of this report 7 List of boreholes 105 Data sources used in the report 8 C. List of shafts sunk for coal 132 Constituent parts of the results 9 D. E. Selective list of shaftsand adits identified as Geographicaland planning background 9 being open surface,at theat time of Geographicalbackground 9 survey 152 Planning background 1 1 F. Logsof boreholes sunk as part of theproject to prove sandand gravel resources with Geological informationrelevant to planning 12 derivedparticle size data 155 Mineral extraction and resources 12 Engineering geology 14 Figures Water resources 15 1. Sketch-map of the study area showing its Geological Sequence 17 regional setting 5 2. Sketch-map showing the component Description of thematic geological maps 18 Notes aboutthe topographic base 18 1:lO OOO/lO 560 sheets of the study area, the outlines of the earlier County Sheet Grid, and List of ThematicElements 18 selected planningfeatures 6 Map 1 Bedrock Geology 18 - 3. Topography, drainage and chief towns of the Map 2 Superficial (Unconsolidated) - studyarea 10 deposits 20 4. Simplified geological map of the study area 19 Map 3 Boreholes, Rockhead and thickness - 5. Detailed map (Scale 1:lO 560) of the of Superficialdeposits 22 distribution of shafts and trial pits on Halkyn - Map 4 Mining activities; - Mountain Coal/Metalliferous 23 a) The area between Pant and Map 5 Resources (Bedrock) except - - Pant-y-pwll-dwr 25 Coal/Metalliferous 29 b) The area between Pen yr Henblas and Map 6 - Resources - Sand and Gravel 34 Brynford 26 Map 7 Hydrogeology and Water Supply 35 - 6. Detailed map (Scale 1:lO 560) of the EngineeringGeology 37 Loggerheads Country Park and Thegeotechnical database 37 Cefn-Mawr/Coed Pwll-y- blawd Site of Special Engineering classification of the rocks ScientificInterest 27 and soils 38 7. Plasticity Diagram for Weathered Mudstones Engineering geology of the bedrock and Shales 42 formations(rock) 38 8. Plasticity Diagram for Head, Alluvial and Engineering geology of the superficial Estuarine Alluvial Cohesive Soils 52 (unconsolidated)deposits (soils) 50 9. Plasticity Diagram for Till (Boulder Clay) and Groupings of superficial deposits in other Glacial Cohesive Soils 56 engineering terms 64 10.Generalised geological sequence of the study Engineering problems associated with area 74 superficial(unconsolidated) deposits 65 1 1 .Detailed correlation of the Limestone sequences of the main working quarries (Graphic logs Summary of Geology 73 compiled by S D G Campbell and J R Davies) Conclusionsand Recommendations 85 a) Cefn Mawr Limestone correlation 76 b) Loggerheads Limestone correlation, with an References 91 inset of the position of the .quarry sites 77 Glossary 94 12.Correlation of the Productive Coal Measures (Westphalian A-C) 8 1 Tables Accompanying documents 1. ‘Correlation’ of Coal Seam Nomenclature for Theaccompanying maps at 1:25 000 scale and the northern ‘Flintshire Coalfield’ 28 printed on amended Ordnance Survey topographic 2. Active limestone quarries at the time of bases, are available separately. The full set is part survey 31 of BGS Research Report WA/88/2 comprising the Summary of mechanical and chemical property 3. following volumes: datafrom limestones 32 4. Summary geotechnical data for Mudstones of Deeside (North Wales) Thematic Geological Buckley Formation (Highly to Completely Mapping - Report Weathered) 43 Map 1 of Bedrock Geology 5. Summary geotechnical data for Map 2 of Superficial (Unconsolidated) deposits Shales/Mudstones of Productive Coal Measures Map 3 of Boreholes, Rockhead and thickness of (Fresh to Slightly Weathered) 44 Superficial deposits 6. Summary geotechnical data for Map 4 of Mining activities; CoallMetalliferous Shales/Mudstones of Productive Coal Measures Map 5 of Resources (Bedrock) - except (Moderately to Highly Weathered) 45 Coal/Metalliferous 7. Summary geotechnical data for Map 6 of Resources - Sand and Gravel Shales/Mudstones of Productive Coal Measures Map 7 of Hydrogeology and Water Supply (Completely Weathered to Residual Soil) 46 8. Summary geotechnical data for Shales of Note: it is emphasised thatthe maps associated Halkyn Formation (Fresh to Slightly with thisreport should be used for preliminary Weathered) 47 studies only and are not to be used as a substitute 9. Summary geotechnical data for Shales of for on-site investigations Halkyn Formation (Moderately to Highly Weathered) 48 10.Summary geotechnical data for Shales of Halkyn Formation (Completely Weathered to Residual Soil) 49 1 1.Summary geotechnical data for Peat 51 12.Summary geotechnical data for Alluvium;