Chonar Farm, Wilmslow to Alderley Edge Pipeline, Cheshire East
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CHONAR FARM, WILMSLOW TO ALDERLEY EDGE PIPELINE, CHESHIRE EAST Palaeoenvironmental Assessment Oxford Archaeology North May 2012 United Utilities Ltd Issue No: 2012-13/1286 OAN Job No: L9974 NGR: SJ 85595 79622 Chonar Farm, Wilmslow to Alderley Edge Pipeline, Cheshire East: palaeoenvironmental assessment 1 CONTENTS SUMMARY .................................................................................................................. 2 ACKNOWLEDGEMENTS .............................................................................................. 3 1. INTRODUCTION ..................................................................................................... 4 1.1 Circumstances of the Project ............................................................................. 4 1.2 Location, Geology, and Topography.................................................................. 4 2. METHODOLOGY .................................................................................................... 6 2.1 Palaeoenvironmental Coring.............................................................................. 6 2.2 Palaeoenvironmental Assessment ...................................................................... 6 3. RESULTS ................................................................................................................ 8 3.1 Radiometric Dates............................................................................................. 8 3.2 Pollen Assessment............................................................................................. 8 3.3 Plant Macrofossil Assessment ......................................................................... 10 4. CONCLUSION ....................................................................................................... 12 BIBLIOGRAPHY ........................................................................................................ 13 Cartographic Sources................................................................................................ 13 Secondary Sources ................................................................................................... 13 FIGURES................................................................................................................... 15 APPENDIX 1: POLLEN COUNTS ................................................................................ 16 For the use of United Utilities Ltd © OA North: May 2012 Chonar Farm, Wilmslow to Alderley Edge Pipeline, Cheshire East: palaeoenvironmental assessment 2 SUMMARY In June 2010, OA North undertook a programme of palaeoenvironmental coring across a small peat basin located close to Chonar Farm, Wilmslow, Cheshire East (centred on NGR: SJ 85595 79622). The work was commissioned by United Utilities Ltd as part of a wider scheme of archaeological investigation connected with the construction of a water pipeline running between Wilmslow and Alderley Edge. Two cores were subjected to pollen and plant macrofossil assessment, and also to radiometric dating. These studies indicated that the peat within the basin mire was formed prior to the Bronze Age, and that the mire contains an assemblage of pollen and plant macrofossils allowing for a partial reconstruction of the local environment. More specifically, these palaeoenvironmental remains are indicative of the transition from open plant communities, probably present in the early Mesolithic period, to mixed woodland, and a local development of alder carr, dating to the early Bronze Age. For the use of United Utilities Ltd © OA North: May 2012 Chonar Farm, Wilmslow to Alderley Edge Pipeline, Cheshire East: palaeoenvironmental assessment 3 ACKNOWLEDGEMENTS Oxford Archaeology North (OA North) would like to thank United Utilities Ltd for commissioning the project. Thanks are also due to Mark Leah, Cheshire Archaeology Planning Advisory Service, and Sue Stallibrass, English Heritage Archaeological Science Advisor for North West England. The palaeoenvironmental coring was undertaken by Denise Druce and Mairead Rutherford and the palaeoenvironmental assessment was completed by Mairead Rutherford. Mark Tidmarsh produced the illustrations. Alison Plummer managed the project, whilst the report was edited by Richard Gregory. For the use of United Utilities Ltd © OA North: May 2012 Chonar Farm, Wilmslow to Alderley Edge Pipeline, Cheshire East: palaeoenvironmental assessment 4 1. INTRODUCTION 1.1 CIRCUMSTANCES OF THE PROJECT 1.1.1 In June 2010, OA North undertook a programme of palaeoenvironmental coring across a small peat basin located close to Chonar Farm, Wilmslow, Cheshire (centred on NGR: SJ 85595 79622; Fig 1). The work was commissioned by United Utilities Ltd as part of a wider scheme of archaeological investigation connected with the construction of a water pipeline running between Wilmslow High Lifting Pumping Station and Alderley Edge Service Reservoir, Cheshire East (NGR: SJ 84974 81534 to SJ 85792 77757). 1.1.2 The peat basin was identified during an archaeological watching brief, which observed the stripping of the topsoil along the route of the pipeline (OA North 2011). The programme of palaeoenvironmental coring followed recommendations made by the Cheshire Archaeology Planning Advisory Service and the English Heritage Archaeological Science Advisor for North West England, and was designed to retrieve samples, which could then be subjected to pollen and plant macrofossil assessment, and also to radiometric dating. 1.2 LOCATION, GEOLOGY, AND TOPOGRAPHY 1.2.1 The peat basin is positioned immediately west of Chonar Farm, which lies at the junction of Hough Lane and Heyes Lane, and falls within an area that was designated as ‘Field 19’ during an earlier archaeological desk-based assessment (OA North 2009). The watching brief established that the peat basin lay in the eastern portion of the field (Pl 1), and that it was present as a thin layer of peat, positioned approximately 3m from the eastern side of the pipeline easement, which then became progressively deeper. Several tree trunks and roots were also observed within the peat (Pl 2). Plate 1: view to the south in Field 19 looking towards the peat basin For the use of United Utilities Ltd © OA North: May 2012 Chonar Farm, Wilmslow to Alderley Edge Pipeline, Cheshire East: palaeoenvironmental assessment 5 Plate 2: Section of tree trunk and roots exposed in the peat basin 1.2.2 Across Field 19 the solid geology, as mapped by the British Geological Survey (1977), consists of the Wilmslow Sandstone Formation, dating to the Early Triassic Epoch, and the peat basin appears to have developed within a hollow contained within the overlying superficial geology, which comprises Devensian Till. Topographically, the peat basin resides at 85m above Ordnance Datum (aOD). 1.2.3 Historically, the peat basin did not exist in isolation, but lay directly adjacent to a former wetland area, known as Lifeless Moss (Leah et al 1997, 46-8). This mossland, although now completely reclaimed, is depicted on Burdett’s 1777 map of Cheshire, and lay immediately west of the exposed peat basin, within an area bounded to the north by Big Brick Hill Farm, to the south by Hough Green Farm, to the east by Hough Lane, and to the west by Moss Farm (op cit, fig 29). 1.2.4 More generally, Lifeless Moss and the exposed peat basin at Chonar Farm are situated within Cheshire’s ‘Eastern Mosses’ as defined by the North West Wetlands Survey (op cit, 45-95). This area of wetlands contains numerous small basin mires, such as that exposed at Chonar Farm, and also several large mosses, principally Danes Moss and Lindow Moss (op cit, 45). For the use of United Utilities Ltd © OA North: May 2012 Chonar Farm, Wilmslow to Alderley Edge Pipeline, Cheshire East: palaeoenvironmental assessment 6 2. METHODOLOGY 2.1 PALAEOENVIRONMENTAL CORING 2.1.1 Following the identification of the peat basin during the watching brief, six gouge cores were initially extracted along a short transect (<20m) running across the basin in order to establish the lithological sequence. These cores indicated that the lower part of the sequence comprised grey silts and clays, which were overlain by a homogenous deposit of black peat. This deposit, in turn, was sealed by a further deposit of peat, containing some moss peat, which then graded upwards into a woody peat. 2.1.2 Once the lithological sequence had been determined, a palaeoenvironmental core (WS-5) was extracted from the deepest area of peat identified along the line of the transect using a Russian core (WS-5). The Russian core collect a 0- 2.40m-deep sample of peat, but, due to increasing silty lithologies, a gouge core had to be used to retrieve the section extending between the depths of 2.40m and 3.20m. A second Russian core (WS-2) was also collected from the transect, though it was suspected that this core might contain younger, more recent sediments. 2.2 PALAEOENVIRONMENTAL ASSESSMENT 2.2.1 Pollen assessment: the palaeoenvironmental cores were cleaned and described prior to sub-sampling. Sixteen sub-samples were taken from WS-5 and five sub-samples were taken from WS-2 (Tables 1 and 2). Two sub-samples were selected for AMS dating, one from the top of the Russian core (WS-5) at 0.04- 0.05m and the second was taken from the base of the Russian core (WS-5) at 2.39-2.40m. 2.2.2 Volumetric samples were taken from the 21 samples and two tablets containing a known number of Lycopodium spores were added so that pollen concentrations could be calculated (Stockmarr 1971). The samples