A59 Kex Gill Diversion: Post-Excavation Palaeoenvironmental Assessment Report

The geoarchaeological investigation comprised the drilling of five purposive geoarchaeological boreholes to a maximum depth of c. 6. 70 m BGL, and the extraction and retention of the cored samples. Together with local geotechnical records, these were used to produce deposit models. Geoarchaeological and geotechnical deposit data can be used to identify areas of archaeological potential by characterising the probable nature and depth of sub-surface deposits. These have been refined following the assessment results, with updated models presented within this document. Palaeoenvironmental assessment was carried out on a representative deposit sequence sampled from the centre of the site (AOC53130WS1). Twelve of each pollen, ostracod, and diatom samples were taken, as well as four bulk samples for plant macrofossil analysis. Two yielded suitable material for radiocarbon dating. Paired humic-humin radiocarbon dating was also carried out on the base of the Holocene sequence. Six stratigraphic units were recorded on site, two of which were subject to palaeoenvironmental assessment. The earliest of the deposits was of the Millstone Grit Group comprising mudstone, siltstone, and sandstone forming 313 to 239 million years ago. Overlying this is Pleistocene till / head, comprising firm to very stiff yellowish brown, dark bluish grey and grey sandy and gravelly clays with frequent cobbles and boulders. These were encountered between 231. 1-153. 1 m OD and followed a west to east reduction across the Site. Holocene alluvium / colluvium comprising soft to firm, bluish grey mottled yellow to orangish brown, clayey silt and silty clays with a gravelly component overlies the till / head at 182. 12-156. 35 m OD. Nine subsamples were taken for pollen, diatom, and ostracods, as well as two for plant macrofossil assessment. Preservation was found to be poor, although remains indicate a herb fen environment with species suited to semi-terrestrial / ephemeral aquatic habitats with nearby woodland. The base was dated to the Devensian glacial (Beta-740302, >43500 BP; Beta-740303, 16887-16709 cal BC / 18837-18659 cal BP, Table 7), showing the reworking of older, glacial material into the sequence. Holocene organics are recorded between 170. 05-157. 91 m OD with an average thickness of 0. 5 m. Two subsamples were taken for pollen, diatom, and ostracods, as well as two for plant macrofossil assessment. Preservation was moderate, and the assemblage's showed stabilisation of the fen herb environment with the introduction of some reworked materials and human activity relating to arable and pastoral farming. The top and base of the peat was dated to the modern period (Beta-740250, 1972-1973 cal AD / -22--23 cal BP; Beta-740249, 1993-1997 cal AD / -43--47 cal BP Table 7) indicating reworking of modern carbon into the sequence. Overlying this is Holocene colluvium comprising soft to firm sands, gravels, and sandy gravelly clays and silts to the northwest of the Site at higher elevations of 232. 06-156. 65 m OD. A mixed deposit of topsoil, including surface peats, and made ground caps the sequence.