EDO8156 - The Moors, Arne; palaeoenvironmental assessment 2024

OASIS: Wessex Archaeology (WA) has been commissioned by Kier Infrastructure Ltd (‘the client’) to undertake a palaeoenvironmental assessment and scientific dating of geoarchaeological boreholes in support of a program of palaeoenvironmental assessment and analysis. The palaeoenvironmental assessment and scientific dating comprises a total of 63 pollen samples, 11 diatom samples, 11 foraminifera/ostracod samples and 12 radiocarbon dates on deposits retained in six boreholes (HHWS-207, WA-03a, WA-05, WA-11, WA-101/22 and WA-102/22) from across the site. Previous work during Phase One identified a laterally extensive sequence of Holocene peat and alluvial deposits in places up to 5 m deep. The peat preserved across the site varies between 0.2 and 4.6 m thick, with the thickest peats preserved in the north-west, south-west and east of the site. Initial range-finder radiocarbon dates indicated the presence of peat of an early Mesolithic date in the south-west freshwater area, supported by initial pollen assessment of deposits in borehole WA-05. Project Results: There is a gap in peat formation between the middle Neolithic and early Bronze Age when large parts of the site were likely under marine influence, with peat formation recommencing from the early Bronze age. The peat in HHWS-207 formed from 2040-1770 cal. BC, with a modelled date for peat formation in WA-101/22 of 1430 1320 cal. BC. A medieval date from an organic alluvium overlying the peat in WA-101/22 is considered an outlier, where repeat measurements failed. The peat in WA-101/22 ceased forming in the late Bronze Age between 935-835 cal. BC. Range-finder dates from the earlier works at the site suggested peat formation ended in some site areas (TP 17 and 19) in the early Iron Age and Romano-British periods (UBA-37355: 780–420 cal. BC and UBA-37353: cal. AD 120–240). These dates were derived from terrestrial plant macrofossils in bulk samples and are currently considered outliners in the absence of supporting age determinations. Palaeoenvironmental assessment indicates that silty-clay deposits underlying the peat in WA-05, and present locally across the site, represent areas of either still or slow-moving water, infilling the uneven topography of the underlying Pleistocene fluvial sands and gravels. The pollen assemblages are indicative of a birch-dominated woodland, mostly likely of early Holocene date. These areas of freshwater eventually filled in with peat in the early Mesolithic. The plant macroremains and pollen suggest that the wetland was dominated by a freshwater swamp including stands of reeds and sedges with open pools containing aquatic plants, which persisted throughout the Mesolithic. Vegetation on the dry ground was dominated by woodland, initially by birch, with pine becoming dominant until a characteristic rise in hazel dated to between 8540-8300 cal. BC, together with an increase in oak and elm. The succession of woodland taxa is characteristic of the migration of trees into Britain from their glacial refugia as climate ameliorated during the early Holocene. The mixed deciduous woodlands containing oak, elm, hazel, ash and later lime became the dominant woodland habitats across much of Britain and lasted until the late Neolithic/early Bronze Age, when human communities began to progressively clear the land for agriculture. There is evidence for cultivation in the pollen diagram of Leslie Haskins, undertaken for a PhD thesis submitted in 1978. The pollen sequences were produced before the widespread application of radiocarbon dating, but an early-middle Neolithic date seems likely. Values for woodland decrease in pollen sequences from Arne in the Bronze Age, indicating the increasing impact of human communities on the associated dry ground. The palaeoenvironmental sequence does not extend beyond the late Bronze Age (935-835 cal. BC) in borehole WA-101/22. Iron Age and Romano-British dates derived from terrestrial macrofossils recovered from bulk samples during the 2018 watching brief are currently considered outliers. It is possible that isolated areas of peat may have survived into the Romano-British period, but these dates have not been replicated during the present study on peats in the same area, and as such, must be treated with caution. Indications of human activity in the palaeoenvironmental record have been identified, including small quantities of microscopic charcoal recorded on pollen slides throughout the peat deposits, with small quantities of samples recorded in bulk samples processed for plant macro remains. The interpretation of charcoal as evidence for human activity must be treated tentatively as fires can occur through natural agencies. Woodland clearance is recorded in the pollen sequences from the Neolithic in Haskins’ pollen sequence, and also in the Bronze Age peat deposits. There is also evidence for dry heath; though this could be a component of wetland environments, Heathlands are in part maintained by grazing pressure on land cleared by human communities. Their development on the site is significant given the location of the site on the edge of the Dorset Heaths National Character Area. Further investigation of the deposits would help to understand the development of these plant communities in this area. Recommendations are made for further analysis of samples with high potential to meet the aims and objectives set out in the Archaeological Management and Mitigation Strategy. The peat deposits assessed across the site represent one of the most complete Holocene environmental sequences in coastal southern Britain, and an important resource for understanding past environment, landscape and human activity.