Twilly Spring (Twilly Springs House), Manor Lane, West Hendred, Oxfordshire: Tree-ring Analysis, Radiocarbon Wiggle-matching, and Oxygen Isotope Dendrochronology of Elm and Oak Timbers

Author(s): Dr Martin Bridge, Cathy Tyers, Daniel Miles, A Bayliss, Silvia Bollhalder, Lukas Wacker, Neil J Loader, Danny McCarroll, Darren Davies, Giles Young

Ring-width dendrochronology was undertaken on elm timbers from two structural phases, producing an undated 93-year long elm site chronology from core samples taken from seven roof timbers. A small number of oak timbers had been analysed previously, with a single timber of the main frame having a likely felling date range of AD 1649–81 and a tiebeam of a later phase of roofing coming from a tree felled in the spring of AD 1807. Radiocarbon dating was undertaken on six single-ring samples from core tswh18a, which was included in the undated elm site chronology. Wiggle-matching of these results suggests that the final ring of tswh18a, the last ring produced prior to felling, formed in the first decade of the nineteenth century AD. As part of an initiative to investigate the potential for oxygen isotope dating of elm timbers using an oxygen isotope chronology developed from oak latewood cellulose, two elm samples from the undated elm site master sequence were selected for isotopic analysis. Eighty-six measurements were obtained on latewood from single growth-rings of core tswh17 sampled from a lower purlin, and seventy-nine isotope measurements were obtained on latewood from single growth-rings of core tswh18c, a duplicate core from the same hip rafter as tswh18a. The two isotopic series cross-match strongly when offset by ten years. This is consistent with the ring-width cross-matching. The resulting ninety-year isotopic mean cross dates with the south-central England oxygen isotope master chronology, suggesting felling dates of winter AD 1806/07I (tswh18c) and between summer AD 1806I and winter AD 1806/07I (tswh17). The dendrochronological analysis of elm timbers remains a significant challenge across England where only six elm timbers have previously been reported as dated by ring-width dendrochronology, even though elm is the second commonest building timber in the country. The successful application of radiocarbon wigglematching and oxygen isotope dendrochronology to provide secure calendar dating for the elm site master sequence from the roof of Twilly Springs House, suggests that potential now exists for scientific dating of elm timbers from historic buildings in England.

Report Number:
97/2019
Series:
Research Report
Pages:
52
Keywords:
Dendrochronology Radiocarbon Dating Standing Building Wiggle-Match Oxygen Isotope

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