a mid to late holocene cryptotephra framework from eastern north america -凯发官网入口

a mid to late holocene cryptotephra framework from eastern northamericahelen mackaya , * , paul d.m. hughes a , britta j.l. jensen b , 1 , pete g. langdon a ,sean d.f. pyne-o'donnellb , gill plunkett b , duane g. froese c , sarah coulter d ,james e. gardnerea geography and environment, university of southampton, southampton, so17 1bj, ukb school of geography, archaeology and palaeoecology, queen's university belfast, belfast, bt7 1nn, ukc department of earth and atmospheric sciences, university of alberta, edmonton, ab, t6g 2e3, canadad omagh minerals ltd, 56 botera upper rd., omagh, bt78 5lh, uke department of geological sciences, jackson school of geosciences, the university of texas at austin, tx, 78705, usaa r t i c l e i n f oarticle history:received 18 august 2015received in revised form29 october 2015accepted 14 november 2015available online 10 december 2015keywords:tephracryptotephravolcanic ashpeatlandslate holocenenorth americaa b s t r a c tholocene cryptotephras of alaskan and pacific northwestern origin have recently been detected ca.7000 km away on the east coast of north america. this study extends the emerging north americantephrochronological framework by geochemically characterising seventeen cryptotephra layers from fournewly explored peatlands. all detected tephras were deposited during the late holocene, with no ho-rizons present in the peat between ca. 3000e5000 years ago. the prevalence of the alaskan white riverash eastern lobe (ad 847 ± 1) is confirmed across the eastern seaboard from newfoundland to maineand a regional depositional pattern from mount st helens set w (ad 1479e1482) is presented. the firstoccurrences of four additional cryptotephras in eastern north america are described, three of which mayoriginate from source regions in mexico, kamchatka (russia) and hokkaido (japan). the possibility ofsuch tephras reaching eastern north america presents the opportunity to link palaeo-archives from thetropics and eastern asia with those from the western atlantic seaboard, aiding inter-regional compari-sons of proxy-climatic records.© 2015 the authors. published by elsevier ltd. this is an open access article under the cc by license(http://creativecommons.org/licenses/by/4.0/).1. introductionprecise palaeoclimatic comparisons between sites and regionsare essential for understanding past climate dynamics. however,inter-site correlation is often limited by poor chronological control.tephrochronology provides an age-equivalent dating method byusing volcanic ash layers with unique geochemical signatures astime-specific marker horizons (isochrons) to connect and syn-chronise archives (e.g. alloway et al., 2013; lowe, 2011). theseisochrons are used to create high-resolution records of palae-oenvironmental or archaeological events, the relative timing ofwhich can be compared across sites and regions (e.g. hall et al.,1993; lane et al., 2013a, b; lowe et al., 2012; plunkett andswindles, 2008). an air-fall ash layer from a volcanic eruption canbe regarded as having been deposited instantaneously in geologicaltime and can thus adopt the eruption's agewherever it is found as awell-defined primary horizon. if the eruption history is unknownor poorly constrained then archives can still be correlated if thesame tephra horizons are present and these fixed tie-points can beused to create a common timescale (lowe, 2011).investigations of far-travelled microscopic volcanic glass shards(cryptotephra e with dimensions typically <~125 m m; sensu loweand hunt, 2001) in sediments allow for the detection of previ-ously unrecognised ash horizons and sometimes unknown erup-tions. these cryptotephras provide the opportunity to obtainprecise chronologies in areas that were thought to be outside therange of tephrochronology, thus greatly expanding the datingframework and increasing the number of regions that can be linkedtogether. cryptotephra studies originally focused on icelandictephras in western europe, but the potential for north americancryptotephra studies is rapidly emerging (payne et al., 2008; pyne-* corresponding author. school of geography, politics and sociology, university ofnewcastle, newcastle upon tyne, ne1 7ru, uk.e-mail address: helen.mackay@newcastle.ac.uk (h. mackay).1current address: royal alberta museum, edmonton, ab, t5n 0m6, canada.contents lists available at sciencedirectquaternary science reviewsjournal homepage: www.elsevier.com/locate/quascirevhttp://dx.doi.org/10.1016/j.quascirev.2015.11.0110277-3791/© 2015 the authors. published by elsevier ltd. this is an open access article under the cc by license (http://creativecommons.org/licenses/by/4.0/).quaternary science reviews 132 (2016) 101e113