Selection and stability of quantitative stratigraphic age mo

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TitleSelection and stability of quantitative stratigraphic age models: Plio-Pleistocene glaciomarine sediments in the ANDRILL 1B drillcore, McMurdo Ice ShelfAbstractInterpretation of glacimarine sedimentary records from Antarctic shelf drillholes has been hampered by the ambiguous age of strata where erosional unconformities and coarse diamictite deposits truncate or omit the magnetostratigraphic and biostratigraphic units used for correlation. However, new quantitative biostratigraphic techniques enable the correlation of sparse, incomplete, and often reworked Plio-Pleistocene records of Ross Sea fossil diatom flora with the more extensively documented but potentially diachronous offshore history of species Ìfirst and last appearance datums (FADs and LADs). The approach uses comprehensive regional databases of fossil records and computer-automated search algorithms to find the multidimensional line of correlation (LOC) that best fits local observations, and to identify regionally isochronous biostratigraphic markers. Different model configurations can be used to produce LOCs that represent alternative working hypotheses regarding reworking and other sources of misfit in the biostratigraphic record, and that together provide an envelope of uncertainty for age interpretation. An integrated, quantitative chronostratigraphic model for the ANDRILL-1B drillcore was developed iteratively: an initial age model was constructed solely from preliminary on-ice observations of fossil diatom highest and lowest occurrences (HOs and LOs) and their correlation with a database of other local event records from 24 DVDP, CIROS, and IODP drillcore sections. The model was subsequently updated as off-ice work yielded additional biostratigraphic marker events and revised event horizons, Ar/Ar ages for volcanic material, better-constrained magnetostratigraphic interpretation, and refinements to computational/analytical methodology. The current quantitative biostratigraphic age model for the AND-1B hole integrates the local ranges of 29 diatom taxa, five dated volcanic samples, and independently constrained ages of five paleomagnetic reversals. During analysis, three model families were compared, each of which make different assumptions about the scale and influence of reworking and caving on observed biostratigraphic ranges, varying from assumption of no reworking/caving to widespread reworking/caving. Of these, the Hybrid Range Model, which allows for intermediate levels of reworking expected in a glaciomarine depositional environment, was found to give the most robust and reliable single LOC, even with immature input biostratigraphic data. However, alternative models used together provide an envelope of uncertainty around this preferred LOC. Results corroborate almost all of the on-ice geomagnetic polarity reversal age interpretations, but identify a previously unrecognized disconformity (Â 800. kyr hiatus) near 440. mbsf. In spite of substantial augmentation and progressive refinement of the AND-1B input dataset, successive versions of the output LOC retain the same fundamental structure and shape with only relatively minor, fine-scale differences. The age modelÅ› remarkable stability indicates that quantitative biostratigraphic analysis is capable of constructing robust and reliable regional correlation schemes and local section chronologies, even in cases of discontinuous stratigraphy and with relatively immature or incomplete datasets. Copyright 2012.AcknowledgementsOur most esteemed thanks to our two reviewers, Gerhard Kuhn and Roger Cooper, for their helpful feedback. Special thanks to Diane Winter and Reed Scherer for their help in preparing the diatom biostratigraphic database for use with CONOP, to Rob McKay for his assistance with ANDRILL-1B lithostratigraphic interpretations, and to Pete Sadler for his advice and support on developing the CONOP models. This material is based upon work supported by the Sarah Beanland Scholarship from GNS Science and postgraduate support from Victoria University of Wellington and from the Endowed Research Fund of the Antarctic Research Centre. The ANDRILL Program is a multinational collaboration between the Antarctic Programs of Germany, Italy, New Zealand and the United States. Antarctica New Zealand is the project operator, and has developed the drilling system in collaboration with Alex Pyne at Victoria University of Wellington and Webster Drilling and Enterprises Ltd. Scientific studies are jointly supported by the US National Science Foundation (Cooperative Agreement No. 0342484 to the University of Nebraska-Lincoln), NZ Foundation for Research Science and Technology (contracts C05X0410 and C05X1001), Royal Society of New Zealand Marsden Fund, the Italian Antarctic Research Programme, the German Research Foundation (DFG) and the Alfred Wegener Institute for Polar and Marine Research (Helmholtz Association of German Research Centres). Antarctica New Zealand supported the drilling team at Scott Base; Raytheon Polar Services supported the science team at McMurdo Station and the Crary Science and Engineering Laboratory. The ANDRILL Science Management Office at the University of Nebraska-Lincoln provided science planning and operational support.

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1st AuthorCody, R.AuthorCody, R.Levy, R.Crampton, J.Naish, T.Wilson, G.Harwood, D.Year2012JournalGlobal and Planetary ChangeVolume96-97Pages143-156DOI10.1016/j.gloplacha.2012.05.017URLhttps://www.scopus.com/inward/recor.....cb9a94deeafd39826f040d110KeywordsANDRILLAntarcticaChronostratigraphyCONOPDiatomPlio-pleistocene, GeomagnetismIceSalinity measurementSedimentologyVolcanoes, Biostratigraphy, algorithmdata setdepositional environmentdiatomfossil recordgenetic markermarine sedimentnumerical modelPliocene-Pleistocene boundaryquantitative analysisselectionstabilizationstratigraphytaxonomy, AntarcticaEast AntarcticaMcMurdo Ice Shelf, Bacillariophyta, rank5Author KeywordsAge modelANDRILLAntarcticaChronostratigraphyCONOPDiatomPlio-PleistoceneQuantitative biostratigraphy

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TypeArticleCitationCody, R., Levy, R., Crampton, J., Naish, T., Wilson, G. and Harwood, D. (2012). Selection and stability of quantitative stratigraphic age models: Plio-Pleistocene glaciomarine sediments in the ANDRILL 1B drillcore, McMurdo Ice Shelf. Global and Planetary Change, 96-97: 143-156 IdentifierCody2012Relevancerank5

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