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Dating Glacial Landforms I: Archival, Incremental, Relative Dating Techniques and Age- Equivalent Stratigraphic Markers

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Dating Glacial Landforms I: Archival, Incremental, Relative Dating Techniques and Age- Equivalent Stratigraphic Markers TREATISE ON GEOMORPHOLOGY, 2ND EDITION. Editor: Umesh Haritashya CRYOSPHERIC GEOMORPHOLOGY: Dating Glacial Landforms I: archival, incremental, relative dating techniques and age- equivalent stratigraphic markers Bethan J. Davies1* 1Centre for Quaternary Research, Department of Geography, Royal Holloway University of London, Egham Hill, Egham, Surrey, TW20 0EX *[email protected] Manuscript Code: 40019 Abstract Combining glacial geomorphology and understanding the glacial process with geochronological tools is a powerful method for understanding past ice-mass response to climate change. These data are critical if we are to comprehend ice mass response to external drivers of change and better predict future change. This chapter covers key concepts relating to the dating of glacial landforms, including absolute and relative dating techniques, direct and indirect dating, precision and accuracy, minimum and maximum ages, and quality assurance protocols. The chapter then covers the dating of glacial landforms using archival methods (documents, paintings, topographic maps, aerial photographs, satellite images), relative stratigraphies (morphostratigraphy, Schmidt hammer dating, amino acid racemization), incremental methods that mark the passage of time (lichenometry, dendroglaciology, varve records), and age-equivalent stratigraphic markers (tephrochronology, palaeomagnetism, biostratigraphy). When used together with radiometric techniques, these methods allow glacier response to climate change to be characterized across the Quaternary, with resolutions from annual to thousands of years, and timespans applicable over the last few years, decades, centuries, millennia and millions of years. All dating strategies must take place within a geomorphological and sedimentological framework that seeks to comprehend glacier processes, depositional pathways and post-depositional processes, and dating techniques must be used with knowledge of their key assumptions, best-practice guidelines and limitations. Keywords Chronology, varves, tephrochronology, dendroglaciology, lichenometry, glacial landforms, Schmidt hammer 1 TREATISE ON GEOMORPHOLOGY, 2ND EDITION. Editor: Umesh Haritashya Glossary Allochthonous Rocks that have been transported & deposited (inc. erratics, alluvial fans, gelifluction, etc. Autochthonous Rocks that have remained at or near site of formation Cryptotephra Distal tephra deposits, preserved as glass shards in sedimentary archives. Dipolar The Earth’s magnetic field is dipolar, with a north and south pole. Ecesis time The colonisation time lag interval on a surface; the time taken for trees, lichens or other species to colonise a surface. Tephra All-inclusive term for explosively erupted, loose, fragmental products of a volcanic eruption. Includes all grain sizes from find dust to large boulders. Tephrochronology The use of tephras as isochrones (time-parallel marker beds) to link stratigraphies in different localities. Enables the operator to establish relative or numerical ages. Tephrostratigraphy Study of sequences of tephra layers or strata and associated deposits and their relative and numerical ages. 2 TREATISE ON GEOMORPHOLOGY, 2ND EDITION. Editor: Umesh Haritashya Contents Abstract ............................................................................................................................................................... 1 Keywords ............................................................................................................................................................. 1 Glossary ............................................................................................................................................................... 2 1 Introduction ................................................................................................................................................. 5 2 Key chronological concepts ......................................................................................................................... 6 2.1 Length of time for different chronometers ......................................................................................... 6 2.2 Absolute and relative dating techniques ............................................................................................. 6 2.3 Direct and indirect dating techniques ................................................................................................. 6 2.4 Different tools for different environments ......................................................................................... 7 2.5 Precision and accuracy ........................................................................................................................ 9 2.6 Minimum and Maximum ages ........................................................................................................... 10 2.7 Quality assurance protocols .............................................................................................................. 10 3 Archival methods ....................................................................................................................................... 11 3.1 Remote sensing ................................................................................................................................. 11 3.2 Topographic maps ............................................................................................................................. 11 3.3 Historical documents ......................................................................................................................... 12 3.4 Integration of techniques .................................................................................................................. 12 3.5 Archival methods quality assurance protocols ................................................................................. 13 4 Relative chronological methods ................................................................................................................ 13 4.1 Introduction ....................................................................................................................................... 13 4.2 Morphostratigraphy .......................................................................................................................... 13 4.3 Schmidt Hammer dating .................................................................................................................... 14 4.3.1 Sampling procedures ................................................................................................................. 15 4.3.2 Calibration and numerical ages ................................................................................................. 17 4.3.3 Schmidt Hammer quality assurance protocols .......................................................................... 17 4.4 Amino acid racemization ................................................................................................................... 17 5 Incremental methodologies ...................................................................................................................... 18 5.1 Introduction ....................................................................................................................................... 18 5.2 Lichenometry ..................................................................................................................................... 18 5.2.1 Assumptions of Lichenometric dating ....................................................................................... 18 5.2.2 Lichenometric species ............................................................................................................... 19 5.2.3 Lichenometry sampling strategies ............................................................................................. 20 3 TREATISE ON GEOMORPHOLOGY, 2ND EDITION. Editor: Umesh Haritashya 5.2.4 Calibration curves of lichen growth rate ................................................................................... 21 5.2.5 Lichenometry quality assurance protocols ................................................................................ 21 5.3 Dendroglaciology ............................................................................................................................... 22 5.3.1 Introduction to Dendroglaciology ............................................................................................. 22 5.3.2 Glacially killed trees ................................................................................................................... 22 5.3.3 Glacially damaged trees ............................................................................................................ 24 5.3.4 Surface dating ............................................................................................................................ 25 5.3.5 Dendrochronology quality assurance protocols ........................................................................ 25 5.4 Varve records ..................................................................................................................................... 25 5.4.1 Introduction to varve chronologies ........................................................................................... 25 5.4.2 Varve counts .............................................................................................................................
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