The Holocene cryptotephra record of Lake Kushu, northern Japan: Towards an integrated tephrostratigraphic framework for East Asia Xuan-Yu Chen Thesis submitted for the degree of Doctor of Philosophy at the University of London September 2018 Institution of study: Department of Geography & Department of Earth Sciences Royal Holloway, University of London Declaration This thesis presents the results of original research undertaken by the author and none of the results, illustrations and text are based on published or unpublished work of others, except where specified and acknowledged. Signature: …………………………………………… Date: ……..………………….. 2 Abstract Tephrochronology is the study of the stratigraphy, age, glass chemistry and distribution of volcanic ash (i.e. tephra) layers and the use of widely dispersed tephra isochrons for precise dating and correlation of geological, paleoclimate and archaeological records. Palaeoclimate records in East Asia, a region where environmental changes are primarily controlled by the Asian monsoon, are essential for our understanding of monsoon dynamics. Importantly, East Asia is a volcanically active region, which possesses great potential for offering widespread tephra layers. As such the region is an ideal area for optimising the use of tephra layers to synchronise palaeoclimate records. However, before this can be achieved, a comprehensive regional tephra framework is required, in order to guide future correlations and minimise miscorrelation. In this PhD project, the proximal volcanic stratigraphy of Changbaishan volcano China/N Korea and a cryptotephra deposit from Lake Kushu northern Japan were investigated. These records were then compared to a range of data sources to attempt to correlate and, where possible provide independent ages for the tephra. Proximal- distal correlations of the Millennium eruption tephra (~1ka) allowed the clarification of controversial proximal stratigraphy of the Changbaishan volcano. In addition, precisely determined tephra ages were used to constrain the radiocarbon chronology of the distal lacustrine record. A detailed investigation of cryptotephra on the entire 16-m-long Holocene Kushu sequence was undertaken. The presented glass chemistry and age results based on Bayesian modelling of available radiocarbon dates for the core allowed the identification of several regional marker tephra layers and previously undocumented tephra horizons. The presented RK12 Holocene tephrostratigraphy integrated local and far-travelled tephras originating from regions in Japan, China, Russia and as far south as Indonesia, which facilitated the construction of an integrated tephra framework for East Asia through providing an important northern element of a regional tephra lattice. A prominent cryptotephra in the sequence exhibited chemical fingerprint that did not match with known Asian northern Hemisphere eruptions. With further investigation of southern Hemisphere tephra sources, this study proposed the identification of a cryptotephra from Krakatau volcano Indonesia, in northern Japan over 6700 km from the vent. An updated and integrated Holocene tephra framework 3 for East Asia was also summarised in this study, based on a thorough review of previous visible tephra work and recent developments of cryptotephra research in the region. A total of twenty-two widespread tephras originating from Russia, China/N Korea, S Korea, Japan and Indonesia were selected and incorporated in the proposed framework, which was an essential first step towards a regional master tephra framework. In addition, the chronostratigraphic relationships between these tephras and climate change events were fully evaluated, in particular the extent to which these isochrons could be used to constrain regional variations of short-lived climate oscillations. Given the fruitful results from recent pioneering cryptotephra studies in East Asia, it is now essential that a more systematic approach to the application of cryptotephra studies is applied to terrestrial and marine records from the region. 4 Acknowledgements I owe a number of people significant gratitude, without them completion of this thesis would not have been possible. To my supervisors at both RHUL and GIGCAS, Professors Simon Blockley, Martin Menzies and Yigang Xu, for their guidance and support over the last four years. Simon has advised me with the directions of the research and has had many stimulating discussions with me throughout the PhD project. Martin has patiently and meticulously revised my writing all the time and has encouraged and motivated me whenever I encountered difficulties or became frustrated. Yigang has initiated the collaborative programme between RHUL and GIGCAS and has provided me the opportunity for studying in the UK. They are all great scientists and advisors, and are role models to me. To Prof. Pavel Tarasov and Dr. Stefanie Müller at the Free University Berlin for providing sub-samples of lake core sediment, and the discussions on sediment core correlation and radiocarbon chronology. To Drs. Emma Tomlinson at the Trinity College Dublin, Victoria Smith and Paul Albert at the University of Oxford, Chris Hayward at the University of Edinburgh for their assistance during geochemical analyses, and the help with data processing. To co-worker Danielle McLean at the University of Oxford, former CQR student for providing information on preliminary investigation of the core, and enlightening discussions on the manuscripts. To Prof. Ian Candy for being my advisor and all the helpful suggestions on annual review meetings, Dr. Simon Armitage for the helpful discussion on the Changbaishan manuscript. To Katy Flowers and Dr. Marta Perez for their great support during my three and half years’ lab work period. To all other staff in CQR and Earth Sciences for their support. To friends in Geography and Earth Sciences for their support and discussion during the last four years: Jacob Bendle, Rhys Timms, Ashley Abrook, Rachel Devine, Angharad Jones, Elizabeth Peneycad, Dorothy Weston, Yajun Li, Alice Carter- 5 Champion, Richard Clark-Wilson, Amy Walsh, Yunting Qi, Shuang Zhang, Liang Liu, Yizhuo Sun, Jie Xiao, Hongdan Deng, Qiong Li. To Jiaqi Qin in SYSU for remote teaching of the use of plotting software when I published my first manuscript, Junting Qiu in the University of Tokyo for the help with accessing Japanese literature, and Cong Chen in SYSU for the discussions of Quaternary scientific questions. To other friends in China who cared about me and encouraged me during the tough time of writing-up. To Tianshu for being a great friend and housemate, our friendship will continue no matter where we are. To Aike for the last four years of friendship and all the support and encouragement throughout my PhD. To Martin again and his wife Lesley Hunter, for inviting me to their home for the tea and cakes, and for celebrating with me every Chinese Lunar New Year. Finally to my family for their unconditional love and support. I am forever grateful to them. 6 Table of Content Declaration ............................................................................................................................... 2 Abstract .................................................................................................................................... 3 Acknowledgements .................................................................................................................. 5 Table of Content ...................................................................................................................... 7 List of Figures ........................................................................................................................ 11 List of Tables .......................................................................................................................... 15 Chapter 1: Introduction ........................................................................................................ 17 1.1 General context ............................................................................................................ 17 1.1.1 Tephrochronology as a dating and correlation tool ........................................... 17 1.1.2 Palaeoclimate studies in East Asia ...................................................................... 18 1.1.3 East Asian tephrochronology ............................................................................... 20 1.2 Regional settings .......................................................................................................... 23 1.2.1 Distal site (Lake Kushu) ....................................................................................... 23 1.2.2 Proximal site (Changbaishan) ............................................................................. 26 1.3 Methodology ................................................................................................................. 27 1.3.1 Cryptotephra extraction and identification ....................................................... 27 1.3.2 Analytical methods ............................................................................................... 30 1.4 Aims and Objectives .................................................................................................... 30 1.5 Thesis Outlines ............................................................................................................. 32 Chapter 2: Clarifying the distal to proximal tephrochronology of the Millennium (B-