The Australian ‘Mega Tsunami’ debate: insights from the geological record and lessons learned for palaeowashover studies in southeast China
主讲人：Dr Adam D. Switzer
Reconstruction of the East Asian monsoon variability since the mid-Holocene from the Pearl River estuary, southern China
主讲人：Dr. Fengling Yu
The Australian ‘Mega Tsunami’ debate: insights from the geological record and lessons learned for palaeowashover studies in southeast China---Dr. Adam Switzer
Research over the last 25 years advocates that the high-energy southeast coast of Australia was repeatedly impacted by tsunami during the Holocene. This body of research can be divided into two main themes. The first, coined the ‘Australian mega-tsunami hypothesis’ refers to work principally by Bryant and a second theme primarily by the speaker and co-authors has focused on boulder accumulations, shell-rich sands and sandsheets found in coastal settings that provide evidence for much smaller, less frequent events. The proposers of the ‘mega-tsunami hypothesis,’ have described a varied and primarily geomorphological record of Holocene palaeotsunami that suggest frequent large tsunami have struck and significantly modified the coast often inundating distances of several kilometers inland (up to 10 km in places) and achieving enormous flood run-ups (up to + 130 m above sea level). Recent criticisms of the mega tsunami hypothesis and a societal demand for tsunami risk assessment after the 2004 Indian Ocean tsunami have prompted a reevaluation of several sites. This talk will summarise this ongoing debate and present new data that indicates the coast has been subject to mid sized tsunami events in the Holocene.
Throughout the course of this talk the speaker will discuss some of the problems and pitfalls encountered when interpreting the geomorphology and stratigraphy of coastal embayments, including problems defining chronology, the equivocal nature of transported boulders and the uncertainty faced when attempting to distinguish between storm and tsunami deposits. In the final part of the talk the speaker will outline new work on palaeotsunami and palaeostorms in southern China and Taiwan where both coasts share a history of historical tsunami and catastrophic storms.
Dr Adam D. Switzer is a Singapore NRF Fellow, Nanyang Assistant Professor and Principal Investigator in the Tectonics Group at the Earth Observatory of Singapore in Nanyang Technological University. He previously held a position of Centenary Research Assistant Professor in Global Climate Change in the Department of Earth Sciences at The University of Hong Kong. He obtained a BSc degree in geosciences and a PhD in sedimentology and geohazards from the University of Wollongong in Australia. He currently has ongoing research projects in Australia, China, Taiwan, India, Vietnam, Lebanon, Tibet, Indonesia, Italy and Malaysia.
Reconstruction of the East Asian monsoon variability since the mid-Holocene from the Pearl River estuary, southern China—Dr. Fengling Yu
This study aims to reconstruct East Asian Monsoon (EAM) variability during the mid-Holocene, developing a relatively new proxy of bulk organic carbon isotopic signature (δ13C) and C/N from the Pearl River estuary, southern China. Sources of sediments within an estuary include river-derived terrestrial input, in situ brackish-water suspended sediment and tide-derived marine input. This study assumes the proxy can help differentiate sources of sediments relating to monsoon-driven freshwater flux and help reconstruct monsoonal precipitation history during the mid-Holocene.
Modern samples were collected from terrestrial areas, including plants and soil samples, through to estuarine areas, including seasonal estuarine suspended organic matter and surface sediment. Results suggest that bulk organic δ13C and C/N ratios are good indicators for sources of estuarine sediments, and thus can be used to infer relative changes in monsoon-driven freshwater flux. For example, lower δ13C values reflect a greater level of contribution of freshwater organic carbon, i.e. stronger monsoonal freshwater discharge.
Analysis of an estuarine core shows that freshwater discharge from the Pearl River catchment gradually declined from 6650 to 2150 cal. years BP, suggesting a gradual weakening of summer monsoon precipitation, responding to the weakening insolation controlled by the orbital-driven precession cycle. Superimposed on this are wet/dry intervals, ranging from centennial- to millennial- scale, driven by solar activities. Changes in ENSO and high-latitude cooling events might be responsible for dry/wet events at centennial- to decadal- scale.
About Dr. Fengling Yu
· 05/2010 – present Research fellow in the Earth Observatory of Singapore, Nanyang Technological University, Singapore
· 10/2005-01/2010 PhD in Department of Geography, University of Durham, UK
· 09/2003-06/2006 MSc in Department of Geography, East China Normal University, Shanghai, China
· 09/1999-06/2003 BSc in Department of Geography, Fujian Normal University, Fuzhou, China