This study examines ground penetrating radar (GPR) records of beach ridge stratigraphy as a proxy for reconstructing regional sea-level and tsunami histories in the tropics. We present topographically corrected GPR profiles on a prograded coast in Phra Thong Island, Thailand where we 1) identify downlap points marking the boundary between foreshore / beachface and upper shoreface facies and use this as past sea-level marker and 2) identify ‘cut and fill’ packages in the upper fill that we infer to be records of past erosion and recovery following repeated tsunami events. Optically Stimulated Luminescence (OSL) dates collected at locations slightly offset from the same profile line were incorporated to create the temporal record. The shore-normal GPR record shows ~0.82 m fall in the sea-level between 2659±139 years BP to 367±27 years BP that is consistent with other proxy based sea-level curves obtained in the region. The early part of the record (before ~2600 years) presents a period of rapid progradation and relatively stable sea level conditions. From ~2600 years BP to ~2200 years BP the record shows a steeper fall in sea level followed by a relatively stable to slightly falling phase between ~2200 years BP and ~550 years BP. Finally, for the seaward side, between ~550 years BP and ~350 years BP, the record indicates falling relative sea-level. The cut and fill packages suggest that Phra Thong has experienced 5 tsunami events in the last 2600 years including two events in close succession around 500 years ago that are recorded in the most landward part of the sequence. This study confirms that the study of tropical beach ridge systems using GPR and OSL techniques can be highly effective for reconstructing regional sea-level trends and tsunami histories through the Common Era and beyond.

Instrumental sea-level records are insufficient to understand the response of sea-level changes to global temperature on centennial timescales. Sea-level histories spanning at least the Common Era have not been widely studied in Southeast Asia. This period is crucial for providing a pre-industrial context to understand sea-level change with climate. Linking sea-level change to climate change is proxy dependant, with most proxies only providing decadal to centennial scale resolution of both sea level and climate. This study examines the efficiency of beach ridge stratigraphy as a proxy for reconstructing regional sea-level histories in the tropics. We present topographically corrected Ground Penetrating Radar (GPR) profiles from a prograded coast in Phra Thong Island, Thailand, where we identify downlap point marking the boundary between the foreshore and shoreface subzones and use this as a past low-tide marker. The low-tide markers were corrected (considering the tidal range) and then connected to approximate the past sea level. Optically Stimulated Luminescence (OSL) samples collected at locations slightly offset from the shore-normal GPR profile line were incorporated to create a relative sea-level record. Overall, the shore-normal GPR record shows a similar to 1.06 m fall in sea level between similar to 2660 and similar to 370 years ago. The study also highlighted stepwise fluctuations in sea level that were not identified in previous studies. Between similar to 2600 and similar to 2200 years ago, the record indicates a steep fall in sea level, followed by a phase of relatively stable to slightly falling sea level between similar to 2200 and similar to 550 years ago. Finally, for the seaward side, between similar to 550 and similar to 350 years ago, the record indicates an accelerating sea-level fall. This study confirms that the investigation of tropical beach ridge systems using GPR and OSL techniques can be a highly efficient and effective means for reconstructing regional sea-level trends throughout the Common Era and beyond.

Few constructional features of coastal geomorphology have been investigated at the northernmost extremity of the Gulf of Thailand (GoT), with a view to establishing the position (height) of local relative sea level (RSL) during the marine regression following the regional mid-Holocene highstand (MHH) that occurred at approximately 6.5 ka BP. Here, the work investigates a 2 m thick exposure of marine gravels on the coast of Ko Khang Khao islet in the eastern Bay of Bangkok. At an elevation of 3.3-5.3 m above modern sea level, the sequence is interpreted to represent a Holocene raised beach. The unlithified sediments comprise rounded quartz and mylonite pebbles and cobbles, oriented predominantly NE-SW, supported by fossiliferous sands that are rich in marine shells, coral fragments and occasional terrestrial gastropods. The juxtaposition of the marine and nonmarine gastropoda of contemporaneous ages makes a compelling story for a coastal storm deposit, thrown up either by a winter monsoon storm, or by a palaeotyphoon that managed to penetrate the upper Gulf. Overlapping results of C14 and OSL age-dating of shell material and mineral sands suggest the raised (storm) beach formed between 3.5 and 4.0 ka BP, i.e. 2.5-3.0 ka after the MHH peak, at a height of 1.3-3.3 m above the local RSL position at that time (according to glacial isostatic adjustment modelling). Given the otherwise paucity of data from the upper GoT, the Ko Khang Khao raised beach provides new information that expands our current understanding of geographical variations in RSL across Southeast Asia during the Late Holocene.

The identification of tsunami deposits in the geological record remains a challenge because the proxies availabilities are subject to the environment. The proxies may degrade over time and inherently inhibit the robustness of event interpretations. Multi-proxy methods, which leverage on each other's advantage/s and limitation/s, are employed to improve the identification of tsunami deposits from the geological record. Here, we assess the utility of environmental DNA (eDNA) for tsunami research by comparing and contrasting the eDNA collected from a sequence of well-documented palaeotsunami deposits spanning the past three millennia. We study swales in a coastal beach ridge sequences on Phra Thong Island, Thailand and test if eDNA can robustly discriminate the tsunami-deposited sand sheets that intercalate between the non-tsunami derived organic mud layers. Our results indicate that the 2004 Indian Ocean tsunami deposit and preceding tsunami deposits (approximately 550 to 700 years ago) contain microbial communities that differ significantly from the overlying and underlying organic mud layers (p-value = 0.0269) but the signal becomes restricted in the older sediment layers up to 2800-year-old that are constantly submerged in groundwater. This work demonstrates the potential for applying eDNA to study tsunami deposits over centennial time frames and perhaps longer.

Preview this conference paper: Sources of Oil and Gas in Recent Offshore Sarawak Wells: Insights from Oil Molecular Composition and Gas Isotope Analysis, Page 1 of 1 < Previous page | Next page > /docserver/preview/fulltext/2214-4609/2023/imog-2023/263-1.gif

Investigating palaeotsunami deposits is a primary way to extend the tsunami database beyond relatively short instrumental and historical records. Such information is essential to reconstruct the frequency and magnitude of past coastal flooding events, which are a key to assess the impact and risk of tsunami to the coastal community. However, palaeotsunami studies are limited as most of the proxies, such as microfossil and geochemical signals, can be modified or degraded with time. Here, we present the application of DNA analysis to investigate a series of palaeotsunami deposits up to ~2800-years-old from a coastal beach ridge sequence on Phra Thong Island (Thailand). Our result shows that it is possible to accurately discriminate palaeotsunami deposits from intercalating organic mud layers using the microbial communities recovered from DNA preserved in the sediment of the geological record. Our work demonstrates that environmental DNA represents a new and promising tool for investigating historical and pre-historical tsunami records.

Sandy onshore deposits from tsunamis are difficult to distinguish from storm deposits, which makes it difficult to assess coastal hazards from the geological record. Here we analyse environmental DNA from microbial communities preserved in known tsunami and storm-deposited sediments and intercalating soils and non-marine sediments near Cuddalore, India, and Phra Thong Island, Thailand. Both sites were impacted by the 2004 Indian Ocean Tsunami and a subsequent storm flooding event (2011 Cyclone Thane at Cuddalore and a 2007 storm at Phra Thong Island). We show that the microbial communities in the overwash deposits are significantly different from soil and sediments that are not derived by overwash processes at both locations. Our method also successfully discriminates between modern tsunami deposits and storm deposits. We suggest molecular techniques have the potential to accurately discriminate overwash deposits from catastrophic natural events. Overwash deposits from tsunamis and storm surges in Thailand and India can be differentiated from each other and from terrestrial and marine sediment through differences in their soil microbial communities, according to DNA meta-barcoding of sediments.

Summary We report character of oil and gas produced from selected Tertiary basins in Thailand. Previously, only limited published data are available for oils generated from lacustrine and fluvio-lacustrine source rocks in Thailand basins. We conclude that shallow water fluvio-lacustrine environment deposited sources receiving fluctuating contribution of terrestrial organic matter input as well as variation in micro-algal communities appear to be the main source type in basins we have studied. This source type is perhaps under-estimated in terms of importance across Sundaland. We believe that a better, more profound understanding of the nature of source rocks within classic Sunda fluvio-lacustrine depositional systems is still needed as they are difficult to delineate, more variable in quality and often occur as local discrete beds in thick sequences.

PreviousNext No Access18th International Conference on Ground Penetrating Radar, Golden, Colorado, 14–19 June 2020Antidune bedforms in tsunami outflow deposits revealed by GPRAuthors: Charlie S. BristowAdam D. SwitzerChris GouramanisRobert WeissKruawun JankaewCharlie S. BristowDepartment of Earth and Planetary Sciences, Birkbeck University of London, London, United KingdomSearch for more papers by this author, Adam D. SwitzerAsian School of the Environment, Nanyang Technological University, SingaporeSearch for more papers by this author, Chris GouramanisDepartment of Geography, National University of Singapore, SingaporeSearch for more papers by this author, Robert WeissDepartment of Geoscience, Virginia Tech, United StatesSearch for more papers by this author, and Kruawun JankaewPTTEP, ThailandSearch for more papers by this authorhttps://doi.org/10.1190/gpr2020-070.1 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract A ground penetrating radar (GPR) survey of sediments deposited by the 2004 Indian Ocean Tsunami (IOT), on the Island of Pra Thong in Thailand, reveal landward dipping reflections at depths of around 2.5 to 5 m beneath more recent beach sediments. The inclined reflections are between 5 and 10 m in length and lie within a 35m long scour. Sedimentary dips are less than 10 degrees. In this paper we discuss the possible origins for landward dipping strata associated with tsunami deposits including: cross-strata from swash bars, antidune or hydraulic jump backsets and washovers. Keywords: sediment, interpretation, reflection, migration, GPRPermalink: https://doi.org/10.1190/gpr2020-070.1FiguresReferencesRelatedDetails 18th International Conference on Ground Penetrating Radar, Golden, Colorado, 14–19 June 2020ISSN (online):2159-6832Copyright: 2020 Pages: 455 publication data© 2020 Published in electronic format with permission by the Society of Exploration GeophysicistsPublisher:Society of Exploration Geophysicists HistoryPublished Online: 11 Nov 2020 CITATION INFORMATION Charlie S. Bristow, Adam D. Switzer, Chris Gouramanis, Robert Weiss, and Kruawun Jankaew, (2020), "Antidune bedforms in tsunami outflow deposits revealed by GPR," SEG Global Meeting Abstracts : 263-266. https://doi.org/10.1190/gpr2020-070.1 Plain-Language Summary KeywordssedimentinterpretationreflectionmigrationGPRPDF DownloadLoading ...

Sediment records left by coastal hazards (e.g. tsunami and/or storms) may shed light on the sedimentary and hydrodynamic processes happening during such events. Modern onshore and offshore sediment samples were compared with the 2004 Indian Ocean Tsunami, three palaeotsunami and a 2007 storm deposit from Phra Thong Island, Thailand, to determine provenance relationships between these coastal overwash deposits. Sedimentological and stratigraphic characteristics are generally inadequate to discriminate tsunami and storm deposits so a statistical approach (including cluster analysis, principal component analysis and discriminant function analysis) was used based on grain size, mineralogy and trace element geochemistry. The mineral content and trace element geochemistry are statistically inadequate to distinguish the provenance of the modern storm and tsunami deposits at this site, but the mean grain size can potentially discriminate these overwash deposits. The 2007 storm surge deposits were most likely sourced from the onshore sediment environment whereas all four tsunami units statistically differ from each other indicating diverse sediment sources. Our statistical analyses suggest that the 2004 tsunami deposit was mainly derived from nearshore marine sediments. The uppermost palaeotsunami deposit was possibly derived from both onshore and nearshore materials while the lower palaeotsunami deposits showed no clear evidence of their sediment sources. Such complexity raises questions about the origin of the sediments in the tsunami and storm deposits and strongly suggests that local context and palaeogeography are important aspects that cannot be ignored in tsunami provenance studies.

Rapid growth of Asian megacities, exemplified by the megacity of Bangkok, Thailand, with a population of over 10 million inhabitants, means that an increasing number of people are living in low-lying coastal areas exposed to hazards such as typhoons. While Bangkok has always been considered not to be at risk from typhoon strikes, recent discoveries of elevated carbonate boulder deposits have started to question this assumption. This work reports on findings from the islands of Ko Khang Khao and Ko Phai, farther north and west than earlier studies, and adds to the existing body of evidence for prehistorical typhoon-driven high energy marine inundation (HEMI) events penetrating northwards into the Bay of Bangkok. Elevated carbonate boulder deposits up to 6 m amsl indicate that these were emplaced by waves generating onshore minimum flow velocities between 3.0 and 5.5 m/s, consistent with typhoon-impacted coastlines elsewhere in the tropical Asia-Pacific region. When viewed in conjunction with other data from the Bay of Bangkok their chronologies indicate age clusters around four major phases of activity in AD 600-700, AD 900-1000, AD 1150-1250 and AD 1400-1650. At 250 years duration, the last phase of activity was the longest, but it has also been followed by the longest period of quiescence that has coincided with rapid urban growth in and around the city of Bangkok. The re-occurrence of typhoon-driven HEMI events on the scale of the prehistorical events reported here would threaten all the lowlying coasts in the Bay of Bangkok, including the Chao Phraya delta, and as such these results indicate an urgent need to re-evaluate coastal hazards for the region.

The 26th December 2004 Indian Ocean Tsunami (IOT) emanated from an Mw 9.2 earthquake that generated a 1600 km-long rupture along the Sumatran Megathrust and generated tsunami waves up to 30 m high. The IOT directly impacted the Bay of Bengal and east Africa, with over 283,000 people perishing. At the time, this catastrophic event was considered unprecedented and sparked intense investigations to test this claim. It is now believed that four pre-2004 IOT events have occurred in the last 2500 years, recurring every 550 to 700 years. Much of this information comes from Phra Thong Island, Thailand, where a sequence of four stacked sandsheets separated by organic units has been recognised and compared to the 2004 IOT event. Recently, ground-penetrating radar on Phra Thong Island identified a region that could not be explained by the known stratigraphy. The stratigraphy of the area was investigated from auger cores and pits, and several previously-unrecognised sandsheets were identified and compared to the known tsunami sandsheets. The proximity of the newly-recognised sandsheets to the palaeo-coastline of Phra Thong Island does not preclude the impacts of localised storms in sandsheet emplacement or that tsunamigenic earthquake recurrence may have been more frequent in the past.

Rapidly rising populations of low‐lying megacities in Asia mean that understanding the potential risk of coastal flooding by storm surge is of paramount concern. The city of Bangkok and the wider Chao Phraya River delta at the head of the Gulf of Thailand is a region topographically vulnerable to coastal flooding, but without the record of a high‐energy marine inundation (HEMI) event in historical time owing to the atypical path that a typhoon must take to be able to produce such an event.

An M-w 6.1 earthquake struck northern Thailand on the 5(th) of May 2014. The epicenter was located near Mae Lao district in Chiang Rai province. The earthquake caused unprecedented damage to structures, the most damaging earthquake ever in recorded Thai history. Five hundred and ninety-four buildings out of 10,863 were damaged to the extent that they were unsafe for occupancy. This article presents a reconnaissance investigation of damage to buildings and bridges in the two districts-Phan and Mae Lao-which suffered the most damage. Attention is paid to the performance of buildings with similar configurations and structural design, but with different layout of unreinforced masonry infills as non-structural components.

Since optically stimulated luminescence (OSL) dating is time-consuming and cost-intensive, the quantity of ages available for individual study sites is usually restricted significantly. In particular the interpretation of complex depositional systems with temporally and spatially diverse sedimentation histories may suffer from the effects of a poor spatial resolution or an ineffective distribution of chronological data. In these cases, time and cost efficient approaches that provide reasonable dating accuracy are required to substitute or complement full luminescence dating. In this study, we evaluate the potential (i) of luminescence profiling using a portable luminescence reader, and (ii) of standardized growth curves applied to quartz extracts and bulk samples in a standard luminescence reader for functioning as age proxies. Since both proxies save time for processing and/or measurements, they would be applicable to larger datasets in future studies and, by this, may allow to improve the spatial resolution and sampling strategy of OSL dating in coastal settings. Both approaches are applied to a set of approximately 50 samples from the sandy beach-ridge plain of Phra Thong Island, Thailand, for which age control is given by regular quartz luminescence dating from previous studies. Results show that although standardized growth curves are also associated with shortcomings in dating accuracy, and luminescence profiling in general does not equal full luminescence dating, both approaches are capable of reproducing some of the main chronostratigraphic features of the island. This includes the differentiation between the Holocene and Last Interglacial parts of the ridge plain, as well as the identification of the general east-west progradation of the Holocene ridges. On the other hand, several pronounced hiatuses of 1500–2000 years within the Holocene sediment succession, were not identified at all or with a poor precision. More robust absolute age estimates can only be achieved by considering the highly variable dosimetry, which is the main contributing factor to bulk luminescence signals apart from deposition age on Phra Thong Island. Thus, for the beach ridges on Phra Thong portable reader signals as a proxy for palaeodoses combined with sample-specific dose rates seem to be the best compromise between rapid data acquisition and adequate dating accuracy. In future studies, this will allow for processing significantly larger numbers of samples compared to regular luminescence dating while keeping dating accuracy at a level that should be adequate for many research questions, which in the end could enable an increased spatial resolution of chronological information.