GM3.17

In Thailand landslides and flooding are two major natural disasters affecting more than 11 million people living in coastal provinces. Such events have significant human and economic impacts. For example, in 1988, landslides resulted in 373 deaths and caused up to US$80 million in damage (Tanavud, 2008); in 2011, floods and landslides affected more than two million people and killed 53 across Southern Thailand with a village of about 100 households being buried by one large slide (EarthObservatory, 2021). Landslides in the Krabi province in Thailand are predominantly shallow and rainfall-induced, they also represent the main source of sediment pulses for coastal environments such as mangroves and beaches. This study aims at investigating the link between sediment availability from 3 river catchments in the province of Krabi in Southern Thailand and sedimentation rate evolution in mangroves directly downstream in order to understand coastal the sediment shortages and therefore coastal erosion in that area.

Landslide inventories were evaluated using high resolution imagery (<10m) such as aerial photographs, Theos and EO-1 satellite imagery, Google Earth historical tool covering a time period from 2007 to present. Calculations of the surface areas and volumes of landslides was calculated in ArcMap using the formulae developed by Larsen et al. (2010). Landslide erosion was modelled using an approach based upon the negative power law scaling properties of rockfall magnitude–frequency distribution to establish total volumes of sediment for specific years or seasons.

Core samples taken in the mangroves near the river mouths were used to identify markers of landslide events and associated sediment cascades based on grain size distribution and ¹³⁷Cs dating.

Preliminary results show sedimentation rates in the mangroves from 0.9 to 2 mm/year since 1963 and sediment volumes made available to transport from 0.3 to 68300 m³/year since 2007 across the 3 catchments.

Grain size analysis shows variations of the D₅₀ and the sorting coefficient throughout the sediment recording indicators of landslides and high intensity rainfall events.

How to cite: Curoy, J., Ward, R., and Barlow, J.: From the Landslide to the Mangrove; Coupling Sediment Supply Pulses and River Sediment Deposits in the context of Climate Change in Thailand., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-839, https://doi.org/10.5194/egusphere-egu21-839, 2021.

High alpine areas are affected disproportionately by global warming and are thus found to be in a transient state. This causes accelerating glacial retreat, which can have severe impacts on discharge and potentially sediment dynamics. Possible effects include changes in water quantities and hydrograph timing as well as changing sediment source areas and the associated magnitude and timing of transport capacities. In turn, the resulting changes in water and sediment supplies and timing have the potential to severely impact downstream ecosystems and infrastructure.

An essential step towards estimating the effects of future changes and developing sustainable management strategies is to quantify the behavior in the past and present. We therefore used the excellent data availability of discharge and suspended sediment concentrations in our study area in the upper Ötztal in Tyrol, Austria, to make such an assessment. We study discharge and suspended sediment concentrations, which have been monitored at three gauges and for a minimum of seven years in the case of the youngest gauge. The resulting nested catchment setup, with catchment sizes ranging between 98 km² and 785 km², allows us to learn about discharge and sediment fluxes and their spatial distribution, thus allowing us to quantify the relative importance of the glaciated areas as compared to the lower-lying catchment areas. It also allows us to study the temporal dynamics, such as the seasonal timing of the peaks and their interannual differences. In turn, the nested catchments allows us to investigate the spatial variability of these temporal dynamics.  

The results confirm the high specific sediment yields for alpine catchments in the order of 10³ t/km² per year and higher yields in areas with higher glacier cover as well as a very pronounced seasonality.

How to cite: Schmidt, L. K., Francke, T., Blume, T., Schöber, J., Pfurtscheller, D., Achleitner, S., and Bronstert, A.: Suspended sediment and discharge dynamics across multiple spatial and temporal scales in a glaciated alpine environment: the case of the upper Ötztal, Austria, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9575, https://doi.org/10.5194/egusphere-egu21-9575, 2021.

The middle Loire riverbed, after its confluence with Allier, is characterised by a morphology of alternate bars more or less vegetated and possesses riverbank flood protections. The suspended particulate matter (SPM) fluxes are therefore originated from these two catchment areas that drain the eastern and southern parts of the Massif Central. The temporal dynamics of the SPM fluxes are very variable, both on an interannual scale and on the scale of a flood event. Furthermore, SPM fluxes also present high spatial heterogeneities as they are governed by complex processes of production (erosion) and transfer (storage/remobilisation). The Loire river plays an important role in supporting the French energy production by providing cooling water to several Nuclear Power Plants (NPP). However, the cooling systems of the NPPs on the middle Loire are exposed to the risk of silting. In order to ensure a safe management of water intakes and prevent the industrial risks arising from sediment transport, it is therefore imperative to understand the spatio-temporal dynamic of sediment production and transfer.

In this context, the objective of this thesis work is to provide keys to improve sediment management of the river between the two NPPs of Belleville and Dampierre. In a first place, the river flow and SPM data available at the upstream NPP of Belleville will be analysed in order to understand the temporal variations of the incoming SPM fluxes. In a second phase, a soil erosion and hydrological model will be implemented to understand the production processes in the upstream catchments. This second part will allow to determine the interactions of the SPM inputs in the river with the morphodynamics of the bed of the Loire between the two stations. We will present the methodology that has been designed to apprehend these two phases and the first results of the river SPM temporal dynamic at the Belleville NPP station.

How to cite: Belbal, B. H., Goutal, N., Antoine, G., and Cerdan, O.: Temporal and spatial dynamic of suspended sediments fluxes and sources and morphological evolution of the bed in the middle Loire river, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15401, https://doi.org/10.5194/egusphere-egu21-15401, 2021.

As sediment is carried through watersheds, it may be stored in floodplains and other alluvial deposits, remaining in place for hundreds to millions of years before being remobilized and transported farther downstream.  Sediment routing models based on reservoir theory can account for time-varying sediment storage and predict lags in sediment delivery imposed by sediment storage, but observational data are needed to construct and validate these models.  Because of the long timescales involved, direct observations are rarely useful, but stratigraphic observations coupled with sediment dating techniques can be used to quantify the amount of sediment stored through time and its associated age and storage (or transit) time distributions. To illustrate this approach, a meta-analysis of published geologic data is used to quantify river corridor storage through time associated with European colonization of the mid-Atlantic U.S.  The history of floodplain growth from Holocene to the present is summarized by empirical distributions extracted from stratigraphic data; distributions were sampled to create thousands of synthetic age-depth curves.  Deposits predating European colonization range in age from >18,000 yrs. to 225 yrs. B.P. and with a median thickness of 40% of the total accumulation; sedimentation rates for these deposits are low (median = 0.06 cm/yr).  The median thickness of sediments deposited between 1750 and 1900 (“legacy sediments”) comprises 36% of the total; the median accumulation rate of legacy sediments is 0.32 cm/yr.  The median thickness of sediments deposited after 1950 represents 11% of total accumulation, and the median contemporary sedimentation rate of 0.26 cm/yr is statistically indistinguishable from that of legacy sediments.  Synthetic vertical sequences can be recast as age distributions, and when combined with geomorphic mapping and assessment of patterns of erosion through time, as storage time distributions as well.  Age and storage time distributions at 1000 yrs. B.P., in 1900 A.D., and at present are highly variable, and could be represented by many different mathematical functions, though averaged data appear to be heavy-tailed.   Records of mass accumulation through time and the present and past age and storage time distributions provide useful summaries of the history of sediment storage, and can be used to calibrate and verify watershed scale sediment routing models over millennial timescales.

How to cite: Pizzuto, J.: Quantitative Sediment Storage Chronology Associated with European Colonization of the Mid-Atlantic U.S. and its Application to Watershed Scale Sediment Routing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5834, https://doi.org/10.5194/egusphere-egu21-5834, 2021.

This study discusses the sedimentary flux, and sedimentary system source tracking on the shelf margins of Yinggehai (YGH) and Qiongdongnan (QDN) Basins, Northern South China Sea. The shelf margin clinoforms of YGH and QDN Basins, have grown since the Late Cenozoic (10.5 Ma), which generated more than 4 km-thick shelf prism above the T40 surface. By using the core, well drilling data, 2D and 3D seismic surveys, this study aims to: ① demonstrate the geometry morphology and architecture of the clinoforms, while the shelf margin trajectory (including the shelf-edge trajectory and toe of slope trajectory) showing down-flatting and rising patterns where the progradation and aggradation happened through the vertical evolution; ② estimate sediment supply values, load volumes, and their changes since the Late Cenozoic, predict ratio of the sediment flux across shelf-edge during their dynamic processes; ③ investigate the contradiction and correlation among the phenomena that sediments show distinctly increasing in flux, decreasing in grain size, and response delay of flux rate peak since 2-4 Ma. The preliminary results show that the vertical sediment accumulation rate increased significantly across the entire YGH and QDN Basin margin system after 2.4 Ma, with a marked increase in mud content that likely caused by long‐distance, alongshore currents with high content of mud during the Pleistocene. Furthermore, laterally, the estimated total sediment flux onto the margin shows a dramatic decline from west to east while moving away from the Red River depocenter, as well as a decrease in the percentage of total discharge crossing the shelf break in this same direction. The overall margin geometry shows a remarkable change from sigmoidal, strongly progradational and aggradational in the west to weakly progradational in the east of QDN Basin margin. The Late Cenozoic shelf margin growth, with its overall increased sediment flux, responded to global, high‐frequency transgressive‐regressive climate cycles during a falling global sea level and gradual cooling temperature in this icehouse period.

How to cite: Chen, S., Wang, H., Ma, J., Gong, T., and Yu, Z.: Clinoform growth and sediment flux of Late Cenozoic Yinggehai and Qiongdongnan shelf margins, Northern South China Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12221, https://doi.org/10.5194/egusphere-egu21-12221, 2021.

Trough mouth fans are large depocentres forming the ultimate sinks in glacial source-to-sink systems. Their architecture, sedimentological aspects (origin and processes) and their role as paleoclimatic archives are essential components in improving our understanding of Pleistocene and ongoing climate changes. For many years, these depocentres were thought to be dominated by debris flows accumulated in front of ice streams located at the shelf break. However, recent studies have shown that meltwater plays a major role in bringing sediment to the most distal parts of these fans, especially in lower latitudes. The North Sea Trough Mouth Fan encompasses ~110,000 km² with water depths of up to 3500 m. It has received sediments throughout the Quaternary, with increased sedimentation rates in the last 1.1 Ma when the Norwegian Channel Ice Stream was active. Recent insight of the fan shows that meltwater turbidites play a major role in sediment delivery to the continental slope and deep-sea basin. The results could entail distinct morphologies for mid-latitude and high-latitude fans. As a result of glacial erosion and the absence of clear imprints of ice sheets on the paleo-shelves, studying trough mouth fan deposits becomes paramount in understanding glacial-interglacial cycles. This project will assess the source-to-sink parameters of the last glaciation (Weichselian) at the North Sea Fan, elucidating the dominant marine and terrestrial processes that led to the studied sedimentary sequences. High-resolution 2D and 3D seismic data, core, volumetric and numerical modeling data will be assimilated to establish a source-to-sink model for the target interval. These results will contribute to the knowledge of how glaciations affect surface mass redistribution, directly affecting the landscape dynamics and sediment routing from Fennoscandia via the North Sea to the slopes and deep basin. Sediment production will be evaluated, assessing whether it increases during the glaciation or if observed higher sedimentation rates are a result of enhanced sediment transport. This project is a part of the Marie Sklodowska-Curie Innovative Training Networks “S2S – Future: Signal propagation in source to sink for the future of the Earth resources and energy” and will further advance how trough mouth flans are highly dynamic areas where sediment transport, dispersal, remobilization and deposition take place, and serve as excellent proxies to the dynamics of glacial pulses in the hinterland.

How to cite: Machado Garcia, A., Midtkandal, I., Bellwald, B., and Anell, I. M.: A Source to Sink Approach to the North Sea Fan Pleistocene Glacial Sediments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12600, https://doi.org/10.5194/egusphere-egu21-12600, 2021.

The Great Indian Desert, Thar is a natural source of the atmospheric mineral dust burden over India and nearby landmasses/seas and regulates the regional climate and ecosystem health. However, the limited geochemical/isotope data of Thar sediments from the source region in Rajasthan restrict their source delineation and implication for characterization of the Thar dust signatures. For this purpose, we have measured major, trace, and rare-earth elemental concentrations, and radiogenic Sr and Nd isotope compositions in 51 surface sediment samples collected over a wide area from the Thar Desert, Rajasthan. The geochemical data reveals a low degree of the chemical index of alteration (CIA ~43–54), a quartz dilution of major oxides, and depletion of heavy minerals such as zircons. The UCC normalized spider diagram, as well as La/Yb–Eu anomaly plot, reveal that the Thar surface sediments collected in this study are geochemically similar to that of a sedimentary sequence from the Luni River originating from the Aravalli mountains. The ⁸⁷Sr/⁸⁶Sr and ε_Nd of Thar sediments overlap with the reported values for the Indus delta and Luni river sediments but are distinctly different from those of the Ghaggar river sediments. Thus, the sediment contribution from the Indus delta cannot be completely ruled out, while the Ghaggar sediment contributions are minimum. Furthermore, the radiogenic isotope compositions of the decarbonated Thar sediments are strikingly contrasting to the reported values for silicate fractions of eolian deposits in northwestern India. These differences could be due to grain size effects during the dust production/transport or local sediment contributions to the eolian deposits.

How to cite: Bhattacharyya, R. and Singh, S. P.: Geochemical/isotope characterization of sediments from the Great Indian Desert, Thar, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12391, https://doi.org/10.5194/egusphere-egu21-12391, 2021.

The Sahara is by far the largest hot desert on Earth. Its composite structure includes large dune fields hosted in sedimentary basins separated by elevated areas exposing the roots of Precambrian orogens or created by recent intraplate volcanism. Such an heterogeneity of landscapes and geological formations is contrasted by a remarkably homogeneous composition of dune sand, consisting almost everywhere of quartz and durable minerals such as zircon, tourmaline, and rutile.

We here present the first comprehensive provenance study of the Sahara Desert using a combination of multiple provenance proxies such as bulk-petrography, heavy-mineral, and detrital-zircon U–Pb geochronology. A set of statistical tools including Multidimensional Scaling, Correspondence Analysis, Individual Difference Scaling, and General Procrustes Analysis was applied to discriminate among sample groups with the purpose to reveal meaningful compositional patterns and infer sediment transport pathways on a geological scale.

Saharan dune fields are, with a few local exceptions, composed of pure quartz with very poor heavy-mineral suites dominated by durable zircon, tourmaline, and rutile. Some more feldspars, amphibole, epidote, garnet, or staurolite occur closer to basement exposures, and carbonate grains, clinopyroxene and olivine near a basaltic field in Libya. Relatively varied compositions also characterize sand along the Nile Valley and the southern front of the Anti-Atlas fold belt in Morocco. Otherwise, from the Sahel to the Mediterranean Sea and from the Nile River to the Atlantic Ocean, sand consists nearly exclusively of quartz and durable minerals. These have been concentrated through multiple cycles of erosion, deposition, and diagenesis during the long period of relative tectonic quiescence that followed the Neoproterozoic Pan-African orogeny, the last episode of major crustal growth in the region. The principal ultimate source of recycled sand is held to be represented by the thick blanket of quartz-rich sandstones that were deposited in the Cambro-Ordovician from the newly formed Arabian-Nubian Shield in the east to Mauritania in the west.

The composition and homogeneity of Saharan dune sand reflects similar generative processes and source rocks, and extensive recycling repeated through geological time after the end of the Neoproterozoic, which zircon-age spectra indicate as the last major event of crustal growth in the region. The geographic zircon-age distribution in daughter sands thus chiefly reflects the zircon-age distribution in parent sandstones, and hence sediment dispersal systems existing at those times rather than present wind patterns. This leads to the coclusion that, provenance studies based on detrital-zircon ages, the assumption that observed age patterns reflect transport pathways existing at the time of deposition rather than inheritance from even multiple and remote landscapes of the past thus needs to be carefully investigated and convincingly demonstrated rather than implicitly assumed.

How to cite: Pastore, G., Baird, T., Vermeesch, P., Resentini, A., and Garzanti, E.: Recycling of Sahara desert sand, a comprehensive provenance study approach., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1095, https://doi.org/10.5194/egusphere-egu21-1095, 2021.

The knowledge acquired on the exhumation of the Pyrenean chain and the evolution of the adjacent foreland basins makes this Alpine-type domain a good laboratory to better constrain a full sediment routing system in a compressive context and to apprehend the driving processes controlling the sediment routing in space and time. This integrated approach aims at enhancing our basin mastering approach as well as improving our predictions of reservoir properties for oil and gas exploration and storage.

This Source-to-Sink study seeks to understand the evolution of sedimentary routing from the Source (orogenic relief, craton, basin recycling) through the transfer zone (peripheral or internal to the basin) to the final sink (flexural basin, deep turbiditic margin). Within the framework of this new cartography, we propose to compile the available and newly acquired data from the S2S project (TOTAL, BRGM), over the entire peri-Pyrenean domain. We produced large scale quantitative and qualitative maps and wheeler diagrams to better observe and interpret the tectonic, climatic and surface processes impacts of the SRS behavior.

The maps include kinematic reconstructions of the Iberian-European-Mediterranean system, restored sequential cross-sections, history/magnitude of exhumation by thermochronology, source tracking, characterization of weathering and erosion surfaces, synthesis of the major structural accidents activity, paleogeographic reconstructions, analysis of sedimentary geometries and transport directions as well as the quantification of volumes preserved in the basins. Their interpretation is combined with a time representation along the routing system, linking classical basin wheeler diagram representation to source erosion and lithologies to obtain a continuous view on the sediment journey.

The time steps chosen for these 5 maps account for the different stages of tectono-sedimentary evolution of the peri-Pyrenean system at the early-orogenic, syn-orogenic and post-orogenic stages. The compilations carried out compare exhumed domains and sedimentation zones in terms of fluxes and volumes and make it possible to map the routing systems and discuss the drivers for the surface evolution during the construction/destruction cycle of an orogen.

Research work financed and carried out as part of the BRGM-TOTAL Source-to-Sink program

How to cite: Ortiz, A., Fillon, C., Lasseur, E., Briais, J., Guillocheau, F., Bessin, P., Baby, G., Baptiste, J., Uzel, J., Robin, C., Calassou, S., Catelltort, S., and Frasca, G.: A new way to predict sediment production and deposition: integrated Source to Sink maps at pluri-basins-scale, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12133, https://doi.org/10.5194/egusphere-egu21-12133, 2021.

The intensity of the Asian summer-monsoon circulation varies over decadal to millennial timescales and impacts surface processes, terrestrial environments, and marine sediment records. The duration and magnitude of this climatic forcing on erosion processes varies, depending on duration and intensity of the climatic events, as well as on the tectonic and geomorphologic preconditioning of the landscape. In this study, we focus on a region in the transition zone between continuous and episodic monsoon impacts: the Spiti River, the largest tributary (12x10³ km² ) to the Sutlej River in the western Himalaya. The river valley is located in the northern lee of the Himalayan orographic barrier in a presently arid environment. The Spiti Valley has received significant precipitation during intensified monsoon periods during the late Pleistocene and Holocene and thus constitutes an ideal location to evaluate effects of episodic moisture transport into an arid, high-relief mountainous region.

Here we present 21 new surface-exposure ages of fluvial-fill terraces combined with previously published data to quantify temporal patterns in river incision and erosion rates. Our data include catchment-wide erosion rates and in-situ cosmogenic nuclide ages derived from ¹⁰Be, ²⁶Al, and ²¹Ne and document that terrace formation (i.e., terrace abandonment) occurred during intensified monsoon phases at ∼100 ka, ∼65 ka, ∼43 ka, and ∼12 ka, although dating uncertainties prevent the calculation of exact correlation between monsoonal strength and terrace formation. We show that incision into Late Pleistocene valley fills that integrate over several cut-and-fill cycles at 10⁵ y are comparable to exhumation rates determined from thermochronology studies averaging over 10^6 y in that area. We argue that the limiting factor for sediment removal and river incision on shorter, millennial timescales is due to large bedrock landslides that impounded the river network and formed transient sedimentary basins lasting for 10³ -10⁴ years. We suggest a feedback process between sediment removal and landsliding, where large landsliding predominantly occurs when the transiently-stored valley fills have been carved out, leading to exposed valley bottoms, bedrock erosion, lateral scouring of rivers, and ultimately to the over-steepening of hillslopes. We suggest that Late Quaternary climatic variability is the main forcing factor in filling and evacuating transiently stored sediments in high mountain ranges and thus plays a direct role in controlling bedrock incision.

How to cite: Bookhagen, B., Strecker, M., Niedermann, S., and Thiede, R.: Late Quaternary Climate Variability Constrains River Incision and Aggradation in the Spiti Valley, Western Himalaya, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15369, https://doi.org/10.5194/egusphere-egu21-15369, 2021.