Flood Deposits Research Articles

Caral, South America’s Oldest City (2600–1600 BC): ENSO Environmental Changes Influencing the Late Archaic Period Site on the North Central Coast of Peru

The Late Archaic Period (2600–1600 BC) site of Caral, located ~20 km inland from the Pacific Ocean coastline in the Supe Valley of the north central coast of Peru, is subject to CFD analysis to determine the effects of ENSO (El Niño Southern Oscillation) events (mainly, El Niño flooding and drought events) on its agricultural and marine resource base that threatened societal continuity. The first step is to examine relics of major flood events that produced coastal beach ridges composed of deposited flood slurries—the C14 dating of material within beach ridges determines the approximate dates of major flood events. Of interest is the interaction of flood slurry with oceanic currents that produce a linear beach ridge as these events are controlled by fluid mechanics principles. CFD analysis provides the basis for beach ridge geometric linear shape. Concurrent with beach ridge formation from major flood events are landscape changes that affect the agricultural field system and marine resource food supply base of Caral and its satellite sites- here a large beach ridge can block river drainage, raise the groundwater level and, together with aeolian sand transfer from exposed beach flats, convert previously productive agricultural lands into swamps and marshes. One major flood event in ~1600 BC rendered coastal agricultural zones ineffective due to landscape erosion/deposition events together with altering the marine resource base from flood deposition over shellfish gathering and sardine and anchovy netting areas, the net result being that prior agricultural areas shifted to limited-size, inner valley bottomland areas. Agriculture, then supplied by highland sierra amuna reservoir water, led to a high water table supplemented by Supe River water to support agriculture. Later ENSO floods conveyed thin saturated bottomland soils and slurries to coastal areas to further reduce the agricultural base of Supe Valley sites. With the reduction in the inner valley agricultural area from continued flood events, agriculture, on a limited basis, shifted to the plateau area upon which urban Caral and the satellite sites were located. The narrative that follows then provides the basis for the abandonment of Caral and its satellite Supe Valley sites due to the vulnerability of the limited food-supply base subject to major ENSO events.

Central Andean (28–34°S) flood record 0–25 ka from Salinas del Bebedero, Argentina

AbstractThe Salinas del Bebedero occupies an isolated basin in the foreland of central Argentina at 33°S and was flooded repeatedly over past 25 ka. Isotopic evidence demonstrates that this flooding was due to overflow of the nearby Río Desaguadero with waters derived from the distant (≥300 km) central Andes between 28–34°S. Stratigraphic and shoreline evidence shows that floods occurred most frequently from 14.3 to 11.4 ka, followed by lesser events between 14.3 to 11.4 ka, and during the late Holocene from 2.6 to ca. 0.2 ka. Hydraulic modeling (2D HEC-RAS) shows that these floods could have originated from repeated subglacial drainage or sudden outbursts with a volume of >100 × 106m3and a peak discharge of >1,000 m3s-1each. The absence of flood deposits from 11 to 3 ka points to exceptionally dry and virtually ice-free conditions in the Andes between 28–34°S. The floods were probably caused by major rainfall or dammed-lake outbursts clustered largely during wet pluvial periods in the otherwise moisture-limited central Andes and Atacama Desert, such as when the Intertropical Convergence Zone was shifted southward. These include Central Andean pluvial events (CAPE) I (17–14.5 ka) and II (12.5–9 ka), and the Neoglacial/Formative archeological period 2500 ka to near-present.

Transport of Potentially Toxic Elements in Solid Particulate Matter during Flash Flood Events in Upper and Lower Stretch of the Sava River

During extreme hydrological conditions such as flood events, sediments and alluvial soils may become re-suspended. As a consequence, the concentration of solid particulate matter (SPM) in the water column increases. As sediments represent a sink for the contaminants, when such perturbation occurs, the toxic substances may be re-dissolved into the water, causing harmful effects to the freshwater habitat. The purpose of this study was to evaluate the release of potentially toxic elements associated to SPM during flash floods. Two sampling sites on the Sava River were chosen: Litija (Slovenia), where the river has still the characteristics of an alpine river, and in Belgrade (Serbia), where Sava is a lowland river with a flat riverbed, slower flow and bigger quantities of fine-grained sediment. The results of the study showed a good correlation between the SPM mass concentration and water level/discharge. At both sampling sites, elevated concentrations of As, Cd, Cr, Cu, Pb, Ni and Zn were determined in SPM, indicating a moderate level of contamination at Litija and a high level at Belgrade. The results demonstrated that during the two investigated flash flood events limited the dissolution of PTE from SPM-bearing particles.

Impact of radiocesium contamination in flood sediment deposited after the 2019 typhoon on decontaminated fields of Fukushima Prefecture, Japan

Sediment that has deposited after the flood generated by the 2019 typhoon (referred to as Flood Sediment, FS) was collected along two rivers in eastern Fukushima Prefecture, Japan to determine the total and exchangeable radiocesium ( 137 Cs), and acid-extractable potassium (K) contents. Then, these FS parameters were compared with those of decontaminated soils (DS) in nearby agricultural fields to discuss the potential transfer risk of 137 Cs from rivers to nearby remediated soils. While FS had about four times higher total 137 Cs content, it showed a three-times lower exchangeable 137 Cs content than DS. Furthermore, acid-extractable K referred to as non-exchangeable K (Nex-K) content was high enough to restrict 137 Cs transfer from soil to crops for both FS and DS. From these comparisons, we concluded that deposition of FS onto DS may not increase the transfer of 137 Cs from soil to crops.

Temporal and spatial hydrological variations of the Yellow River in the past 60 years

Understanding water and sediment variations of the Yellow River is significant for future management of the river from perspectives of water resources utilization and ecology protection. The study characterized the temporal and spatial variations in its flow and sediment load based on the daily datasets of the past 60 years from all main-stem hydrological gauge stations, and proposed a new five-segment river reach division scheme instead of the traditional three- or four-segment division. Furthermore, we distinguished the key factors and their contributions that caused the flow and sediment variations, offering reference for the river management strategies as per the local conditions. A significant decreasing trend in annual flow and sediment load was observed in the river basin, except for certain reaches in Segment 1 (upstream of Tangnaihai). The maximum flood-event duration decreased significantly in Segment 2 (from Tangnaihai to Shizuishan). The flood volume and sediment load during the maximum flood event also showed significant downward trend in Segments 2–5 (downstream of Tangnaihai). Operation of cascade reservoirs, especially in Segment 2, has smoothed the annual flow process in the upstream. Sediment trapping in the reservoirs had little effect on the change in sediment load, but reservoir regulation of flow greatly influenced siltation in the upstream river channel. Water abstraction has also played a significant role in flow variation. Consequently, the ratio of flood sediment load to annual sediment load decreased significantly in the upper reach, but increased significantly in the lower reach. Temporally, the recorded period was divided into three periods using change point detection: pre- 1987, 1987–1999, and post 1999. The ratio of flood volume to annual flow decreased significantly in the first two periods, and generally increased post 1999, with the impact of aforementioned anthropogenic activities.

Florida\u2019s urban stormwater ponds are net sources of carbon to the atmosphere despite increased carbon burial over time

Stormwater ponds are engineered ecosystems designed for flood control and sediment retention in urban watersheds. They are the most commonly used stormwater control measure in the USA, but their biogeochemical processes and impacts are often overlooked. Here, we assessed the potential impact of stormwater ponds on regional carbon cycling by coupling carbon burial rates and fluxes of carbon dioxide and methane gases in five sites over an age gradient of 14–34 years. Carbon burial increased logarithmically with site age, ranging from 22 to 217 g carbon m−2 y−1, while, median floating chamber diffusive gas fluxes were 1290 g carbon dioxide m−2 y−1 and 5 g methane m−2 y−1, which, when combined as carbon dioxide equivalents, equates to 2900 g carbon dioxide eq m−2 y−1. Comparing carbon burial to gas flux reveals that stormwater ponds can be net carbon sources and need to be considered for regional and global carbon models.

Numerical Simulation of Alpine Flash Flood Flow and Sedimentation in Gullies With Large Gradient Variations

Compared with floods occurring over plains, alpine flash floods are formed over scattered locations with complex terrain and data is often lacking regarding the land topography, flow and sedimentation, causing difficulties when developing mathematical models to predict flash floods. The existing flash flood models mainly focus on the influence of water flow, such as the sharp increase in flow discharge caused by convergence at steep slopes, disregarding the sediment load carried by the water flow. However, under the effect of high-intensity sediment transport, the sedimentation in gullies may lead to surges in water level, causing the phenomenon of “great disasters resulting from minor flooding”. In this study, an efficient and accurate water-sediment coupling model was established with a Godunov-type finite volume method based 2D flow model, and a sediment module and OPENMP parallel computing module were added as well. Firstly, a common gully in mountainous area with large gradient variations was used as a generalized model to explore the impact of sedimentation on the flow field of the gully and compared with the physical model. Then, the alpine flash flood incident in Gengdi Village was simulated with the computer model. The calculation results show that the high-intensity sedimentation significantly increased the magnitude of alpine flash floods. Calculated by this mathematical model, the research results verified that this mathematic model can efficiently, accurately and concisely predict the occurrence of flash floods in gullies with large gradient variations. The model also provides a flow and sediment modeling method that incorporates the effect of high-intensity sediment transport into the traditional flash flood flow model. Thus, this model can be a powerful tool for detecting flash floods.

Using a fluvial archive to place extreme flood sediment (dis)connectivity dynamics in context of a longer-term record

The aim of this study was to establish the source and provenance of sediments deposited in a large floodplain sink during extreme floods in the Lockyer Creek catchment, Australia, in 2011 and 2013. We place the sediment source patterns in context of the longer-term record to determine whether coarse-grained sediment sources (i.e., very fine sand to very coarse sand) and the spatio-temporal pattern of (dis)connectivity have changed over time. We do this by matching the geochemical properties and age structure of a sediment profile located in a downstream floodplain sink to the elemental composition of source sediments. One hundred and fifty-seven sediment samples from 20 sites across the catchment are analysed using X-ray fluorescence (XRF) spectrometry to compare the elemental ratio composition of the downstream floodplain sink to its source materials. We use Optically Stimulated Luminescence (OSL) dating to determine the age structure of the sediments in the floodplain sink. The northern tributaries and parts of the Lockyer River trunk stream are the primary sources of coarse sediment. These areas are connected (coupled) to the lower trunk stream and floodplain sediment sink. Southern tributaries are largely disconnected (decoupled) and supply little sediment to the floodplain sediment sink. This pattern of sediment source contribution has remained similar over the last 6.8 ka at least. Sediment sources as observed in the 2011 flood have predominated over the mid-late Holocene whilst those in the 2013 flood are rare.

Characterization of potential fugitive dust emissions within the Keeler Dunes, an inland dune field in the Owens Valley, California, United States

Fugitive dust sources within the Keeler Dunes, a small shoreline dune system in the northeast corner of Owens (dry) Lake in Owens Valley, California, U.S.A. were investigated. PM10 flux potential was quantified using measurements from a Portable In-Situ Wind Erosion Laboratory (PI-SWERL). Stratified random sampling was used to evaluate potential PM10 fluxes from eight landforms, as determined by high-resolution satellite imagery and ground observations, found within the vicinity of the Keeler Dunes. Within each landform, potential PM10 flux for one or more representative surface types was measured. A total of seven surface types were identified, several of which existed on different landforms. The results indicate that the major determinant of potential PM10 flux is the landform type. Furthermore, the highest potential PM10 fluxes are from landforms characterized by surface deposition of alluvial sediment. Within the Keeler Dunes Complex, these landforms are associated with the severely eroded 1944 shoreline coppice dunes, flash flood channels, and flash flood deposits. In the Owens Valley, studies of dust emissions have tended to focus on aeolian landforms. However, similar to measurements of potential PM10 flux from desert landforms across the globe, this investigation points to the importance of alluvial landforms as major sources of dust emissions within the Owens Valley region. This article is a part of a larger investigation into the modern destabilization and migration of the Keeler Dunes (Schaaf et al. this issue).

Reconstructing Paleoflood Occurrence and Magnitude from Lake Sediments

Lake sediments are a valuable archive to document past flood occurrence and magnitude, and their evolution over centuries to millennia. This information has the potential to greatly improve current flood design and risk assessment approaches, which are hampered by the shortness and scarcity of gauge records. For this reason, paleoflood hydrology from lake sediments received fast-growing attention over the last decade. This allowed an extensive development of experience and methodologies and, thereby, the reconstruction of paleoflood series with increasingly higher accuracy. In this review, we provide up-to-date knowledge on flood sedimentary processes and systems, as well as on state-of-the-art methods for reconstructing and interpreting paleoflood records. We also discuss possible perspectives in the field of paleoflood hydrology from lake sediments by highlighting the remaining challenges. This review intends to guide the research interest in documenting past floods from lake sediments. In particular, we offer here guidance supported by the literature in how: to choose the most appropriate lake in a given region, to find the best suited sedimentary environments to take the cores, to identify flood deposits in the sedimentary sequence, to distinguish them from other instantaneous deposits, and finally, to rigorously interpret the flood chronicle thus produced.

Channel Response and Reservoir Delta Evolution From Source to Sink Following an Extreme Flood

AbstractDisturbances such as floods, fires, and mass movements introduce large volumes of sediment into fluvial systems. Tracking the movement of disturbance‐generated sediment provides insight into the processes of fluvial system response. Few studies document a post‐disturbance response that explicitly links channel change to evolution of a reservoir delta. We exploit the tight coupling in a sediment source‐to‐sink analysis of flood deposits over 6 years. Within the first year after the flood, the channel incised 1.5 m and widened 10 m. Limited channel morphologic change thereafter is attributed to bed armoring. Morphodynamic modeling of the channel predicted transport of Radio‐Frequency Identification‐tagged clasts from which we infer a discharge threshold of >14 m3/s for future geomorphic adjustments. Post‐flood discharges and reservoir drawdowns deposited 3 times the volume of sediment in the delta than was deposited during the flood and prograded the delta 200 m. Overall system response followed a characteristic sediment decay flux. Despite the sediment flux decline, comparable rates of delta progradation occurred due to reservoir drawdowns that shifted the sediment source from the channel to incision of the delta. Thus, the delta evolved via distinct processes based on sediment source and reservoir level: (a) aggradation of the delta topset and progradation of the Gilbert‐type clinoform when sediment is sourced from the channel during years when reservoir level fluctuated seasonally; and (b) delta progradation through incision of the delta topset during reservoir drawdowns. Our results reveal a genetic relationship between post‐disturbance channel and delta evolution.

Fractionation of stable carbon isotopes during acetate consumption by methanogenic and sulfidogenic microbial communities in rice paddy soils and lake sediments

Abstract. Acetate is an important intermediate during the degradation of organic matter in anoxic flooded soils and sediments. Acetate is disproportionated to CH4 and CO2 by methanogenic or is oxidized to CO2 by sulfate-reducing microorganisms. These reactions result in carbon isotope fractionation, depending on the microbial species and their particular carbon metabolism. To learn more about the magnitude of the isotopic enrichment factors (ε) involved, acetate conversion to CH4 and CO2 was measured in anoxic paddy soils from Vercelli (Italy) and the International Rice Research Institute (IRRI, the Philippines) and in anoxic lake sediments from the northeastern and the southwestern basins of Lake Fuchskuhle (Germany). Acetate consumption was measured using samples of paddy soil or lake sediment suspended in water or in phosphate buffer (pH 7.0), both in the absence and presence of sulfate (gypsum), and of methyl fluoride (CH3F), an inhibitor of aceticlastic methanogenesis. Under methanogenic conditions, values of εac for acetate consumption were always in a range of −21 ‰ to −17 ‰ but higher in the lake sediment from the southwestern basin (−11 ‰). Under sulfidogenic conditions εac values tended to be slightly lower (−26 ‰ to −19 ‰), especially when aceticlastic methanogenesis was inhibited. Again, εac in the lake sediment of the southwestern basin was higher (−18 ‰ to −14 ‰). Determination of εCH4 from the accumulation of 13C in CH4 resulted in much lower values (−37 ‰ to −27 ‰) than from the depletion of 13C in acetate (−21 ‰ to −17 ‰ ), especially when acetate degradation was measured in buffer suspensions. The microbial communities were characterized by sequencing the bacterial 16S rRNA (ribosomal ribonucleic acid) genes as well as the methanogenic mcrA and sulfidogenic dsrB genes. The microbial communities were quite different between lake sediments and paddy soils but were similar in the sediments of the two lake basins and in the soils from Vercelli and the IRRI, and they were similar after preincubation without and with addition of sulfate (gypsum). The different microbial compositions could hardly serve for the prediction of the magnitude of enrichment factors.

Initial soil formation in an artificial river valley - Interplay of anthropogenic landscape shaping and fluvial dynamics

Land rehabilitation is a strategy for restoring near-natural landscape systems in anthropogenically influenced environments. Especially in post-mining landscapes after open-pit mining, land rehabilitation gives opportunities and potential for near-natural landscape modeling. To evaluate its success, biological monitoring approaches with a focus on biodiversity are common. However, the loss of natural soils, which are the result of long-term formation, is an irreversible damage to the pedosphere. The natural soil functions must be completely re-established and it is difficult to examine its success.Our study area is located in the Inde River catchment (North Rhine-Westphalia, Western Germany), which is part of the international River Basin District Meuse. Due to the progress of the open-pit lignite mining, a 5 km long river course had to be relocated. To create a near-natural landscape and an appropriate development corridor for the river, a ~ 12 km long river relocation was designed. The artificial river section “Neue Inde” is still geomorphologically “naive” and characterized by temporary, highly energetic morphodynamic processes resulting in strong erosion processes in the river bed and the surrounding area. Our study investigated initial soil formation in a morphodynamically active artificial river valley, constructed with a restoration substrate called “Forstkies”.To characterize morphodynamics and to detect initial soil formation processes, we analyzed a transect of seven soil profiles. It includes floodplains and slope areas further away from the river. Allochthonous flood sediments can be differentiated from the underlying artificial restoration substrate by inherited enrichment of the pollutants Pb, Zn, and Cu. First initial post-sedimentary alterations are detected employing common soil parameters (grain size, CaCO3, total organic carbon and pH value) and geochemical weathering indices. The quality of the soils is appropriate to the state of development. The results obtained can be helpful for the planning of future restoration in post-mining landscapes.

Provenance of Baker River sediments (Chile, 48°S): Implications for the identification of flood deposits in fjord sediments

AbstractFloods are among the most destructive natural hazards on Earth. In paleohydrology, sediments are generally considered as one of the best archives to extend flood records to pre‐historical timescales. Doing so requires being able to identify flood deposits from sediment archives and decipher between flood types. The latter is particularly important in glacierized regions, where meteorological floods frequently co‐occur with glacial lake outburst floods (GLOFs). In Patagonia, results from a recent study suggest that GLOFs are recorded in downstream fjord sediments as fine‐grained and organic‐poor layers, representing the high amount of glacier rock flour transported during lake outbursts, whereas meteorological floods are represented by coarser and more organic deposits. However, not all fine‐grained organic‐poor deposits could be associated with historical GLOFs. Here, we reconstruct the provenance of these Baker River flood deposits using 87Sr/86Sr and εNd, taking advantage of the clear lithological differences that exist between both sides of the watershed. Our results show that both 87Sr/86Sr and εNd are suited to reconstruct sediment provenance in the Baker River watershed but that εNd is the most effective and the least affected by grain‐size variations. Our provenance results confirm that the 21st‐century fine‐grained and organic‐poor deposits represent GLOFs and that the largest winter meteorological flood on record has a distinct coarse and organic‐rich signature. However, our results show that rain‐on‐snow events that occur in summer, and therefore primarily affect the western glacierized part of the watershed, have the same fine‐grained organic‐poor signature as GLOFs. Therefore, this study shows that the sedimentary signature of rain‐on‐snow floods in partially glacierized watersheds depends on the season during which they occur. We anticipate that our findings will contribute to a better interpretation of flood records from partially glacierized watersheds.

Tributary fans of the Middle Teesta Basin in Sikkim‐Darjeeling Himalaya, NE India: Their contribution to valley‐filling processes

Tributary fan deposits in the Sikkim Himalaya are well preserved in the Teesta Valley in the tectonic zone bounded by the Main Central Thrust and the Main Boundary Thrust. The lithofacies characteristics and assemblage patterns of these deposits bear imprints of the linked effects of tectonic and climatic factors on the sedimentation processes in the river valley. Two tributary streams, namely Turung Khola and Bembung Khola have been studied in detail. Three major fanlobes are preserved at Turung Khola and two fanlobes are preserved at the Bembung Khola. Terraces, floodplains, channel bars, and chute bars are associated with geomorphic features in this part of the Teesta Basin. Longitudinal profiles of the tributaries and that of the trunk river indicate a relationship between the knick points and high SL‐Index values, where fault/thrust intersections are present. Sediment characteristics of these fan deposits indicate that four types of flows viz. debris flows (DF), hyperconcentrated flows (HF), sheet flows (SF), and channel flows (CF) deposited these sequences. The CF deposits are dominant in the fan sequence of the Turung Khola followed by SF deposits, HF deposits, and debris flow deposits respectively. HF deposits are dominant in the F1 fanlobe sequence, whereas the active channel fanlobe is dominated by the CF deposits. The rest of the active channel sequence is composed of SF deposits. On the other hand, the F1 fanlobe of Bembung Khola is made up of DF deposits and F0 fanlobe is composed of channel flow deposits and flood sediment. Interactions between the tributary fans and the main Teesta River are studied using lithofacies and the associated morphological context. From the above analysis, an evolutionary model for depositional and incision processes at the tributary stream fan confluence allows the reconstruction of five phases of incision and aggradation through the last ~45 ka.

Coastal Alluvial Fans of the Raghama Formation, Northern East Red Sea, Saudi Arabia

Tawfik, M.; Al-Hashim, M.; El-Sorogy, A.; Alharbi, T., and Wadani, M., 2021. Coastal alluvial fans of the Raghama Formation, Northern East Red Sea, Saudi Arabia. Journal of Coastal Research, 37(6), 1193–1203. Coconut Creek (Florida), ISSN 0749-0208. Four Miocene outcrops of the Raghama Formation have been investigated for the first time in NW Saudi Arabia to identify facies types, facies associations, and sequence stratigraphy. These sections have been controlled by fans that flow into the sea from higher altitudes. The fans can be divided into alluvial fans and a braided fluvial environment that pass seaward into lagoons and fringing reefs. The continental deposits of the fan are characterized by the fan apex, which passes downslope into alluvial plains. These alluvial deposits are located beside high hinterlands and contain dwindling gravel pavement and local dunes. The transitional zone between the continental and marine deposits comprises mainly erosional beaches and sheet flood sediments. The fan in the marine environment is regulated by longshore drift and wave action. The fringing reef is located offshore from the fan and close to the shore with no lagoons. The fringing reefs are locally affected by the force of the water rushing down the active streams, as indicated by the occurrence of irregularities, remnants, and gravels in the reef cervices. One third-order depositional sequence is well preserved within the studied sections. This sequence is bounded by unconformities and is controlled by the ratio between accommodation and sediment supply (A/S ratio). Variations in the A/S ratio are related to eustatic sea level, climate, and tectonics related to the collision between the Eurasian and Arabian plates, the latter which is responsible for the uplift of the studied areas and the widening of the Red Sea, leading ultimately to subsidence during the Middle Miocene.

The Potential Role of S-and Fe-Cycling Bacteria on the Formation of Fe-Bearing Mineral (Pyrite and Vivianite) in Alluvial Sediments from the Upper Chicamocha River Basin, Colombia

S- and Fe-cycling bacteria can decisively affect the crystallization of Fe-bearing minerals in sediments from fluvial environments. We have studied the relationships between the Fe-bearing mineral assemblage and the bacterial community composition in the sediments rich in organic matter from the upper Chicamocha river basin (Colombia). Rapid flowing sections of the river contain sediments that have a high redox potential, are poor in organic matter and are enriched in kaolinite and quartz. On the other hand, the mineral assemblage of the sediments deposited in the La Playa dam with a high content in organic matter is enriched in Fe-bearing minerals: (a) vivianite and pyrite in the permanently flooded sediments of the dam and (b) pyrite and goethite in the periodically emerged sediments. The bacterial community composition of these sediments reveals anthropic organic matter pollution processes and biodegradation associated with eutrophication. Moreover, periodically emerged sediments in the La Playa dam contain bacterial groups adapted to the alternation of dry and wet periods under oxic or anoxic conditions. Cell-shaped aggregates with a pyritic composition suggest that sulfate-reducing bacteria (SRB) communities were involved in the precipitation of Fe-sulfides. The precipitation of vivianite in the flooded sediments was favored by a greater availability of Fe(II), which promoted the iron-reducing bacteria (IRB) enrichment of the sediments. The presence of sulfur-oxidizing bacteria (SOB) in the flooded sediments and the activity of iron-oxidizing bacteria (IOB) in the periodically emerged sediments favored both pyrite crystallization under a high sulfide availability and the oxidation of microbially precipitated monosulfides. Moreover, IOB enhanced goethite formation in the periodically emerged sediments.

Analysis of event stratigraphy and hydrological reconstruction of low-frequency flooding: A case study on the Fenhe River, China

Low-frequency but high-magnitude flooding is becoming more frequent and can be well-documented by event stratigraphy. Low-frequency flooding deposits (LFDs) were discovered during a field investigation in the Holocene loess-palaeosol profile at Xucun (FHXC), which is situated at the front of the second terrace (T2) along the middle Fenhe River. A multi-prong approach combining geochemical and sedimentological indexes (i.e. concentrations of Cr, V, Ni, Co, Cu, Zn, Rb, Mn, Pb, and Sr, magnetic susceptibility, and particle size distribution) was used to distinguish the sedimentary characteristics and environmental dynamics of LFDs. These proxies show that LFDs were well sorted clayey silt and carried in suspension during high-energy extreme flooding currents with: firstly, a high water level; and secondly, the river having a relatively stagnant environment. Based on the flooding stage indicators, magnitudes of the low-frequency flooding discharges at the site were reconstructed to be 13,480–13,590 m3/s. The timing of the identified low-frequency flooding cluster episode was dated to 4200–3900 a BP by the Optically Stimulated Luminescence (OSL) dating technique. It agreed well with stratigraphic correlations of other existing well-dated flooding profiles in the middle reaches of the Yellow River. This case study presents long-term low-frequency flooding records and their sedimentary dynamics based on high spatial–temporal resolution systematic event stratigraphy, which advances understanding low-frequency flooding generation mechanism and improves upon predictions for occurrences and magnitudes of future extreme flooding.

Neolithic cultural sites and extreme climate related channel avulsion: Evidence from the Vaigai River Basin, southern India

We document evidence for the role of fluvial dynamics-stream channel avulsion and flooding, tectonics and climatic conditions on the occurrence, shifting and burial of ancient cultural sites in the Vaigai River Basin in southern India. Systematic regional mapping, geophysical investigations and archaeological excavations in the flood plains of the Vaigai River led to the unearthing of an ancient culture that thrived at least since 752 BCE (2435 ± 34 BP). Evidence for early human activities include sites of ancient and now buried industries that were manufacturing steel, glass bead, dye, gold jewelry and earthenware, in addition to dwelling-habitation, sites of religious sacrificial ceremonies, and places of worship, and burial. These information together with the occurrences of microlithic age stone tools in the vicinity led to the proposition of continued habitation of the Vaigai River Basin until today. Radiometric dating shows oldest age of 2435 ± 34 BP (752 BCE) obtained at 2.5 m depth in a pit excavated at Keezhadi, a location situated far from the present day channel course whereas the youngest age of 689 ± 24 BP is obtained at Agaram, a location situated nearest to the present day channel course. The bone fragments were dated as 1115 ± 39 BP (778 CE – 1016 CE) and 1229 ± 30 BP (689 CE – 883 CE). The organic carbon/peat layers recovered between flood deposits at the upper reaches of the Vaigai River are dated as 830 ± 30 BP and 1250 ± 30 BP. The natural levee deposits show evidences of habitation-related disturbances in the internal sedimentary structure, texture and packing. In addition to occurrences of hearth etc., recurrences of overbank-channel deposits over natural levee-habitation surfaces indicate habitation-colonization over relatively highgrounds along river bank, followed by marooning/burial under overbank-channel deposit and abandonment of habitation site and/or shifting of habitat. The same sequence of events occurred again, showing two habitation surfaces that are buried under surface currently. Together with facies characteristics and other artifact occurrences, the ages obtained in our study indicate shifting of the Vaigai River from prior to 2435 BP and colonization of ancient population, which might have been affected by a catastrophic flood and stream avulsion at about 1250–830 BP. These resulted in the ancient habitation getting marooned, industries and other structural infrastructure destroyed, and were transported and deposited as interbeds in flood deposits. Following a reduction in the stream energy, the point bar-natural levee environmental setting paved way for the deposition of organic carbon layer at Agaram at about 690 BP. This was followed by lateral shifting of the channel from Agaram towards the present-day course.

Perseverance rover reveals an ancient delta-lake system and flood deposits at Jezero crater, Mars.

Observations from orbital spacecraft have shown that Jezero crater on Mars contains a prominent fan-shaped body of sedimentary rock deposited at its western margin. The Perseverance rover landed in Jezero crater in February 2021. We analyze images taken by the rover in the 3 months after landing. The fan has outcrop faces, which were invisible from orbit, that record the hydrological evolution of Jezero crater. We interpret the presence of inclined strata in these outcrops as evidence of deltas that advanced into a lake. In contrast, the uppermost fan strata are composed of boulder conglomerates, which imply deposition by episodic high-energy floods. This sedimentary succession indicates a transition from sustained hydrologic activity in a persistent lake environment to highly energetic short-duration fluvial flows.