Sediment Remobilization Research Articles

Riverine Cu-distribution in sediments of the Jaba-Kawerong river system 30 years after cease of mining at Panguna/Bougainville

The investigation of surface and river sediments over 30 years after the cease of large scale Cu and Au mining operation at Panguna (Bougainville) shows the impact of mining and tailings disposal on the associated riverine environment. While Zn, Pb and Cd have elevated concentrations in the former mining area and are low (< 100, < 28, < 1 mg/kg, respectively) in sediment of the Jaba-Kawerong river system, Cu represents the dominant environmental metal emission. Sediments of active streams and overbank deposits range between 1000 and 3000 mg/kg Cu. Most samples exceed freshwater sediment or soil quality guideline values, indicating the probability of toxic effects on sediment dwelling or aquatic organisms and ecological or health risks associated to agricultural use of the former mining area and floodplains. Copper in surface and river sediments is associated to bornite, chalcopyrite and chloritized biotite of the primary Panguna ore mineral assemblage. This attests to ongoing remobilization of sediment and/or reflects mobilization of additional Cu bearing material from the waste rock dump of the Panguna mine. Copper in surface and river sediments is also contained in secondary Cu-phases such as covellite as well as hydrated basic Cu-sulfates, which formed under locally variable redox conditions. Fe-oxihydroxides, occurring in variable abundance as reflected by Fe concentrations between 18,200 and 379,000 mg/kg (Mn 145–3086 mg/kg), can be identified as further Cu-carriers, taking up the metal from the aqueous phase in the sedimentary pore space. Mine derived input of Cu bearing minerals is confined to the sedimentary body of the Jaba-Kawerong river system. The diversity of Cu bearing phases with different environmental and processing properties sets constraints on re-processing sediments as secondary Cu-ores or re-using of sediments as building material.

Sediment remobilization over subaqueous sand waves: In-situ observation in the northern South China Sea

High-resolution tripod observations were conducted in a subaqueous sand-wave field in the northern South China Sea. The objective was to gain insight into the dynamic mechanism by which sandy sediments are remobilized by oceanic dynamic processes, in particular internal solitary waves and internal tides. Daily-recurring high suspended sediment concentrations were observed, likely due to lateral transport of sediments resuspended by critical reflection of diurnal internal tides at the shelf break. The passage of extreme internal solitary waves results in resuspension of sediments from the seabed and ejection of these sediments out of the boundary layer. The resuspension of sediments from the seabed is controlled by current-induced strong bed shear stress, while the ejection of sediments out of the bottom boundary layer is driven by the compression and subsequent expansion of the mixing layer, together with the developments of the separation bubbles behind the internal solitary waves. These findings provide new insights into understanding the dynamic mechanism of sediment remobilization by internal solitary waves. Moreover, they contribute to our understanding of the migration of subaqueous sand waves.

Dating post-LGM aeolian sedimentation and the Late Palaeolithic in Central Yakutia (northeastern Siberia)

Central Yakutia is a large region in northeastern Siberia characterized by extensive permafrost, large river valleys, mountain glaciers, and large massifs of aeolian sands; the geological history of the region is complex and, at present, poorly constrained. In recent years, it has been shown that aeolian sands cover up to 60% of large parts of Central Yakutia. This paper presents the results of luminescence dating of aeolian sedimentation at the Diring Yuriakh Palaeolithic site located in the middle reaches of the Lena River. Field studies identified several thick units of aeolian sand, which cover an old deflation surface with Late (Duktai culture) and Early Palaeolithic (Diring culture) artefacts. The reliability of the OSL chronology was assessed by comparison of ages based on the optically stimulated luminescence from quartz and the infra-red stimulated luminescence from potassium-rich feldspars; these age pairs are in good agreement, implying that at least the quartz grains were sufficiently bleached before sedimentation. We obtained OSL ages that reflect three periods of accumulation between the LGM and the Holocene: ∼21 ka, 15-14 ka, and 12.5–10 ka. These periods of accumulation broadly coincide with global cooling episodes during the Last Glacial Maximum, the Older Dryas, and the Younger Dryas, with some extension into subsequent warmer intervals, whereas the intervening intervals without preserved sediments are taken to reflect dune stability during warmer periods. The sand on the terraces, sourced from alluvial bars in the river channel, was blown up the valley slope during cold and dry periods when the vegetation cover was sparse. When the climate warmed, the vegetation took some time to spread, and so the accumulation of aeolian sand on the high terraces continued into the warm periods. We also infer periods of deflation (wind erosion) that occurred before 21 ka and between 20 and 15 ka, presumably due to increased aeolian activity and localized remobilization of sediment. The new OSL chronology shows that the younger artefacts located at the cape of Diring Yuriakh, belonging to the Late Palaeolithic Duktai culture, are older than 15 ka. The new ages also show that the post-LGM aeolian sand sequences at Diring Yuriakh are correlated with the regionally developed subaerial Dolkuma Formation.

Paleo-valley infills record landscape response to late-Quaternary glacial/interglacial climate oscillations in the French western Alps

Reconstructing mountainous landscape evolution throughout the Quaternary is challenging because of the poor long-term preservation of geomorphic records in a context of rapid surface dynamics and topographic rejuvenation. The Quaternary geomorphic evolution of the western European Alps has been strongly controlled by climatic oscillations between glacial and interglacial periods. Significant erosion and sediment remobilization during these glacial/interglacial cycles have left very few sedimentary archives to quantify the surface dynamics and paleo-environmental conditions within the mountain belt over the last hundreds of thousands of years. Alpine valleys within the periglacial zone are potential candidates to target long-term geological archives, since they may contain alluvial deposits that have been preserved from subsequent glaciations. In the Drac valley (French western Alps), three generations of paleo-valleys are preserved, each of which was filled with alluvial and lacustrine sediments in response to glacial damming downstream. The valleys were incised during subsequent times of glacial retreat, leading to the formation of epigenetic valleys. Detailed 3D mapping of the paleo-valleys was carried out using photogrammetric models to constrain their geometry. Mapping was combined with luminescence dating of alluvial deposits to reconstruct the temporal evolution of the Drac valley. This chronological framework, together with additional data from the literature, allowed us to quantitatively constrain the complex alluvial dynamics along the Drac river during the last ca. 230 ka. Poly-phased alluvial deposition occurred in the most recent paleo-valley between ca. 90 and 20 ka (i.e., from late MIS 5 to MIS 2) in a context of global climate cooling and major Alpine glaciation. Sediment infilling of the intermediate paleo-valley is dated at around 130 ka; i.e., during the late-glacial phase of the penultimate glaciation, at the abrupt warming transition between MIS 6 and MIS 5. Finally, the oldest paleo-valley was filled around 230 ka (during a sub-stage of MIS 7) probably in a cooling and glacial context. The overall alluviation pattern and chronology of the study area highlight the asynchronous and partially contrasting glacial dynamics between the different glacier systems (i.e., Drac, Bonne and Romanche/Isère glaciers) within the Ecrins-Pelvoux massif of the French western Alps.

Coastal degradation regulates the availability and diffusion kinetics of phosphorus at the sediment-water interface: Mechanisms and environmental implications

Coastal wetlands have experienced considerable loss and degradation globally. However, how coastal degradation regulates sediment phosphorus (P) transformation and its underlying mechanisms remain largely unknown in subtropical coastal ecosystems. This study conducted seasonal field measurements using high-resolution diffusive gradient in thin films (DGT) and dialysis (Peeper) techniques, as well as a DGT-induced fluxes in sediments (DIFS) model, to evaluate the mobilization and diffusion of P along a degradation gradient ranging from pristine wetlands to moderately and severely degraded sites. We observed that sediment P is diminished by coastal degradation, and severely degraded sites exhibit a decline in the concentration of available P, despite the presence of distinct seasonal patterns. High-resolution data based on DGT/Peeper analysis revealed that labile P and soluble reactive P (SRP) concentrations varied from 0.0006 mg L−1 to 0.084 mg L−1 (mean 0.0147 mg L−1) and from 0.0128 mg L−1 to 0.1677 mg L−1 (mean 0.0536 mg L−1), respectively. Coastal degradation had a substantial impact on increasing SRP and labile P concentrations, particularly at severely degraded sites. Although severely degraded wetlands appeared to be P sinks (negative P flux at these sites), we did also observe positive diffusive flux in October, indicating that coastal degradation may accelerate the diffusion and remobilization of sediment P into overlying water. The simulations of the DIFS model provided compelling proof of the high resupply capacity of sediment P at severely degraded sites, as supported by the increased R and k-1 values but decreased Tc values. Taken together, these results suggest coastal degradation reduces the sediment P pool, primarily attributed to the strong remobilization of P from the sediment to porewater and overlying water by enhancing the resupply capability and diffusion kinetics. This acceleration induces nutrient loss which adversely impacts the water quality of the surrounding ecosystem. To reduce the adverse effects of coastal degradation, it is essential to adopt a combination of conservation, restoration, and management efforts designed to mitigate the risk of internal P loading and release, and ultimately maintain a regional nutrient balance.

Holocene geochronology and sedimentation in the southern Brazil shelf depocenters

Latitudinal modulation of proxies for environmental changes over the mid to late-Holocene was analyzed in four cores retrieved along mud depocenters on the South Brazilian Shelf, between 33.8°S and 25.1°S. To the south, early to mid-Holocene northwards migrations of the Southern Westerly Wind Belt (SWWB) and the post-LGM sea level rise are expressed as an increase in sand content, while the low Ti/Ca and Ti/K ratios point to dry climatic conditions. During the mid-Holocene, the sea level highstand coincided with a period of stabilization in atmospheric conditions, which led to a pulse of coarser sediment deposition in the southern area. In 3000 cal yr BP, a rapid and latitudinally simultaneous increase of Ti/Ca and Ti/K mark the late-Holocene more humid and warmer onset linked to an intensification of the South American Monsoon System (SAMS). Across-shelf branches of the Brazil Current (BC) that mix with the Plata Plume Water (PPW) to flow northwards could be responsible for sediment remobilization leading to clay depletion in the south extreme of the study area. The amplitude of grain size changes gets lower as we go further north, suggesting a buffering effect exerted by the distance to the source.

Influence of a small submarine canyon on biogenic matter export flux in the lower St. Lawrence Estuary, eastern Canada

Abstract. Submarine canyons enhance shelf–slope sediment exchange and influence hydrodynamic processes, with consequences for biogeochemical cycles. This work documents variations in the vertical export of biogenic matter on the northern shore of the lower St. Lawrence Estuary (LSLE, Quebec, eastern Canada), which is characterized by the presence of an active submarine canyon system. A total of three moorings were deployed from November 2020 to September 2021. One nearshore mooring (PDMc) was deployed in the main axis of the Pointe-des-Monts (PDM) canyon system and was equipped with an acoustic Doppler current profiler (ADCP), and two moorings equipped with sediment traps were deployed in the distal PDM canyon system (PDM-154, PDM-224) and offshore Baie-Comeau (BC-133). The ADCP data revealed the occurrence of a minor sediment remobilization event (December 2020) and a small turbidity current (February 2021) in the canyon. Concurrent elevated fluxes of total particulate matter, particulate organic carbon, particulate nitrogen, and chloropigments showed that these events left a signature in sediment traps PDM-154 and PDM-224 located &gt; 2.6 km further offshore by enhancing lateral dispersion of resuspended sediments. The composition of diatom and dinoflagellate assemblages was similar in the canyon system and offshore BC, but the diatom bloom occurred 2 weeks earlier (in mid-April) at the PDM site. A bloom of the potentially toxic diatom Pseudo-nitzschia seriata was also observed during the second half of September 2021 at the BC site. Annual diatom and dinoflagellate fluxes were almost 2 times lower at the PDM site than at the BC site, possibly due to differences in riverine input and the structure of the water column, as well as increased sediment input and resuspension at the PDM site, leading to limited light availability. This study notably helps identify the relationship between near-bed canyon processes and biogenic matter export in the water column, thereby directly influencing the ecosystem offshore PDM. The study period further covered an anomalously nearly ice-free winter, and thus, in the context of climate change, it provides valuable insight into future trends of biogenic matter export in the LSLE.

Field-Measurement of Surface Wind and Sediment Transport Patterns in a Coastal Dune Environment, Case Study of Cala Tirant (Menorca, Spain)

Blowouts are integral features of coastal dune fields. Their presence enhances both geomorphological and ecological diversity and enables the movement of sand by wind. Their role as a ‘transport corridor’ may be, however, considered negative from a coastal management perspective in heavily touristic areas, where the existence of blowouts close to the foredune can enhance the loss of sediment from the beach. This paper investigated the relationship between airflow dynamics and patterns of sediment transport from the beach to established dunes through a trough blowout located on the foredune. Seven three-cup anemometers were used to measure wind speed and direction over a 24 h sampling period at a frequency of 1 min under onshore (parallel to the blowout axis) medium and high wind speeds (max of 17.9 ms−1). To measure sediment transport, a total of 12 vertical sand traps were located at three positions along the length of the deflation basin. The results indicated that small amounts of sediments went into the blowout from the beach and that the highest rates of sediment remobilization took place within the deflation basin. These results highlight two processes: (a) flow channelization induced by the blowout topography caused an increase in wind speed and sediment transport toward the depositional lobe, and (b) the presence of embryo dunes and herbaceous vegetation at the beach–blowout boundary effectively reduced the amount of sediment transport from the beach to the landform. The results confirmed the significant role that vegetation plays in controlling sediment movement and conserving the beach–dune system.

Climate change impacts on streamflow, sediment load and carbon fluxes in the Lena River delta

Water and sediment supply are essential to the health of deltaic ecosystems. Diverse datasets were integrated to better understand how climate change is shifting the supply of water and sediment to the largest polar distributary channel pattern – the Lena River Delta. Here the increase in warming rate from an average air temperature is from 4.1 °C for the period 1950–99 to 6.1 °C during 2000–21, which is higher than in the adjacent polar regions. Streamflow and sediment yield entering the Lena Delta have increased since 1988 by 56.3 km3 and 6.1×106 t, respectively; meanwhile, the Lena River’s increases in water temperature in June, July–August and September were found to be as much as 1.1, 0.6 and 0.05 °C. These changes have a pronounced effect on sediment regimes in particular parts of the delta. Based on analyses of correlations between various hydroclimatic drivers and sediment concentration changes across particular distributaries of the Lena Delta extracted from Landsat datasets, bank degradation driven by thermal erosional processes (which are in turn related to air and soil temperature increases) is proved to be the primary factor of the sediment regime in the delta. The study also highlights that sediment load changes are sensitive to wind speed due to remobilization of bottom sediment. Sums of daily air temperature and wind speed over 3 days are correlated with sediment concentration changes in the delta. The results also indicate that carbon transport across the delta (both POC and DOC) depends on sediment transport conditions and water discharge and might increase by up to 10 %. We conclude that the Lena Delta can be recognized as the global hot spot in terms of the hydrological consequences of climate change, which is altering sediment regimes, stream hydromorphology and carbon transport.

Assessing the ecological risk of heavy metal sediment contamination from Port Everglades Florida USA.

Port sediments are often contaminated with metals and organic compounds from anthropogenic sources. Remobilization of sediment during a planned expansion of Port Everglades near Fort Lauderdale, Florida (USA) has the potential to harm adjacent benthic communities, including coral reefs. Twelve sediment cores were collected from four Port Everglades sites and a control site; surface sediment was collected at two nearby coral reef sites. Sediment cores, sampled every 5 cm, were analyzed for 14 heavy metals using inductively coupled plasma-mass spectrometry. Results for all three locations yielded concentration ranges (µg/g): As (0.607-223), Cd (n/d-0.916), Cr (0.155-56.8), Co (0.0238-7.40), Cu (0.004-215), Pb (0.0169-73.8), Mn (1.61-204), Hg (n/d-0.736), Mn (1.61-204), Ni (0.232-29.3), Se (n/d-4.79), Sn (n/d-140), V (0.160-176), and Zn (0.112-603), where n/d = non-detected. The geo-accumulation index shows moderate-to-strong contamination of As and Mo in port sediments, and potential ecological risk indicates moderate-to-significantly high overall metal contamination. All four port sites have sediment core subsamples with As concentrations above both threshold effect level (TEL, 7.24 µg/g) and probable effect level (PEL, 41.6 µg/g), while Mo geometric mean concentrations exceed the background continental crust level (1.5 µg/g) threshold. Control site sediments exceed TEL for As, while the reef sites has low to no overall heavy metal contamination. Results of this study indicate there is a moderate to high overall ecological risk from remobilized sediment due to metal contamination. Due to an imminent dredging at Port Everglades, this could have the potential to harm the threatened adjacent coral communities and surrounding protected habitats.

Geomorphic evolution of the craton-derived Sone megafan in the southern Ganga plain, India: A tectono-climatic interplay

The Ganga plain neotectonics has been studied from surface and sub-surface faults, frequent geomorphic readjustment, changing sedimentation pattern, piedmont progradation, pedological variation, and frequent earthquake occurrences. However, being neotectonically stable, the peninsular region’s geomorphic changes are governed by climatic fluctuations, contributing to the Ganga plain’s sedimentation. Therefore, peripheral craton sourced marginal alluvial deposits in the Ganga basin are appropriate features to study the control of both the Himalayan tectonics and climate of core peninsular region away from their respective source areas. This study uses a process-response approach model to describe the geomorphic development of the Sone megafan, located at the marginal part of the Ganga plain to the south of the Ganga River, bordering the Indian craton.Geomorphological mapping, field investigation of the depositional features, soil profiles, and Optical Stimulated Luminescence (OSL) chronology suggest four phases of geomorphic evolution, i.e., in 22–8 Ka, 8.0 Ka–7.3 Ka, 7.3 Ka–2.4 Ka, and 2.4 Ka–0.5 Ka on the Sone megafan. The different evolutionary phases are marked by channel and floodplain abandonment and soil profile development. The megafan surface is divided into four distinct geomorphic units (OdSP – Oldest Sone Plain, OSP – Old Sone Plain, YSP – Young Sone Plain, and AFP – Active Floodplain) based on OSL ages and soil properties. Geomorphology and soil suggest a mixed climate in the source and sink area. The arid climate in the catchment contributed to the sediment production, and the humid climate promoted its transport, which resulted in the largest depositional unit of the megafan, even during the arid period in the Ganga basin. Contrast to the north of the Ganga River, no surface faults are found on the Sone megafan. However, the tectonic activity of the bounded basement faults, i.e., the East and the West Patna faults, are well pronounced in the sediment distribution and fluvial response. Tilting and twisting the fault-bounded block controls the sediment remobilization in space and time. Thus, the climatic fluctuation in the source, the sink, and the activity of the basement faults, propelled by the Himalayan tectonics, contributed to the Sone megafan’s geomorphic evolution. Two events of the Ganga River’s encroachment at the distal part of the Sone megafan were recorded (2.4 ± 0.14 and 1.3 ± 0.16 ka). The correlation between OSL ages of megafan units, climatic fluctuations in the Sone River’s catchment, and established time windows of tectonic episodes in the Ganga basin has also been investigated. As the Sone and the Gandak megafans rest on the same tectonic blocks, their tectono-geomorphic responses to the Himalayan neotectonics are similar.

The Maracangalha injectite complex: An overlooked hydrocarbon play in the Lower Cretaceous Recôncavo Basin, NE Brazil

The Recôncavo Basin is the third major natural gas producer in Brazil. Lower Cretaceous sandstones of the Maracangalha Formation (Caruaçu and Pitanga Members) hold the largest volumes of non-associated gas in this basin. However, these reservoirs are extremely complex due to a range of soft-sediment deformational process that modify the depositional architecture and impact on the original structure of the porous system. The cause of soft-sediment deformation is still contradictory because both mass movements and post-depositional fluidization has been proposed by previous studies. This uncertainty has drastic implications for reservoir predictability in the subsurface since mass-transport deposits and fluidization-remobilization complexes have very different architectures. To test these hypotheses, this study examines soft-sediment deformation structures (SSDS) in outcrop and core in order to interpret remobilization processes and to infer the main trigger mechanisms involved. Outcrop description was carried out in the coastal zone of the Todos os Santos Bay, NE Brazil, where the Maracangalha Formation is very well exposed. High-resolution core images from four producing fields located northward (Miranga, Jacuípe, Lamarão and Massapê) were also described. SSDS include a great variety of structures: 1) dish, 2) pillar, 3) consolidation lamination, 4) load structures, 5) tilted, convoluted, distorted and disrupted laminations, 6) flames, ball and pillow structures and pseudonodules, 7) large-scale mounded geometries, 8) penecontemporaneous faults and 9) sandstone intrusions/extrusions (dikes, sills, breccias and volcanoes). Intensely deformed sandstones are connected to sandstone intrusions that cut through finer-grained, low-permeability strata. Orientation of normal faults and sandstone intrusions suggests that they are genetically related. The Pitanga and Caruaçu Members are better described as facies, since they differ only by the degree of deformation. Pitanga facies is the product of remobilization of an undeformed (Caruaçu) facies. Unlike previous interpretations that indicated the action of slumps, we concluded that the upward movement of interstitial fluids (liquefaction and fluidization) was the main mechanism of remobilization, deformation and mixing of sediments. The overpressure of pore fluids and syn-rift faults propagation broke up seal-strata, releasing the fluids pressure and driving the upward movement of sediments. Key architectural elements of a sand complex are recognized in outcrop and core, including parent units, host-strata and sandstone intrusions. For the origin of this injectite complex we suggest a seismic trigger related to extensional tectonics of the rift system. The Maracangalha injectite complex comprises a new hydrocarbon play to be considered in further exploration and production (E&P) activities in the Recôncavo Basin.

Controls on Surface and Downcore Sedimentary Organic Matter in a Constructed Oyster Reef

Oysters provide a suite of important ecosystem services, and recent research shows that oyster restoration rapidly enhances sedimentary organic carbon deposition. In 2012, an oyster reef enhancement project began in the GTM National Estuarine Research Reserve in Northeast FL, USA. We analyzed the spatial and downcore variability in sedimentary organic matter (OM) and particle sizes in the intertidal zone between the reefs and the marsh, along with oyster reef characteristics, to better understand physical and/or biological influences on sediment. Our data indicate that OM in the top 20 cm of sediment cores was negatively correlated with reef age. Similar decreases in particles &lt;63 μm suggest remobilization of sediment, likely driven by the degradation of the reef structure over its approximately 9-year lifetime. Likewise, a survey of surface sediments showed that adjacent reef structural metrics were the best predictor of sediment OM and particle size. These results highlight the importance of reef structure as a control on sedimentary organic carbon deposition and stability in areas where physical energy is relatively high. This result is discussed in the context of implications for carbon budgets and biogeochemical ecosystem services of oysters as a part of living shorelines.

Critical areas for sediment delivery to the Chubut River, Patagonia Argentina: geomorphological evidence from the Sagmata pilot basin

ABSTRACT Sediment discharge events in the lower basin of the Chubut River (Patagonia, Argentina) associated with rainfall events generate serious problems for drinking water purification of more than 250,000 inhabitants and the support of livestock farming activity of about 42,000 ha in the region. Identifying the areas of potential sediment contribution to the Chubut River and the conditions necessary for erosion and sediment transfer is of vital importance to mitigate the negative impact of sediment discharge into the river and to establish water management plans. We conducted a detailed geomorphological study in a 110 km2 tributary watershed of the Chubut River (Sagmata pilot Basin), and identify potential sediment production zones. We based our analyzes on concomitant studies that indicate that the sediment remobilization is linked to the location of the drainage networks, especially in regions associated with badlands and erosional scarps formed on Paleogene continental deposits.

Robust estimations of areal grain size distribution from geometric surface roughness in a proglacial outwash area

Rapid glacier mass loss in high-alpine catchments exposes unconsolidated sediments to erosion by meltwater-fed mountain streams, with impact on the catchment-scale sediment dynamics. Proglacial outwash areas (OWA) are a key spatial element in this sediment flux cascade, with grain size distributions (GSD) as an integral variable in current and future glacio-fluvial processes and associated effects.In this study, surface grain size estimation methods based on linear correlations between geometric surface roughness and GSD data are adapted to test this new mapping approach for areal GSD patterns and their changes in a proglacial OWA. Surface roughness is computed with adaptive kernel sizes from high-resolution topographic point clouds derived from UAV-based photogrammetry. For model calibration, ground truth data is manually obtained from 30 dry-exposed GSD sampling patches of 1 m2 each. The novelty and potential of this surface roughness regression model lies in its capability to robustly map GSD percentiles at 1-m cell resolution in highly dynamic proglacial environments and inherent data scarcity, drastically reducing the portion of labour-intensive and time-consuming manual surveying.Our optimized linear regression function for the key figure D84, which is widely used in practice, returns a coefficient of determination of 76.4 %. The linear relation found between the D84 of field GSD and the 84th distribution percentile of surface roughness metrics has a slope of α = 6.01, which is consistent with the range of recently published studies using LiDAR-based and photogrammetric surveys. The presented surface roughness regression model provides realistic surficial estimations of areal GSD patterns in a proglacial domain of sediment remobilization. In addition, this work analyses and discusses detected changes in the estimated D84 over a three-month period. A systematic shift is identified for sediment compositions with an initial D84 above 60 mm. This is thought to be an effect of the original image quality and variable lighting conditions between photogrammetric surveys and indicates that best practice should include careful survey planning for most uniform flight settings. Nevertheless, visually verified significant changes in D84 along frequently wet low-flow channels can be detected automatically, and thus the findings demonstrate the feasibility of this GSD monitoring approach for tracking fluvial re-working of surface sediment.

Rapid fluvial remobilization of sediments deposited by the 2021 Chamoli disaster, Indian Himalaya

Abstract High-magnitude mass flows can have a pervasive geomorphological legacy, yet the short-term response of valley floors to such intense disturbances is poorly known and poses significant observational challenges in unstable landscapes. We combined satellite remote sensing, numerical modeling, and field observations to reconstruct the short-term geomorphological response of river channels directly affected by the 7 February 2021 ice-rock avalanche–debris flow in Chamoli district, Uttarakhand, India. The flow deposited 10.4 ± 1.6 Mm3 of sediment within the first 30 km and in places reset the channel floor to a zero-state condition, requiring complete fluvial re-establishment. In the 12 months post-event, 7.0 ± 1.5 Mm3 (67.2%) of the deposit volume was removed along a 30-km-long domain and the median erosion rate was 2.3 ± 1.1 m a–1. Most sediment was removed by pre-monsoon and monsoon river flows, which conveyed bedload waves traveling at 0.1–0.3 km day–1 and sustained order-of-magnitude increases in suspended sediment concentrations as far as 85 km from the event source. Our findings characterize a high-mountain fluvial cascade with a short relaxation time and high resilience to a high-magnitude geomorphological perturbation. This system response has wider implications, notably for water quality and downstream hydropower projects, which may be disrupted by elevated bedload and suspended sediment transport.

Lacustrine evidence reveals spatially and temporally distinct Holocene ruptures on the Sawtooth Fault, Central Idaho, USA

ABSTRACTThe Sawtooth Fault in central Idaho, USA, is a range‐bounding normal fault with a Late Pleistocene–Holocene scarp near the up‐valley ends of several range‐front lakes. Cores from Redfish Lake, which spans the fault, exhibit evidence of catastrophic sediment re‐mobilization in two sequences consisting variably of intraclastic mud‐clast conglomerate, massive homogenite, and graded silt and clay. Event strata of the younger sequence are in unconformable contact with Pleistocene sediments in two cores on the northern lake‐basin slope, suggesting transport from the down‐valley portion of the lake toward the basin center. A silt cap associated with the event strata is preserved at all coring sites. The event sequence, distributed lake‐wide, dates to ca. 4300 cal a bp, while additional event strata in two Redfish Lake cores pre‐date the 7627 cal a bp Mazama ash. We propose seismic triggering of the sediment disruptions. Asynchronous event stratigraphy in Pettit Lake, 15 km south of Redfish Lake, suggests distinct ruptures along two portions of the Sawtooth Fault. The sedimentology and geochemistry of remobilized sediments in both lakes indicates that sources included Late Pleistocene and early Holocene lake‐floor sediments and suggests failures that cut deeply into the sedimentary sequence. Cores collected from Stanley Lake (17 km northwest of Redfish Lake) following the nearby 2020 M6.5 Stanley earthquake exhibit a thin, sandy event horizon associated with documented delta collapse. Subaerial slope failures associated with the 2020 event left no widespread disturbance stratigraphy in Redfish Lake. We conclude that the large‐magnitude lake‐floor sediment remobilization events probably required rupture of fault sections proximal to Redfish and Pettit lakes.

Biological soil crusts as a major ecosystem component in sandization areas of the Brazilian Pampa

In the Brazilian Pampa, vegetation disturbance and soil degradation led to an expansion of sediment remobilization areas, a process locally termed as sandization. Transported sands generate severe environmental problems and hamper the growth of vegetation. However, parts of these sandization areas are quickly covered by biological soil crusts (biocrusts), which have not been investigated in this biome before.This study describes biocrust occurence in sandization areas of the Brazilian Pampa for the first time and analyses their distribution patterns related to the local topography. We studied biocrusts at two research sites where their presence appeared to be essential for soil protection. First, the occurrence of different biocrust types were assessed and a taxonomic survey was conducted. Second, UAV-based imagery was created and biocrusts were classified, using a random forest approach to understand the relation of their abundance to topography.We observed that biocrusts occurred widely in areas prone to sandization with an approx. 25% distribution on the land surface. They are mostly dominated by cyanobacteria and secondarily by bryophytes. Among the observed genera, the cyanobacterial genus Stigonema sp. was dominating in both study sites. Campylopus pilifer was the dominating moss species. The mapped biocrusts represented all major morphological types and were classified as rolling, pinnacled, rugose, and smooth crusts. Local topography was a major driver for biocrust distribution, but also the establishment of vascular plants. Slope and aspect had a strong influence on biocrust development, but the presence of protective topographic positions against atmospheric influences most prominently facilitated their occurrence.This pilot study proves that biocrusts can potentially play a key role as ecosystem engineers in the Brazilian Pampa with a positive effect on general vegetation growth and soil-stabilization. In this biome, however, they have been largely overlooked compared to other areas globally. Thus, biocrusts need to be further studied and their effects considered in land management to constrain further soil degradation.

Lunar nodal tidal cycle influences on the input of coarse sediments during the last glaciation in the deep South China Sea

Cross-slope transport of coarse sediments is thought to be dominated by gravity-flow or hyperpycnal-flow processes triggered by hydrodynamic events. However, whether long-term non-event hydrological processes can affect longitudinal transport is still unclear. Here, high-resolution (1 mm) X-ray fluorescence core scanning combined with coarse-fraction observation has been conducted on a laminated sequence (dated as last glacial 14.3–20.8 cal ka BP) of Core MD05-2892 in the South China Sea. The laminae show interbedded millimeter-scale dark and light layers. Dark layers are distinguished by coarse-grained (sand-containing clayey silt) sediments rich in Ca, Zr, and Si, whereas light layers are characterized by fine-grained (silty clay) deposits rich in K, Ti, and Fe. Accordingly, Zr/K and Si/K ratios are used to indicate lamina occurrences, and the ratios are well correlated to grayness. Spectral analyses of the ratios and grayness all present a persistent ∼18.6-yr cycle, which is interpreted as the lunar nodal tidal cycle. This signal in laminae could be related to remobilization of coarse sediments via mean high-water-line variations driven by the lunar nodal tide during the last glacial sea-level lowstand. Coarse sediments were more likely transported from the shelf break via suspended-load-dominated hyperpycnal flow to the slope to form dark layers during periods of strengthened tidal activity, while fine sediments were dispersed via hemipelagic transport to form light layers during periods of weakened tidal activity. Our study highlights for the first time that the lunar nodal tide could periodically trigger the transport of coarse sediments from the shelf to the deep sea.

Shallow and deep subsurface sediment remobilization and intrusion in the Middle Jurassic to Lower Cretaceous Agardhfjellet Formation (Svalbard)

Abstract Sedimentary injectites are increasingly documented in many hydrocarbon plays at various scales, either interpreted as potential risks (e.g., topseal bypass, a drilling hazard) or benefits (e.g., reservoir interconnection, increased hydrocarbon volumes) for production operations. As such, they have potential critical implications for the assessment of suitability for CO2 injection and sequestration. Detailed characterization of such units, especially in terms of diagenesis and (paleo) fluid flow, is directly achievable at outcrop scale, overcoming dimensional and time constraints otherwise unresolvable at seismic scale. Two sedimentary injection complexes have been recognized in the succession of the Middle Jurassic–Lower Cretaceous Agardhfjellet Formation exposed at Deltaneset, central Spitsbergen, Norway, at different stratigraphic levels. The upper complex comprises two main clastic dikes characterized by different orientation and consolidation, tapering out vertically (upward and downward) within a stratigraphic thickness and lateral extent of more than 50 m and 200 m, respectively. The lower complex is coarser grained, made up by a network of interconnected dikes and sills, shooting off from isolated lenticular and morphologically articulated bodies, interpreted as sedimentary intrusions linked to seafloor extrusion (sand volcano). Petrographic and micromorphological analyses were used to identify the underlying lithologies of the Late Triassic to Middle Jurassic Wilhelmøya Subgroup as the possible source of this remobilized material for both the upper and lower complexes. This subsurface remobilization and consequent intrusion were first achieved in the lower complex during the Late Jurassic at shallow burial conditions, and then at higher confinement pressure for the upper complex, probably during the Late Cretaceous. These results highlight how field data can be used to constrain longlived spatiotemporal relationships of sedimentary intrusions, allowing a finely tuned upscaling of seismic data and interpretations.