Deposition Of Fine-grained Sediments Research Articles

Along-Slope Bottom Current and Sediment Resuspension and Transport Induced by Internal Tides on a Continental Slope

Abstract Moored observations on a critical continental slope in the northeastern South China Sea (SCS) are presented to reveal along-slope bottom current and sediment resuspension and transport caused by internal tides. During spring tides, the bottom-intensified diurnal internal tides were observed, and their breaking generated an along-slope bottom current toward the southwest direction, with a clear ∼14-day spring–neap cycle and a maximum low-frequency velocity exceeding 0.25 m s−1. The diurnal internal tides and along-slope bottom currents showed the same seasonal variations. There were larger near-bottom along-slope velocities in winter (∼9.0 cm s−1) and summer (∼8.9 cm s−1) than in spring (6.3 cm s−1) and autumn (7.4 cm s−1). The previous theory based on radiation stress caused by wave breaking is used to reproduce the observed along-slope bottom current velocity. Strong bottom flows caused by internal tides on the critical slope inhibit deposition of fine-grained sediments and may erode bottom coarse-grained sediments, leading to the generation of near-bottom nepheloid layer with a thickness H > 130 m, as demonstrated by the fact that seafloor sediments on the critical slope are dominated by coarse-grained sediments (sands). The suspended sediments can be southwest transported by the persistent along-slope bottom current generated by internal tide breaking. It was estimated that approximately three million tons of sediments during the observation were carried along the slope to the south of the SCS. Our observations suggest that internal tide-induced sediment resuspension/deposition and along-slope transport could be important for seafloor sediment distribution of the SCS.

Impact of seasonal variations in fronts on suspended sediments transport off the coastal area of Fujian Province

The Zhejiang-Fujian (Zhe-Min) coastal muddy area plays a crucial role in facilitating sediment exchange through a cross-front. The mud depocenter off the Zhe-Min coastal area is a source of suspended sediment that can be transported to the continental shelf of the East China Sea (ECS). Although the front of the inner shelf of the ECS has been extensively reported, the cross-front material transport off the coastal area of Zhe-Min in summer has not been well studied, especially using measured data. To reveal how the front controls the transport of suspended sediment, this study focuses on the impact of fronts on the dispersion of suspended sediment off the coastal area of Fujian Province in different seasons. The results indicate that the front acts as a barrier, inhibiting the dispersion of suspended sediment into the sea. The high-concentration suspended sediment is mainly found to the northwest of the front, with an average SSC of 8.5 mg/L in winter and 3.1 mg/L in summer. The suspended sediment concentration (SSC) follows a V-shaped distribution along the cross-isobath transects, with lower SSC observed at the 50-m isobath compared with the shallow water area and the deep water area. The SSC at the front was the lowest, with an average concentration of 2.3 mg/L in winter and 1.9 mg/L in summer. The front is crucial for the development of the Zhe-Min coastal muddy area. The winter monsoon is strong, resulting in a sufficient supply of suspended sediments in the muddy area and a high transport flux of suspended sediments in the nearshore. The front hinders the dispersion of high-concentrated sediment from the nearshore to the offshore, resulting in the deposition of fine-grained sediments in the nearshore and the formation of an inner shelf muddy sedimentary zone. The findings of this study will help improve our understanding of the sediment source-to-sink processes in the ECS and land–sea interactions.

Reconciling Coulter Counter and laser diffraction particle size analysis for aquaculture monitoring

The disaggregated inorganic grain size (DIGS) of bottom sediment analyzed with a Coulter Counter (CC) has been used to show that the fraction of sediment deposited in flocs (floc fraction) increased in both the near and far field after the introduction of open cage salmon aquaculture, altering benthic habitat and species composition. As a result, DIGS was identified as a potential indicator of regional environmental changes due to aquaculture. Laser diffraction is an attractive alternative to the CC because of its greater efficiency and larger size range. To determine if a laser diffraction instrument, Beckman-Coulter LS 13 320 (LS), could replace the CC within a Canadian national aquaculture monitoring program, the DIGS of 581 samples from five different regions in eastern Canada were analyzed with an LS and a CC. Results show that the LS could not be used to calculate floc fraction. Instead, % sortable silt and the volume % of inorganic particles < 16 µm were evaluated as alternative proxies for fine sediment properties. LS and CC values for these parameters were correlated, but they were significantly different and the relationship between the instruments was dependent on the area sampled. The LS did not capture variations between areas seen in the CC DIGS data. Where the DIGS from the CC found no sorting in the finest size classes, all the LS samples had similar size distributions characterized by smooth modal peaks. The LS and CC both return values that can be used to monitor changes in the deposition of fine-grained sediment, but the LS cannot determine changes in floc deposition and caution is required if comparing different sedimentary environments.

System-scale dynamics of long-term sediment and phosphorus accumulation in contrasting valley-bottom wetlands in dryland landscapes of South Africa

Anthropogenic-induced acceleration of sediment and associated nutrients presents a serious challenge to water resource management across the globe. While wetlands are potential natural solutions, little is known of how well key wetland types attenuate downstream sediment fluxes and how these relate to local- and catchment-scale factors. This research aimed to develop an understanding of patterns and rates of sediment and phosphorus retention in valley-bottom wetlands in South Africa. The geomorphology, sedimentology and historical accretion rates of three wetlands which offered diversity in size, catchment position and degree of organic accumulation were compared to ascertain the impact of local- and catchment-scale factors. Estimates of sediment and associated phosphorus accumulation suggest higher rates in clastic sediment-dominated wetlands (1089–7655 g sediment m−2 yr−1, 0.4–1.6 g-P m−2 yr−1) compared to an organic sediment-dominated system (601–1308 g-sediment m−2 yr−1, 0.2–0.3 g-P m−2 yr−1). Sediment accretion rates generally increased longitudinally, indicating that distal wetland reaches act as sediment and phosphorus retention hotspots. Phosphorus distribution patterns were primarily attributed to variations in organic matter content and associated aluminium and iron complexing agents in fine-grained sediment deposits, while particle size distributions were less important. However, the relevance of individual complexing agents in phosphorus dynamics varied among wetlands with differing landscape conditions. Contrasts between these systems reflect variations in catchment lithology and hydroclimatic regime, which influence the relative magnitude of sediment supply and vegetation productivity. We postulate that intermediate-sized wetlands characterised by catchments around 900 ha in size, gentle longitudinal slopes (∼2 %), a high proportion of fine sediment deposition, limited organic matter breakdown, and a long vegetation growing season provide optimal conditions for sediment and phosphorus accumulation. This system-scale information is essential to guide management decisions to identify and prioritize within-catchment ‘hotspots’ of sediment and phosphorus retention.

A magnetic and geochemical approach to the changing sedimentation accumulation on the upper slope of the great barrier reef, northeastern Australian margin

The Great Barrier Reef (GBR) located along the northeastern margin of Australia is the largest coral reef system in the world. Modern climatic alterations are quickly changing the GBR ecosystem. To understand the implications of these changes it is important to reconstruct the geological history of GBR. Here we use geochemical and magnetic proxies to evaluate past climatic fluctuations and their consequences on sediment deposition along the GBR margin. IODP Expedition 325 – Hole M0058A, drilled on the uppermost slope at ca. 170 m water depth, reveals the depositional history of the GBR margin during the interval of MIS 7 to 5 and MIS 1. Magnetic and geochemical variations along the core section reveal detailed information on sediment accumulation and on the variations in terrigenous input in relation to sea-level fluctuations and climate change. Sea-level variations influenced margin deposition between MIS 7 and 6 impacting shoreline progradation/retrogradation and siliciclastic redistribution, resulting in a mixture of finer to coarser magnetic assemblages with no significant changes in terrigenous input. At the end of MIS 6 a decline in the deposition of carbonate sediments concomitant with the deposition of fine-grained magnetite-rich terrigenous sediments suggests an intensification of the monsoon in response to global warming trends. Arid periods over NE Australia were established after the glacial/interglacial transition (the MIS 6-5e) and at the middle Holocene (after the MIS 2–1 transition at ca. 7 ka), which favored dust deposition over the region. Enhanced dust fertilization subsequently promoted primary productivity at these intervals resulting in the presence of biogenic magnetite at Hole M0058A produced by magnetotactic bacteria.

Deglacial and Holocene sediment dynamics and provenances off Lancaster Sound: Implications for paleoenvironmental conditions in northern Baffin Bay

Since the last deglaciation, Baffin Bay between Greenland and Canada developed from an isolated marginal sea to a major Arctic-Atlantic throughflow closely linked to the North Atlantic circulation. While the initial steps of gateway openings through Lancaster Sound and Nares Strait to northern Baffin Bay are reasonably well documented, far less is known about related regional deglacial-to-Holocene changes in sediment sources and depositional processes due to a lack of continuous and well-dated paleoenvironmental records from northern Baffin Bay. Sedimentological, mineralogical, and radiogenic isotope data of the well-dated sediment core GeoB22336-4 from the mouth of Lancaster Sound provide new insights on the impacts of ice-sheet retreat and opening of the gateways to the Arctic Ocean on the depositional setting. Basal subglacial till deposits point to a grounded ice stream at the mouth of Lancaster Sound before ∼14.5 ka BP. Subsequent glaciomarine sedimentation is characterized by the input of ice-rafted detritus (IRD), bioturbation traces, and foraminifera shells. Decreasing sediment supply and input of IRD through time reflects a period of ice-sheet recession to predominantly land-terminating positions during the Early Holocene. Changes in radiogenic isotope signatures reveal the openings of Lancaster Sound between ∼10.4 and 9.9 ka BP and of Nares Strait between 8.5 and 8.2 ka BP, in alignment with earlier studies. The rapid mid-Holocene (up to ∼5.8 ka BP) deposition of fine-grained sediments is most likely caused by enhanced sea ice-rafted sediment input released under a strong West Greenland Current influence. Finally, a slight increase in IRD input during the last ∼2 ka BP is linked to the neoglacial re-advance of regional glaciers.

New insights for origin of fine-grained sediments from the early neogene Qaidam Basin: Wind and fluvial–lacustrine source-to-sink processes

Fine-grained sediment deposition is widely distributed in lacustrine and marine facies and significant for petroleum geology. However, the causes of fine-grained sediment deposition remain controversial. In this study, we examine the cause of fine-grained sedimentation in the Neogene saline lacustrine Qaidam Basin, and propose a new insight into the sedimentary process for fine-grained sediments. Various sedimentary structures identified from the fine-grained sediments such as erosional structures with lag deposits, hummocky cross-stratification (HCS)-like structures, asymmetrical ripples, or sandy ball-and-pillow structures, are generated by winter storms. These winter storms are related to the winter winds that cause eolian sedimentation in Asia. Abundant detrital material may be rapidly transported into lakes by winter storms, favoring extensive terrigenous detrital deposition in the lacustrine basin, hardly controlled by the division of sedimentary facies and topographical differentiation. The genetic features and shallow-water origin with wind and fluvial–lacustrine source-to-sink processes, may be the main reason for the poor hydrocarbon potential of the Neogene fine-grained sediments in the Qaidam Basin.

The interplay of fluvial, lacustrine and aeolian deposition and erosion along the Neales Cliffs and its relevance to the evolution of Kati Thanda-Lake Eyre, central Australia, during the Quaternary

ABSTRACT A high-resolution record of fluvial, aeolian and lacustrine deposits of Late Pleistocene age is exposed along the Neales Cliff in the lower reaches of the Nappamurra-Neales River, western Kati Thanda-Lake Eyre (KT-LE). Five major stratigraphic units reflect a variety of changes in sedimentary processes, depositional environments and hence palaeo-lake level fluctuations. This detailed record of a dryland terrestrial sedimentary succession in the northern part of KT-LE enables comparison to contemporaneous sequences in the southern part of KT-LE. The sedimentary record from the Neales Cliff area is placed into a continental stratigraphic framework, in which changes in sediment accumulation and depositional style are linked to climatically driven palaeo-lake level fluctuations independent of eustatic sea-level changes. Following the ~200 ka interglacial maximum, a drying-up systems tract is represented by a fluvial fining-upward trend, capped by palaeosols. A wettening-up systems tract followed, when lake level rose to +10 m AHD during the last interglacial, resulting in a lacustrine succession but punctuated by regular desiccation events. During the following drying-up systems tract, progressive lake-level fall resulted in deep incision around 100 ka, followed by enhanced fluvial deposition of fine-grained sediments. A brief rise in base level resulted in a wettening-up systems tract comprising a thin veneer of fluvial/alluvial sediments followed by extensive dune build-up and desert pavement development during the Last Glacial Maximum. Subsequent lake level fall to the present lake level of −15 m AHD, resulted in deep incision of up to 10 m by the modern day Nappamurra-Neales River.

Sedimentological, petrophysical, and geochemical controls on deep marine unconventional tight limestone and dolostone reservoir: Insights from the Cenomanian/Turonian oceanic anoxic event 2 organic-rich sediments, southeast Constantine Basin, Algeria

The Cenomanian/Turonian period is characterized by the deposition of organic-rich and fine-grained sediments that form important source rocks and unconventional reservoir units in North Africa and other parts of the world. The Lower Turonian deposits of the Djebel Darmoun Field, southeast Constantine Basin, Algeria, comprise a thick carbonate succession that has potential as an unconventional reservoir unit. This research aims to investigate the Lower Turonian succession in terms of microfacies, diagenesis, petrophysical, and geochemical characteristics, which were previously unknown. Sedimentological and diagenesis analyses were performed based on the core and thin section observations. Furthermore, geochemical and petrophysical analysis methods were carried out to assess the resource potential based on geochemical measurements, core measurements, and well logging evaluation in an arrangement. Based on sedimentological investigation, the Lower Turonian carbonate section is composed of tight limestone and dolostone rocks characterized by four bioclastic limestones and two dolomicrite microfacies, while paleontological investigation indicates that the faunal content is dominated by planktonic assemblages, revealing a pelagic deep marine setting environment. The primary pores of the Lower Turonian carbonate rocks are seldom preserved due to multi-stage diagenetic alteration (i.e., cementation, compaction, fracturing, dolomitization, dissolution, asphaltene), while dominant secondary pores are represented by dissolution-enlarged and open fractures/fissures, while intercrystal pores might be added in dolostone intervals. Dissolution and fracturing diagenetic events play a major role in enhancing the pore network, while compaction, cementation, and asphaltene diagenesis processes share in the obliteration of the petrophysical properties. Dolomitization played a dual role in the dolostone intervals, where it tended to develop the porosity at the early stages of diagenesis, while it tended to decrease the porosity at the latest diagenesis stages. The geochemical analysis indicated high amounts of organic matter in these intervals, where the higher estimated organic richness reaches a maximum TOC of 7.8% at the lowermost part. The petrophysical analysis inferred that the Lower Turonian carbonate sediments are characterized by low porosity (avg. 4%), very low permeability (<0.01mD), with dominant micro and meso porosities, and therefore they can be classified as tight carbonate unconventional resources. This study provides an insight into factors controlling the pore system network (microporosity) of fine-grained carbonate rocks as an excellent analog of the deep marine unconventional tight limestone and dolostone reservoirs and improves the knowledge and modeling of these unconventional resources. The study sheds light on the organic-rich sediments that are associated with oceanic anoxic events (OAEs) across the North African region and other parts elsewhere, forming high quality source rocks that might be neglected as excellent unconventional resources.

Late Miocene Cymodocea seagrass in the Guadalquivir Basin (southern Spain)

Despite the abundance of seagrass-related deposits in the geological record, seagrass macrofossils are scattered in time and space, due to the low preservation potential of marine angiosperms. Fossil seagrass impressions, mainly rhizomes occur in Messinian (late Miocene) marl beds intercalated in cross-bedded bioclastic limestones in the Guadalquivir Basin near Alcalá de Guadaíra in southern Spain. Vegetative characters indicate that most remains can be attributed to Cymodocea cf. nodosa, to which also probably belong a few molds of fruits. Two other fossil fragments can only be assigned to Alismatales indet. The plants lived in sheltered ephemeral areas among shallow-water submarine dunes, in which deposition of fine-grained sediment favored their fossilization. During the late Miocene the Guadalquivir Basin was open to the Atlantic Ocean and, therefore, these fossil occurrences lie within the modern biogeographic distribution of C. nodosa, the only species of the genus out of the Indo-West Pacific region. At the moment, it is the only record of seagrass fossils in the Miocene of Europe.

Sedimentation history and excess metal deposition in estuarine barrier-island system of the Nakdong River, South Korea

Human activities, such as dam construction and reclamation, can affect sedimentation rates as well as sediment topography and transport in estuaries such as the Nakdong River Estuary. To investigate the sedimentation history, two sediment cores (1–2 m long) were sampled in tidal flats of the estuary. In addition, surface sediments were collected to study present sedimentation environments that appear to be three environments locally: 1) fine-grained sediment deposition; 2) sediments under stronger hydraulic energy; and 3) sandy sediments with good sorting. At the fine sediment deposition, environmental sensitive fraction of elements (Cu, Pb, As, and Co) show an increased sedimentation flux after the dam construction. On the other hand, organic matter-normalized Pb-210 concentrations in sediment core reveal that marine-originated organic matter is predominant in the upper ~45 cm of sediment layers, indicating a significant change in sedimentation history related to massive sedimentation within the Nakdong River Estuary.

Sedimentary Evolution Characteristics of Fine-Grained Lithofacies under the High-Resolution Isochronous Shelf System: Insights from the Wufeng-Longmaxi Shales in the Sichuan Basin

Abstract The deposition and evolution of fine-grained sediments is a hot topic in fine-grained sedimentary rock studies and is important for accurately evaluating shale gas sweet spots. In this paper, the fine-grained deposition and evolution characteristics of the Wufeng-Longmaxi shales, major targets for Chinese shale gas exploration, were studied by using core observations, thin section analyses, scanning electron microscopy, geochemical analysis, and fossil identification. This work accurately identified six typical lithofacies; among them, the organic matter-rich siliceous shale facies (OMRSSF), the high-organic matter siliceous argillaceous shale facies (HOMSASF), and the medium-high organic matter low calcareous siliceous shale facies (M-HOMLCSASF) are favorable facies for shale gas exploration. The high-resolution isochronous unit in the shelf fine-grained sedimentary system was established, and the differential evolution of lithofacies in the system tract was discussed. The lithofacies deposition and differentiation in the transgressive system tract were controlled by the transgressive scale and tectonics under increasingly shallow water conditions. The lithofacies deposition and differentiation in the regressive system tract were controlled by tectonics and the preexisting lithofacies. The lithofacies in the regressive system tract had more frequent facies transitions and greater differentiation than those in the transgressive system tract, and they exhibited significant spatiotemporal inheritance. Sequential differential sedimentary sequences and symmetric differential sedimentary sequences were distinguished in the continental shelf sedimentary system. The lithofacies depocenters and subsidence centers were consistent in the transgressive system tract, while the tectonically active paleocontinent was important in the regression system tract. This study is of great significance for further high-resolution exploration of marine shale and improvement of the theory of shelf fine-grained sedimentary systems.

Watershed Suspended Sediment Supply and Potential Impacts of Dam Removals for an Estuary

Observations and modeling are used to assess potential impacts of sediment releases due to dam removals on the Hudson River estuary. Watershed sediment loads are calculated based on sediment-discharge rating curves for gauges covering 80% of the watershed area. The annual average sediment load to the estuary is 1.2 Mt, of which about 0.6 Mt comes from side tributaries. Sediment yield varies inversely with watershed area, with regional trends that are consistent with substrate erodibility. Geophysical and sedimentological surveys in seven subwatersheds of the Lower Hudson were conducted to estimate the mass and composition of sediment trapped behind dams. Impoundments were classified as (1) active sediment traps, (2) run-of-river sites not actively trapping sediment, and (3) dammed natural lakes and spring-fed ponds. Based on this categorization and impoundment attributes from a dam inventory database, the total mass of impounded sediment in the Lower Hudson watershed is estimated as 4.9 ± 1.9 Mt. This represents about 4 years of annual watershed supply, which is small compared with some individual dam removals and is not practically available given current dam removal rates. More than half of dams impound drainage areas less than 1 km2, and play little role in downstream sediment supply. In modeling of a simulated dam removal, suspended sediment in the estuary increases modestly near the source during discharge events, but otherwise effects on suspended sediment are minimal. Fine-grained sediment deposits broadly along the estuary and coarser sediment deposits near the source, with transport distance inversely related to settling velocity.

Sedimentation and erosion patterns within anabranching channels in a lowland river restoration project

ABSTRACT Anabranching channel designs are seldom utilized for river restoration projects despite their potential for efficient hydraulic conveyance and robust floodplain habitat. We evaluated a stream restoration project that concentrates base flows within a single deep, narrow channel overflowing into secondary channels and an alternating series of higher elevation active benches at flood stages. The design represents an implementation of a Cluer and Thorne SEM Stage 8 anastomosing system aimed at increasing transport efficiency of water and sediment through low gradient river reaches to alleviate flooding on adjacent properties. We investigated the performance of the project’s hydraulic conveyance and the general utility of anabranching channels as a restoration alternative by assessing the distribution and magnitude of deposition and erosion response patterns. High-resolution survey indicate aggradation is not occurring within the main channel. Between summer 2016 and summer 2017, reaches experienced mean elevation decreases between 0.08 and 0.29 m indicating effective discharge rates transported dominant grain sizes. Along some reaches, bed scour was sufficient to undercut banks, producing slumps, which may affect long-term conveyance capacities. Lateral bank scour was limited to reaches exposed to daily tidal flows. Variable deposition patterns were observed within secondary channels, depending on cumulative precipitation, dominant hydrology, and channel entrance orientation. Isolated tidal flows resulted in deposition, while long duration flood flows produced intertidal floodplain scour. Within fluvially-dominated benches, uniform longitudinal deposition of fine-grained sediments was associated with low channel entrance flow rates. Higher entrance flow rates resulted in concentrated deposition of coarse-grained particles, up to 0.21 m, and a longitudinal gradient of decreasing sediment sizes and magnitude. This study builds upon previous work by providing a high-resolution assessment of a constructed anabranching channel system and confirms its suitability for efficient hydraulic conveyance within fluvial reaches of lowland rivers and provides general recommendations for future designs.

Multiproxy analysis of a Lateglacial-Holocene sedimentary section in the Fuegian steppe (northern Tierra del Fuego, Argentina): Implications for coastal landscape evolution in relation to climatic variability and sea-level fluctuations

We report the sedimentology, palynology, geochemistry, and diatom assemblages of a well-dated succession at Laguna Las Vueltas (LV) on the Atlantic coast of the Fuegian steppe in southern Argentina. The multiproxy analysis offers a unique opportunity to study the evolution of this coastal landscape in relation to past sea level and climate changes in the southern high latitudes. After ca. 19,000 cal yr BP, the sediments were subjected to subaerial exposure and oxidation linked to a low sea level. The Sr/Ba ratio (a paleosalinity geochemical parameter) indicates variations in the water body level, and diatoms imply the existence of an ephemeral and brackish-freshwater body subject to desiccation under arid conditions. Between ca. 11,600 and 8500 cal yr BP, a shrubby steppe vegetation, mainly composed of Asteraceae subf. Asteroideae, spread over the coastal area associated with a shallow freshwater body and the deposition of fine-grained sediments in low-energy environments, all indicative of low effective moisture and warm climate conditions. Between ca. 8500 and 8100 cal yr BP, salt carpet vegetation, dominated by Chenopodiaceae, developed around a coastal lagoon in response to the Holocene marine transgression. The record of dinocysts and geochemical data indicate marine influence at this time. Between ca. 8100 and 7000 cal yr BP, salt marshes colonized the coastal area. A coastal lagoon with a more restricted connection to the sea and minor freshwater input are inferred, linked to the beginning of a regressive phase. After ca. 7000 cal yr BP, grassland vegetation and an open shrub stratum developed along with a shallow lake (pan) that was disconnected from the sea, following a fall in the sea level and regression. Fluctuations in the water level of the pan and changes in the physical-chemical conditions, as indicated by fluctuations in Mn/Fe, Ti/Ca, Rb/Sr, Ca, TIC and TOC, suggest abrupt events of desiccation and flooding. Between ca. 4500 and 2000 cal yr BP a drier phase is indicated by changes in vegetation, algal content and geochemistry of the pan. A grassland vegetation and a shallow lake with seasonal water level variations characterized the last 2000 years. Our results from LLV area match well with Andean forest fluctuations and regional climatic conditions recorded from Tierra del Fuego and Chilean southwest.

Geochemistry and Nd isotopic composition of the Permian Ko Sire Formation, Phuket Island, Thailand: implications for palaeoclimate and palaeogeographical configuration of the Sibumasu Terrane

The Sibumasu Terrane is a continental block in SE Asia that is considered to have been attached to Gondwana before its collision with Indochina during the Triassic. The elemental geochemistry and Sm–Nd isotopic composition of mudrocks from the lower Permian Ko Sire Formation of the Phuket Group on Phuket Island (central Sibumasu Terrane), Thailand, were analysed to investigate its provenance, weathering history and palaeogeographical location prior to its separation from Gondwana. The whole-rock elemental geochemistry identified a felsic, granodioritic source rock, which is consistent with the general consensus regarding Gondwanan sediment provenance. Despite the evidence for sediment recycling, such as abundant dropstone clasts derived from sedimentary rocks, the low degree of chemical weathering and lack of zircon enrichment indicate a cold and arid palaeoclimate in its source area, which resulted in ice-rafted transportation of clasts and suspension deposition of fine-grained clastic sediments. Sm–Nd isotopic data and previously published detrital zircon U–Pb age spectra provide more detailed information on the source-rock composition, which was similar to that of the North Australian crustal element, suggesting that the central Sibumasu Terrane was located on the northern margin of north Australia during the late Paleozoic. Supplementary material : A table of trace element concentrations is available at https://doi.org/10.6084/m9.figshare.c.4877289

Distribution, composition profiles, source identification and potential risk assessment of Polychlorinated Biphenyls (PCBs) and Dechlorane Plus (DP) in sediments from Liaohe Estuary

Polychlorinated biphenyls (PCBs) and Dechlorane Plus (DP) were analyzed to evaluate the environmental quality in sediments from Liaohe Estuary (LHE), northern China. The concentration of ∑24PCBs ranged from 106.7 to 270.0 pg g−1 dry weight, with a mean value of 186.6 pg g−1 in surface sediments. The PCBs concentrations in the eastern region of Gaizhou Beach (GZB) were higher than those in the western region, indicating that the effects of hydrodynamic transportation and deposition of fine-grained sediments are the factors controlling the distribution and behaviors of PCBs in LHE. Principal component analysis (PCA)-multiple linear regression (MLR) revealed that 15.9% of PCBs in LHE originated from local sources directly discharged by anthropogenic activities, 73.9% from surface runoff of eroded soils contaminated by PCBs and 10.2% from atmospheric deposition and microbial degradation. The concentration of DP varied from 10.1 to 45.7 pg g−1 dry weight, with an average value of 28.0 pg g−1 dry weight. The spatial distribution pattern of DP indicated that hydrodynamic forces and the sedimentary environment were prominent factors influencing the accumulation and distribution of DP in LHE. The mass inventories for a sediment thickness of 2 cm in the whole area of LHE were 4.1 kg and 0.6 kg for ∑24PCBs and DP, respectively. At present, the ecological risk for sediments of LHE is low for both PCBs and DP.

Depositional environment and organic matter accumulation of Lower Jurassic nonmarine fine-grained deposits in the Yuanba Area, Sichuan Basin, SW China

Abstract This study investigated the lithological, sedimentological and geochemical characteristics of Lower Jurassic strata (Ziliujing Formation) in the Sichuan Basin to identify the lithofacies and understand the depositional environments and differences in organic matter accumulation of these nonmarine fine-grained sediments. Based on mineralogy and petrology, rock types were recognized, with mudstones, siltstones, and limestones being the most common. Rock types, sedimentary structures, biota, and well log data were used to define and characterize 17 lithofacies and the following five facies associations of the fine-grained sediments: (1) delta front; (2) clastic lakeshore; (3) clastic shallow lake; (4) clastic semi-deep lake; and (5) carbonate lake. The content of total organic carbon ranges between 0.04% and 3.84%, with an average of 0.74%. The organic matter primarily consists of Type Ⅲ kerogen. Major processes inferred from the lithofacies analyses include suspension, biogenic, and storm deposition. On the basis of facies associations, redox, climate and salinity conditions, biotic productivity, and terrigenous input, a total of six depositional environments are proposed: (I) high-productivity low-oxygen swamp (II) low-oxygen semi-deep lake (III) high-oxygen semi-deep lake (IV) high-oxygen shallow lake (V) deep-water low-oxygen semi-deep lake and (VI) high-salinity low-oxygen shallow lake. The nonmarine environments changed frequently, unlike more stable environments. The development of bivalves in the shallow lake is suggested to be related to high salinity caused by dry climate, together with limited terrigenous input. Organic-rich nonmarine fine-grained sediments in the Ziliujing Formation formed in swamp and semi-deep lake with settings under reducing conditions, in a humid climate, with relatively high terrigenous input. Results of the study may help us to understand the deposition of nonmarine organic-rich fine-grained Lower Jurassic sediments in southwest, China.

Origin of deep-water fine-grained sediments as revealed from the Lower Cretaceous rifting basin sequence in the Lingshan Island, Yellow Sea, Eastern China

Understanding the sediment dynamics responsible for the deposition of fine-grained sediments is essential for studying fine-grained sediment origin and its distribution, which is of a great significance for unconventional oil and gas exploration and development. Fine-grained sediments from a Lower Cretaceous rift-basin sequence in the Lingshan Island, the middle of the Dengta section in the Lingshandao Formation were studied. On the basis of detailed outcrop investigation, thin section observation, and laboratory measurements, seven types of lithofacies and three lithofacies associations were identified in the fine-grained sediment sequence. The sediment dynamics were deduced from a comprehensive examination and interpretcation of the sedimentary structures and lithofacies associations. The fine-grained sediments in the research area belong to a silt dominated subclass, which is composed mainly of thin-bedded siltstones with normal grading and mudstones with horizontal lamination. Suspension settling is responsible for the development of horizontal lamination in some mudstone. The Bouma-like lithofacies associations are developed by downslope fine-grained turbidity currents. The hybrid event bed-like lithofacies associations are formed by hybrid flow, while turbidity currents transformed to muddy debris flows downslope. The interbedded thin sandstone and mudstone banded lithofacies associations may be resulted from a downslope transitional flow between a turbidity current and a muddy debris flow. The vertical facies stacking patterns of the fine-grained sediment sequence indicatec that the fine-grained gravity flow may have been evolved from a transitional flow to a debris flow then to a low-density turbidity flow and finally to a hybrid flow. Lithofacies associations deposited by hybrid flow and transitional flow are potential sweet spots for unconventional oil and gas exploration in such fine-grained sediment formation.

Fingerprinting sub-basin spatial suspended sediment sources by combining geochemical tracers and weathering indices.

Transport and deposition of fine-grained sediment, a pervasive nonpoint source pollutant, cause deleterious off-site impacts for water quality and aquatic ecosystems. Sediment fingerprinting provides one means of identifying the spatial sources of mobilised sediment delivered to fluvial systems in order to help target sediment control strategies and uptake of such source tracing procedures has been steadily increasing. Nonetheless, there remains a need to continue testing and comparing different composite signatures for source discrimination including the incorporation of physically grounded information relevant to erosion patterns. Accordingly, the objective of this study was to compare the discrimination and apportionment of sub-basin spatial suspended sediment sources in a mountainous basin in northern Tehran, Iran, using composite signatures comprising conventional geochemical tracers combined with lithological weathering indices or only the former. The list of conventional geochemical properties comprised Al, Ca, Cu, Fe, K, Mg, Mn, Na, Ni, Sr, Ti, and Zn whilst three weathering indices were included: the chemical index of alteration (CIA), the weathering index of Parker (WIP), and the indicator of recycling (IR) which were all calculated based on elemental oxides. Using a composite signature combining conventional geochemical tracers and one weathering index (IR), the relative contributions from the sub-basin spatial sources were estimated at 1 (Imamzadeh Davood; 1.4%), 2 (Taloon; 13.4%), 3 (Soleghan; 35.9%), and 4 (Keshar; 48.4%) compared with corresponding respective estimates of 0.7%, 45.5%, 40.2%, and 13.3% using conventional geochemical tracers alone. Wald-Wolfowitz Runs test pairwise comparisons of the posterior distributions of predicted source proportions generated using the two different composite signatures confirmed statistically significant differences. These differing proportions demonstrated the sensitivity of predicted source apportionment to the inclusion or exclusion of a weathering index providing information reflecting the relative coverage of more erodible lithological formations in each of the sub-basins (32.7% sub-basin 1, 53.6% sub-basin 2, 58.5% sub-basin 3, and 63.2% sub-basin 4). The outputs of this study will be used to target sediment mitigation strategies.