Sediment Mixing Research Articles

Erratum for ‘The provenance of the Devonian Old Red Sandstone of the Dingle Peninsula, SW Ireland; the earliest record of Laurentian and peri-Gondwanan sediment mixing in Ireland,’ Journal of the Geological Society, London, 175, 411–424

Samples in this paper have been assigned formations based on the Geological Survey of Ireland shapefile released prior to the commencement of the study. However, the authors were not aware that, since obtaining the samples, an updated shapefile had been released. This update affects three of the four apatite samples assigned to the Lower Devonian Ballymore Formation. The location of samples Mb-1, Mb-4 and Mb-5 now places them well within the undifferentiated, Upper Devonian Slieve Mish Group. As outlined in our paper, the apatite ages were originally produced concurrently with apatite fission track analysis and were later used in our study to provide additional provenance information in support of the detrital zircon geochronological data. In the second paragraph of the discussion section we say the following: et al. (1999) obtained an age of 411 Ma for the Cooscrawn Tuff Bed in the Ballymore Formation, which is older than 22 of the 70 detrital apatites analysed in this formation. The reassignment of the three samples to the Upper Devonian Slieve Mish Group nullifies the above statement. However, our interpretation that the depositional age of the Ballymore Formation is younger than the 411 Ma age given by Williams et al. (1999) is predominantly based upon the evidence given by the six youngest detrital zircons from the formation which underlies the Ballymore Formation (i.e. the Slea Head Formation). These zircons give a concordia age of 405 ± 4 Ma. This suggests that the Ballymore Formation was more than likely deposited after 409 Ma. We do not believe that the reassignment of the three samples has any major impact on our provenance interpretations. The ∼420 Ma age of the majority of the apatites in samples Mb-1, Mb-4 and Mb-5 actually fits with the range of Palaeozoic detrital zircons in sample AK-17 which was taken from the Slieve Mish Group, thereby supporting minor input of rocks affected by end-Scandian metamorphism.

Small dynamic mountainous rivers in Taiwan exhibit large sedimentary geochemical and provenance heterogeneity over multi-spatial scales

Taiwan rivers are characterized by extremely rapid mass wasting and sediment transfer due to active tectonics and frequent typhoons. Various methods have been applied to constrain processes affecting their sediment source-to-sink routing. In most cases, the sediment at the outlet is considered to be a representative average of the whole upstream basin due to the short sediment routes (<200 km). However, this assumption may be inappropriate because huge compositional heterogeneity can exist even within such small dynamic river systems. To reveal their intra-station and basin-wide geochemical heterogeneity, we collected sediment samples along the Zhuoshui and Liwu Rivers in Taiwan. Multiple samples deposited in different locations or with different grain-sizes were collected at each station, and the <63 μm fractions were measured for their elemental and Sr–Nd isotopic compositions. Elemental ratios and dimension-reducing technique were firstly applied to discriminate the sediment provenances. They show that the large elemental heterogeneity exists between samples at the same station and also between stations along each river, explainable by variable sediment mixing and local lithological heterogeneity. When combining our Sr–Nd isotopic data with literature data from Taiwan rivers, five discrete clusters of river sediments can be distinguished, reflecting the inter-catchment heterogeneity of sediment provenance in Taiwan Island. We also applied a Sr–Nd isotopic mixing model coupled with Monte-Carlo simulations to quantify the provenance heterogeneity in both rivers. The sediment contribution of the Western Foothills/Tailuko Belt to the Zhuoshui/Liwu downstream can vary by a factor of ∼2 between sediment samples that were considered as spatial or temporal replicates. Combined with field in-situ observations, we propose that fast-changing sediment transport modes cause the provenance heterogeneity in small dynamic mountainous rivers attacked by frequent heavy storms or typhoons. Sediments transported during different events and with different provenances can be preserved at each station, which leads to the intra-station and basin-wide geochemical heterogeneity. This study shows that “small” dynamic mountainous rivers can exhibit “large” geochemical and provenance heterogeneity over multi-spatial scales, and thus the common assumption that “let nature do the averaging” should be treated cautiously in this kind of river. Therefore, we propose several effective sediment sampling approaches on small mountainous rivers for reference. Future studies relying on detrital sediments, e.g. applying cosmogenic nuclides or Li isotopes, should also be aware of the heterogeneous nature in small mountainous rivers, because fast-changing provenances can simultaneously bias the weathering and erosion signals and lead to unrepresentative results.

Response of lake-catchment processes to Holocene climate variability: Evidences from the NE Tibetan Plateau

Investigating the so-called Third Pole Environment (TPE) became a major concern during the last decades since it was recognized that the high-altitude region of the Tibetan Plateau (TP) is a key area for the understanding of cause-effect mechanisms driven by climate change and geodynamic processes. Studies on the hydro-climatic evolution during the Late Quaternary were mainly carried out by single lake records or alternatively by individual terrestrial sites. Integrated source-to sink studies considering lake–catchment interactions were extremely seldom utilized. We investigated such relationships in the Kuhai Basin on the north-eastern Tibetan Plateau and analysed sedimentary processes based on 30 onshore sections and three sediment cores from different locations and water depth in the lake basin. Grain size variations, ostracod assemblages, geochemical proxies and absolute dating (luminescence, radiocarbon, 210Pb/137Cs) were applied as key indicators that reveal interacting sediment fluxes under different hydro-climatic settings during the Younger Dryas interval and the Holocene. Our results indicate that wind-induced transportation processes and allocation of respective aeolian sands in the catchment are attributed to distinct phases of reduced effective moisture availability during summer time. Those phases corresponded to weak summer monsoon influence during the Younger Dryas interval, the Early Holocene (11.6–7.5 ka), dry-cold interlude (DCI: ca. 4.5–3.0 ka), Dark Ages Cold Period (DACP: ca. 1.8–1.1 ka) and the Little Ice Age (LIA: ca. 0.6–0.1 ka). Contemporaneous low lake levels during these periods corresponded with respective aeolian sand flux and variable composition of mixed sediments (fluvial and aeolian) in lake deposits. Different flux rates at the core sites could be assigned to local conditions in respect to inflow behaviour of individual drainage systems and nearshore morphology. Aeolian deposits in the catchment were not always preserved and underwent re-mobilisation during succeeding episodes and/or erosion during phases of high water availability. Wetter climatic conditions during the Mid-Holocene (ca. 7.5–5.1 ka), Roman Warm Period (RWP: ca. 2.8–1.5 ka) and Medieval Climate Anomaly (MCA: ca. 0.9–0.6 ka) revealed significant lake level rise due to enhanced river discharge, well documented by highest suspended flux rates, disappearance of ostracod communities at core sites and very low sand input. Climate shifts during the Holocene were linked to variations in effective moisture supply under the influence of the Asian summer monsoon (ASM) and the interplay with the mid-latitude westerlies (MLW). Cold-dry phases were likely a response to North Atlantic climatic anomalies transmitted by the MLW across the TP.

Geochemical Insights Into Provenance of the Middle Devonian Hamilton Group of the Central Appalachian Basin, U.S.A.

Abstract In order to better understand the relationship of clastic influx and organic-matter accumulation and preservation in the Middle Devonian Acadian foreland basin, we conducted a high-resolution provenance analysis of a composite section of the Hamilton Group. The Hamilton Group includes the organic-rich Marcellus Shale, one of the most lucrative unconventional shale gas plays in the world, and the overlying Mahantango Formation. Geochemical analysis of 121 samples from two nearby wells in Monongalia County, West Virginia, reveals subtle changes in clay provenance throughout deposition of the Marcellus Shale and the Mahantango Formation. Major-element and trace-element geochemistry suggest derivation from a felsic igneous, granodioritic, upper-continental crustal source with additional influx from a recycled quartzose sedimentary source. All weathering indices indicate increasing chemical weathering intensities throughout deposition of the Marcellus Shale, followed by consistently moderate chemical weathering associated with accumulation of the Mahantango Formation. Sm-Nd isotopic analysis of ten samples throughout the Hamilton Group yield eNd values ranging from –7.06 to –11.75, and Nd depleted-mantle model ages (τDM) ranging from 1.63 to 1.85 Ga, with ages becoming younger upsection. Our results suggest that the extrabasinal detritus of the Hamilton Group originated from a mixed sediment source, with clay influx from both rocks associated with the Superior Craton to the north and northwest (τDM > 2.7 Ga) and Grenville-sourced sediments derived from the adjacent Acadian fold–thrust belt to the east (τDM ∼ 1.4–1.6 Ga). Older Sm-Nd model ages, felsic composition, and evidence of sediment recycling suggest little to no contribution from the Acadian volcanic arc, indicating that volcanic tuff of the Tioga ash beds represent isolated episodes of volcanic input into the basin. Model ages, eNd values, and trace-element geochemistry indicate increased sediment influx from the Acadian fold–thrust belt throughout deposition of the Hamilton Group, with the highest sediment influx having occurred during Mahantango Formation deposition. Increased clay influx from sediment shed off from the Acadian fold–thrust belt associated with marginal marine regression increased delivery of clastic detritus, diluting the flux of organic matter and likely disrupting basin water stratification that aided in preservation of organic matter in the lower Marcellus Shale. The Middle Devonian Acadian Basin serves as an example of the influence of detrital influx on organic-matter accumulation and preservation in mud-dominated depositional systems.

Sensitivity of multiple life stages of 2 freshwater mussel species (Unionidae) to various pesticides detected in Ontario (Canada) surface waters.

Freshwater mussels contribute important ecological functions to aquatic systems. The water filtered by mussel assemblages can improve water quality, and the mixing of sediments by burrowing mussels can improve oxygen content and release nutrients. However, nearly 70% of North American freshwater mussel species are listed as either endangered, threatened, or in decline. In Ontario, 28 species are in decline or in need of protection. Even though freshwater mussels have a heightened sensitivity to some contaminants, few studies have investigated the risks that various pesticide classes pose to one freshwater mussel species or among life stages. Lampsilis siliquoidea and Villosa iris were the focus of the present study, with the latter currently listed as of "special concern" in Canada. A potential risk to the recovery of freshwater mussel species is the presence and persistence of pesticides in Ontario surface waters. Acute (48 h) toxicity tests were performed with V. iris glochidia to determine the effect on viability (surrogate for survival) following exposure to 4 fungicides (azoxystrobin, boscalid, metalaxyl, and myclobutanil), 3 neonicotinoids (clothianidin, imidacloprid, and thiamethoxam), 2 carbamates (carbaryl and malathion), 1 organophosphate (chlorpyrifos), and 1 butenolide (flupyradifurone). Juvenile and adult L. siliquoidea were also exposed to azoxystrobin, clothianidin, imidacloprid (juvenile only), and carbaryl (adult only). Our study found in general that all life stages were insensitive to the pesticides tested, with median effect and lethal concentrations >161 µg/L. The pesticides tested likely represent a minimal risk (hazard quotients <5.4 × 10-3 ) to freshwater mussel viability and survival in acute (48 h) and subchronic (28 d) exposures, respectively, in Ontario streams where pesticide concentrations were considerably lower than those tested in the present study. Environ Toxicol Chem 2018;37:2871-2880. © 2018 SETAC.

Can we detect ecosystem critical transitions and signals of changing resilience from paleo‐ecological records?

AbstractNonlinear responses to changing external pressures are increasingly studied in real‐world ecosystems. However, as many of the changes observed by ecologists extend beyond the monitoring record, the occurrence of critical transitions, where the system is pushed from one equilibrium state to another, remains difficult to detect. Paleo‐ecological records thus represent a unique opportunity to expand our temporal perspective to consider regime shifts and critical transitions, and whether such events are the exception rather than the rule. Yet, sediment core records can be affected by their own biases, such as sediment mixing or compression, with unknown consequences for the statistics commonly used to assess regime shifts, resilience, or critical transitions. To address this shortcoming, we developed a protocol to simulate paleolimnological records undergoing regime shifts or critical transitions to alternate states and tested, using both simulated and real core records, how mixing and compression affected our ability to detect past abrupt shifts. The smoothing that is built into paleolimnological data sets apparently interfered with the signal of rolling window indicators, especially autocorrelation. We thus turned to time‐varying autoregressions (online dynamic linear models, DLMs; and time‐varying autoregressive state‐space models, TVARSS) to evaluate the possibility of detecting regime shifts and critical transitions in simulated and real core records. For the real cores, we examined both varved (annually laminated sediments) and non‐varved cores, as the former have limited mixing issues. Our results show that state‐space models can be used to detect regime shifts and critical transitions in some paleolimnological data, especially when the signal‐to‐noise ratio is strong. However, if the records are noisy, the online DLM and TVARSS have limitations for detecting critical transitions in sediment records.

Sediment Dynamics in Wind Wave‐Dominated Shallow‐Water Environments

AbstractSediment dynamics driven by waves and currents in shallow‐water estuarine environments impacts many physical and biological processes and is important to the estuary‐wide sediment budget. Observational restrictions have limited our ability to understand the physics governing sediment entrainment and mixing in these environments. To this end, we use direct numerical simulation to simulate sediment transport processes in shallow, combined wave‐ and current‐driven flows. Simulations are run with depth‐averaged currents ranging from 0 to 9 cm/s, while wave conditions are held constant with a bottom orbital velocity and period of 10 cm/s and 3 s, respectively. Our results indicated that for wave‐dominated conditions, waves reduce vertical momentum fluxes and the associated bottom drag, thereby accelerating mean currents. Conversely, currents do not significantly affect the wave velocity field. However, they increase the bed shear stress and change the timing and duration of sediment entrainment throughout the wave cycle. Counterintuitively, these effects lead to lower suspended sediment concentrations near the bed for a portion of the wave cycle. By analyzing sediment fluxes, waves are shown to drive near‐bed sediment dynamics while currents control vertical mixing above the buffer layer, where downward settling is predominantly balanced by the current‐generated vertical turbulent sediment flux. In the absence of currents, sediment concentrations are negligible above the wave boundary layer because mixing is weak. We show that the time‐ and phase‐averaged sediment concentration profiles for wave and current conditions resemble the theoretical Rouse profile derived for equilibrium conditions in statistically steady, unidirectional turbulent channel flow.

Bottom‐Slope‐Induced Net Sediment Transport Rate Under Oscillatory Flows in the Rippled‐Bed Regime

AbstractFull‐scale experiments in the rippled‐bed regime were conducted in an oscillatory water tunnel to study the net sediment transport rate due to oscillatory flows on sloping bottoms (up to 2.6°). The tests cover a variety of sinusoidal flows, under which uniform two‐dimensional ripples are generated from a coarse sand movable bed. A laser‐based bottom profiler was developed to measure ripple geometry and net sediment transport rate. Under the same flow condition, a small bottom slope can slightly change the shape of the equilibrium ripples; for example, ripples become upslope leaning, but the ripple dimensions remain almost unchanged. Ripples are also found to migrate in the downslope direction with uniform speed and permanent shape, which is due to the spatial variation of net bedload transport rate. For a given flow condition, the slope‐induced net sediment transport rates are in the downslope direction and increase linearly with the bottom slope. A conceptual model, which is an extension of a sheet flow model (Yuan, Li, &amp; Madsen, 2017, https://doi.org/10.1002/2016JC011996), was also developed. This calibration‐free model can reasonably predict the net transport rate, despite that a moderate underestimate (a factor slightly less than 2) is observed. Both our experiments and model suggest that the presence of ripples significantly enhances sediment mixing and leads to a large net suspended‐load transport rate, which will not occur under sheet flow conditions. Therefore, net transport rate in the ripple‐bed regime can be comparable to that in the sheet flow regime, although the flow condition is much weaker.

Does size matter? Particle size vs. quality in bivalve suspension feeding

Abstract Increases in total suspended solids (TSS) in rivers have likely contributed to the decline in unionid mussel population sizes as feeding and reproduction are reduced at high TSS concentrations. Surprisingly, however, unionids are often found in turbid rivers. We predicted that clay‐sized particles, which comprise &gt; 80% of river seston (particles in suspension), were too small to affect unionid clearance rate (CR) and thus explain this conundrum. We examined this hypothesis in laboratory experiments involving four unionid species exposed to four particle‐size based TSS treatments (mixed sediment: 0–63 μm; clay: 0–5 μm; fine silt: 5–38 μm; coarse silt: 38–63 μm; sourced from mussel sites) at 20 mg/L, which is a TSS concentration sufficient to reduce CR. Whereas the CR for all species was lower for mixed sediment, coarse silt and clay treatments—the latter was opposite to our prediction—the CR of mussels given the fine silt treatment was similar to the no‐TSS control for two species and higher than the other TSS treatments in the other two species. Fine silt contained the most fluorescent (i.e. algal) particles and the highest protein and lipid content, which suggests that CR were higher on the more nutritious diet. Particle quality, rather than size, is what modulates suspension feeding in turbid rivers. Our current understanding of the ecological effects of bivalve suspension feeding will need to be revised to incorporate field‐based measurements.

Three-dimensional flow structure, morphodynamics, suspended sediment, and thermal mixing at an asymmetrical river confluence of a straight tributary and curving main channel

Past field studies of confluence dynamics have focused mainly on experimental or small stream confluences and confluences of large rivers. Few studies have explored fluvial processes and forms at confluences of medium-size rivers, especially those where river planform varies from a straight alignment. This study examines changes in flow structure, bed morphology, sediment suspension, and mixing with changing incoming flow conditions at a river confluence where a straight tributary joins a curving main channel at the upstream end of a bend. Data include five sets of field measurements of three-dimensional velocity components, bed topography, acoustic backscatter intensity, and water-surface temperatures at the confluence of the curving Wabash River and its straight tributary, the Embarras River. Results show that, in contrast to large river confluences, channel-scale helical motion is a prominent feature of flow structure at this confluence. Dual counter-rotating helical cells, separated by a distinct shear layer, develop over a region of scour within the confluence and contribute to maintenance of scour by sweeping sediment away from this region. Helical motion develops through channel curvature and flow deflection within the confluence. The location and geometry of the scour hole are subject to change depending on the relative momentum fluxes of the two rivers with the zone of scour shifting outward and enlarging as the momentum flux of the tributary increases relative to the momentum flux of the main river. Patterns of backscatter intensity, used here as a surrogate for suspended sediment concentration, confirm that near-bed suspended sediment moves around the scour hole. The thermal mixing interface between the two rivers corresponds to the position of the shear layer, and thermal mixing at the surface within the immediate vicinity of the confluence is limited. The hydrodynamics, morphodynamics, and patterns of sediment suspension and thermal mixing at this river confluence reflect a combination of confluence and bend dynamics.

Modeling the Transport and Fate of Sediments Released from Marine Construction Projects in the Coastal Waters of British Columbia, Canada

Major marine construction projects, resulting in the release of sediments, are subject to environmental assessment and other regulatory approval processes. An important tool used for this is the development of specialized numerical methods for these marine activities. An integrated set of numerical methods addresses four distinct topics: (1) The near-field release and mixing of suspended sediments into the water column (i.e., the initial dilution zone); (2) the transport of the suspended sediments under the influence of complex ocean currents in the far-field; (3) the settling of the transported suspended sediments onto the seabed; and (4) the potential for resuspension of the deposited sediments due to sporadic occurrences of unusually large near-bottom currents. A review of projects subjected to environmental assessment in the coastal waters of British Columbia, from the year 2006 to 2017, is presented to illustrate the numerical models being used and their ongoing development. Improvements include higher resolution model grids to better represent the near-field, the depiction of particle size dependent vertical settling rates and the computation of resuspension of initially deposited sediments, especially in relation to temporary subsea piles of sediments arising from trenching for marine pipelines. The ongoing challenges for this numerical modeling application area are also identified.

Platform drowning leading to cool-water carbonate deposition: evolution of a Late Ordovician (Turinian–Chatfieldian) mixed-sediment platform within the Taconic orogen (Long Point Group, Newfoundland Appalachians)

Late Ordovician (Turinian–Chatfieldian) drowning of a mixed carbonate–siliciclastic platform within the Taconic Orogen (Newfoundland Appalachians) is recorded by net deepening of an initial warm, shallow-water platform succession (Lourdes Formation) culminating in a metre-scale thick condensed interval that characterizes a drowning succession punctuated by storm deposits. Composition of transported material suggests that seaward drowning was coupled with back-stepping of a high-energy carbonate factory related to hinterland uplift and erosion that would eventually lead to drowning of the outer platform beneath marine-transported siliciclastic sediments (Winterhouse Formation). In the new offshore shelf setting, a sparse reciprocal stratigraphy of fine- to very coarse-grained phosphatic carbonate and mixed sediment is interpreted to document gravity-flow deposition downgradient from either a sustained or episodically developed high-energy cool-water carbonate source along the inner shelf. Transported carbonate was cemented rapidly at temperatures no warmer than 16 °C–23 °C, possibly within a seasonal oceanic thermocline. An upsection decrease in abundance of carbonate by the early Edenian is associated with a dramatic increase in siliciclastic supply. The Turinian–Edenian succession of platform drowning, oceanographic transition to cool-water carbonate production, and, later, its termination by increased siliciclastic supply reflects a first-order tectonic control proximal to uplift within the Taconic Orogen. Similar structural and oceanographic changes along the contemporary distal Laurentian margin provides the basis, with improved biostratigraphic control, for future analysis of the significance of proximal–distal stratigraphies in response to regional foreland tectonism.

Mixed siliceous-carbonate sedimentation in a Late Cretaceous epeiric sea: New evidence from the eastern Russian Platform

Mixed siliceous-carbonate sedimentation in a Late Cretaceous epeiric sea: New evidence from the eastern Russian Platform

Improving marine habitat mapping using high-resolution acoustic data; a predictive habitat map for the Firth of Lorn, Scotland

Habitat mapping is an important tool for marine spatial planning and is required for most ecosystem-based management approaches. The Firth of Lorn Special Area of Conservation (SAC), west Scotland, was originally designated for its rocky reef habitat but it is also an area of high importance for the Flapper skate (Dipturus intermedius) and Harbour porpoise (Phocoena phocoena). Here we present an improved predictive habitat map for the SAC utilising multibeam backscatter and bathymetry data collected as part of the Ireland, Northern Ireland and Scotland Hydrographic Survey Project.Backscatter, bathymetry and bathymetric derivatives were analysed using Principal Component Analysis (PCA) and acoustic signatures were created from drop-down video habitat location data. A predictive habitat map was created from Maximum Likelihood Classification using the PCA. Dominant habitat types identified included; moderate energy circalittoral rock (CR.MCR), sublittoral mixed sediment (SS.SMx) and sublittoral sand and muddy sand (SS.SSa). Drop down video showed variable accuracy with 0–100% correctly classified habitats due to the small sample size. The initial validation points were added and the model was rerun. In areas with no previous sea truthing points, some predictions changed to SS.SMx at depths > 100 m and SS.SSa in depths < 50 m, suggesting that the model can be improved with a greater depth-range of sea truthing data. Modern acoustic surveys undertaken for other purposes, such as navigational charting, can thus be used to generate broad-scale predictive habitat maps in a cost and time effective manner. Such maps have the potential for a wide range of use by marine stakeholders, in particular, for establishing environmental baselines for long term monitoring of benthic habitats. Given the high costs of surveying, such an approach supports the rationale of “Collect once and use many times”.

Labile organic carbon dynamics in continental shelf sediments after the recent collapse of the Larsen ice shelves off the eastern Antarctic Peninsula: A radiochemical approach

Labile organic carbon (LOC) dynamics (i.e., of recently produced, planktonic material) and sediment dynamics were studied in the seabed using naturally occurring 14Corg and 210Pb measurements in the region where the Larsen Ice Shelves A and B were floating almost two decades ago. A non-steady-state diagenetic model was used to estimate sediment mixing coefficients as well as LOC fluxes to the seabed and LOC turnover times (i.e., mean residence times) in a suite of 14 sediment cores from the continental shelf, including a glacial trough. At four of the stations, cores were collected during 2007 and 2011 cruises, enabling a time-series approach for understanding the evolution of sedimentary processes and LOC dynamics in the deposits below a collapsed ice shelf. Sediment mixing coefficients, based on non-steady-state 210Pb profiles, varied between 0.01 cm2 y−1 and 1.6 cm2 y−1 in these post-ice shelf sediments. These values were similar to those found in polar deep-sea environments, where sedimentary conditions are less dynamic than in shallower provinces. LOC, whose abundance decreased uniformly with depth, was detected to depths ranging from 2 to 16 cm, with LOC seabed inventories varying from 1.5 to 22 mg LOC cm−2. Excess 210Pb and LOC fluxes were relatively uniform across the study area suggesting that similar particle fluxes have taken place within the Larsen system since the disintegration of the various ice shelves. The LOC mean residence time at the different stations varied from 3 y to >60 y. The 14Corg approach, calculating LOC content based on a two-end member model with planktonic 14Corg as the labile carbon end member, most closely correlated with the lipid content of the sediment, which has been considered one of the best descriptors of reactive organic matter readily available to benthic consumers. We suggest that the irregular combination of sea ice coverage, organic matter production and supply to the sea floor introduce scatter in the determination of sediment and LOC dynamics such that short-term temporal (<5 years) and spatial trends could not be readily resolved.

Measurement of bottom backscattering strength using single-beam echosounder

A quantified single beam echosounder was applied to detect and quantify the bottom echoes. Bottom backscattering strength (SB) is necessary to be quantified for accurate seabed mapping and classification. The SB can be measured by Lambert’s Law that enabled to interpret the bottom echo and to measure the SB values. The research was conducted in Tidung Island, Jakarta which had several seabed types, such as coral reef, seagrass, sand, silt, clay, mud, and mixed sediment. Acoustic data was acquired using SIMRAD EK15 with the frequency of 200 kHz and sediment grain size was analyzed using Wentworth grain size classification. The results show that the backscattering of each seabed type is different. Sediment with greater mean diameter had greater SB value, and seabed with rougher surface had greater SB value as well.

Mesozoic Development of Nonmarine Basins in the Northern Yidun Terrane: Deposition and Deformation in the Eastern Tibetan Plateau Prior to the India‐Asia Collision

AbstractTo determine the timing and spatial patterns of syntectonic nonmarine deposition and deformation in the eastern Tibetan Plateau, we present field data, thin section petrology, and detrital U‐Pb zircon geochronology from the west Ganzi basin (WGB) and east Ganzi basin (EGB) in the northern Yidun terrane. The WGB and EGB contain ~800 and ~1,300–1,600 m of nonmarine strata, respectively, deposited in alluvial environments. Along the southern margins of both the WGB and EGB and the northwestern margin of the WGB, reverse faults place Triassic Ganzi Pluton and Triassic Yidun Grouprocks on top of nonmarine strata. Growth strata in the footwalls of basin‐bounding faults indicate that deposition was synchronous with fault development. The western and eastern margins of the WGB, as well as the northern margin of the EGB, exhibit uncomformable contacts with the underlying Triassic Ganzi Pluton and Triassic Yidun Grouprocks. Provenance results suggest a regionally mixed sediment source from the Yidun and Songpan‐Ganzi terranes. Maximum deposition ages from detrital U‐Pb zircon geochronology, as well as previously reported thermochronology and palynology results, indicate a Late Mesozoic depositional age for WGB and EGB strata. We interpret the spatial and temporal developments of the WGB and EGB to be associated with the Lhasa‐Qiangtang collision.

Sedimentary features and their controls in a mixed siliciclastic–carbonate system in a shallow lake area: An example from the BZ‐X block in the Huanghekou Sag, Bohai Bay Basin, Eastern China

Mixed siliciclastic–carbonate sediments were well developed in the BZ‐X block as a subunit in the Huanghekou Sag in the southeastern part of the Bohai Bay Basin (China) during the Member 1 of the Shahejie Formation. An integrated approach based on detailed microscopic observation and core descriptions was applied to characterize the lithofacies types, facies associations, and depositional environment of the mixed sediments system. A detailed sedimentary facies analysis suggests that various lithofacies types can be grouped into four facies associations: mixed bioclastic sandy beaches (FA1), mixed clastic bioclastic shoal (FA2), mixed sandy oolitic shoals (FA3), and mixed distal bioclastic sandy beaches (FA4). These facies associations are interpreted to be deposited in varying depositional environments ranging from foreshore to shoreface setting in a shallow lake setting. An interplay of the climate regime, nearshore carbonate productivity, and current activity was proved to control the lithofacies types, dispersion and depositional environment change of mixed sediments in different depositional phases. Meter‐scale mixed cycles were found in this shallow lake setting and their features seem to differ from the classical mixed sediment models. It is suggested that these particular cycles in the stratigraphic record might indicate a typical mark of mixed sediment system in shallow areas of the lacustrine basin.

Arc-like magmas generated by m\xe9lange-peridotite interaction in the mantle wedge

The mechanisms of transfer of crustal material from the subducting slab to the overlying mantle wedge are still debated. Mélange rocks, formed by mixing of sediments, oceanic crust, and ultramafics along the slab-mantle interface, are predicted to ascend as diapirs from the slab-top and transfer their compositional signatures to the source region of arc magmas. However, the compositions of melts that result from the interaction of mélanges with a peridotite wedge remain unknown. Here we present experimental evidence that melting of peridotite hybridized by mélanges produces melts that carry the major and trace element abundances observed in natural arc magmas. We propose that differences in nature and relative contributions of mélanges hybridizing the mantle produce a range of primary arc magmas, from tholeiitic to calc-alkaline. Thus, assimilation of mélanges into the wedge may play a key role in transferring subduction signatures from the slab to the source of arc magmas.

A multi‐scale approach interpreting sediment processes and distribution from desert sand colour in central Saudi Arabia

AbstractIn central Saudi Arabia the redness of sands observed on satellite imagery, often related to iron oxide amount, was used to better interpret geomorphic processes operating in the area. To compare variations between dune and interdune morphology, linear and dome dunes, and an ephemeral river partly buried under a sand sea, Nafud Al‐Thuwayrat, a multi‐scale approach was used to identify the spatial variation in causes of iron oxide amounts and colour. Macro‐scale mapping of Image Spectral Redness identified that the extent and intensity of colour grading across the orientation of well‐defined linear and dome dune types, interdunes and the Wadi Al‐Rimah, indicated sediment mixing of different provenance. Meso‐scale chemical, physical and colour analysis of surface samples indicated that iron oxide coated grains were present within all the samples and was not the sole control on Image Spectral Redness. The reddest sediments were the best sorted medium‐to fine‐quartz sands with iron oxide bearing chemistry and the paler sediments contained coarser sands with additional feldspars, calcite and gypsum. Micro‐scale analysis of grain characteristics found dune–interdune contrasts and that the reddest sands with iron coatings were of aeolian origin and the paler sands contained larger fluvial material mixed with reworked aeolian deposits. Dust in the area consists of high amounts of iron oxide and appears to be a major contributor to redness in the sand dunes. These controls on colour show the sand seas are paler westwards because a major river and local drainage systems deliver fluvial sediments from the carbonate and sandstone bedrock into the quartz‐rich aeolian material from the linear dunes. Evaporite deposits dominate in the paler interdunes, and south of the Wadi the dome dunes are the reddest as they are not migrating but building up. This multi‐scale approach has provided a modern analogy of processes for palaeoenvironmental studies. © 2018 John Wiley &amp; Sons, Ltd.