Sediment Dispersal Research Articles

A Well‐Posed Alternative to the Hirano Active Layer Model for Rivers With Mixed‐Size Sediment

The active layer model (Hirano, 1971) is frequently used for modeling mixed‐size sediment river morphodynamic processes. It assumes that all the dynamics of the bed surface are captured by a homogeneous top layer that interacts with the flow. Although successful in reproducing a wide range of phenomena, it has two problems: (1) It may become mathematically ill‐posed, which causes the model to lose its predictive capabilities, and (2) it does not capture dispersion of tracer sediment. We extend the active layer model by accounting for conservation of the sediment in transport and obtain a new model that overcomes the two problems. We analytically assess the model properties and discover an instability mechanism associated with the formation of waves under conditions in which the active layer model is ill‐posed. Numerical simulations using the new model show that it is capable of reproducing two laboratory experiments conducted under conditions in which the active layer model is ill‐posed. The new model captures the formation of waves and mixing due to an increase in active layer thickness. Simulations of tracer dispersion show that the model reproduces reasonably well a laboratory experiment under conditions in which the effect of temporary burial of sediment due to bedforms is negligible. Simulations of a field experiment illustrate that the model does not capture the effect of temporary burial of sediment by bedforms.

Using provenance analysis in an Anthropocene natural laboratory

Globally, anthropogenic perturbations to sediment dispersal systems produce detrital signals that are evident in the recent sedimentary record. We review the study of anthropogenic perturbations to sediment dispersal systems from the perspective of detrital signals and discuss the use of provenance analysis in Anthropocene sedimentology. Anthropocene provenance analysis is illustrated by a case study from the Monterey Bay Sediment Dispersal System (MBDS) of coastal and offshore central California, U.S.A. The MBDS records two phases of alterations to sediment flux, an early increase in fine flux recognized in increased sedimentation rates and a later decrease in coarse flux recognized in detrital provenance signatures. Results from the MBDS suggest that a multi-methodological approaches employing provenance analysis, and detailed, short-timescale (102–104 yr) depositional chronology markers combined with the study of other Anthropocene indicators like the introduction of non-natural detritus are valuable tools for describing natural sedimentary processes in addition to human alterations to natural systems. The recognition and description of such perturbations to sediment supply is increasingly recognized as an important variable in understanding the effects of human-driven landscape alteration, particularly in the face of a changing climate. The broad concepts and approach outlined in this study provide tools that can extend environmental observations past the period of historical record and can be used to understand past, and predict future, impacts of altered sediment flux in response to drivers like climate change and sea level rise.

Sediment routing in the Zagros foreland basin: Drainage reorganization and a shift from axial to transverse sediment dispersal in the Kurdistan region of Iraq

AbstractIn the northwestern sector of the Zagros foreland basin, axial fluvial systems initially delivered fine‐grained sediments from northwestern source regions into a contiguous basin, and later transverse fluvial systems delivered coarse‐grained sediments from northeastern sources into a structurally partitioned basin by fold‐thrust deformation. Here we integrate sedimentologic, stratigraphic, palaeomagnetic and geochronologic data from the northwestern Zagros foreland basin to define the Neogene history of deposition and sediment routing in response to progressive advance of the Zagros fold‐thrust belt. This study constrains the depositional environments, timing of deposition and provenance of nonmarine clastic deposits of the Injana (Upper Fars), Mukdadiya (Lower Bakhtiari) and Bai‐Hasan (Upper Bakhtiari) Formations in the Kurdistan region of Iraq. Sediments of the Injana Formation (~12.4–7.75 Ma) were transported axially (orogen‐parallel) from northwest to southeast by meandering and low‐sinuosity channel belt system. In contrast, during deposition of the Mukdadiya Formation (~7.75–5 Ma), sediments were delivered transversely (orogen‐perpendicular) from northeast to southwest by braided and low‐sinuosity channel belt system in distributive fluvial megafans. By ~5 Ma, the northwestern Zagros foreland basin became partitioned by growth of the Mountain Front Flexure and considerable gravel was introduced in localized alluvial fans derived from growing topographic highs. Foredeep accumulation rates during deposition of the Injana, Mukdadiya and Bai‐Hasan Formations averaged 350, 400 and 600 m/Myr respectively, suggesting accelerated accommodation generation in a rapidly subsiding basin governed by flexural subsidence. Detrital zircon U‐Pb age spectra show that in addition to sources of Mesozoic‐Cenozoic cover strata, the Injana Formation was derived chiefly from Palaeozoic‐Precambrian (including Carboniferous and latest Neoproterozoic) strata in an axial position to the northwest, likely from the Bitlis‐Puturge Massif and broader Eastern Anatolia. In contrast, the Mukdadiya and Bai‐Hasan Formations yield distinctive Palaeogene U‐Pb age peaks, particularly in the southeastern sector of the study region, consistent with transverse delivery from the arc‐related terranes of the Walash and Naopurdan volcano‐sedimentary groups (Gaveh‐Rud domain?) and Urumieh‐Dokhtar magmatic arc to the northeast. These temporal and spatial variations in stratigraphic framework, depositional environments, sediment routing and compositional provenance reveal a major drainage reorganization during Neogene shortening in the Zagros fold‐thrust belt. Whereas axial fluvial systems initially dominated the foreland basin during early orogenesis in the Kurdistan region of Iraq, transverse fluvial systems were subsequently established and delivered major sediment volumes to the foreland as a consequence of the abrupt deformation advance and associated topographic growth in the Zagros.

Detrital Zircon U-Pb Geochronology and Provenance of the Sundance Formation, Western Powder River Basin, Wyoming

This study uses detrital zircon U-Pb geochronology to investigate the provenance of the Jurassic Sundance Formation in the western Powder River Basin, Wyoming. Understanding the provenance of the Sundance Formation is critical as it was deposited during the transition from cratonic to synorogenic sedimentation derived from the Sevier-Laramide foreland. The Sundance in the western Powder River Basin consists of an oolitic limestone and green glauconitic sandstone at the base, green shales in the middle, and a yellow quartz arenite with coquina “oyster” beds at the top. U-Pb analyses of detrital zircons using LA-ICP-MS were conducted on two samples collected in the Bud Love Wildlife Habitat Management Area, 20 km northwest of Buffalo, WY. The two samples were taken from the upper and lower sandstone members of the Sundance Formation (n=289 concordant U-Pb zircon ages). The samples show a distinct difference in detrital zircon age spectra. The lower sandstone age spectrum ranges from 260-3172 Ma with 23% of the ages being Paleozoic, 71% being Proterozoic, and 6% being Archean. This lower stratum has detrital zircon age peaks at 343, 432, 686, 1039, 1431, 1662, 1748, 1941, 2433, and 3179 Ma. The lower sandstone shows an easterly Appalachian-Ouachita provenance, which persisted in the region beginning in the Carboniferous. In comparison to the upper strata, ages range from 157-2949 Ma and age peaks at 170, 243, 440, 545, 1082, 1467, 1681, and 1985 Ma. The maximum deposition age for the upper member is 160 Ma. Mesozoic aged grains make up 15.6% of the zircons, 14.7% were Paleozoic, 65.7% were Proterozoic, and 4% were Archean in age. The appearance of Mesozoic zircons in the upper sandstone marks the first significant appearance of westerly sourced zircons, and perhaps reflects the earliest uplift of the Sevier fold and thrust belt. Previous research has found this same signature in the Sundance but not in the underlying Triassic Chugwater Formation, resulting in a broad boundary of the change in sediment dispersal and the onset of the Sevier Orogeny between the Triassic and Jurassic. This study was conducted for a higher resolution to the provenance of the Sundance Formation and to further narrow the boundary of differing sedimentation from an eastern recycled to western synorogenic source.

Sediment dispersal and accumulation off the Ayeyarwady delta – Tectonic and oceanographic controls

Recent sediment dispersal and accumulation on the Northern Andaman Sea continental shelf, off the Ayeyarwady (Irrawaddy) and Thanlwin (Salween) Rivers, are investigated using seabed, water column, and high-resolution seismic data collected in December 2017. 210Pb and 137Cs derived sediment accumulation rates are highest (up to 10 cm y−1) in the mid-shelf region of the Martaban Depression, a basin that has formed on the eastern side of the N-S trending Sagaing fault, where rapid progradation of a muddy subaqueous delta is occurring. Landward of the zone of highest accumulation, in the shallow Gulf of Martaban, is a highly turbid zone where the seabed is frequently mixed to depths of ~1 m below the sediment water interface. Frequent resuspension in this area may contribute to the formation of extensive fluid muds in the water column, and consequent re-oxidation of the shallow seabed likely reduces the carbon burial efficiency for an area where the rivers are supplying large amounts of terrestrial carbon to the ocean. Sediment cores from the Gulf of Martban have a distinctive reddish brown coloration, while x-radiographs show sedimentary structures of fine silt laminations in mud deposits, which indicates strong tidal influences. The seaward part of the Martaban Depression off the modern subaqueous delta is covered by relict sediment, with no apparent connection between the modern sediment deposit and the offshore Martaban canyon. On the western side of the Sagaing fault, the “Mouths of the Ayeyarwady” represent a large promontory where the subaerial delta has prograded seaward some ~200 km along the eastern flank of the Indo-Burman range since the Holocene maximum transgression. The shelf area off the “Mouths of the Ayeyarwady” presently exhibits low sediment accumulation rates (~1 cm y−1) and a relative coarse (sandy) texture. The reduced accumulation and coarse texture in the western shelf region at the present time is attributed to frequent wave resuspension, and subsequent transport of finer river-derived sediment eastward (into the Martaban Depression) during the SW Monsoon. A mud drape (accumulation rates <1 cm/yr) is present on the northwestern part of the delta, where some sediment likely escapes the shelf to the deeper Bay of Bengal. In contrast with the Gulf of Martaban, sediments in this mud drape show olive grey coloration, while sedimentary structures are dominated by mottled sandy mud with shells, and occasional sand layers. The mud drape is likely derived from a mixture of local rivers draining westward from the Indo-Burman range, and a contribution from the Ayeyarwady system delivered during the NE monsoon. Overall, the shelf offshore the Ayeyarwady and Thanlwin rivers represents a compound subaqueous delta with marked differences from east to west that are controlled by a combination of oceanographic and tectonic factors.

A model for oblique accretion on the South China Sea margin; Red River (Song Hong) sediment transport into Qiongdongnan Basin since Upper Miocene

Located on the northwestern margin of the South China Sea, the origin of asymmetrical shelf-slope clinoforms accumulated on the continental margin of the Qiongdongnan Basin since the late Miocene is ambiguous and it likely is the first case of oblique sediment transport and dispersal among the most studied mud-rich shelves of the world during Neogene to Recent sea-level changes. We calculate the paleo-sediment flux required to build the shelf-slope clinoforms based on 2-D seismic data, and the results are 3 to 17 time larger than the estimated paleo-sediment discharge from the proximal catchment area of Hainan Island. This large mismatch suggests that sediments on the shelf-edge of Qiongdongnan Basin were not only from Hainan Island but more likely from a larger drainage system. The strong (tens km) southward migration of the western portion of the Qiongdongnan shelf-edge break compared to the weak (1–2 km) shelf-edge progradation in the eastern portion, suggests that the Qiongdongnan shelf prism is highly asymmetric and is caused by a large sediment supply centered to the west, with most likely the Red River (Song Hong) as the sediment supply driver. The fine-grained lithology of the studied shelf margin sediments off Hainan Island, especially since the end Miocene, suggests that they were derived mainly from the Red River and were transported southeastward from the Gulf of Tonkin by shelf currents. We propose a model for asymmetric shelf-slope accretion of mud-rich shelves in which a significant part of the sediment-prism volume was obliquely dispersed across the subsiding shelf as fluid mud during highstand sea-levels. The model presented here describes oblique construction of shelf-slope clinoforms in a mud-rich system in response to variations in sediment dispersal and depocenter during multiple sea-level cycles. This model of long-term (~107 years), lateral asymmetric accretion contrasts with oblique sediment transport in other source-to-sink sedimentary systems around the world.

Distribution and dispersal of surface sediments on the continental margins of India

Abstract The vast area, varying climate regimes, diverse source terrain lithology of the mainland India generate complex weathering and erosional patterns and leads to diverse sediment distribution and dispersal on the surrounding continental margins of India. Thus, to delineate the sources, distribution and sediment dispersal pathways around India, 254 sediment cores from the eastern and western continental margins of India were investigated for physical properties using non-destructive, whole core logging technique combined with grain-size analyses. The distribution of magnetic susceptibility, gamma ray density and grain-size traces the sources in the Indian landmass which contribute sediments to the margins and demarcates their extent of influence. The results from the magnetic susceptibility distribution indicate that the dominant influx of modern high susceptibility sediment into the margins of India originates from the weathering of Deccan Basalts and its subsequent transportation by Narmada and Tapti Rivers in the west coast and Krishna and Godavari Rivers in the east coast. Though the Himalayan sources are the second largest supplier of magnetic minerals to the shelf, their contribution, when compared to the Deccan sediments is not significant. The lack of present-day sedimentation in the outer shelf regions of margins of India is evident from the gamma ray density distribution and is confirmed by the discrete sample grain-size analysis. Gamma ray density variations in the margins follow the same pattern as the grain size variations and demarcate the boundary between inner shelf modern clayey sediments and the outer shelf relict carbonate sands. Regional distribution maps of physical properties and grain-size for both the margins of India are presented and geographical limits of each provenance are defined, thus providing a comprehensive picture of sediment distribution and dispersal patterns in the area and highlights the use of magnetic susceptibility as a powerful tool in deciphering the source to sink pathways of sediments.

Sedimentological and Geochemical Characterization of Surficial Sediment of a Meander Section of Mbaa River at Nneise–Ugiri Community in Imo State of Nigeria

Sediment deposition has increased at a meander section of Mbaa river resulting in a drastic reduction of water storage. It has necessitated calls for sand-mining or periodic dredging which could have far-reaching impacts on the aquatic ecosystem, depending on the texture and chemical compositions of the sediment. Therefore, surficial sediments samples were analyzed for textural characteristics, mineralogy and chemical compositions. Grain sizes and mineralogical analysis showed that the sediments were moderately sorted, mesokurtic, near symmetrical - slightly positive skewed, subangular – subrounded medium grained-sands, and consist of about 2.5% feldspar, 2.7% rock fragments, 5.4% hematite and 89% quartz. Mean TOC and pH were 0.39 wt% and 6.48 respectively. Atomic Absorption Spectrophotometer (AAS) analysis results showed general low concentrations of metal elements: mean values of alkali/alkali earth metals ranged from 1.33 - 3.72ppm, transition metals ranged from 0.12 - 23.07ppm; while Pb (a poor metal) was not detected. General low concentrations of metals and TOC; and non-detection of Pb suggest lack of mineralization zones and minimal anthropogenic impacts in the upstream areas. Textural and chemical characteristics and moderate energy of river water flow suggest that human resuspension of the sediment deposit will result in minimal lateral dispersion of sediment in the water column, except during heavy rainfall. Therefore, periodic dredging or sand mining will cause minimal impact on the aquatic ecosystem, especially in the distant downstream areas, whereas within the meander section and nearby areas of the river, it is expected that there will be a significant change in water quality parameters due to the increase in the concentrations of suspended and dissolved compounds.

Detrital zircons and sediment dispersal from the Coahuila terrane of northern Mexico into the Marathon foreland of the southern Midcontinent

AbstractNew analyses of U-Pb ages along with previously published analyses of detrital zircons from sandstones in the foreland of the Marathon orogen in west Texas have significant implications regarding provenance. The most prominent concentrations of U-Pb ages are at 1200–1000, 700–500, and 500–290 Ma. The accreted Coahuila terrane in the Marathon hinterland and nearby terranes with Gondwanan (Amazonia) affinity include Paleozoic volcanic and plutonic rocks, as well as Precambrian basement rocks. Late Paleozoic Las Delicias arc rocks have ages of 331–270 Ma. Detrital zircons from Upper Jurassic and Lower Cretaceous sandstones, which were deposited in local basins around the Coahuila terrane, provide a record of detritus available from proximal sources within Coahuila, including important peaks at 1040, 562, 422, 414, 373, and 282 Ma. Components of the detrital-zircon populations in the Marathon foreland have unique matches with primary and/or detrital sources in the Coahuila terrane. Although some components of the Marathon populations also have age matches in Laurentia (Appalachians), others do not; however, all components of the Marathon populations have potential sources in Coahuila. Analyses of εHft show generally more negative values in Amazonia than in Laurentia, and εHft values for Marathon sandstones have distributions similar to those in Amazonia. Therefore, the Coahuila terrane provides a provenance for all of the detrital-zircon ages in the Marathon foreland, requiring no mixing from other sources.

Chronology of deposition and unconformity development across the Cretaceous–Paleogene boundary, Magallanes-Austral Basin, Patagonian Andes

The Magallanes-Austral foreland basin preserves an important record of orogenesis and landscape evolution in the Patagonian Andes of Chile and Argentina. Throughout the retroarc foreland basin, a regional disconformity with little to no angular discordance separates Upper Cretaceous–lower Paleocene strata from overlying deposits of diachronous Eocene to Miocene age. Here we report detrital zircon U-Pb geochronological results for 11 sandstone samples, and vitrinite reflectance data for 6 samples of organic matter from a fossiliferous dinosaur-bearing mixed nonmarine and marine clastic succession in the Río de las Chinas valley (50–51°S) of central-southern Patagonia to: (1) determine the timing and duration of the unconformity using U-Pb maximum depositional age constraints, (2) reconstruct sediment provenance and dispersal patterns, (3) assess possible temporal variations in arc magmatism, (4) evaluate the amount of sedimentary overburden removed during unconformity development, and (5) confirm the presence of a fossiliferous southern hemisphere Cretaceous–Paleogene (K/Pg) boundary site. Samples from the Dorotea Formation yield maximum depositional ages spanning Maastrichtian to Danian time (with ages as young as ∼65–63 Ma), confirming preservation of the K/Pg boundary in a section with recently discovered fossils of dinosaurs, other terrestrial vertebrates, and plants. Samples from directly above the unconformity in the Man Aike Formation, yield middle Eocene maximum depositional ages (with a prominent 45–40 Ma age cluster), indicating a long-lived ∼20 Myr hiatus representative of nondeposition or erosion. Analyses of organic matter preserved in multiple coal horizons of the uppermost Dorotea Formation show consistently low vitrinite reflectance values, requiring limited sedimentary burial, consistent with nondeposition or sediment bypass rather than deposition and later erosional removal of a previously proposed thick package of Paleocene to middle Eocene clastic material. On the basis of regional trends in the age and geometry of the unconformity, timing of arc magmatism, and temporal variations in sediment provenance, we consider a range of potential mechanisms for unconformity genesis, including (1) shortening-related uplift of the frontal fold-thrust belt, (2) cratonward advance of a flexural forebulge, (3) accommodation changes driven by regional or eustatic variations in sea level, (4) ridge collision and slab-window genesis, (5) isostatic rebound during tectonic quiescence (or minor extension), or (6) regional foreland uplift during flat-slab subduction.

Late Cenozoic structure and tectonics of the southern Sierra Nevada–San Joaquin Basin transition, California

AbstractThis paper presents a new synthesis for the late Cenozoic tectonic, paleogeographic, and geomorphologic evolution of the southern Sierra Nevada and adjacent eastern San Joaquin Basin. The southern Sierra Nevada and San Joaquin Basin contrast sharply, with the former constituting high-relief basement exposures and the latter constituting a Neogene marine basin with superposed low-relief uplifts actively forming along its margins. Nevertheless, we show that Neogene basinal conditions extended continuously eastward across much of the southern Sierra Nevada, and that during late Neogene–Quaternary time, the intra-Sierran basinal deposits were uplifted and fluvially reworked into the San Joaquin Basin. Early Neogene normal-sense growth faulting was widespread and instrumental in forming sediment accommodation spaces across the entire basinal system. Upon erosion of the intra-Sierran basinal deposits, structural relief that formed on the basement surface by the growth faults emerged as topographic relief. Such “weathered out” fossil fault scarps control much of the modern southern Sierra landscape. This Neogene high-angle fault system followed major Late Cretaceous basement structures that penetrated the crust and that formed in conjunction with partial loss of the region’s underlying mantle lithosphere. This left the region highly prone to surface faulting, volcanism, and surface uplift and/or subsidence transients during subsequent tectonic regimes. The effects of the early Neogene passage of the Mendocino Triple Junction were amplified as a result of the disrupted state of the region’s basement. This entailed widespread high-angle normal faulting, convecting mantle-sourced volcanism, and epeirogenic transients that were instrumental in sediment dispersal, deposition, and reworking patterns. Subsequent phases of epeirogenic deformation forced additional sediment reworking episodes across the southern Sierra Nevada–eastern San Joaquin Basin region during the late Miocene break-off and west tilt of the Sierra Nevada microplate and the Pliocene–Quaternary loss of the region’s residual mantle lithosphere that was left intact from the Late Cretaceous tectonic regime. These late Cenozoic events have left the high local-relief southern Sierra basement denuded of its Neogene basinal cover and emergent immediately adjacent to the eastern San Joaquin Basin and its eastern marginal uplift zone.

Trace Elements and Sr, Nd Isotope Compositions of Surface Sediments in the Indian Ocean: An Evaluation of Sources and Processes for Sediment Transport and Dispersal

AbstractTo decipher sediment provenance, understand dispersal pattern and its controlling factors in the Indian Ocean, we have studied major and trace element abundances and isotope compositions of Sr (87Sr/86Sr) and Nd (εNd) in silicate fractions of 38 surface sediment samples collected at ~1.5° interval from India (~10°N) to Antarctica (~70°S). The 87Sr/86Sr ratio and εNd vary from 0.70527 and 0.1 near Crozet Island to 0.77854 and −34.8 near Antarctica, respectively. Higher 87Sr/86Sr ratio and lower εNd near Antarctica indicate source of old granitic rocks, and the opposite is observed in sediments from the Central and the Southwest Indian Ridges indicating source of seafloor spreading and mid‐ocean ridge hydrothermal activity. Chondrite normalized Rare Earth Elements (REEs) pattern reveals positive Europium anomaly for Central and Southwest Indian Ridge sediments, while positive Gadolinium anomaly is observed in Indian and Antarctic coastal sediments. Sediments in the Indian sector of Southern Ocean and coastal Antarctica are highly dispersed through deep, bottom, and Antarctic circumpolar currents. The εNd spatial map generated for the entire Indian Ocean based on compilation of present study and results from literature shows dominance of terrigenous inputs from continental erosion with minor contribution from the ridges in the Indian Ocean. The εNd map together with trace elements can be employed for reconnaissance for mineral exploration associated with hydrothermal deposits. Further, comparison of detrital εNd with its counter phases, that is, authigenic fractions and modern seawater at the sampling sites, would enhance our knowledge of benthic exchange processes, with an implication in using Nd isotopes as a water mass circulation proxy.

General aspects of continental margin sediments of the Ceará State, northeast Brazil, from mineralogy and principal component analysis

Granulometry, mineralogy, portable X-ray fluorescence (XRFp), portable X-ray diffractometry (XRDp), and principal component analysis (PCA) have been made in samples of two deep cores of the continental margin of the Ceara State, northeast Brazil, aiming to detail the general aspects of deep sedimentation, including mechanical dispersion of continental minerals, environmental chemistry, and clay identification. The samples comprised biogenic oozes, clays, coarse silt, and fine sand to a lesser extent. The granulometric composition suggests slow and calm sediment accumulation over time. XRDp analysis pointed out that pelagic clays consist of chlorite, kaolinite, nontronite, and vermiculite. High oxidation levels are suggested for the two core samples, represented by the light brown color 5YR 6/4 of the sediments. Traces of minerals existing at the continental shelf were found, although in the core SIS-454 at 160 to 164 cm depth, there is a total absence of both heavy and light continental minerals. In core SIS-515, the total absence of heavy and light minerals was found at the depth of 87 to 92 cm. The levels with absence of continental minerals are probably associated with the absence of mechanical dispersion due to transgression and regression events in the Ceara continental shelf. The high oxidation levels can probably be linked to shallow waters caused by sea level changes, or to large period of sedimentation in the slope. From the statistical analysis, it is suggested that element contents are related to each other according to the provenance setting, whereas the pelagic sediment has provenance from marine water, resurgence currents, wind transport, cosmic dust, and from slow transportation, originated from the continent. It was deduced that sedimentation in the area was affected by at least two events with absence of mechanical dispersion of continental sediments, associated with geochemical characteristics represented by antagonism between elements of terrigenous and biogenic origin. These events are possibly associated with small-scale regressions occurred during the Flandrian Transgression in the Ceara Basin.

Mathematical Modeling Framework of Physical Effects Induced by Sediments Handling Operations in Marine and Coastal Areas

In recent years increasing attention has been paid to environmental effects that may result from marine dredging and disposal operations. In general, the fine-grained fraction of handled sediments can be dispersed far from the intervention site as a turbidity plume, depending on the specific site and operational parameters. Starting from a literature review, this paper suggests standards for estimating and characterizing the sediment source term, for setting up far-field modeling studies and analyzing numerical results, with the aim of optimizing, also from an economic point of view, the different project, execution and monitoring phases. The paper proposes an integrated modeling approach for simulating sediment dispersion due to sediment handling operations in different marine-coastal areas (off-shore, near-shore and semi-enclosed basins). Attention is paid to the characterization of sediment source terms due to different operational phases (removal, transport and disposal). The paper also deals with the definition of accuracy level of modeling activities, with regard to the main physical processes characterizing the different marine–coastal areas and to the type of environmental critical issues near the intervention site (if any). The main relationships between modeling and monitoring are given for the different design and management phases to support the selection of appropriate technical alternatives and monitoring actions and to ensure the environmental compliance of the proposed interventions.

Sm–Nd and Sr isotope fingerprinting of iron mining tailing deposits spilled from the failed SAMARCO Fundão dam 2015 accident at Mariana, SE-Brazil

This work presents the first Sm–Nd and Sr isotope TIMS data on the fine-grained fraction (<74 μm) of iron-rich deposits related to the November 5th, 2015 Mariana accident, caused by the rupture of the Fundão dam, an iron tailings pond operated by SAMARCO Mining. The failure of the Fundão dam provoked the gravitational flow of approximately 62 Mi m3 of a quartz and iron oxide-rich slurry composed of water, fine sand and silt, that flowed into the Gualaxo do Norte and Carmo rivers, and eventually along the whole Doce River. Samples were collected between 5 and 80 km downstream from the Fundão Dam, along the Santarém creek and the Gualaxo do Norte and Carmo rivers. XRD analyses show that samples are >90% composed of quartz and iron oxides (hematite, goethite and magnetite), with minor phyllosilicates (kaolinite and mica). Owing to sediment transport processes, heavy (hematite, goethite, magnetite) to light (quartz, phyllosilicates) mineral fractionation is observed. As with XRD data, major and trace element compositions also closely match those of the original Paleoproterozoic Cauê Formation BIF iron ore. The studied samples yielded δNd between −17.0 and −19.7 pptt (part per ten thousand), with the exception of one sample, with δNd of −23.2 pptt. Strontium 87Sr/86Sr ratios show variability between 0.7351 and 0.7729. The TDM ages scatter between 1.94 Ga and 2.75 Ga, with a negative correlation with phyllosilicate contents, indicating that the latter has preferential provenance from younger, more juvenile sources than the Cauê Fm itabirites. This interpretation is corroborated by two component mixing models of Nd and Sr isotope ratios, where the Nd–Sr isotopic signatures of the studied samples are compatible with >98% of the Cauê Fm itabirite component, mixed with a Neoproterozoic juvenile mafic rocks component, such as those from the ophiolitic assemblages of the distal Macaúbas Group, or tholeiitic mafic rocks of the Pedro Lessa suite. The reported Sm–Nd and Sr isotope compositions closely match those of the original iron ore and contrast with either those of the upriver or downriver Precambrian to Ordovician bedrock units. The firstly defined isotope signature can thus be potentially used as a proxy for ongoing suspended sediment dispersion studies farther downstream along the Doce River and in adjacent marine environment.

Tectonics of the Eastern Kunlun Range: Cenozoic Reactivation of a Paleozoic‐Early Mesozoic Orogen

AbstractThe Eastern Kunlun Range in north Tibet, located along the northern margin of the eastern Tethyan orogenic system, records evidence for continental break‐up and ocean development in the Neoproterozoic, Paleozoic‐early Mesozoic subduction and continental collision, Mesozoic intracontinental extension, and Cenozoic contractional deformation. The Kunlun region is marked by active left‐lateral strike‐slip deformation of Kunlun fault system, one of the major intracontinental strike‐slip faults in Tibet that developed in response India‐Asia. To better constrain the tectonic evolution of the Eastern Kunlun Range and the closure of the various Kunlun oceans, we conducted detailed investigation integrating new geologic mapping, geochronology, and whole‐rock geochemistry with a synthesis of existing datasets across north Tibet. The Eastern Kunlun Range experienced three major deformation events in the Neoproterozoic, early Paleozoic, and Late Paleozoic‐early Mesozoic, which were associated with collision of the Proto‐, Paleo‐, and Neo‐Kunlun arcs, respectively. Our new detrital zircon analyses from Mesoproterozoic‐Cenozoic strata constrain stratigraphic age and sediment provenance and highlight the importance of three periods of arc activity. Our stratigraphic synthesis, including new field observations, provides new insights into connections between sediment dispersal and changes in tectonism and paleogeography. Miocene‐to‐present strike‐slip activity on the Kunlun fault and the associated strain pattern can be explained by clockwise rotation of the Kunlun fault and its wall rock as a bookshelf‐fault system, which has been proposed for northern Tibet as a result of distributed north‐south right‐lateral shear. The development of this fault system was facilitated by the presence of a Triassic suture that provided a preexisting weakness.

Tectonic control on the evolution of depositional systems in a fossil, marine foreland basin: Example from the SE Austral Basin, Tierra del Fuego, Argentina

Abstract Combined research on the structural and stratigraphic evolution of the southeastern Austral Basin identifies three major depositional systems strongly influenced by the tectonic stages of the Fuegian Andes between the Late Cretaceous and the Miocene. During orogenic growth, a submarine ramp system characterized by oblique progradational clinoforms with transverse sediment dispersal, formed adjacent to the deformation front in the wedge-top or proximal foredeep. In moments when the tectonic load and flexural subsidence were reduced, this system was replaced by a progradational-aggradational system with oblique to sigmoidal clinoforms. This occurred during a short span in the middle Eocene, but especially and definitively after contractional deformation ceased in the early Miocene. The third depositional system was long lived, and comprised axial turbidite channel systems located at the clinoform bases, which re-routed sediment toward the deeper foredeep of the western Malvinas Basin. Distinct facies types develop in each depositional system, and their recognition allows evaluating sediment fairways in the foreland basin system.

Statistical study of eolian sediment distribution risk in human ecosystems on the health of respiratory system and the eyes of inhabitants of Sistan, East Iran

Sistan in east Iran is vast, low slope tectonic lowland of which a great portion is consisted of alluvial-saline lands of dried out Hamoon lakes. Sistan district with a population density of 43 people per square kilometer is the most densely populated human ecosystem in east Iran. This population is distributed in more than 1000 cities, villages, and nomadic settlements. Sistan plain is extensively exposed to vigorous winds. In the last 5 years, with the spread of drought and drastic reduction of Hirmand River’s water flow, dust storms have become more severe and long lasting. Winds of 120 days are the most significant wind in the region which starts every year at the end of the spring and lasts all through the beginning of autumn, with a mean velocity of 100 km/h. This research utilizes a survey/descriptive method coupled with medical documents to rank the risk of destructive eolian sediment dispersion in different regions of Sistan alongside the frequency of citizen’s reference to medical centers due to respiratory problems or eye damages caused by these sediments during the summer of 2017. The research findings show more risk of dispersion of eolian sediments in human environment in near the Iranian-Afghan border. The Level of the risk of respiratory and eye damages for citizens exposed to dust distribution with the rate of distribution of eolian sediments in the environment is statistically significant. Human ecosystems (1) Dehno-Piran, (2) Bazzi-Allari, (3) Muhammad-Shah-Karam, and (4) Abbas-Rostam regions in Sistan area have the highest risk for citizens due to respiratory problems and eye damages caused by eolian sediment dispersion.

Storm-driven dispersal of fluvial fine sediment on a low-energy inner shelf

Prolonged in-situ measurements and satellite images were analyzed to investigate storm-driven dispersal patterns of fluvially derived fine sediment in the Atchafalaya Bay/Shelf during winter storms and tropical cyclones and how they remotely influence fine-sediment distribution of an offshore sand shoal. It was revealed that storm-driven offshore advection coinciding with sediment re-suspension transports re-suspended sediment and fine sediment from the river and from the bay to the inner shelf regardless of the storm types. However, we found that the process leading to the dispersal varies with the types of storms, their intensity and tracks. On the shelf, while tropical cyclones were capable of bringing re-suspended sediment to the surface, winter storms limited the extent of sediment suspension up to approximately 10 m above the bottom. Thus, only the sediment suspension on the shallower part of the shelf (< 10 m in depth) was expected to contribute significantly to sediment dispersal during winter storms. The estimated mass of re-suspended sediment in the bay during a single storm event accounted for more than a quarter of the total sediment mass from the river in the entire summer; more than half of the re-suspended sediment was expected to be transported to the shelf. It was also found that the storm-driven advection plays an important role in the migration of the fine sediment plumes to the offshore shoal. Despite the patchy and ephemeral nature of fine sediment on the shoal, the findings have established an important link between storm-driven sediment dispersal and sediment dynamics of ecologically sensitive shoals along the Louisiana coast.

The development and application of an autonomous working turbidity measurement network: Assessing the spatial and temporal distribution of suspended particulate matter on tidal flats in the North Frisian Wadden Sea

Measuring suspension load (i.e. turbidity) in tide-dominated shallow marine systems like the North-Frisian Wadden Sea forms a major challenge with respect to understanding and modelling sediment origin, transport and dispersal. Sediment transport and deposition in highly dynamic and vulnerable coastal regions becomes especially relevant in terms of the natural adaption capacity of intertidal and supratidal areas to global sea-level rise.We have developed a network of eight autonomously operating turbidity measuring stations in an island-like salt marsh area (Hallig Langeness) in the tidal flats of the North-Frisian Wadden Sea. Using this system we got first insights about the availability of suspended particulate matter (SPM). In order to obtain the best possible estimation of the SPM concentrations in our study area, each measuring station has been individually calibrated considering the local conditions by using sediment collected by self-built sediment accumulators which are installed next to the respective measuring station. With this method we have investigated the availability of SPM and its spatial and temporal distribution during several spring and winter months.The results indicate strong and systematic SPM variability between individual stations ranging on average from 0.04 to 0.56 g/l. Control factors include installation altitude, the proximity to tidal channels, the positive influence on SPM availability by adjacent land reclamation areas or the negative influence on SPM availability due to a shielded position between two spur dykes. Further results show a strong increase of the SPM concentration under harsh weather conditions and inundation events whereby strong winds alone are not sufficient for a significant SPM increase. Instead, the combination of suitable wind direction, its strength and duration play a major role. The increase in SPM concentrations under harsh weather conditions tends to be highest at stations with less protection against the open water. Our new extensive network of turbidity measurements also allows for detecting areas with predominantly low SPM availabilities, the so-called low spots.