Sediment Dispersal Research Articles

Sediment budget and morphological change in the Red River Delta under increasing human interferences

The Red River sediment dispersal system has been increasingly altered by human activities, but the resultant morphodynamic change and sediment budget in the Red River Delta (RRD) has been little studied in a holistic perspective. In this study, time-series analysis of river water and sediment discharges from 1960 to 2010 was carried out to trace human interferences on sediment routing processes, and historical charts from 1930 to 2008 were digitized to reconstruct the Digital Elevation Models for investigating spatiotemporal variations in the RRD morphology and calculating their depositional and erosional fluxes. The results show that sediment reduction by 61.3% in the Red River is mainly induced by constructing the Hoa Binh Dam at the lower reach of the Da river, and deforestation and other land-use change have recently increased significantly the sediment loads in the Thao and Lo rivers. Intertidal and subtidal morphological changes in the RRD are highly site-specific in response to natural and anthropogenic drivers. Rapid intertidal accretion majorly occurs near the distributary mouths because of abundant sediment supply and artificially promoted siltation by land reclamation projects, but severe coastal erosion may occur secularly after the distributary outlet shifting or temporarily by storm events. The subaqueous RRD is generally featured by the contour-parallel zonation of erosion and accretion determined by strong longshore currents associated with monsoon winds. Net accretion was observed in the tide-dominated northern subaqueous RRD and has recently changed into a slight erosion due to reduced sediment input in the last two decades, while net erosion was monitored in the southern subaqueous RRD predominated by wave and longshore currents and has recently entered into a slight accretion phase in response to the distributary outlet shifting and secular morphodynamic adjustment. The study RRD region received on average 41.1 Mt./yr (Mt = 106 t) of suspended sediments, and 14.2 Mt./yr and 28.6 Mt./yr were estimated to accumulate on the intertidal flats and in the northern subaqueous RRD, respectively. However, erosion in the southern subaqueous RRD could contribute 42.9 Mt./yr of sediment to the system. Therefore, 41.2 Mt./yr of suspended sediment was indicated to escape from the study RRD region and transport further southward by longshore current to form the distal muddy clinoform along the inner Vietnam shelf. This sediment budget estimation should bear a significant uncertainty, but provides important information for multi-decadal sediment dispersal in a mega-delta system and coastal management.

Inferring sandstone grain size using spectral datasets: An example from the Bresnahan Group, Western Australia

Remotely sensed hyperspectral datasets were integrated with petrographic data to map the distribution of sedimentary rocks in order to infer grain size variations within the siliciclastic, Paleoproterozoic Bresnahan Group in Western Australia. Finer sandstones have greater compositional variation compared to coarser sandstones, with higher modal proportions of mudstone intraclasts, K-feldspar, and muscovite laths, and lower modal quartz. Partial Least Squares modelling indicates a link between visible to shortwave infrared spectral data collected on samples and their average grain size. Specific electronic absorptions are important for defining this relationship, particularly in the blue-green visible spectra, wavelengths related to water or hydroxyl bonds, along with certain wavelengths in the shortwave infrared (SWIR) spectra. The results from field samples were compared to airborne hyperspectral datasets which showed broad scale regional variations in composition could be discerned from processed white mica abundance maps and images that use spectral bands 2350 nm and 2200 nm. The remotely sensed compositional variations are relatable to changes in sandstone grain size. Diagenetic alteration and surface weathering may influence the absorption spectra, although the effect of the latter can be reduced by using processed white mica abundance maps. Overall, the results show that airborne hyperspectral datasets, particularly the SWIR part of the spectra, can be useful to remotely map spatial compositional variations associated with sandstone grain size. This shows the method can be used to remotely map siliciclastic successions in other sedimentary basins by aiding recognition of grain size trends and significant stratal surfaces associated with changes in composition. However, the important wavelengths may differ due to other controls on sandstone composition such as uplift history of the source region, changes in sediment dispersal, and transport mechanisms.

Permian to early Triassic tectono-sedimentary evolution of the Mahu sag, Junggar Basin, western China: sedimentological implications of the transition from rifting to tectonic inversion

The Permian to early Triassic terrestrial successions in the Mahu sag constrain the tectonic evolution of northwestern edge of the Junggar basin. This study analyzes the sequence stratigraphy of the Mahu sag in order to understand the interplay between tectonic process and the sedimentary fill of the basin. It uses detailed analysis of drill cores, geophysical well logs, 2D seismic reflection profiles and isopach maps. Sixteen lithofacies are grouped into three facies associations: fan delta, fluvial delta and lacustrine. The Permian to Triassic strata are organized into two second-order transgressive-regressive (T-R) sequences, further separated into transgressive systems tracts (TST) and regressive system tracts (RST). Based on seismic profiles, paleogeographic facies distribution and isopach maps, two stages of tectonic evolution are recognized: 1) early Permian syn-rift to middle Permian post-rift; 2) late Permian to early Triassic tectonic inversion. During the early Permian, sediments of TST1 record two cycles of depositional system transition from fan delta to deep lacustrine setting within the half-graben structure shown by 2D seismic profiles. At this time, tectonic mechanical subsidence exceeded sediment supply. The middle Permian post-rift stage (RST2) is characterized by gradual and slow peneplanation, which is documented by sediment supply exceeding thermal subsidence, so that the location of depocenter shifted and the depositional system transitioned from lacustrine to fan delta setting. Late Permian-early Triassic tectonic inversion is demonstrated by a striking change of the sediment dispersal patterns along the Hong-Che, Ke-Bai and Wu-Xia fault zones and alluvial fan deposition at the base of TST2. Tectonism is the main factor controlling sediment dispersal, paleogeographic evolution and hence hydrocarbon accumulation, providing a new perspective to oil and gas exploration and development in the Mahu sag.

Neogene shallow-marine and fluvial sediment dispersal, burial, and exhumation in the ancestral Brahmaputra delta: Indo-Burman Ranges, India

ABSTRACTThe stratigraphic record of Cenozoic uplift and denudation of the Himalayas is distributed across its peripheral foreland basins, as well as in the sediments of the Ganges–Brahmaputra Delta (GBD) and the Bengal–Nicobar Fan (BNF). Recent interrogation of Miocene–Quaternary sediments of the GBD and BNF advance our knowledge of Himalayan sediment dispersal and its relationship to regional tectonics and climate, but these studies are limited to IODP boreholes from the BNF (IODP 354 and 362, 2015-16) and Quaternary sediment cores from the GBD (NSF-PIRE: Life on a tectonically active delta, 2010-18). We examine a complementary yet understudied stratigraphic record of the Miocene–Pliocene ancestral Brahmaputra Delta in outcrops of the Indo-Burman Ranges fold–thrust belt (IBR) of eastern India. We present detailed lithofacies assemblages of Neogene delta plain (Tipam Group) and intertidal to upper-shelf (Surma Group) deposits of the IBR based on two ∼ 500 m stratigraphic sections. New detrital-apatite fission-track (dAFT) and (U-Th)/He (dAHe) dates from the Surma Group in the IBR help to constrain maximum depositional ages (MDA), thermal histories, and sediment accumulation rates. Three fluvial facies (F1–F3) and four shallow marine to intertidal facies (M1–M4) are delineated based on analog depositional environments of the Holocene–modern GBD. Unreset dAFT and dAHe ages constrain MDA to ∼ 9–11 Ma for the Surma Group, which is bracketed by intensification of turbidite deposition on the eastern BNF (∼ 13.5–6.8 Ma). Two dAHe samples yielded younger (∼ 3 Ma) reset ages that we interpret to record cooling from denudation following burial resetting due to a thicker (∼ 2.2–3.2 km) accumulation of sediments near the depocenter. Thermal modeling of the dAFT and dAHe results using QTQt and HeFTy suggest that late Miocene marginal marine sediment accumulation rates may have ranged from ∼ 0.9 to 1.1 mm/yr near the center of the paleodelta. Thermal modeling results imply postdepositional cooling beginning at ∼ 8–6.5 Ma, interpreted to record onset of exhumation associated with the advancing IBR fold belt. The timing of post-burial exhumation of the IBR strata is consistent with previously published constraints for the avulsion of the paleo-Brahmaputra to the west and a westward shift of turbidite deposition on the BNF that started at ∼ 6.8 Ma. Our results contextualize tectonic controls on basin history, creating a pathway for future investigations into autogenic and climatic drivers of behavior of fluvial systems that can be extracted from the stratigraphic record.

The arrival of the paleo–Orinoco Delta at Trinidad: The Cruse Formation delta lobes and delivery to deepwater Atlantic

ABSTRACT Icehouse continental-shelf-margin accretion is typically driven by high-sediment-supply deltas and repeated glacio-eustatic, climate-driven sea-level changes on a ca. 100 ky time scale. The paleo–Orinoco margin is no exception to this, as the paleo–Orinoco River Delta with its high sediment load prograded across Venezuela, then into the Southern and Columbus basins of Trinidad since the late Miocene, depositing a continental-margin sedimentary prism that is > 12 km thick, 200 km wide, and 500 km along dip. The Cruse Formation (> 800 m thick; 3 My duration) records the first arrival of the paleo–Orinoco Delta into the Trinidad area. It then accreted eastwards, outwards onto the Atlantic margin, by shallow to deepwater clinoform increments since the late Miocene and is capped by a major, thick flooding interval (the Lower Forest Clay). Previous research has provided an understanding of the paleo–Orinoco Delta depositional system at seismic and outcrop scales, but a clinoform framework detailing proximal to distal reaches through the main fairway of the Southern Basin has never been built. We integrate data from 58 wells and outcrop observations to present a 3-D illustration of 15 mapped Cruse clinoforms, in order to understand the changing character of the first Orinoco clastic wedge on Trinidad. The clinoforms have an undecompacted average height of 550 m, estimated continental slope of 2.5° tapering to 1°, and a distance from shelf edge to near-base of slope of > 10 km. The clinoform framework shows trajectory changes from strong shelf-margin progradation (C10–C13) to aggradation (C14–C20) and to renewed progradation (C21–24). Cruse margin progradational phases illustrate oblique clinothem geometries that lack well-developed topsets but contain up to 70 m (200 ft) thick, deepwater slope channels. This suggests a high supply of sediment during periods of repeated icehouse rise and fall of eustatic sea level, with fall outpacing subsidence rates at times, and delivery of sand to the deepwater region of the embryonic Columbus channel region. Also, evidence of wholesale shelf-edge collapse and canyon features seen in outcrop strongly suggest that deepwater conduits for sediment dispersal and bypass surfaces for Cruse basin-floor fans do exist. The change to a topset aggradational pattern with a rising shelf trajectory may be linked to increased subsidence associated with eastward migration of the Caribbean plate. The Cruse-margin topsets were dominated by mixed fluvial–wave delta lobes that were effective in delivery of sands to the basin floor. The preservation of a fluvial regime of the delta may have been impacted by basin geometry which partly sheltered the area from the open Atlantic wave energy at the shelf edge. Ultimately, understanding shelf-edge migration style as well as process-regime changes during cross-shelf transits of the delta will help to predict the location of bypassed sands and their delivery to deepwater areas.

How tropical cyclone flooding caused erosion and dispersal of mercury-contaminated sediment in an urban estuary: The impact of Hurricane Harvey on Buffalo Bayou and the San Jacinto Estuary, Galveston Bay, USA

Hurricane Harvey (Harvey), a slow-moving storm, struck the Texas coast as a category 4 hurricane. Over the course of 53 days, the floodwaters of Harvey delivered 14 × 109 m3 of freshwater to Galveston Bay. This resulted in record flooding of Houston bayous and waterways, all of which drained into the San Jacinto Estuary (SJE,) with its main tributaries being Buffalo Bayou and the San Jacinto River. The lower SJE and lower Buffalo Bayou has experienced up to 3 m of land subsidence in the past 100 years and, as a result, prior to Hurricane Harvey, up to 2 m of sediment within the upper seabed contained an archive of high concentrations of Total Hg (HgT) and other particle-bound and porewater contaminants. Within the SJE, Harvey eroded at least 48 cm of the sediment column, resulting in the transport of an estimated 16.4 × 106 tons of sediment and at least 2 tons of Hg into Galveston Bay. This eroded sediment was replaced by a Harvey storm deposit of 7.73 × 106 tons of sediment and 0.96 tons within the SJE, mostly sourced from Buffalo Bayou. Considering that the frequency of slow-moving tropical cyclones capable of delivering devastating rainfall may be increasing, then one can expect that delivery of Hg and other contaminants from the archived sediment within urbanized estuaries will increase and that what happened during Harvey is a harbinger of what is to come.

Sedimentary Architecture of Storm-Influenced Tidal Flat Deposits of the Upper Mulichinco Formation, Neuquén Basin, Argentina

This study reports on the Lower Cretaceous upper Mulichinco Formation in the Neuquén Basin, west-central Argentina. The studied succession comprises shallow marine strata, deposited in a mixed wave and tidal flat environment where ebb-tidal currents dominated. We describe mixed storm- and tide-influenced deposits within progradationally stacked high-frequency sequences, and discuss process interaction, sediment dispersal and preservation potential. These storm and tidal deposits mix spatially on bed-, bedset- and sequence scales, suggesting multiscale process interaction. The study investigates a 12 km long continuous outcrop, oriented sub-parallel to the paleocoastline. The succession comprises subtidal flat and meandering tidal channel complexes, with interbedding and interfingering of storm and tidal deposits. The tidal deposits are widespread and comprise moderately sorted sandstones with bimodal paleocurrent directions, single and double mud drapes, reactivation surfaces, and inclined heterolithic stratification. Varying bimodal paleocurrent directions suggest that the paleocoastline was irregular, consisting of both protrusions and bays. Storm deposits are mainly found erosively interbedded with subtidal flat sandstones, and exhibit dm-thick well sorted hummocky and swaley cross-stratified sandstones. These storm deposits show systematic lateral variations in abundance, from dominant to absent, which is linked to subtle variations in water depth along the irregular paleocoastline. As the tidal deposits are widespread across the study area, and with no significant facies change, the varying dispersal of storm-influenced deposits is considered a product of wave refraction, with converging and diverging wave energy at interpreted positions of coastal protrusions and embayments, respectively. Consequently, the irregular paleocoastline morphology caused spatial variability in wave impact and controlled preservation of interbedded storm and tidal deposits at the coastal protrusions, while facilitating complete tidal remobilization of sediments in the embayments. With no evidence for fluvial influence, ebb-tidal currents are considered as the main drivers for sediment dispersal onto the subtidal flat, through the meandering tidal channels.

Geological controls on dispersal and deposition of river flood sediments on the Hidaka shelf, Northern Japan

Abstract The distribution and characteristics of marine surface sediments are a basic marine geological information. Large river floods are a frequent natural hazard that transport substantial terrigenous sediments into the marine environment. In August 2003, TY ETAU (0310) caused heavy rainfall in the southern coast of Hokkaido, north Japan, where some mountainous rivers in the Hidaka region flooded. Two deposition modes for the 2003 flood sediments can be identified by comparing the pre- and post-flood surface sediment distribution. Shore-normal shallow depressions off the mouth of the Saru and Atsubetsu rivers served as channels for the discharged floodwater preventing dispersion and maintaining the necessary water density to transport the materials as density bottom currents. This action also promoted long-distance transport of flood materials across the continental shelf. Absence of depression on the inner shelf off the mouth of the Niikappu and Shizunai rivers may have dispersed floodwaters near the river mouth and deposited the flood materials close to the shore. Marine geological mapping suggests that the differences in submarine topography (the presence or absence of shallow depressions) are closely related to the regional geological structure. Thus, submarine geology is a controlling factor of the seafloor environments influenced by the river flood.

The Fate of Mud Nourishment in Response to Short-Term Wind Forcing

In this study, results from a realistic 3D hydrodynamic and sediment transport model, applied to a channel in the Dutch Wadden Sea, are analyzed in order to assess the effect of short-term wind forcing, the impact of fresh water effects, and the variability induced by the spring-neap cycle on the transport of suspended sediment. In the investigated region, a pilot study for sediment nourishment, the so-called Mud Motor, is executed. This project aims for the beneficial re-use of dredged harbor sediments through the disposal of these sediments at a location where natural currents are expected to transport them toward a nearby salt marsh area. The model results presented in this study advance the understanding of the driving forces that determine sediment transport in shallow, near-coastal zones, and can help to improve the design of the Mud Motor. In the investigated channel, which is oriented parallel to the coastline, tidal asymmetries generally drive a transport of sediment in flood direction. It was found that already moderate winds along the channel axis reverse (wind in ebb direction), or greatly enhance this transport, up to an export of sediment over the adjacent water shed (wind in flood direction). The most beneficial wind conditions (moderate westerly winds) can cause an accumulation of more than 90% of the initial 200 tons sediment pool on the intertidal area; during less favorable conditions (northeasterly winds), less than a third of the dumped sediment is transported onto the mudflat. On-shore winds induce a transport toward the coast. Surprisingly, sediment pathways are only sensitive to the exact disposal location in the channel during wind conditions that counteract the tidally driven transport, and freshwater effects play no significant role for the dispersal of sediment.

Evidence of rift segmentation and controls of Middle to Late Jurassic synrift deposition in the Ryggsteinen ridge area, northern North Sea

Multiple episodes of rifting and preexisting structure reactivation may result in rift segmentation, which is a fundamental factor in deformation variability and sediment dispersal. To understand the structural framework and basin evolution in segmented rift systems, this study addresses an integrated structural and stratigraphic analysis of the Middle–Upper Jurassic sequences in the northern North Sea. Four major fault systems were active during the Jurassic oblique rifting: (1) east-northeast–striking synthetic shear faults along preexisting Caledonian structures, which developed into basin-wide transfer fault zones and induced first-order rift segmentation. Each rift segment shows independent deformation; (2) north-south–striking reactivated Permian–Triassic faults, which uplifted the footwall developing major structural highs; (3) southwest-northeast–striking normal faults; and (4) northwest-southeast–striking antithetic shear (oblique-slip) faults, which caused internal deformation and induced second-order rift segmentation within rift segments. Rift segmentation led to stepovers from the Viking graben to the Sogn graben. The entry of regional drainages was determined by first-order rift segmentation. Prior to segmentation (Bathonian–Callovian), drainage shows a northeast-southwest line-source nature, and facies changes are quite homogenous. During the Oxfordian–Kimmeridgian, segmentation took place and modified the drainage system into a point source. Facies show a large spectrum of variability from shallow-marine to deep-water turbidites over short distances. Furthermore, drainage routes were influenced by second-order rift segmentation. West-directed drainages deflected toward the northwest by adapting to gradient surfaces established by oblique-slip faults. As such, the structural and stratigraphic expressions in this study provide an example of synrift deposition controlled by different orders of rift segmentation.

Evaluation of a virus-based control method to protect cultured oysters from the harmful dinoflagellate Heterocapsa circularisquama

This study evaluates a novel control method for harmful algal blooms (HABs) that uses natural sediment including associated viruses. In Japan, commercial aquaculture of bivalves such as oysters, pearl oysters and clams is severely threatened by blooms of the harmful dinoflagellate, Heterocapsa circularisquama. HcRNAV is a single-stranded RNA virus that specifically infects H. circularisquama. Given that high concentrations of HcRNAV remain in bottom sediment following a H. circularisquama bloom, dispersal of sediments containing HcRNAV was expected to provide a promising tool to mitigate blooms of this dinoflagellate. A laboratory experiment demonstrated the effectiveness of a) HcRNAV alone, and b) sediments with HcRNAV, in reducing H. circularisquama densities. For the first time, a field test was implemented in an active oyster farm on Sado Island, Japan in which sediment containing HcRNAV collected from nearby waters was dispersed into 15,000 L floating mesocosms during early stages of a H. circularisquama bloom. In the treatment spraying with sediment containing HcRNAV, the density of H. circularisquama decreased significantly until it reached only ~1% of the initial after five days, while that of HcRNAV increased significantly by Day 2 (one-way ANOVA, n = 3, P < .01). These results indicate that the virus + sediment treatment was very effective in mitigating the H. circularisquama bloom under field conditions. Only a very low sediment concentration achieved these results, thereby reducing potential ecological impacts. Given the high diversity and mutation potential of HcRNAV, and the variable host response, it is recommended that field application of this mitigation strategy use indigenous sediment. This study provides the first field test of viral control of HAB worldwide and will facilitate its further practical application.

Storm-induced hydrodynamic changes and seabed erosion in the littoral area of Yellow River Delta: A model-guided mechanism study

Morphological evolution of large river deltas is highly vulnerable to extreme storm events due to insufficient sediment supply. As an abandoned delta lobe, the coasts along the northern Yellow River Delta (YRD) and Gudong Oil Field have recently suffered serious erosion due to extreme storm events and become increasingly vulnerable. In this study, a well validated and tested Delft 3D module by the observing hydrodynamic and sediment data to simulate the hydrodynamics and seabed erosion during a storm event in the littoral area of YRD. Observed wave, current and sediment data under both fair-weather and storm conditions were collected in the study area and used to validate the model. The results indicated that the model can reproduce well the hydrodynamic and sediment transport processes. A series of numerical experiments were carried out to examine the hydrodynamic changes and sediment transports. In the numerical experiment of normal condition, there is hardly any sediment transport off the YRD. The numerical experiment of storm condition showed that storms enhanced tidal residual currents, weakened tidal shear front, and significant wave heights up to 2 m, considerably intensified the sediment resuspension and dispersal. The local sediment resuspension due to the increased wave-induced bottom stress promoted the sediment plume to expand to the central area of Laizhou Bay, which seemed to provide sediment source for offshore and southward transport. During the storm, the active nearshore sediment resuspension provided sediment source for offshore and southward transport. The intensive dynamics and sediment transport under storm conditions caused significant changes in seabed erosion and siltation. The main erosion occurred off the Gudong and northern YRD, while the main siltation appeared in the central area of Laizhou Bay. No significant recovery after a storm and frequent strong winds have an accumulative effect on the erosion, which is very likely to dominate the erosive states of the YRD coast in the future.

Quaternary sediment dispersal in the Zambezi turbidite system (SW Indian Ocean)

This study investigates the Late Quaternary sediment distribution of the Zambezi turbidite system (Mozambique Channel, Western Indian Ocean) from a set of piston cores that characterizes the sedimentation in the Intermediate Basin and in the proximal and distal parts of the Zambezi Fan. Sedimentological and geochemical analyses permit to define variations in sediment composition, sediment accumulation rates and timing of turbiditic deposits over the past 720 kyr. Our study reveals low sediment inputs and rare turbiditic deposits in the Zambezi turbidite system, and the deep (>2,500 m) Mozambique Channel in general, over the studied time interval. The reconstruction of the terrigenous flux in the upper part of the system suggests monsoon-related precipitation changes as the main forcing for riverine inputs variability in the Zambezi system. However, the occurrence of turbiditic deposits in the cores suggests that there is no genetic link between their triggering and evolving climate and sea-level conditions, thus emphasizing transformation of failed (slide-generated) sediment from the continental slope as the main initiation process for turbidity currents in the Zambezi system. Finally, our data highlight regional-scale changes in sedimentary facies through time, interpreted as successive ‘on-off’ switches in the activity of the distal Zambezi Fan, and by extension, regional-scale depocenter shifts. The last one likely occurred at 350 ± 42 kyr, and is concomitant with a significant increase in terrigenous inputs into the proximal Intermediate Basin. It is speculated that this depocenter shift is related to a major southward migration of the Zambezi delta.

Sediment dispersal and redistributive processes in axial and transverse deep‐time source‐to‐sink systems of marine rift basins: Dampier Sub‐basin, Northwest Shelf, Australia

AbstractMorphological scaling relationships between source‐to‐sink segments have been widely explored in modern settings, however, deep‐time systems remain difficult to assess due to limited preservation of drainage basins and difficulty in quantifying complex processes that impact sediment dispersals. Integration of core, well‐logs and 3‐D seismic data across the Dampier Sub‐basin, Northwest Shelf of Australia, enables a complete deep‐time source‐to‐sink study from the footwall (Rankin Platform) catchment to the hanging wall (Kendrew Trough) depositional systems in a Jurassic late syn‐rift succession. Hydrological analysis identifies 24 drainage basins on the J50.0 (Tithonian) erosional surface, which are delimited into six drainage domains confined by NNE‐SSW trending grabens and their horsts, with drainage domain areas ranging between 29 and 156 km2. Drainage outlets of these drainage domains are well preserved along the Rankin Fault System scarp, with cross‐sectional areas ranging from 0.08 to 0.31 km2. Corresponding to the six drainage domains, sedimentological and geomorphological analysis identifies six transverse submarine fan complexes developing in the Kendrew Trough, ranging in areas from 43 to 193 km2. Seismic geomorphological analysis reveals over 90‐km‐long, slightly sinuous axial turbidity channels, developing in the lower topography of the Kendrew Trough which erodes toe parts of transverse submarine fan complexes. Positive scaling relationships exist between drainage outlet spacing and drainage basin length, and drainage outlet cross‐sectional area and drainage basin area, which indicates the geometry of drainage outlets can provide important constraints on source area dimensions in deep‐time source‐to‐sink studies. The broadly negative bias of fan area to drainage basin area ratios indicates net sediment losses in submarine fan complexes caused by axial turbidity current erosion. Source‐to‐sink sediment balance studies must be done with full evaluating of adjacent source‐to‐sink systems to delineate fans and their associated up‐dip drainages, to achieve an accurate tectonic and sedimentologic picture of deep‐time basins.

Persistence of Grenvillian dominance in Laurentian detrital zircon age systematics explained by sedimentary recycling: Evidence from detrital zircon double dating and detrital monazite textures and geochronology

Abstract Grenvillian ages dominate Neoproterozoic to Paleozoic detrital zircon (DZ) populations across eastern Laurentia and persist through the present. The persistence of this dominance is inferred to result from recycling of DZ grains ultimately sourced from exceptionally Zr-rich and zircon-fertile Grenvillian granitoids. Pennsylvanian arenites of the Appalachian Basin (eastern United States) exhibit DZ U-Pb age distributions that are nearly identical to those of Neoproterozoic to Cambrian strata, and contain detrital diagenetic monazite grains formed via metamorphism or diagenesis of sedimentary rocks in the source region. Detrital zircon (U-Th)/He ages are mostly 475–300 Ma, yielding lag times [Δt = U-Pb age − (U-Th)/He age] of 500–1000 m.y. and 1200–2400 m.y. for Grenvillian and Paleoproterozoic to Archean DZ grains, respectively. Detrital monazite Th-Pb ages are comparable to (U-Th)/He cooling ages, reflecting formation of monazite during Paleozoic regional metamorphism of Neoproterozoic to Cambrian strata that reset the (U-Th)/He systematics of Grenvillian DZ grains within those metasediments. These results are either consistent with or prove recycling. Incorporation of other geological constraints permits definition of at least three (and potentially five) recycling events and their timing following initial post-Grenvillian exhumation and erosion (the “great Grenvillian sedimentation episode”). Recycling events include dispersal of post-Grenvillian sediment during deposition of Neoproterozoic to Cambrian strata (formation of the “Great Unconformity”: cycle 1), subsequent erosion of metamorphosed Neoproterozoic to Cambrian strata generating detritus for the Pennsylvanian arenites sampled here (cycle 2), and modern erosion of those arenites (cycle 3). Pancontinental river systems facilitated dispersal of sediment of ultimate Grenvillian age during or after each cycle.

Detrital-zircon analyses, provenance, and late Paleozoic sediment dispersal in the context of tectonic evolution of the Ouachita orogen

Abstract New analyses for U-Pb ages and εHft values, along with previously published U-Pb ages, from Mississippian–Permian sandstones in synorogenic clastic wedges of the Ouachita foreland and nearby intracratonic basins support new interpretations of provenance and sediment dispersal along the southern Midcontinent of North America. Recently published U-Pb and Hf data from the Marathon foreland confirm a provenance in the accreted Coahuila terrane, which has distinctive Amazonia/Gondwana characteristics. Data from Pennsylvanian–Permian sandstones in the Fort Worth basin, along the southern arm of the Ouachita thrust belt, are nearly identical to those from the Marathon foreland, strongly indicating the same or a similar provenance. The accreted Sabine terrane, which is documented by geophysical data, is in close proximity to the Coahuila terrane, suggesting the two are parts of an originally larger Gondwanan terrane. The available data suggest that the Sabine terrane is a Gondwanan terrane that was the provenance of the detritus in the Fort Worth basin. Detrital-zircon data from Permian sandstones in the intracratonic Anadarko basin are very similar to those from the Fort Worth basin and Marathon foreland, indicating sediment dispersal from the Coahuila and/or Sabine terranes within the Ouachita orogen cratonward from the immediate forelands onto the southern craton. Similar, previously published data from the Permian basin suggest widespread distribution from the Ouachita orogen. In contrast to the other basins along the Ouachita-Marathon foreland, the Mississippian–Pennsylvanian sandstones in the Arkoma basin contain a more diverse distribution of detrital-zircon ages, indicating mixed dispersal pathways of sediment from multiple provenances. Some of the Arkoma sandstones have U-Pb age distributions like those of the Fort Worth and Marathon forelands. In contrast, other sandstones, especially those with paleocurrent and paleogeographic indicators of southward progradation of depositional systems onto the northern distal shelf of the Arkoma basin, have U-Pb age distributions and εHft values like those of the “Appalachian signature.” The combined data suggest a mixture of detritus from the proximal Sabine terrane/Ouachita orogenic belt with detritus routed through the Appalachian basin via the southern Illinois basin to the distal Arkoma basin. The Arkoma basin evidently marks the southwestern extent of Appalachian-derived detritus along the Ouachita-Marathon foreland and the transition southwestward to overfilled basins that spread detritus onto the southern craton from the Ouachita-Marathon orogen, including accreted Gondwanan terranes.

Impact of river discharge on hydrodynamics and sedimentary processes at Yellow River Delta

During the Anthropocene, regulating river discharge by high dams may have met the need for water demands in river basins, but resulted in carrying less freshwater and sediment to the sea, inducing land degradation and shoreline retreat in worldwide mega-river deltas. In land-ocean interaction, tide response to water discharge changes plays an important role and is crucial for the river-laden sediment transfer and dispersal, affecting both nearshore and estuarine deposits. The Yellow River Delta (YRD), which is under an increasing pressure of the new discharge regime of the Yellow River, has undergone drastic changes in terms of sediment dynamics and morphologic evolution. To gain a better understanding of the overall fluvial and marine hydrodynamics and morphodynamic processes in the YRD, in this study, a full-scale numerical model is built to investigate the interaction and impacts of changing environmental forcing and dynamics on flow and sediment transport in the estuary of YRD and its adjacent coasts. The results show that the river discharge strongly affects the tidal dynamics and morphology of the delta, particularly in the close vicinity of the outlet and the intertidal zone. Tidal constituents M2 and K1, which are the most significant ones in the YRD, are found to be noticeably affected with a decreasing trend when the river discharge increases. The model results also indicate that river discharge affects the location and intensity of the shear front that occurs in the nearshore areas of the YRD. Increasing the river discharge can induce a seaward movement of the shear front, reduce its width and concentrate its shear intensity. It is found that the reverse of the flow direction at each side of the shear front and strong longshore tidal current can act as a barrier for the sediment dispersal process by keeping suspended sediment in the inner zone, thus to form a particular sediment deposition zone and the depo-center.

Routing of terrestrial organic matter from the Congo River to the ultimate sink in the abyss: a mass balance approach (André Dumont medallist lecture 2017)

We address the role of the Congo River sediment dispersal in exporting and trapping organic carbon into deep offshore sediments. Of particular interest is the Congo submarine canyon, which constitutes a permanent link between the terrestrial sediment sources and the marine sink. The Congo River delivers an annual sediment load of ~40 Tg (including 2 Tg of C) that feed a mud-rich turbidite system. Previous estimates of carbon storage capacity in the Congo turbidite system suggest that the terminal lobe complex accounts for ~12% of the surface area of the active turbidite system and accumulates ~18% of the annual input of terrestrial particulate organic carbon exiting the Congo River. In this paper, we extend the approach to the whole active turbidite depositional system by calculating an average burial of terrestrial organic matter in the different environments: canyon, channel, and levees. We estimate that between 33 and 69% of terrestrial carbon exported by the Congo River is ultimately trapped in the different parts of turbidite system and we evaluate their relative efficiency using a source to sink approach. Our carbon budget approach, which consider annual river discharge versus offshore centennial accumulation rates, indicates that about half of the total particulate organic matter delivered yearly by the Congo River watershed escapes the study area or is not correctly estimated by our deep offshore dataset and calculations.

Depth-dependent soil mixing persists across climate zones

Soil mixing over long (>102 y) timescales enhances nutrient fluxes that support soil ecology, contributes to dispersion of sediment and contaminated material, and modulates fluxes of carbon through Earth's largest terrestrial carbon reservoir. Despite its foundational importance, we lack robust understanding of the rates and patterns of soil mixing, largely due to a lack of long-timescale data. Here we demonstrate that luminescence, a light-sensitive property of minerals used for geologic dating, can be used as a long-timescale sediment tracer in soils to reveal the structure of soil mixing. We develop a probabilistic model of transport and mixing of tracer particles and associated luminescence in soils and compare with a global compilation of luminescence versus depth in various locations. The model-data comparison reveals that soil mixing rate varies over the soil depth, with this depth dependency persisting across climate and ecological zones. The depth dependency is consistent with a model in which mixing intensity decreases linearly or exponentially with depth, although our data do not resolve between these cases. Our findings support the long-suspected idea that depth-dependent mixing is a spatially and temporally persistent feature of soils. Evidence for a climate control on the patterns and intensities of soil mixing with depth remains elusive and requires the further study of soil mixing processes.

Detrital zircons and sediment dispersal in the eastern Midcontinent of North America

Abstract Results of detrital-zircon analyses (U-Pb ages and initial Hf values, εHft) of Mississippian–Pennsylvanian sandstones in the Michigan, Illinois, and Forest City basins are remarkably similar to data for coeval sandstones in the Appalachian basin, indicating dispersal of sediment from the Appalachian orogen through the Appalachian basin to the eastern Midcontinent during the late Paleozoic. The similarities of results include matches of the two most prominent age groups (1300–950 Ma and 490–350 Ma), as well as matches of the less abundant age groups. Comparisons of the data are from observations of probability density plots and multidimensional scaling of U-Pb age data and of εHft values. Despite the dominance of an Appalachian signature in all samples, some samples contain grains with ages that suggest intermittent additional sources. Four samples (three ranging in depositional age from Morrowan to Atokan–Desmoinesian in the Illinois basin, and one of Desmoinesian age in the Forest City basin), in addition to typical Appalachian age distributions, have prominent age modes between 768 and 525 Ma, corresponding in age to Pan-African/Brasiliano rocks in Gondwanan accreted terranes in the Appalachian orogen, suggesting intermittent dispersal from the Moretown terrane of the northern Appalachians. Sandstones in the Appalachian basin and those in the Midcontinent basins have very few grains with ages that correspond to the Alleghanian orogeny in the Appalachian orogen. Nevertheless, three sandstones each in the Illinois basin and Forest City basin with depositional ages of 312–308 Ma have a few zircon grains in the age range of 321 ± 5 to 307 ± 4 Ma. The nearly identical crystallization and depositional ages suggest reworking at the depositional sites of air-fall volcanic ash from the Alleghanian orogen, rather than fluvial transport from the orogen. The basal Pennsylvanian sandstones lap onto a regional unconformity around the northern rims of the Illinois and Forest City basins, suggesting sources for recycled grains. Along the northern edge of the Illinois basin, Ordovician sandstones beneath the unconformity may have contributed minor concentrations of Superior-age zircons in the basal Pennsylvanian sandstones. Basal Pennsylvanian sandstones in the Forest City basin lap onto Mississippian strata, suggesting possible recycling of zircons from eroded Mississippian sandstones.