Variations In Sediment Supply Research Articles

Spatial Variation in Coastal Dune Evolution in a High Tidal Range Environment

Coastal dunes have global importance as ecological habitats, recreational areas, and vital natural coastal protection. Dunes evolve due to variations in the supply and removal of sediment via both wind and waves, and on stabilization through vegetation colonization and growth. One aspect of dune evolution that is poorly understood is the longshore variation in dune response to morphodynamic forcing, which can occur over small spatial scales. In this paper, a fixed wing unmanned aerial vehicle (UAV), is used to measure the longshore variation in evolution of a dune system in a megatidal environment. Dune sections to the east and west of the study site are prograding whereas the central portion is static or eroding. The measured variation in dune response is compared to mesoscale intertidal bar migration and short-term measurements of longshore variation in wave characteristics during two storms. Intertidal sand bar migration is measured using satellite imagery: crescentic intertidal bars are present in front of the accreting portion of the beach to the west and migrate onshore at a rate of 0.1–0.2 m/day; episodically the eastern end of the bar detaches from the main bar and migrates eastward to attach near the eastern end of the study area; bypassing the central eroding section. Statistically significant longshore variation in intertidal wave heights were measured using beachface mounted pressure transducers: the largest significant wave heights are found in front of the dune section suffering erosion. Spectral differences were noted with more narrow-banded spectra in this area but differences are not statistically significant. These observations demonstrate the importance of three-dimensionality in intertidal beach morphology on longshore variation in dune evolution; both through longshore variation in onshore sediment supply and through causing longshore variation in near-dune significant wave heights.

Carboniferous–Permian transgression/regression mechanisms in the Eastern Ordos Basin and their sea-level spatiotemporal variability: Insights from source-to-sink systems

Developed on the North China Craton, the intracratonic Ordos Basin contains a complete Paleozoic-to-Cenozoic sediment record, allowing for long-term paleoenvironmental and climate change investigation. During the Carboniferous–Permian period, convergence between the North China block and the paleo-Yangtze plate to the south resulted in a general marine regression characterized by a series of second-order transgression/regression cycles diachronous along the eastern margin of the Ordos. However, the detailed mechanisms that induced these cycles, as well as the associated paleoecological changes, remain unknown. In this study, we integrate multiple indices, including δ18O and δ13C, rare earth element (REE), paleontological assemblages, and clay content (w (chlorite + kaolinite)/w((Illite) ratio) planar distribution, to restore the paleo-water depth distribution. These parameters are then used to reconstruct the paleo-sea level from the Pennsylvanian to the middle Permian. We conclude that the direction of second-order transgression/regression was mainly toward the east during the Pennsylvanian–early Permian and switched clockwise toward the north during the middle Permian. We suggest that the second-order cycles, diachronous in space and time, are mainly linked to local variations in sediment supply and regional uplift. Using detrital zircon U–Pb data and the REE and trace element content and heavy mineral assemblages (HMA), we estimate the sediment provenance area. The sediment volumes deposited in the basin through time are obtained using 2D seismic data. During the Carboniferous, the coarse-grained sediments deposited in the eastern Ordos were derived from the uplifting Helan Mountain (Qiandam–Qilian orogenic belt). By the middle Permian, the detrital material became multi-sourced, thus issuing the Yinshan range to the north and the Qinling range to the south. We then integrate the description of numerous core samples with electric log and 2D seismic data to reconstruct the sediment facies associations across the first-order regression from the Carboniferous tidal flat depositional system to the middle Permian prograding fluvial delta system. According to the transfer of the glacial epoch, the sedimentation rate, and the transgression/regression rate above, we classify the evolution process into three patterns: low-transgression rate and less-sediment supply pattern (the late Carboniferous), high regression rate and mass sediment supply pattern (the north block during the early Permian), and low regression rate and mass sediment supply pattern (the south block during the Sakmarian stage). Lastly, with the quantitative calculation of the source-to-sink (S2S) parameters, including the S2S system volume and the elevated height of regional uplift with the 2D seismic data, we propose the mechanism of transgression/regression in the Ordos Basin, responding to the above three pattern s. The first pattern was controlled by regional uplift, whereas the second pattern was controlled by sediment supply. As to the third one, uplift and sediment supply could affect the transgression/regression process.

Width control on event‐scale deposition and evacuation of sediment in bedrock‐confined channels

AbstractIn mixed bedrock–alluvial rivers, the response of the system to a flood event can be affected by a number of factors, including coarse sediment availability in the channel, sediment supply from the hillslopes and upstream, flood sequencing and coarse sediment grain size distribution. However, the impact of along‐stream changes in channel width on bedload transport dynamics remains largely unexplored. We combine field data, theory and numerical modelling to address this gap. First, we present observations from the Daan River gorge in western Taiwan, where the river flows through a 1 km long 20–50 m wide bedrock gorge bounded upstream and downstream by wide braidplains. We documented two flood events during which coarse sediment evacuation and redeposition appear to cause changes of up to several metres in channel bed elevation. Motivated by this case study, we examined the relationships between discharge, channel width and bedload transport capacity, and show that for a given slope narrow channels transport bedload more efficiently than wide ones at low discharges, whereas wider channels are more efficient at high discharges. We used the model sedFlow to explore this effect, running a random sequence of floods through a channel with a narrow gorge section bounded upstream and downstream by wider reaches. Channel response to imposed floods is complex, as high and low discharges drive different spatial patterns of erosion and deposition, and the channel may experience both of these regimes during the peak and recession periods of each flood. Our modelling suggests that width differences alone can drive substantial variations in sediment flux and bed response, without the need for variations in sediment supply or mobility. The fluctuations in sediment transport rates that result from width variations can lead to intermittent bed exposure, driving incision in different segments of the channel during different portions of the hydrograph. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

A Holistic Modeling Approach to Project the Evolution of Inlet-Interrupted Coastlines Over the 21st Century

Approximately one quarter of the World’s sandy beaches, most of which are interrupted by tidal inlets, are eroding. Understanding the long-term (50-100 year) evolution of inlet-interrupted coasts in a changing climate is therefore of great importance for coastal zone planners and managers. This study therefore focuses on the development and piloting of an innovative model that can simulate the climate-change driven evolution of inlet-interrupted coasts at 50-100 year time scales, while taking into account the contributions from catchment-estuary-coastal systems in a holistic manner. In this new model, the evolution of inlet-interrupted coasts is determined by: (1) computing the variation of total sediment volume exchange between the inlet-estuary system and its adjacent coast, and (2) distributing the computed sediment volume along the inlet-interrupted coast as a spatially and temporally varying quantity. The exchange volume, as computed here, consists of three major components: variation in fluvial sediment supply; basin (or estuarine) infilling due to the sea-level rise-induced increase in accommodation space; and estuarine sediment volume change due to variations in river discharge. To pilot the model, it is here applied to three different catchment-estuary-coastal systems: the Alsea estuary (Oregon, USA), Dyfi estuary (Wales, UK), and Kalutara inlet (Sri Lanka). Results indicate that all three systems will experience sediment deficits by 2100 (i.e. sediment importing estuaries). However, processes and system characteristics governing the total sediment exchange volume, and thus coastline change, vary markedly among the systems due to differences in geomorphic settings and projected climatic conditions. These results underline the importance of accounting for the different governing processes when assessing the future evolution of inlet-interrupted coastlines.

Stratigraphic evolution of the Nakdong River valley in response to late Quaternary sea-level changes

Sequence analysis using borehole samples and high-resolution seismic data in the Nakdong River valley yielded a good example of a river-valley sequence influenced by the complex interplay between the bottom morphology of the steep paleo-valley, varying sediment supply, and Holocene sea-level change associated with coastal currents. The late Quaternary stratigraphic sequence in the Nakdong River Estuary, approximately 60–70 m thick, forms a high-frequency sequence consisting of a set of lowstand, transgressive, and highstand systems tracts that corresponds to a fifth-order (20 ka) sea-level cycle. Four main depositional systems, including ten sedimentary facies, constitute these systems tracts: fluvial, estuarine, coastal/shoreface, and deltaic. The lowstand systems tract (LST), consisting of gravelly sand, forms a fluvial depositional system (Unit I) which fills the thalweg of river valley mainly developed before 12 ka. The transgressive systems tract (TST), showing a succession of retrograding or backstepping depositional arrangements, can be divided into two depositional systems (Unit II and III). The riverine sediments were trapped within the paleo-estuary, forming an estuarine depositional system (Unit II) developed between 12 and 7 ka. As the transgression continued, the coarse sediments were deposited and redistributed by coastal processes, resulting in coastal/shoreface depositional system (Unit III). It is characterized by an isolated sand body and thin sand veneer. The HST is composed of deltaic depositional system including delta plain, delta front, and prodelta (Unit IV). During the delta progradation, most coarse-grained sands derived from the river were deposited in the lower delta plain and delta front, forming sand bars and shoals less than 15 m deep. The remaining fine-grained sediments were transported further offshore in a suspension mode and deposited in the inner shelf off the present river mouth, forming a subaqueous prodelta. Radiocarbon and optically stimulated luminescence (OSL) dating suggest that the Holocene deltaic system was initiated by aggradational and progradational stacking patterns at approximately 8 ka during the last stage of decelerated sea-level rise, and was then followed by a prograding clinoform after the highest sea level at approximately 7 ka.

Morphometry of a glacier-linked esker in NW Tempe Terra, Mars, and implications for sediment-discharge dynamics of subglacial drainage

We present a systematic, metre-scale characterisation of the 3D morphometry of an esker on Mars, and the first attempt to reconstruct the multi-stage dynamics of esker formation on Mars. Eskers are sinuous ridges comprising sediment deposited by meltwater draining through ice-confined tunnels within or beneath glaciers. Detailed morphometric insights into eskers on Mars are important for (i) informing morphometric tests of whether sinuous ridges elsewhere on Mars are eskers, and (ii) informing modelling experiments which aim to reconstruct the glaciological and environmental controls on esker formation on Mars. We use a digital elevation model generated from High Resolution Imaging Science Experiment (HiRISE) images to characterise the height and width of an extremely rare esker associated with a late-Amazonian-aged viscous flow feature (debris-covered glacier) in NW Tempe Terra, Mars. Our measurements suggest that the NW Tempe Terra esker is a ‘stacked’ formation comprising an underlying ‘lower member’ ridge that is superposed by a narrower ‘upper member’ ridge. We used a novel morphometric approach to test whether the apparent stacking records two distinct esker deposition regimes (either within the same drainage episode, or within temporally-separated drainage episodes). This approach posits that esker crest morphology is controlled by primary esker formation processes and, by extension, that portions of eskers with similar crest morphologies should have similar morphometric relationships. We predicted the morphometric relationships described by the constituent upper and lower member ridges based on ‘reference relationships’ observed for morphologically-similar portions of the esker where no evidence of stacking was observed. Our observations corresponded well with the predicted relationships, supporting our stacked esker hypothesis. We propose conceptual models, which invoke spatial and temporal variations in sediment supply and meltwater discharge, to explain the stacked morphology. These models are informed by morpho-sedimentary relationships observed along eskers on Earth.

Paraglacial coasts: challenges for coastal conservation in the Anthropocene

A challenge for coastal conservation over the next decades is to predict and then effectively manage the outcomes of ongoing climate change in the context of the Anthropocene. Paraglacial coasts are those on or adjacent to present or formerly glaciated terrain and which are still influenced by glacigenic processes. Ongoing response of paraglacial coasts to the influences of glaciation can give rise to diverse regional-scale coastal responses that may variously amplify or suppress any effects caused by global climate change. Here we provide insight into the richness of landforms and coastal system responses from two contrasting paraglacial environments, in Svalbard where glaciers are still present but are actively retreating, and in Ireland where late Pleistocene glaciers melted away around 14,000 years ago. Svalbard and Ireland exhibit different paraglacial coastal responses which reflect long-term variations in sediment supply from inland source areas to the coast, and variations in sediment residence times and storage areas within the coastal zone. The conservation of paraglacial coasts in the context of Anthropocene global warming requires an understanding of regional glacial history and longer term coastal responses to paraglacial relaxation.

Relating Hydrodynamic Forcing and Topographic Response for Tide-Dominated Sandy Beaches

To relate hydrodynamic forcing and topographic response for a tide-dominated sandy beach, extensive field measurements were carried out in the intertidal zone. Hydrodynamics and beach topography were monitored during a total of 12 weeks at two different study sites: one with a featureless intertidal zone and one with intertidal bars. The results of both study sites indicate that the intertidal beach grows when wave steepness is small, whereas it erodes when wave steepness is large. Spring-neap variations in tidal current direction heavily distort this trend: strong spring tidal currents transport sediment away from the beach, resulting in enhanced erosion. Tide-induced beach volume changes are on the same order of magnitude as wave-induced changes. Besides waves and tides, the effect of variations in the amount of sediment supply is substantial, with enhanced accretion when the sediment supply is large. The effect of variations in sediment supply on the intertidal beach topography is subordinate to the effect of waves and tide, though. From this study, it is concluded that larger waves are primarily erosive, but they can also enhance the natural sediment supply. Furthermore, it is found that tidal currents can be equally important as waves in shaping the beach topography, especially during spring tide on macrotidal beaches.

Sequence stratigraphy in the context of the ‘modeling revolution’

Abstract Confusions between methodology and modeling created a false premise to question the ‘future of sequence stratigraphy’. In reality, the future is already here in terms of a standard methodology. Despite the variability of the stratigraphic architecture, there are only a few stacking patterns that are diagnostic to the definition of stratal units and bounding surfaces, which can be observed at all stratigraphic scales. The identification of the diagnostic stacking patterns, at scales defined by the purpose of the study or by the resolution of the data available, provides the guiding principle of the sequence stratigraphic methodology. The modeling of the possible controls on sequence development plays no role in the methodological workflow, and can continue indefinitely after the construction of a sequence stratigraphic framework. Therefore, it is important to separate methodology from modeling in sequence stratigraphy. The standard methodology does not prevent future developments in the field of stratigraphic modeling. Uncalibrated modeling can ‘demonstrate’ any stratigraphic scenario, whether realistic or not. While the methodology evolved from a model-driven to a data-driven approach, uncalibrated modeling has become the new ‘triumph of interpretation over facts and common sense’. The latest trend in forward modeling is the shift from an overemphasis on accommodation to an overemphasis on sediment supply, to the point that all aspects of the stratigraphic architecture are explained by variations in sediment supply or even solely by autocyclicity. In reality, it is always a combination of accommodation and sedimentation, and both elements of this ‘dual control’ contribute in discernible ways to the architecture and makeup of the sequence stratigraphic framework. The methodology does not require an interpretation of the underlying controls on accommodation and sedimentation, but only the observation of stratal stacking patterns and stratigraphic relationships that result from their interplay. Muddling the distinction between methodology and modeling leads to unnecessary confusion and a reversal of the progress made in the development of sequence stratigraphy as a data-driven methodology.

Geochemical anomalies of potentially hazardous elements reflect catchment geology: An example from the Tyrrhenian coast of Italy

Assessing soil contamination by hazardous metals and estimating the extent to which metal concentrations in surficial sediments may pose risks to human health are increasingly important environmental issues. An integrated sedimentological and geochemical study of 57 Holocene beach sands from the shallow subsurface (120–130 cm depth) of the heavily urbanized Tyrrhenian Sea coast of Italy (Tuscany and adjacent coastal stretches) allowed a remarkable compositional heterogeneity to be identified as a function of spatial variations in riverine sediment supply and alongshore sediment dispersal patterns.Concentrations of Cr, Ni, and As exceeding maximum permissible limits for recreational/industrial sites (150 mg/kg, 120 mg/kg, and 20 mg/kg, respectively) reveal spatial trends that fit the petrography of modern beach sands and closely reflect the geology of river catchments, thus indicating a geogenic origin. Extremely high concentrations of Cr (and Ni), even 10 times greater than threshold values, are interpreted to reflect sediment supply from river catchments rich in ultramafic rocks (ophiolite sequences of Cecina and Campiglia areas), with subsequent transport via the longshore drift. On the other hand, high As concentrations in the Campiglia region and along the southern stretch of coast reflect leaching of felsic volcanic and plutonic parent rocks and hydrothermal products related to the Tuscan and Roman magmatic provinces cropping out in the Fiora, Albegna, and Cornia river catchments.This study shows that coastal sediment derived from particular source rocks is likely to contain potentially harmful metals in predictable proportions, which may easily exceed maximum allowable concentrations. Assessing spatial distribution of such metals based on catchment geology and sediment transport pathways may help separate natural concentrations from the anthropogenic contribution, providing a valuable source of information for appropriate remediation strategies and management options.

Drainage and Sedimentary Responses to Dynamic Topography

AbstractDynamic topography due to mantle flow contributes to shaping Earth's evolving landscapes by affecting sediment routing, which has rarely been explored in source‐to‐sink contexts. Here we design a generic model to investigate the impact of dynamic topography on both landscape evolution and stratigraphic formations. An imposed wave of dynamic topography propagates laterally under a fixed continent, exerting transient surface uplift and subsidence. We find that a migrating dynamic topography can induce significant drainage reorganizations and affect sediment routing from source to sink. Variations in sediment supply driven by the lateral migrating dynamic topography contribute to the formation of diachronous unconformities along the margin. The predicted sediment flux histories are then put into perspective with the Cretaceous sedimentary records along the Southern African margins. Finally, we demonstrate that correlating offshore depositional hiatuses and unconformities has the potential to constrain the spatiotemporal evolution of past dynamic topography events.

Morphodynamic Resilience of Intertidal Mudflats on a Seasonal Time Scale

AbstractIntertidal mudflats are morphodynamic features present in many estuaries worldwide. Often located between vegetated shores and deep channels they comprise valuable ecosystems and serve to protect the hinterland by attenuating waves. Although mudflats are persistently present on yearly to decadal time scales, little is known on their morphodynamic adaptation to short‐term variations in forcing such as storms, spring‐neap tidal cycles, and sediment supply. This study aims to explore the morphodynamic resilience of mudflats to seasonal variations in forcing. First, we compare transects observed in South Bay, California, at 3‐ to 6‐monthly intervals. Second, we present the results of a process‐based, morphodynamic profile model (Mflat). Mflat is an open source, Matlab code that describes both cross‐shore and alongshore tidal hydrodynamics as well as a stationary wave model. An advection‐diffusion equation solves sediment transport while bed level changes occur by the divergence of the sediment transport field. Mflat reproduces the observed South San Francisco Bay profile in equilibrium with significant skill. Short‐term variations in hydrodynamic forcing and sediment characteristics disturb the profile mainly at the channel‐shoal edge. The modeled profile disturbance is consistent with observations. The modeled profile is remarkably resilient since it recovers to the equilibrium profile within weeks to months. The model results suggest that 3‐monthly observation intervals are probably too long to discriminate processes responsible for the profile disturbance. These processes may include variations in sediment supply, mudflat erodibility, and wave action as well as the spring‐neap tidal cycle.

Sediment Supply Explains Long‐Term and Large‐Scale Patterns in Salt Marsh Lateral Expansion and Erosion

AbstractSalt marshes often undergo rapid changes in lateral extent, the causes of which lack common explanation. We combine hydrological, sedimentological, and climatological data with analysis of historical maps and photographs to show that long‐term patterns of lateral marsh change can be explained by large‐scale variation in sediment supply and its wave‐driven transport. Over 150 years, northern marshes in Great Britain expanded while most southern marshes eroded. The cause for this pattern was a north to south reduction in sediment flux and fetch‐driven wave sediment resuspension and transport. Our study provides long‐term and large‐scale evidence that sediment supply is a critical regulator of lateral marsh dynamics. Current global declines in sediment flux to the coast are likely to diminish the resilience of salt marshes and other sedimentary ecosystems to sea level rise. Managing sediment supply is not common place but may be critical to mitigating coastal impacts from climate change.

2D Numerical Modeling on the Transformation Mechanism of the Braided Channel

This paper investigates the transformation mechanism between different channel patterns. A developed 2D depth-averaged numerical model is improved to take into account a bank vegetation stress term in the momentum conservation equation of flow. Then, the extended 2D model is applied to duplicate the evolution of channel pattern with variations in flow discharge, sediment supply and bank vegetation. Complex interaction among the flow discharge, sediment supply and bank vegetation leads to a transition from the braided pattern to the meandering one. Analysis of the simulation process indicates that (1) a decrease in the flow discharge and sediment supply can lead to the transition and (2) the riparian vegetation helps stabilize the cut bank and bar surface, but is not a key in the transition. The results are in agreement with the criterion proposed in the previous research, confirming the 2D numerical model’s potential in predicting the transition between different channel patterns and improving understanding of the fluvial process.

The effects of differential compaction on clinothem geometries and shelf-edge trajectories

AbstractThe geometry of basin-margin strata documents changes in water depth, slope steepness, and sedimentary facies distributions. Their stacking patterns are widely used to define shelf-edge trajectories, which reflect long-term variations in sediment supply and relative sea-level change. Here, we present a new method to reconstruct the geometries and trajectories of clinoform-bearing basin-margin successions. Our sequential decompaction technique explicitly accounts for downdip lithology variations, which are inherent to basin-margin stratigraphy. Our case studies show that preferential compaction of distal, fine-grained foresets and bottomsets results in a vertical extension of basin-margin strata and a basinward rotation of the original shelf-edge trajectory. We discuss the implications these effects have for sea-level reconstructions and for predicting the timing of sediment transfer to the basin floor.

Changes in stream morphology protected by best management practices under effects of upstream disturbances

Stream channels are usually more stable in forested watersheds. However, intensive land disturbances in forested watersheds may disrupt the balance between flow and sediment supply, and result in variations in stream morphology even in the presence of well-designed best management practices (BMPs). This study evaluated the impacts of upstream land disturbances on downstream stream morphology where streamside management zones (SMZs) were present in two small adjacent watersheds in Auburn, Alabama, USA. Field surveys including the measurements of channel cross sections at bankfull stage were conducted at 12 survey sites over an 18-month period. Both in-stream sediment deposition and erosion were observed downstream of the disturbed areas in the study watersheds. As a result, channel cross sections exhibited very dynamic patterns changing frequently over short time periods. Overall, the dominant process was in-stream deposition in both watersheds due to large amount of sediment delivered from upstream-disturbed areas. In spite of the dynamic patterns of the channel cross sections in response to upstream disturbances, the commonly used parameters of Rosgen stream classification remained stable, suggesting that the upstream disturbances did not lead to changes in stream classification. In general, bank erosion was not observed. Therefore, it is likely that SMZs in each watershed were sufficient to stabilize streambanks by hindering in-stream bank erosion. Moreover, the poorly designed BMPs such as silt fences and straw bales near the disturbed area seemed insufficient to balance the variations in sediment supply under the impacts of upstream disturbances. This study emphasized that proper installation and continuous monitoring of BMPs should play a critical role on watershed management. It also indicated that watershed management should be handled using a holistic approach with well-distributed BMP applications within the entire watershed.

Origin and Evolution of Stacked Cut-and-fill Structures On the Southwestern Margin of the Ulleung Basin, East Sea (Japan Sea)

AbstractMultichannel seismic reflection profiles and well data were analyzed to unravel the origin and depositional history of stacked cut-and-fill structures (CF) in the southwestern margin of the Ulleung Basin, East Sea. The CFs in a syn-compressional megasequence are characterized by discontinuous, low-amplitude, chaotic, and transparent seismic reflections. They display both U-shaped and V-shaped morphologies along their lengths. The CFs are thickest and widest at the shelf edge and taper both landward and basinward. Based on the stratigraphic position, the CFs are found in three depositional sequences (DS8–DS10). Thirty CFs have been identified that range from 0.5 to 8.8 km in width and 58 to 453 m in thickness (assuming a 2000 m/s seismic velocity of the sediments). The larger and numerous CFs occurred in the middle depositional sequence. Seismic characteristics, spatial distribution, hundred-meter-scale incisions, and high gamma-ray responses indicate that the CFs were caused by submarine canyons. During the period of DS8, small CFs were formed locally on the shelf margin, and were little influenced by the deformation of the thrust-fold (Dolgorae Thrust Belt). Extensive and numerous CFs in DS9 developed in the oversteepened shelf margin, where uplift of both the thrust-fold and anticline (Gorae V structure) occurred simultaneously, and where a large volume of sediment was supplied. During the period of DS10, a general decreasing pattern in the occurrence and dimensions of the CFs resulted from waning tectonic activity of the thrust-fold that reduced sediment supply. Consequently, this study suggests that variation in contractional tectonic activity and sediment supply, associated with the back-arc closure of the East Sea, mainly controlled the evolution of the CFs rather than eustasy.

From quantitative 3D seismic stratigraphy to sequence stratigraphy: Insights into the vertical and lateral variability of shelf-margin depositional systems at different stratigraphic orders

Abstract A major challenge in sequence stratigraphy is objectively identifying stratigraphic surfaces and sequences across multiple scales of observation. Identification is commonly dependent on the resolution of the data used (i.e., seismic vs. well data), its dimension (i.e., 1D vs. 2D vs. 3D) or the criteria chosen to select sequence boundaries. Through shelf-edge trajectory analysis, the clinothem (i.e., highest order seismic sequence identified on seismic data) can constitute the elementary building block of an observation-based and data-driven quantitative workflow to develop sequence stratigraphic frameworks across different orders and ranks of hierarchy. Here, we use high-quality 3D seismic data to interpret a Late Tithonian–Early Cretaceous shelf margin, the Lower Barrow Group (LBG), developed in the Northern Carnarvon Basin on the North West Shelf of Australia. Based on full-volume seismic interpretation techniques that integrate the 3D variability of the data when identifying seismic unconformities, a high-resolution seismic stratigraphic framework was built (73 interpreted clinothems with an average time duration of ~63,000 yrs). The computation of high-frequency shelf-edge trajectory angle (Tse) curves on selected seismic cross-sections is used to objectively pick sequence stratigraphic surfaces based on the accommodation succession method, thereby highlighting small changes in trajectory and proposing a method reproducible by interpreters based on the same quantitative data. Within the D. lobispinosum interval (142.3–140.9 Ma), the definition of stratigraphic sequences and composite stratigraphic sequences through this workflow is used to discriminate the controls at high and low temporal frequency on the vertical and lateral variability (which is here quantified) of this shelf-slope-basin system. The results show that the high-frequency interplay between short-term glacio-eustasy (i.e., Milankovitch eccentricity cycles of ~100,000 yrs) and sediment supply (locus of fluvial input along the margin) impacted the three-dimensional stratigraphic architecture of the LBG. In contrast, tectonic subsidence had a significant impact on the stratigraphic architecture of the LBG within the main depocentre at lower temporal frequency by overprinting the eustatic signal and accelerating/decelerating the rates of accommodation creation. However, identification of long-term glacio-eustatic Milankovitch cycles (~400,000 yrs) outside the main depocentre, where the rates of accommodation creation due to rift-related subsidence are moderate, also suggests low-frequency eustatic control. Therefore, the vertical and lateral variability of the LBG results from variations in sediment supply and subsidence regime under local (i.e., process regime, currents), regional (i.e., tectonics) and global (i.e., eustasy, climate) forcing parameters interplaying across timescales. In contrast to standard sequence stratigraphic workflows that are based on model-dependent choices to select sequence boundaries, quantitative 3D seismic stratigraphy constitutes an improved method to interpret 3D seismic data in shelf-margin depositional systems within a sequence stratigraphic framework, which provides an observation-based and model-independent tool allowing the definition of stratigraphic sequences with results that are reproducible across multiple stratigraphers. This work highlights the need for developing new sequence stratigraphic tools and methods that integrate the 4D variability of depositional systems and moves beyond the two-dimensionality inherent to current sequence stratigraphic methods. Quantitative 3D seismic stratigraphy represents a first step towards the creation of 3D sequence stratigraphic workflows that could improve the prediction of stratigraphic patterns and facies relationships (source, reservoir, seal distribution) across shelf margins.

Disentangling the relative impacts of climate change and human activities on fluvial sediment supply to the coast by the world\u2019s large rivers: Pearl River Basin, China

The world’s large rivers are under stress and experiencing unprecedented changes in hydrology, ecosystems, and fluvial sediment loads. Many of these rivers terminate at the great deltas of the world (home to 500 million people), which depend on fluvial sediments for their very existence. While fluvial sediment loads of large rivers have already been greatly modified by human activities, climate change is expected to further exacerbate the situation. But how does the effect of climate change on fluvial sediment loads compare with that of human impacts? Here, we address this question by combining historical observations and 21st century projections for one of the world’s largest 25 rivers containing two mega dams; Pearl River, China. Our analysis shows that variations in fluvial sediment supply to the coast from the Pearl river over a ~150 year study period are dominated by human activities. Projected climate change driven 21st century increases in riverflow will only compensate for about 1% of the human induced deficit in sediment load, leading to the coastal zone being starved of about 6000 Mt of sediment over the remainder of this century. A similar dominance of human impacts on fluvial sediment supply is likely at other heavily engineered rivers.

Continuous improvement of laboratory quality systems through upper management support: Lodwar county referral hospital (LCRH), Kenya experience

Pliocene and Pleistocene sediments from West Turkana (Kenya, East African Rift System) form emblematic syn-rift successions for understanding the evolution of extensional basin and continental rifting. They also constitute world-renowned fossil-bearing strata from which >500 hominin fossils were discovered over the past decades, with >100 inventoried archeological sites. However, associated sedimentary dynamics and architectures as well as paleoenvironments are only partially reconstructed and the relative contribution of climate and tectonism to paleoenvironmental change over time remains unclear. Here, through the interpretation of sedimentary facies, the delineation of sequences and the analysis of δ13C in soil carbonates, we provide the first exhaustive reconstruction from ~4.00 to ~0.75 Ma of (i) fluctuations of the paleolake that occupied the Turkana Depression, (ii) the successive sedimentary dynamics and related paleolandscapes that characterized the West Turkana area and (iii) respective roles of climate and tectonism in the sedimentation. We show evidence for seven major transgression-regression (T-R) cycles between ~4.00 and ~ 0.75 Ma superimposed locally by lower amplitude T-R cycles. Comparing the sedimentological interpretations and the δ13C values in soil carbonates (literature data), we reveal that fluctuations of rainfall over the Ethiopian Dome, which hosts the drainage basin of the Omo River — the main tributary of Lake Turkana — controlled high-amplitude lake level fluctuations during the Plio-Pleistocene period. We also demonstrate that vegetation and tree cover evolved differently in the Omo Valley and West Turkana. Furthermore we outline that two different sedimentary systems reflecting two distinct modes of sedimentation alternated through times in the West Turkana area as a response to the variations in sediment supply coming from the western rift shoulder (i.e. Lapurr Range) that alternatively generated wave- or river-dominated sedimentary systems. In conclusion, we reveal that climate regulated water input, paleolake water-level fluctuations and vegetation. Tectonism determined sediment supply to the basin controlled in West Turkana by pulses of increased activity of the main border fault (i.e., the Murua Rith Lapurr Fault).