Depositional Events Research Articles

7Be/210Pbxs Ratio-Derived Age and Residence Time of Suspended Sediments in Galveston Bay

The winds associated with the passage of meteorological fronts cause waves that induce sediment remobilization/resuspension, especially within shallow estuaries such as Galveston Bay. The passage of cold fronts, collectively, on an annual to decadal basis, generate more sediment resuspension than most hurricanes and tropical storms. With a warming climate, the intensity of all meteorological events is shifting toward having greater impacts on these biologically productive environments. To better understand sediment resuspension within the bay, water samples were collected during frontal passages at two locations in Galveston Bay, including one location in the middle portion of the bay and another closer to the mouth of the bay. By collecting precipitation, water samples in both the middle and lower bay, and measuring the ratio of 7Be/210Pbxs in these samples; we quantified the residence times of total suspended sediment (TSS) in middle and lower Galveston Bay. Our results showed that suspended sediment age increased and percent of new suspended sediment decreased along the axis from the middle bay to the lower bay. This results from the initial introduction of newly labeled isotopes and suspended load coming from fluvial discharges which enter at the top of the bay and travel through the bay. The age of suspended sediment from the first sampling event was 70 ± 10 days, whereas the age in the second event was 16 ± 3 days greater. In the last sampling event, the age of suspended sediment event was 35 ± 7.4 days younger than the second, suggesting that the majority of suspended sediments was likely transported entirely out of the bay by the second cold front, prior to the final sampling event. This indicates that there are longer suspended sediment residence times when the water is trapped within the bay. Our estimated residence time of suspended sediments (51–105 days) suggest the particle-bound contaminants adsorb to suspended sediment may spend months suspended in the bay before exiting the bay or being accreted into the bay sediment column, increasing the exposure time of living organisms to various particle-bound contaminants.

Taphonomic and spatial analyses from the Early Pleistocene site of Venta Micena 4 (Orce, Guadix-Baza Basin, southern Spain)

Venta Micena is an area containing several palaeontological sites marking the beginning of the Calabrian stage (Early Pleistocene). The richness of the fossil accumulation including species of Asian, African and European origin, makes Venta Micena a key site for the the palaeoecological and palaeoenvironmental study of southern Europe during the Early Pleistocene. Thus, research has been focused on Venta Micena 3, which was originally interpreted as a single palaeosurface associated with a marshy context, in which most of the fauna was accumulated by Pachycrocuta brevirostris. Recent excavations have unearthed a new site, Venta Micena 4, located in the same stratigraphic unit (Unit C) and in close proximity to Venta Micena 3. Here we show the first analyses regarding the taphonomic and spatial nature of this new site, defining two stratigraphic boundaries corresponding to two different depositional events. Furthermore, the taphonomic analyses of fossil remains seem to indicate a different accumulative agent than Pachycrocuta, thus adding more complexity to the palaeobiological interpretation of the Venta Micena area. These results contribute to the discussion of traditional interpretations made from Venta Micena 3.

Molecular Markers of Biogenic and Oil-Derived Hydrocarbons in Deep-Sea Sediments Following the Deepwater Horizon Spill

Following the Deepwater Horizon oil spill (DWHOS), the formation of an unexpected and extended sedimentation event of oil-associated marine snow (MOSSFA: Marine Oil Snow Sedimentation and Flocculent Accumulation) demonstrated the importance of biology on the fate of contaminants in the oceans. We used a wide range of compound-specific data (aliphatics, hopanes, steranes, triaromatic steroids, polycyclic aromatics) to chemically characterize the MOSSFA event containing abundant and multiple hydrocarbon sources (e.g., oil residues and phytoplankton). Sediment samples were collected in 2010–2011 (ERMA-NRDA programs: Environmental Response Management Application – Natural Resource Damage Assessment) and 2018 (REDIRECT project: Resuspension, Redistribution and Deposition of Deepwater Horizon recalcitrant hydrocarbons to offshore depocenter) in the northern Gulf of Mexico to assess the role of biogenic and chemical processes on the fate of oil residues in sediments. The chemical data revealed the deposition of the different hydrocarbon mixtures observed in the water column during the DWHOS (e.g., oil slicks, submerged-plumes), defining the chemical signature of MOSSFA relative to where it originated in the water column and its fate in deep-sea sediments. MOSSFA from surface waters covered 90% of the deep-sea area studied and deposited 32% of the total oil residues observed in deep-sea areas after the DWHOS while MOSSFA originated at depth from the submerged plumes covered only 9% of the deep-sea area studied and was responsible for 15% of the total deposition of oil residues. In contrast, MOSSFA originated at depth from the water column covered only 1% of the deep-sea area studied (mostly in close proximity of the DWH wellhead) but was responsible for 53% of the total deposition of oil residues observed after the spill in this area. This study describes, for the first time, a multi-chemical method for the identification of biogenic and oil-derived inputs to deep-sea sediments, critical for improving our understanding of carbon inputs and storage at depth in open ocean systems.

Mass balance of Neogene sediments in the Colombia basin relationship with the evolution of the Magdalena and Cauca River basins

The Colombia basin contains large volumes of sediment accumulated during the last 17 My. The use of isochore maps, exploratory wells, micropaleontological and geochronological dates has enabled us to estimate the volumes of sediment and accumulation rates in this basin. The analysis of source of sediments and exhumation data from the Northern Andes of South America led to the definition of areas and thicknesses of material eroded during the Neogene - Quaternary, to obtain volumes or material eroded from the continent that can be correlated with sediment volumes accumulated in the Colombia Basin. The analyzed sediment volumes suggest that during the last 17 My ~72.06x1015 Tons accumulated in the Colombia Basin, while ~ 7.16x1013 Tons accumulated in the continental catchment areas. The sedimentation in the Colombian Basin has occurred at variable rates, with values ranging from 55 MTons/My to 295 MTons/My, with a peak of 803 MTons/My in the early Pleistocene (between 2.4 and 2.2 Ma). The evaluation between the total volumes of sediment accumulated in the offshore and onshore, suggests that in the continental part of the basin less than 4% of the total volume of eroded sediment is trapped and, therefore, the behavior of the accumulation rates calculated in the offshore directly reflect the relief evolution of South America’s Northern Andes. It seems, at large, that the lithospheric convergence rates and subduction angle (South America vs Nazca and Meso Atlantic opening) have controlled the regional exhumation of the Northern Andes, with the exception of the Pleistocene high sedimentation event, which seems to coincide with local events such as the collision of the Panama Arch against Western Antioquia. It may be concluded that thanks to this collision, drainage systems such as those of the Magdalena and Cauca rivers were modified, which resulted in the formation of the Magdalena Submarine Fan.

Quaternary history of the Ayot Paleogene Outlier, Southeast England: A field and laboratory case-study in local geology with regional implications

Despite limited exposures, detailed field mapping and sedimentological analyses – particle size, clast petrography and fine-sand mineralogy (plus limited coarse silt and clay mineralogy) – have elucidated the ages, provenance and depositional environments of the complex and controversial Quaternary deposits covering the Ayot Paleogene Outlier. Most of the sediments were largely derived directly and/or indirectly from local facies of the Woolwich and Reading Formation. The oldest deposits are (Pre-)Pastonian proto-Thames gravels overlain by thin sands, which collectively represent crucial evidence for the earliest (Stoke Row) terrace of the proto-Thames. These materials were later thrust southwards by the Anglian ice close to its margin, which deposited a thin yet heterogeneous till at Ayot. This unit is correlated with the Ware Till, suggesting that the Anglian ice was thicker during the earlier of its two major southwestward incursions into the Vale of St Albans. An aeolian mantle was deposited on the Outlier during the Late Devensian; most of the blown material was incorporated into the upper regions of the till but some accumulated in depressions to form brickearths that resemble some Chiltern Brickearths. A colluvial apron developed during the Holocene, together with three swallow-holes. Some of these depositional events were separated by periods of poorly-preserved pedogenesis.

EVENT STRATIGRAPHY AND CORRELATION PROBLEMS OF THE ORDOVICIAN STRATA OF GORNY ALTAI AND SALAIR

Study of the Ordovician sedimentary sequences of Gorny Altai and Salair has revealed lithological and paleontological features correlating with global sedimentary events:(1) The Acerocare Regressive Event (an initial event in the Early Tremadocian);(2) Black Mountain Transgressive Event (Early Tremadocian);(3) Peltocare Regressive Event (Tremadocian);(4) Kelly Creek Regressive Event (Late Tremadocian);(5) Ceratopyge Regressive Event (Late Tremadocian);(6) Billingen Transgressive Event (Early Floian);(7) Stein Lowstand Event (Middle Darriwilian);(8) Vollen Lowstand Event (Sandbian);(9) Arestad Drowning Event (Middle Sandbian);(10) Frognerkilen Lowstand Event (Early Katian);(11) Linearis Drowning Events 1 and 2 (Middle Katian);(12) Terminal Husbergoya Lowstand Event (Hirnantian); and(13) Hirnantian Lowstand Event (HICE) (Late Ordovician).The chronostratigraphic levels with traces of the global sedimentary events in the Uymen-Lebed structural-facies zone (SFZ) (Gorny Altai) differ from those in the Charysh-Inya and Anui-Chuya SFZ (Altai). In the Ordovician, the Altai basin located in the Charysh-Inya and Anui-Chuya SFZ was a marine area separated from both the Uymen-Lebed basin and the coeval Salair basin. The traces of the global sedimentary and/or biotic events in the Altai and Salair sections can be used as a precise basis for direct correlation of the local stratigraphic units with the units of the International Stratigraphic Chart.

Petrogenesis and tectonic significance of the middle Neoproterozoic highly fractionated A-type granite in the South Qinling block

AbstractThe South Qinling block, a segment of the Yangtze craton involved in the Qinling–Dabie orogen, is critical for understanding the tectonic evolution of eastern China. However, the tectonic setting of the South Qinling block and the northern margin of the Yangtze block during middle Neoproterozoic time has long been the subject of debate, with two distinctly different models (continental rift or volcanic arc) proposed. Here, a comprehensive study of zircon U–Pb geochronology and geochemistry has been carried out on the Chengwan granitic pluton from the Suizao terrane in the South Qinling block. The granites are monzogranite and syenogranite in lithology, and are mainly composed of potash feldspar, quartz, plagioclase and biotite. This suite has long been regarded as a Palaeozoic magmatic pluton, but zircon U–Pb ages of 809 ± 9 Ma and 816 ± 4 Ma are obtained in this study. The granites are metaluminous to strongly peraluminous with high alkali contents, and exhibit highly fractionated features, including high SiO2, low Zr/Hf ratios, rare earth element tetrad effects and enrichment of K and Rb. They show Hf–Nd isotopic decoupling, which may be genetically related to their petrogenetic process. Based on the geochemical features and the positive εHf(t) values of the zircons, it is indicated that the granites may have been derived from partial melting of juvenile tonalitic rocks by biotite breakdown under fluid-absent conditions. The Chengwan granite geochemically belongs to the A2-subtype granites, suggesting that it might have formed in a post-orogenic tectonic setting. The highly fractionated A-type granite in this study may represent extensional collapse shortly after the collisional events in the South Qinling block, and thus indicate a tectonic regime switch, from compression to extension, as early as middle Neoproterozoic time. Integrating our new data with documented magmatic, metamorphic and sedimentary events during middle Neoproterozoic time in the region may support a continental rift model, and argues against arc models.

Assessing the hydrological and geomorphic behaviour of a landscape evolution model within a limits‐of‐acceptability uncertainty analysis framework

AbstractLandscape evolution models (LEMs) have the capability to characterize key aspects of geomorphological and hydrological processes. However, their usefulness is hindered by model equifinality and paucity of available calibration data. Estimating uncertainty in the parameter space and resultant model predictions is rarely achieved as this is computationally intensive and the uncertainties inherent in the observed data are large. Therefore, a limits‐of‐acceptability (LoA) uncertainty analysis approach was adopted in this study to assess the value of uncertain hydrological and geomorphic data. These were used to constrain simulations of catchment responses and to explore the parameter uncertainty in model predictions. We applied this approach to the River Derwent and Cocker catchments in the UK using a LEM CAESAR‐Lisflood. Results show that the model was generally able to produce behavioural simulations within the uncertainty limits of the streamflow. Reliability metrics ranged from 24.4% to 41.2% and captured the high‐magnitude low‐frequency sediment events. Since different sets of behavioural simulations were found across different parts of the catchment, evaluating LEM performance, in quantifying and assessing both at‐a‐point behaviour and spatial catchment response, remains a challenge. Our results show that evaluating LEMs within uncertainty analyses framework while taking into account the varying quality of different observations constrains behavioural simulations and parameter distributions and is a step towards a full‐ensemble uncertainty evaluation of such models. We believe that this approach will have benefits for reflecting uncertainties in flooding events where channel morphological changes are occurring and various diverse (and yet often sparse) data have been collected over such events.

BUILDING HIGH-PRECISION AMS14C BAYESIAN MODELS FOR THE FORMATION OF PERI-ABANDONMENT DEPOSITS AT BAKING POT, BELIZE

ABSTRACTDeposits linked to abandonment have been widely recorded across the Maya lowlands, associated with the final activities occurring in ceremonial areas of Classic Maya centers. Various models have been applied to explain the activities that lie behind the formation of these contexts, including those linked to rapid abandonment (e.g., warfare) and others focused on more protracted events (termination rituals, and/or pilgrimages). Here, we assess Bayesian models for three chronological scenarios of varying tempo to explain the formation of peri-abandonment deposits at Baking Pot, Belize. Using stratigraphic information from these deposits, hieroglyphic dates recovered on artifacts, and direct dates on human skeletal remains and faunal remains from distinct layers in three deposits in Group B at Baking Pot, we identify multiple depositional events that spanned the eighth to ninth centuries AD. These results suggest that the processes associated with the breakdown of institutionalized rulership and its command of labor to construct and maintain ceremonial spaces were protracted at Baking Pot, with evidence for the final depositional activity dated to the mid-to-late ninth century. This interval of deposition was temporally distinct from the earlier deposition(s) in the eighth century. Together, these data offer a detailed view of the end of the Classic period at Baking Pot, in which the ceremonial spaces of the site slowly fell into disuse over a period of more than a century.

Geology and history of the Malea Planum region: A new view of Mars’ oldest large volcanic province

Geology and history of the Malea Planum region: A new view of Mars’ oldest large volcanic province

Multi-Proxy Records of Late Holocene Flood Events From the Lower Reaches of the Narmada River, Western India

Analyses of a fluvial sedimentary sequence from the lower reaches of the Narmada River establish a record of rhythmic cycles of sediment facies that represent floods during the late Holocene. The south-west Indian monsoon strongly influences the study area, and heavy rainfall or cyclones which originate from either the Bay of Bengal or the Arabian Sea, also affect the region. Optically stimulated luminescence dating places the 8 m thick sediment sequence in the climate transition phase which ranges from the Medieval Warm Period to the Little Ice Age. Multi-proxy analyses including high-resolution granulometry, magnetic susceptibility, ferromagnetic mineral concentration, facies major oxide geochemistry, and micro-fossil records (from two sedimentary units) are used to study these late Holocene flood events. The latter are characterised by multiple sediment facies, depositional events, changes in channel morphology, and distinctive flood signatures. Integration of these records enables to identify two distinct aggradations viz. phase I and phase II, as well as a relative change in channel morphology. The study describes 11 flooding events and their imprints over multi-proxy records. Historic documents and instrumental records from the town of Bharuch referring to floods, movement of channel sand, channel shallowing, and the dysfunction of the ancient port of Bharuch further validate the inferences drawn from the sedimentary sequence. The study exemplifies the need to use high resolution and multi-proxy studies to interpret paleoflood records and climate signatures in order to build archives of monsoonal rivers.

Middle Pleistocene to Holocene palaeoenvironmental evolution of the south-eastern Alpine foreland basin from multi-proxy analysis

The multidisciplinary analysis of two long sedimentary successions of continental and shallow marine deposits from the Venetian plain (NE Italy) provides new data on the stratigraphic architecture and the landscape evolution of the south-eastern Alpine foreland basin during the last 210–220 ka, with further evidences of a warm temperate phase older than MIS 8.We present and discuss a detailed multi-proxy data set from these successions (GER1 and CB cores). The results of stratigraphic, palynological and micropalaeontological analyses are cross-interpreted, showing the potentiality of building a composite section of two close continental successions within the same alluvial system, the Brenta megafan, with 15 km distance between cores along a downstream direction. The chronology of the upper part of the cores is supported by radiocarbon dating, showing the presence of Last Glacial Maximum (LGM) and post-LGM fluvial deposits. Lower down, the estimated chronology relies on the tight integration between palynostratigraphy and lithostratigraphy, on the recognition of main unconformities, as well as on the correlation with other regional biostratigraphic records and the Northern Hemisphere/global isotopic record.The only marine transgression recorded in the studied successions is attributed to the MIS 7.3 and represents the basal tiepoint for the correlation between the two cores. Below the MIS 7.3 transgressive marine surface there is a fluvial succession with weakly-developed palaeosoils and a poor pollen content suggesting cold climate (possibly MIS 8), that lies on top of a thick peat layer showing palynological evidence of a warm temperate climate. The occurrence of well-preserved Pterocarya and Carya pollen in the basal peat level (GER1 core) is compared to that of other pollen sequences in Europe, providing new insights for the chronological framing of the problematic last occurrence of these taxa in the southern alpine area.Whilst mixed temperate forest persisted throughout MIS 7c-7a, conifers spread during MIS 6. By this time, a glaciofluvial aggradation phase is recorded, highlighting the strong relationship between glacial maxima and alluvial aggradation in the Venetian plain. None of the drilling sites were reached by the Last Interglacial sea transgression. However, the Eemian forest signature is well recorded in CB core, and the following Early to Middle Würm stadial-interstadial sequence is clearly outlined thanks to the joint analysis of the two successions. Broad-leaved thermophilous forests disappeared at the end of the Early Würm and only Pinus and Betula persisted throughout the LGM, during which a chronologically well-constrained glaciofluvial aggradation occurred. The last depositional event corresponds to the post-LGM cut-and-fill of fluvial incised valleys in GER1 core, and to soil evolution and very thin burial by Brenta River fluvial deposits in CB core. The comparison between the results of this study with data of previous deep cores in the distal alluvial plain remarks an increasing long-term subsidence towards Venice area.

A solution to the Albian fit challenge between the South American and African plates based on key magmatic and sedimentary events late in the rifting phase in the Pernambuco and Paraíba basins

Global, full-fit plate reconstruction models predict a significant presence of oceanic floor in Northeast Brazil and West Africa during Albian time, while rifting was under earlier stages in the Pernambuco and Paraíba basins. We call it the Albian breakaway gap. Sedimentary, biostratigraphic and geochronological data from the Pernambuco and Paraíba basins challenge the timing of sea floor spreading in this region. In the onshore Pernambuco Basin, there are abundant outcrops of syn-rift continental siliciclastic rocks of Aptian–Albian age interbedded with intrusive and extrusive magmatic rocks (dated ca. 102 ± 2 Ma). Salt has been recognized on seismic data within the Pernambuco Basin, but there is no record or seismic indication of salt within the Paraíba Basin. Three interpreted seismic transects provide important clues about the type of intraplate margin developed in this region. Syn and post-rift magmatism within the onshore and offshore segments of the Pernambuco Basin indicate significant melt production during (and after) the main stretching phase. On the other hand, the abruptly-necked Paraíba Basin displays seismic evidence of seaward dipping reflectors, side by side with rift sediments, suggesting the development of an Albian volcanic intraplate margin. In addition, gravity and magnetic data, on the Brazilian side, suggest a wide transition from continental to pure oceanic crust in the Pernambuco and Paraíba basins, as well as at their African counterparts: Douala, Rio Del Rey, and Lower Benue, where either oceanic crust or proto-oceanic wide crust has been recognized. Instead of pure oceanic crust, as predicted by globally balanced plate motion reconstructions, the continent-ocean transitional domain was composed in part by stretched continental crust and partially by a wide embryonic or proto-oceanic crust. In fact, a continuous and regional mid ocean ridge was only defined at the end of Albian/early Cenomanian when the South America plate was completely separated from the African plate.

Event-dominated transport, provenance, and burial of organic carbon in the Japan Trench

The delivery of organic carbon (OC) to the ocean's deepest trenches in the hadal zone is poorly understood, but may be important for the carbon cycle, contain crucial information on sediment provenance and event-related transport processes, and provide age constraints on stratigraphic sequences in this terminal sink. In this study, we systematically characterize bulk organic matter (OM) and OC signatures (TOC/TN, δ13C, 14C), as well as those from application of serial thermal oxidation (ramped pyrolysis/oxidation) of sediment cores recovered along an entire hadal trench encompassing high stratigraphic resolution records spanning nearly 2000 years of deposition. We analyze two cores from the southern and northern Japan Trench, where submarine canyon systems link shelf with trench. We compare results with previously published data from the central Japan Trench, where canyon systems are absent. Our analyses enable refined dating of the stratigraphic record and indicate that event deposits arise from remobilization of relatively surficial sediment coupled with deeper erosion along turbidity current pathways in the southern and central study site and from canyon flushing events in the northern study site. Furthermore, our findings indicate deposition of predominantly marine OC within hemipelagic background sediment as well as associated with event deposits along the entire trench axis. This implies that canyon systems flanking the Japan Trench do not serve as a short-circuit for injection of terrestrial OC to the hadal zone, and that tropical cyclones are not major agents for sediment and carbon transfer into this trench system. These findings further support previous Japan Trench studies interpreting that event deposits originate from the landward trench slope and are earthquake-triggered. The very low terrestrial OC input into the Japan Trench can be explained by the significant distance between trench and hinterland (>180 km), and the physiography of the canyons that do not connect to coast and river systems. We suggest that detailed analyzes of long sedimentary records are essential to understand OC transfer, deposition and burial in hadal trenches.

Late Pleistocene rates of rock uplift and faulting at the boundary between the southern Coast Ranges and the western Transverse Ranges in California from reconstruction and luminescence dating of the Orcutt Formation

AbstractThe western Transverse Ranges and southern Coast Ranges of California are lithologically similar but have very different styles and rates of Quaternary deformation. The western Transverse Ranges are deformed by west-trending folds and reverse faults with fast rates of Quaternary fault slip (1–11 mm/yr) and uplift (1–7 mm/yr). The southern Coast Ranges, however, are primarily deformed by northwest-trending folds and right-lateral strike-slip faults with much slower slip rates (3 mm/yr or less) and uplift rates (<1 mm/yr). Faults and folds at the boundary between these two structural domains exhibit geometric and kinematic characteristics of both domains, but little is known about the rate of Quaternary deformation along the boundary.We used a late Pleistocene sedimentary deposit, the Orcutt Formation, as a marker to characterize deformation within the boundary zone over the past 120 k.y. The Orcutt Formation is a fluvial deposit in the Santa Maria Basin that formed during regional planation by a broad fluvial system that graded into a shoreline platform at the coast. We used post-infrared–infrared-stimulated luminescence (pIR-IRSL) dating to determine that the Orcutt Formation was deposited between 119 ± 8 and 85 ± 6 ka, coincident with oxygen isotope stages 5e-a paleo–sea-level highstands and regional depositional events. The deformed Orcutt basal surface closely follows the present-day topography of the Santa Maria Basin and is folded by northwest-trending anticlines that are a combination of fault-propagation and fault-bend-folding controlled by deeper thrust faults. Reconstructions of the Orcutt basal surface and forward modeling of balanced cross sections across the study area allowed us to measure rock uplift rates and fault slip rates. Rock uplift rates at the crests of two major anticlinoria are 0.9–4.9 mm/yr, and the dip-slip rate along the blind fault system that underlies these folds is 5.6–6.7 mm/yr. These rates are similar to those reported from the Ventura area to the southeast and indicate that the relatively high rates of deformation in the western Transverse Ranges are also present along the northern boundary zone. The deformation style and rates are consistent with models that attribute shortening across the Santa Maria Basin to accommodation of clockwise rotation of the western Transverse Ranges and suggest that rotation has continued into late Quaternary time.

Understanding stream bank erosion and deposition in Iowa, USA: A seven year study along streams in different regions with different riparian land-uses

Agricultural activities such as row-cropping and grazing, have accelerated stream bank erosion. Accelerated stream bank erosion increases nonpoint source pollutants in aquatic ecosystems, significantly degrading them. Mitigating stream bank erosion is a priority worldwide, especially in agricultural watersheds. The objective of this study was to analyze the impacts of riparian land-use management on stream bank erosion and deposition, along with analyzing its temporal and spatial patterns. The study was conducted in three regions of Iowa (central, northeast and southeast) along 30 stream reaches adjacent to seven different riparian land-uses. The riparian land-uses were riparian forest buffers, grass filters, pastures with the cattle excluded from the stream, intensive rotational grazing, rotational grazing, continuous grazing and row crop fields. Seasonal erosion and deposition data (Spring, Summer and Autumn) were collected along these reaches for 5 years and yearly for the following two years. To analyze the data, conventional statistical methods (ANOVA and Tukey's test) along with innovative techniques (percentile plots, cumulative erosion curves and bubble charts) were utilized. Based on the analysis, of this extensive in time (seven years) and large in size (1500 pins measured 17 times in three regions) field dataset, major results were obtained in regard to stream bank erosion in Iowa, USA. Stream banks exhibited high year-to-year variation in erosion and deposition showcasing the need for long-term datasets to better understand stream bank erosion and deposition. Seasonal erosion, also had high variability with Spring recording the most erosion followed by Summer and Autumn. Certain seasons exhibited high stream bank erosion indicating that managers need to focus on these seasons, to reduce erosion effectively. In addition, seasonal measurements can highlight depositional events that might be masked with annual measurements. Riparian land-uses significantly impacted stream bank erosion. Riparian forest buffers and grass filters significantly mitigated stream bank erosion while traditional agricultural practices like continuous grazing and row-crop agriculture had accelerated stream bank erosion. Finally, the percentile plots, cumulative erosion curves and bubble charts captured some stream bank responses that would have been unnoticed using conventional statistical methods, allowing decision makers, stakeholders and the general public, to support and approve measures to mitigate this environmental problem. Nature-based solutions utilizing riparian perennial vegetation can sustainably mitigate stream bank erosion.

Grain-Size Analysis of Hurricane-Induced Event Beds in a New England Salt Marsh, Massachusetts, USA

Castagno, K.A.; Donnelly, J.P., and Woodruff, J.D., 2021. Grain-size analysis of hurricane-induced event beds in a New England salt marsh, Massachusetts, USA. Journal of Coastal Research, 37(2), 326–335. Coconut Creek (Florida), ISSN 0749-0208.Tropical cyclones pose a growing threat to coastal infrastructure and livelihood. Because instrumental and historic records are too short to help us understand interactions between tropical cyclones and climate on a longer scale, proxy records are the only means for reconstructing millennia of tropical cyclone impacts. This study determines grain-size trends in storm-induced overwash deposits along a transect of sediment cores from a salt marsh in Mattapoisett, Massachusetts, to characterize sorting trends and compare deposits associated with individual storms. The overwash deposits preserved within the high-marsh peat provide a record spanning the last two millennia. Building on a 2010 study, a different approach was used to accurately determine the grain-size distribution of overwash deposits from cores in a transect running perpendicular to the adjacent sandy/gravely barrier. Although maximum grain-size values are expected to decrease as distance from the barrier increases, not all event deposits that were studied follow this trend within uncertainty. Analysis of the storm event beds reveal a significant difference in settling trends between historic and prehistoric deposits, with historic deposits largely displaying landward-fining trends and prehistoric deposits largely displaying landward-coarsening trends. This suggests changes in the hydrodynamic or that geomorphic regime may have altered the way in which storm beds were deposited at this site. This new in-depth, transect-based approach has utility for improving the accuracy of future storm reconstructions, particularly for events for which no historic record exists.

Debris-Flow and Debris-Flood Susceptibility Mapping for Geohazard Risk Prioritization

ABSTRACT Regional-scale assessments for debris-flow and debris-flood propagation and avulsion on fans can be challenging. Geomorphological mapping based on aerial or satellite imagery requires substantial field verification effort. Surface evidence of past events may be obfuscated by development or obscured by repeat erosion or debris inundation, and trenching may be required to record the sedimentary architecture and date past events. This paper evaluates a methodology for debris-flow and debris-flood susceptibility mapping at regional scale based on a combination of digital elevation model (DEM) metrics to identify potential debris source zones and flow propagation modeling using the Flow-R code that is calibrated through comparison to mapped alluvial fans. The DEM metrics enable semi-automated identification and preliminary, process-based classification of streams prone to debris flow and debris flood. Flow-R is a susceptibility mapping tool that models potential flow inundation based on a combination of spreading and runout algorithms considering DEM topography and empirical propagation parameters. The methodology is first evaluated at locations where debris-flow and debris-flood hazards have been previously assessed based on field mapping and detailed numerical modeling. It is then applied over a 125,000 km2 area in southern British Columbia, Canada. The motivation for the application of this methodology is that it represents an objective and repeatable approach to susceptibility mapping, which can be integrated in a debris-flow and debris-flood risk prioritization framework at regional scale to support risk management decisions.

Combining 137Cs, 210Pb and dendrochronology for improved reconstruction of erosion–sedimentation events in a loess gully system (southern Poland)

AbstractDetailed knowledge on the past events of erosion and redeposition is necessary to assess the frequency and magnitude of soil degradation and to provide more complete data, among all, to calculate rainfall thresholds and to develop strategies for controlling erosion. Therefore, in this study, we aimed to obtain a more comprehensive and accurate reconstruction of erosion–sedimentation events in a gully system by combining analyses of 137Cs and 210Pb with dendrochronological dating in the same sediment profiles. We aimed to precisely determine the number and the age of erosion–sedimentation events, which led to the development of study deposits and to determine the type of erosion providing material for deposition in particular events. To this purpose, 136 soil samples and 62 roots and tree stems samples were collected in eight research profiles at the gully bottom. We compared the results obtained with the two methods. Isotope analysis allowed us to estimate more general age of sediments and the type of erosion that provided material for individual layers. Dendrochronology provided a more precise reconstruction of the age of soil degradation events. By combining both techniques, we determined rainfall events responsible for erosion and sedimentation in the studied gully since 1980s and a rainfall threshold of 60 mm day−1 for soil erosion and redeposition in the study area.

A tsunamigenic delta collapse and its associated tsunami deposits in and around Lake Sils, Switzerland

Large lacustrine mass movements and delta collapses are increasingly being considered as potential tsunamigenic sources and therefore hazardous for the population and infrastructure along lakeshores. Although historical reports document tsunami events in several lakes in Switzerland, and although the propagation of lake tsunamis has been studied by numerical wave modeling, only little is known about on- and offshore lacustrine tsunami deposits. In Lake Sils, Switzerland, a large prehistoric mass-movement deposit originating from the Isola Delta with a minimum estimated volume of 6.5 × 106 m3 and a basinal thickness of > 6 m in the seismic record has been identified by previous studies and radiocarbon dated to around 700 Common Era. Here, we combine (i) comprehensive sedimentological investigation of sediment cores recovered from the on- and offshore settings, (ii) mineralogical fingerprinting of the inflows from key catchments to characterize sediment provenance, and (iii) numerical tsunami modeling, to test the hypothesis of a tsunamigenic delta collapse in Lake Sils. We observe a clastic event deposit consisting of coarse-grained, fining-upward sand overlying an organic-rich peat deposit in the shallow water. This layer thins and fines landward on the coastal plain. Toward the deeper water (20–40 m), the deposit transforms into a thicker and more heterogeneous sediment package with multiple sequences of fining-upward sand and a well-pronounced clay cap at the top. Radiocarbon dating of the peat underlying the event deposit yields a maximum age of 225–419 calibrated Common Era. The tsunami models, which indicate wave heights reaching up to 5 m, simulate areas of inundation that coincide with the location of event deposits. Based on our results, we propose that the historically undocumented Isola Delta collapse generated a basin-wide tsunami that inundated the lakeshore, transporting large amounts of unconsolidated sediment along the lakeshore toward the coastal plain and into the deeper lake basin.