Sediment Accumulation Processes Research Articles

Pattern of spatial variability in granulometric and mineralogical characteristics across an ecologically sensitive sub-tropical wetland (Bihar, India)

Floodplain wetlands are dynamic systems undergoing frequent hydro-sedimentological changes. Tropical/subtropical wetlands have even more pronounced climatic and biological influences on the sediment dynamics. In the current study, a protected subtropical wetland in Bihar (India) has been assessed for its sedimentary and mineralogical status. Sediment characteristics and associated granulometric parameters are discussed to highlight the wetland's hydrogeomorphic character, energy dimension, and the depositional processes taking place. Statistical grain size parameters like graphic mean, graphic skewness, graphic kurtosis, and their interrelations studies have helped in understanding the sources of deposited materials. Multivariate statistics have identified, sand fractions, measures of central tendencies (mean, median, and mode), percent organic matter (%OM) and percent carbonates (%carbonates) as primary factors explaining the maximum variance in the data. The non-parametric Kruskal–Wallis test has identified %sand, %clay, electrical conductivity (EC), and %carbonates as the major factors responsible for significant spatial variability. The grain texture analysis shows that the majority of samples fall in the brackets of clayey silt; silty sand; and sand, silt, and clay. Common mineral components associated with these are quartz, feldspar, clay minerals, etc. The range for the mean grain size lies between 3Φ to 9Φ (Φ is diameter of the sediments) where most of the grain size distributions are symmetrically to fine symmetrically skewed, indicating intermediate energy to adjust to environmental conditions. The granulometric and physicochemical characteristics of the sediment samples also indicate the directional distribution pattern of sediment along the hydrological pathway. Future studies concentrating on the fluvial discharges of water and sediment will be highly insightful in reconstructing the past net sediment accumulation processes in the Baraila Wetland.

Thickener as an automatic control object

Introduction. Grain motion in the process of pulp sedimentation in a radial thickener was studied to use the typical links of the automatic control system. Research objective is to explore the possibility of describing the sedimentation process by means of typical links of the automatic control theory based on the physics of grain motion in a radial thickener and the equation of grain motion under laminar and turbulent flow conditions. Methods of research. Stokes’ law that determines the drag force resisting a solid sphere when it slowly moves forward in an unbounded viscous fluid (laminar motion) and the Newton– Rittinger law for the turbulent motion of grain formed the basis of the mathematical model, making it possible to develop a program that chooses a particular equation to calculate the grain sedimentation time in accordance with the grain size. The equations helped to obtain the sedimentation time and hence the time taken to reach the thickener’s bottom, which, in their turn, together with the fractional composition, determine the performance of the thickener. Transition curves were thereby obtained for various granulometric composition, percentage of ore in the pulp, thickener height, ore and pulp density. In the future, this made it possible to approximate the process of sediment accumulation by the equations of one or two lag blocks of the automatic control system. Research results. A computer program has been used that describes the process of sediment accumulation in a thickener, considering the granulometric composition as well as pulp and ore grain density. The program showed that the process of sediment accumulation in a thickener can be described with fair accuracy by a first-order lag block for laminar or turbulent grain motion. For a mixture of coarse and fine fractions, ore sedimentation can be approximated by two parallel lag blocks. Conclusions. Sedimentation process approximation by lag blocks, obtained with fair accuracy, can be used when analyzing, designing and adjusting sedimentation automatic control systems.

Two-dimensional model of flow and transport in porous media: Linking heterogeneous anisotropy with stratal patterns in meandering tidal channel deposits of the Venice Lagoon (Italy)

Understanding the internal structure of permeable and impermeable sediments (e.g. point-bars and tidal-flat deposits) generated by the evolution of meandering tidal channels is essential for accurate modeling of groundwater flow and contaminant transport in coastal areas. The detailed reconstruction of stratal geometry and hydraulic properties from measurements must be accompanied by depositional history information. In this work, we use high resolution reconstructions of ancient tidal channels of the Venice Lagoon (Italy) to drive 2D simulations of groundwater flow and transport, showing the importance of incorporating information on the sediment accumulation processes into the hydraulic characteristics and how horizontal anisotropy emerging from these processes significantly influences transport. Effective hydraulic conductivity is modeled with a heterogeneous 2D anisotropic tensor with principal directions aligned with observed sedimentation sequences. Comparison of flow and solute dynamics simulated using reconstructed and theoretical hydraulic properties show drastically different pathways of solute propagation.

Biostratigraphic ages and depositional environments of the upper Oligocene to lower Miocene Veldhoven Formation in the central Roer Valley Rift System (SE Netherlands-NE Belgium)

Abstract Discussions on the age and the depositional environments of the Veldhoven Formation and its members are persistent in Belgium and the Netherlands. Uncertainties on stratigraphy and the constructive process of sediment accumulation continue today as a result of lack of data on this succession within the Roer Valley Rift System. The present study provides new information on the bio- and lithostratigraphy and facies from two boreholes based on dinoflagellate cyst taxa. The results were correlated by gamma-ray logs towards other key boreholes in the region and show a good consistency for stratigraphy and depositional environments for the members of the Veldhoven Formation. After marginal to restricted marine conditions in the latest Rupelian (early Oligocene), the start of deposition of the Veldhoven Formation marked the transition towards a higher sea level, expressed by increased glauconite contents and gamma-ray values. The Voort Member in the lower part of the Veldhoven Formation has an early to late Chattian (Late Oligocene) age and comprises predominantly shallow marine (fluctuating restricted to open marine) conditions. The lithology in the lower part of this unit is often very clayey but is coarsening upward into sands. The superjacent Wintelre Member has a latest Chattian to early Aquitanian (early Miocene) age. This member is distinct by its clayey nature which is expressed by relatively high gamma-ray values. Earlier studies suggest a deeper marine facies for the Wintelre Member compared to the Someren and Voort members. However, the dinoflagellate cyst assemblages in this unit are mostly dominated by a single genus indicating a restricted marine setting, including salinities that deviate from normal marine conditions, most probably due to minor ventilation by narrow or lack of connection to the Atlantic Ocean. A glacio-eustatic sea-level fall around the Oligocene/Miocene boundary limited the sea coverage to the strongest subsiding areas, where deposition of the Wintelre Member is recorded, while non-deposition or erosion occurred in the surrounding highs, hence creating an isolated (sub)basin. The superjacent Someren Member was deposited during the late Aquitanian to middle Burdigalian and consists of shallow to open marine clayey fine sands. Increasing clay contents indicate a gradual development towards a higher sea level, which coincide with upward increasing gamma-ray values. The biostratigraphic results of this study suggest that no major hiatuses are present in the differentially subsiding blocks of the Roer Valley Rift System during the late Oligocene to early Miocene.

Impact of Flooding and Urbanisation on the Content of Heavy Metals in the Water and Bottom Sediments of the Amur River

The impact of floods on the migration activity of elements coming from urbanized territories to the Amur river was assessed. The influence of large cities on pollution of water and floodplain ecosystems is revealed. The content of heavy metals in water, bottom sediments, and small watercourses draining urban areas is characterized. The processes of sediment accumulation in the floodplain, their influence on the redistribution of elements and geochemical transformations in the soil space of floodplain soils are studied. Conditions for the accumulation of heavy metals in soils are described, their concentration levels and migration activity are determined. The role of organic matter in swamps and silts on water pollution and bottom sediments of the Amur river is shown. It was found that the main mass transfer of soluble substances and pollutants dispersed fractions of nailc is carried out by water flow during floods.

Microplastics on sandy beaches of the southern Baltic Sea

Microplastic occurrence and composition were investigated along the Polish coast (southern Baltic Sea) on 12 beaches differing in terms of intensity of their touristic exploitation, urbanisation and sediment characteristics. Their mean concentrations varied between 76 and 295 items per kg dry sediment. Fibres and plastic fragments were the dominant microplastic types. Overall, no relationship was found between their concentrations and sediment characteristics. Fine sediments were not identified as microplastic pollution traps. The highest microplastic concentrations were recorded at some urban beaches indicating that population density and the level of coastal infrastructure development are important factors affecting microplastic pollution level on beaches. On the other hand, microplastic concentrations in national parks did not differ substantially from the other beaches. Our results suggest that sediment accumulation processes may exceed microplastic accumulation, and overcome the effect of tourism and/or urbanisation, highlighting the role of the beach hydrodynamic status in structuring beach microplastic pollution.

The relative contribution of near-bed vs. intragravel horizontal transport to fine sediment accumulation processes in river gravel beds

Understanding flow-sediment interactions is important for comprehending river functioning. Fine sediment accumulation processes, in particular, have key implications for ecosystem health. However, the amount of fines generated by intragravel flows and later accumulated in gravel streambeds may have been underestimated, as the hydraulic-related driving transport mechanisms in play are not clearly identified. Specifically, the relative contribution of fines from upper vs. lower sediment layers in gravel beds is not well understood. By recreating flooded and dewatered conditions in an experimental flume filled with natural sediment, we estimated such contributions by observing and collecting intragravel transported fines that were later accumulated into a void in the middle of the sediment matrix. Near-bed transport in the upper sediment layers (named Brinkman load) during flooded conditions accounted for most (90%) of the accumulated fines. Intragravel transport in the lower sediment layers (named Interstitial load) was the sole source of transport and accumulation during dewatered conditions with steeper hydraulic gradients. Interstitial load accounted for 10% of the total transport during flooded conditions. Although small, such estimations demonstrate that hydraulic-gradient transport in the lower sediment layers occurs in spite of the contradicting analytical assessments. We provide a case study to challenge the traditional approaches of assessing intragravel transport, and a useful framework to understand the origin and relative contribution of fine sediment accumulation in gravel beds. Such knowledge will be highly useful for the design of monitoring programs aiding river management, particularly in regulated rivers.

Chronology and formation processes of the Middle to Upper Palaeolithic deposits of Ifri n'Ammar using multi-method luminescence dating and micromorphology

The existence of an early Upper Palaeolithic culture at the transition from the Middle Palaeolithic to the Upper Palaeolithic in North African cave sites is currently under debate. We studied Ifri n‘Ammar in North-East Morocco, which is one of the oldest settlement sites of anatomically modern humans (AMH) in the Maghreb and contains several sediment layers which are attributed to Middle and Upper Palaeolithic occupations. In order to investigate processes of sediment accumulation and postdepositional alteration, we studied thin sections from these levels. According to micromorphological analysis, aeolian input considerably contributed to sediment accumulation and postdepositional mixing by bioturbation occurred. We compared multiple and single-grain quartz and multiple-grain feldspar luminescence dating of three samples from corresponding sediment layers to achieve a comprehensive chronology. The single-grain dose distributions scatter strongly and the source of the scatter is unclear. We used an arithmetic mean to calculate the equivalent doses. Archaeological evidence and age control from radiocarbon dating was essential to interpret the data. Quartz and feldspar multiple-grain luminescence ages are between 15 and 80 ka. The central part of the profile shows an intermediate accumulation, which lacks specified lithic artefacts. This supports the idea of an occupational gap between Middle and Upper Palaeolithic layers.

Paleoenvironments and human occupation in the El Bolsón Valley of northwest Argentina (province of Catamarca, dept. of Belén)

Using an interdisciplinary perspective that integrates archaeological, geomorphological, and palynological data, this work analyzes the relationship between environmental changes and cultural landscapes in the El Bolsón Valley in the province of Catamarca, Argentina. The palynological and sedimentological studies took place using a sediment core extracted from a seasonal lake, while the geomorphological studies made use of stratified fluvial deposits. The palynological sequence indicates that wetter conditions existed at 6400calBP, but that this wetness decreased to create the current more arid conditions along with increases in anthropogenic disturbance. There is also evidence for intense processes of sediment accumulation and erosion, including changes in the uses of space by human populations as recorded for the last 2000years in fine deposits from the valley floor. The present work also makes an effort to insert this local history into its broader context, in order to contribute to existing knowledge regarding late Holocene changes at the regional level.

The transitional depositional environment and sequence stratigraphy of Chasma Boreale

The depositional system within Chasma Boreale is unique in that it contains active aeolian environments, expressed as dune fields, and active cryosphere environments, present as layered ice deposits, as well as environments that transition between these. This work presents a new analysis of the Chasma Boreale sediment system that creates an interpretative framework addressing: (a) controls on the balance between aeolian and cryospheric processes in the modern depositional system, (b) the stratigraphic architecture of related sedimentary deposits, and (c) processes of sediment accumulation and preservation. Images from Context Camera (CTX; 6 m/pixel) are used to classify and map sedimentary environments, surfaces, and deposits on the reentrant floor, to refine the established geologic map of the reentrant, and to infer the stratigraphic record of the accumulation from Chasma Boreale's depositional system. A spectrum of sedimentary environments occurring between those dominated by aeolian and by cryospheric processes are identified. Through time, the boundaries of these sedimentary environments have shifted, resulting in complex lateral changes in the configuration of sedimentary environments on the reentrant's floor. Vertically, the stratigraphic record is characterized by the punctuation of sandy aeolian deposits by icy surfaces that indicate episodes of ice growth that preserve underlying deposits, resulting in accumulation. Stabilized icy surfaces occur at multiple vertical (temporal) scales and lateral extents, suggesting the influence of both regional climate change due to allogenic forcing, as well as autogenic dynamics within the transitional system. These observations demonstrate that the Chasma Boreale accumulation can be interpreted in an aeolian sequence stratigraphic framework. This work contributes the first detailed description of the processes forming polar aeolian sequences, with an emphasis on the competing and complementary dynamics between aeolian and cryospheric systems.

Key hydraulic drivers and patterns of fine sediment accumulation in gravel streambeds: A conceptual framework illustrated with a case study from the Kiewa River, Australia

Fine sediment processes in gravel beds may have significant impacts to overall river ecosystem function. In addition to gravitational deposition, horizontal intragravel transport has been recognized to influence fine sediment accumulation. However, the specific hydraulic mechanisms and origin of fine sediment movement are not clearly identified. The purpose of this study was to investigate key hydraulic drivers and patterns of fine sediment accumulation. Using a conceptual framework to set the scene, we implemented an experimental setup in a gravel lateral bar subject to irregular flow fluctuations in the Kiewa River (Australia). We installed nine sets of sediment collector pairs and piezometers into the gravel. Each pair included one horizontally and one horizontally-vertically perforated collector. Mid-range, rather than peak flows, covering the site in water drove fine sediment deposited in the collectors. We estimated horizontal contribution to final deposition as 59%. Such contribution resulted from shear stresses >3Nm−2 promoting streamwise near-bed turbulence at the water-sediment interface during flooded conditions. Despite high subsurface hydraulic gradients, intragravel transport in the lower sediment layers via Darcy flow did not show any influence to fine sediment deposition. Our findings contribute to an improved understanding of fine sediment accumulation processes, key for overall river ecosystem functioning, particularly in regulated rivers.

Spatiotemporal variations of deep-sea sediment components and their fluxes since the last glaciation in the northern South China Sea

Sediment components and their fluxes of Cores MD12-3428 (water depth: 903 m), MD12-3433 (water depth: 2125 m), and MD12-3434 (water depth: 2995 m), obtained along a transect on the continental slope of the northern South China Sea, have been conducted to reveal the spatiotemporal variations and the controlling factors of the sediment components and of their fluxes. Results show that deep-sea sediments in the northern South China Sea are composed mainly of terrigenous (59–89%) and carbonate (6–38%) particles, with minor components of opal (1.6–9.4%) and organic matter (0.7–1.9%). Fluxes of terrigenous and carbonate particles reach up to 2.4–21.8 and 0.4–6.5 g cm–2 kyr–1, respectively, values that are one to two orders of magnitude higher than the fluxes of opal and organic matter. Temporal variations of the percentages and fluxes of deep-sea sediment components have displayed clear glacial-interglacial cyclicity since the last glaciation. Terrigenous, opal, and organic matter percentages and their fluxes increas clearly during marine isotope stage 2, while carbonate percentages and fluxes show an opposite variation pattern or are characterized by an unremarkable increase. This implies that deep-sea carbonate in the South China Sea is affected by the dilution of terrigenous inputs during the sea-level lowstand. With increasing water depth along the transect, the terrigenous percentage increases but with largely decreased fluxes. Both the percentage and flux of carbonate decrease, while the percentages and fluxes of opal and organic matter display much more complicated variational features. The spatiotemporal variations of deep-sea sediment components and of their fluxes since the last glaciation in the northern South China Sea are strongly controlled by sea-level fluctuations. Simultaneously, terrigenous supply associated with monsoonal rainfall, marine primary productivity, and the dilution effect between terrigenous and biogenic particles, also play interconnected roles in the sediment accumulation processes.

Sediment sequence and site formation processes at the Arbreda Cave, NE Iberian Peninsula, and implications on human occupation and climate change during the Last Glacial

Abstract. The Arbreda Cave provides a detailed archaeological record of the Middle to Upper Palaeolithic and is a key site for studying human occupation and cultural transitions in NE Iberia. Recently, studies of lake archives and archaeological sites presented new evidence on climate changes in NE Iberia correlating with Heinrich events. It, therefore, needs to be determined whether climate signals can be identified in the cave sequence of Arbreda, and if so, whether these signals can be correlated with stratigraphic indicators suggesting the continuity or discontinuity of human occupation. We conducted a high-resolution sedimentological and geochemical study, including micromorphological investigations, to shed light on stratigraphy, processes of sediment accumulation and post-depositional alteration in the cave. Seven major sediment units were distinguished which partly correlate with archaeological levels. The lower part of the sequence including Mousterian levels J and K consists of fluvial deposits truncated by a sharp erosional disconformity between Mousterian levels J and I. Strong enrichment with phosphorus and strontium reflect zoogenic inputs. The transition from Mousterian to Archaic Aurignacian in levels I and H, respectively, is reflected by more gradual changes in colour, grain size and geochemical composition. However, a peak in potentially wind-blown particles (40–125 μm in diameter) reflects higher aeolian input, and banded microstructure suggests reworking of sediments at the interface. Both properties correlate with low density of finds suggesting low intensity of human occupation related to a dry spell. More arid conditions than during the Holocene are indicated for the Gravettian to Solutrean levels. These findings are in agreement with previous palaeoclimatic interpretations as based on palaeontological proxies. The detailed multi-proxy analyses of the sequence adds to our understanding on sediment accumulation and alteration in the Arbreda Cave. The transition from the Middle to Upper Palaeolithic probably includes a gap in human occupation. Assessing the significance and duration of this gap and correlating the climate signal requires three-dimensional reconstructions of find densities and more reliable geochronological control.

Dissolved inorganic carbon and alkalinity fluxes from coastal marine sediments: model estimates for different shelf environments and sensitivity to global change

Abstract. We present a one-dimensional reactive transport model to estimate benthic fluxes of dissolved inorganic carbon (DIC) and alkalinity (AT) from coastal marine sediments. The model incorporates the transport processes of sediment accumulation, molecular diffusion, bioturbation and bioirrigation, while the reactions included are the redox pathways of organic carbon oxidation, re-oxidation of reduced nitrogen, iron and sulfur compounds, pore water acid-base equilibria, and dissolution of particulate inorganic carbon (calcite, aragonite, and Mg-calcite). The coastal zone is divided into four environmental units with different particulate inorganic carbon (PIC) and particulate organic carbon (POC) fluxes: reefs, banks and bays, carbonate shelves and non-carbonate shelves. Model results are analyzed separately for each environment and then scaled up to the whole coastal ocean. The model-derived estimate for the present-day global coastal benthic DIC efflux is 126 Tmol yr−1, based on a global coastal reactive POC depositional flux of 117 Tmol yr−1. The POC decomposition leads to a carbonate dissolution from shallow marine sediments of 7 Tmol yr−1 (on the order of 0.1 Pg C yr−1. Assuming complete re-oxidation of aqueous sulfide released from sediments, the effective net flux of alkalinity to the water column is 29 Teq. yr−1, primarily from PIC dissolution (46%) and ammonification (33%). Because our POC depositional flux falls in the high range of global values given in the literature, the reported DIC and alkalinity fluxes should be viewed as upper-bound estimates. Increasing coastal seawater DIC to what might be expected in year 2100 due to the uptake of anthropogenic CO2 increases PIC dissolution by 2.3 Tmol yr−1and alkalinity efflux by 4.8 Teq. yr−1. Our reactive transport modeling approach not only yields global estimates of benthic DIC, alkalinity and nutrient fluxes under variable scenarios of ocean productivity and chemistry, but also provides insights into the underlying processes.

The geoarchaeology of Mycenaean chamber tombs

This study presents a revised methodology for the excavation and analysis of the stratigraphy in Mycenaean chamber tombs and other multi-use burials. For our excavation of chamber tombs at Ayia Sotira and Barnavos, Nemea, we followed a geoarchaeological approach to provide details about the process of backfilling and re-opening of the tombs and to identify the location, number, and slope of these re-openings.In the studied fill of tomb entrance corridors (dromoi) at Ayia Sotira we observed a suite of sedimentary structures based on field and micromorphological observations. These are attributed to grain flow and debris fall processes associated with the formation of small piles during the shoveling of debris into the tomb. During ancient re-opening of the tombs extensive planar erosional surfaces were produced, occasionally associated with a basal stone line feature and an abrupt change in the degree of compaction. Constructed plastered floors were identified in the dromoi and the chambers during both the initial opening and the subsequent re-openings of the tombs.The proposed geoarchaeological analysis will enable the reconstruction of complex histories of mortuary practices and their social meanings. Moreover, this analysis shows that some anthropogenic processes of sediment accumulation can be analyzed and interpreted with paradigms of natural processes. Therefore, it provides a framework for understanding other types of earthworks that involve digging and filling.

Field investigation of clogging in a permeable pavement system

Permeable pavements are commonly used around commercial and industrial buildings to reduce the environmental impact. Results are presented from a forensic investigation of a permeable interlocking concrete paving (PICP) system that has been in service for over eight years. The aims were to quantify the sediment accumulation processes that occurred in the different pavement layers and to improve understanding of the change in the pavement hydraulic conductivity due to the trapped sediments. The majority of the sediment (by mass) was retained in the 2–5 mm aggregate bedding layer, irrespective of the pavement blockage conditions. While geofabrics are efficient at retaining sediment particles less than 33 µm in diameter, a maximum of only 8.3% of the total sediment mass was retained in the geofabric layers. Over 90% of the sediments were trapped in the paving and bedding aggregate layers. The beneficial role of geofabric in filtering out sediments and protecting the integrity of the underlying basecourse may not be significant enough to warrant its inclusion in permeable pavement installations. The PICP system was very effective at filtering and retaining sediments from stormwater runoff. While this resulted in reduced permeability over time, the overall infiltration performance of the PICP system was still satisfactory after eight years of continuous service. Des dallages perméables sont couramment utilisés autour des bâtiments commerciaux et industriels afin de réduire l'impact environnemental. Sont présentés les résultats d'une étude de type médico-légal sur un système de dalles autobloquantes perméables en béton qui est en service depuis plus de huit ans. Les objectifs étaient de quantifier les processus d'accumulation de sédiments intervenus dans les différentes couches de dallage et de mieux comprendre l'évolution de la conductivité hydraulique des dallages du fait des sédiments emprisonnés. La majeure partie des sédiments (en masse) a été conservée dans la couche de granulats de 2-5 mm du lit d'assise, indépendamment des conditions de blocage des dalles. Bien que les géotextiles retiennent efficacement des particules sédimentaires inférieures à 33 µm de diamètre, un maximum de seulement 8,3 % de la masse totale des sédiments a été retenu dans les couches de géotextiles. Plus de 90 % des sédiments ont été emprisonnés dans les couches de granulats du dallage et du lit d'assise. Le rôle bénéfique du géotextile dans le filtrage des sédiments et la protection de l'intégrité de l'assise de base sous-jacente peut ne pas être suffisamment significatif pour justifier son inclusion dans des installations utilisant des dalles perméables. Le système de dalles autobloquantes perméables en béton a filtré et retenu très efficacement les sédiments provenant du ruissellement des eaux pluviales. Bien que cela ait entraîné une réduction de la perméabilité au fil du temps, les performances globales d'infiltration du système de dalles autobloquantes perméables en béton demeuraient satisfaisantes après huit ans de service continu. Mots clés: colmatage géotextile dallages perméables migration des sédiments ruissellement des eaux pluviales hydrologie urbaine

Influence of climate fluctuations and changes in catchment land use on Late Holocene and modern beach-ridge sedimentation on a tropical macrotidal coast: Keppel Bay, Queensland, Australia

Beach ridges at Keppel Bay, central Queensland, Australia, preserve a record of sediment accumulation from the historical period back to middle Holocene times. The ridges comprise fine, well-sorted, feldspar-rich quartz sand that was eroded from the Fitzroy River catchment, deposited in Keppel Bay during floods of the Fitzroy River, and reworked onshore into beach and foredune deposits by the prevailing currents, waves and wind. These floods have an average recurrence interval of at least 7 yr and are induced by the passage of cyclones onshore into the large Fitzroy catchment. The youngest series of beach ridges sit sub-parallel to the modern beach and comprise six accretional units, each unit formed by a set of ridges and delineated by prominent swales. Optically stimulated luminescence (OSL) ages of beach ridges in these units indicate they were deposited in periods of rapid progradation approximately 1500, 1000, 450 and 230 yr BP, when there was an enhanced supply of sediment to the beach from the Fitzroy River via Keppel Bay. Estimates of the mass of sediment stored in the beach-ridge strandplain show that it represents a significant sediment store, potentially trapping the equivalent of 79% of the estimated long-term (100 yr) average annual bedload of the Fitzroy River that is deposited in Keppel Bay. There has been a reduction in the rate of sediment accumulation in the strandplain since around 1000 yr BP, which is consistent with other coastal records in eastern Australia of a relatively wetter phase of climate in the late Holocene compared to the present. The youngest beach ridges (OSL ages < 100 yr BP) are tall relict foredunes that reflect a low rate of sediment accumulation. These ridges have a distinctive trace-element composition produced by a greater contribution from catchment areas with basaltic soils. The change in catchment provenance has likely been a consequence of erosion that followed clearing of native vegetation in these areas. Our findings demonstrate the important insights that beach-ridge deposits proximal to a river sediment source can provide into processes of sediment accumulation and the response to variations in climate in tropical coastal sedimentary systems.

Chronology of the sedimentary processes during the postglacial sea level rise in two estuaries of the Algarve coast, Southern Portugal

Four profiles of estuarine sediments obtained from boreholes drilled in the Algarve, Southern Portugal were studied in order to reconstruct the process of sediment accumulation driven by the postglacial sea level rise. In addition to the sedimentological analysis, the Foraminifera Index of Marine Influence (FIMI) permitted assessment of the nature and organization of sedimentary facies in the Beliche–Guadiana and Gilão–Almargem estuaries. The Beliche–Guadiana CM5 and Almargem G2 profiles accumulated in a sheltered environment, with the former presenting an almost continuous record of the sea level rise since ca 13 000 cal yr BP. The G1 and G3 profiles from the Gilão–Almargem area represent a more discontinuous record of the last 8000 years, which accumulated in the more dynamic environment of an outer estuary. The integration of all radiocarbon ages of dated levels, led to an estimate of sediment accumulation rates. Assuming a constant position of the sediment surface with respect to the tidal range and a negligible compaction of sediment, the sea level rose at the rate of 7 mm yr −1 in the period from 13 000 to 7500 cal yr BP. This process slowed down to ca 0.9 mm yr −1 from 7500 cal yr BP until the present. The marked historical change in the rate of sediment accumulation in these estuaries also occurred with the accumulation of organic matter and is, therefore, important data for global biogeochemical models of carbon. The main obstacle to obtain higher temporal resolution of the sedimentary processes was the intense anaerobic respiration of organic matter via sulphate reduction, which did not allow any accumulation of peat and, furthermore, led to erasure of the palaeontological record by acid formed from the subsequent oxidation of sulphides.

BIOSTRAT: a program for simulating the stratigraphic occurrence of fossils

BIOSTRAT is a program for simulating the stratigraphic occurrence of marine fossils in single outcrops or in cross-sections through a sedimentary basin. It is primarily for use as a forward model, but could be used to inverse model a particular outcrop or basin. BIOSTRAT combines a random-branching model of evolution with a Gaussian ecological model of species with respect to water depth. Several modules are included that facilitate using the output of the sedimentary basin model, STRATA. BIOSTRAT has applications in the testing of biostratigraphic methods, for exploring how evolutionary events get filtered by the stratigraphic record, for testing paleoecological statistical methods, and for understanding how patterns of morphologic change in fossil species are distorted by the processes of sediment accumulation.

Spatial variability in sedimentary processes on the Eel continental slope

The northern California continental margin receives episodically large quantities of sediment from the Eel River, which seasonally discharges to the shelf. Regional circulation broadcasts this sediment widely, not only affecting sedimentation on the shelf, but on the slope as well. A suite of 60 cores has been collected to examine the processes of sediment accumulation and sediment delivery to the Eel continental slope in waters <800 m deep. Spatial surveys of accumulation rate (0.2–1.3 g cm −2 year −1) and surficial sediment grain size (4–8.5 φ) demonstrate that sediment is accumulating throughout the Eel margin, reflecting a rapid and widespread redistribution of the fluvial discharge. Downcore grain-size profiles of heterogeneous sediments suggest that hemipelagic and other episodic sediment-delivery processes may be important for the slope in areas proximal to the river. In more distal areas, downcore profiles reveal relatively homogeneous sediments, delivered dominantly by hemipelagic processes. A budget for fine-grained sediment shows that this upper portion of the slope contains, at a maximum, 20% of the river's annual discharge; a combined budget for the shelf and upper slope suggests that at least 60% of the annual sediment load is not accounted for in these areas. The Eel continental slope, because of the large terrigenous sediment input, the narrow width of the adjacent shelf, and its energetic environment, is a good analogue for slopes during transitional stands of sea level and for modern, tectonically active settings. Processes typically associated with these geological settings (i.e., supply of sediment to the slope, and downslope mass movement) are actively occurring.