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Fluvial facies models based on river planform are flawed and not fully fit for purpose. An alternative approach to classifying fluvial deposits is based on river discharge characteristics. A recent paper showed that the co‐efficient of variance of annual peak discharge (CVQp) correlates well with the characteristics of preserved alluvium for a suite of modern rivers. Here, the database of rivers is expanded and augmented, and the utility of this statistic confirmed. For modern rivers, plotting the running‐value of CVQp for a set interval (for example, 30 years) over a longer discharge record shows that the statistic varies both spatially and temporally. The CVQp can rise abruptly at a given location in response to a single flow event if that event is significantly larger than is common in that river. Such abrupt changes in CVQp are superimposed on longer‐term patterns of more gradual change stimulated by environmental factors or anthropogenic effects such as dam construction. If the period of calculation for CVQp is relatively short, 'anomalous' events appear more frequently. Sequential studies of modern rivers indicate that such anomalous events have a high probability of being preserved in the alluvial record of the river, and suggest that, over the timeframes of channel filling and abandonment, they may constitute the dominant (characteristic) portion of the record in high CVQp systems. Since flow events with strongly peaked hydrographs (flashy discharges) are more common in high CVQp systems and leave a record dominated by upper flow regime stratification styles, it follows that the alluvial record of high CVQp rivers will be dominated by upper flow regime stratification. In contrast, in lower CVQp systems the occurrence of an event that changes the running CVQp value significantly may form a distinct event deposit, and the temporarily changed CVQp is unrepresentative for the duration of the channel's life. The dominance of upper flow regime stratification, together with decreased preservation of identifiable macroform structure, increased lateral lithological heterogeneity, and in many cases increased preservation of in situ tree fossils in channel deposits of higher CVQp rivers, forms the basis for a series of new facies models for low, moderate, high and very high/ultra‐high CVQp alluvial systems and deposits. The new models can be applied to ancient successions either in combination with traditional, planform‐based models, or not. These models provide information about ancient palaeoenvironmental conditions, and changes in such conditions over time at various scales via stratigraphic investigations. [ABSTRACT FROM AUTHOR]

The Cretaceous Period is characterised by a peak in ocean surface acidity, which may have altered the fossil representation of its marine biota. Thus, we propose to study the dissolution of Caenogastropoda shells and to verify the number of fossil occurrences of the respective families during the Cretaceous, aiming to produce insights on which groups present a higher chemical preservation potential in low pH environments. An experimental taphonomy approach was used to obtain the mass loss rate of 12 shells without taphonomic damage. Morphometric measurements were conducted, and each shell was subjected to a solution of acetic acid diluted in distilled water, remaining for 24 h. At each interval of four and eight hours, the samples were dried, weighed, and pH of each container was checked. As result, it was recognised that the samples with lower dissolution rates, in other words more resistant to the chemical conditions of the simulated benthic taphonomically active zone, are those that distribute the shell mass over a smaller surface area. This corroborates with the high occurrence of their respective families during the Cretaceous. The Caenogastropoda shells that show the highest chemical preservation potential, therefore, are those with the lowest surface area to mass ratio. [ABSTRACT FROM AUTHOR]

Recent years witnessed an increasing consumer interest for the consumption of fruits preserved with non-chemical, eco and health-friendly approaches. This led to continuous work on deriving plant based natural treatments such as essential oils (EOs) for managing postharvest fruit loss. However, selection of EO which bear preservation potential along with the quality retention (sensory and shelf-life attributes) is now a prime concern for the postharvest researchers. Present study uncovers the preservation ability of EOs such as thyme oil (0.1 % v/v), clove oil (0.06 % v/v), neem oil (2 % v/v) and citronella oil (0.01 % v/v) on keeping quality, fruit decay and shelf life of mangoes cv. 'Amrapali'. The fruit were subjected to EOs coating dip treatment for 3 min, followed by storage at ambient condition. Observations on postharvest attributes (physical, physiological, biochemicals, decay and sensory) were recorded at 3 days interval up to storage period completion (12th day). The results showed that all EOs positively influenced the studied preservation characteristics. Interestingly, thyme oil (0.1 %) application exhibited the excellent level of overall fruit quality and preservation potential. This treatment exhibited highest overall fruit quality (7.71) and sensory score (6.47) while controlling the 'quality deterioration attributes' such as physiological loss (6.91 %), fruit respiration-ethylene activity and fruit softening enzymes activities to the least level. Moreover 3 days extension of storage period along with >90% decay control was achieved over control fruit. It was concluded that thyme oil (0.1 %) exhibited the best preservation potential on keeping mangoes fresh. The outcome of this study bears practical utility for fruit preservation industry, organic farming, and fruit traders. [Display omitted] • Among the attempted EOs, thyme oil (0.1 %) application exhibited excellent fruit quality and preservation potential on mango fruit. • Thyme oil application for keeping mangoes fresh in terms of both preservation potential and fruit quality were un-envisaged till now. • The plant EOs are of GRAS nature, health-eco, consumer friendly and cost-effective promising technique. • This is first report on the quadrupole effect of EOs and recommends thyme postharvest application for PHM of mango fruit. • The results of present study bear practical utility for fresh fruit industry and researchers. [ABSTRACT FROM AUTHOR]

This research explores how decay works and how different variables can affect this process in marine environments. The results are based on asterozoan echinoderms to cover one of the most complex multi-element skeletons in nature. Long-term experiments evaluated the effects of light, energy, salinity, sediment, oxygenation, temperature, and scavenger activity. The results showed that seven major agents can accelerate decay, including algal growth, water energy, microbial activity, microscavengers, macroscavengers, bubble production, and water acidification. Rapid burial of living organisms is the main shortcut to the fossilization of articulated specimens, but burial days to weeks after death can still lead to preservation if exceptional conditions delay the decay agents. Abrupt changes in salinity and temperature can restrict the distribution of scavengers and microorganisms, helping to preserve carcasses in the long term. Deeper or turbid seafloors can prevent small skeletons from destabilising due to the rapid growth of filamentous algae. Stagnant waters can also protect carcasses from waves and bottom currents, while water stratification can attenuate the attack of microscavengers. Although anoxia favours the preservation of soft parts, it is unable to prevent the anaerobic attack of microscavengers, which accelerates the destruction of small hard parts. Microbial reduction in anoxic regions can also drive the production of bubbles and the acidification of the water column, accelerating the destruction and dissolution of carbonate elements. These insights review important taphonomic concepts and provide a useful guide for interpreting the preservation potential of delicate organisms throughout the geological record. • Exceptional conditions slow decay agents and favour preservation potential. • Fluctuations in salinity and temperature restrict scavengers and microorganisms. • Algae can inflate, destabilise, and disarticulate fragile skeletons by trapping gases. • Anoxia retains soft tissues but can promote collapse and dissolution of hard parts. • Stagnation protects against currents and temporarily reduces attack by scavengers. [ABSTRACT FROM AUTHOR]

Rising sea levels and associated coastal topography changes are expected to increase coastal vulnerability to tsunamis. Reliable records of the periodicity of the most damaging tsunamis, with recurrence intervals of several centuries, are often incomplete. To understand the likelihood of coastal disasters that would be worsened by sea-level rise, as well as their possible occurrence leading to the actual extent of inland inundation, it is useful to examine the geological record of the mid-Holocene highstand periods to supplement the written archives. However, the formation and preservation potential of event layers depends heavily on the depositional environment resulting from coastal evolutions. This study attempted to reconstruct the depositional environment changes using diatom and chemical analyses on the Hidaka coast of Hokkaido, Japan, to examine the preservation of event layer archives.Following field investigations, we found three sand layers formed by extreme waves from field investigations. The relationship between the depositional environment and the timing of the event layer formation over the past 7000 years along the central Hidaka coast indicates that supratidal to freshwater marsh environments are the most suitable for preserving tsunami deposits in this region. Since sand layers in the distant areas from wave sources were not well preserved in upland (as at elevations above marsh environment) and saltmarsh environments, the time windows of preservation were very limited depending on the depositional environments with relative sea-level changes. On the other hand, in areas closer to the Kuril Trench, sand layers were preserved not very sensitive to the depositional environment, suggesting that the event archive length is related to the magnitude of tsunamis.

We aim to identify conditions that influence the preservation of a complete record of channel planforms in the topmost layer of floodplains, prior to the maintenance in the rock record. We have tested a hypothesis that a successive decrease of stream power and channel belt width are necessary to preserve the record of channel planforms in the topmost floodplain layer over 10−3 to 10−4‐year time scales. A literature review was conducted for rivers of the temperate zone of the Northern Hemisphere. Stream power, valley, and channel belt widths, paleodischarges, sediment grain‐size, and age of paleochannels were used to identify four groups of rivers with preservation potential ranging from tens of thousands years to annual time scales. The decrease in stream power followed by sustained low stream power, and successive decrease of channel belt width were identified in rivers preserving a 10−3 to 10−4‐year record of channel planforms. River valleys with the record of at least two generations of paleochannels, and valley width/channel belt width ratios between 6 and 12, potentially preserve fluvial records over 10−3 to 10−4‐year time scales. We analyzed unusually well‐preserved records of channel planforms from the Obra and Sió Rivers (central Europe). A determination of trends in changes of stream power and channel belt widths based on an extensive set of geophysical, geological data, and sediment dating from earlier studies, confirmed the tested hypothesis. The proposed framework can be extended by fluvial records preserved by large, and coastal rivers, with the potential to include ancient fluvial records. Plain Language Summary: Sediments deposited by rivers are archives preserving memory of past events, such as floods or changes in the type of channel (e.g., from braided to meandering). The memory of some rivers reaches back to thousands of years whereas others contain the record of channel changes from the last few years. We aim to define what conditions influence these differences. We analyzed changes in past discharges, flow energy, and widths and age of channel belts preserved in valley floors, in rivers situated in the temperate zone of the Northern Hemisphere. We found that a decrease in flow energy followed by sustained low energy of the flow, and successive decrease of channel belt width, favor the preservation of past fluvial events over 10−3 to 10−4‐year time scales. Rivers containing annual records are shaped by high flow energy, often eroding the record of past events. We analyzed unusually well‐preserved sedimentary records from the middle Obra and Sió Rivers (central Europe). They contain traces of former river channels from the last 13,000 and 18,000 years, respectively. In both cases, the flow energy and channel belt width decreased in particular generations of former channels, and this confirms the findings from the other analyzed rivers. Key Points: We aim to identify conditions influencing the preservation of complete record of channel planforms in the topmost layer of floodplainsA successive decrease of stream power and channel belt width favor the preservation of channel planforms over 10−3 to 10−4‐year time scalesRiver valleys with valley width/channel belt width ratios from 6 to 12, potentially contain fluvial record over 10−3 to 10−4 ky time scales [ABSTRACT FROM AUTHOR]

The relationship between storm activity and global warming remains uncertain. To better understand storm—climate relationships, coastal lagoon deposits are increasingly being investigated because they could provide high-resolution storm records long enough to cover past climate changes. However, site-specific sediment dynamics and high barriers may bias storm reconstructions. Here, we aimed to investigate these factors through the reconstruction of five distinct storm records (XCL-01, XC-03, XC-06, XC-07, XC-08) from different water depths in a lagoon with a high barrier (i.e., Xincun Lagoon of Hainan Island). Sediment cores were characterized using high-resolution grain size and XRF measurements, to identify storm events. These data were coupled with a numerical simulation to obtain bed shear stress data with high-spatial resolution to better understand storm-induced sediment transport mechanisms. 210Pb dating and Pb pollution chronostratigraphic markers indicated that the chronology of the storm deposit sequences of the cores span the period between 117 a and 348 a. The grain size and XRF results indicated numerous, highly variable and short-duration fluctuations, suggesting that storm-induced coarse-grained sediments were deposited at these core sites. The inconsistent storm events recorded in these cores suggest that these sites have different preservation potentials for storm deposits. However, the consistence between storm sediment records and historical documents for Core XCL-01 indicates that high-barrier lagoons could provide long-term storm event records with high preservation potential. [ABSTRACT FROM AUTHOR]

Variation in preservation and sampling probability clouds our estimates of past biodiversity. The most extreme examples are Lagerstätten faunas and floras. Although such deposits provide a wealth of information and represent true richness better than other deposits, they can create misleading diversity peaks because of their species richness. Here, we investigate how Lagerstätten formations add to time series of vertebrate richness in the UK, Germany and China. The first two nations are associated with well‐studied fossil records and the last is a country where palaeontology has a much shorter history; all three nations include noted Lagerstätten in their fossil records. Lagerstätten provide a larger proportion of China's sampled richness than in Germany or the UK, despite comprising a smaller proportion of its fossiliferous deposits. The proportions of taxa that are unique to Lagerstätten vary through time and between countries. Further, in all regions, we find little overlap between the taxa occurring in Lagerstätten and in 'ordinary' formations within the same time bin, indicating that Lagerstätten preserve unusual faunas. As expected, fragile taxa make up a greater proportion of richness in Lagerstätten than the remainder of the fossil record. Surprisingly, we find that Lagerstätten account for a minority of peaks in the palaeodiversity curves of all vertebrates (18% in the UK; 36% in Germany and China), and Lagerstätten count is generally not a good overall predictor of the palaeodiversity signal. Vastly different sampling probabilities through taxa, locations and time require serious consideration when analysing palaeodiversity curves. [ABSTRACT FROM AUTHOR]

The 2 to 5 km thick, sandstone‐dominated (>90%) Jura Quartzite is an extreme example of a mature Neoproterozoic sandstone, previously interpreted as a tide‐influenced shelf deposit and herein re‐interpreted within a fluvio‐tidal deltaic depositional model. Three issues are addressed: (i) evidence for the re‐interpretation from tidal shelf to tidal delta; (ii) reasons for vertical facies uniformity; and (iii) sand supply mechanisms to form thick tidal‐shelf sandstones. The predominant facies (compound cross‐bedded, coarse‐grained sandstones) represents the lower parts of metres to tens of metres high, transverse fluvio‐tidal bedforms with superimposed smaller bedforms. Ubiquitous erosional surfaces, some with granule–pebble lags, record erosion of the upper parts of those bedforms. There was selective preservation of the higher energy, topographically‐lower, parts of channel‐bar systems. Strongly asymmetrical, bimodal, palaeocurrents are interpreted as due to associated selective preservation of fluvially‐enhanced ebb tidal currents. Finer‐grained facies are scarce, due largely to suspended sediment bypass. They record deposition in lower‐energy environments, including channel mouth bars, between and down depositional‐dip of higher energy fluvio‐ebb tidal bars. The lack of wave‐formed sedimentary structures and low continuity of mudstone and sandstone interbeds, support deposition in a non‐shelf setting. Hence, a sand‐rich, fluvial–tidal, current‐dominated, largely sub‐tidal, delta setting is proposed. This new interpretation avoids the problem of transporting large amounts of coarse sand to a shelf. Facies uniformity and vertical stacking are likely due to sediment oversupply and bypass rather than balanced sediment supply and subsidence rates. However, facies evidence of relative sea level changes is difficult to recognise, which is attributed to: (i) the areally extensive and polygenetic nature of the preserved facies, and (ii) a large stored sediment buffer that dampened response to relative sea‐level and/or sediment supply changes. Consideration of preservation bias towards high‐energy deposits may be more generally relevant, especially to thick Neoproterozoic and Lower Palaeozoic marine sandstones. [ABSTRACT FROM AUTHOR]

Beachrock may be considered a reliable indicator of sea level, in addition to a reliable and recognizable source for onshore movement of beachrock clasts by overwash processes associated with extreme events. Key to this is its geomorphology and preservation potential, both of which are poorly understood. Here we examine the processes and deposits associated with beachrock breakdown from Camurupim, NE Brazil and compare its preservation to beachrocks found on continental shelves in South Africa. We study a prominent and continuous 50–60 m-wide beachrock complex that crops out along a 10 km stretch of coastline, and which mostly comprises 1.5 to 2 m-thick trough-crossbedded sandstones. These have generated large joint-bounded blocks that have been transported landwards under extreme energy conditions (based on numerical modelling and comparisons to the contemporary wave climate). Tabular clasts have accumulated as isolated, very coarse boulders on the seaward margin, small clasts in various topographic traps, boulder ridges with large landward- and seaward-dipping clasts on the uppermost part of the outcrop, and subaqueous and subaerial washover fans. Isolated fine meso-boulders emplaced during extreme waves (H s = ca. 12 m) exhibit fitted textures and pressure-solution contacts, pointing to subsequent rocking and shaking. Smaller clasts in boulder ridges and overwash settings are initially liberated and transported by waves within the annual-decadal frequency spectrum, deposited on the high points of the outcrop. Subsequent movement during less extreme wave action progressively transports the clasts across the surface, where they are often trapped in the fitted fabric on top of the platform. Our breakdown model and overall beachrock preservation scheme is consistent with reported seismic signatures of submerged Holocene beachrock shorelines. Beachrock preservation during transgression is strongly influenced by the original sedimentary facies; thick, trough-crossbedded joint-bound clasts preserve the former shoreline. Clasts from the planar units accumulate as washover fans to landwards of the ridge. [ABSTRACT FROM AUTHOR]

The Appalachian landscape provides an excellent opportunity to examine an environment that promotes sediment subsidence, accumulation and possible preservation: mantled karst. Mantled karst exists along the Blue Ridge-Great Valley margin from south-central Pennsylvania to central Virginia. Topographically, the mantled karst contains low-relief irregular topography with abundant surface depressions, some of which contain ponds, and in places lacks continual surface drainage and springs. Sand and gravel quarries along the valley margin expose predominantly stream flow, hyperconcentrated flow, debris flow and hillslope (colluvial) deposits that mantle karstic Paleozoic bedrock and carbonate residuum. Unconformable and sometimes erosive contacts between carbonate residuum and clastic sediments, and soft-sediment deformation features have been observed within exposures suggesting subsidence into accumulation and/or preservation space created by geochemical dissolution and collapse that continues today. The likelihood of long-term survival in the geological record is dependent upon the relationship between the subsiding sediment and geomorphic base level. The Blue Ridge-Great Valley mantled karst likely contains both short-term accumulation space that is closer to geomorphic base level, thus more prone to removal by fluvial processes, and preservation space, which occurs well below geomorphic base level, where sedimentary sequences may be stored for prolonged periods of time. Ultimately, both accumulation and preservation spaces can provide insight into depositional processes, landscapes and possibly paleoenvironmental conditions, but the geologic record becomes more distorted and fragmented further back into deep time and as this landscape evolves into the future. [ABSTRACT FROM AUTHOR]

An uncommon trackway of a seabird consisting of impressions of the right foot accompanied at the left side at the supposed position of the foot only by holes was produced by a gull having two legs, but only one foot. Foot size and stride are typical of an adult herring gull. The stride is unequal between right-left and left-right impression by ∼15% as the digitigrade producer experienced re-distribution of load due to the missing foot. Tracks of disabled seabirds are underrepresented in reports of both modern settings as well as the fossil record when compared with modern observations. In present time, about 2% of the seabirds have injured feet or legs. Today, however, injuries of seabirds might have increased due to human fishery activities. Actual observations show that fossilisation of such trackways is favoured by microbes preferentially growing in the impressions that are moist for a prolonged period of time. [ABSTRACT FROM AUTHOR]

Channel confluences are key nodes within large river networks, and yet surprisingly little is known about their spatial and temporal evolution. Moreover, because confluences are associated with vertical scour that typically extends to several times the mean channel depth, the deposits associated with such scours should have a high preservation potential within the rock record. Paradoxically, such scours are rarely observed, and their preservation and sedimentological interpretation are poorly understood. The present study details results from a physically‐based morphodynamic model that is applied to simulate the evolution and alluvial architecture of large river junctions. Boundary conditions within the model were defined to approximate the junction of the Ganges and Jamuna rivers, Bangladesh, with the model output being supplemented by geophysical datasets collected at this junction. The numerical simulations reveal several distinct styles of sedimentary fill that are related to the morphodynamic behaviour of bars, confluence scour downstream of braid bars, bend scour and major junction scour. Comparison with existing, largely qualitative, conceptual models reveals that none of these can be applied simply, although elements of each are evident in the deposits generated by the numerical simulation and observed in the geophysical data. The characteristics of the simulated scour deposits are found to vary according to the degree of reworking caused by channel migration, a factor not considered adequately in current conceptual models of confluence sedimentology. The alluvial architecture of major junction scours is thus characterized by the prevalence of erosion surfaces in conjunction with the thickest depositional sets. Confluence scour downstream of braid bar and bend scour sites may preserve some large individual sets, but these locations are typically characterized by lower average set thickness compared to major junction scour and by a lack of large‐scale erosional surfaces. Areas of deposition not related to any of the specific scour types highlighted above record the thinnest depositional sets. This variety in the alluvial architecture of scours may go some way towards explaining the paradox of ancient junction scours, that while abundant large scours are likely in the rock record, they have been reported rarely. The present results outline the likely range of confluence sedimentology and will serve as a new tool for recognizing and interpreting these deposits in the ancient fluvial record. [ABSTRACT FROM AUTHOR]

A complete, but fractured and crushed, echinoid corona from early to middle Miocene of Sarawak, Malaysia, is described as a new species, Clypeaster sarawakensis nov. sp. Although similar to modern C. rarispinus, the new species shows a distinct set of characters including petal length, periproct position and gut coiling. The discovery of a new Clypeaster, a genus characterised by a high preservation potential, illustrates that little is known about echinoid evolution and diversification in the Central Indo-Pacific, which features as a biodiversity hotspot since the Oligocene. Besides describing Clypeaster sarawakensis, we also compiled the known Central Indo-Pacific echinoid fossil record and used it to examine the Cenozoic diversity of echinoids. The overall diversity throughout the Cenozoic, and especially the rapid diversity increase at the Oligocene-Miocene boundary, corresponds to diversity trends observed in other taxa from the region. [ABSTRACT FROM AUTHOR]

Beachrock is present in deep, stable sections of a mixed sand and gravel beach at Whitepark Bay (55 o 14′N) on the paraglacial coast of Northern Ireland. The beachrock was revealed following progressive and extreme beach erosion during two particularly stormy winters (2013/14 and 2014/15). It occurs as large (up to 1 m diameter, 0.2 m thick), rounded, disc-shaped concretions in which original beach bedding structures are preserved. Both sand and gravel beach facies are cemented. The cements are similar to those of tropical beachrocks and comprise an initial thin micrite rim, and subsequent grain rims of aragonitic needles. The cementation is attributed to saturation of beach groundwater with calcium carbonate sourced from adjacent Cretaceous chalk outcrop in cliffs behind the beach and dunes. The micrite rims suggest microbial activity in the initial cementation, possibly by scavenging from chalk and skeletal carbonate grains. Subsequent aragonite rims were formed through degassing of CO 2 aided by tidal water level fluctuations. Despite similar cementation processes to low latitude beachrocks, only isolated concretions occur rather than extensive shore-parallel outcrops. Conditions necessary for cementation (and ultimately preservation) in this cold temperate and paraglacial setting include long-term beach stability, a carbonate source (in this case, adjacent chalk cliffs and stream sapping) and tidal water level fluctuations. Bacterial activity may initiate calcite precipitation. Following extreme storms and with progressive shoreline retreat prompted by rising sea levels, increased reporting of cold-water beachrocks is to be expected as formerly stable sections of beaches are exposed to wave action. [ABSTRACT FROM AUTHOR]

After the 2011 Tohoku-oki earthquake that occurred off the Pacific coast, significant problems arose concerning the Pacific coastal area (Sanriku Coast) such as the lack of the historical and paleo-tsunami records and the paradox between long-term and short-term vertical crustal movements. The data necessary to solve the issues are also essential for understanding the mechanisms of tsunami generation and earthquakes and assessing the risk of large, low-frequency disasters. Thus, we conducted excavation and coring surveys and reconstructed the paleoenvironment at Onuma on the southern Sanriku Coast, based on sedimentary facies, age data (radiocarbon dating and tephra), fossils (diatoms and mollusks), and topography. First, we discussed the preservation potential of tsunami deposits considering the geomorphologic and geologic evolution of the study area. Subsequently, we identified tsunami deposits and estimated their occurrence ages and inundation height. We discovered six tsunami beds deposited during ca. 5–1 ka when the preservation potential of tsunami deposits was high in the study site. We divided them into two types of deposits—sand and gravel. These deposits reflect different sources and flow processes of paleo-tsunamis. Therefore, we estimated the heights of the paleo-tsunamis that is 5–10 m for sand tsunami deposits (S1–S3 deposits) and > 10 m for gravel tsunami deposits (G1–G3 deposits). The tsunami deposits were dated at 690–1040 BP (S1), 2240–3310 BP (G1), 3320–3630 BP (G2), 3620–4060 BP (G3), 4030–4400 BP (S2), and 4440–5570 BP (S3). This approach and the setting of the study site enabled us to evaluate not only the ages of paleo-tsunami deposits but also the paleo-tsunami heights. Moreover, we estimated the paleo-sea level between 8 and 7 ka based on the sedimentary facies and paleoenvironment deduced from the fossil shells, and calculated the vertical crustal movement during the Holocene at − 0.4 to − 1.0 mm/yr by comparing with the theoretical relative sea-level curve. This information is significant for reconstructing the tectonic evolution along the subduction zone and for paleogeography to estimate the paleo-tsunami magnitudes. [ABSTRACT FROM AUTHOR]

Interpreting how far organisms within fossil assemblages may have been transported and if they all originated from the same location is fundamental to understanding whether they represent true palaeocommunities. In a three-factorial experimental design, we used an annular flume to generate actualistic sandy sediment-density flows that were fast (2 ms−1) and fully turbulent in order to test the effects of flow duration, sediment concentration, and grain angularity on the states of bodily damage experienced by the freshly euthanized polychaete Alitta virens. Results identified statistically significant effects of flow duration and grain angularity. Increasing sediment concentration had a statistically significant effect with angular sediment but not with rounded sediment. Our experiments demonstrate that if soft-bodied organisms such as polychaetes were alive and then killed by a flow then they would have been capable of enduring prolonged transport in fast and turbulent flows with little damage. Dependent upon sediment concentration and grain angularity, specimens were capable of remaining intact over flow durations of between 5 and 180 min, equating to transport distances up to 21.6 km. This result has significant palaeoecological implications for fossil lagerstätten preserved in deposits of sediment-density flows because the organisms present may have been transported over substantial distances and therefore may not represent true palaeocommunities.

Algal palynomorphs can provide key ecological information about aquatic environments, yet the preservation potential for most varieties of algae is poorly understood. Cores from Pine Forest and Bray Area lakes, two man-made lakes in the Rolla area of south–central Missouri, USA, provided an opportunity to relate the algal palynomorphs in the top 9 cm of sediments to the processes that lead to preservation. By comparing algal palynomorphs in the sediments to the algal crop in the water, this study seeks to assess the effects of taphonomy on the assemblage in a palynological sample. The lakes were ecologically monitored four times in one year (late fall, spring, summer, winter) to determine the algal crop, and surficial sediment was sampled in Pine Forest Lake once in early winter. The annual average abundance of algae in the lake water was compared with sediment data, and statistical techniques (Kruskal–Wallis test, Mann–Whitney U-test and Pielou's Equitability index) were used to determine ecological stability in the sediments. While Sphaerocystis and Ceratium hirundinella did not apparently preserve well, moderate to high preservation potential was determined for Staurastrum and Botryococcus. In addition, Pediastrum simplex var. pseudoglabrum, P. integrum and P. boryanum var. pseudoglabrum were well preserved in the sediments. This preliminary study shows that a highly abundant algal species in the water may not be well preserved in the sediment. Therefore, higher resolution studies are needed to further explore the preservation potential of algae in lake sediments. [ABSTRACT FROM AUTHOR]

The Early-Middle Miocene marine sedimentary succession of the Borutta Formation cropping out at Porto Torres (northern Sardinia) represents one of the most diverse and well-preserved spatangoid-dominated sedimentary successions in the Miocene of the Mediterranean area. The echinoid-bearing succession is studied with the twofold purpose of firstly reconstructing the palaeoenvironmental setting in which these echinoids occurred, and secondly investigating factors influencing the preservation potential of spatangoid echinoids in the fossil record. These goals are accomplished by 1) detailed logging of sedimentary facies, 2) applying functional morphological interpretations of echinoid skeletons in order to reconstruct their behaviour and life habits, 3) quantifying the relative abundance of taxa and taphonomic features of test preservation, and 4) analyzing associated trace fossils within the beds. The sedimentary succession is composed mainly of fine-grained sandstones which are intensely bioturbated by Thalassinoides -like burrows. Spatangoid abundance is high throughout the profile declining only in intercalated dm-thick rhodolith beds. A 20-cm-thick bed with a bedding surface of approximately 250 m 2 was investigated in detail with respect to relative abundance of spatangoid taxa and taphonomic signatures. The echinoids consist almost exclusively of deposit-feeding irregular forms with a dominance of the spatangoids Ova and Brissopsis and the minute clypeasteroid Echinocyamus . The spatangoids Opissaster , Holanthus , Metalia and Hemipatagus as well as the clypeasteroid Clypeaster marginatus are also present. A low energy, moderately deep, outer sublittoral environment with high rates of bioturbation and episodes of sediment deposition by storms is inferred. Interspecific competition among deposit-feeding echinoids appears to be limited by their different burrowing depths, feeding strategies and resource partitioning. The gregarious behaviour of spatangoid echinoids, their habitat in quiet, deeper environments and episodes of rapid deposition seem to represent the main factors leading to this spatangoid-bearing deposit. Since both shallow- and deep-burrowing spatangoid echinoids are well represented as complete specimens, mode of life does not appear to play a major role in their preservation potentials. [ABSTRACT FROM AUTHOR]

The distribution and geomorphology of aeolianite outcrop on the coast of KwaZulu-Natal, South Africa are described in the context of its preservation potential in the geological record. Aeolianite on the contemporary coast comprises discontinuous, widely spaced, outcrops less than 100 m in longshore extent and typically 50–60 m wide that reflects the combined action of subaerial weathering and physical abrasion in the coastal zone since the mid-Holocene (approximately 7000 yrs). The dominant morphological component is an intertidal erosional platform that slopes gently landward. It is fronted by a notch in the mid intertidal zone (0 m MSL) and contains active erosional potholes on its seaward margin. The platform surface is encrusted by a variety of marine organisms. Landward of and contiguous with the intertidal surface are small elevated outcrops of aeolianite in the supratidal zone. These comprise a 3 m-high seaward scarp with a basal notch in the high intertidal zone + 1 m MSL. Gullies in the scarp trap coarse clasts of eroded aeolianite as well as bedrock. The upper surface of the supratidal aeolianite is planar with large potholes within which accumulations of coarse clasts and oyster shells have been cemented. The upper surface is interpreted as a remnant of an intertidal platform formed at a higher mid-Holocene sea level. The supratidal outcrop is subject to weathering and disintegration. Major joints divide the outcrop into cuboid blocks with axes of 3–4 m. Eroded blocks on the seaward face that exceed 1 m diameter, remain in-situ and become locked in place by repeated shaking. Smaller blocks that collapse from the seaward face accumulate in small gullies or are dispersed. The facet most likely to be preserved in the geological record is the planar intertidal platform. The morphology of aeolianite on the contemporary coast is markedly different from submerged aeolianite ridges on the adjacent shelf which are of higher relief, wider and more laterally extensive. Preservation potential of aeolianite under subaerial conditions is low and the widespread high-relief aeolianite on the shelf is attributed to rapid inundation or burial during transgression. [ABSTRACT FROM AUTHOR]

In order to understand heterogeneity distribution of hydraulic properties, many studies have proposed models of coarse, braided river deposits. However, they often focus either on the surface/near surface or on ancient deposit analysis. Furthermore, the link between morphological (surface) and sedimentological (outcrops) information has not been fully explored yet. This publication aims to characterize the morphodynamics of a braided, gravel-bed reach of the Tagliamento River (NE Italy) and to assess its relationship with the subsurface heterogeneity. The morphological analysis is based on a LiDAR-derived DEM, aerial and satellite photographs from 1998 to 2011, as well as field observations. A water-stage time series allows the morphological changes to be related to the discharge dynamics. The sedimentological knowledge on coarse, braided deposits was mainly gained from the observation of analog Pleistocene coarse deposits in Switzerland. The main geomorphological elements are identified in terms of their topographic signature and genesis, setting apart the trichotomy water–vegetation–bar. The braidplain is characterized by higher-lying zones with dentritic gully drainage networks and active zones where most of the morphology reworking occurs. Furthermore, two morphologies mark the active zones: a low-discharge morphology (low-discharge incisions and channels, slip-face lobes, etc.) superimposed on a high-discharge morphology (gravel sheets, scours, etc.). Each morphological element is related to a depositional (i.e., sedimentological) element whose preservation potential in the subsurface is assessed as a function of the river-bed aggradation dynamic. The settings that impact the subsurface flow in terms of fast pathway and connectivity are addressed. [ABSTRACT FROM AUTHOR]

The style of early diagenesis and preservation of onshore tsunami deposits are poorly constrained. Only tsunami surveys and subsequent re-surveys can fill this information gap. Here we present the results of a first re-survey in 2012 on Isla Mocha following the original survey in 2010 in the wake of the February 27, 2010, Maule earthquake and tsunami in central Chile. As a result of this tsunami, a large number of boulders consisting of clay-rich fine sandstones representing the Miocene age bedrock of the island had been transferred from the tidal to shallow subtidal zone onto the coastal plain. Coarse clastic sediment mixtures of pebbles, granules, and sand entrained at coastal plain terraces and transported up to the maximum runup position c. 600 m from the coast by the inflow had been left behind as extensive backflow blankets on the lower coastal plain. In 2012, vegetation had covered the 2010 tsunami deposits. Sediment beyond 200 m from the coast had been removed by a combination of surface processes and grazing cattle. Grain-size distributions of the preserved sediment show an increase of the sand fraction at the expense of the coarser grain sizes. Boulders show patterns resembling mud cracks on the surface and evidence of disintegration into smaller fragments and sand. Veneers of dried algae documenting the derivation of the boulders from the tidal zones had flaked off partly or completely from most rock surfaces. At the northern, wind-facing coast of the island, a c. 130 m long and 1.2 m high beach ridge had accumulated, most likely from reworked tsunami sediment. Boulders deposited by tsunamis are commonly assigned a high preservation potential. We demonstrate for the first time that such boulders may in fact disintegrate rapidly and disappear from the record over short geological time scales, given a lithology susceptible to weathering. The degree of modification to the lsla Mocha tsunami boulders and deposits strongly questions the applicability of inverse models using paleotsunami deposit thickness and grain-size distributions to infer parameters and magnitudes of the causative tsunamis. Inverse models would consequently underestimate tsunami flow parameters and may result in the inference of erroneous transport modes and event magnitudes. Our study gives strong evidence in support of re-survey studies following the deposition of tsunami sediments by tracing and quantifying the changes affecting them. [ABSTRACT FROM AUTHOR]

Abstract: The Cretaceous Luzong and Ningwu volcanic basins in eastern China contain numerous magnetite–apatite deposits with similar geological characteristics and mineralization ages (~130Ma). These deposits, however, occur at distinctly different burial depths. To explain this difference, LA-ICP-MS apatite U–Pb and fission track double dating of five samples were carried out to establish the thermal histories from crystallization to the exhumation of four representative deposits: the deeply buried Nihe (665–1065m underground) and Luohe deposits (425–856m underground) from the Luzong basin; the shallow Meishan deposit (40–530m underground) and the exposed Dongshan deposit from the Ningwu basin. The cooling histories of the four deposits could be divided into rapid cooling for the Dongshan deposit and slow continuous cooling for the Nihe, Luohe, and Meishan deposits. Combined with geological evidence, it can be determined that the Dongshan and Meishan deposits formed at shallow depths with the Dongshan deposit emplaced at a very high level while the Meishan deposit was emplaced relatively deeper. The Nihe and Luohe deposits were emplaced deeper than the Dongshan and Meishan deposits and the burying of the Shuangmiao volcanic cycle after mineralization increased the burial depth. However, this burial event did not occur in the Ningwu basin. All of these resulted in the different burial of the magnetite–apatite deposits between the two basins prior to 120Ma while the exhumation after 120Ma among these deposits was similarly slow and continuous. The metallogenic conditions of both basins were similar but the smaller number and gross reserve of magnetite–apatite deposits in the Luzong basin, we believe that the Luzong basin has better preservation potential for the magnetite–apatite deposits. [Copyright &y& Elsevier]

Abstract: This work presents a synthesis of major metallic deposits formed during Columbia supercontinent cycle. Main deposits, such as orogenic Au, volcanogenic massive sulphides (VMS), Mississippi Valley-type (MVT) Pb–Zn, unconformity-associated uranium, Mo–Cu–Ag deposits, and perhaps clastic-dominated (CD) Pb–Zn deposits (Rajasthan, India) were formed during the assembly of Columbia. The ~1.9Ga global-scale mafic-ultramafic event, aided by large-scale mantle upwelling, played a significant role in the formation of granular iron formations, VMS, and magmatic Ni–Cu sulphides. The enveloping cratonic blocks of the supercontinent seem to have exerted a significant control in the selective preservation of the rock record, and thus there was a greater preservation potential of mineral deposits during the assembly of Columbia. Very few deposits were recorded in the Earth history during the assumed dispersal of Columbia at around 1.3–1.2Ga because of poor preservation potential or destruction of rock record during the breakup phase of a supercontinent cycle. The intervening time period between assembly and breakup of Columbia, which was marked by many attempted breakup phases, formed some major deposits, such as iron oxide–copper–gold (IOCG) and U (e.g. Olympic Dam), CD Pb–Zn (e.g. Broken Hill), CD Pb–Cu, sedimentary-rock hosted stratiform copper, Fe–Ti–V deposits, and perhaps Sn deposits of the Amazonian craton. [Copyright &y& Elsevier]

Abstract: Numerous post-tsunami surveys have been conducted in the last two decades, especially since the 2004 Indian Ocean tsunami. These studies have documented a variety of characteristic sedimentary and erosional features that can be ascribed to known events. Nevertheless, the question arises whether these structures are just ephemeral or have a potential to be preserved in the geological record. This review describes the changes that have affected muddy to sandy siliciclastic tsunami deposits in Peru. Each of these was surveyed in the first months after the tsunami: Chimbote (1996), Camaná (2001) and Pisco-Paracas (2007). Here, we describe the changes we observed during re-surveys in 2007 and 2008. It has long been recognized that onshore tsunami deposits may suffer from surficial processes, tectonic movements and anthropogenic alteration. Earthquake-induced uplift or subsidence may subject a tsunami deposit to erosion or burial, respectively. Quick burial in rapidly subsiding coastal areas may enhance preservation. Deposits of the last or most landward-reaching wave may be preferentially preserved if they escape erosion by subsequent tsunami waves; however, inland areas are also vulnerable to subaerial reworking, including by wind and by humans. The Peruvian examples reviewed here show that the preservation of arid-coast tsunami deposits depends on interactions that are more complex that hitherto perceived. These involve sediment type, grain size, depositional setting, co-seismic movement, bioturbation, winds, and anthropogenic modification. In one example, all traces of the tsunami have been removed or reworked by flash floods and ocean waves. In another example, clasts on a coastal plain from tsunami-backwash began to be rounded and abraded by eolian sands immediately after the event. Eolian processes also smoothed and filled tsunami scours. By contrast, muddy tsunami deposits in certain areas escaped erosion by wind, probably because of their greater cohesion. In still another example, 0.5m of co-seismic uplift was not enough to prevent ocean waves from removing a tsunami sand sheet that had mantled a coastal marsh. The buried record of tsunami deposits on modern coasts may therefore not fully represent the vulnerability of these regions to tsunamigenic hazards. [Copyright &y& Elsevier]

Abstract: Through funding from the National Park Service's American Battlefield Protection Program, geographic information technologies were employed to create a high resolution, spatially accurate representation of the 1775 landscape of Boston's Inner Harbor and to conduct a geospatial and temporal assessment of the location, extent, and preservation potential of an American Revolutionary War battlefield and its associated cultural resources. Geographic information technologies provide the tools and methodologies to accurately create digital representations of historical landscapes. These tools enable the visualization and geospatial analysis of landscapes and significant historical events, greatly enhancing the understanding of temporal and spatial interactions between these events and the physical landscape upon which they occurred. Data sources include historical bibliographic and cartographic records, high resolution orthophotographs, constant value raster grids, and LIDAR data. A military terrain model was created utilizing American Battlefield Protection Program's KOCOA system categories, in order to identify defining features of the battlefield. KOCOA is an acronym which stands for Key terrain, Obstacles, Cover and Concealment, Observation and Fields of Fire, and Avenues of Advancement and Withdrawal. The KOCOA analysis provides an established method for identifying critical defining features of the battle and determining the influence of the landscape on the ephemeral battle events. The base map was created utilizing U.S. Navy Coast Survey maps dating from the mid-19th century. A digital elevation model was created to represent the 1775 topography, utilizing LIDAR data and constant value raster layers. The military terrain analysis provided valuable insights into battlefield events and decisions. Defining features of the battle were also identified and mapped. A detailed Environmental Systems Research Institute's ArcGIS Citation Data Model was used to link landscape and KOCOA features to the historical sources they were derived from. A comprehensive source table was created as part of this effort. The results of this investigation have provided a high resolution dataset of Boston's historical landscape during the time of the American Revolution. The geospatial analysis will aid in the development of long-range management strategies for the Chelsea Creek Battlefield and facilitate the assessment of threats to cultural resources posed by both anthropogenic activities and environmental change. The methodologies and interdisciplinary approach will also be applicable to other investigations seeking to recreate historical landscapes within a geographic information system. [Copyright &y& Elsevier]

Abstract: Marine geophysical techniques and geological measurement of sea-level change allow detailed mapping of seafloor archeological sites and development of models. In the northwestern Gulf of Maine, the lowstand of sea level is only at −60m depth, but a prolonged stasis during the late Quaternary sea-level rise, herein termed the slowstand, occurred between 11,500 and 7500 calibrated years before present (calyr BP) at depths of 15–25m. This slowdown caused substantial erosion of glacial deposits and formed terrestrial beaches, wetlands and lakes. These landforms attracted people, whose tools were later discovered during present day scallop-fishing activities. Our study areas at the Green Islands and Bass Harbor are within the lowstand and slowstand depth ranges, but at highly exposed and sheltered sites, respectively. The Green Islands site has lost most of its former terrestrial sediment and there is no longer any context for recovered artifacts. At the protected Bass Harbor site, the remains of eroded moraines are associated with drowned spits and a former lacustrine/estuarine basin. Cores at the Bass Harbor location encountered freshwater peat deposits and numerous shallow subtidal shell and plant fossils all deposited during the slowstand. The two most important controls on the preservation of terrestrial landforms and associated human artifacts in the northwestern Gulf of Maine are the rate of sea-level rise and degree of shelter of the site from waves. [Copyright &y& Elsevier]

The Indian Ocean tsunami flooded the coastal zone of the Andaman Sea and left tsunami deposits with a thickness of a few millimetres to tens of centimetres over a roughly one-kilometre-wide tsunami inundation zone. The preservation potential and the post-depositional changes of the onshore tsunami deposits in the coastal plain setting, under conditions of a tropical climate with high seasonal rainfall, were assessed by reinvestigating trenches located along 13 shore-perpendicular transects; the trenches were documented shortly after the tsunami and after 1, 2, 3 and 4 years. The tsunami deposits were found preserved after 4 years at only half of the studied sites. In about 30% of the sites, the tsunami deposits were not preserved due to human activity; in a further 20% of the sites, the thin tsunami deposits were eroded or not recognised due to new soil formation. The most significant changes took place during the first rainy season when the relief of the tsunami deposits was levelled; moderate sediment redeposition took place, and fine surface sediments were washed away, which frequently left a residual layer of coarse sand and gravel. The fast recovery of new plant cover stabilised the tsunami deposits and protected them against further remobilisation during the subsequent years. After five rainy seasons, tsunami deposits with a thickness of at least a few centimetres were relatively well preserved; however, their internal structures were often significantly blurred by roots and animal bioturbation. Moreover, soil formation within the deposits caused alterations, and in the case of thin layers, it was not possible to recognise them anymore. Tsunami boulders were only slightly weathered but not moved. Among the various factors influencing the preservation potential, the thickness of the original tsunami deposits is the most important. A comparison between the first post-tsunami survey and the preserved record suggests that tsunamis with a run-up smaller than three metres are not likely to be preserved; for larger tsunamis, only about 50% of their inundation area is likely to be presented by the preserved extent of the tsunami deposits. Any modelling of paleotsunamis from their deposits must take into account post-depositional changes. [ABSTRACT FROM AUTHOR]

Microscopically, modern tufas, sinters, and travertines (TSTs) may contain filaments, spirilla, clotted micrite (peloids and/or grumeleuse), tubules, coccoids, or spheres that suggest a biological component to their constitution. However, examination of progressively older TST deposits reveals that the preservation of primary depositional features, including biological morphologies, is commonly obscured by diagenetic overprinting that may mask or obliterate original features. In the study reported here, we examined modern and ancient spring deposits to determine which biological morphologies remain identifiable through geologic time. The focus is on the preservation potential of fossil microorganisms, independent of the mineralogy or formation temperature of the original TST. Biologically induced biomineralization likely fossilizes microorganisms in situ within TST deposits. Biofilms, composed primarily of extracellular polymeric substances, bind calcium or silica ions, serve as nucleation sites, and change local microchemistries to favor precipitation of calcite, aragonite, or chert (less commonly, other minerals). The resultant precipitation entombs microbial material and may yield a fossilized remnant of the microbe’s former presence, albeit lacking details beyond general morphology. The preserved dimensions are almost always larger than those of the original microorganism. Recrystallization and the formation of cement, either calcite (or aragonite) or silica, are diagenetic processes that may occur early and rapidly, with resultant blurring of primary fabrics. Curiously, the commonly recognized spherule and coccoid forms from Holocene and Cenozoic deposits are rarely observable in Mesozoic and Paleozoic deposits, except as indistinct clots in thin section or as rounded mineralized forms. Filaments, however, retain much of their original dimensions, particularly their diameter, and if discovered stretching across a primary pore space may be considered one of the more reliable indicators of former microbial activity in ancient spring deposits. [ABSTRACT FROM AUTHOR]

Abstract: A forward modeling approach is proposed to simulate the preservation potential of tidal flat deposits. The preservation potential is expressed as a function of net deposition rate and a factor that represents the vertical flux of suspended load, or seabed lowering during erosion periods associated with bedload transport. The model takes into account a number of geometric parameters of a tidal flat sediment system and sediment dynamic processes. The former includes high water level, total sediment supply, the annual rate of the supply, the ratio of mud to bilk sediment in the supply, the bed slope of the tidal flat profile, as well as the slope of the stratigraphic boundary; the latter includes spring-neap cycles of tidal water level changes, boundary layer processes, resuspension of fine-grained sediments, bedload transport due to tidal currents, and bed elevation changes in response to sediment movement. Using this model, numerical experiments are carried out for a tidal flat system on the Jiangsu coast, eastern China, with the input data being derived from literature and from a series of sediment cores collected along an onshore–offshore transect. The results show that the preservation potential is highest over the upper part of the inter-tidal zone and in the lower part of the sub-tidal zone, and lowest near mean sea level and at low water on springs. The preservation potential tends to decrease with the advancement of the shoreline. The bed slope, tidal current direction and resuspension intensity influence the spatial distributions of the preservation potential. An implication of these results is that the temporal resolution of the tidal flat record depends upon the location and depth within the deposit; this should be taken into account in the interpretation of sedimentary records. Further studies are required to improve the model, on the hydrodynamic processes associated with extremely shallow water depths, sediment dynamic modeling of bed slope and profile shape, and the combined action of tides and waves for sediment transport on tidal flats. [Copyright &y& Elsevier]

Ebb tidal deltas (ETDs) are highly dynamic features of sandy coastal systems, and coastal management concerns (e.g., nourishment and navigation) present a pressing need to better describe and quantify their evolution. Here we propose two techniques for leveraging the availability of high-resolution bathymetric surveys to generate new insights into the dynamics and preservation potential of ebb-tidal deltas. The first technique is conformal mapping to polar coordinates, using Ameland ebb-tidal delta in the Netherlands as a case study. Since the delta tends to evolve in a clockwise direction around the inlet, this approach provides an improved quantification and visualization of the morphodynamic behaviour as a timestack. We clearly illustrate the sediment bypassing process and repeated rotational migration of channels and shoals across the inlet from updrift to downdrift coasts. Secondly, we generate a decadal scale (1975–2021) stratigraphic model from the differences between successive bathymetries. This stratigraphy showcases the delta's depositional behaviour through space and time, and provides a modern analogue for prehistoric ebb-tidal deltas. During the surveyed period, inlet fills form the largest and most stable deposits, while the downdrift swash platform is the most stable structure over longer periods. Together, these approaches provide new perspectives on ebb-tidal delta dynamics and preservation potential which are readily applicable to other sites with detailed bathymetric data. These findings are valuable at annual to decadal timescales for coastal management (e.g., for planning sand nourishments) and also at much longer timescales for interpreting stratigraphy in ancient rock records. [ABSTRACT FROM AUTHOR]

Abstract: The sedimentation on the Mauritanian shelf off the western Saharan desert is strongly influenced by dust supply and is investigated in this study by combining surface mapping, shallow-acoustic profiling and the analysis of sediment cores. Coarse-grained carbonates dominate wide areas of the open shelf at places where the shelf is exposed to the Atlantic Ocean. The sheltered Golfe d''Arguin, in contrast, is characterized by muddy shoals in its inner area, and locally restricted and wedge-shaped muddy depocenters which extend contour-parallel in mid-shelf settings. In both cases, cross-shelf currents control sediment distribution and accumulation, not location or amount of primary eolian input. A major discontinuity on the outer shelf is located in 85–110 m water plus sediment depth and is refilled by a sedimentary facies succession of shoreface, tidal and open-shelf deposits. This succession has formed during temporary lower sea levels along the last overall regression (MIS-4 and MIS-3), the Last Glacial Maximum, and during the past deglacial sea-level rise. Significant sediment deposition and preservation is limited to very restricted areas. Concerning the overall shelf architecture, sea level was the main factor enabling or suppressing deposition in terms of 1) creating local erosional swales which have favored subsequent trapping and preservation of sediments; 2) determining the type of sedimentary facies refilling these depressions under a variety of nearshore conditions; 3) interacting with the seafloor morphology and, by this, controlling timing of initiation and growth geometry of mud wedges. These mud wedges have formed since ca. 9 cal. ka under a continuous sedimentation regime. These bodies must have formed in hydraulic equilibrium but they are detached from a defined sediment point source which is in contrast to common mudbelt formation on shelves. In general, sediment storage on shelves under hyperarid conditions seems to be very limited due to comparably low sediment input, strong ravinement activity during changing sea levels, significant bypassing and winnowing processes, and a low preservation potential of the non-cohesive materials. These conditions lead to the development of almost sediment-starved systems with low subsidence rates over longer geological timescales. [Copyright &y& Elsevier]

A 5-year artificial-tracer study was used to mimic bioturbation of foraminifera in the back-barrier marshes of Folly and Rat Islands, South Carolina. Mixing rates decrease with subenvironment elevation, and decadal- to centennialscale ecological signals and smaller hurricane deposits would not survive passage through the low-marsh mixing zone. However, the lower mixing rates in the high-marsh subenvironment allows for the preservation of such signals in the stratigraphic record. Bioturbation rates correlate poorly with plant density (primarily Spartina alterniflora). The Pearson correlation coefficient between mixing rate (Im in centimeters) and halophyte density (stems per squaremeter) is only 0.46, while the correlation between mixing and burrow density (apertures per square meter) is a much stronger 0.83. This corroborates earlier reports that spatiolateral variability in bioturbation is primarily a result of bioturbator (Uca spp.) preference for the low marsh and not halophyte distribution. Two factors contribute to the preservation of storm layers in the marshes behind Folly Island: (1) Hurricane deposits are laterally continuous and deposited across both low and high marsh, and (2) the coarser grain size of the washover sediments and the thickness of the larger storm deposits inhibit crab burrowing. Although the extensive paleostorm record from Folly Island appears to show a decrease in category 4 and 5 hurricanes through time, this record may reflect change in marsh paleo-subenvironment. In a transgressive setting, where a formerly high marsh is submerged into low marsh, the preservation potential of storm deposits decreases through time. [ABSTRACT FROM AUTHOR]

During most of the last glaciation, the southern North Sea floor was exposed and accessible to humans. Archaeological finds are concentrated around Brown Bank, Dogger Bank and the Norfolk Banks, but the Palaeolithic and Mesolithic archaeological potential of these areas is poorly known. Management of submerged archaeological heritage requires knowledge about location (potential) and context, ascribing significance (value) and determining risk. Thus, the preservation potential of primary and secondary archaeological material around these three areas is considered a) in the context of the post-glacial evolution of the southern North Sea and b) regarding natural and anthropogenic processes. A detailed review is followed by original research material describing an approach to assessing preservation potential. In general, low-energy deposits associated with former intertidal, floodplain or lacustrine environments are likely to preserve primary archaeological material, including organic remains, whilst (high-energy) riverine environments are more likely to preserve inorganic secondary archaeological material. The main possible anthropogenic impacts on submerged archaeology result from beam trawling, which may disturb deposits at the seafloor, and aggregate dredging, which may remove secondary deposits. Trawling and aggregate dredging are increasingly contributing to knowledge, through reporting finds through established protocols, and through assisting in funding relevant to multi-disciplinary research. [ABSTRACT FROM AUTHOR]

Abstract: A model for the emplacement, bioturbation, and preservation of fine-scaled sedimentary strata has been used to evaluate the impact of interacting physical and biological sedimentary processes on preserved sedimentary fabric in three depositional settings. The settings, which have contrasting hydrodynamic, geological, and biological characteristics, are Eckernförde Bay, German Baltic Sea; the Eel Shelf, northern California, USA; and the northern Gulf of Alaska continental shelf, USA. We have compared field measurements of sedimentation and bioturbation (from 7Be, 234Th, 210Pb, and 137Cs measurements), and observations of sedimentary fabric derived from core X-radiographs with model predictions of preserved sedimentary fabric. The one-dimensional model is forced by fluctuations in the instantaneous sedimentation rate, which deposits sediment with primary sedimentary fabric. Primary sedimentary fabric is then modified by bioturbation, which is represented as a first-order depth-limited reaction term, the rate of which is derived from radioisotopic and time-series estimates of bioturbation depth and intensity. Model output includes depth in seabed and corresponding preservation quotient, a measure of relative primary versus biogenic fabric. Although measured rates and depth scales of sedimentation and bioturbation vary across the three study areas by more than a factor of ten, model results strongly resemble actual sedimentary fabric in core X-radiographs in each case. Our results support and expand on concepts that invoke episodic sedimentation and depth-dependent bioturbation as important competing factors in the preservation or destruction of primary depositional fabric, and also suggest that radioisotopic estimates of bioturbation rates can adequately portray natural conditions. [Copyright &y& Elsevier]

The late Holocene stratigraphic evolution of a back-barrier tidal basin in the East Frisian Wadden Sea, southern North Sea, was investigated on the basis of a conceptual model relating the rate of sea-level rise to the rate of sediment supply. For this purpose, more than 20 vibra-cores and box-cores were evaluated, complemented by 14C ages of in situ peats and historical charts. In spite of interspersed short regressive events, the late Holocene stratigraphy generally reveals upward-coarsening grain-size trends indicative of transgressive deposition in the course of sea-level rise rather than erosion and redeposition by migrating channels. A particular feature is the general absence of down-core bioturbation traces, which stands out in sharp contrast to the intensely burrowed modern surface layer. Thus, in the Wadden Sea, high sediment turnover in the course of rapid transgression evidently obliterates most bioturbation traces and other tidal signals such as minor regressive deposits, thereby emphasising the importance of preservation potential. [ABSTRACT FROM AUTHOR]

Holocene inner-shelf storm deposits preserved beneath the Sendai coastal plain facing the Pacific coast of north-eastern Japan were formed during a transgressive–regressive cycle. The evolution of the Holocene wave-dominated depositional system along the Sendai coast is reconstructed using 76 AMS (accelerator mass spectrometers) 14C ages and the origin of bed thickness variations in the inner-shelf storm deposits is explored. The Holocene succession is <30 m thick and overlies latest Pleistocene to early Holocene non-marine deposits above a transgressive ravinement surface. It comprises transgressive ravinement and inner-shelf deposits, and regressive inner shelf, shoreface, and coastal plain deposits. The inner-shelf deposits comprise alternating sand and mud layers interpreted as stacked storm beds. The average preservation interval of a single storm bed is shortest during the transgression (5·7–20·6 years), and then increases to a maximum during the early regression (83·3–250·0 years), decreasing to 7·7–31·3 years with shoreline progradation. Average accumulation rates decreased during the transgression and then increased during the regression, but the sand/mud ratio varies little, reflecting inefficient sediment segregation downdip on the inner shelf. The vertical pattern of sand-layer thicknesses also shows no relationship to position within the cycle, although small-scale intervals of upward thickening and thinning probably relate to lateral switching of river mouths and/or random storm processes. The average thickness of storm beds is the highest in the interval deposited during the period from maximum flooding to early regression. This is probably because of the low preservation potential of thin beds associated with frequent, low-magnitude storms during this period of low accumulation rates and extensive reworking. This preservation bias and the nature of the Sendai inner shelf resulted in an absence of characteristic bed thickness trends in the preserved storm deposits. [ABSTRACT FROM AUTHOR]

Paleontological data suggest that coral populations in the Caribbean were consistently healthy for the past 2-3 k.y. Beginning in the 1980s, however, disease outbreaks, bleaching episodes, hurricanes, and other perturbations caused catastrophic coral mortality and regional turnover. An alternative hypothesis, based on historical sources, posits that coral populations were already declining more than a century ago. These hypotheses can be distinguished only if turnover events are reliably preserved in the Holocene record of coral reefs. Push-cores extracted from uncemented lagoonal reefs in Belize showed that a direct hit by Hurricane Iris in 2001 did not disrupt the signature of the recent turnover event, which entered the subfossil record essentially intact. Cores from lagoonal systems in several areas of the Caribbean do not support the hypothesis that corals declined before the 1980s. [ABSTRACT FROM AUTHOR]

Channel-scale sedimentary units associated with bedrock-controlled riffle-pool morphology are examined in detail along Sandy Creek gorge, an ephemeral stream in arid south-eastern central Australia. Pool-fills comprise cut-and-fill assemblages of poorly sorted sediments ranging in texture from muds to boulders. Five unit types are defined based on particle size, sedimentary structures, geometry and bounding surface character: (1) coarse-grained bar platform; (2) fine-grained bar supraplatform; (3) fine-grained pool-fill; (4) fine-grained bench; and (5) modern pool-fill. The last coarse-grained unit currently lining the pools suggests an altered sedimentation style over the post-settlement period (post-ad 1860s). Situated at bedrock valley constrictions, pool-fills are compared with other sedimentary units associated with recirculating currents: eddy bars and slackwater deposits. But only the fine-grained bench units reflect eddy recirculation; the pool-fills are principally forced-bars associated with bedrock-controlled or‘forced’ riffle-pool morphology. A late Holocene palaeoflood history is proposed based on radiocarbon ages from the pool-fills: multiple phases of cut-and-fill activity were preceded by a superflood 3400–1900 years ago that eroded the pool-fills to bedrock. The resilience of the pool-fills was illustrated by the passage of a 1-in-100-year flood in 1992, which caused only minor erosion. The presence of pool-fills may provide a window to past phases of river activity that cannot be extracted from either historical records/observations or palaeoflood slackwater sediment analyses. The formation and sedimentary preservation potential of these landforms reflect a combination of hydraulic and structural influences, but the occurrence of high-magnitude floods exerts the dominant control. [ABSTRACT FROM AUTHOR]

Floods on the Eel River in Northern California during the winter of 1995 deposited a sediment layer 5–10 cm thick on the adjacent shelf, north of the river mouth and seaward of the 50-m isobath. Additional thinner oceanic flood layers were deposited over the same region in 1996 and 1997. Physical and biological modification of the 1995 event layer has been studied over a 2.5-year period and examined by means of sedimentary-fabric, radiotracer, and macrofaunal analyses of box cores collected across the shelf from 50- to 70-m water depth. Depositional sedimentary fabric of the 1995 flood deposit (as determined here and by Drake, 1999; Sommerfield and Nittrouer, 1999; Wheatcroft and Borgeld, 2000) indicates that it was deposited by three separate events over a period <3 months, each of which deposited a basal layer of silty sediment (containing crossbeds in some locations) and an overlying layer of clay-rich sediment that displays no obvious grading. Following each depositional event, biological mixing of the upper few centimeters resumed within a matter of weeks. This mixing produced millimeter-scale burrow mottling that replaced depositional sedimentary fabric in the upper 3–5 cm over a period of <6 months. Physical modification of the upper few cm includes reworking and deposition of coarse silt and fine sand on top of the uppermost clay-rich bed, which, along with shallow biodiffusive mixing, has produced coarse-grained bioturbated sedimentary fabric similar to that of the pre-flood seabed. Below ∼5 cm, the event layer has been modified by deep burrowing activity (including incipient Teichichnus traces), which can mix the upper ∼20 cm of the seabed over time scales of 6–350 years. Tiered ichnofabrics are produced by a vertically zoned macrofaunal community, which includes significant numbers of both surface- and deep-deposit feeders. Analysis of preservation potential for event layers indicates that basal portions of layers significantly thicker than 5 cm (such as the 1995 deposit) are likely to be preserved, especially when buried rapidly by subsequent depositional events, as occurred in 1997. Piston-core study shows that such partially preserved event layers compose ∼10% of the upper 3 m of the seabed, and have mean recurrence intervals of ∼100 years over the past ∼500 years. [Copyright &y& Elsevier]

Monitoring of sedimentation and erosion was conducted on an open coastal tidal flat on the southern flank of the Yangtze delta. Various elevation references were established in the intertidal zone and monitored intensively for 4 months in order to examine fortnightly and seasonal (calm weather and storm season) sedimentation and erosion. Longer term (100 years) sedimentation and preservation were investigated through examination of cores and trenches. Two different vertical grouping patterns of tidal bedding were distinguished with thinner and thicker sandy laminae. The number of sand-dominated layers and individual muddy and sandy lamina in the cores were compared with theoretically derived sedimentation rates in order to assess long-term preservation potential. Waves, especially high storm waves, have a significant influence on sedimentation and the preservation of intertidal deposits along the open-coast tidal flat. Monitoring during one season indicated that the sand-dominated layer was directly related to storm deposits, while the mud-dominated layer was deposited during calm weather conditions. The variation in sandy lamina thickness was not related to spring–neap tidal cycles during the monitoring period. The assumption of 100% preservation of sandy laminae deposited during every tidal cycle, which has been assumed in previous time-series analyses for the identification of palaeotidal periodicity, was found to be unrealistic along this open-coast tidal flat. Preservation potential decreases as temporal scale increases. During one neap–spring tidal cycle, the preservation potential of individual sandy and muddy laminae was of the order of 10%. Over a period of 100 years, the estimated preservation potential of individual laminae, including both calm weather and storm deposits, decreased to 0·2%. The 100-year preservation potential of storm-induced, sand-dominated layers was estimated to be of the order of 10%. [ABSTRACT FROM AUTHOR]