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This study presents a micromorphological analysis of liquefaction features (dykes, sills and sand blows) associated with the 2010 to 2011 Canterbury Earthquakes Sequence, dykes of an earlier generation of liquefaction (palaeoliquefaction) and hosting soil. The aim of this research was to determine whether diagnostic features existed that would allow robust identification of liquefaction features and discrimination of different generations of liquefaction features in thin sections. This study serves to enhance the tools available to support palaeoliquefaction studies and earthquake hazard assessment. Similarities were found in the sedimentary fabric between all forms and ages of liquefaction features distinct from hosting soil. Palaeoliquefaction features could also be distinguished on the basis of microscopic pedogenic characteristics. Liquefaction and palaeoliquefaction were investigated in two distinctive sedimentary settings: the floodplain of the Halswell River, and coastal sand dunes near or in Christchurch. Analysis was carried out on thin sections prepared from resin‐impregnated blocks of soil sediment hosting the liquefaction features. The fabric of modern liquefaction features in the alluvial and coastal system is similar, both showing a single grain micro‐structure, with moderate to well‐sorted grains with many simple packing voids and planar voids. In both environments it was possible to see evidence of fluidization such as water escape structures, cutans and silt caps. The palaeoliquefaction fabric can be distinguished from the modern liquefaction fabric by the presence of textural pedogenic features in the form of silt coating of grains, infilling of planar voids, coating and hypocoating of voids and excrement pedofeatures. The results presented in this manuscript demonstrated how thin section analysis can be a valuable tool to corroborate field identification of liquefaction features, and to discriminate between features of different relative ages where stratigraphic evidence is equivocal. [ABSTRACT FROM AUTHOR]

Current understanding of dune dynamics in rivers and estuaries in response to varying flows remains incomplete, particularly with respect to pattern evolution. This study presents observations of dune crestline change during the gradually varied flow caused by the influence of a diurnal tide on the fluvially‐dominated Fraser Estuary, British Columbia, Canada. Observations consist of a 1·0 km long and 0·5 km wide patch of a dune field mapped repeatedly during a falling and rising spring tide, on the rising limb of annual hydrograph immediately prior to peak freshet. The fundamental relations between dune geometry, translation rate, sediment flux and the birth, death and piracy of dune crestlines are explored. The data show that the bedform field consists of primary, channel‐spanning dunes with a series of interconnected secondary crestlines. The primary crestlines are two‐dimensional and experience little change over the tide cycle. The secondary crestlines impart a three‐dimensionality to the bedform field that is dynamic with the flow. There is a predominance of dune crestline bifurcation 'deaths' (disappearances) over 'births' (appearances) as flow velocity in the channel increases, suggesting that the crestline configuration is moving towards a more two‐dimensional configuration. As the flow wanes, bifurcation births outweigh deaths, suggesting that the dune field becomes more complex and three‐dimensional. The results suggest that the primary response to variable flow may be a simplification of the dune field towards a two‐dimensional configuration as flow increases and added complexity towards a more three‐dimensional configuration as the dune flow wanes. [ABSTRACT FROM AUTHOR]

Models relating sediment supply to catchment properties are important in order to use the geological record to deduce landscape evolution and interplay between tectonics and climate. Water discharge (Qw) is an important factor in the widely used 'BQART' model, which relates sediment load to a set of measurable catchment parameters. Although many of the factors in this equation may be independently estimated with some degree of certainty in ancient systems, water discharge (Qw) certainly cannot. An analysis of a world database of modern catchments with 1255 entries shows that the commonly applied equation relating catchment area (A) to water discharge (Qw = 0·075A0·8) does not predict water discharge from catchment area well in many cases (R2 = 0·5 and an error spanning about three orders of magnitude). This is because the method does not incorporate the effect of arid and wet climate on river water discharge. The inclusion of climate data into such estimations is an opportunity to refine these estimates, because generalized estimates of palaeoclimate can often be deduced on the basis of sedimentological data such as palaeosol types, mineralogy and palaeohydraulics. This paper investigates how the relationship between catchment area and river discharge varies with four runoff categories (arid, semi-arid, humid and wet), which are recognizable in the geological record, and modifies the coefficient and exponent of the above-mentioned equation according to these classes. This modified model yields improved results in relating discharge to catchment area (R2 = 0·95 and error spanning one order of magnitude) when core, outcrop or regional palaeoclimate reconstruction data are available in nonarid systems. Arid systems have an inherently variable water discharge, and catchment area is less important as a control due to downstream losses. The model here is sufficient for many geological applications and makes it possible to include variations in catchment humidity in mass-flux estimates in ancient settings. [ABSTRACT FROM AUTHOR]

The wavelength of stationary water-surface waves and their associated antidune bedforms are related to the mean velocity and depth of formative flow. In past published sand-bed flume experiments, it was found that lens structures were preserved during antidune growth and change, and the dimension of the lenses was empirically related to antidune wavelength, and thus could be used to estimate flow velocity and depth. This study is the first to compare observations of formative flow conditions and resulting sedimentary structures in a natural setting, testing the previously published relationship at a field-scale. Trains of stationary and upstream migrating water-surface waves were prevalent during the flash flood in October 2012 in the Belham Valley, Montserrat, West Indies. Wave positions and wavelengths were assessed at 900 sec intervals through the daylight hours of the event within a monitored reach. The wave data indicate flow depths up to 1·3 m and velocity up to 3·6 m sec−1. Sedimentary structures formed by antidune growth and change were preserved in the event deposit. These structures include lenses of clast-supported gravel and massive sand, with varying internal architecture. The lenses and associated low-angle strata are comparable to sand-bed structures formed from stationary and upstream migrating waves in flume experiments, confirming the diagnostic value of these structures. Using mean lens length in the event deposit underestimated peak flow conditions during the flood and implied that the lenses were preserved during waning flow. [ABSTRACT FROM AUTHOR]

Anastomosing rivers, systems of multiple interconnected channels that enclose floodbasins, constitute a major category of rivers for which various sedimentary facies models have been developed. While the sedimentary products of anastomosing rivers are relatively well-known, their genesis is still debated. A rapidly growing number of ancient alluvial successions being interpreted as of anastomosing river origin, including important hydrocarbon reservoirs, urge the development of robust models for the genesis of anastomosis, to facilitate better interpretation of ancient depositional settings and controls. The upper Columbia River, British Columbia, Canada, is the most-studied anastomosing river and has played a key role in the development of an anastomosing river facies model. Two hypotheses for the origin of upper Columbia River anastomosis include the following: (i) downstream control by aggrading cross-valley alluvial fans; and (ii) upstream control by excessive bedload input from tributaries. Both upstream and downstream control may force aggradation and avulsions in the upper Columbia River. In order to test both hypotheses, long-term (millennia-scale) floodplain sedimentation rates and avulsion frequencies are calculated using 14C-dated deeply buried organic floodplain material from cross-valley borehole transects. The results indicate a downstream decrease in floodplain sedimentation rate and avulsion frequency along the anastomosed reach, which is consistent with dominant upstream control by sediment overloading. The data here link recent avulsion activity to increased sediment supply during the Little Ice Age ( ca 1100 to 1950 ad). This link is supported by data showing that sediment supply to the upper Columbia study reach fluctuated in response to Holocene glacial advances and retreats in the hinterland. Upstream control of anastomosis has considerable implications for the reconstruction of the setting of interpreted ancient anastomosing systems. The present research underscores that anastomosing systems typically occur in relatively proximal settings with abundant sediment supplied to low-gradient floodplains, a situation commonly found in intermontane and foreland basins. [ABSTRACT FROM AUTHOR]

Deltas contain sedimentary records that are not only indicative of water-level changes, but also particularly sensitive to earthquake shaking typically resulting in soft-sediment-deformation structures. The Kürk lacustrine delta lies at the south-western extremity of Lake Hazar in eastern Turkey and is adjacent to the seismogenic East Anatolian Fault, which has generated earthquakes of magnitude 7. This study re-evaluates water-level changes and earthquake shaking that have affected the Kürk Delta, combining geophysical data (seismic-reflection profiles and side-scan sonar), remote sensing images, historical data, onland outcrops and offshore coring. The history of water-level changes provides a temporal framework for the depositional record. In addition to the common soft-sediment deformation documented previously, onland outcrops reveal a record of deformation (fracturing, tilt and clastic dykes) linked to large earthquake-induced liquefactions and lateral spreading. The recurrent liquefaction structures can be used to obtain a palaeoseismological record. Five event horizons were identified that could be linked to historical earthquakes occurring in the last 1000 years along the East Anatolian Fault. Sedimentary cores sampling the most recent subaqueous sedimentation revealed the occurrence of another type of earthquake indicator. Based on radionuclide dating (137Cs and 210Pb), two major sedimentary events were attributed to the ad 1874 to 1875 East Anatolian Fault earthquake sequence. Their sedimentological characteristics were determined by X-ray imagery, X-ray diffraction, loss-on-ignition, grain-size distribution and geophysical measurements. The events are interpreted to be hyperpycnal deposits linked to post-seismic sediment reworking of earthquake-triggered landslides. [ABSTRACT FROM AUTHOR]

The profile of a river that conveys sediment without net deposition and net erosion is referred to as 'graded' with respect to vertical aggradation of the river segment. Three experimental series, designed in terms of the autostratigraphic view of alluvial grade, were conducted to clarify the diagnostic spatial behaviour of graded alluvial-deltaic rivers: an 'R series', which utilized a moving boundary setting with a stationary base level; an 'F series' in a fixed boundary setting with a stationary base level to produce 'forced grade'; and an 'M series' in a moving boundary setting with constant base-level fall to produce 'autogenic grade.' The results of the three experimental series, combined with geometrical modelling of the effects of basin water depth and other experimental data, suggest the following: (i) in a graded alluvial-deltaic system, lateral shifting and avulsing of active distributary channels are suppressed regardless of whether the downstream boundary of the deltaic system is fixed; (ii) in a delta with a downstream-fixed boundary, the graded streams are stabilized within a valley that is incised in the axial part of the delta plain, whereby the alluvial plain outside the valley is abandoned and terraced; (iii) in moving boundary settings, the graded river simply extends basinward as a linearly elongated channel and lobe system without cutting a valley; and (iv) a modern forced-graded alluvial river is most likely to be found in a valley incised into a fan delta in front of very deep water, and the stratigraphic signal of fossil autogenic-graded rivers will be found in deltaic successions that accumulated in the outer to marginal areas of deltaic continental shelves during sea-level falls. This renewed autostratigraphic view of alluvial grade suggests a thorough reconsideration of the conventional understanding that an alluvial river feeding a progradational delta is graded with a stationary base level. [ABSTRACT FROM AUTHOR]

Boulders moving in flash floods cause considerable damage and casualties. More and bigger boulders move in flash floods than predicted from published theory. The interpretation of flow conditions from the size of large particles within flash flood deposits has, until now, generally assumed that the velocity (or discharge) is unchanging in time (i.e. flow is steady), or changes instantaneously between periods of constant conditions. Standard practice is to apply theories developed for steady flow conditions to flash floods, which are however inherently very unsteady flows. This is likely to lead to overestimates of peak flow velocity (or discharge). Flash floods are characterised by extremely rapid variations in flow that generate significant transient forces in addition to the mean-flow drag. These transient forces, generated by rapid velocity changes, are generally ignored in published theories, but they are briefly so large that they could initiate the motion of boulders. This paper develops a theory for the initiation of boulder movement due to the additional impulsive force generated by unsteady flow, and discusses the implications. [ABSTRACT FROM AUTHOR]

This study addresses gaps in understanding the relative roles of sea-level change, coastal geomorphology and sediment availability in driving beach erosion at the scale of individual beaches. Patterns of historical shoreline change are examined for spatial relationships to geomorphology and for temporal relationships to late-Holocene and modern sea-level change. The study area shoreline on the north-east coast of Oahu, Hawaii, is characterized by a series of kilometre-long beaches with repeated headland-embayed morphology fronted by a carbonate fringing reef. The beaches are the seaward edge of a carbonate sand-rich coastal strand plain, a common morphological setting in tectonically stable tropical island coasts. Multiple lines of geological evidence indicate that the strand plain prograded atop a fringing reef platform during a period of late-Holocene sea-level fall. Analysis of historical shoreline changes indicates an overall trend of erosion (shoreline recession) along headland sections of beach and an overall trend of stable to accreting beaches along adjoining embayed sections. Eighty-eight per cent of headland beaches eroded over the past century at an average rate of −0·12 ± 0·03 m yr−1. In contrast, 56% of embayed beaches accreted at an average rate of 0·04 ± 0·03 m yr−1. Given over a century of global (and local) sea-level rise, the data indicate that embayed beaches are showing remarkable resiliency. The pattern of headland beach erosion and stable to accreting embayments suggests a shift from accretion to erosion particular to the headland beaches with the initiation of modern sea-level rise. These results emphasize the need to account for localized variations in beach erosion related to geomorphology and alongshore sediment transport in attempting to forecast future shoreline change under increasing sea-level rise. [ABSTRACT FROM AUTHOR]

Current understanding of bedform dynamics is largely based on field and laboratory observations of bedforms in steady flow environments. There are relatively few investigations of bedforms in flows dominated by unsteadiness associated with rapidly changing flows or tides. As a consequence, the ability to predict bedform response to variable flow is rudimentary. Using high-resolution multibeam bathymetric data, this study explores the dynamics of a dune field developed by tidally modulated, fluvially dominated flow in the Fraser River Estuary, British Columbia, Canada. The dunes were dominantly low lee angle features characteristic of large, deep river channels. Data were collected over a field ca 1·0 km long and 0·5 km wide through a complete diurnal tidal cycle during the rising limb of the hydrograph immediately prior to peak freshet, yielding the most comprehensive characterization of low-angle dunes ever reported. The data show that bedform height and lee angle slope respond to variable flow by declining as the tide ebbs, then increasing as the tide rises and the flow velocities decrease. Bedform lengths do not appear to respond to the changes in velocity caused by the tides. Changes in the bedform height and lee angle have a counterclockwise hysteresis with mean flow velocity, indicating that changes in the bedform geometry lag changes in the flow. The data reveal that lee angle slope responds directly to suspended sediment concentration, supporting previous speculation that low-angle dune morphology is maintained by erosion of the dune stoss and crest at high flow, and deposition of that material in the dune trough. [ABSTRACT FROM AUTHOR]

Thick till sheets deposited during the Quaternary form significant aquitards in many areas of North America. However, the detailed sedimentary heterogeneity and architecture and depositional history of till units are not well understood. This study utilizes architectural element analysis to delineate the internal sedimentary architecture of the Tiskilwa Formation exposed at two outcrop sections in north-central Illinois, USA. Architectural element analysis facilitates systematic delineation of sedimentary architecture based on the nature of facies contacts and change in facies associations, delineation of unit geometries and understanding of depositional processes at different scales of resolution; making architectural element analysis suitable for the sedimentological analysis and palaeoenvironmental reconstruction of subglacial deposits. Eleven facies types are identified in this study, including sand, gravel and diamict facies that record a suite of subglacial depositional processes. Detailed analysis of facies contacts (bounding surface hierarchy) and change in facies associations allows the delineation of five architectural elements, including coarse-grained lens, coarse-grained sheet, mixed zone, diamict lens and diamict sheet elements. The spatial arrangement and genetic interpretation of elements, and their spatial relationship with fifth-order bounding surfaces, allows the delineation of five larger scale architectural units ('element associations'), which can be mapped in the local study area and record at least three stacked successions of meltwater accumulation and till deposition. The results of this study can be utilized for architectural analysis of till sheets and provide insight to groundwater flow pathways through till in the study area and elsewhere. [ABSTRACT FROM AUTHOR]

Small vertically oriented traction carpets are reported from the collapsed sandy fills of 100 m deep Devonian limestone sinkholes underlying the Lower Cretaceous Athabasca oil sands deposit in north-eastern Alberta, Western Canada. Dissolution of 100 m of underlying halite salt beds caused cataclysmic collapse of the sinkhole floors and water saturated sinkhole sand fills to descend very rapidly. Turbulent currents flushed upper sinkhole fills of friable sandstone blocks and disaggregated sand and quartz pebble for tens of metres. Laminar deposits with inverse grading accumulated as many as six to eight curvilinear entrained pebble streaks, 10 to 30 cm long, vertically impinged against the sides of descending collapse blocks. These deposits were initiated as vertically oriented early stage traction carpets that interlocked fine sand grains and inversely graded overlying pebbles entrained below the dilute overlying turbulent flows. Vortexes that flushed these sinkhole fills and induced these depositional processes may have lasted only seconds before the very rapid descents abruptly halted. Some of the fabrics were suspended vertically in-place and preserved from unlocking and obliteration. These small fabrics provide insight into the instability and ephemeral character of the transition from strong gravity-driven grain falls to very early stages of traction carpet formation. These short-lived deposits of very thin sand layers resulted from sufficient incipient frictional freezing that grain interlocking overcame, however briefly, the strong gravity drives of the vertical falls that would have otherwise dispersed grains and obliterated any organized fabric patterns. Tenuous frictionally locked grains were also suspended at the centres of hyperbolic grain fall flows that briefly developed between turbulent flow eddies, some of which were fortuitously preserved. Some of these suspended grain locking zones passed downward onto the relatively more stable surfaces of the rapidly descending block surfaces. The morphogenesis of these early stage traction carpets differ from more fully developed deposits elsewhere because of their short-lived transport, dynamic instability and vertical orientation. [ABSTRACT FROM AUTHOR]

To achieve a more robust interpretation of sediment conditions and transport based on grain size, this study combines the perspectives of two different interpretation techniques that have been developed separately and applied in the literature: (i) 'grain size trend analysis' interprets changes between interrelated sampling sites assuming that sediment in the direction of transport should become either coarser, better sorted and more positively skewed, or finer, better sorted and more negatively skewed; and (ii) the 'population anomalies' method, which estimates the balance between erosion and accumulation processes at each sampling site based on individual site deviations compared with average values for grain-size parameters in the area of interest. The simultaneous use of both approaches enables sedimentological conditions and transport alternatives to be distinguished. This improvement is necessary because site-specific changes and general textural trends provide information that complements the strengths and weaknesses of each perspective. The methods are implemented here using two-dimensional Geographic Information System tools and illustrated for the Lithuanian coast. Grain-size characteristics of 712 surface samples of sandy sediments are used to interpret sediment transport pathways and predominant sedimentological conditions in the Lithuanian coastal zone. In general, coast-parallel sediment transport dominates the entire investigation area, although wave-induced movement perpendicular to the coastline is inferred in the shallow nearshore zone. The deepest areas offshore are characterized by sea floor erosion in the north, whereas an accumulation zone occurs in the relatively deep central part of the study area. [ABSTRACT FROM AUTHOR]