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In 2015, an active dune field on Mars was visited up close by the Curiosity rover in Gale Crater providing the first high resolution ground images of fine scale windblown features not previously resolved from orbital-based imagery. For the first time, these images allow for direct comparison with terrestrial aeolian dynamics and provide critical ground truth data to bridge the gap between model predictions and satellite observations. The image data from the slipface on the Namib dune within the Bagnold dune field shows grainflow morphologies that are similar to dunes on Earth. Quantitative estimates of flow thickness, based on shadow length are presented for the grainflows on the Namib dune slipface and compared to grainflow characteristics measured by terrestrial laser scans from the Maspalomas dune field located in Gran Canaria, Spain. Using observations from Maspalomas to support interpretations of martian slipface dynamics, we discuss implications for the local wind regime, style of grainflow, seasonal activity, and dune migration. The presence of multiple large-magnitude grainflows on the Namib slipface suggests an active aeolian environment, capable of delivering enough sediment to the slipface to initiate these flows and transport sediment to the bottom of the lee slope. However, the thinness of grainflows on the Namib dune, the formation of smaller grainflows directly below the dune brink and limited grainfall suggest a lower wind energy environment, at least for the most recent slipface activity. Large, actively migrating stoss ripples obliquely oriented to the dune crest regularly deposit sediment on to the upper slipface and may be a mechanism in which larger grainflow occur during seemingly low energy wind events. This mechanism of sediment delivery may also explain the existence of a variety of slipface morphologies, both young and old, which are otherwise quickly erased on Earth due to sediment redistribution and grainfall.

Airflow dynamics and potential sediment transport were measured and modelled across various barchan dune topographies and incident wind conditions. Modification of near surface flow was recorded simultaneously in three dimensions (3D) using dense arrays of high-resolution 3D ultrasonic anemometers. In situ measurements provided rigorous validation and calibration for computational fluid dynamics (CFD) modelling. Measured and modelled results show good agreement between flow velocity, directionality, and turbulence intensity. Modelling of characteristic airflow conditions and surface shear stress beyond the instrument locations, elucidated airflow dynamics across the entire landform surface at an unprecedented level of detail. Emergent turbulent airflow patterns were identified in the form of two counter-rotating vortices that converge at the dune centreline downwind of the dune crest. Integrating a sediment transport function with CFD surface airflow allows for the spatial mapping of flux patterns across the entirety of the dune and interdune surface. On the stoss slope and laterally along the outer barchan arms, there is strong potential sediment flux in response to increased streamwise stress. In lee-side locations, sediment transport remains at ‘above threshold’ conditions and is redirected in response to complex turbulent vortices identified in the overlying wake zone. The precision of the models allows for the identification of complex flow perturbations and associated surface stresses that prove difficult to measure in the field. CFD in combination with a sediment transport function is demonstrated to be a useful tool in investigating morphodynamics of mobile dune systems.

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.

Ireland experienced a spatially complex pattern of relative sea-level (RSL) changes and shoreline development caused by the interplay of isostatic and eustatic (ice equivalent sea level) processes since the Last Glacial Maximum (LGM). Using a combination of high-resolution marine geophysical data, vibrocores, foraminiferal analysis and 10 AMS radiocarbon dates, we reconstruct the Late Quaternary evolution and RSL history of Bantry Bay, a large (40 km long, 5–10 km wide) embayment in SW Ireland. The data indicate two infill phases: one before and one after the LGM, separated by glacial and lowstand sediments. The pre-LGM history is not dated and the depositional history is inferred. A large sediment lobe formed at the outer edge of Bantry Bay as a lowstand ice-proximal glacimarine outwash system as the ice retreated after the LGM, at a sea level ca. 80 m lower than present. Iceberg scour immediately west of this location likely relate to the break-up of the local Kerry–Cork Ice Cap. Long curvilinear ridges, seen both offshore and on top of the sediment lobe, probably formed as shoreface ridges under stronger-than-present tidal currents during a period of RSL stability (pre-14.6 ka cal BP). A subsequent infill phase is characterised by a basin-wide erosional (ravinement) surface and the deposition of inter- and sub-tidal estuarine sediments. Although our data support the general trends, our stratigraphic and radiocarbon data suggest a higher sea level between 11 and 13.5 ka cal BP than predicted by existing glacial isostatic adjustment models.

The seismic stratigraphy, architecture and evolution of a large subtropical embayment, Maputo Bay, Southern Mozambique is described. Nine seismic units are documented; and show repeated phases of incised valley formation and transgressive infilling. Trangressive infilling alternates between the classic wave-dominated transgressive succession of fluvial and central estuarine bay deposits and the filling by intertidal flat and tidal bedforms developed during stages of inlet restriction and shallowing associated with barrier growth at stillstand intervals. Imprinted on the succession are several key facets of subtropical stratigraphy, hurricane-generated erosional surfaces and beachrock horizons. The upper stratigraphy comprises the highstand bayhead delta, a prograding feature constructed by several flood events. In comparison with literature from other similar systems such as lagoons, coastal lakes and estuaries, a generic three stage stratigraphic model of large marine embayments is proposed that includes incision during glaciations; transgressive infilling during deglaciations; and shallowing during the stillstand episodes of the recent deglaciation.

Late Pleistocene–Holocene shoreline sequences and associated shelf stratigraphy are described from a high gradient, high wave-energy shelf. Although shoreline preservation by overstepping is considered unlikely in such an environment as a result of intense ravinement during shoreline translation, the development and preservation of two distinct shorelines at − 100 m and − 60 m are evident and attributed to century to millennial scale periods of stillstand. During these periods shoreline equilibrium forms developed, characterised by early diagenesis of beachrock and aeolianite. Between these features the shelf is dominated by erosional surfaces reflecting ravinement during periods of slowly rising sea-level. Where shorelines are not preserved, areas of scarping in the ravinement surface, at similar depths to the adjoining shorelines, represent rocky headlands separating the sandy coastal compartments where the depositional shorelines formed. Shoreline preservation by overstepping was facilitated by rapid relative sea-level rise associated with meltwater pulses 1A and 1B, although the features preserved are likely to represent only the cemented cores of the coastal dunes and linear beachrock outcrops formed. The steep antecedent shelf gradient fostered the erosion of significant portions of the shorelines by ravinement, with loose sediment re-organised into a thick post-ravinement drape. The removal of shorelines during ravinement was countered by the rapid rate of sea-level rise and early sub-tropical diagenesis. It is clear that due to the combined effects of subtropical diagenesis, long periods of stillstand and drowning by meltwater pulses, the governing controls on shoreline preservation can be over-ridden by combinations of local (climatic) and global (eustatic) factors.

Use of parametric classification of beach morphodynamic state has been steadily increasing in coastal research, despite identification of several shortcomings of their representativeness as elementary beach descriptors. In this paper, we analyse the parametric classification of beach morphodynamic state in a set of six embayed beaches in southwestern Portugal, exposed to diverse settings, from high-energy (dissipative to intermediate) to low-energy (intermediate to reflective) conditions. Applicability of parametric approaches considered within the dimensionless space defined by Ω (dimensionless fall velocity) and RTR (relative tidal range) according to averaged wave, tide and sediment characteristics of beaches, was assessed in association with a probabilistic analysis, implemented through a Bayesian network model, that considered the full range of wave, tide and sediment conditions at each site. Both parametric approaches were compared to field-based beach state classification implemented using a novel hierarchical framework for beach state analysis. The classification obtained within a probabilistic framework provided an innovative approach for analysis of beach state and mobility, extending the insights on beach morphodynamic behaviour obtained from averaged environmental parameters. Reflective to lower-intermediate beach conditions showed better agreement with parametric approaches, while poor beach state differentiation was achieved for intermediate beach types. Limitations in the application of beach classification models result from (i) an inadequacy of existing beach state types in differentiating beaches, particularly within the intermediate domain and for geologically controlled embayed beaches, and (ii) shortcomings involved in the parametric approaches. The beach state models disregard the major role of geological control in embayed beach morphodynamic behaviour (in modulating beach shape and segmentation, influencing sediment size and availability, causing alongshore variations in the wave field and creating topographically induced nearshore circulations). Existing beach state models are unable to adequately represent the widely variable conditions observed in embayed beaches.

This paper presents an analysis of decadal (mesoscale) geomorphic change on sandy barrier islands in thefetch-limited environment of Chesapeake Bay. Low energy barrier islands exist in two settings: on the fringe of marshes and in open water and this analysis shows the various types of barrier island to be genetically related.Barrier islands that face the dominant wind and wave direction (E or W) retreat via barrier translation, preserving the barrier island volume. Those that exist in re-entrants are dominated by longshore transport processes, are strongly affected by sediment supply and are subject to disintegration.Marsh fringe barrier islands are perched on or draped over the surface of the underlying marsh. They migrate landwards via barrier translation during periodic high water events accompanied by large waves (hurricanes and northeasters). The underlying marsh surface erodes under all water levels and the rate of retreat of the barrier island and underlying marsh may take place at different rates, leading to various configurations from perched barrier islands several metres landward of themarsh edge, to barrier islands that have a sandy shoreface extending into the subtidal zone. The coastal configuration during landward retreat of marsh fringe barrier islands is subject to strong local control exerted by the underyling marsh topography. As erosion ofmarsh promontories occurs and marsh creeks are intersected and bypassed, the configuration is subject to rapid change. Periodic sediment influxes cause spits to develop at re-entrants in themarsh. The spits are initiated as extensions of adjacentmarsh fringe barrier islands, but as the sediment volumeis finite, the initial drift-aligned spits become sediment-starved and begin to develop a series of swash-aligned cells as they strive formorphodynamic equilibrium.The individual cells are stretched until breaches form in the barrier islands, creating inlets with tidal deltas. At this stage the low energy barrier islands closely resemble open ocean barrier islands. Continued reworking leads towidening of the inletswith consequent loss of constriction of tidal flow. The tidal deltas are, thus, no longermaintained and ultimately the island systemdisintegrates through inlet widening and is transformed to subtidal shoals. Barrier islands at various stages in this evolutionary cycle can be observed around the bay. Mid-bay barrier islands are affected by wave processes from both sides. This helps maintain the barrier island form and enables barrier islands to persist as sediment is exchanged between both sides of the island.Rates of barrier island translation are extremely high (up to 30 m/year over a 12 year period). This is attributed to the lowvolume of sand, which facilitates complete rollover in short periods. Accelerated sea level rise is likely to hasten the translation rates ofmarsh fringe barrier islands. The rapid disintegration ofmost spits compared to the persistence of marsh fringe barrier islands points to a reliance on the marsh as a stabilising point. If the marshes are overstepped by rising sea level as appears to be happening, the complete disintegration of the barrier islands is highly likely.

Wind flow within blowouts is extremely complex as streamline compression, expansion and reversal may occur over and around a single landform. As a result high resolution temporal and spatial measurements are required during a range of incident wind conditions to resolve near surface airflow patterns and turbulent structures. This study examined three-dimensional airflow within a coastal dune trough–bowl blowout using 15 ultrasonic anemometers (UAs) and a high resolution computational fluid dynamics model. Measured total wind speed and vertical wind speed behaved consistently through 5 Beaufort wind scales ranging from ‘fresh breeze’ to ‘strong gale’, increasing relative to incident wind speed, whilst wind direction at each UA did not alter. Due to the agreement of modelled and measured data, ‘hurricane’ (37 m s −1 ) incident winds were also simulated and were consistent with modelled and measured wind direction at lower wind speeds. Modelled wind turbulence data was not compared with measured as only average conditions were simulated. However, the standard deviation of measured wind direction remained constant at each anemometer throughout the range of incident wind speeds, whilst the standard deviation of wind speed and turbulent kinetic energy increased relative to incident wind speed. This paper demonstrates that wind flow behaviour within blowouts throughout this range of wind speeds is governed by topography and is relative to, but does not change structurally with incident wind speed. As a result the extent of streamline compression, expansion, steering and reversal remain constant.

Blowouts are common landforms found within coastal dunes. Their dynamics are primarily driven by aeolian transport caused by surface wind stress, though patterns of deflation and deposition within blowouts are poorly understood as near surface wind flow is complex. Three‐dimensional wind flows around blowouts have yet to be properly quantified, especially within zones of separation, re-attachment and acceleration. This has been largely due to inadequate measurement of airflow and a lack of suitable airflow models. With this in mind, we present results from a study that has quantified alongshore and oblique onshore wind flow dynamics over a bowl blowout on the Belmullet Peninsula, Ireland. Using ultrasonic three-dimensional anemometry (measuring at 50 Hz) and three-dimensional computational fluid dynamic (CFD) modelling, we measure and model for the first time in 3D a detailed picture of the heterogeneity of wind flow over this type of terrain. During alongshore wind conditions, wind speeds within the deflation basin were retarded by 50% compared to the foredune zone and flow separation restricted to a small zone in lee of the windward rim. Wind was directed into the deflation basin through a gap in a western erosional wall, termed the blowout throat. In oblique onshore wind, airflow orientated with the blowout throat remained unchanged in direction and slowed by only 30% compared to wind speed on the foredune. In lee of the erosional wall adjacent to the blowout throat, small zones of flow separation occurred close to the erosional wall. In both cases, the highest variation in wind speed and direction occurred in zones of separation and attachment whilst flow increased in steadiness with height over the erosional walls. The results illustrate that wind is manipulated according to localised topography within the bowl blowout itself. Resulting zones of potential sediment transport (erosion and deposition) are spatially complex and alter with wind direction. The presence of a blowout throat has a significant influence on airflow patterns within a deflation basin. Modelled (CFD) and measured anemometer data demonstrated excellent comparisons for wind direction and speed, allowing much greater spatial measurement resolution than physical instrumentation. Simulated turbulence did not correlate well with measured data, highlighting the requirement for high frequency, three-dimensional anemometry in areas of complex flow.

Headlands, rock outcrops and engineering structures impact beach and nearshore dynamics of coastal embayments, inducing boundary effects that constrain the lateral and vertical beach variability. This study analyses morphological change in six embayed beaches with diverse levels of exposure to wave action and various degrees of geological control in the mesotidal coast of southwestern Portugal. The aim is to identify whether geological boundaries constrain the morphological behaviour of embayed beaches and assess whether their effects can be decoupled from datasets of morphological change. Topographic data, obtained over a two-year period on each of the six embayments, were analysed using empirical orthogonal functions (EOF) to decompose temporal and spatial variability in the datasets. First and second mode eigenfunctions were explored using time-variable linear correlation analysis with several nearshore parameters that include hydrodynamic variables, sedimentary and geometric characteristics of each embayment in order to derive forcing–response relationships. Our results demonstrate that natural geological boundaries constrain the morphological behaviour of embayed beaches, producing conspicuous alongshore variability in all embayments. Localised responses induced by lateral and vertical boundary interference with beach and nearshore dynamics include beach rotation, topographically-controlled rip circulation and restrained profile fluctuation. Spatial decoupling in cross- and longshore responses is accompanied by a temporal decoupling in response times, both of which are slower in more constrained embayments (from 1 day in exposed embayments to 1 week or more in the most sheltered ones). Normalised wave power was correlated at the 99% confidence level with the primary mode of morphological variability at most embayments, which represent 67% to 94% of the variance in the datasets. This correlation stresses the importance of combined parameterization of wave and tide forcing in process–response relations between hydrodynamics and morphological change for mesotidal coastal environments. Lateral and vertical geological boundaries exert their effects fundamentally by restraining longshore sediment transport, inducing cellular surf zone circulation and by impacting cross-shore sediment transport. It is postulated that decreasing sediment abundance and substrate depth intensify vertical boundary effects, while higher indentation and wave obliquity enhance the effects of lateral boundaries.

Surveys of beach visitor motivation in Ireland, Wales, Turkey and the USA indicate that beach awards play an insignificant role in motivation to visit beaches. However, a number of criteria closely identified with awards, notably cleanliness and water quality, are revealed to be very important. Aesthetic and emotional factors such as scenic setting and general ambience, and practical concerns such as proximity and range of activities available are much more important than beach awards in attracting visitors to beaches. The merits of beach awards are critically reviewed and it is concluded that any benefits that might accrue are in areas other than attracting visitors.

The equilibrium planform concept (EPC) for bayed beaches has achieved wide currency in coastal morphodynamics. The north coast of Ireland comprises a series of discrete headland-embayment beaches within which waves and currents recycle a finite sediment volume. It is therefore an ideal setting in which to explore the applicability of the concept. Application of the approach to 9 embayment beaches on the north coast of Ireland provides some insights into the application of the concept. The planform of some beaches does correspond to that predicted while others do not. Those whose measured planform does not correspond to the predicted planform can be interpreted through, (a) difficulty in identifying the wave diffraction point, (b) disequilibrium on the beach (sediment scarcity or excess), (c) geological control of beach morphology. The subjectivity in selecting the diffraction point renders alternative explanations difficult and reduces the utility of the approach on natural shorelines, where significant irregularities render identification of such points difficult.

A 2-year investigation into shoreface morphodynamic behaviour off a high-energy headland-embayment coast in Northern Ireland reveals important process–response mechanisms that cannot be explained solely by existing conceptual models. Fourteen sequential bathymetric surveys, conducted every 1–2 months, show that morphologic (seabed) change is not directly related to oceanographic forcing—extensive nearshore and shoreface accretion and erosion occurs under fair-weather, modal and high-energy conditions. The main factors which seem to cause significant change are long-duration (swell) events coupled with onshore winds, availability of (recently) introduced sediment, surges and elapsed time between storms and the next scheduled survey. Several high-energy events over a short time period ( −2 of shoreface accretion from the nearshore to 24 m depth. Net erosion was not observed anywhere, including the subaerial beach. Geologic evidence strongly suggests that the source of the significant volume (7.7×105 m 3 ) of sediment introduced into the study area must have been derived from the lower shoreface and/or inner shelf, beyond 24 m depth.

Experiments carried out at Magilligan Strand on the north coast of Ireland suggest that topographic steering of offshore winds is an important facet of the aeolian sediment transport system at this location. A five-day study (18-22 June 2005) investigated the pattern of airflow over the foredune while simultaneously collecting data on sediment flux. A simple instrument setup was used to characterise the airflow: a sonic anemometer was placed at the dune crest, with another on the mid-beach. Horizontal traps, electronic and integrating, measured sediment flux on the supra-tidal beach. Results show that offshore wind flow deviated from its original direction in the lee of the dune (seaward of foredune). The change in direction was not a simple steering of flow to a singular new direction, but rather flow separation resulting in turbulent multidirectional flow - including reversal. Traps located at the foot of the dune scarp recorded sediment transport during events forced by offshore winds. Data from sediment traps, wind and observational evidence have been used to argue that sedimentation was occurring in this zone. When budgeting for sediment movement within beach-dune systems it is important to take into account the effect of secondary airflow patterns during offshore winds and their role in constructive processes of foredune formation, particularly in post-storm recovery. (C) 2008 Elsevier B.V. All rights reserved.

New seismic stratigraphic, vibracore and AMS C-14 dates from two sites off the Northern Ireland coast yield information on the deglacial to present sea-level history and shelf evolution of the region. A lowstand of sea level at about 30 m below present sea level recorded by fossils in a lowstand shoreline deposit occurred around 13.4 cal ka B.P. following a period of rapid isostatic uplift associated with a RSL fall of 6-7 cm/yr. Following the lowstand, contrasting styles of sedimentation characterized the two study sites. In the sheltered environment of Belfast Lough, the lowstand shoreline was overtopped and buried by transgressive facies of intertidal and shallow sub-tidal mud and sandy mud. On the high-energy Portrush coast, the inner shelf sedimentary sequence is characterized by a basal conglomerate overlain by well-sorted sands with occasional interbedded gravel. (c) 2006 Elsevier B.V. All rights reserved.

In the face of a global rise in sea level, understanding the response of the shoreline to changes in sea level is a critical scientific goal to inform policy makers and managers. A body of scientific information exists that illustrates both the complexity of the linkages between sea-level rise and shoreline response, and the comparative lack of understanding of these linkages. In spite of the lack of understanding, many appraisals have been undertaken that employ a concept known as the “Bruun Rule”. This is a simple two-dimensional model of shoreline response to rising sea level. The model has seen near global application since its original formulation in 1954. The concept provided an advance in understanding of the coastal system at the time of its first publication. It has, however, been superseded by numerous subsequent findings and is now invalid. Several assumptions behind the Bruun Rule are known to be false and nowhere has the Bruun Rule been adequately proven; on the contrary several studies disprove it in the field. No universally applicable model of shoreline retreat under sea-level rise has yet been developed. Despite this, the Bruun Rule is in widespread contemporary use at a global scale both as a management tool and as a scientific concept. The persistence of this concept beyond its original assumption base is attributed to the following factors: 1. Appeal of a simple, easy to use analytical model that is in widespread use. 2. Difficulty of determining the relative validity of ‘proofs’ and ‘disproofs’. 3. Ease of application. 4. Positive advocacy by some scientists. 5. Application by other scientists without critical appraisal. 6. The simple numerical expression of the model. 7. Lack of easy alternatives. The Bruun Rule has no power for predicting shoreline behaviour under rising sea level and should be abandoned. It is a concept whose time has passed. The belief by policy makers that it offers a prediction of future shoreline position may well have stifled much-needed research into the coastal response to sea-level rise.

Coastal zone management is often hampered by ineffective collection of multidisciplinary information and, even when adequate data is available, ineffectual transfer of information from scientist to end-user. This may result in either poor or non-reproducible data collection procedures or sub-optimal utilisation of information, which ultimately impact on the quality of coastal zone management decisions. In this paper the authors outline an approach to the acquisition and effective transfer of integrated, multidisciplinary, environmental information from scientist to end-user. The Estuarine Health Index (EHI) was developed by focusing process research on physical, chemical and biological aspects of estuaries with an additional aesthetic component, into an integrated measure of estuarine health. The results may be portrayed either as a series of simple icons on a map, or as a stacked bar chart for a section of the coast and thus convey multidisciplinary information easily. In this paper the development of the individual components of this index is briefly described and the use of the index is illustrated by reference to results collected on over fifty estuaries on the South African coast. Finally, management uses of this approach and some of its benefits in terms of temporal and spatial environmental assessment are outlined.

Beachrock is present in many parts of the world, particularly on low-latitude coastlines. Its formation during stillstands or minor regressions in subtropical areas involves cementation of clastic grains and thus prevents grain transport in the littoral zone during later transgression or regression. Existing short and medium-term conceptual and numerical models of coastal evolution fail to take into account this effective reduction of littoral sand supply and the effects of the beachrock itself on shoreline development. In the short term, reduction of sediment supply through beachrock formation during transgression should enhance landward translation of the shoreline: conversely the beachrock itself may afford a degree of protection from erosion. In the medium to long term, beach-rock formation during multiple Pleistocene transgressions and regressions in areas which lack significant sediment input from land drainage systems may have caused a long-term reduction in sediment volume during the course of the Pleistocene. (This assumes that beachrock formation is not matched by its destruction through physical and bioerosion and chemical weathering.) Preservation of coastal facies is greatly enhanced by beachrock formation which may promote overstepping and drowning of strandline facies during transgression or preferential preservation during regression. Precise records of sea-level fluctuations may be preserved by beachrock formation, a situation rendered almost impossible in other areas due to littoral transport of mobile sediment. In the widespread areas in low latitudes where it occurs, beachrock formation may be an important element in models of horizontal shoreline displacement and coastal evolution.

In exposures of Pleistocene rocks on the east coast of South Africa, eight sedimentary facies were distinguished on the basis of petrology, grain size, internal structures and field relationships. These are interpreted as deposits of surf zone, breaker zone, swash zone, backbeach, boulder beach and dune environments. Three phases of deposition and diagenesis are recognized. As a result of the stabilising effect of pre-existing coastal facies, the deposits from successive sea level stands are stacked vertically in a narrow coast-normal strip. Early cementation prevented erosion of the deposits during subsequent transgressions. Deposition of subsequent facies took place on an existing coastal dune (Facies 1). A terrace was cut into this dune at a sea level 4.5 to 5 m above present. At this sea level, clastic shoreline sediments were deposited which make up the main sedimentary sequence exposed (Facies 2-7). The steep swash zone, coarse grain size, and comparison with modern conditions in the study area indicate clastic deposition on a high-energy, wave-dominated, microtidal coastline. Vertical stacking of progressively shallower water facies indicates progradation associated with slightly regressive conditions, prior to stranding of the succession above sea level. During a subsequent transgression to 5.5 or 6 m above present sea level, a second terrace was cut across the existing facies, which by then were partly lithified. A boulder beach (Facies 8) deposited on this terrace is indicative of high wave energy and a rocky coastline, formed by existing cemented coastal facies. Comparison with dated deposits from other parts of the South African coast suggest a Late Pleistocene age for Facies 2-8. Deposition was terminated by subsequent regression and continuing low sea levels during the remainder of the Pleistocene. Cementation of the facies took place almost entirely by carbonate precipitation. The presence of isopachous fibrous cements suggests early cementation of Facies 1, 2, 3 and 4 under marine conditions, initially as aragonite which has since inverted to calcite. Facies 5, 6 and 7 are cemented only by equant calcite spar, evidence of cementation in the meteoric phreatic and vadose zones. Lowering of the water table during regression caused the remaining pore space in Facies 1, 2, 3 and 4 to be filled with equant calcite spar. Decementation in a 130 cm wide zone is attributed to water table shifts associated with the later transgression which deposited Facies 8. The vertical stacking of the two depositional sequences may be attributed to rapid cementation of Facies 2, 3, 4, 5, 6 and 7 under humid, subtropical conditions. This lithified sequence then acted as a focus for deposition of coarse-grained shoreline facies (Facies 8) during the subsequent transgression.