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An intertidal sandstone reef, named barra de Las Canteras, protects the western coast of Las Palmas de Gran Canaria city (Canary Islands, Spain). The beach-reef system of Las Canteras constitutes one of the most valuable coastal geomorphological sites in the archipelago. Stratigraphic studies have identified the formation of the reef in the Last Interglacial (MIS 5e) in a coastal sedimentary paleo-environment. The rock structure is highly exposed to the Atlantic swell and consists mainly of a sandstone beachrock with a medium resistance to erosional processes. However, the historical and current erosion rates and the original extent of the reef are not known to date. This paper explores the geomorphological structure of the reef by combining a topo-bathymetric analysis (obtained by differential GPS, multibeam echosounder and hyperspectral sensor) and the analysis of geomorphological features on high-resolution images, obtained with a hyperspectral camera mounted on a UAV. The results provide a comprehensive, high-resolution image of the subaerial and submerged morphology of the reef. The structure reflects the distribution of erosional fronts and the existence of collapsing submarine blockfields and nearshore, uneroded, remnant reliefs. Detailed analysis of these features allows to estimate the probable original extent of the sandstone reef and to relate the erosional retreat processes to the sea-level dynamics during the Holocene. [ABSTRACT FROM AUTHOR]

Evidence for sea-level change during and around Marine Isotope Stage (MIS) 5e (ca. 125 ka) in southern Africa derives from a wide variety of geomorphic and sedimentological sea-level indicators, supported in the past 2 decades by absolute chronological control, particularly on littoral deposits, some of which have a quantifiable relationship to former sea level. In addition to these proxies, data provided by both terrestrial (dune sediments and archaeological remains) and marine (lagoonal and nearshore littoral sediments) limiting points provide broad constraints on sea level. Here, we review publications describing such data points. Using the framework of the World Atlas of Last Interglacial Shorelines, we insert in a standardized database (10.5281/zenodo.4459297, Cooper and Green, 2020) all the elements available to assess former palaeo-relative sea level (palaeo-RSL) and the chronological constraints associated with them (including uncertainties). Overall, we reviewed 71 studies, from which we extracted 39 sea-level indicators and 26 limiting points. As far as age attribution is concerned, early analysis of molluscs and whole-rock beachrock samples using U series allowed dating of several sea-level indicators during the 1980s, but the more widespread application of optically stimulated luminescence (OSL) dating since 2004 has yielded many more (and more accurate) sea-level indicators from several sites. This has helped resolve the nature and timing of MIS 5e shorelines and has the potential to further elucidate the apparent presence of two or more sea-level peaks at several South African sites during this interval. The standardized sea-level database presented in this paper is the first of its kind for this region. Future research should be directed to improve the stratigraphic description of last interglacial shorelines and to obtain better dating, high-accuracy elevation measurements with better palaeo-RSL interpretation. [ABSTRACT FROM AUTHOR]

Different parent rocks, climate, and relief control the provenance of beach sands on the coast of Mexico. This is the first paper to address the provenance problem of beach sands in south‐eastern Mexico considering a homogeneous climate and relative similarity in parental rocks but different relief. Two coastal areas are confined in this study: (a) the Western Gulf of Tehuantepec (WGT) and (b) the Eastern Gulf of Tehuantepec (EGT). The WGT beach sands are probably controlled by the denudation of orthogneisses, Eocene–Miocene basaltic–andesites–dacites–rhyolites from the Volcanic Belt of the Sierra Madre del Sur (VBSMS), and granites to diorites from the Coastal Plutonic Belt (CPB). The rocks exposed in the EGT are represented by orthogneisses and tonalite, granodiorite, and gabbro suites from the Palaeozoic–Mesozoic Chiapas Coastal Plutonic Belt (CHCPB). Quaternary andesites and dacites from the Tacaná Volcano are located in the eastern coastal area. The Chemical Index of Alteration (CIA) and Plagioclase Index of Alteration (PIA) values indicate that the less weathered beach sands are in the WGT compared to the EGT coastal area. Plagioclase transport is preserved in a narrow coastal plain that contributes to a lower a weathering rate compared to the EGT sands deposited in a wider coastal plain. Geochemical analyses show that the WGT and EGT beach sands are admixtures of felsic, intermediate, metamorphic, and volcanic sources in their sands composition. Relief seems to play a major role in the composition of beach sand in both coastlines, since parental rocks are mostly similar in composition and climate remains homogeneous along the coast. [ABSTRACT FROM AUTHOR]

The loess caves developed on Chinese loess plateau are not only a typical phenomenon of soil and water loss, but also a special kind of geological hazard. Many loess dilapidations, collapses and medium to small-sized landslides are related to the loess caves. To understand the characteristics and the geo-disasters induced by loess caves, the loess caves developed on Chinese loess plateau were rigorously investigated. Based on a long-term field surveys on about 800 fixed points in Gansu, Ningxia and northern Shaanxi, the classifications and characterization of loess caves in Chinese loess plateau are discussed in detail. Moreover, the regionally developmental regularity hierarchical development regularity of loess cave and its characteristics are studied in this paper, which show that the density of loess caves on the northwestern loess plateau is higher than that in the southeastern loess plateau than that in the southeast in China. And the main control factors affecting the development of loess caves are analyzed. Interestingly, the development of the caves is related to the loess layer, land characteristics, geologic structure (including the joints and the fracture system), micro topography, hydro-geological factors and climatic conditions. [ABSTRACT FROM AUTHOR]

Understanding ancient climate changes is hampered by the inability to disentangle trends in continental ice volume from records of relative sea-level change. As a unique coastal deposit in tropical and subtropical regions, beachrock has been proved to be reliable for constraining the glacial meltwater signal and thus the total volume of land-based ice in Quaternary. However, beachrock is rarely recognized in the fossil record due to (a) the two-dimensional distribution of beach deposits, as opposed, for example, to extended platform sediments, and (b) the fact that specific environmental conditions are required in order to lithify sediments directly on the beach. By combining the stratigraphic architecture with petrography of characteristic carbonate cements, we demonstrate the first known occurrence of Ordovician beachrock in the Tarim Block, northwestern China. According to biostratigraphic data, a middle Katian (Upper Ordovician) palaeokarst surface is capped by carbonate conglomerate beachrock and this is suggesting a significant relative sea-level rise in late Katian. The beachrock can be correlated with widespread subaerial exposure surfaces and a pronounced stratigraphic gap within the Katian in northwestern Tarim. We suggest that the beachrock ‘fingerprinted’ a strong melt-water pulse in high latitudes after a short-lived Katian glaciation, which has not received much attention in scientific papers so far. [ABSTRACT FROM AUTHOR]

Powerful typhoons frequently affect eastern Taiwan. On Dabaisha beach on the SW coast of Ludao Island, a small volcanic island lying SE off mainland Taiwan, the presence of numerous beachrock slabs provides evidence of the sediment transport capabilities of high-energy waves generated by these storms. With a well-defined beachrock source from which the slabs were derived, it is easy to differentiate clasts transported in run-up or backwash flow based on their current position relative to the outcrop. In order to estimate the wave-generated flow velocities from the measured beachrock slabs, the hydrodynamic equations for boulder transport by Nandasena et al. (2011) have been rearranged so that they are appropriate for this particular geomorphic setting, where exposed in situ beachrock outcrops liberate clasts which may then be transported either by run-up onto the beach or backwash flow onto adjacent reef platforms. Such settings are common on tropical coastlines with fringing coral reefs and beaches comprising mostly biogenic sediments. In the Dabaisha beach case, the lowest flow velocities required to transport all measured beachrock slabs from their source outcrop to current positions are 2.18–3.16 m/s for run-up and 1.76–3.24 m/s for backwash. With a discussion of advantages and limitations on the use of beachrock clasts for interpreting wave behaviour, this paper presents another proxy for studying high-energy wave events that is highly suitable for certain carbonate-rich coastlines. [ABSTRACT FROM AUTHOR]

Abstract: A standard assumption in coastal engineering is that the porosity of natural beach sand (non-cohesive) is 40%. However, is this assumption correct for all beach sand? This paper proposes an accurate and simplified method to assess changes in sand porosity after beach nourishment by means of in-situ density surveys through a nuclear densimeter. This novel application has been applied to different beaches in the southwest of Spain according to the tidal range, grain size and beach morphology in several terms. General results show that sand porosities range from 25.6% to 43.4% after beach nourishment works. This research can be considered a support tool in coastal engineering to find shifting sand volumes as a result of sand porosity variability after beach nourishment and later marine influence. [Copyright &y& Elsevier]

Abstract: The Lefkada–Preveza coastal zone, NW Greece, is characterised by an active barrier system and related extensive beachrock sequences. Besides the gradual coastal processes of longshore drift and spit evolution, the presence of active tectonics and the occurrence of tsunamis have been documented in previous studies and are part of the coastal geomorphological system. In this paper, we present the results of detailed multi-proxy sedimentological and geomorphological investigations carried out along the northern part of the barrier system and in back-beach positions. Our findings suggest that extreme wave events contributed to coastal and environmental changes and involved temporary breakdown of the barrier system. Sedimentary findings suggest that one generation of event deposits may be related to the 365AD Crete earthquake and associated tsunami. According to our results, the Lefkada coastal system formed by the interaction of both long-term, gradual and sudden, impulsive littoral geomorphodynamics. Extreme wave events are assumed to have played a significant role in the evolution of the present coastline, acting as recurrent impulsive disturbances of the coastal system. Subsequently, the onset of long-term gradual coastal processes, such as longshore drift, re-established a state of natural coastal balance by re-arranging the coastal sediments. [Copyright &y& Elsevier]

Abstract: Tromelin is a small coral reef island (1 km2) located in the Indian Ocean, approximately 440km east of Madagascar and 580km north of La Réunion. Despite the presence of a permanent Météo France weather station on Tromelin since the 1950s, a detailed geomorhological study of the island has never been undertaken. In this paper, we describe results from the 2008 field season, which enabled us to map and describe seven geomorphological zones on the atoll. (1) Tromelin''s bathymetry is characterised by a pronounced submarine slope, which attains depths of 1000 m at only 2.5km from the island''s coastline. This geomorphology is typical of volcanic hotspots. (2) A coral platform borders the emerged crown of the island. This platform is exposed at low tide and has been fashioned in an ancient Pleistocene substratum. The substratum has been eroded by abrasive marine action to its present shape since the stabilisation of relative sea level around 6000 years ago. Erosion of the reef yields most of the biogenic sediment supply to the island. (3) The upper foreshore is characterised by outcrops of beachrock. These formations show a stratfication in slabs and dip gently towards the sea in the same manner as the contemporary clastic sediments. (4) Tromelin''s beaches are divided into three sub-units, which reflect the different energy dynamics around the island, in addition to the transfer of sediment from the windward to the leeward side: (i) the southern storm beaches are characterised by coral blocks reworked during episodic high-energy events; they form boulder ramparts. Four perched rampart ridges have been recorded at ∼1 m, ∼3 m, ∼4.5 m and ∼7 m above mean sea level; (ii) transitional beaches are observed between the south and the north, constituting storm blocks and coarse sands and gravels; and (iii) sandy beaches are noted on the northern leeward side, comprising rounded gravels and coarse sands. The northern tip of the island is characterised by a sand spit (∼125 × ∼225 m), whose geometry varies based on the seasonal and meteo-marine contexts. (5) On Tromelin, a number of dune formations are observed. These are best developed in the north of the island due to the south-north translation of clastic sediments by aeolian wind action, and the trapping of sands by the well-developed vegetation. The height of the dunes varies between 10cm (the southern micro-dunes) to 250cm in the Northeast of Tromelin. (6) Exceptional waves have deposited storm tracts up to 250 m from the foreshore zone, comprising coarse gravels and coral blocks. The storm tract deposits are most prevalent on the windward side of the island, due not only to the high-energy dynamics, but also to the absence of vegetation cover in this area. (7) The southern depression covers an area of ∼40,000 m2. At its lowest point it is only 1.2 m above sea level. [Copyright &y& Elsevier]

This paper addresses the possibilities of the combined use of airborne hyperspectral data and airborne laserscanning data to study sand dynamics on the Belgian backshore and foreshore. In August 2000, August 2001, and October 2002, airborne hyperspectral imagery was acquired with a CASI-2 sensor from the entire Belgian beach at low tide. Hyperspectral images contain a reflectance spectrum for each pixel. The characteristics of this spectrum are influenced by the state, the composition, and the structure of the topsoil of the beach. After radiometric, geometric, and atmospheric correction of the images, a normalization of the spectral signatures was necessary to allow comparison of wet and dry pixels. Consequently, the first derivative of the normalized spectra was taken, followed by a spectral angle mapper algorithm that was used to perform a supervised classification. The beach was classified into eight sand classes. Almost simultaneous with the first two CASI campaigns (in September 2000 and September 2001), a laserscan survey was performed to generate digital terrain models with a mean vertical accuracy of 5 cm. By differencing both digital terrain models, a map with sedimentation and erosion zones could be extracted. The combined interpretation of the erosion/sedimentation map with the classified hyperspectral data yields an appropriate method for studying the processes of sand transport along the Belgian coastline. The method was tried out with success on the Belgian east coast. [ABSTRACT FROM AUTHOR]

• The Strait of Messina (Sicily, Italy) includes a long-shore beachrock structure. • Beachrock microtidal pools represent a highly biodiverse and variable environment. • Beachrock communities structure allows the insurgence of prey-predator interaction. • Interactions between C. erythropus and P. turbinatus follow a Holling type-III model. The Strait of Messina (Sicily, Italy) attracts the interest of marine ecologists for the presence of a large variety of habitat and mutually-interacting communities. Among them, beachrock formations, despite their wide geographic distribution, which also includes the Mediterranean area, have been poorly investigated from the biotic viewpoint. In this paper, the spatial and seasonal variability of benthic megafauna from the Messina microtidal beachrock is described. Combining in situ collected data (measurements of abiotic parameters and underwater visual census) with theoretical post-processing analyses (analysis of similarity percentages and cluster analysis), we deduced the possibility to model the dynamics observed between the most dominant species, a top snail, Phorcus turbinatus (Born, 1778), and a hermit crab, Clibanarius erythropus (Latreille, 1818), in terms of a prey-predator interaction. These species gave rise to different intriguing dynamical regimes (including periodic oscillations) that were qualitatively captured by a mathematical model focused on the respective trophic chain levels. The identification of all model parameters and the use of numerical simulations complemented the above analysis and allowed to gain more insights into the complex dynamics of these oligotypic communities and on the most relevant factors determining the ecosystem equilibria. [ABSTRACT FROM AUTHOR]

Up until the last ten years, remote sensing data and especially high-resolution satellite data and airphotos were mainly used in shallow water mapping. The evolution and low cost of unmanned aerial vehicles (UAVs) provides a new tool for coastal area monitoring. This paper presents the synergistic use of a small commercial UAV and an unmanned surface vehicle (USV) for beachrock mapping in Syros Island, Greece. RGB images collected with a quadcopter were processed using Structure from Motion (SFM) photogrammetry in order to create digital surface models (DSMs) and orthophotos of the coastline. A beachrock lying in shallow waters was detected and mapped using the UAV derived products. At the same time, a USV equipped with a compact side scan sonar (SSS) and bathymetric sonar system, provided the shape of the beachrock by mosaicking the backscatter strength of the SSS. In order to evaluate the results of the UAV and USV data derivatives, the beachrock perimeter and its depth were also mapped using a differential global navigation satellite system (GNSS) receiver. During the fieldwork, samples from the beachrock were collected and analyzed in the laboratory. The mineralogical composition of the bulk samples was determined by powder X-ray diffraction (XRD). Further petrographic study was also performed by petrographic polarizing microscope, macroscope, and scanning electron microscopy (SEM). Beachrock samples are classified as fine to medium grain sandstones and conglomerates. The mineral compositions of their grains and lithoclasts reflect the bedrocks of Syros Island (mainly metamorphic rocks) while a micritic high-Mg calcite constitutes the cement of these rocks. [ABSTRACT FROM AUTHOR]