Search Results (21)

Beachrocks are common coastal sedimentary rocks in tropical and subtropical seas. They are widely spread especially in islands and coastal areas. These rocks are important for island geological evolution research. Research on beachrocks aids in protecting island ecosystems and enhances islands’ ability to prevent and mitigate damage from natural disasters. This study uses unmanned aerial vehicle (UAV) images and the U-Net model based on deep learning to identify beachrocks. To enhance identification accuracy, the efficient channel attention (ECA) mechanism was integrated, leading to improvements of 0.49% in overall accuracy, 1.41% in precision, 0.97% in recall, 1.10% in F1-score, and 2.09% in intersection over union (IoU) compared to the baseline U-Net model. The final results demonstrate that the model effectively identified beachrocks, achieving 97.47% accuracy, 93.27% precision, 94.73% recall, 93.95% F1-score, and 88.65% IoU. This study offers a valuable tool for island geological evolution research and supports the development of large-scale island conservation efforts. Full article

This study examines the relative sea-level changes during the Upper Holocene period along the south coastline of Cyprus through the investigation of beachrock formations and their impact on archaeological sites. Beachrock, as a natural indicator of past relative sea levels, provides valuable insights into the dynamic interplay between sea-level fluctuations and human settlements. The research integrates field observations, mineralogical and geochemical analysis, geochronological studies, and archaeological data to reconstruct past sea-level variations and their implications for coastal archaeological sites. The results reveal significant fluctuations in relative sea levels during the Upper Holocene, influencing the development and occupation of coastal archaeological sites. By elucidating the complex relationship between sea-level changes and human activity, this study contributes to our understanding of past coastal environments and their socio-cultural dynamics. Moreover, it underscores the importance of considering geological factors in archaeological interpretations and coastal management strategies in the face of contemporary sea-level rise. Full article

Beachrock is a sedimentary rock that forms rapidly through the cementation of beach-associated clasts by calcium carbonate within the intertidal zone. On the southern coast of Israel, Holocene beachrock exposures typically appear as linear, shore-parallel platforms that dip seawards. In the archeological record, beachrock was exploited as a natural resource for various purposes, including the production of querns, millstones, basins, building stones, and other architectural elements. At Tel Yavne, a site continuously settled from the Chalcolithic period to the present day, excavations in the eastern and southern fringes revealed an extensive industrial compound dating to the Byzantine and early Islamic periods. This compound underscores the settlement’s economic and industrial prominence during those eras. Numerous beachrock artifacts were uncovered, and this study examines their practical applications while characterizing their composition and microstructure. This research highlights the role of beachrock as a key resource, providing insights into inland–coastal economic interactions in antiquity and broadening our understanding of its use within the socio-economic landscape of the region. Full article

The present study examines the recent evolution of a cliff coast along the Aegean Sea, considering its geotectonic context, oceanographic factors, sediment dynamics, and human impact. Initially, the formation of this coastal stretch was influenced by neotectonic faults, oriented both semi-parallel and diagonally relative to the present coastline orientation (NE–SW). Subsequently, the delivery of terrestrial sediment from ephemeral rivers and cliff erosion, along with nearshore wave-induced hydrodynamics have played a secondary role in shaping its current configuration, which includes a beach zone along the base of the cliff. This secondary phase of coastal evolution occurred over the past 4–5 thousand years, coinciding with a period of slow sea level rise (approximately 1 mm/year). Evidence such as uplifted notches and beachrock formations extending to around 5 m water depth suggests intervals of relative sea level stability, interrupted by episodic tectonic events. Anthropogenic interventions, related to both changes in coastal sediment budget and coastal engineering projects, have caused beach erosion, particularly in its central and northern sectors. Full article

Beachrock is a type of coastal carbonate sedimentary rock developed in the sandy beach intertidal zone, widely distributed along the beach front, and the loss of beach sediment is the main cause of beachrock exposure. Based on the analysis of measured data of different exposure forms of beachrocks in profiles, this paper analyzes the main features and influences of non-dynamic factors, such as the exposure position and morphology, of beachrocks on the dynamic geomorphic processes of beaches. Studies have shown that (1) changes between beach energy dissipation bodies are significant features of coastal geomorphic processes under the influence of beachrocks. The first spatial mode of EOF analysis shows that the erosion position of beach-rock-exposed profiles is mainly concentrated in the protected and real sections of beachrock, and the first temporal mode indicates that the exposure of beachrock results in a lagged response of its profile to dynamic environmental changes. (2) The differences in the exposure forms of beachrocks determine the sand-holding space of the beach, and the differences in the lateral exposure positions of beachrocks determine the main areas where erosion occurs on the profile. Meanwhile, the geomorphic processes of their profiles show different degrees of feedback, and such geomorphic phenomena can serve as reference indicators for the stage-wise evolution process influenced by beachrocks. Full article

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. Full article

Geology usually deals with rocks formed long ago, which are static and stable over the span of human lifetime. This study aims to analyze anthropogenic influence on the formation of geological features in the southeastern Mediterranean. Tel Dor, along Israel’s northern coast, was chosen due to the continuous presence of humans in the area for over 4000 years and the protective environment of its natural bays that preserve geomorphological changes. This allows for the examination of whether and how humans affect their (geological) environment. Three rocky platforms were chosen in the shallow waters of the South Bay adjacent to the Tel, and four cores were extracted. Results show the extent of the direct and indirect anthropological influences on the landscape. The presence of building stones consisting of dolomite, which is not found along the Carmel coast, is an example of direct influence (importation). The evolution of a biological and non-biological reef upon the sturdy base of the port constructions is an indirect influence. The formation of a non-biological reef upon an archaeological feature is a unique process. It would not have consolidated without the presence of anthropogenic activity. This study shows how human interference in the coastal area can trigger a chain reaction of geological processes lasting more than 2000 years. Full article

Geomorphological and sedimentological indicators are often used to reconstruct not only coastal evolution, but also relative sea level changes. In this work, we studied the coastal sediments of Psatha bay (Alkyonides Gulf, Greece) and beachrock outcrops in order to reconstruct the coastal evolution of the area. The drillings analysis included stratigraphy, sediment texture and radiocarbon dating. Detailed mapping of the beachrocks was accomplished using DGPS-GNSS, as well as mineralogical analysis and OSL dating of beachrock samples. The new beachrock index points indicate a sea level that fell by 0.64 ± 0.13 m since 2200 ± 210 years BP and by 0.95 ± 0.13 m since 4160 ± 320 years BP, as a direct result of its location near the uplifting footwall of Psatha fault, suggesting further a rate of tectonic uplift of ~0.26 mm/yr for the late Holocene. Full article

Beachrock is composed of intertidal-associated sediments, rapidly cemented by calcium carbonate, and has important implications for understanding coastal morphological processes. This study focuses on the morphodynamic erosion patterns of Late Holocene beachrock outcrops along the Mediterranean coast of Israel that have formed since the sea reached its present level about 4000 years ago. Exposed beachrock is subjected to erosion, affecting its seaward and landward facing fronts and upper surface, and creating distinct morphological features due to wave pounding and coastal currents which remove unconsolidated sediment supporting layers. The current state of beachrock morphology is presented, based on field measurements and field relation interpretations of selected sites, backed by petrographic and sedimentological data. It shows and studies selected beachrock exposures along Israel’s coast, and characterizes their morphological features in various field-relation configurations. A classification is developed of the main erosion patterns of beachrock embedded on loose, hard, partly hard and partly loose substrate. Full article

Beachrocks are generally mapped on the coastline surface and/or in a low depth in the subtidal zone in coastlines and are cemented chiefly by carbonate material. Their outcrops may vary from a tenth of meters to a tenth of kilometers in length. Along the Epirus coast, in Greece, beachrocks outcrops are laying on the coastline for more than ten kilometers. In the present work, we used Unmanned Aerial Vehicles (UAVs), in situ sampling, and the Geographical Information System (GIS) to map three beachrock areas with a length of 500 m to 600 m each. In synergy with extended mineralogical and petrographic analyses, we provide preliminary data about the geographical distribution and the mineralogical differences of these beachrocks. Furthermore, for the first time, we tried to investigate the correlation between the geotectonic setting of the broader area and the beachrock extent, shape, and petrographic parameters. The laboratory analyses proved that the beachrocks belong to a similar depositional zone of a marine–vadose environment. Despite variations in the textural petrographic, features among the specimen’s analyses permit us to consider these sedimentary rocks as not a uniform outcrop. It is indicated that the beachrock formation and the cementation progress in the study area are both controlled by active reverse faults and diapiric or tectonic anticlines. Full article

Beachrocks are well known as significant proxies for paleoenvironmental analysis as they indicate the coastal evolution. The combination of geomorphological and archaeological sea level indicators has a significant contribution to the coastal paleogeographic reconstruction. In this study, we studied a beachrock from the Diolkos area (West Corinth canal, Greece) and remnants of Diolkos slipway to reconstruct the coastal evolution before Diolkos construction until today. We conducted detailed mapping of Diolkos beachrock using DGPS-GNSS, as well as mineralogical analysis and OSL dating of beachrock samples. The results showed that a beachrock slab was preserved before the construction of Diolkos below it, followed by its submergence by a co-seismic event after Diolkos abandonment during 146 B.C. Consequently, a new beachrock was developed on top of the submerged Diolkos around 120 ± 14 A.D. The RSL was stable until 1596 ± 57 A.D. when the beachrock developed even closer to the present-day coastline. After 1596 A.D., it was uplifted by 12 cm until it reached today’s condition. Full article

Beachrocks are a window to the past environmental, geological, sedimentological and morphological conditions that were dominant in the coastal zone during their formation. Furthermore, beachrocks have the ability to reduce coastal erosion impact on sandy beaches. This study focuses on the beachrock formation mechanism through the comparison of cement characteristics, mineral chemistry and sedimentology of beachrock occurrences from two different geological and geographical localities: Diolkos, Corinth, Greece and Sumuide, Okinawa, Japan. In addition, in order to investigate a potential soft engineering method to protect coasts from erosion, artificial beachrock samples were created in vitro using sand samples and ureolytic bacteria from both areas under accelerating conditions. For Okinawa artificial beachrock experiments, the bacteria Pararhodobacter sp. was used, and for Diolkos, it was the bacteria Micrococcus yunnainensis sp. For the natural beachrocks, a multi-analytical approach was accomplished with the use of microscopic investigation, a scanning electron microscope, energy-dispersive X-ray spectroscopy, X-ray diffraction and X-ray fluorescence. Correlations were made between natural and artificial beachrocks. Results have shown that Diolkos beachrock was formed in the upper part of the intertidal zone, consisting of detrital material originating from the local bedrock, while Sumuide beachrock formed in the low intertidal–upper subtidal zone, consisting of coral sand and foraminifera fragments. For the artificial beachrocks, three samples were created using the microbial-induced carbonate precipitation (MICP) method, one from Diolkos (Corinth, Greece) and two from Sumuide (Okinawa, Japan). Diolkos artificial beachrock was better consolidated in comparison to Sumuide. Our investigation has shown that bacterial density was the key factor for the creation of the artificial beachrocks, while the samples’ granulometry played a secondary role in the process. The laboratory artificial beachrocks show encouraging results for a new soft engineering method to encounter beach erosion while keeping an ecofriendly character by saving energy, material resources and gas emissions. Artificial beachrocks can share the same properties of a natural beachrock and can contribute positively to marine biodiversity as a natural rocky habitat. Full article

Marine bacterial biomineralisation by CaCO₃ precipitation provides natural limestone structures, like beachrocks and stromatolites. Calcareous deposits can also be abiotically formed in seawater at the surface of steel grids under cathodic polarisation. In this work, we showed that this mineral-rich alkaline environment harbours bacteria belonging to different genera able to induce CaCO₃ precipitation. We previously isolated 14 biocalcifying marine bacteria from electrochemically formed calcareous deposits and their immediate environment. By microscopy and µ-Raman spectroscopy, these bacterial strains were shown to produce calcite-type CaCO₃. Identification by 16S rDNA sequencing provided between 98.5 and 100% identity with genera Pseudoalteromonas, Pseudidiomarina, Epibacterium, Virgibacillus, Planococcus, and Bhargavaea. All 14 strains produced carbonic anhydrase, and six were urease positive. Both proteins are major enzymes involved in the biocalcification process. However, this does not preclude that one or more other metabolisms could also be involved in the process. In the presence of urea, Virgibacillus halodenitrificans CD6 exhibited the most efficient precipitation of CaCO₃. However, the urease pathway has the disadvantage of producing ammonia, a toxic molecule. We showed herein that different marine bacteria could induce CaCO₃ precipitation without urea. These bacteria could then be used for eco-friendly applications, e.g., the formation of bio-cements to strengthen dikes and delay coastal erosion. Full article

This study utilizes lithofacies characteristics, petrographic, XRD, and stable isotope data of Al-Mejarma beachrocks, Red Sea, Saudi Arabia, to interpret its depositional setting, origin of cement, and coastal evolution. The beachrock is 1.15 m thick, medium to very coarse-grained sandstone with scattered granules. It shows massive to graded bedding, horizontal, ripple, and shore parallel to slightly oblique planar cross-laminations, with a remarkable absence of bioturbation. It was deposited by shore-parallel longshore currents in a relatively high-energy beach environment. The framework comprises quartz, feldspars, and lithic fragments admixed with biogenic remains of algae, mollusca, foraminifera, corals, and echinoids. They are cemented by high magnesium calcite in the form of isopachous rims and pore-filling blades, and rarely, as a meniscus bridge. The mean values of δ¹⁸O_VPDB and δ¹³C_VPDB are 0.44‰ and 3.65‰, respectively, suggesting a seawater origin for the cement. The framework composition, facies geometry, and association with back-barrier lagoon impose a deposition as a shoreface-beach barrier through two stages corresponding to the middle and late Holocene. The first stage attests landward migrating sediment accumulation and rapid marine cementation. The sediments stored offshore during the early and middle Holocene humid periods migrated landward from offshore and alongshore by onshore waves and longshore drift during the middle and late Holocene sea-level highstand. They were cemented to form beachrock and subsequently emerged as the late Holocene sea-level fell. Full article

The present study concerns the Holocene inland beachrocks that are exposed in the Red Sea coastal plain at the mouth of Wadi Al-Hamd, South Al-Wajh City, Saudi Arabia, and their utility as an indicator for Holocene climate and sea level changes. In addition, the framework composition, and carbon and oxygen isotopic data, are employed to interpret the origin of their cement. The beachrock consists mainly of gravel and coarse-grained terrigenous sediments dominated by lithic fragments of volcanic rocks, cherts and rare limestones along with quartz, feldspars and traces of amphiboles and heavy minerals. In addition, rare skeletal remains dominated by coralline algae, benthic foraminifera and mollusca remains are recognized. The allochems are cemented by high Mg-calcite (HMC) formed mainly in the intertidal zone under active marine phreatic conditions. The cement takes the form of isopachous to anisopachous rinds of bladed crystals, micritic rim non-selectively surrounding siliciclastic and skeletal remains, and pore-filling micrite. Pore-filling micrite cement occasionally displays a meniscus fabric, suggesting a vadose environment. The δ¹⁸O and δ¹³C values of carbonate cement range from −0.35‰ to 1‰ (mean 0.25‰) and −0.09‰ to 3.03‰ (mean 1.85‰), respectively, which are compatible with precipitation from marine waters. The slight depletion in δ¹⁸O and δ¹³C values in the proximal sample may suggest a slight meteoric contribution. Full article