Microbial Carbonates

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.

The late Mesoproterozoic Era (1300-1000 Ma) was a critical period that witnessed the origin and early evolution of multicellular eukaryotes. Multiple studies have reported observations that the carbon isotope composition of carbonate ( 13 Ccarb) underwent a substantial increase after ca. 1250 Ma. The high  13 Ccarb values suggest that the fraction of organic carbon burial (forg) had increased, which, consequently, might have promoted the oxidation of surface environments and the diversification of multicellular eukaryotes. However, details of the carbon cycle during this critical time interval remain elusive, which is pivotal to testing this hypothesis. In this study, we analyzed the stable carbon isotope composition of paired organic matter ( 13 Corg) and carbonate, as well as the thermal characteristics of the organic matter, from the Shennongjia Group in South China, which has been constrained to an age of ~1340-1150 Ma. A gradual increase in  13 Ccarb, from ~-2‰ to >+4‰, is observed in the interval from the middle Shennongjia Group. Above which, the  13 Ccarb declines to ~-2‰ in the uppermost. The paired  13 Corg values show an extensive range of compositions, from ~-22 to -32‰. Raman spectral data revealed that the organic matter in the Shennongjia Group experienced a wide range of thermal history, which might be ascribed to the involvement of detrital organic matter. We reconstructed the  13 Ccarb-org and forg values in two different scenarios: one included all the  13 Corg data, while the other screened the  13 Corg data to minimize the possible effects of detrital organic matter. The results of these two reconstructions show similar temporal trends. Intriguingly, the  13 Ccarb-org are generally larger than the modern counterpart, which can be attributed to higher pCO2. The calculated forg of the Shennongjia Group is generally lower than the modern value, 20%. However, the forg experienced a substantial increase between ca. 1250 and 1190 Ma, suggesting enhanced oxidation of surface environments, which might have paved the way for the diversification of multicellular eukaryotes.

Precambrian rocks is an important requirement in the search for evidence of life on other ancient planetary surfaces. Three major kinds of biosignatures are crucially important: primary microbial sedimentary textures, diagenetic organo-mineral assemblages, and stable isotope compositions. This study presents new petrographic, mineralogical, and organic geochemical analyses of biosignatures in dolomitic stromatolites from the Pethei Group (N.W.T., Canada) and the Kasegalik Formation of the Belcher Group (Nunavut, Canada). Both are approximately contemporary late Paleoproterozoic stromatolite-bearing dolomitic units deposited after the Great Oxidation Event. Micro-Raman and optical microscopy are used to identify and characterise possible diagenetic biosignatures, which include close spatial association of diagenetic materials (such as ferrous-ferric oxide and anatase) with disseminated organic matter, dolomitic groundmass textures, and mineralised balls. Many of these petrographic relationships point to the oxidation of organic matter either biotically or abiotically in association with iron reduction and chemically oscillating reactions. Oxidation of organic matter in these stromatolites is consistent with the widespread oxidation of biomass during the late Paleoproterozoic Shunga-Francevillian Event. Biosignatures identified in this study are also compared to possible carbonate outcrops on Mars, and thereby contribute a basis for comparison with potential biosignatures in ancient Martian terrains. Similarities are drawn between the paleoenvironments of the studied units to the Isidis and Chryse planitia as locations for potential extraterrestrial dolomitic stromatolites.

The genesis of dolomite is a contentious issue partly due to the difficulty in its synthesis at ambient temperature. Certain types of microorganisms have been demonstrated to be effective in promoting the precipitation of disordered dolomite, an important precursor of sedimentary ordered dolomite. In contrast to a growing body of research on the catalytic role of microbial exopolymers in the crystallization of disordered dolomite, the role of other microbial exudates (e.g., carboxylic acids) remains unknown. To fill in this knowledge gap, precipitation experiments, mimicking the carbonation process within microbial mats, were conducted in saline solutions containing 0-30 mM succinic acid or citric acid, which are commonly produced by microbes. The starting salinities of experiment solutions were set to 35‰ and 70‰, in order to evaluate the effect of solution salinity on dolomite formation. Our results showed that both succinic acid and citric acid enhanced the incorporation of Mg 2+ into growing Ca-Mg carbonates. Solution salinity also played a positive role in enhancing Mg signature in Ca-Mg carbonates. Disordered dolomite with 40.92 mol% MgCO3 was detected under the conditions of 30 mM succinic acid and 70‰ salinity, whereas in other reactors with succinic acid, Mg-calcites formed. Citric acid was more effective in loading Mg 2+ into Ca-Mg carbonates compared with succinic acid, as evidenced by the predominant occurrence of disordered dolomite with MgCO3 content ranging from 40.91 mol% to 46.75 mol% in most conditions tested. The results of this study have implications for the formation mechanism of sedimentary dolomite.

Stromatolites, organosedimentary structures formed by microbial activity, are found throughout the geological record and are important markers of biological history. More conspicuous in the past, stromatolites occur today in a few shallow marine environments, including Hamelin Pool in Shark Bay, Western Australia. Hamelin Pool stromatolites often have been considered contemporary analogs to ancient stromatolites, yet little is known about the microbial communities that build them. We used DNA-based molecular phylogenetic methods that do not require cultivation to study the microbial diversity of an irregular stromatolite and of the surface and interior of a domal stromatolite. To identify the constituents of the stromatolite communities, small subunit rRNA genes were amplified by PCR from community genomic DNA with universal primers, cloned, sequenced, and compared to known rRNA genes. The communities were highly diverse and novel. The average sequence identity of Hamelin Pool sequences compared to the >200,000 known rRNA sequences was only ϳ92%. Clone libraries were ϳ90% bacterial and ϳ10% archaeal, and eucaryotic rRNA genes were not detected in the libraries. The most abundant sequences were representative of novel proteobacteria (ϳ28%), planctomycetes (ϳ17%), and actinobacteria (ϳ14%). Sequences representative of cyanobacteria, long considered to dominate these communities, comprised <5% of clones. Approximately 10% of the sequences were most closely related to those of alpha-proteobacterial anoxygenic phototrophs. These results provide a framework for understanding the kinds of organisms that build contemporary stromatolites, their ecology, and their relevance to stromatolites preserved in the geological record.

The distribution of major phosphate deposits in the Precambrian sedimentary rock record is restricted to periods that witnessed global biogeochemical changes, but the cause of this distribution is unclear. The oldest known phosphogenic event occurred around 2.0 Ga and was followed, after more than 1.3 billion years, by an even larger phosphogenic event in the Neoproterozoic. Phosphorites (phosphate-rich sedimentary rocks that contain more than 15% P 2 O 5) preserve a unique record of seawater chemistry, biological activity, and oceanographic changes. In an attempt to emphasize the potentially crucial significance of phosphorites in the evolution of Proterozoic biogeochemical cycles, this contribution provides a review of some important Paleoproterozoic phosphate deposits and of models proposed for their origin. A new model is then presented for the spatial and temporal modes of occurrence of phosphorites along with possible connections to global changes at both ends of the Proterozoic. Central to the new model is that periods of atmospheric oxygenation may have been caused by globally elevated rates of primary productivity stimulated by high fluxes of phosphorus delivery to seawater as a result of increased chemical weathering of continental crust over geological timescales. The striking similarities in biogeochemical evolution between the Paleo-and Neoproterozoic are discussed in light of the two oldest major phosphogenic events and their possible relation to the stepwise rise of atmospheric oxygen that ultimately resulted in significant leaps in biological evolution.

The genesis of dolomite is a contentious issue partly due to the difficulty in its synthesis at ambient temperature. Certain types of microorganisms have been demonstrated to be effective in promoting the precipitation of disordered dolomite, an important precursor of sedimentary ordered dolomite. In contrast to a growing body of research on the catalytic role of microbial exopolymers in the crystallization of disordered dolomite, the role of other microbial exudates (e.g., carboxylic acids) remains unknown. To fill in this knowledge gap, precipitation experiments, mimicking the carbonation process within microbial mats, were conducted in saline solutions containing 0-30 mM succinic acid or citric acid, which are commonly produced by microbes. The starting salinities of experiment solutions were set to 35‰ and 70‰, in order to evaluate the effect of solution salinity on dolomite formation. Our results showed that both succinic acid and citric acid enhanced the incorporation of Mg 2+ into growing Ca-Mg carbonates. Solution salinity also played a positive role in enhancing Mg signature in Ca-Mg carbonates. Disordered dolomite with 40.92 mol% MgCO 3 was detected under the conditions of 30 mM succinic acid and 70‰ salinity, whereas in other reactors with succinic acid, Mg-calcites formed. Citric acid was more effective in loading Mg 2+ into Ca-Mg carbonates compared with succinic acid, as evidenced by the predominant occurrence of disordered dolomite with MgCO 3 content ranging from 40.91 mol% to 46.75 mol% in most conditions tested. The results of this study have implications for the formation mechanism of sedimentary dolomite.

Extensive stromatolitic carbonate platforms developed during and after the Palaeoproterozoic Great Oxidation Event (GOE), which records a significant increase of oxygen in the atmosphere and oceans. Stromatolites link biological and non-biological processes through their microscopic organo-sedimentary structures that have the potential to provide information about microbial and diagenetic processes that operate during their formation. This study aims to document the mineralogy and organic geochemistry of microscopic diagenetic structures in the exceptionally-preserved late Palaeoproterozoic stromatolitic dolomite from the McLeary Formation of the Belcher Islands, in Nunavut, Canada. This is done to test the hypothesis that chemically oscillating reactions can influence the formation of diagenetic spheroids such as rosettes, granules, concretions, and botryoids; these reactions occur over short timescales during diagenesis, i.e. before the lithification of the sediment. Decimetresize columnar stromatolites from the McLeary Formation contain centimetre-size pyrite concretions, which themselves also contain framboids. Inside rounded, black chert concretions and coarse quartz granules, there are filamentous microfossils composed of organic matter partly replaced by pyrite. These observations are consistent with post-depositional oxidation-reduction reactions involving organic matter and sulphate. In comparison, decimetre-size tabular bioherms of millimetre-to-centimetre size stromatolite columns contain microscopic dolomitic carbonate structures including circularly-concentric rosettes, zoned dolomite rhombs, and cavity structures of rounded equidistant laminations, all of which are layered with organic matter. All these diagenetic spheroids co-occur with circularly-concentric, equidistant and laminated minerals associated with degraded organic matter or microfossils. The composition and geometry of these features are consistent with the nonbiological oxidation of biological carboxylic acids during diagenetic chemically oscillating reactions. Hence, both biological and non-biological processes play a major role in the precipitation of diagenetic spheroids in McLeary stromatolites. Increased abundance of organic matter as microbial biomass, as well as oxidised halogens and sulphate, led to widespread organic decomposition in the Palaeoproterozoic McLeary Formation. Ultimately, chemically oscillating reactions after periods of oxygenation likely play a more significant role than previously thought in the formation of diagenetic spheroids inside stromatolitic dolomite.

The documentation of biosignatures in Precambrian rocks is an important requirement in the search for evidence of life on other ancient planetary surfaces. Three major kinds of biosignatures are crucially important: primary microbial sedimentary textures, diagenetic organomineral assemblages, and stable isotope compositions. This study presents new petrographic, mineralogical, and organic geochemical analyses of biosignatures in dolomitic stromatolites from the Pethei Group (N.W.T., Canada) and the Kasegalik Formation of the Belcher Group (Nunavut, Canada). Both are approximately contemporary late Paleoproterozoic stromatolite-bearing dolomitic units deposited after the Great Oxidation Event. Micro-Raman and optical microscopy are used to identify and characterize possible diagenetic biosignatures, which include close spatial association of diagenetic materials (such as ferric-ferrous oxide and anatase) with disseminated organic matter (OM), dolomitic groundmass textures, and mineralized balls. Many of these petrographic relationships point to the oxidation of OM either biotically or abiotically in association with iron reduction and chemically oscillating reactions. Oxidation of OM in these stromatolites is consistent with the widespread oxidation of biomass during the late Paleoproterozoic Shunga-Francevillian Event. Biosignatures identified in this study are also compared with possible carbonate outcrops on Mars, and thereby contribute a basis for comparison with potential biosignatures in ancient martian terrains. Similarities are drawn between the paleoenvironments of the studied units to the Isidis and Chryse planitia as locations for potential extraterrestrial dolomitic stromatolites.

Stromatolites have been widely reported from the Archean and Paleoproterozoic successions worldwide, and they could represent one of oldest life forms on Earth. Of these, a group of small stromatolites occur as microdigitate low-relief columns, and are also conspicuous in the field. However, biogenicity of these microdigitate stromatolites (MDSs) has long been disputed due to to the abundance of radial-fibrous texture and a lack of convincing microfossils. New examples of MDS are documented from the Mesoproterozoic Wumishan Formation of the Jixian area, North China. Vertically oriented fibrous fabrics are conspicuous and penetrate laminae as well as microscopic spheroids, which point to an abiotic genesis for this specific fabric. Stromatolite laminae contain abundant spheroids, typically 15–30 μm in diameter, with single or double outlines and they occur as solitary coccoid-like microfossils or in small aggregated colonies. Spheroids show strong fluorescence under both green and purple exciting lights, consistent with their composition of organic matter. Spheroids are abundant in the Wumishan stromatolites and they are categorized into two types. The first kind comprises micrite nuclei surrounded by sparitic sheaths, without nano-particle coatings. A smooth to grainy spheroidal surface defines the first kind of spheroids that also has a distinct rounded opening, which is often broken probably due to diagenesis and silicification. The second kind of spheroids is usually covered with nano-particles and lacks circular opening on surface. These spheroids possess large nuclei of single sparitic calcite coated with thin sparry sheaths. Overall, the Wumishan spheroids resemble coccoidal microorganisms reported from other Archean-Paleoproterozoic strata worldwide, but they are also better preserved. The rounded opening on spheroid surface is interpreted as division point of unicells during reproduction of the life cycle of bacteria akin to Myxococcoides grandis. Clump-like micro-particle aggregates in nuclei could represent daughter cells released from the parental envelope, similar to the reproduction process and life cycle suggested for similar spheroidal microfossils from other similar Precambrian occurrences. The Wumishan spheroids therefore may represent fossilized prokaryotes that could have contributed to construct the MDS. Moreover, filamentous microfossils are occasionally present in the coloumns of stromatolites, and they resemble filamentous cyanobacteria, but may not be major constructors of MDS due to their rarity in the buildups. Three types of nano-particles are also conspicuous: (1) putative organic relics, such as fragmented filaments and mucuslike biofilms (purported EPS), (2) organominerals, including nanoglobules, polyhedrons, and their aggregates, and (3) dumbbell-shaped nano-particle aggregates. All of these nano-particles are interpreted to be likely biogenic in origin, and many of them were found from the radialfibrous fabrics of carbonate precipitates in the MDS, implying that some heterotrophic bacteria may have afficliated the precipitation of radial fibers in deep-time radial-fibrous carbonate precipitates. Therefore, abundant and diverse biosignatures (spheroids, tubular filaments, and nano-particles) are identified in the Wumishan MDSs, and we conclude that diverse filamentous and coccoidal micro organisms contributed to the formation of the Wumishan stromatolites.

The late Mesoproterozoic Era (1300-1000 Ma) was a critical period that witnessed the origin and early evolution of multicellular eukaryotes. Multiple studies have reported observations that the carbon isotope composition of carbonate (δ 13 C carb) underwent a substantial increase after ca. 1250 Ma. The high δ 13 C carb values suggest that the fraction of organic carbon burial (f org) had increased, which, consequently, might have promoted the oxidation of surface environments and the diversification of multicellular eukaryotes. However, details of the carbon cycle during this critical time interval remain elusive, which is pivotal to testing this hypothesis. In this study, we analyzed the stable carbon isotope composition of paired organic matter (δ 13 C org) and carbonate, as well as the thermal characteristics of the organic matter, from the Shennongjia Group in South China, which has been constrained to an age of ~ 1340-1150 Ma. A gradual increase in δ 13 C carb , from ~-2‰ to >+4‰, is observed in the interval from the middle Shennongjia Group. Above which, the δ 13 C carb declines to ~-2‰ in the uppermost. The paired δ 13 C org values show an extensive range of compositions, from ~-22 to-32‰. Raman spectral data revealed that the organic matter in the Shennongjia Group experienced a wide range of thermal history, which might be ascribed to the involvement of detrital organic matter. We reconstructed the Δ 13 C carb-org and f org values in two different scenarios: one included all the δ 13 C org data, while the other screened the δ 13 C org data to minimize the possible effects of detrital organic matter. The results of these two reconstructions show similar temporal trends. Intriguingly, the Δ 13 C carb-org values are generally larger than the modern counterpart, which can be attributed to higher pCO 2. The calculated f org of the Shennongjia Group is generally lower than the modern value, 20%. However, the f org experienced a substantial increase between ca. 1250 and 1190 Ma, suggesting enhanced oxidation of surface environments, which might have paved the way for the diversification of multicellular eukaryotes.

The large, thick beachrock of Arrigunaga beach (Bizkaia, Spain) is unusual among beachrocks because of (a) Its location, at 43ºN latitude; (b) The substrate that was cemented, largely consisting on smelter slag mixed with natural beach sediment; (c) The timing and amount of slag dumping at sea, with millions of tons of waste dumped in the short interval AD 1902–1966; (d) The sudden cessation of dumping (AD 1966), followed by immediate beachrock exhumation and retrogradation and (e) An aggressive engineering intervention (AD 1999), supposedly aimed at beach regeneration, with imported bioclastic sands, resulting in additional weak cementation of the residual blocks. Thickness of the beachrock and the identification of internal clasts attest for a multiepisodic process with at least three main cementation steps and several CaCO3 polymorphs precipitated from mixed marine and freshwaters. Evidence of bacterial remains suggests that biological activity helped to trigger cementation. C an...

What are Microbialites? WHAT ARE MICROBIALITES? Do you know what a microbialite is? Not many people do. This is MICROBIALITE A rock-like structure made by millions of microbes that precipitate carbonate. because microbialites look like slimy underwater rocks, but they are actually reefs made up of microbes (simple, one-celled organisms). MICROBE An organism that is seen under the microscope. Microbialites are fascinating, because these rock-like structures are made by the interaction of millions of microbes that live in certain aquatic environments. The microbes facilitate the precipitation of minerals from the water, to form the microbialite structure [ ]. Since microbialites are like rocks, they have remained on earth since extremely ancient times. Fossilized microbialites, known as stromatolites (from the Greek strõma, meaning bed or layer, and STROMATOLITE Fossilized microbialites, and are the oldest fossils dated so far. lithos, meaning rock), are the oldest evidence of life on Earth, dating back to. billion years ago [ ]. Cyanobacteria are one type of microbe found in microbialites, and CYANOBACTERIA A phylum of bacteria that can make photosynthesis.

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 approa...

The present study describes the petrographic and petrophysical characteristics of three stratigraphically asynchronous beachrocks (A, B, and C) along the Red Sea coast at Al-Shoaiba area, Saudi Arabia, to identify the compositional, depositional, and diagenetic controls on beachrock formation and their petrophysical properties. The beachrocks at the three locations consist basically of calcareous skeletal remains of different types and grain size reflecting the composition of adjacent beach sediments and the depositional conditions. They were cemented by aragonite and high-Mg calcite (HMC) in intertidal zone. The cement exhibits three major fabrics: (1) micritic coatings, (2) isopachous to asymmetric aragonite rim, and (3) cryptocrystalline pore-fillings HMC. In addition, some intergranular and intragranular pores were partially filled with infiltrated siltsized carbonate and siliciclastic sediments. The cementation was accomplished by the combination of inorganic and organic processes, and the former was dominant through evaporation of pore-filling seawater under hot and dry climatic conditions. Cementation in the present beachrocks is selective; carbonate grains are cemented, whereas siliciclastic grains are cement free. The cement nucleation on carbonate grains was easier than on siliciclastic grains which do not provide good "seed crystals" for carbonate cement growth. The petrophysical measurements are in agreement with petrographic studies. The degree of cementation is the major control on petrophysical characteristics where the lowest and highest porosity and permeability values were obtained from the least cemented beachrocks of location A and the highest cemented beachrocks of location B, respectively. The thickness of cement seems to be controlled by cement precipitation rate, grain size, and size and shape of pore spaces. The coarse sediments of beachrocks at location B were deposited under higher depositional energy than those at locations A and C, and therefore, their primary pore spaces were large enough to be filled with seawaters. Under hot and dry climate, cement precipitation increases leading to partial to complete occlusion of pore spaces.

Beachrock is coastal sediment that has been
cemented primarily by calcium carbonate within the intertidal
zone in tropical and subtropical regions. Considering that
beachrock has the potential to inhibit coastal erosion, we
performed laboratory tests to understand the formation
mechanism of beachrocks in southern coastal regions of Sri
Lanka. The mineralogical composition of beachrock samples
were identified by FT-IR spectroscopic technique. The
constituents of minerals present in the beachrocks were further
confirmed by XRD analysis. Elemental concentrations of
beachrock samples have been examined using WD-XRF
spectrometry. The formative environment (sea water) was
analyzed using EDTA titration, AAS, UV/Vis spectroscopy and
Iron Chromatography. The results reveal the presence of
minerals aragonite, calcite, orthoclase, quartz, albite, kaolinite
and lime in the beachrocks. According to the results, there is a
high probability to precipitate CaCO3 from the sea water in
southern coastal regions indicating a positive formative
environment for beachrocks. Hence, by appropriate regulation
of the conditions could foster the development of manmade
beachrocks to control the coastal erosion.

Organic geochemical techniques were applied to study the lipid conte nt of living reef organisms and rock sampies trom different carbonate facies. The characterization of individual organic compounds (&quot;biomarkers&quot;) yields information on the biology and paleontology of microbially derived carbonate rocks, sponges and sponge-microbiota communities on a molecular level.

Holocene beachrocks of the Jaguaribe beach, State of Pernambuco, northeastern Brazil, consist of horizontal, cemented layers approximately 40 cm thick. The cement shows three textural varieties: (a) calciferous, surrounding siliciclastic grains, (b) micritic, with an acicular fringe; and (c) cryptocrystalline calcite in pores. Early cementation took place at the water table below beach ridges, where geochemical, hydrodynamic and, perhaps, also microbiological conditions favored rapid precipitation of aragonite and/or high-Mg calcite. delta13C values range from -1.8 to +1.5‰ for dissolved carbonate in interstitial water and from +0.2 to +2.1‰ for bioclastic components. delta18O values range from -2.8 to +0.5‰ for seawater, freshwater and interstitial water. delta13C values and diagenetic features suggest that cementation occurred in meteoric-vadose and/or marine-phreatic water by loss of CO2 during evaporation of the interstitial water. Locally, superimposed low-Mg calcite cements po...

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 dep...

The present study describes the petrographic and petrophysical characteristics of three stratigraphically asynchronous beachrocks (A, B, and C) along the Red Sea coast at Al-Shoaiba area, Saudi Arabia, to identify the compositional, depositional, and diagenetic controls on beachrock formation and their petrophysical properties. The beachrocks at the three locations consist basically of calcareous skeletal remains of different types and grain size reflecting the composition of adjacent beach sediments and the depositional conditions. They were cemented by aragonite and high-Mg calcite (HMC) in intertidal zone. The cement exhibits three major fabrics: (1) micritic coatings, (2) isopachous to asymmetric aragonite rim, and (3) cryptocrystalline pore-fillings HMC. In addition, some intergranular and intragranular pores were partially filled with infiltrated siltsized carbonate and siliciclastic sediments. The cementation was accomplished by the combination of inorganic and organic processes, and the former was dominant through evaporation of pore-filling seawater under hot and dry climatic conditions. Cementation in the present beachrocks is selective; carbonate grains are cemented, whereas siliciclastic grains are cement free. The cement nucleation on carbonate grains was easier than on siliciclastic grains which do not provide good "seed crystals" for carbonate cement growth. The petrophysical measurements are in agreement with petrographic studies. The degree of cementation is the major control on petrophysical characteristics where the lowest and highest porosity and permeability values were obtained from the least cemented beachrocks of location A and the highest cemented beachrocks of location B, respectively. The thickness of cement seems to be controlled by cement precipitation rate, grain size, and size and shape of pore spaces. The coarse sediments of beachrocks at location B were deposited under higher depositional energy than those at locations A and C, and therefore, their primary pore spaces were large enough to be filled with seawaters. Under hot and dry climate, cement precipitation increases leading to partial to complete occlusion of pore spaces.

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 approa...

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 approa...

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.

Holocene beachrocks of the Jaguaribe beach, State of Pernambuco, northeastern Brazil, consist of horizontal, cemented layers approximately 40 cm thick. The cement shows three textural varieties: (a) calciferous, surrounding siliciclastic grains, (b) micritic, with an acicular fringe; and (c) cryptocrystalline calcite in pores. Early cementation took place at the water table below beach ridges, where geochemical, hydrodynamic and, perhaps, also microbiological conditions favored rapid precipitation of aragonite and/or high-Mg calcite. delta13C values range from -1.8 to +1.5‰ for dissolved carbonate in interstitial water and from +0.2 to +2.1‰ for bioclastic components. delta18O values range from -2.8 to +0.5‰ for seawater, freshwater and interstitial water. delta13C values and diagenetic features suggest that cementation occurred in meteoric-vadose and/or marine-phreatic water by loss of CO2 during evaporation of the interstitial water. Locally, superimposed low-Mg calcite cements po...

Abstract: The beachrock formation on the Arıburnu coast situated in the Gelibolu Peninsula has been studied by field observation, thin-section interpretation, physicochemical analyses including ICP-AES and SEM/EDS, and OSL dating. These analyses reveal the presence of different ...

What are Microbialites? WHAT ARE MICROBIALITES? Do you know what a microbialite is? Not many people do. This is MICROBIALITE A rock-like structure made by millions of microbes that precipitate carbonate. because microbialites look like slimy underwater rocks, but they are actually reefs made up of microbes (simple, one-celled organisms). MICROBE An organism that is seen under the microscope. Microbialites are fascinating, because these rock-like structures are made by the interaction of millions of microbes that live in certain aquatic environments. The microbes facilitate the precipitation of minerals from the water, to form the microbialite structure [ ]. Since microbialites are like rocks, they have remained on earth since extremely ancient times. Fossilized microbialites, known as stromatolites (from the Greek strõma, meaning bed or layer, and STROMATOLITE Fossilized microbialites, and are the oldest fossils dated so far. lithos, meaning rock), are the oldest evidence of life on Earth, dating back to. billion years ago [ ]. Cyanobacteria are one type of microbe found in microbialites, and CYANOBACTERIA A phylum of bacteria that can make photosynthesis.

Geochemical signatures and carbonate microfacies highlight contrasts between two distinctive mid-late Triassic reef communities in the Dolomite Alps, Italy. In the first community, sponges, bryozoans, calcified cyanobacteria and problematic organisms (Archaeolithoporella, Shamovella), together with a variety of micritic fabrics, formed compact reefs in high energy shallow-water at the margins of high-rise Ladinian-Carnian carbonate platforms. Debris from these margins created steep foreslopes, and some large blocks of the allochthonous material (Wengen-Cassian formations, Cipit Boulders) were buried in basinal shales that protected them from subsequent alteration and regional dolomitization. In the second and slightly younger community, small Carnian patch reefs (Heiligkreuz Formation, Alpe di Specie) developed in quieter shallow water, where they too were protected against alteration by enclosing shales. They were constructed mainly by scleractinian corals, sponges and red algae, and contain relatively large framework cavities with clotted-peloidal micrite. These early examples of coralgal reefs have broad similarities to present-day examples, whereas the community represented by the Cipit Boulders has more in common with Late Permian reefs. Both bioconstructions preserve primary microfabrics and biomarkers. The Cipit Boulder samples contain bacterial, mainly cyanobacterial biomarkers, lack specific molecules typical of sulfate-reducing bacteria (SRB), and have Rare Earth Element (REE) values indicative of oxic conditions. These signatures are consistent with their original high-energy platform margin location, compact structure, and presence of calcified cyanobacteria such as Cladogirvanella and Girvanella. In contrast, the coralgal patch reefs contain SRB biomarkers, lack specific molecules typical of cyanobacteria, and have REE values indicative of sub-oxic conditions. These signatures are consistent with their lower energy depositional conditions and well-developed skeletal framework that created protected low-oxygen micro-habitats. The SRB biomarkers can be linked to the associated clotted-peloidal fabrics which resemble those commonly present in younger coral-reef frameworks. These details of redox conditions and bacterial processes underscore the important biotic, structural and environmental changes that affected shallow marine reefs during the Triassic.

Induration of beach material as a result of carbonate cementation to form sedimentary beachrock has rarely been reported from high latitude coastlines. The stratified beachrock exposed in the upper intertidal zone in Harlyn Beach, Harlyn Bay, north Cornwall, UK, appears homologous to the now poorly exposed cemented beachrock first described in the 1960's from the adjacent Little Cove in Mother Ivey's Bay, Cornwall. This study focuses on the field characteristics and mineralogy of the Harlyn beachrock deposit. The beachrock appears as an eroding relict deposit set in a currently high wave energy environment. Preliminary studies utilising petrography, scanning electron microscopy (SEM), Inductively Coupled Plasma Emission spectroscopy (ICP) and X-Ray diffraction (XRD) indicate that the Harlyn beachrock is composed of medium to coarse grained comminuted shell sand, lithologically comparable to the present beach sand, cemented by at least one phase of epitaxial low-Mg calcite. Limited development of beachrock with broadly similar features in the intertidal zone along the east side of the Camel Estuary, north Cornwall, UK, is also reported. Further work is required to develop a model for the development of beachrock in the context of geochemistry, sea-level fluctuations, local dune formation and movements and climate change during the Late Quaternary along the north Cornwall coast.

Beachrocks represents a coastal deposition in the intertidal area, and studying their properties may lead to create a model which identifies the conditions of their formation (paleo-environment). This paper focuses most intently on the cement material which is able to recover the paleo-environment conditions during diagenesis of such coastal sediment. We used optical microscopy, secondary electron microscopy and Raman Spectroscopy to characterize the cement texture, mineralogy and chemistry in the beachrocks. The existence of pure calcite primarily controlled by the meteorite water, while Mg-calcite appears between the lowermeteoric and the upper marine phreatic zone. Finally, the presence of aragonite associated with the marine phreatic to lower marine vadose environment.

The 1200m thick carbonate sequence of the Chudleigh Limestone Subgroup (Gordon Group) near Mole Creek conformably overlies the siliciclastics of the Magog Subgroup (Denison Group) and is conformably overlain by over 45m of siliciclastic Eldon Group correlate. The Chudleigh Limestone Subgroup is divisible into six conformable formations: the Standard Hill Fm. (145m thick), the Ugbrook Fm. (120m), the Sassafrass Creek Fm. (145m) the Dogs Head Fm. (470m) the Mole Creek Fm. (30-75m), the Overflow Creek Fm. (240m) and the Den Fm. (133m). The Den Fm. is conformably and sharply overlain by 15m of siltstone containing Isorthis and then 20m of white quartzite. Both of these units are placed in the Eldon Group by Burrett whilst Banks places the lower unit in the Gordon Group. The Chudleigh Limestone Subgroup contains a record of tropical, shallow water, dominantly peritidal, carbonate environments and faunas lasting about 25 my from the Late Whiterockian (Chazyan) through the Edenian. Deposition and basinal subsidence averaged 0.05mm per year.

La fotosíntesis de las algas calcificantes es un relevante conductor de la formación de carbonatos en las costas. El carbono inmovilizado en los talos calcificados de estas algas es un componente estructural de
diferentes tipos de carbonatos. Entre ellos, la calcita magnesiana es el mineral más comúnmente reportado. El contenido de otros cationes (además del calcio) en estos biominerales les brinda características particulares. Por ello, los biominerales son objeto de investigación actual, en particular frente a los panoramas de cambio ambiental. En este trabajo utilizamos a las algas coralinas de las pozas intermareales de Calerita (Bahía de la Paz, BCS, México) como modelos para estudiar la diversidad mineral (en microescala) del talo de Neogoniolithon thrichotomum, el alga coralina más abundante en las pozas estudiadas. Los resultados preliminares indican la presencia de aragonita, calcita magnesiana con alto contenido de Mg (~ 18%), también ankerita y siderita (Fe-carbonatos) espacialmente segregada
a microescala.
Palabras clave: bio-carbonatos; calcita magnesiana; bio-minerales; carbonatos costeros.

Beachrocks are a window in the past environmental, geological, sedimentological and geographical conditions that were dominant on the coastal zone. The minerochemical examination of cement and the sedimentological analysis are the most efficient methods for understanding the formation mechanism. However, the examination of beachrock samples have limitations and the evidence of formation mechanism are not enough. This study emphasizes on the beachrock formation mechanism through the comparison of cement characteristics, mineral chemistry and sedimentology of beachrock occurrences from different geological and geographical setting areas Diolkos, Corinth, Greece and Sumuide, Okinawa, Japan. Furthermore, in order to investigate the beachrock formation, artificial beachrock samples were created in-vitro using sand samples and ureolytic bacteria from Okinawa under accelerating conditions. Bulk samples were collected from the study areas in order to analyze their mineralogical (XRD and SEM-EDS) and chemical (XRF) composition. Microscopy studies (optical and SEM-EDS) revealed that the cement agent from Diolkos is mainly composed of High-Magnesian Calcite (HMC) in comparison to the Sumuide beachrock which is characterized by the presence of calcite and aragonite. Additionally, the analysis revealed clastic silicate and aluminosilicate minerals. The grain composition of Diolkos slab consists of quartz, plagioclase, K-feldspar with 20% bioclasts compared to the Sumuide beachrock grains that consist of calcareous residuals from the local coral reef. The artificial beachrock investigation indicated that ureolytic bacteria that reside in the Sumuide beach sediment, are capable to precipitate aragonite coating the sediment grains and filing the pores. The cementation was most active in the top part of the samples than the bottom part. This is an indicator that the beachrock formation might occur in depths were these bacteria can be found. The artificial beachrock analysis included its physicochemical parameters using UCS penetration, pH and Ca2+ measurements, X-Ray CT-scanning, petro-graphic polarized microscopy, XRD, and SEM-EDS.

Beachrocks are hard coastal sedimentary formations consisted from various beach sediments, coastal fauna residues and anthropogenic articles. Beachrocks are rapidly cemented through precipitation of carbonate cements typically consisted of High-Magnesian Calcite (HMC), which commonly precipitates in shallow marine environments, (>4 mol % CaCO3 or 1.2 wt. %) or aragonite (Ar). However, debate still exists concerning the accurate depositional environment of beachrocks and data for the mechanism of their formation are considered necessary. This study aims to contribute to the understanding of the beachrock formation, using mineralogical and geochemical methods, analyzing the cement and the consolidated sediments. Bulk samples were collected from three consecutive beaches located at the West part of Akrotiri Peninsula (Cyprus island). The samples were examined under polarizing microscope for the determination of the cement (HMC as micritic and sparitic crystals), its characteristics (isopachous bladed coating, formation of meniscus etc) and the participation of well-preserved fossil fragments. The mineralogical analysis, with the use of XRD analyzer, indicated a variety of minerals which consisting the beachrock (quartz, carbonates, plagioclase, olivine, biotite, zircon etc). Using SEM-EDS it was possible to accurately determine the cement composition and to observe its crystal characteristics. The cement agent was mainly consisted by High-Magnesian Calcite (HMC) of different crystal sizes and matrix material was present as secondary pores filling. The three studied beachrocks at the west of Akrotiri peninsula, were formed in the middle-low intertidal zone.

Microbialites are rock-like underwater structures that look like reefs
but are made entirely of millions of microbes. These structures
are very ancient and can be found in di􀀀erent environments on
every continent on Earth. Mexico has many microbialite reefs,
in desert valleys, crater-lakes, and coastal lagoons. Science helps
us to understand the microbes that build microbialites, to know
whether the same kinds of microbes make up microbialites in
di􀀀erent regions of the world, and to figure out how the microbes
organize into microbialites. Many things are damaging microbialites
in Mexico, including poorly planned development, pollution from
lack of sewage treatment, too much water usage, and the fertilizers
used for agriculture. Policies that regulate development are urgently
needed to help save these diverse and ancient microbial reefs.

The present study describes the petrographic and petrophysical characteristics of three stratigraphically asynchronous beachrocks (A, B, and C) along the Red Sea coast at Al-Shoaiba area, Saudi Arabia, to identify the compositional, depositional, and diagenetic controls on beachrock formation and their petrophysical properties. The beachrocks at the three locations consist basically of calcareous skeletal remains of different types and grain size reflecting the composition of adjacent beach sediments and the depositional conditions. They were cemented by aragonite and high-Mg calcite (HMC) in intertidal zone. The cement exhibits three major fabrics: (1) micritic coatings, (2) isopachous to asymmetric aragonite rim, and (3) cryptocrystalline pore-fillings HMC. In addition, some intergranular and intragranular pores were partially filled with infiltrated siltsized carbonate and siliciclastic sediments. The cementation was accomplished by the combination of inorganic and organic processes, and the former was dominant through evaporation of pore-filling seawater under hot and dry climatic conditions. Cementation in the present beachrocks is selective; carbonate grains are cemented, whereas siliciclastic grains are cement free. The cement nucleation on carbonate grains was easier than on siliciclastic grains which do not provide good "seed crystals" for carbonate cement growth. The petrophysical measurements are in agreement with petrographic studies. The degree of cementation is the major control on petrophysical characteristics where the lowest and highest porosity and permeability values were obtained from the least cemented beachrocks of location A and the highest cemented beachrocks of location B, respectively. The thickness of cement seems to be controlled by cement precipitation rate, grain size, and size and shape of pore spaces. The coarse sediments of beachrocks at location B were deposited under higher depositional energy than those at locations A and C, and therefore, their primary pore spaces were large enough to be filled with seawaters. Under hot and dry climate, cement precipitation increases leading to partial to complete occlusion of pore spaces.

In this work, the degradation processes that take place in bricks exposed to marine environments have been studied. Taking into account the importance of this building material where the silicates present in the final product act as stabilizer in the porous material itself, it is necessary to understand the decay processes that occur in these aggressive environments. As is known, the marine aerosol carries different types of salts, such as chlorides, sul-fates, nitrates, etc., present in surrounding environment exerting a negative influence on the materials producing cracking and disintegration processes of the material and consequently loss of brick wall stability. Nowadays the development of portable devices is taking much more importance helping researchers to resolve problems in the field in a fast and easy way. In order to extract fast and satisfactory results about the conservation state of different bricks from Punta Begoña Galleries (Getxo, Basque Country, Spain), an in-situ analytical methodology was developed based on the use of hand-held Energy Dispersive X-ray fluorescence spectrometry (HH-ED-XRF) assisted with other laboratory techniques (μ-ED-XRF and X-Ray Diffraction) in order to corroborate and complement the information obtained in-situ. This construction undergoes the influence of marine aerosol, industrial port, power generation plants, and a fuel refinery among others. The pathologies visually observable in these bricks are disintegration, breakup and detachment of the bricks. The presence of deterioration compounds in the bricks has been studied according to the orientations of the bricks inside the construction.

The beachrock formation on the Arıburnu coast situated in the Gelibolu Peninsula has been studied by field observation, thin-section interpretation, physicochemical analyses including ICP-AES and SEM/EDS, and OSL dating. These analyses reveal the presence of different amounts of major (Si, Ca, Mg, K, Fe, Al and Na) and trace elements within the beachrock cement with Si (36.2%) and Ca (32.68%) dominating the overall composition. Beachrocks composed of highly-fractured and friable beds reach a total thickness of 80 cm extending from +60 cm at the uppermost level down to -1 m at their most seaward extent and grade from conglomerate to lithic arkose in vertical section. The total amount of CaCO 3 ranges between 59.08% and 36% and the cement consists of high-Mg calcite based on EDS analysis. From SEM examination, four main morphologies were identified in cement material: (1) micritic coatings, (2) cryptocrystalline pore-filling cement, (3) meniscus cement and (4) microbial cement and suggest the presence of marine phreatic conditions with the exception of meniscus bridges, which imply that cementation may have been dominated by carbonate-rich meteoric waters at any successive stage of cementation. Five buried beachrock samples under unconsolidated beach sand were sampled for Optically Stimulated Luminescence (OSL) dating and show that the minimum and maximum ages of beachrock are 1.42±0.20 ka and 2.28±0.28 ka BP, respectively.

Geochemical signatures and carbonate microfacies highlight contrasts between two distinctive mid–late Triassic reef communities in the Dolomite Alps, Italy. In the first community, sponges, bryozoans, calcified cyanobacteria and problematic organisms (Archaeolithoporella, Shamovella), together with a variety of micritic fabrics, formed compact reefs in high energy shallow-water at the margins of high-rise Ladinian–Carnian carbonate platforms. Debris from these margins created steep foreslopes, and some large blocks of the allochthonous material (Wengen–Cassian formations, Cipit Boulders) were buried in basinal shales that protected them from subsequent alteration and regional dolomitization. In the second and slightly younger community, small Carnian patch reefs (Heiligkreuz Formation, Alpe di Specie) developed in quieter shallow water, where they too were protected against alteration by enclosing shales. They were constructed mainly by scleractinian corals, sponges and red algae, and contain relatively large framework cavities with clotted-peloidal micrite. These early examples of coralgal reefs have broad similarities to present-day examples, whereas the community represented by the Cipit Boulders has more in common with Late Permian reefs. Both bioconstructions preserve primary microfabrics and biomarkers. The Cipit Boulder samples contain bacterial , mainly cyanobacterial biomarkers, lack specific molecules typical of sulfate-reducing bacteria (SRB), and have Rare Earth Element (REE) values indicative of oxic conditions. These signatures are consistent with their original high-energy platform margin location, compact structure, and presence of calcified cyanobacteria such as Cladogirvanella and Girvanella. In contrast, the coralgal patch reefs contain SRB biomarkers, lack specific molecules typical of cyanobacteria, and have REE values indicative of sub-oxic conditions. These signatures are consistent with their lower energy depositional conditions and well-developed skeletal framework that created protected low-oxygen micro-habitats. The SRB biomarkers can be linked to the associated clotted-peloidal fabrics which resemble those commonly present in younger coral-reef frameworks. These details of redox conditions and bacterial processes underscore the important biotic, structural and environmental changes that affected shallow marine reefs during the Triassic.

Please cite this article as: Gattolin, G., Preto, N., Breda, A., Franceschi, M., Isotton, M., Gianolla, P., Sequence stratigraphy after the demise of a high-relief carbonate platform (Carnian of the Dolomites): sea-level and climate disentangled, Palaeogeography, Palaeoclimatology, Palaeoecology (2015),

Raman spectroscopy, including in-situ and laboratory analyses, were carried out in beachrock outcrops located in temperate latitude (Arrigunaga beach, Bilbao Estuary, North of Spain) to characterise the wide variety of sediments and wastes trapped within the cements. In the examined beachrocks (coastal sedimentary structures formed in the intertidal zone through the early precipitation of carbonates) the presence of abundant slag and anthropogenic wastes is noticeable. In-situ Raman analysis revealed the presence of cristobalite (SiO 2), tephroite (Mn 2 SiO 4), quartz (SiO 2), rhodonite (MnSiO 3), labradorite (Ca,Na)(Si,Al) 4 O 8 , hematite (α-Fe 2 O 3), gypsum (CaSO 4 ·2H 2 O) and amorphous carbon (C) as the main constituents in the trapped materials. Those were also identified off site together with other phases such as limonite (FeO(OH)·nH 2 O), lepidocrocite (γ-FeOOH), arsenopyrite (FeAsS), fayalite (Fe 2 SiO 4) and anatase (TiO 2). As secondary compounds, portlandite (Ca(OH) 2), C–S–H (Ca 3 Si 2 O 7 ·3H 2 O), gypsum and possibly ettringite (3CaO·Al 2 O 3 ·3CaSO 4 ·32H 2 O) were identified only in-situ, and a possible evolution to the more stable thaumasite (3CaO·SiO 2 ·CO 2 ·SO 3 ·15H 2 O) was found in the laboratory analyses. Therefore, the applied methodology and specifically the in-situ Raman spectroscopy analyses resulted particularly valuable, allowing an accurate description of the trapped materials and the compounds formed by hydration and/or sulphate attack (probably from the high level of atmospheric aerosols coming from seawater or industrial activity nearby), giving an insight of the complexity of the examined outcrops.

Beach sediment cementation (beachrock formation) is a sedimentary process that can transform significant sections of beaches into rock outcrops. This contribution reports the results of two questionnaire surveys (one focusing on foreign tourists and the other on local people) carried out in coastal resorts of the island of Lesbos (Greece), on the perceptions of beach users regarding the impacts of beachrocks on their recreational activities. The survey focusing on foreign tourists showed that the majority of the interviewees took notice of the formations and commented negatively on them. Although most of the interviewees did not consider beachrocks a significant safety risk, a considerable proportion of the sample stated that beachrocks influenced their beach ratings that they would prefer beachrock-free beaches and would be willing to contribute financially to preventative and protective measures. In contrast, the results of the survey focusing on local people, who are more familiar with the phenomenon, showed a high perception of beachrock-related risks and limited beachrock tolerance. In addition to the safety risks that the irregular, slippery, beachrock surfaces may pose to beach users, beachrocks may also degrade beach aesthetics, promote beach sediment erosion and decrease the beach carrying capacity. As beachrocks are a common attribute of tropical, subtropical and low-temperate beaches that are typically associated with major tourist destinations, and are likely to spread under global warming conditions, they may be considered as a significant threat to the coastal tourist industry.

Beachrocks are sedimentary structures derived from the precipitation of carbonates in the intertidal zone.
Because of this cementation process, they can involve a significant variety of grain types within their
structures. This is the case for beachrock outcrops located in the vicinity of the Nerbioi-Ibaizabal estuary
(Getxo, Basque Country), an area highly influenced by industrialization. Concretely, a vertical beachrock
outcrop located in Arrigunaga Beach, in the inner part of the mouth of the estuary, was studied using a
novel analytical methodology to simplify and understand the heterogeneity of the deposits. First, a
granulometric separation was carried out followed by the optical microscopic inspection of the fractions
and their Raman spectroscopic analysis, revealing the probable heterogeneity of the main beachrock
constituents (carbonates and metallic compounds) in each fraction. The total carbonates (acid–base
back titration) and the acid-extractable elements (ICP-MS) were quantified, followed by chemometric
analyses (correlation analysis and principal component analysis). The combined use of these
conventional techniques was particularly relevant for concluding that although the main elements were
Fe, Ca, Mg, Mn, Al, Na and K, the key point lies in their distribution in different particle sizes. Indeed,
heavy metals, particularly Fe, were accumulated in the 75–250 mm fraction, in contrast to a higher
content of carbonates and Ca in the <75 mm fraction. The fact that heavy metals were more
concentrated in the coarser fraction led us to believe that an external income of these elements existed,
which is likely to come from industrial wastes. Furthermore, the complementarity of the techniques used
corroborated the isolation of cements in the finest fraction. Thus, the analytical methodology proposed
here helped in distinguishing anthropogenic elements from those comprising the cements, suggesting
that both the trapped materials and the components responsible for the cementation occurred in this
temperate latitude.

Beachrocks are coastal sedimentary formations resulting from a relative rapid cementation of beach sediments
by the precipitation of carbonate cements. These lithified structures are not usually observed at
temperate settings. The present work is focused on the occurrence of a significant intertidal cementation
in sand-gravel beaches formed among 43 ◦N latitude coastline, close to the Nerbioi-Ibaizabal
estuary (Bilbao, Bay of Biscay, North of Spain). Raman micro-spectroscopy combined with SEM-EDX
analyses and petrographic descriptions have been applied for the determination of the cement generations
and the cemented materials compositions of the beachrock outcrops. In general terms, the cements
described were: Cement Generation 1 (CG 1, aragonite, high-magnesium calcite and silicate mixtures),
Cement Generation 2 (CG 2, aragonite) and Cement Generation 3 (CG 3, mixtures of CaCO3 polymorphs
and iron oxides). The rest of the interstitial porosity of the rocks appeared either empty or filled with
heterogeneous cemented mixtures of previously reworked compounds. The mineralogy, the regular distribution
and the isopachous character of the carbonate cements together with the accurate cementation
at advanced seaward bands propose a possible marine-phreatic context for the beachrock formation.
However, the impure cements and the materials covering the interstitial porosity seem to be the result
of both, the weathering actions consequences and the surface alterations of specific grains. Moreover,
the presence of modern cemented materials (e.g. slag, bricks and pebbles) suggest a recent formation of
the phenomenon.