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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]

Biomineralization is a generic term used to indicate biological‐mediated mineral formation. In carbonate mineralization, nucleation of crystals can be: (1) controlled directly by the organisms, like in the skeletal formation of most metazoans; (2) induced by microbial communities, by indirect precipitation mediated by their metabolic activities; or (3) influenced by organic matter decay, with mineral precipitation on specific non‐living organic cell surfaces. Recognition of these products is a direct marker of biological activity in time and space and is a key element in the study of the biological evolution and of its interactions with the geological processes. In this paper, primary carbonate cements from the Anisian microbial build‐up of the ‘Monte Facito’ Formation (Basilicata region, Southern Italy) have been studied from a geobiological point of view. Optical microscopy, UV‐epifluorescence and micro‐Raman spectroscopy have been applied to investigate the organic mediation on their precipitation. The cements formed in microcavities or on grain substrates, and often show a microstromatolite‐like pattern of growth. They are composed of alternations of cloudy organic and whitish inorganic bands that point to a double phase of mineralization. In the first phase, a biologically induced/influenced biomineralization is confirmed by the presence of organic matter strictly connected with the cloudy bands. This phase is followed by a pure abiotic mineralization that leads to the formation of whitish bands. This process repeated cyclically, ending at the complete filling of the microcavities or because of changes in the chemical conditions of the microsystem, for example, due to burial processes. This model of mineralization is similar to that proposed for primary cements forming in recent beach rocks. The Monte Facito Formation cements could be considered as the product of unconventional biomineralization, and the understanding of their growth process could provide an innovative tool in the research of biological signatures in the fossil record. The term unconventional is here utilized to discriminate this type of biomineralizations from those related to well‐known biotic mineralization processes, like those involved in skeletons and microbialites growth, which can be considered as conventional biomineralizations. [ABSTRACT FROM AUTHOR]

Coastal sand dune sediments with associated intraformational aeolianite, palaeosols and beachrock are found throughout much of the southern African coast, and have important roles as both Quaternary environmental archives and in recording the interplay of sediment supply, coastal processes and sea-level change. This paper examines the stratigraphy and palaeoenvironmental significance of coastal sand dunes and associated sediments, using examples mainly from South Africa but also with reference to the sandy coasts of Namibia and southern Mozambique. Based on morphological, sedimentary and dating evidence reported in the diverse literature, the stratigraphic relationship of coastal sand dune sediments to Marine Isotope Stages (MIS) is summarized, and a chronostratigraphic diagram for the period MIS 6 to 1 along the South African coast is used to identify spatially coherent sedimentary units that correspond to different regional climatic and sea-level phases. This framework provides a stratigraphic context to better examine the relationship between coastal sand dunes and external forcing during the late Quaternary in southern Africa, and to guide future field studies. [ABSTRACT FROM AUTHOR]

The selected effect account is regarded by many as one of the most attractive accounts of function. This account assumes that the function of a trait is what it has been selected for. Recently, it has been generalized by Justin Garson to include cases in which selection is understood as a simple sorting process, i.e., a selection process between entities that do not reproduce. However, once extended, this generalized selected effect account seems to ascribe functions to entities for which it looks unintuitive to do so. For instance, the hardness of rocks on a beach being differentially eroded by waves would be ascribed the function of resisting erosion. Garson provides one central argument why, despite appearance, one should not ascribe functions in cases of such sorting processes. In this paper, I start by presenting his argument, which hinges on whether a collection of entities form a population. I find it wanting. I argue instead that some selection processes are evolutionarily more or less interesting and that when a selection process is regarded as evolutionarily uninteresting, it will yield an uninteresting form of function rather than a reason for withholding the concept of function altogether. [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]

Rocas Atoll is a remote place and the only atoll in the southwestern Atlantic Ocean. This study presents new paleo-sea level reconstructions and a new interpretation on former ones. The new data indicate that sea level was higher at the Late-Holocene than it is at present and that the hydrodynamic factors overlap with sea-level changes, precluding more precise paleo-sea level reconstructions. According to previous works, the Rocas Atoll presents one of the most conspicuous paleo-sea level indicators, represented by reef remains. But, in this paper, these supposedly reef remains are reinterpreted as algal-reef boulders detached from the atoll reef-front by high-wave energy events and deposited over the reef rim, where they remain detached or are cemented and, sometimes, mushroom shaped. It is considered that the bigger boulders may have been deposited in their current position by the cumulative effects of past energetic wave events. Furthermore, the use of beachrocks as paleo-sea level indicators in former studies is discussed, leading to the conclusion that they actually indicate beach progradation and lateral accretion resulting from a positive sand budget. Finally, a schematic morphological evolution of the atoll during the Late-Holocene is proposed. At the atoll, leveling with RTK and imagery with laser scanner were collected, and eleven radiocarbon ages were measured by accelerator mass spectrometry (AMS). • New paleo sea-levels were determined and former ones were reinterpreted. • A field of boulders detached from the atoll reef front is described. • Beachrock sedimentary facies are described. • A schematic morphological evolution of the atoll during the Late Holocene is provided. [ABSTRACT FROM AUTHOR]

The present paper supplies biological and lithological evidence for the mechanisms of biochemical cementation in modern beachrocks on the tropical Yongle Atoll, Xiasha Islands in the South China Sea. High-throughput sequencing was used to precisely determine the epilithic microbial community in beachrocks. Microscopic mineralogical examination of sedimentary grains further showed complex processes from rapid carbonate precipitation. The results from 18/16 s rRNA diversity examination indicated that green algae and cyanobacteria only occupied a small proportion of the community, albeit they had considerable amounts. The occurrences of Lyngbya (Family Oscillatoriaceae), Calothrix and Dichothrix (Family Rivulariaceae) with light colour may be related to calcified sheaths coated on the living cells. The short rod-like Mg calcite in Lyngbya sheaths and anhedral to euhedral Mg calcite in Calothrix or Dichothrix sheaths were organominerals mediated most likely by photosynthesis of microorganisms with chloroplasts. Different initial crystal patterns were closely related to different cyanobacterial extracellular polymeric substance (EPS) structures. After cell death, these microcrystals were released into the voids and removed by interstitial water. The carbonate seeds scattered all around the particle surface and then began to enlarge the grain size with the degradation of organic matter. Different paths of crystal growth eventually cemented the intertidal grains abiotically or biotically. This case sheds light on cryptic microbially mediated mineralization in beachrock. Even though chemical processes were considerable in the formation of the beachrocks on the modern reef flat, the pervasive microbial geological processes occurred quietly but effectively. • Epilithic biotic communities in the beachrock were studied by genetic sequencing. • Cyanobacteria filaments Lyngbya , Calothrix and Dichothrix have calcified sheaths. • Magnesium calcite seeds in cyanobacterial EPS are biominerals. • Microbially-mediated carbonates rapidly consolidate the beachrock. [ABSTRACT FROM AUTHOR]