Carbonate Beach Sand of Abaiang Atoll, Kiribati: Geochemistry, Biogenic Sources, and Properties

Carbonate sand and gravel dredged for cement production from the Nukubuco barrier reef at Laucala Bay near Suva, Fiji, have magnesium contents close to the acceptable limits for cement manufacture. The sediments are mainly fragments of coral, calcareous algae, molluscs, and foraminifera, with bulk MgO contents averaging 2.9 percent (usual range 2.5–4.5 percent). MgO comes partly from the foraminifer Marginopora vertebralis and rare echinoderm fragments, but mainly from calcareous red algae. Selectively dredging areas with lower magnesium content is difficult because of the unpredictable distribution of high-magnesium clasts; however, the magnesium content of the sediment can be reduced after dredging in two ways. Because larger clasts have higher MgO content, removal of grain sizes coarser than 1 mm (0.0 ϕ) by sieving lowered the MgO level by up to 0.2 percentage points (from 3.5 percent to 3.3 percent on average), but this gave inconsistent results and led to the loss of 25 to 50 percent of the raw material. Abrasion of larger clasts by tumbling to remove encrusting red algae rapidly and consistently lowered MgO values by 0.6 percentage points (from average 4.1 percent to average 3.5 percent), with loss of only 3 to 4 percent of the initial raw material to produce magnesium-rich lime residues. This efficiency is caused by the selective removal of outer, algal-encrusted and high-magnesium layers of the clasts, which are already weakened by natural processes of bio-erosion. Results should be widely applicable wherever tropical carbonates are used for cement manufacture. The technique should be readily scalable to commercial levels and has the potential to greatly reduce the amounts of reef material dredged.

In Tane-ga-shima Island, which is located in the northern-most part of the Nansei-shoto Islands and is giving its long axis in the same direction as the Ryukyu Arc, are recognized eight coastal terraces built mainly by wave abrasion. These coastal terraces are classified and correlated by the continuity of altitudes of their surfaces and tephra on the surfaces. They are widely distributed as marginal terraces surrounding hills which originated from abrasion platforms in the northern part, and as plateau-like ones in the southern part, but they do not occur in the northern-most and south-eastern parts. The island is divided into five fault blocks by four faults parallel to NW-SE direction, and extent of the development of terraces is different in each block. The author made the geomorphological survey of these terraces to con-sider the geomorphic history and crustal movements of the island. The results are summarized as follows; A) Altitudes of the coastal terraces classified into eight are 120m-180m on the first, 120m-170m on the second, 30m-210m on the third, 25m-130m on the fourth, 50m-90m on the fifth, 25m-75m on the sixth, 20m-30m on the seventh, and 5m-8m on the eighth terrace. They are more clearly distinguished in the southern and western parts than they are in the northern and eastern parts. B) The third, the fourth and sixth terraces are comparatively more widely developed and distributed in a larger area. However, terraces are not found in the northern-most portion of the island where they are submerged into the Osumi strait, and in the south-eastern portion they have not been preserved as terrace surfaces but are recognized only as level summits because of the erosiveness of the Miocene series. C) The characteristics of the terraces are almost same and they form mostly rock-cut terraces, although extents of their developments are different in each fault block. Marine deposits of the terraces composed mainly of ill-sorted gravels and boulders form very thin layers and rarely exceed ten metres thick even in waste-buried valleys. In the marine deposit of the fourth terrace are seen tests of Foraminifera and fragments of corals which indicate warm climatic conditions. And also raised coral reefs are observed on the lowest terrace in Mageshima Island which belongs to Tane-ga-shima Island. This terrace is correlated to the eighth terrace of Tane-ga-shima Island. From these facts the fourth and eighth terraces are to be correlated to the main transgressions; the former is to the transgression prior to the regression of the last glacial age, and the latter is to the transgression of the early Holocene. D) The crustal movements inferred from the displacement of the terraces are as follows;(1) Upwarping has been taking place with the axis in the vicinity of Yakutsu, southwest of the island, showing the older the terrace is the larger the displacement.(2) Activities of the four faults occurred mainly in the age between the formation of the third terrace and the fourth. These faultings made tilted blocks with fault scarps in the southern edge of each block, and shattered terrace gravels are found along fault lines. The fault which runs from Kerisaki to Tanowaki in the north of the island has been active before and after the construction of the fourth terrace.(3) Relations of the altitudes of the raised strandlines among the third (T3), fourth (T4) and sixth (T6) terrace are formularized as: T3=1.5T4+2, T4=1.4T6+30, and T3=2.5T6+30 in meters. These formulae indicate that there are positive correlations between the altitudes and ages of the terraces.(4) The tendency of the strike and dip of the Miocene series and the crustal movements in more recent geological time shown by the terraces are very similar to each other.(5) The facts mentioned in (1), (2), (3), and (4) lead to the deduction that two kinds of crustal movements have been taking place, upwarping and faulting.

The origin, age, and dynamics of carbonate sediments in Kailua Bay on Oahu, Hawaii, are described. The shoreface (from shoreline to 4 km offshore) consists of a broad (5 km2) fringing coral reef ecosystem bisected by a sinuous, shore-normal, sand-filled paleostream channel 200–300 m wide. The median grain diameter of surface sands is finest on the beach face ( 90% biogenic carbonate, dominated by skeletal fragments of coralline algae (e.g. Porolithon, up to 50%) followed by the calcareous green alga Halimeda (up to 32%), coral fragments (1–24%), mollusc fragments (6–21%), and benthic foraminifera (1–10%). Sand composition and age across the shoreface are correlated to carbonate production. Corals and coralline algae, principal builders of the reef framework, are younger and more abundant in sands along the channel axis and in offshore reefal areas, while Halimeda, molluscs, and foraminifera are younger and more dominant in nearshore waters shoreward of the main region of framework building. Shoreface sediments are relatively old. Of 20 calibrated radiocarbon dates on skeletal constituents of sand, only three are younger than 500 years b.p.; six are 500–1000 years b.p.; six are 1000–2000 years b.p.; and five are 2000–5000 years b.p. Dated fine sands are older than medium to coarse sands and hence may constitute a reservoir of fossil carbonate that is distributed over the entire shoreface. Dominance of fossiliferous sand indicates long storage times for carbonate grains, which tend to decrease in size with age, such that the entire period of relative sea-level inundation (∼5000 years) is represented in the sediment. Despite an apparently healthy modern coral ecosystem, the surficial sand pool of Kailua Bay is dominated by sand reflecting an antecedent system, possibly one that existed under a +1–2 m sea-level high stand during the mid- to late Holocene.

A new dasycladalean alga Salpingoporella? popgrigorei n. sp. was identified in Pădurea Craiului Mountains (northern Apuseni, Romania) in the Lower Aptian limestone of the Valea Bobdei Member. The new alga was found within the external platform coarse bioclastic facies with fragments of corals, sclerosponges, bivalves (including rudists), gastropods, echinoderms, brachiopods, and bryozoans. The micropaleontological assemblage consists of foraminifera, calcareous algae, rare rivulariacean-type cyanobacteria, and some problematic microfossils. The deposits are Early Bedoulian in age, as clearly indicated by the orbitolinid foraminifera Orbitolinopsis pygmaea, Paracoskinolina sunnilandensis and Palorbitolina lenticularis. Salpingoporella? popgrigorei n. sp. is a medium-sized dasycladalean alga showing funnel-like laterals with an euspondyl arrangement. The laterals consist of two distinctive parts. The proximal part is narrow and flattened. The distal part widens relatively suddenly, and then narrows slightly before the final widening towards the exterior, in the place where the laterals most probably formed an assimilatory cortex. The distinctive features of the new species are represented by the shape of the laterals. The new Salpingoporella best resembles the Upper Hauterivian–Lower Barremian p.p. Salpingoporella genevensis (Conrad), especially due to the quadrangular aspect of the laterals in middle-deep tangential section. However, differences refer to the laterals’ general shape, and to the typical features of the laterals in deep tangential section of Salpingoporella? popgrigorei n. sp.

A first systematic study of composition, texture, and distribution of modern sediments in two Maldivian atolls reveals the predominance of skeletal carbonates. Fragments of corals, calcareous algae, mollusks, benthic foraminifera, and echinoderms are identified in the grain-size fraction >125 μm. Non-skeletal grains such as cemented fecal pellets and aggregate grains only occur in small percentages. Fragments of skeletal grains, aragonite needles, and nanograins (<1 μm) are found in the grain-size fraction <125 μm. Needles and nanograins are interpreted to be largely of skeletal origin. Five sedimentary facies are distinguished (1–5), for which the Dunham-classification is applied. Fore reef, reef, back reef, as well as lagoonal patch reef and faro areas in both atolls are characterized by the occurrence of coral grainstones (1), which also contain fragments of red coralline algae, the codiacean alga Halimeda, and mollusks. On reef islands, coral-rich sediment is cemented to form intertidal beachrock and supratidal cayrock. Skeletal grains in atoll-interior lagoons are mainly mollusks and foraminifera. The lagoon of Rasdhoo Atoll is covered in the west by mudstones (2), in the center by mollusk packstones (3) and mollusk wackestones (4), and by hard bottoms with corals in the east adjacent to channels through the atoll reef margin. The interior lagoon of Ari Atoll contains mollusk wackestones (4) in the center and mollusk-foraminifer packstones (5). Marginal lagoon areas are characterized by hard bottoms with corals. Facies distribution appears to be an expression of depositional energy, which decreases from the atoll margin towards the center in Ari Atoll, and towards the west in Rasdhoo Atoll. Predominant sediment mineralogies include aragonite and high-magnesium calcite. Mean aragonite content decreases from 90% in coral grainstone to 70–80% in mollusk packstone, mollusk wackestone, and mudstone, and to 50% in mollusk-foraminifer packstone. Stable isotopes of oxygen and carbon in bulk samples range from −3 to −1.5 (δ18O) and from +0.4 to +3.2 (δ13C). It is not possible to delineate facies based on O- and C-isotopes.

The existence of a conspicuous zone of islands and banks fringing the northern coast of the Japan Sea is well known. In 1922, H. I. M. S. “Musasi” discovered a large bank at the northern end of that zone, Iookm west off the coast of Tesio Province, Hokkaidô. It is outlined by 200m bathymetric line, gourd-shaped, and its shallowest part, which is in the center of the northern part, 31m. The bank has a significant flat, broad plain at a depth of 140-160m., the margin of the flat plain descending abruptly to the deep sea-floor. In the course of the soundings, thirty bottom samples were obtained from the bank and these samples were placed at my disposal through the courtesy of Commander Asahina, Hydrographic Department, Imperial Japanese Navy. An examination of the bottom samples, showed a predominance of gravels, followed by sand, mud, and rock fragments. I Rock fragments. The rock fragments, which were obtained from three stations, are plagio-liparite, glassy basalt, siliceous shale, and diatom-earth. The diatom-earth and siliceous shale show, under the microscope, some organic remains, such as fossil coscinodiscus sp., sponge spicules, etc. Although the fossil diatom and other organisms in the sedimentary rock fragments are of little value for accurate correlation of the rock strata, the fact remains that the general character of the rock fragments in question closely resembles those of the Tertiary rocks developed in the adjoining ter-restrial region, where, it may be added, liparite and basalt are also common in the Tertiary and Quaternary formations. 2 Gravels. Gravels were obtained from II stations on flat plain of the bank and the deep sea floor around it. They are quite water-worn, with neither striae nor pits on the surface, although rarely encrusted with calca-reous algae, bryozoa, etc. The lithological characters of the gravels micro-scopically determined may be classified into igneous and sedimentary rocks. The gravels of igneous rocks are liparite and basalt, probably derived from the bed rocks. The gravels of sedimentary rocks are diatomaceous sandy shale, siliceous shale containing fossil sponge spicules, their lithological charac-ters being closely related to the Tertiary rocks developed in the adjacent terrestrial regions. Gravels of hornstone and siliceous shale are rarely found among them, suggesting that they were derived from the Tertiary conglome-rate bed containing abundant pebbles of Palaeozoic. rocks. 3 Sand. Sand was obtained from many stations on the bank and the deep sea floor around it. The sand grains consist of angular quartz, feldspar, coloured minerals, glauconite, and organic remains. The most noticeable fact is that tests of foraminifera are abundant in the coarse sand obtained from sea floor shallower than 200m., decreasing abruptly in number. with increase of depth. 4 Mud. Mud is found below 400m. That obtained from the deep sea floor contained abundant diatom remains, sometimes looking like diatom ooze. Since the Musasi-tai, which rises from the deep sea floor outside the con-tinental shelf along Hokkaido, is separated from the mainland by a trench more than 300m. deep, it is natural to conclude that transportation of rocks and gravels from the mainland of Hokkaido across this trench is impossible, for which reason the soundings are of geological impotance, due to their yielding rock components that probably from the main part of the bank. The lithological charactesr of the rock fragments and gravels just mentioned are found to be the same as the geological elements making up the Neogene Tertiary developed in the adjacent mainland. From the foregoing facts, the bank as a whole represents a recently sub-merged land block, closely related, geologically as well as topographically, to the mainland of Hokkaidô.

Dissolved silicon isotope compositions (d30Si) have been analysed for the first time in groundwaters of beach sediments, which represent a subterranean estuary with fresh groundwater discharge from a freshwater reservoir and mixing with recirculated seawater. The fresh groundwater reservoir has high and variable dissolved silica concentrations between 136 and 736 µM, but homogeneous d30Si of +1.0 ± 0.15 per mil. By contrast, the seawater is strongly depleted in dissolved silica with concentrations of 3 µM, and consequently characterised by high d30Si of +3.0 per mil. The beach groundwaters are variably enriched in dissolved silica compared to seawater (23-192 µM), and concentrations increase with depth at all sampling sites. The corresponding d30Si values are highly variable (+0.3 per mil to +2.2 per mil) and decrease with depth at each site. All groundwater d30Si values are lower than seawater and most values are lower than dissolved d30Si of freshwater discharge indicating a significant amount of lithogenic silica dissolution in beach sediments. In contrast to open North Sea sediments, diatom dissolution or formation of authigenic silica in beach sediments is very low (ca. 5 µmol Si g). Silica discharge from the beach to the coastal ocean is estimated as approximately 210 mol Si yr per meter shoreline. Considering the extent of coastline this is, at least for the study area, a significant amount of the total Si budget and amounts to ca. 1% of river and 3.5% of backbarrier tidal flat area Si input.

Beach sediments were collected from four selected beaches along the barrier bar lagoon coastal system Lagos Nigeria namely Badagry, Takwa, Alpha and Eleko beaches. The sediments were texturally analyzed in order to determine the statistical parameters of their grain size distribution. The result shows that Badagry and Alpha beach sands are medium grained with average mean values of (1.10 Ф and 1.14Ф respectively). Eleko beach sediment is coarsely grained with an average mean value of (0.56 Ф) while Takwa Bay beach sediment is fine grained and very well sorted with an average mean value of (2.25 Ф.). This suggest that Eleko beach sediment being coarse grained is deposited in a high energy condition hence less vulnerable to erosion compared to Takwa bay beach sediment which is fine grained and deposited in low energy condition hence more vulnerable to erosion. Alpha and Badagry beach sediment are medium grain and deposited in a moderate energy condition hence more stable to erosional forces than Takwa bay beach sediment. The grain size and amount of sand on a beach depends on wave energy and geological sensitivity of the sediments to the forces of erosion

Sea cliffs 40 km east of Almeria, southeastern Spain, expose upper Miocene reefs and patch reefs of the Plomo formation. These reefs are formed of scleractinian corals, calcareous algae, and mollusks. The reef cores are as much as 65 m thick and several hundred meters wide. Fore-reef talus beds extend 1,300 m across and are 40 m thick. The reefs and reef breccias are composed of calcitic dolomite. They lie on volcanic rocks that have a K-Ar date of 11.5 m.y. and in turn are overlain by the upper Miocene Vicar Formation. In the reef cores and fore-reef breccia beds, porosity is both primary and postdepositional. Primary porosity is of three types: (a) boring clam holes in the scleractinian coral heads, cemented reef rocks, and breccias; (b) intraparticle porosity within the corals, Halimeda plates, and vermetid worm tubes; and (c) interparticle porosity between bioclastic fragments and in the reef breccia. Postdepositional moldic porosity was formed by the solution of aragonitic material such as molluscan and coral fragments. The Plomo reef carbonate rocks have high porosity and permeability, and retain a great amount of depositional porosity. Pores range in size from a few micrometers to 30 cm. The extensive intercrystalline porosity and high permeability resulted from dolomitization of micritic matrix. Dolomite rhombs are between 10 and 30 µ across. More moldic porosity was formed by the dissolution of the calcite bioclasts. Some porosity reduction has occurred by incomplete and partial sparry calcite infilling of interparticular, moldic, and intercrystalline voids. The high porosity and permeability of these reefs make them important targets for petroleum exploration in the western Mediterranean off southern Spain. In these offshore areas in the subsurface the volcanic ridge and the Plomo reef complex are locally onlapped or overlapped by 350 m or more of Miocene(?) and Pliocene fine-grained sedimentary rocks. The possibility exists that the buried Plomo reef deposits may form traps for oil and gas in the offshore areas southwest of the type locality. Stratigraphic traps also may occur where the Neogene sequence above the Plomo reef complex onlaps the volcanic ridge.

A stratigraphic section from the Tirgan Formation was selected in Arkan village nearby Bojnourd city in order to study echinoderm fauna systematically. Many specimens of echinoderms, especially toxasteridae which is associated with brachiopods were collected and studied systematically in this paper. Microscopie slides were also prepared and studied. All slides contain benthic foraminifers and calcareous algae as well as gastropod and coral fragments. Based upon diagnostic micro and macro fossils, a Barremian-Aptian age is assigned to the Tirgan Formation which suggests Urgonien facies type indicating shallow water of open marine environment The Urgonien is named after the village with this name in the east of Tarascon, France. This facies type is characteristic of shallow-water carbonate facies which was accumulated along the Tethys northern shelf from the Barremian to the late Albian. The facies consists of hard, white-gray limestones which contains Orbitolina (foraminifers) and transitional sediments – detrital or siliceous limestones (Foury, 1968).

The great physiographic diversity of the Dendê Coast favors the production of different beach sediment types, including bioclastic components. In this study 74 beach samples collected at 2 km intervals were used to evaluate beach sediment composition. For each sample, 300 grains were identified for each grain size class coarser than 0.125 mm, using a binocular microscope. The beach sediments of the Dendê Coast are essentially siliciclastic (80-100%). Quartz is the major component (70-100%). Only at the Tinharé and Boipeba islands bioclasts are major components of beach sands reaching up to 80-100%. These sediments are made up essentially of fragments of Halimeda, reaching percentages up to 70%. Coralline algae and mollusks also contribute significantly to these sediments (up to 30%). The results obtained show that the spatial distribution of the bioclastic components provide important information on the environmental conditions present at the shoreline (energy levels, availability of hard substrates and protected areas, pattern of sediment dispersion) and on the sediment sources as well. The composition of the beach sediments on the Dendê Coast reflects the present day environmental conditions and show that these sediments do not experience significant lateral transport. This situation is favored by an impeded longshore transport that characterizes most of the region. Although, in general, the rivers that discharge on the Dendê Coast appear to transport few sediments to the coastal zone, the presence of heavy minerals, micas and feldspars suggests river contributions to the beach sediments. On the other hand, the coral and coralline algae reefs, besides offering a natural protection to the shoreline, also represent an important source of beach sands.

Relationships between sand and water quality at recreational beaches

Using the concept of bleaching in optical dating, a new index of sediment sample bleaching percentage (BLP‐2) was developed and applied to evaluate sand grain transport from riverine to deep‐marine environments. As bleached grains in modern sediments have no optically stimulated luminescence (OSL)/infrared stimulated luminescence (IRSL) signal, bleached and unbleached feldspar grains are distinguished byIRSLintensity. TheBLP‐2 distribution of present deposits around theKumano area, on thePacific coast of centralJapan, suggests that sand grains in surface turbidites obtained from the bottom of theKumanoTrough are of flood/storm origin rather than seismogenic origin. The distribution ofBLP‐2 tentatively suggests sand grain erosion–transport–depositional processes; for example, origin and transport agencies of shelf sand, and influence of coastal erosion on the beach deposit. Although the presentBLPanalysis is not yet supported by a rigorous statistical test, it is useful to distinguish recent deposition and remobilization of sand grains. Furthermore, if the depositional age and the luminescence age of sand grains are accurately estimated, sand grain transport processes of old (lateQuaternary) sediments may be estimated by the methodology similar to that of the present study.

Recent specimens of Spiculidendron were found on Late Pleistocene (21,400–22,500 BP) cold-water corals from the sea floor at 457 m depth of the inter-atoll Kardiva Channel of the eastern row of the Maldives archipelago. Spiculidendron and other dendrophryid foraminifera (Rhizammina-like forms) exclusively colonized specimens of the genus Enallopsammia, which was characterized by a phosphatic-stain surface. The Spiculidendron wall was composed of sponge spicules, elongated diatom frustules, tests of juvenile benthic and planktic foraminifera, and calcareous nannoplankton, among other materials. Sponge spicules and elongated diatom frustules were arranged longitudinally, with foraminiferal tests and other bioclasts packed in between, indicating that the agglutination process of Spiculidendron is selective with respect to the manner of growth. In the most distal parts of the branches, only sponge spicules and elongated diatom frustules were present, working as guides for the test construction, prior to the agglutination of juvenile foraminiferal tests and other bioclasts. Moreover, in the sediment associated with the coral fragments, 94 species of benthic foraminifera were identified, an assemblage distinct from the taxa incorporated into the agglutinated Spiculidendron tests. The process of wall growth is complex and ordered. This foraminifer, as well as the Rhizammina-like specimens, tolerates dysoxic conditions (0.896 ml/l) and low temperature (12°C). This observation represents a new record of Spiculidendron from the Indian Ocean and from deeper (aphotic) environments than previously reported from the shallow waters of the Caribbean. A cryptobiontic habitat is interpreted for Spiculidendron.

Talus formations hold potential for hydrocarbon reserves, yet drilling and assessment in these areas are not commonly favoured. Central Luconia's carbonate fields have seen limited talus appraisal. The field of study (Field-X) is one of few fields in here drilled and appraised talus as part of its development drilling campaign. Insights derived from this campaign offer valuable data to address and mitigate various uncertainties on depositional concept, and assess future regional potential. Six wells were drilled during the development campaign in the study area, with two specifically targeting the appraisal of the talus zone. These wells underwent comprehensive logging programs and conventional coring. Pressure data and fluid sampling were conducted to ascertain connectivity between the talus and reef pinnacle, essential for volumetric reserve estimations. Biostratigraphic descriptions of the cores offer valuable evidence for identifying the origin of talus materials, aiding in concluding the depositional concept. Additionally, correlations between field data and regional events, such as sea level variations and wind direction, was studied to strengthen the depositional model. The conventional core biostratigraphy analysis reinforces the depositional theory of talus formation. Core features provide compelling evidence supporting this theory. Talus zones are primarily characterized by skeletal packstone and skeletal wackestone lithofacies, with prominent allochems such as skeletal fragments dominated by red algae, forams, echinoderms, occasional mollusc fragments, and bryozoans. Bryozoa and coral fragments are exceedingly rare, with occasional presence of dark pyritised grains. Physical structures like solution seams and stylolites indicate chemical compaction, leading to decreased porosity. Solution seams often accompany organic cumulates and occasionally clay lenses. Talus originates from eroded carbonate fragments and reef debris, deposited at flanks in deeper waters. Its composition includes non-skeletal particles (carbonate grains, mud, and clasts) alongside erosional skeletal particles (mollusc, foram, algae, echinoderm, coral fragments). Talus generally exhibits lower reservoir quality due to poor sorting and chemical compaction. Absence of sub-aerial exposure limits diagenesis processes altering porosity. Through this appraisal campaign, the presence of hydrocarbon potential in talus formations has been proven. With limited wells drilled for talus appraisal in Central Luconia, this paper serves as a valuable reference for other fields where talus occurs. Offering essential insights and lessons learned, this study provides critical information applicable to all carbonate fields featuring talus. Understanding talus formation is crucial for fostering confidence in future appraisal programs, and optimizing development and production strategies effectively.