Aragonite Content Research Articles

Nature and composition of shore-zone sediments between Jeddah and Yanbu, eastern Red Sea

The shore-zone sediments between Jeddah and Yanbu, west coast of Saudi Arabia, are composed mostly of skeletal carbonate sands. The nearshore sediments containing benthic foraminifera, algal fragments and molluscs are multimodal, the mean grain size varying between 0.76 and 2.35 ø. The beach sediments, except samples dominated by cerithid gastropods in some localities, are relatively finer than the nearshore sediments. Although the beaches to a great extent comprise sand-sized material, fine lime muds and coarse clastic gravels occur in certain areas. The dune sediments comprising mostly algal grains and ooids are very fine with 50 percent of the material in the 0.25–0.18 mm size grade. Except a general northward decrease in mean grain size, regional trends in the textural parameters of the sediments between Jeddah and Yanbu are not quite apparent. Lateral variations in the textural characteristics suggest a landward migration of the sediments in the shore zone under the influence of northerly and northwesterly winds. The carbon and oxygen ( δ 13 C + 4.80 to 4.84‰ PDB ) ( δ 13 O − 0.04 to + 0.53‰ PDB ) isotopic ratios of the lime muds occurring in certain shallow margins in the shore-zone, which are much higher than those of the green algae, indicate that the fine carbonates are at least in part inorganic in origin. Like the shallow-water carbonates in tropical seas, aragonite and high Mg-calcite are the dominant carbonate minerals in the shore-zone sediments. There is a landward increase in aragonite contents caused by the landward migration of fine material from the nearshore. The dominant clay mineral in the nearshore sediments is kaolinite with subordinate swelling chlorite and little illite. Kaolinite is contributed by the coastal regions under the sub-tropical humid climate. Swelling chlorite is considered to have been formed in the nearshore by mechanical mixture of chlorite and montmorillonite derived from the metamorphic and igneous terrains of the Tertiary mountains bordering the coastal plain.

Porosity of the Miami Limestone (Late Pleistocene), Lower Florida Keys

ABSTRACT This study investigates the amount and variability of porosity in the approximately 130,000-year-old politic grainstones of the Miami Limestone in the lower Florida Keys. Porosity is derived from porosimeter measurements of 326 plugs and core pieces representing 11 locations spanning about 65 km. Because larger voids in our samples result primarily from scouring by circulating water used in coring and plugging, measurements of matrix porosity, rather than of bulk porosity, represent the formation better in situ. X-ray diffraction analyses show that the rocks have undergone substantial inversion of aragonite to calcite (mean aragonite content of the matrix is 40 percent), but are not yet approaching mineralogical stabilization. Porosity of these partially stabilized rocks averages 36 percent, a decrease of 5-10 percent from that of the initial sediments. A qualitative interpretation suggests that the reduction in pore volume correlates with the degree of inversion of aragonite to calcite, and that the porosity decrease associated with complete mineralogical stabilization could be on the order of 15-20 percent. Porosity is narrowly distributed. The standard deviation of porosity for the entire data set is only 4 percent, and much of this variability is on the relatively small scale of primary sedimentary fabric. Although the pre-burial, near-surface meteoric environment may set the stage for subsequent porosity evolution, results imply that significant porosity loss and porosity diversity in similar but much older rocks develop during burial diagenesis.

Sr, Mg, and Ca chemistry of the skeleton of Nautilus

Concentrations of Sr, Mg, and Ca were quantified for the shell and septa formed during the final 3 to 4 yr of growth for four species of the extant cephalopod genus Nautilus [ N. belauensis Saunders 1981, N. macromphalus Sowerby 1849, N. scrobiculatus (Lightfoot 1786), and N. pompilius Linnaeus 1758]. These data are used to describe several aspects of the physiochemistry of Nautilus in relation to biomineralization of shell and septal aragonite. Species of Nautilus discriminate against the concentrations of Sr and Mg relative to Ca in seawater by 79% and 99.9%, respectively. The power of this discrimination against Sr and Mg varies for shell and septal aragonite within and among species. Although the among-species variation in the Sr and Mg content of shell and septal aragonite is greater than the within-species variation, differences in these concentrations are not unique among all species. However, when the covariance of Sr and Mg is computed as a transformed variable (discriminant function), species can be distinguished with significance ( P <0.001) by the combined Sr and Mg chemistry of septal aragonite. Similarly, all species with the exception of N. macromphalus and N. pompilius can be distinguished by the combined Sr and Mg chemistry of shell aragonite.

Mineralogical variations in the unconsolidated sediments of El Qasr reef, north of Jeddah, west coast of Saudi Arabia

Carbonate mineralogy of El Qasr reef sediments, north of Jeddah on the west coast of Saudi Arabia, was studied by X-ray analysis. Although the mineralogical composition varies only little, there are significant differences in the proportions of aragonite and high Mg-calcite between the environments. Lagoon sediments, which contain relatively more fine-grained material, are characterized by higher aragonite concentrations than the reef flat sediments. Decreasing grain size and increasing aragonite contents towards the centre of the lagoon suggest a transport of aragonitic mud from the shallow reef flat to the lagoon. The amount of fine fraction and occasionally the nature of the coarse fraction rather than the sand-sized skeletal material controls the aragonite concentrations in the reef sediments. Low Mg-calcite, which occurs in minor quantities and is erratically distributed in the reef sediments, is derived from the Pleistocene coral limestone in the coastal plain. Aragonite abundances in the sediments may be considered to delineate lagoon and reef flat environments in a coral reef complex.

Oxygen- and carbon-isotope composition of cold shallow-marine carbonates of Tasmania, Australia

In contrast to warm, shallow-marine carbonates, cold shallow-marine carbonate δ O 18 values from the shelf off Tasmania are only slightly enriched ( < 0.3‰ PDB ) relative to pure calcite deposited under equilibrium conditions, because of their low aragonite content, and low concentrations of Mg +2 in low-Mg to Mg-calcite. They may be somewhat depleted in δO 18 due to deposition in water of slightly lower than normal salinity. Their δC 13 values are in equilibrium with CO 2-rich, cold, upwelling deep-waters, depleted in δC 13. In both warm and cold shallow-marine carbonates there exists a positive correlation between δO 18 and δC 13 with variation in water temperatures. These distinct equilibrium trend lines occur both in surface water (in equilibrium with atmospheric CO 2 with a relatively constant δ C 13 ∼ 7.2‰ PDB ) and in bottom water (⩾ 500 m) and regions of upwelling, deep water (where aqueous ΣCO 2 is again relatively constant, but δ C 13 ∼ 0‰ PDB ).

Quaternary aragonite cycles and oxygen-isotope record in Bahamian carbonate ooze

Research Article| April 01, 1983 Quaternary aragonite cycles and oxygen-isotope record in Bahamian carbonate ooze A. W. Droxler; A. W. Droxler 1Comparative Sedimentology Laboratory, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Fisher Island Station, Miami Beach, Florida 33139-7392 Search for other works by this author on: GSW Google Scholar W. Schlager; W. Schlager 1Comparative Sedimentology Laboratory, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Fisher Island Station, Miami Beach, Florida 33139-7392 Search for other works by this author on: GSW Google Scholar C. C. Whallon C. C. Whallon 2Department of Geology, University of Miami, Coral Gables, Florida 33124 Search for other works by this author on: GSW Google Scholar Geology (1983) 11 (4): 235–239. https://doi.org/10.1130/0091-7613(1983)11<235:QACAOR>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation A. W. Droxler, W. Schlager, C. C. Whallon; Quaternary aragonite cycles and oxygen-isotope record in Bahamian carbonate ooze. Geology 1983;; 11 (4): 235–239. doi: https://doi.org/10.1130/0091-7613(1983)11<235:QACAOR>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Carbonate ooze in Bahamian troughs displays cyclic variation in the content of aragonite. A 10 m core devoid of turbidites shows 3.5 cycles, each defined by a sharp increase, followed by a gradual decrease of aragonite. The aragonite curve matches closely the oxygen-isotope curve of planktic foraminifera from the same core. Aragonite highs correspond to light oxygen-isotope values and thus to interglacial stages. Content of terrigenous material is low during interglacials and higher during glacial periods. Intermittent flooding and exposure of the Bahama Banks is most probably not the cause of the cycles, because the latest increase in aragonite precedes bank flooding by 8,000 yr and because the cycles are distinctly asymmetric, with rapid increase and gradual decrease of aragonitic content. Carbonate dissolution cycles tied to the glacial rhythm of Earth's climate are a more likely explanation of the variations in aragonite content. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Environmental influences on the shell mineralogy ofMytilus edulis

The shells ofMytilus edulis in the Tay estuary, Scotland, show mean aragonite contents of 55%, but in one zone the average aragonite proportion is only 45%. Comparison with data forMytilus edulis from other regions indicates the temperature and salinity are not the only significant determinants of the aragonite/calcite ratio. Elimination of other variables suggests that sewage discharges may influence the mineralogy of the shell secreted byMytilus edulis in the relatively nutrient-enriched areas.

EARLY SUBMARINE LITHIFICATION IN THE RED CHALK AND LOWER CHALK OF EASTERN ENGLAND: A BACTERIAL CONTROL MODEL AND ITS IMPLICATIONS

SUMMARY Early submarine lithifications are common in the Albian and Cenomanian Red Chalk and Lower Chalk of eastern England. They have developed generally in shallow water sediments deposited relatively slowly in the aphotic zone of the Chalk sea. Five varieties of early lithification are described and interpreted in detail. The lithification has occurred during the intrinsic diagenesis of the sediment ranging from very close to the water/sediment interface to some metres below. It has been caused by the precipitation of a ferroan calcite cement (2940–8900 ppm Fe 2+ ) under anaerobic alkaline conditions. The preservation of aragonitic fossils indicates that sources from within the sediment and the external reservoir of sea water supplied the necessary Ca 2+ and CO 3 2− . Indirect evidence suggests that (1) bacterial ammonification and sulphate-reduction have effected the precipitation of the ferroan calcite cement, and (2) porewater temperature, depositional rates, and the content of aragonite and organic matter in the sediment were important factors in controlling the development of early lithification. The importance or the bacterial mechanism as a general lithification process in the aphotic marine environment is discussed.

Uptake of fluoride by aragonite

The uptake of F by aragonite is attributed to the ion-exchange process, in which one CO 3 2− ion in the structure is replaced by two F − ions. Under the equilibrium condition at 15° C and 1 atm., the partition of F between aragonite and aqueous solution is described by: log ( [ F] a F )=1.95 + 0.54 log a Ca were [F] denotes the F content of aragonite in mol/g, and a F and a C a are the aqueous activities of F − and Ca 2+, respectively. The equation was successfully applied to estimating the F content of marine aragonite.

Shelf Basin Sedimentation: Mixing and Diagenesis of Pelagic and Clastic Turonian Carbonates, Israel

ABSTRACT The Turonian shelf edge, which delimited a large carbonate shelf platform, closely corresponds to the present-day shoreline of Israel. A NE-trending shelf basin, over 30 km long and about 5-10 km wide, had been cut into the shelf rocks during the regression which terminated the Cenomanian depositional cycle. The basin sediments include lithoclast calcarenites, oligosteginid calcilutites, mixtures of both and some small hippuritid patch reefs. The contemporaneous platform sediments include dolostones, pellet miliolid limestones and a caprinid fringing reef belt. The cyclic interbedding of well sorted, frequently cross-bedded lithoclast calcarenites and pelagic oligosteginid calcilutites in the basin points to a sedimentary regime controlled by periodic currents, such as tide or storm induced currents. The clastic carbonate material, forming the calcarenites, had been eroded and was transported from the shelf platform to the basin by these currents. Occasional calcarenite shoals, probably at the outlets of a tidal channel, were favorable sites for patch reef development within the basin. Differential recrystallization and cementation of the oligosteginid calcilutites is attributed to differences in primary detrital aragonite and clay contents and to proximity to aquiferial rocks. The high aragonite and low clay content of the calcilutites deposited at the basin's margin and their contact with an active aquiferal system resulted in the formation of limestones, whereas the low aragonite and high clay content of the calcilutites deposited in the basin center and their isolation from fresh water circulation resulted in the formation of chalks.

Incorporation of sodium, chloride and sulfate with calcium carbonate.

Calcite and/or aragonite were formed from calcium bicarbonate solutions containing sodium sulfate, sodium chloride and magnesium chloride of various concentrations. Sodium, chloride and sulfate contents of synthetic calcite or aragonite were measured. Sodium and chloride ions are incorporated into aragonitic calcium carbonate more easily than into calcitic calcium carbonate, although sodium and chloride ions in the parent solution favor the formation of calcitic calcium carbonate. On the other hand, sulfate ions are incorporated into calcitic calcium carbonate more easily than into aragonitic calcium carbonate, although sulfate ions in the parent solution favor the formation of aragonitic calcium carbonate. Sodium content of aragonite, which is precipitated from calcium bicarbonate solution containing sodium sulfate, sodium chloride and magnesium chloride, exhibits a maximum value together with sulfate content of aragonite.

Submarine and vadose cements in Pleistocene Bermuda reef rock

Well-rounded pebbles and cobbles of reef rock, which in bio- and lithofacies closely resembles the Recent algal cup reefs, occur in the basal conglomerate of the Pleistocene Devonshire Formation cropping out along Grape Bay on the south shore of Bermuda. The framebuilders of this rock include coralline red algae, vermetid gastropods, and barnacles. Study by petrographic microscope, electron microprobe, and SEM revealed aragonite-needle and spherulitic cements, high-Mg calcite micrite and palisade cements including calcified algal filaments. Two or three generations of these may occur in a given pore. By analogy with the Recent cup-reef material, on the basis of their composition (high strontium content of aragonite, high magnesium content of calcite) and of circumstantial evidence, these are considered submarine cements. In addition, a vadose blocky low-Mg calcite cement occurs, which never precedes any, but frequently succeedes one, two, or three of the above cements. Its fabrics vary: it may exhibit an increase in crystal size toward the center or not, it may or may not be bounded by the meniscus outline characteristic of the vadose diagenetic environment. The limitation of cement precipitation by a meniscus gives rise to a large diversity of forms determined by respective combinations of solution supply, permeability of the micro-environment, and substrate morphology. To illustrate the diversity, the meniscus cement is shown in relation to sediment particles, aragonite-needle cement, and calcified filaments. From the blocky low-Mg cement, selective neomorphism extends into some aragonitic gastropod shells; it is controlled, in part, by original shell structure. The resulting low-Mg calcite mosaic is characterized by relic structures and plane crystalline boundaries. Aragonite needles between blocky calcite cement and neomorphic calcite were not affected by the process of mineralogic alteration. This study shows that cements recognized earlier in Recent Bermuda cup reefs can be traced into the past and that additions to the diagenetic sequence can be distinguished. Knowledge of these features and their sequences should help decipher the diagenetic history of other fossil reefs.

The distribution of strontium in limestones on Barbuda, West Indies

ABSTRACTThe Sr2+ content of Barbudan limestones is proportional to the aragonite content. The Sr2+ content of calcite which has replaced aragonite varies from 3000 p.p.m. in the youngest limestones to 50 p.p.m., average values are approximately 300 p.p.m.The (mSr2+/mCa2+)L ratios from well waters within the limestone fall within the predicted values assuming KSrC∼0·1. The high (mSr2+/mCa)2+L ratios expected by a lower value of KSrC do not occur.The build up of (mSr2+/mCa2+)L ratios seen in waters from Barbados is not seen in the well waters from Barbuda. The Sr2+ content of calcite is generally lower than is seen in Barbados, but similar to that seen in parts of the Miami Oolite. Diagenesis of aragonite in Barbudan limestones is probably occurring in a more open system than in Barbados.

Generic and Environmental Control of Carbonate Mineralogy in Serpulid (Polychaete) Tubes

Calcareous tubes of the polychaete family Serpulidae are composed of magnesian calcite, aragonite, or mixtures of these two minerals. Mineralogy is controlled principally by generic factors, but may be modified-at least in some genera-by environmental factors. The percentage of aragonite in most serpulid tubes shows little or no correlation with water temperature. The $MgCO_{3}$ concentration in the entirely calcitic tubes generally increases with increasing temperature, but the $MgCO_{3}$ content in the calcite of tubes with mixed mineralogy appears to be dependent upon mineralogy-that is, as aragonite content increases, the magnesium carbonate within the calcite also increases so that the magnesium within the entire tube remains about constant. In tubes with more than 60% aragonite, however, the total magnesium content drops markedly.

ARAGONITIC OOIDS1: EXPERIMENTAL PRECIPITATION FROM SEAWATER IN THE PRESENCE OF HUMIC ACID2.

ABSTRACTHumic acid dissolved in artificial seawater influenced the morphology, internal structure, and composition of aragonite when precipitation was induced with dilute Na2CO3 solution. At sodium humate concentrations of around 20 mg/1, numerous brownish spherical aragonite bodies developed within one day at 25 °C. The spheres ranged in size from 10–100 microns and resembled natural marine ooids. They formed with gentle agitation of the solution as well as with no water movement at all. The typical structure of natural ooids consisting of concentric alternating aragonite and organic laminae was experimentally duplicated as layers of aragonite crystals alternating with humate membranes; however, in contrast to natural ooids, the individual aragonite crystals here were oriented radially with their c‐axes. The aragonite of the spheres contained about 20 wt. % more strontium than the aragonite precipitated experimentally without the addition of sodium humate, and organic carbon content of the spherical aragonite was about 7% by weight.

Size, grain type and mineralogical relationships in recent marine calcareous beach sands

Ten samples of Recent marine carbonate beach sands from the Florida Keys, Bahamas, Virgin Islands and Bermuda were analyzed for sorting parameters, grain genesis, and gross mineralogy. These sands are similar to other beach sands reported in the literature in their tendency toward negative skewness and leptokurtosis. Molluscan fragments are the major grain type in most samples, followed in importance by Halimeda. A decrease in molluscan fragments and an increase in “unknown” material with decreasing size are the only major trends found in grain type. Grain identification was hampered, increasingly in the finer classes, by recrystallization (or micritization) and infilling of intragranular cavities either by lime mud or crystal growth. X-ray diffraction revealed no trend in aragonite content with decreasing size in the sand range. A positive correlation between aragonite content and molluscan fragments plus Halimeda exists. An increase in high-magnesium calcite with decreasing size was noted and is due to increase in foraminifers and coralline algae. No trend in MgCO 3 content of low-Mg or high-Mg calcite with size was found. The influence of the juxtaposed sublittoral biota is great, and along with processes at work in the intertidal zone tends to homogenize the beach sands even when they are from different parts of a large subtropical geographic area.

Mineralogy of some Hawaiian Coastal and Marine Carbonates: ABSTRACT

The Hawaiian beaches are predominantly calcareous sands of skeletal origin washed in across the reef flats. Calcareous deposits also are present in the island shelf and bank environments. The carbonate minerals listed in order of decreasing abundance are high-Mg calcite, aragonite, and low-Mg calcite. Relative abundance of these carbonate mineral assemblages was determined by X-ray diffraction analyses to correlate the mineralogy, the sources, and the depositional environments. Beaches of the island of Hawaii, the youngest of the Hawaiian Island chain, have a higher aragonite content (65%) than those of the other islands, and the older the island, the lower is the aragonite content of its beach sands. This phenomenon is probably due to the maturity of the reefs. Coral and Halimeda, being the first to develop, formed the aragonitic framework which gradually was filled by high-Mg calcite skeletal sands, and, locally by low-Mg calcite skeletal sands. Aragonite is most abundant in the upper part of the island shelf (50 m) and high-Mg calcite increases in abundance in the lower part of the island shelf. Low-Mg calcite makes up less than 20% of the island shelf and is uniformly distributed in it. Aragonite in the lower part of the island shelf is transported from the shallow part of the shelf. The abundance of high-Mg calcite and aragonite in Hawaiian marine sediments indicates the recentness of the calcareous deposits. End_of_Article - Last_Page 617------------

The influence of sea level changes on sediment carbonate mineralogy, Tongue of the Ocean, Bahamas

Large fluctuations occur in the aragonite content of fine silt and clay-sized material sampled by piston cores in Tongue of the Ocean, Bahamas. Electron microscopy reveals that sedimentary sequences with high aragonite content are characterized by abundant aragonite needles. Sedimentary sequences containing small amounts of aragonite but large amounts of low-Mg calcite are dominated by coccoliths. The variation in both mineralogy and grain morphology is interpreted to be related to sea level fluctuations and the consequent presence or absence of sediment contribution (needles) from the adjacent Bahama Banks. These fluctuations are useful chronological indicators in these cores and should be applicable in other areas adjacent to carbonate banks. In particular, the last rise in sea level is clearly marked in all the cores.

Environmental and biological controls on bivalve shell mineralogy.

SummaryBivalves lay down two forms of calcium carbonate in their shells, aragonite and calcite. Shells may be wholly aragonitic, or may contain both aragonite and calcite, in separate monomineralic layers. Shells are built up of several layers of distinct aggregations of calcium carbonate crystals. These aggregations are referred to as shell structures and their general features are described. Aragonite occurs as prismatic, nacreous, crossed‐lamellar, complex crossed‐lamellar and homogeneous structures. Calcite occurs as prismatic or foliated structures. Myostracal layers (calcium carbonate laid down below sites of muscle attachment) are always aragonitic. The ligament and byssus when calcined are also invariably aragonitic. A summary of the occurrence of calcite and aragonite and the associated shell structures is given. Calcite is found only in the outer layer of superfamilies belonging to the subclass Pterio‐morphia with the exception of two species only from the Heterodont superfamily Chamacea. Generally within a superfamily shell structure and mineralogy are very constant. In all superfamilies these combinations have existed for many millions of years.It is therefore demonstrated that the prime control on shell mineralogy is genetic. Possible controls on mineralogy by the mantle cells, nature of the extrapallial fluid, nature of the periostracum and the organic matrix of the shell layers are discussed.It is known that environmental factors may modify the basic mineralogy/shell structure pattern within a superfamily. Thus there is an inverse relationship between the percentage of calcite in the shell and the mean temperature of the environment inhabited by the bivalve.A critical examination of published data shows that the evidence is convincing only in the superfamily Mytilacea. The species Mytilus californianus, which shows the greatest temperature effects, is peculiar amongst the Mytilacea in having an inner calcite layer as well as an outer one.Conflicting evidence for an inverse relationship between salinity and aragonite content is reviewed. The differences of opinion cannot be resolved without experimental work.We are grateful to the following for much useful discussion, and encouragement in many ways: Dr J. R. Baker, Dr G. E. Beedham, Dr B. C. M. Butler, Dr A. Hallam, Dr J. D. Hudson, Dr R. P. S. Jefferies, Mr J. Macrae, Dr W. S. McKerrow, Mr N. J. Morris, Mr C. P. Palmer, Mr N. Tebble, Dr E. R. Trueman and Professor A. Williams. Our best thanks are to Mr R. Cleevley for critically reviewing the manuscript.The following have rendered us considerable technical assistance: the staff of the electromicroscopy unit of the British Museum (Natural History), under the direction of Mr B. Martin; the technical staff of the Department of Geology, King's College, London and of the Department of Geology and Mineralogy, Oxford; Mrs J. M. Hall, and Mr G. Burton.

Carbonate Mineralogy of Sediments of Exuma Sound, Bahamas

ABSTRACT The carbonate mineralogy of the sediments in ten cores from Exuma Sound is interpreted to reflect Pleistocene sea level changes. Sediments in the lower parts of the cores contain abundant low-magnesium calcite and relatively little aragonite. This carbonate mineral assemblage is interpreted as representing a mineralogically stable, recycled sediment derived from the extensive Bahama Banks which were exposed during the latest Pleistocene sea level lowering. During this period of exposure the mineralogically unstable, aragonite-rich bank sediments were subaerially altered to low-magnesium calcite. The restoration of sea level and the return to the normal biological aragonite producing processes are reflected in the increased aragonite content in the upper parts of the cores studied. The mineralogic inflection with increasing core depth from the aragonitic to the calcitic sediments is abrupt and does not appear to be related to textural changes in the cores.