共查询到20条相似文献，搜索用时 46 毫秒
1.
《Russian Geology and Geophysics》2015,56(9):1322-1331
Experimental data on Fe-CaCO3 interaction at 6 GPa and 1273–1873 K are presented. The system models the hypothetical redox interaction in subducting slabs at the contact with the reduced mantle and a putative process at the core-mantle boundary. The reaction is accompanied by carbonatite melt formation. It also produces Fe3C and calcium wustite, which form solid or liquid phases depending on experimental conditions. In iron-containing systems at 6 GPa, calcium carbonate melts in the range 1473–1573 K, which is consistent with aragonite disappearance from complex carbonate systems. The composition of calcium carbonate liquid is not influenced by metallic Fe. It corresponds to nearly pure CaCO3. Along the mantle adiabat or at slightly higher temperatures, nearly pure CaCO3 coexists with metallic iron or calcium wustite. This hypothesis explains the coexistence of metallic iron and carbonate inclusions in lithospheric and superdeep diamonds. 相似文献
2.
Pablo Cubillas Stephan Köhler Carole Causserand 《Geochimica et cosmochimica acta》2005,69(23):5459-5476
Coupled CaCO3 dissolution-otavite (CdCO3) precipitation experiments have been performed to 1) quantify the effect of mineral coatings on dissolution rates, and 2) to explore the possible application of this coupled process to the remediation of polluted waters. All experiments were performed at 25°C in mixed-flow reactors. Various CaCO3 solids were used in the experiments including calcite, aragonite, and ground clam, mussel, and cockle shells. Precipitation was induced by the presence of Cd(NO3)2 in the inlet solution, which combined with aqueous carbonate liberated by CaCO3 dissolution to supersaturate otavite. The precipitation of an otavite layer of less than 0.01 μm in thickness on calcite surfaces decreases its dissolution rate by close to two orders of magnitude. This decrease in calcite dissolution rates lowers aqueous carbonate concentrations in the reactor such that the mixed-flow reactor experiments attain a steady-state where the reactive fluid is approximately in equilibrium with otavite, arresting its precipitation. In contrast, otavite coatings are far less efficient in lowering aragonite, and ground clam, mussel, and cockle shell dissolution rates, which are comprised primarily of aragonite. A steady-state is only attained after the precipitation of an otavite layer of 3-10 μm thick; the steady state CaCO3 dissolution rate is 1-2 orders of magnitude lower than that in the absence of otavite coatings. The difference in behavior is interpreted to stem from the relative crystallographic structures of the dissolving and precipitating minerals. As otavite is isostructural with respect to calcite, it precipitates by epitaxial growth directly on the calcite, efficiently slowing dissolution. In contrast, otavite’s structure is appreciably different from that of aragonite. Thus, it will precipitate by random three dimensional heterogeneous nucleation, leaving some pore space at the otavite-aragonite interface. This pore space allows aragonite dissolution to continue relatively unaffected by thin layers of precipitated otavite. Due to the inefficiency of otavite coatings to slow aragonite and ground aragonite shell dissolution, aragonite appears to be a far better Cd scavenging material for cleaning polluted waste waters. 相似文献
3.
D.E. Jacob A.L. Soldati J. Huth W. Hofmeister 《Geochimica et cosmochimica acta》2008,72(22):5401-5415
Freshwater and marine cultured pearls form via identical processes to the shells of bivalves and can therefore serve as models for the biomineralization of bivalve shells in general. Their nanostructure consists of membrane-coated granules (vesicles) which contain amorphous calcium carbonate (ACC) at the beginning of the biomineralization sequence, preceding the crystallization of aragonite and vaterite. In contrast to the commonly accepted view, crystallization of ACC occurs rapidly and within the granular nano-compartments mediated by organic molecules much earlier than platelet formation. The interlamellar organic sheets in nacre that form the platelet structure of nacre themselves form by self-organization after the crystallization process of CaCO3 is completed and, thus, cannot serve as a nucleation template for aragonite. Pores in the organic sheets are postulated to be a result of this process rather than to represent the pathways for CaCO3 through pre-existing interlamellar sheets. The amorphous phase has the highest concentrations of Mg (5.8 mol%), Mn (6.6 mol%), S (4.7 mol%) and P (1 mol%) of the three CaCO3-polymorphs. Mg/Ca and Mn/Ca ratios are found to decrease in the order ACC > vaterite > aragonite, corresponding to decreasing organic content in the different phases. This, as well as an observed enrichment of Mg in the organic-rich growth-banding of the pearls, suggests an at least partially organic speciation of Mg and Mn in bivalves and may be responsible for the observed physiological influence on Mg/Ca and Mn/Ca ratios in bivalves as a proxy for environmental parameters. 相似文献
4.
The early diagenetic chemical dissolution of skeletal carbonates has previously been documented as taking place within bioturbated, shallow water, tropical carbonate sediments. The diagenetic reactions operating within carbonate sediments that fall under the influence of iron‐rich (terrigenous) sediment input are less clearly understood. Such inputs should modify carbonate diagenetic reactions both by minimizing bacterial sulphate reduction in favour of bacterial iron reduction, and by the reaction of any pore‐water sulphide with iron oxides, thereby minimizing sulphide oxidation and associated acidity. To test this hypothesis sediment cores were taken from sites within Discovery Bay (north Jamaica), which exhibit varying levels of Fe‐rich bauxite sediment contamination. At non‐impacted sites sediments are dominated by CaCO3 (up to 99% by weight). Pore waters from the upper few centimetres of cores show evidence for active sulphate reduction (reduced SO4/Cl? ratios) and minor CaCO3 dissolution (increased Ca2+/Cl? ratios). Petrographic observations of carbonate grains (specifically Halimeda and Amphiroa) show clear morphological evidence for dissolution throughout the sediment column. In contrast, at bauxite‐impacted sites, the sediment is composed of up to 15% non‐carbonate and contains up to 6000 μg g?1 Fe. Pore waters show no evidence for sulphate reduction, but marked levels of Fe(II), suggesting that bacterial Fe(III) reduction is active. Carbonate grains show little evidence for dissolution, often exhibiting pristine surface morphologies. Samples from the deeper sections of these cores, which pre‐date bauxite influence, commonly exhibit morphological evidence for dissolution implying that this was a significant process prior to bauxite input. Previous studies have suggested that dissolution, driven by sulphate reduction and sulphide oxidation, can account for the loss of as much as 50% of primary carbonate production in localized platform environments. The finding that chemical dissolution is minor in a terrigenous‐impacted carbonate environment, therefore, has significant implications for carbonate budgets and cycling, and the preservation of carbonate grains in such sediment systems. 相似文献
5.
6.
Resulting from static experiments performed to study the phase state of CaCO3, it was found that its melting is congruent at 20–22 GPa and 3500 K. The obtained experiment data show that the field of
congruent melting of calcium carbonate is rather broad (form 2300 to 3500–3800 K at 20–22 GPa). However, the potential presence
of a high-temperature phase boundary at which CaCO3 is decomposed into CaO and CO2 is not ruled out. The existence of a wide area of congruent melting of calcium carbonate (a common primary inclusion in diamonds
of the transition zone and lower mantle of the Earth) allow one to consider deep-seated melts as potential parental media
for ultradeep diamonds. 相似文献
7.
Calcium carbonate dissolution in deep sea sediments: reconciling microelectrode, pore water and benthic flux chamber results 总被引：1，自引：0，他引：1
We report the benthic fluxes of O2, titration alkalinity (TA), Ca2+, NO3−, PO43−, and Si(OH)4 from in situ benthic flux chamber incubations on the Ceara Rise and Cape Verde Plateau and compare them to previously published results. We find within analytical uncertainty that the TA flux is twice the calcium flux, suggesting that dissolution/precipitation of CaCO3 is the principal mechanism controlling benthic TA and Ca2+ fluxes. At sites where the sediments contain significant (>35%) CaCO3 and the overlying waters are supersaturated with respect to CaCO3, the ratios of the total dissolution rate to the remineralization rate are significantly less than at all other study sites. We propose that these observations can be explained by precipitation of fresh CaCO3 at the supersaturated sediment surface followed by redissolution deeper in the sediments because of metabolically-produced CO2. A numerical simulation is presented to demonstrate the feasibility of this explanation. In addition, surface exchange reactions in high-CaCO3 sediments coupled with high rates of particle mixing may also impact rates of metabolic dissolution and depress chamber-derived estimates of carbonate alkalinity and calcium benthic fluxes. These results suggest that at supersaturated, high CaCO3 locations, previous models of sediment diagenesis may have overestimated the impact of metabolic dissolution on the preservation of CaCO3 deposited on the sea floor. 相似文献
8.
A combination of both water chemistry and sedimentological information was used to investigate the carbonate-producing mechanism
in Littlefield Lake, a small lake located in Isabella County, central Michigan. Data on temperature, dissolved oxygen, pH,
calcium carbonate (CaCO3) saturation, alkalinity, calcium, and magnesium were obtained on a monthly basis over a 13-month period, with each parameter
determined at 1m intervals over a depth range of 20m. The loss of dissolved carbon dioxide (CO2) from warm surface waters during direct degassing, and to a lesser extent during photosynthetic uptake by lacustrine macrophytes
and phytoplankton during the summer, results in massive precipitation of the low-magnesium calcite which predominates in all
Littlefield Lake sedimentary facies However, despite the fact that carbonate precipitation in this rather typical temperate-region
marl lake is directly related to, and may be driven by, seasonal variation in these physiochemical parameters, most calcite
forms as encrustations around cyanophytic and chlorophytic macrophytes. Such relationships demonstrate that carbonate precipitation
in marl lakes may result from complex interactions between both biochemical and physiochemical processes. As such, marl formation
in this, and probably many other calcareous lake systems, can not be simply ascribed to one or the other of these two general
mechanisms. 相似文献
9.
Contents of rare earth elements in waters and bottom sediments are maximum in the most mineralized soda lakes. It is shown that REE occur in waters mainly as carbonate (LnСО3)+ and oxyhydroxide LnO2H, LnO+, (LnO2)– complexes, whose activity in the La → Lu series changes in opposite directions. It has been determined that increase of mineralization leads mainly to higher concentrations of the dissolved HREE. Prevalence of the absolute values of MREE and HREE is recorded in basins with the development of bacterial processes. Geochemical barrier for the accumulation of LREE in waters can be represented by fluorcarbonates, whose saturation degree in the soda lake waters can be several orders of magnitude higher than the solubility products (SP). Oxidative and reductive settings in lakes are favorable for the formation of Ce(OH)4 and Ce(OH)3, respectively. 相似文献
10.
A.C. Narayana P.D. Naidu N. Shinu P. Nagabhushanam B.S. Sukhija 《Quaternary International》2009,206(1-2):72
Two Gravity cores (AAS 38-4 and AAS 38-5) recovered from the eastern Arabian Sea were analyzed for calcium carbonate (CaCO3), organic carbon, aluminium (Al) and titanium (Ti) in order to understand the calcium carbonate and terrigenous fluctuations during the Holocene and Last Glacial Period. High CaCO3 and low Al and Ti during the Holocene, and low CaCO3 and high Al and Ti during the Last Glacial Period suggest that CaCO3 content in these two cores appears to be controlled by the dilution of terrigenous material. The supply of terrigenous material to the core sites was higher during the Last Glacial Period than in the Holocene. Organic carbon values were lower (<2%) during the Holocene and higher (>2%) during the Last Glacial Period in core AAS 38-4; but the opposite was found in core AAS 38-5. This inconsistent pattern of organic carbon changes in the two cores studied indicates that the distribution of organic carbon in the eastern Arabian Sea is controlled not only by the supply of organic matter from the water column but also by sediment texture and dilution of sediment components. 相似文献
11.
Mariusz Pełechaty Andrzej Pukacz Karina Apolinarska Aleksandra Pełechata Marcin Siepak 《Sedimentology》2013,60(4):1017-1035
A significant portion of calcium carbonate is deposited in lake sediments as a result of biological processes related to the photosynthetic activity of phytoplankton in the pelagic realm and, in addition, macrophytes in the littoral zone. Lake Wigry, one of the largest lakes in Poland (north‐east Poland), is characterized by: (i) carbonate sediments with a CaCO3 content exceeding 80% within the littoral zone; and (ii) large areas of submerged vegetation dominated by charophytes (macroscopic green algae, Characeae family). It is claimed that charophytes are highly effective in utilizing HCO3? and forming thick CaCO3 encrustations. Thus, this study was aimed at evaluating the CaCO3 production by dense Chara stands overgrowing the lake bottom reaching a depth of 4 m. In late July 2009, the fresh and dry mass of plants, the percentage contribution of calcium carbonate and the production of CaCO3 per 1 m2 were investigated along three transects at three depths (1 m, 2 m and 3 m, with each sample area equal to 0·0625 m2) per transect. The composition and structure of phytoplankton and the physico‐chemical properties of the water analysed in both the littoral and pelagic zones served as the environmental background and demonstrated moderately low fertility in the lake. The greatest dry plant mass exceeded 1000 g m?2 and CaCO3 encrustations constituted from 59% to over 76% of the charophyte dry weight. Thus, the maximum and average values of carbonates precipitated by charophytes were 685·5 and 438 g m?2, respectively, which exceeded previously reported results. A correlation of carbonate production with the depth of Chara stands was detected, and intermediate depths offered the most favourable conditions for carbonate precipitation (589 g m?2 on average). As precipitated carbonates are ultimately stored in bottom deposits, the results highlight the significance of charophytes in lacustrine CaCO3 sedimentation. 相似文献
12.
Giovanni Aloisi 《Geochimica et cosmochimica acta》2008,72(24):6037-6060
Through early lithification, cyanobacterial mats produced vast amounts of CaCO3 on Precambrian carbonate platforms (before 540 Myr ago). The superposition of lithified cyanobacterial mats forms internally laminated, macroscopic structures known as stromatolites. Similar structures can be important constituents of Phanerozoic carbonate platforms (540 Myr to present). Early lithification in modern marine cyanobacterial mats is thought to be driven by a metabolically-induced increase of the CaCO3 saturation state (ΩCaCO3) in the mat. However, it is uncertain which microbial processes produce the ΩCaCO3 increase and to which extent similar ΩCaCO3 shifts were possible in Precambrian oceans whose chemistry differed from that of the modern ocean. I developed a numerical model that calculates ΩCaCO3 in cyanobacterial mats and used it to tackle these questions. The model is first applied to simulate ΩCaCO3 in modern calcifying cyanobacterial mats forming at Highborne Cay (Bahamas); it shows that while cyanobacterial photosynthesis increases ΩCaCO3 considerably, sulphate reduction has a small and opposite effect on mat ΩCaCO3 because it is coupled to H2S oxidation with O2 which produces acidity. Numerical experiments show that the magnitude of the ΩCaCO3 increase is proportional to DIC in DIC-limited waters (DIC < 3-10 mM), is proportional to pH when ambient water DIC is not limiting and always proportional to the concentration of Ca2+ in ambient waters. With oceanic Ca2+ concentrations greater than a few millimolar, an appreciable increase in ΩCaCO3 occurs in mats under a wide range of environmental conditions, including those supposed to exist in the oceans of the past 2.8 Gyr. The likely lithological expression is the formation of the microsparitic stromatolite microtexture—indicative of CaCO3 precipitation within the mats under the control of microbial activity—which is found in carbonate rocks spanning from the Precambrian to recent. The model highlights the potential for an increase in the magnitude of the ΩCaCO3 shift in cyanobacterial mats throughout Earth’s history produced by a decrease in salinity and temperature of the ocean, a decrease in atmospheric pCO2 and an increase in solar irradiance. Such a trend would explain how the formation of the microsparitic stromatolite microtexture was possible as the ΩCaCO3 of the ocean decreased from the Paleoproterozoic to the Phanerozoic. 相似文献
13.
The onset of pelagic sedimentation attending the radiation of pelagic calcifiers during the Mesozoic was an important divide in Earth history, shifting the locus of significant carbonate sedimentation from the shallow shelf environments of the Paleozoic to the deep sea. This shift would have impacted the CO2 cycle, given that decarbonation of subducted pelagic carbonate is an important return flux of CO2 to the atmosphere. Coupled with the fact that the mean residence time of continental platform and basin sedimentary carbonate exceeds that of the oceanic crust, it thus becomes unclear whether carbon cycling would have operated on a substantially different footing prior to the pelagic transition. Here, we examine this uncertainty with sensitivity analyses of the timing of this transition using a coupled model of the Phanerozoic atmosphere, ocean, and shallow lithosphere. For purposes of comparison, we establish an age of 250 Ma (i.e., after the Permo-Triassic extinctions) as the earliest opportunity for deposition of extensive biogenic pelagic carbonate on the deep seafloor, an age that predates known occurrences of pelagic calcifiers (and intact seafloor). Although an approximate boundary, we do show that attempts to shift this datum either significantly earlier or later in time produce model results that are inconsistent with observed trends in the mass–age distribution of the rock record and with accepted trends in seawater composition as constrained by proxy data. Significantly, we also conclude that regardless of the timing of the onset of biogenic pelagic carbonate sedimentation, a carbon sink involving seawater-derived dissolved inorganic carbon played a critical role in carbon cycling, particularly in the Paleozoic. This CaCO3 sink may have been wholly abiogenic, involving calcium derived either directly from seawater (thus manifest as a direct seafloor deposit), or alternatively from basalt–seawater reactions (represented by precipitation of CaCO3 in veins and fissures within the basalt). Despite the uncertainty in the source and magnitude of this abiogenic CaCO3 flux, it is likely a basic and permanent feature of global carbon cycling. Subduction of this CaCO3 would have acted as a basic return circuit for atmospheric CO2 even in the absence of biogenically derived pelagic carbonate sedimentation. Lastly, model calculations of the ratio of dissolved calcium to carbonate ion (Ca2+/CO3 2?) show this quantity underwent significant secular evolution over the Phanerozoic. As there is increasing recognition of this ratio’s role in CaCO3 growth and dissolution reactions, this evolution, together with progressive increases in nutrient availability and saturation state, may have created a tipping point ultimately conducive to the appearance of pelagic calcifiers in the Mesozoic. 相似文献
14.
《Applied Geochemistry》2003,18(11):1705-1721
Armoring of limestone is a common cause of failure in limestone-based acid-mine drainage (AMD) treatment systems. Limestone is the least expensive material available for acid neutralization, but is not typically recommended for highly acidic, Fe-rich waters due to armoring with Fe(III) oxyhydroxide coatings. A new AMD treatment technology that uses CO2 in a pulsed limestone bed reactor minimizes armor formation and enhances limestone reaction with AMD. Limestone was characterized before and after treatment with constant flow and with the new pulsed limestone bed process using AMD from an inactive coal mine in Pennsylvania (pH=2.9, Fe =150 mg/l, acidity =1000 mg/l CaCO3). In constant flow experiments, limestone is completely armored with reddish-colored ochre within 48 h of contact in a fluidized bed reactor. Effluent pH initially increased from the inflow pH of 2.9 to over 7, but then decreased to <4 during the 48 h of contact. Limestone grains developed a rind of gypsum encapsulated by a 10- to 30-μm thick, Fe-Al hydroxysulfate coating. Armoring slowed the reaction and prevented the limestone from generating any additional alkalinity in the system. With the pulsed flow limestone bed process, armor formation is largely suppressed and most limestone grains completely dissolve resulting in an effluent pH of >6 during operation. Limestone removed from a pulsed bed pilot plant is a mixture of unarmored, rounded and etched limestone grains and partially armored limestone and refractory mineral grains (dolomite, pyrite). The ∼30% of the residual grains in the pulsed flow reactor that are armored have thicker (50- to 100-μm), more aluminous coatings and lack the gypsum rind that develops in the constant flow experiment. Aluminium-rich zones developed in the interior parts of armor rims in both the constant flow and pulsed limestone bed experiments in response to pH changes at the solid/solution interface. 相似文献
15.
Different sources of lime for the production of precipitated calcium carbonate were studied. The reactivity of lime, its optical properties and those of the final products are reported and discussed, and a comparison made between lime from different sources. The influence of the temperature of hydration water on the optical properties and particle sizes after hydration and precipitation was also studied. It was found that coarser granulations of lime have better optical properties than finer granulations. The hydration temperature does not have an appreciable impact on the optical properties, but influences the intermediate, i.e. the calcium hydroxide particle sizes and subsequently the particle sizes of the precipitated calcium carbonate. Furthermore, the maximum temperatures of lime hydration from different European sources do not vary significantly, but they differ in the kinetics of the hydration process. 相似文献
16.
Sets of 20 soda ash glasses, 16 soda lime glasses and 23 wood ash glasses mainly from excavations in Europe (additional soda ash glasses from Egypt) were analysed on 61 chemical elements. Average SiO2 is about 62% in soda glasses and 50% in wood ash glasses. The three groups of glasses contain on average 13% Na2O, 18% Na2O and 13% K2O as fluxes to lower the melting temperature of quartz at their production. The starting materials beside quartz were halophytic plant ash for soda ash glass, trona (Na3H(CO3)2·2H2O) and lime (clamshells) for soda lime glass and beech ash for wood ash glass. Each of the three major glass types contains specific Rare Earth Element (REE) concentrations mainly contained in quartz and its intergrown minerals. 50 Paleozoic and Mesozoic sandstones from Central Europe represent the quartz composition. The REE pattern of these glasses apparently indicates major compositional stages of the Continental Earth's Crust. The boron to lithium and sodium to potassium ratios as in seawater suggest reactions of materials for soda glass with seawater. Negative Ce anomalies in the three glasses are caused by reactions of quartz with seawater. 相似文献
17.
Molar tooth (MT) structures are enigmatic, contorted millimetre‐ to decimetre‐long veins and spheroids of microcrystalline calcite that formed during very early diagenesis in Precambrian sediments. MT structures in the ca 2·6 Ga Monteville Formation are 600–800 Myr older than previously reported occurrences and establish that conditions necessary for MT genesis were met locally throughout much of the Precambrian. In the Monteville Formation, MT structures were formed shallow subtidally, extending to depths near storm wave base, in shale host sediments intercalated with storm‐generated carbonate sand lenses. They are filled with microcrystalline calcite and rare pyrite. Microcrystalline calcite identical to that in MT structures fills other pore space, including porosity between grains in carbonate sand lenses, moldic porosity in sand grains, sheet cracks in columnar stromatolites, and shallow cracks on sandy bedding planes. Relationships in the Monteville Formation demonstrate that microcrystalline CaCO3 precipitated in fluid‐filled cracks and pores; microcrystalline calcite characteristics, as well as the paucity of carbonate mud in host rocks, are inconsistent with injection of lime mud as the origin of MT structures. Locally, MT cracks were filled by detrital sediment before or during precipitation. Precipitation occurred in stages, and MT CaCO3 evolved from granular cores to a rigid mass of cores with overgrowths – allowing both plastic and brittle deformation of MT structures, as well as reworking of eroded MT structures as rigid clasts and lime mud. Crystal size distributions and morphology suggest that cores precipitated through nucleation, Ostwald ripening and size‐dependent crystal growth, whereas overgrowths formed during size‐independent crystal growth. 相似文献
18.
Early marine lithification of the nodular limestones in the Silurian of New Brunswick 总被引：1，自引：0，他引：1
A sequence of irregular nodular limestones in the Silurian of northern New Brunswick appear to have undergone early marine lithification. Nodules and crusts formed soon after deposition in the argillaceous lime sediments by sporadic diagenetic precipitation of calcium carbonate and were subsequently modified by differential compaction and minor flowage. While lack of both borings and encrusting organisms on the nodules indicates they were not ‘hard grounds’, computed porosities at the time of lithification based on the ratio of carbonate to insoluble residues suggest lithification depths within a few tens of feet of the sediment-water interface. Consideration of the availability of calcium carbonate suggests lithification very close to the sediment surface. 相似文献
19.
Surface carbonate and land-derived deposits in the sea off southern Chile were investigated for their mineralogical and geochemical composition. The data were related to environmental features and compared with those of similar temperate and polar carbonate deposits from Tasmania, New Zealand, Arctica, and Antarctica. The mineralogy of the siliciclastic fraction is typical of cold areas and is mainly composed of chlorite, mica, quartz, feldspars and amphibole. The CaCO3 content varies from 30 to 90%; carbonate mineralogy is made up of low-Mg calcite, high-Mg calcite and minor amounts of aragonite. The Ca, Mg, Sr, Fe, and Mn contents of bulk carbonates and some selected skeletal hard parts are comparable to those of carbonates from Tasmania. The elemental composition is mainly related to carbonate mineralogy, skeletal components, and seawater conditions. The δ13C and δ18O values of carbonates are positive, and their field falls between the “seafloor diagenesis” and “upwelling water” trend lines, because the sediments are likely to be in equilibrium with waters of Antarctic origin. The mineralogical, elemental, and isotopic compositions of carbonates from southern Chile show better similarities with the “temperate” carbonates from Tasmania and New Zealand than with the “polar” carbonates from Arctica and Antarctica. Carbonate deposition is allowed by the low terrigenous input, the low SPM concentration and, probably, the upwelling of seawater from Antarctica. 相似文献
20.
Yi-Pin Lin 《Geochimica et cosmochimica acta》2005,69(18):4495-4504
We studied the effects of seed material and solution composition on calcite crystal precipitation using a pH-stat system. The seed materials investigated included quartz, dolomite, two calcites with different particle size and specific surface area, and two dried precipitates from precipitative softening water treatment plants. Our results indicated that, of the seed materials examined, only calcite had the ability to initiate calcite precipitation in a solution with a degree of supersaturation of 5.3 over a period of two hours, and that the precipitation rate was proportional to the available surface area of the seed. For different solution compositions with the same degree of supersaturation, the calcite precipitation rate increased with increasing carbonate/calcium ratio, which contradicts the generally accepted empirical rate expression that the degree of supersaturation is the sole factor controlling precipitation kinetics. By applying a surface complexation model, the surface concentrations of two species, >CO3− and >CaCO3−, appear to be responsible for catalyzing calcite precipitation. 相似文献