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Influence of Mg2+, Fe2+ and Zn2+ Cations on 13C-18O Bonds in Precipitated Aragonite, Calcite and Dolomite: An ab Initio Study  [PDF]
Jie Yuan
Open Journal of Geology (OJG) , 2015, DOI: 10.4236/ojg.2015.55023
Abstract: The influence of metal cations on 13C-18O bonds in carbonates is still under debate. This paper used ab initio method to investigate this kind of influence of Mg2+, Fe2+ and Zn2+ cations on 13C-18O bonds in precipitated aragonite, calcite and dolomite. The polynomials of Δ47 and reduced partition function ratios (RPFRs) for 13/12C,
13C-18O Bonds in Precipitated Calcite and Aragonite: An ab Initio Study  [PDF]
Jie Yuan, Zhigang Zhang, Yigang Zhang
Open Journal of Geology (OJG) , 2014, DOI: 10.4236/ojg.2014.49034
Abstract: The 13C-18O bonds in carbonates are potential single-phase geo-thermometers. However, their theoretical distributions (noted as Δ47s) in CO2 degassed from calcite and aragonite with phosphoric acid are unclear. Thus, the isotope reactions of 13C-18O bonds on the growing surfaces of calcite (0001) and aragonite (001) planes were investigated using ab initio techniques. It was found that these reactions determined 13C-18O clumped isotope signatures in bulk calcite and aragonite minerals with novel Δ47 polynomials: \"\"
Discovery of seep carbonate nodules as new evidence for gas venting on the northern continental slope of South China Sea
Chen Zhong,Yan Wen,Chen Muhong,Wang Shuhong,Lu Jun,Zhang Fan,Xiang Rong,Xiao Shangbin,Yan Pin,Gu Senchang
Chinese Science Bulletin , 2006, DOI: 10.1007/s11434-006-1228-8
Abstract: Seep carbonate nodules were firstly collected from the southwestern Dongsha area on northern continental slope of South China Sea for mineralogical and geochemical studies. The results of X-ray diffraction show that carbonate nodules are composed of Fe-rich domolite, siderite and a few calcite and aragonite, as well as a small quantity of non-carbonate minerals such as goethite, quartz and clay minerals. Fe-rich dolomite and siderite characterized by euhedral microcrystalline structure were directly precipitated at cold seeps. The δ13C values for Fe-rich dolomite and siderite in the bulk nodules vary from 18.24‰ to 36.07‰, and the δ18O values range from 0.42 to 2.76‰. Their moderate depleted 13C reflects that carbon origin is possibly thermogenetic gas or mixed gas, which is evidence of gas ventings in the seafloor. Moreover, massive worm tube fossils related to cold seeps were found on the surfaces of carbonate nodules, and the conduits and/or channels in semi-solidified nodules which were not filled by carbonate or sediment were also observed. A preliminary conclusion is that active micro gas venting with a conduit/channel diameter range from 200 μm to 600 μm possibly exists in modern seafloor of the carbonate nodule area.
Discovery of seep carbonate nodules as new evidence for gas venting on the northern continental slope of South China Sea
CHEN Zhong,YAN Wen,CHEN Muhong,WANG Shuhong,LU Jun,ZHANG Fan,XIANG Rong,XIAO Shangbin,YAN Pin,GU Senchang,
CHEN
,Zhong,YAN,Wen,CHEN,Muhong,WANG,Shuhong,LU,Jun,ZHANG,Fan,XIANG,Rong,XIAO,Shangbin,YAN,Pin,GU,Senchang

科学通报(英文版) , 2006,
Abstract: Seep carbonate nodules were firstly collected from the southwestern Dongsha area on northern continental slope of South China Sea for mineralogical and geochemical studies. The results of X-ray diffraction show that carbonate nodules are composed of Fe-rich domolite, siderite and a few calcite and aragonite, as well as a small quantity of non-carbonate minerals such as goethite, quartz and clay minerals. Fe-rich dolomite and siderite characterized by euhedral microcrystalline structure were directly precipitated at cold seeps. The δ13C values for Fe-rich dolomite and siderite in the bulk nodules vary from 18.24‰ to 36.07‰, and the δ18O values range from 0.42 to 2.76‰. Their moderate depleted 13C reflects that carbon origin is possibly thermogenetic gas or mixed gas, which is evidence of gas ventings in the seafloor. Moreover, massive worm tube fossils related to cold seeps were found on the surfaces of carbonate nodules, and the conduits and/or channels in semi-solidified nodules which were not filled by carbonate or sediment were also observed. A preliminary conclusion is that active micro gas venting with a conduit/channel diameter range from 200 μm to 600 μm possibly exists in modern seafloor of the carbonate nodule area.
Biotic Control of Skeletal Growth by Scleractinian Corals in Aragonite–Calcite Seas  [PDF]
Tomihiko Higuchi, Hiroyuki Fujimura, Ikuko Yuyama, Saki Harii, Sylvain Agostini, Tamotsu Oomori
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0091021
Abstract: Modern scleractinian coral skeletons are commonly composed of aragonite, the orthorhombic form of CaCO3. Under certain conditions, modern corals produce calcite as a secondary precipitate to fill pore space. However, coral construction of primary skeletons from calcite has yet to be demonstrated. We report a calcitic primary skeleton produced by the modern scleractinian coral Acropora tenuis. When uncalcified juveniles were incubated from the larval stage in seawater with low mMg/Ca levels, the juveniles constructed calcitic crystals in parts of the primary skeleton such as the septa; the deposits were observable under Raman microscopy. Using scanning electron microscopy, we observed different crystal morphologies of aragonite and calcite in a single juvenile skeleton. Quantitative analysis using X-ray diffraction showed that the majority of the skeleton was composed of aragonite even though we had exposed the juveniles to manipulated seawater before their initial crystal nucleation and growth processes. Our results indicate that the modern scleractinian coral Acropora mainly produces aragonite skeletons in both aragonite and calcite seas, but also has the ability to use calcite for part of its skeletal growth when incubated in calcite seas.
Aragonite-calcite transformation in fossil snail shells of loess sequences in Loess Plateau, Central China
Sheng Xuefen,Chen Jun,Cai Yuanfeng,Chen Yang,Ji Junfeng
Chinese Science Bulletin , 2005, DOI: 10.1007/BF02897383
Abstract: The methods of X-ray diffraction (XRD) and ICP-AES are applied to analyzing the mineral composition of modern and fossil snail shells in Luochuan section and Xifeng section. The results show that the mineral phase of calcium carbonate in modern snail shells is aragonite, but for some fossil snail shells in certain layers of loess sequences, a part of aragonite is transformed into calcite. In Luochuan and Xifeng sections, the stratigraphic borderline of aragonite-calcite transformation appearing obviously is between L5 and L6. Under the earth surface condition, the aragonite-calcite transformation is influenced by the factor of temperature only in a long time scale. It seems that the pressure is not the factor influencing the aragonite-calcite transformation. The results also show that existing age of snail shells is possibly the dominant and principal factor for the aragonite-calcite transformation. To a certain extent, the degree of aragonite-calcite transformation in snail shell is controlled by the content of trace element, such as Mg2+. The trace element can improve the stability of snail shell aragonite and impede the process of aragonite transforming into calcite.
Comparison of Dissolution and Surface Reactions Between Calcite and Aragonite in L-Glutamic and L-Aspartic Acid Solutions  [PDF]
Miyoung Ryu,Hwan Kim,Mihee Lim,Kwangsuk You,Jiwhan Ahn
Molecules , 2010, DOI: 10.3390/molecules15010258
Abstract: We have investigated dissolution and surface reaction of calcite and aragonite in amino acid solutions of L-glutamic (L-glu) and L-aspartic acid (L-asp) at weak acidity of above pH 3. The surface reactions of calcite and aragonite were related with the dissolution. Calcite was dissolved in both solutions but the dissolution was limited by an adsorption of Ca-carboxylate salt. Aragonite was neither dissolved nor reacted in amino acid solutions because the crystal surface consisted of a hard to dissolve structure.
Aragonite-calcite transformation in fossil snail shells of loess sequences in Loess Plateau, Central China
Sheng Xuefen,Chen Jun,Cai Yuanfeng,Chen Yang,Ji Junfeng,
SHENGXuefen
,CHENJun,CAIYuanfeng,CHENYang,JIJunfeng

科学通报(英文版) , 2005,
Abstract: The methods of X-ray diffraction (XRD) and ICP-AES are applied to analyzing the mineral composition of modern and fossil snail shells in Luochuan section and Xifeng section. The results show that the mineral phase of calcium carbonate in modern snail shells is aragonite, but for some fossil snail shells in certain layers of loess sequences, a part of aragonite is transformed into calcite. In Luochuan and Xifeng sections, the stratigraphic borderline of arago- nite-calcite transformation appearing obviously is between L5 and L6. Under the earth surface condition, the arago- nite-calcite transformation is influenced by the factor of temperature only in a long time scale. It seems that the pres- sure is not the factor influencing the aragonite-calcite trans- formation. The results also show that existing age of snail shells is possibly the dominant and principal factor for the aragonite-calcite transformation. To a certain extent, the degree of aragonite-calcite transformation in snail shell is controlled by the content of trace element, such as Mg2+. The trace element can improve the stability of snail shell arago- nite and impede the process of aragonite transforming into calcite.
Calibration of δ18O of cultured benthic foraminiferal calcite as a function of temperature
C. Barras, J.-C. Duplessy, E. Geslin, E. Michel,F. J. Jorissen
Biogeosciences (BG) & Discussions (BGD) , 2010,
Abstract: The geochemical composition of deep-sea benthic foraminiferal calcite is widely used to reconstruct sea floor paleoenvironments. The calibration of the applied proxy methods has until now been based on field observations in complex natural ecosystems where multiple factors are interfering. However, laboratory experiments with stable physico-chemical conditions appear to be the ideal way to evaluate the influence of a single parameter. In this paper, we present the oxygen isotopic composition of deep-sea benthic foraminiferal shells entirely calcified under controlled experimental conditions over a large temperature range (4 to 19 °C). The new laboratory protocols developed for this study allowed us to produce large quantities of shells in stable conditions, so that also the shell size effect could be investigated. It appears that when considering a narrow test size range, the curve describing the temperature dependency of δ18O in Bulimina marginata is parallel to the thermodynamically determined curve observed in inorganically precipitated calcite ( 0.22‰ °C 1). This observation validates the use of δ18O of this benthic species in paleoceanographical studies. Over the studied size range (50 to 300 μm), the effect of test size was 0.0014‰ μm 1, confirming previous suggestions of a substantial test size effect on δ18O of benthic foraminifera. This study opens new perspectives for future proxy calibrations in laboratory set-ups with deep-sea benthic foraminifera (e.g. quantification of the influence of the carbonate chemistry).
Isotopic characteristics of shells Mytilus galloprovincialis from eastern coastal area of Adriatic Sea
Tja?a Kandu?,Davorin Medakovi?,Tadej Dolenec
Geologija , 2006,
Abstract: Samples of Mytilus galloprovincialis were collected from entire Eastern Adriatic coast to determine δ18O and δ13C performed on calcite and aragonite shell layers. The aim of this work was to check whether shells of M. galloprovincialis are good environmental indicators (water temperature, salinity). Based on measured isotopic composition of oxygen in shell layers and assumed isotopic composition in water temperatures of calcite and aragonite of shell layers were calculated. The calculated temperatures for M. galloprovincialis shell growth of calcite and aragonite shell layer are in good agreement with measured temperatures of sea water. According to our results of δ18O and δ13C in shell layers we canseparate the locations of the investigated area into three groups: those with more influence of fresh water, those with less influence of fresh water and those of marine environments.
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