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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.
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: \"\"
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.
Effect of Hydraulic Activity on Crystallization of Precipitated Calcium Carbonate (PCC) for Eco-Friendly Paper  [PDF]
Jung-Ah Kim,Gi-Chun Han,Mihee Lim,Kwang-Suk You,Miyoung Ryu,Ji-Whan Ahn,Toyohisa Fujita,Hwan Kim
International Journal of Molecular Sciences , 2009, DOI: 10.3390/ijms10114954
Abstract: Wt% of aragonite, a CaCO3 polymorph, increased with higher hydraulic activity (°C) of limestone in precipitated calcium carbonate (PCC) from the lime-soda process (Ca(OH)2-NaOH-Na2CO3). Only calcite, the most stable polymorph, was crystallized at hydraulic activity under 10 °C, whereas aragonite also started to crystallize over 10 °C. The crystallization of PCC is more dependent on the hydraulic activity of limestone than CaO content, a factor commonly used to classify limestone ores according to quality. The results could be effectively applied to the determination of polymorphs in synthetic PCC for eco-friendly paper manufacture.
Review: geological and experimental evidence for secular variation in seawater Mg/Ca (calcite-aragonite seas) and its effects on marine biological calcification
J. B. Ries
Biogeosciences (BG) & Discussions (BGD) , 2010,
Abstract: Synchronized transitions in the polymorph mineralogy of the major reef-building and sediment-producing calcareous marine organisms and abiotic CaCO3 precipitates (ooids, marine cements) throughout Phanerozoic time are believed to have been caused by tectonically induced variations in the Mg/Ca ratio of seawater (molar Mg/Ca>2="aragonite seas", <2="calcite seas"). Here, I assess the geological evidence in support of secular variation in seawater Mg/Ca and its effects on marine calcifiers, and review a series of recent experiments that investigate the effects of seawater Mg/Ca (1.0–5.2) on extant representatives of calcifying taxa that have experienced variations in this ionic ratio of seawater throughout the geologic past. Secular variation in seawater Mg/Ca is supported by synchronized secular variations in (1) the ionic composition of fluid inclusions in primary marine halite, (2) the mineralogies of late stage marine evaporites, abiogenic carbonates, and reef- and sediment-forming marine calcifiers, (3) the Mg/Ca ratios of fossil echinoderms, molluscs, rugose corals, and abiogenic carbonates, (4) global rates of tectonism that drive the exchange of Mg2+ and Ca2+ along zones of ocean crust production, and (5) additional proxies of seawater Mg/Ca including Sr/Mg ratios of abiogenic carbonates, Sr/Ca ratios of biogenic carbonates, and Br concentrations in marine halite. Laboratory experiments have revealed that aragonite-secreting bryopsidalean algae and scleractinian corals and calcite-secreting coccolithophores exhibit higher rates of calcification and growth in experimental seawaters formulated with seawater Mg/Ca ratios that favor their skeletal mineral. These results support the assertion that seawater Mg/Ca played an important role in determining which hypercalcifying marine organisms were the major reef-builders and sediment-producers throughout Earth history. The observation that primary production increased along with calcification within the bryopsidalean and coccolithophorid algae in mineralogically favorable seawater is consistent with the hypothesis that calcification promotes photosynthesis within some species of these algae through the liberation of CO2. The experiments also revealed that aragonite-secreting bryopsidalean algae and scleractinian corals, and bacterial biofilms that secrete a mixture of aragonite and high Mg calcite, began secreting an increased proportion of their calcium carbonate as the calcite polymorph in the lower-Mg/Ca experimental seawaters. Furthermore, the Mg/Ca ratio of calcite secreted by the coccolithophores, coralline red algae, reef-dwelling animals (crustacea, urchins, calcareous tube worms), bacterial biofilms, scleractinian corals, and bryopsidalean algae declined with reductions in seawater Mg/Ca. Notably, Mg fractionation in autotrophic organisms was more strongly influenced by changes in seawater Mg/Ca than in heterotrophic organisms, a probable consequence of autotrophic organisms inducing a less
Genetic Mechanism of the Dolomite in Dolomitic Glutenite of the Shahejie Formation—A Case Study of QHD 29-2 Oilfield in Bohai Bay Basin, China  [PDF]
Liya Da, Deying Wang, Haibo Yu, Jianmin Zhu
Open Journal of Geology (OJG) , 2019, DOI: 10.4236/ojg.2019.98030
Abstract: The dolomite in dolomitic glutenite of the shahejie formation in the eastern steep slope of the Shijiutuo bulge in Bohai is a high-quality reservoir, and the content of dolomite is positively correlated with reservoir physical properties.
In this paper, by using thin section, core, wall core, geochemical data and analyzing petrology and mineralogy characteristic, we systematically analyzed the paleogeographic environment and genetic mechanism of this kind of dolomite and established the genetic models. The dolomite in the glutenite body has many characteristics of development, which is formed by three kinds of genesis: quasi-synergy dolomitization, buried dolomitization and hydrothermal dolomitization. The dolomite in glutenite is produced in the form of matrix, grain (sandstone, oolith), biological skeleton (conch, ostracod), clastic shell and dolomite cement. The minor elements, carbon and oxygen isotopes, trace minerals and paleontological combinations reveal that the paleogeographic environment was closed continental salt-brackish water bay, the climate was arid and hot, and the evaporation was strong. It provides favorable conditions for the production of the dolomite in dolomitic glutenite. There are three genetic models of dolomite. The first model is penecontemporaneous dolomitization. The climate was arid and hot, the aragonite and high-magnesium calcite deposited with sand and gravel. Due to the effect of evaporation, dolomitization occurred. The second model is buried dolomitization. The water from dehydration of clay minerals causes the Mg2+ in the high-magnesium formation migrating into the rock, leading to the occurrence of dolomitization. The third model is hydrothermal dolomitization. Deep faults can bring geothermal fluids into the overlying reservoir and form the hydrothermal dolomite.
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