50 results on '"Tucker, Maurice"'
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2. Impacts of WWII bomb explosions on weathering damage of architectural heritage: Bath, England
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Wang, Xiaoyu, Mol, Lisa, Tucker, Maurice, Blenkinsop, Tom, Gilbert, Oscar, and Campbell, Oliver
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- 2024
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3. Interaction of microorganisms with carbonates from the micro to the macro scales during sedimentation: Insights into the early stage of biodegradation
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Gao, Xiao, Han, Zuozhen, Zhao, Yanyang, Zhou, Gang, Lyu, Xiaowei, Qi, Zhenhua, Liu, Fang, Tucker, Maurice E., Steiner, Michael, and Han, Chao
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- 2024
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4. Viruses participate in the organomineralization of travertines
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Słowakiewicz, Mirosław, Perri, Edoardo, Tagliasacchi, Ezher, Działak, Paweł, Borkowski, Andrzej, Gradziński, Michał, Kele, Sándor, and Tucker, Maurice E.
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- 2023
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5. Calcium ion biorecovery from industrial wastewater by Bacillus amyloliquefaciens DMS6
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Li, Dan, Zhao, Hui, Li, Guijiang, Yan, Huaxiao, Han, Zuozhen, Chi, Xiangqun, Meng, Long, Wang, Jihan, Xu, Yudong, and Tucker, Maurice E.
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- 2022
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6. Biofilms in modern CaCO3-supersaturated freshwater environments reveal viral proxies.
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Słowakiewicz, Mirosław, Borkowski, Andrzej, Perri, Edoardo, Działak, Paweł, Tagliasacchi, Ezher, Gradziński, Michał, Kele, Sándor, Reuning, Lars, Kibblewhite, Tom, Whitaker, Fiona, Reid, R. Pamela, and Tucker, Maurice E.
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MICROBIAL mats ,PRINCIPAL components analysis ,FOSSIL DNA ,CLUSTER analysis (Statistics) ,NUTRIENT cycles - Abstract
Biofilms are mucilaginous-organic layers produced by microbial activity including viruses. Growing biofilms form microbial mats which enhance sediment stability by binding particles with extracellular polymeric substances and promoting growth through nutrient cycling and organic matter accumulation. They preferentially develop at the sediment-water interface of both marine and non-marine environments, and upon the growing surfaces of modern tufa and travertine. In this context, however, little is known about the factors, environmental or anthropogenic, which affect viral communities in freshwater spring settings. To explore this issue, geochemical and metagenomic data were subjected to multidimensional analyses (Principal Component Analysis, Classical Multidimensional Scaling, Partial Least Squares analysis and cluster analysis based on beta-diversity), and these show that viral composition is specific and dependent on environment. Indeed, waters precipitating tufa and travertine do vary in their geochemistry with their viruses showing distinct variability between sites. These differences between virus groups allow the formulation of a viral proxy, based on the Caudoviricetes/Megaviricetes ratio established on the most abundant groups of viruses. This ratio may be potentially used in analysing ancient DNA preserved in carbonate formations as an additional source of information on the microbiological community during sedimentation. [ABSTRACT FROM AUTHOR]
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- 2024
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7. Recovery of phosphate, magnesium and ammonium from eutrophic water by struvite biomineralization through free and immobilized Bacillus cereus MRR2
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Han, Zuozhen, Guo, Na, Yan, Huaxiao, Xu, Yudong, Wang, Jihan, Zhao, Yanyang, Zhao, Yanhong, Meng, Long, Chi, Xiangqun, Zhao, Hui, and Tucker, Maurice E.
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- 2021
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8. The bio-precipitation of calcium and magnesium ions by free and immobilized Lysinibacillus fusiformis DB1-3 in the wastewater
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Yan, Huaxiao, Han, Zuozhen, Zhao, Hui, Pan, Juntong, Zhao, Yanhong, Tucker, Maurice E., Zhou, Jingxuan, Yan, Xiaoyun, Yang, Haiyan, and Fan, Di
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- 2020
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9. Lacustrine-evaporitic microbial dolomite from a Plio-Pleistocene succession recovered by the SG-1 borehole in the Qaidam Basin, NE Tibetan Plateau
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Zhao, Yanyang, Wei, Xiangyu, Han, Zuozhen, Han, Chao, Gao, Xiao, Meng, Ruirui, Wang, Qiyu, Tucker, Maurice E., Li, Minghui, Sánchez-Román, Mónica, Zhao, Yanyang, Wei, Xiangyu, Han, Zuozhen, Han, Chao, Gao, Xiao, Meng, Ruirui, Wang, Qiyu, Tucker, Maurice E., Li, Minghui, and Sánchez-Román, Mónica
- Abstract
The Plio-Pleistocene evaporitic lacustrine succession in the Qaidam Basin, which was recovered by drill core SG-1, provides the material for understanding the maturation of dolomite since dolomite is present in the core from 7.6 to 870 m depth, spanning a time interval of 0.1–2.8 Ma. Twenty-two samples were collected at different burial depths. The samples were examined by thin-section petrography and SEM for textures, and analyzed for mineralogy (XRD), trace elements and carbon and oxygen isotopes. The main mineral compositions of each sample are dolomite, quartz, halite and gypsum. Dolomite is mostly scattered with spheroidal to ellipsoidal shapes, several microns in diameter, partially encapsulated in gypsum. Microbial micropores and calcified microorganisms are observed on and within the dolomite crystals and in the thin sections. The degree of ordering of the dolomite gradually increases with burial depth, which basically conforms to the first-order reaction function. The crystal constants of dolomite decrease with burial depth, indicating recrystallisation with increasing overburden. The trace elements of the dolomites are significantly different from those of hydrothermal dolomites, but close to lacustrine microbial carbonate. It is concluded that the dolomites in core SG-1 are mainly authigenic, with microbial processes a likely facilitator of dolomite precipitation. The dolomite formed and then evolved in crystal structure during burial, gradually approaching ordered stochiometric dolomite. This study gives clues to link microbial dolomite to the massive ideal dolomite rock encountered in the geological record.
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- 2023
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10. Bio-Precipitation of Calcium Ions Induced by Free and Immobilized Virgibacillus dokdonensis WLR1 in Hypersaline Wastewater
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Yan, Huaxiao, Wei, Lirong, Han, Zuozhen, Tucker, Maurice E., Zhao, Yanhong, Meng, Long, Zhao, Lanmei, Wang, Jihan, Xu, Yudong, Geng, Heding, Zhang, Xiyu, Qiu, Ziyang, Li, Guijiang, and Zhao, Hui
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Earth and Planetary Sciences (miscellaneous) ,Environmental Chemistry ,Microbiology ,General Environmental Science - Abstract
Hypersaline wastewater has been widely used in industrial processes in some countries short of freshwater, but calcium ions in such wastewater should be removed due to the danger of limescale being produced. In this study, calcium ions in hypersaline (sodium chloride: 5%) wastewater was biomineralized into different carbonate minerals under the action of free and immobilized Virgibacillus dokdonensis WLR1 bacteria. The results show that the calcium ion precipitation rate was much higher under the conditions of immobilized bacteria (p < 0.01), and that there was a significant difference in the mineral phases, the diversity of protein secondary structures and morphologies, and chemical characteristics of the mineral surfaces between the free and the immobilized bacteria based on XRD, FTIR, SEM-EDS, and XPS analyses. TG, DTG, and DSC results show that with increasing calcium ion concentrations, the thermal stability of calcium carbonate under the conditions of free bacteria decreased due to the decline in crystallinity. The stable carbon isotope values (δ13CPDB) of calcium carbonate formed by free bacteria changed from −16.80‰ to −18.17‰; the much more negative δ13CPDB values suggest that the calcium carbonate minerals are biotic. From ultrathin slices analyzed by HRTEM-mapping-SAED, it was observed that calcite is formed inside the cell, thus also facilitating calcium ion removal. Research concerning intracellular calcite has rarely been reported. This study helps to further understand the mechanisms of biomineralization, and also provides an environmentally friendly method to remove calcium ions from hypersaline wastewater.
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- 2022
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11. Effect of Magnesium and Ferric Ions on the Biomineralization of Calcium Carbonate Induced by Synechocystis sp. PCC 6803.
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Zhao, Hui, Han, Yongkui, Liang, Mengyi, Han, Zuozhen, Woo, Jusun, Meng, Long, Chi, Xiangqun, Tucker, Maurice E., Han, Chao, Zhao, Yanyang, Zhao, Yueming, and Yan, Huaxiao
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MAGNESIUM ions ,CALCITE ,IRON ions ,CALCIUM ions ,CALCIUM carbonate ,MAGNESIUM isotopes ,CALCIUM channels ,FOURIER transform infrared spectroscopy ,X-ray photoelectron spectroscopy - Abstract
The discovery of cyanobacteria fossils in microbialite prompts the investigation of carbonate biomineralization using cyanobacteria. However, the impact of coexisting magnesium and iron in microbialite on carbonate biomineralization has been overlooked. Here, Synechocystis sp. PCC 6803 was used to induce calcium carbonate in the presence of coexisting magnesium and ferric ions. The findings demonstrate that cell concentration, pH, carbonic anhydrase activity, and carbonate and bicarbonate concentrations decreased with increasing concentrations of magnesium and calcium ions. Ferric ions yielded a contrasting effect. The levels of deoxyribonucleic acid, protein, polysaccharides, and humic substances in extracellular polymeric substances increased in the presence of separated or coexisting calcium, magnesium, and ferric ions. Magnesium ions inhibited calcium ion precipitation, whereas ferric ions exhibited the opposite effect. Protein secondary structures became more abundant and O-C=O and N-C=O contents increased with increasing ion concentrations by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses. Scanning electron microscopy revealed that ferric ions lead to rougher surfaces and incomplete rhombohedral structures of calcite, whereas magnesium ions promoted greater diversity in morphology. Magnesium ions enhanced the incorporation of ferric ions. This work aims to further understand the effect of magnesium and ferric ions on calcium carbonate biomineralization induced by cyanobacteria. [ABSTRACT FROM AUTHOR]
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- 2023
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12. The incorporation of Mg2+ ions into aragonite during biomineralization: Implications for the dolomitization of aragonite
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Han, Zuozhen, primary, Meng, Ruirui, additional, Zhao, Hui, additional, Gao, Xiao, additional, Zhao, Yanyang, additional, Han, Yu, additional, Liu, Fang, additional, Tucker, Maurice E., additional, Deng, Jiarong, additional, and Yan, Huaxiao, additional
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- 2023
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13. Mineralogy of Bioprecipitate Evolution over Induction Times Mediated by Halophilic Bacteria under Various Mg/Ca Molar Ratios
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Han, Zuozhen, primary, Li, Dan, additional, Zhao, Yanyang, additional, Wang, Jiajia, additional, Guo, Na, additional, Yan, Huaxiao, additional, Han, Chao, additional, Li, Qiang, additional, and Tucker, Maurice E., additional
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- 2022
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14. Milankovitch-driven cycles in the Precambrian of China: The Wumishan Formation
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Mingxiang, Mei and Tucker, Maurice E.
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- 2013
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15. Facies-succession and architecture of the third-order sequences and their stratigraphic framework of the Devonian in Yunnan-Guizhou-Guangxi area, South China
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Mingxiang, Mei, Tucker, Maurice E., Yuan, Wang, and Min, Liu
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- 2013
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16. High Mg/Ca Molar Ratios Promote Protodolomite Precipitation Induced by the Extreme Halophilic Bacterium Vibrio harveyi QPL2
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Han, Zuozhen, Qi, Peilin, Zhao, Yanyang, Guo, Na, Yan, Huaxiao, Tucker, Maurice E., Li, Dan, Wang, Jiajia, and Zhao, Hui
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Microbiology (medical) ,Microbiology - Abstract
Bacterial activities have been demonstrated as critical for protodolomite precipitation in specific aqueous conditions, whereas the relationship between the various hydrochemical factors and bacterial activity has not been fully explored. In this study, biomineralization experiments were conducted using a newly isolated extreme halophilic bacterium from salina mud, Vibrio harveyi QPL2, under various Mg/Ca molar ratios (0, 3, 6, 10, and 12) and a salinity of 200‰. The mineral phases, elemental composition, morphology, and crystal lattice structure of the precipitates were analyzed by XRD, SEM, and HRTEM, respectively. The organic weight and functional groups in the biominerals were identified by TG-DSC, FTIR, and XPS analysis. The amounts of amino acids and polysaccharides in the EPS of QPL2 cultured at various Mg/Ca molar ratios were quantified by an amino acid analyzer and high-performance liquid chromatography. The results confirm that disordered stoichiometric protodolomite was successfully precipitated through the activities of bacteria in a medium with relatively high Mg/Ca molar ratios (10 and 12) but it was not identified in cultures with lower Mg/Ca molar ratios (0, 3, and 6). That bacterial activity is critical for protodolomite formation as shown by the significant bacterial relicts identified in the precipitated spherulite crystals, including pinhole structures, a mineral coating around cells, and high organic matter content within the crystals. It was also confirmed that the high Mg/Ca molar ratio affects the composition of the organic components in the bacterial EPS, leading to the precipitation of the protodolomite. Specifically, not only the total EPS amount, but also other facilitators including the acidic amino acids (Glu and Asp) and polysaccharides in the EPS, increased significantly under the high Mg/Ca molar ratios. Combined with previous studies, the present findings suggest a clear link between high Mg/Ca molar ratios and the formation of protodolomite through halophilic bacterial activity.
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- 2022
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17. Effects of Chloride, Sulfate and Magnesium Ions on the Biomineralization of Calcium Carbonate Induced by Lysinibacillus xylanilyticus DB1-12
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Yan, Huaxiao, Huang, Meiyu, Wang, Tiantian, Xu, Yudong, Meng, Long, Zhao, Lanmei, Han, Zuozhen, Wang, Jihan, Tucker, Maurice E., and Zhao, Hui
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Earth and Planetary Sciences (miscellaneous) ,Environmental Chemistry ,Microbiology ,General Environmental Science - Abstract
Microbially-induced calcium carbonate precipitation (MICP) has been studied extensively. However, the effect of different sources of magnesium ions on calcium carbonate biomineralization has rarely been examined. In this study, Lysinibacillus xylanilyticus DB1-12 bacteria isolated from petroleum samples were used to biomineralize calcium ions under the action of different sources of magnesium (magnesium chloride and magnesium sulfate). The results show that calcium ion precipitation ratios were much higher in MgSO4 group experiments than in the MgCl2 group (p < 0.01). The mineral phases in the MgCl2 group experiments were the same as those in MgSO4 group at each Mg/Ca ratio. Minerals with a ‘twisted’ shape were much more common in the MgSO4 group; the protein secondary structures hidden in minerals were much more abundant in the MgCl2 group, and the activation energy of biotic monohydrocalcite at a Mg/Ca ratio of 11 was also much higher in the MgCl2 group than in the MgSO4 group. The main reasons for these differences are closely related to the lower magnesium content and the more common protein secondary structures in the monohydrocalcite in the MgCl2 group. The shift of Mg1s XPS spectra suggests that the chemical interactions occurring on the monohydrocalcite surfaces in the MgCl2 group were different from those in the MgSO4 group. The δ13CPDB values of the biominerals in the MgSO4 group are in the range of −16.93 to −18.87‰, lower than those in the MgCl2 group (-15.77 to −18.69‰). The morphology of L. xylanilyticus DB1-12 became deformed and some rod-shaped protrusions developed on the cell surface during the process of biomineralization. This study not only contributes to the understanding of biomineralization mechanisms generally, but is also helpful in the interpretations of paleo-environmental conditions.
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- 2022
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18. Selective Adsorption of Amino Acids in Crystals of Monohydrocalcite Induced by the Facultative Anaerobic Enterobacter ludwigii SYB1
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Zhao, Yanyang, primary, Han, Zuozhen, additional, Yan, Huaxiao, additional, Zhao, Hui, additional, Tucker, Maurice E., additional, Gao, Xiao, additional, Guo, Na, additional, Meng, Ruirui, additional, and Owusu, Daniel Cosmos, additional
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- 2021
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19. Bacterial fossils and microbial dolomite in Triassic stromatolites
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Perri, Edoardo and Tucker, Maurice
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Stromatolites -- Research ,Dolomite -- Research ,Earth sciences - Abstract
Triassic stromatolitic dolomite from Italy preserves mineralized bacterial remains, one of the first unequivocal identifications of such structures in the geological record. They consist of empty spheroids ~1.0 pm diameter resembling coccoid bacteria, and smaller, 150-400 nm, objects interpreted as dwarf bacterial forms, occurring within and between syn-sedimentary dolomite crystals. Moreover, gently folded sheets, 100-200 nm thick and several micrometers long, form a sub-polygonal network reminiscent of EPS (extracellular polymeric substance). Their granular-textured surfaces suggest bacterial degradation of original organic matter. These features confirm a biological origin for the stromatolites, as in modern microbial mats, and the preserved original geochemical signatures indicate early precipitation of Mg-carbonates induced through microbial sulfate-reducing metabolic activities. Keywords: bacterial fossils, microbialite, dolomite, stromatolite, Triassic.
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- 2007
20. Carbonate crusts around volcanic islands: composition, origin and their significance in slope stability
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Tucker, Maurice E., Carey, Steven N., Sparks, R. Stephen J., Stinton, Adam, Leng, Melanie, Robinson, Laura, Li, Tao, Lewis, Jamie, Cotton, Laura, Tucker, Maurice E., Carey, Steven N., Sparks, R. Stephen J., Stinton, Adam, Leng, Melanie, Robinson, Laura, Li, Tao, Lewis, Jamie, and Cotton, Laura
- Abstract
Extensive carbonate crusts discovered forming on the slopes of seamounts in many parts of the world's oceans are providing extra stability to the volcanic edifices. These crusts are hardgrounds composed of mixtures of volcaniclastic debris and bioclastic material, in most cases cemented by calcite, in the form of isopachous coatings around grains and pore-filling spar. Such crusts, which have been collected by a remotely-operated vehicle (ROV), are described here from moderate-depth to deeper-water slopes (180–820 m) around the volcanic island of Montserrat in the Caribbean, and from the nearby Kick'em Jenny submarine volcano off Grenada. Radiogenic 87Sr/86Sr isotope ratios from the carbonates give an indication of age (up to 0.4 Ma years old) but they also demonstrate that some samples have been altered by hydrothermal-volcanic processes, to give ages much older than expected (14 to 18 Ma) based on the foraminifera present. Such alteration is also supported by carbon and oxygen isotope (δ13C and δ18O) ratios, although most samples retain typical marine values. In many cases δ18O is usually a little more positive than expected from modern Caribbean shallow-water carbonates, likely reflecting cooler water at their moderate depths of lithification. Just one sample, from Kick'em Jenny, has very negative δ13C (−42‰) indicating methanogenesis. Crusts are also reported here from the Mediterranean Sea, with an example described from Kolumbo submarine volcano, northeast of the Santorini volcanic complex in the Hellenic subduction zone, that are similar in many respects to those from the Caribbean. Typically, the biota of the crusts consists of calcareous red algae (commonly encrusting volcanic clasts), foraminifera (benthic, some also encrusting, and planktic), subordinate serpulids, bivalves, pteropods and heteropods, and rare deeper-water corals. Some bioclasts are derived from shallower water, others from the moderate depths of the slope itself, and planktic fallout. In
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- 2020
21. The Upper Devonian Saltern Cove Goniatite Bed is an intraformational slump
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Van Straaten, Peter, Tucker, Maurice E, and BioStor
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- 1972
22. Biomineralization of Carbonate Minerals Induced by The Moderate Halophile Staphylococcus Warneri YXY2
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Han, Yu, primary, Sun, Bin, additional, Yan, Huaxiao, additional, Tucker, Maurice, additional, Zhao, Yanhong, additional, Zhou, Jingxuan, additional, Zhao, Yifan, additional, and Zhao, Hui, additional
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- 2020
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23. Bio-Precipitation of Carbonate and Phosphate Minerals Induced by the Bacterium Citrobacter freundii ZW123 in an Anaerobic Environment
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Sun, Bin, primary, Zhao, Hui, additional, Zhao, Yanhong, additional, Tucker, Maurice, additional, Han, Zuozhen, additional, and Yan, Huaxiao, additional
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- 2020
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24. Aspects of pelagic sedimentation in the Devonian of Western Europe
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Tucker, Maurice E.
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551 - Published
- 1971
25. The Significant Role of Different Magnesium: Carbonate Minerals Induced by Moderate Halophile Staphylococcus epidermis Y2
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Han, Zuozhen, Yu, Wenwen, Zhao, Yanhong, Tucker, Maurice E., and Yan, Huaxiao
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geology - Abstract
Carbonate precipitation induced by microorganism has become a hot spot in the field of carbonate sedimentology, while the effect of different magnesium on biominerals has rarely been studied. Therefore, magnesium sulfate and magnesium chloride were used to investigate the significant role played on carbonate minerals. In this study, Staphylococcus epidermidis Y2 was isolated and identified by 16S rDNA homology comparison. The ammonia, pH, carbonic anhydrase, carbonate and bicarbonate ions were investigated. The mineral phase, morphology and elemental composition were analyzed by XRD and SEM-EDS. The ultrathin slices of bacteria were analyzed by HRTEM-SAED and STEM. The result showed that this bacterium could release ammonia and carbonic anhydrase to increase pH, and elevate the supersaturation via a large number of carbonate and bicarbonate ions released through carbon dioxide hydration catalyzed by carbonic anhydrase. The crystal cell density of monohydrocalcite was lower in magnesium chloride medium than that in magnesium sulfate medium. The crystal grew in a mode of spiral staircas in magnesium sulfate medium, while in a concentric circular pattern in magnesium chloride medium. There was no obvious intracellular biomineralization. This study may be helpful to further understand the biomineralization mechanism, may also provide some references for the reconstruction of paleogeological environment.
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- 2018
26. The Extracellular and Intracellular Biomineralization Induced by Bacillus licheniformis DB1-9 at Different Mg/Ca Molar Ratios
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Han, Zuozhen, Gao, Xiao, Zhao, Hui, Tucker, Maurice E., Zhao, Yanhong, and Yan, Huaxiao
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environmental_sciences - Abstract
Biomineralization has become a research hotspot and attracted widespread attention in the field of carbonate sedimentology. In this study, Bacillus licheniformis DB1-9 was used to induce the calcium carbonate precipitation at different magnesium calcium molar ratios in the laboratory to further explore the biomineralization mechanism. Phylogenetic tree shows that the bacteria belongs to Bacillus licheniformis species. The ammonia and carbonic anhydrase can be released by this bacteria, resulting in the pH increase, and the carbonic anhydrase can also promote the hydration reaction of carbon dioxide and subsequently produce the bicarbonate and carbonate ions to elevate the supersaturation of calcium carbonate in the liquid culture medium to facilitate the precipitation of carbonate minerals. The calcites have a shape of rhombohedron, dumbell, and elongation, and aragonite often appears in the form of mineral aggregates, besides that there are also the spherical and the fusiform minerals. FTIR result shows there are some organic functional groups, such as C-O-C and C=O, beside of the characteristic peaks of the calcite and the aragonite, indicating that microbial metabolism is closely related to the mineral formation. The superthin slices of the bacteria analyzed by HRTEM, SAED, EDS and STEM show that the surface and EPS can adsorb a large number of calcium ions and magnesium ions and EPS may act as the nucleation sites, what’s more, the intracellular nanometer-scale sphere areas show the amorphous structures, and the intracellular calcium ions and magnesium ions suggeste that they can be transported from the outside to inside the cell by diffusion along the concentration grade from high to low. This study may provide some references to further understand the biomineralization mechanism induced by microorganisms in the laboratory and the field, and also helps to explore the reason of the transition of calcite sea to aragonite sea in the geological history.
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- 2018
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27. Bio-Precipitation of Calcium and Magnesium Ions through Extracellular and Intracellular Process Induced by Bacillus Licheniformis SRB2
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Zhao, Yanyang, primary, Yan, Huaxiao, additional, Zhou, Jingxuan, additional, Tucker, Maurice E., additional, Han, Mei, additional, Zhao, Hui, additional, Mao, Guangzhou, additional, Zhao, Yifan, additional, and Han, Zuozhen, additional
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- 2019
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28. Tonian-Cryogenian boundary sections of Argyll, Scotland
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Fairchild, Ian J., Spencer, Anthony M., Ali, Dilshad O., Anderson, Ross P., Anderton, Roger, Boomer, Ian, Dove, Dayton, Evans, Jonathan D., Hambrey, Michael J., Howe, John, Sawaki, Yusuke, Shields, Graham A., Skelton, Alasdair, Tucker, Maurice E., Wang, Zhengrong, Zhou, Ying, Fairchild, Ian J., Spencer, Anthony M., Ali, Dilshad O., Anderson, Ross P., Anderton, Roger, Boomer, Ian, Dove, Dayton, Evans, Jonathan D., Hambrey, Michael J., Howe, John, Sawaki, Yusuke, Shields, Graham A., Skelton, Alasdair, Tucker, Maurice E., Wang, Zhengrong, and Zhou, Ying
- Abstract
The Tonian-Cryogenian System boundary is to be defined at a GSSP (Global Boundary Stratigraphic Section and Point) beneath the first evidence of widespread glaciation. A candidate lies within the Dalradian Supergroup of Scotland and Ireland, which is least deformed and metamorphosed in Argyll, western Scotland. We present new stratigraphic profiles and interpretations from the Isle of Islay and the Garvellach Islands, update the chemostratigraphy of the Appin Group Tonian carbonates underlying the thick (ca. 1 km) glacigenic Port Askaig Formation (PAF) and demonstrate an environmental transition at the contact. The Appin Group forms a regionally extensive, >4 km-thick, succession of limestones, shales and sandstones deposited on a marine shelf. On Islay, the upper part of the lithostratigraphy has been clarified by measuring and correlating two sections containing distinctive stratigraphic levels including molar tooth structure, oolite, stromatolitic dolomite and intraclastic microbial mounds. Significantly deeper erosion at the unconformity at the base of the overlying PAF is demonstrated in the southern section. Carbonate facies show a gradual decline in δ13CVPDB from +5 to +2‰ upwards. In NE Garbh Eileach (Garvellach Islands), a continuously exposed section of Appin Group carbonates, 70 m thick, here designated the Garbh Eileach Formation (GEF), lies conformably beneath the PAF. The GEF and the GEF-PAF boundary relationships are re-described with new sedimentological logs, petrological and stable isotope data. Interstratified limestone and dolomicrosparite with δ13C of −4 to −7‰ (a feature named the Garvellach anomaly, replacing the term Islay anomaly) are overlain by dolomite in which the isotope signature becomes weakly positive (up to +1‰) upwards. Shallow subtidal conditions become peritidal upwards, with evidence of wave and storm activity. Gypsum pseudomorphs and subaerial exposure surfaces are common near the top of the GEF. The basal diamictite (D1) of th
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- 2018
29. Bio-Precipitation of Carbonate and Phosphate Minerals Induced by the Bacterium Citrobacter freundii ZW123 in an Anaerobic Environment.
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Bin Sun, Hui Zhao, Yanhong Zhao, Tucker, Maurice E., Zuozhen Han, and Huaxiao Yan
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PHOSPHATE minerals ,CALCITE ,CITROBACTER freundii ,CARBONATE minerals ,SCANNING transmission electron microscopy ,VATERITE ,X-ray photoelectron spectroscopy - Abstract
In this study, a facultative anaerobic strain isolated from marine sediments and identified as Citrobacter freundii, was used to induce the precipitation of carbonate and phosphate minerals in the laboratory under anaerobic conditions. This is the first time that the ability of C. freundii ZW123 to precipitate carbonate and phosphate minerals has been demonstrated. During the experiments, carbonic anhydrase, alkaline phosphatase and ammonium released by the bacteria not only promoted an increase in pH, but also drove the supersaturation and precipitation of carbonate and phosphate minerals. The predominant bio-mediated minerals precipitated at various Mg/Ca molar ratios were calcite, vaterite, Mg-rich calcite, monohydrocalcite and struvite. A preferred orientation towards struvite was observed. Scanning transmission electron microscopy (STEM) and elemental mapping showed the distribution of magnesium and calcium elements within Mg-rich calcite. Many organic functional groups, including C=O, C-O-C and C-O, were detected within the biominerals, and these functional groups were also identified in the associated extracellular polymeric substances (EPS). Fifteen kinds of amino acid were detected in the biotic minerals, almost identical to those of the EPS, indicating a close relationship between EPS and biominerals. Most amino acids are negatively charged and able to adsorb cations, providing an oversaturated microenvironment to facilitate mineral nucleation. The X-ray photoelectron spectroscopy (XPS) spectrum of struvite shows the presence of organic functional groups on the mineral surface, suggesting a role of the microorganism in struvite precipitation. The ZW123 bacteria provided carbon and nitrogen for the formation of the biotic minerals through their metabolism, which further emphasizes the close relationship between biominerals and the microorganisms. Thermal studies showed the enhanced thermal stability of biotic minerals, perhaps due to the participation of the bacteria ZW123. The presence of amino acids such as Asp and Glu may explain the high magnesium content of some calcites. Molecular dynamics simulations demonstrated that the morphological change and preferred orientation were likely caused by selective adsorption of EPS onto the various struvite crystal surfaces. Thus, this study shows the significant role played by C. freundii ZW123 in the bioprecipitation of carbonate and phosphate minerals and provides some insights into the processes involved. [ABSTRACT FROM AUTHOR]
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- 2020
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30. The Significant Roles of Mg/Ca Ratio, Cl− and SO42− in Carbonate Mineral Precipitation by the Halophile Staphylococcus epidermis Y2
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Han, Zuozhen, primary, Yu, Wenwen, additional, Zhao, Hui, additional, Zhao, Yanhong, additional, Tucker, Maurice, additional, and Yan, Huaxiao, additional
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- 2018
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31. Extracellular and Intracellular Biomineralization Induced by Bacillus licheniformis DB1-9 at Different Mg/Ca Molar Ratios
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Han, Zuozhen, primary, Gao, Xiao, additional, Zhao, Hui, additional, Tucker, Maurice, additional, Zhao, Yanhong, additional, Bi, Zhenpeng, additional, Pan, Juntong, additional, Wu, Guangzhen, additional, and Yan, Huaxiao, additional
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- 2018
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32. Shale-gas potential of the Mid-Carboniferous Bowland-Hodder Unit in the Cleveland Basin (Yorkshire), Central Britain
- Author
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Słowakiewicz, M., Tucker, Maurice E., Vane, C.H., Harding, R., Collins, A., Pancost, R.D., Słowakiewicz, M., Tucker, Maurice E., Vane, C.H., Harding, R., Collins, A., and Pancost, R.D.
- Abstract
The shale-gas potential of mid-Carboniferous mudrocks in the Bowland-Hodder unit in the Cleveland Basin (Yorkshire, northern England) was investigated through the analysis of a cored section from the uppermost part of the unit in the Malton-4 well using a multidisciplinary approach. Black shales are interbedded with bioturbated and bedded sandstones, representing basinal-offshore to prodelta – delta-front lithofacies. The total organic carbon (TOC) content of the shales ranges from 0.37 to 2.45 wt %. Rock-Eval pyrolysis data indicate that the organic matter is mainly composed of Type III kerogen with an admixture of Type II kerogen. Tmax (436–454°C), 20S/(20S+20R) C29 sterane ratios, and vitrinite reflectance values indicate that organic matter is in the mid- to late- mature (oil) stage with respect to hydrocarbon generation. Sedimentological and geochemical redox proxies suggest that the black shales were deposited in periodically oxic-dysoxic and anoxic bottom waters with episodic oxic conditions, explaining the relatively low TOC values. The Rock-Eval parameters indicate that the analysed mudrocks have a limited shale-gas potential. However, burial and thermal history modelling, and VRr data from other wells in the region, indicate that where they are more deeply-buried, the Bowland-Hodder shales will be within the gas window with VRr > 1.1 % at depths in excess of 2000 m. Therefore although no direct evidence for a high shale-gas potential in the Cleveland Basin has been found, this cannot be precluded at greater depths especially if deeper horizons are more organic rich.
- Published
- 2014
33. Sequence stratigraphy: methodology and nomenclature
- Author
-
Catuneanu, Octavian, Galloway, William E., Kendall, Christopher G. St. C., Miall, Andrew D., Posamentier, Henry W., Strasser, André, Tucker, Maurice E., Catuneanu, Octavian, Galloway, William E., Kendall, Christopher G. St. C., Miall, Andrew D., Posamentier, Henry W., Strasser, André, and Tucker, Maurice E.
- Abstract
The recurrence of the same types of sequence stratigraphic surface through geologic time defines cycles of change in accommodation or sediment supply, which correspond to sequences in the rock record. These cycles may be symmetrical or asymmetrical, and may or may not include all types of systems tracts that may be expected within a fully developed sequence. Depending on the scale of observation, sequences and their bounding surfaces may be ascribed to different hierarchical orders.Stratal stacking patterns combine to define trends in geometric character that include upstepping, forestepping, backstepping and downstepping, expressing three types of shoreline shift: forced regression (forestepping and downstepping at the shoreline), normal regression (forestepping and upstepping at the shoreline) and transgression (backstepping at the shoreline). Stacking patterns that are independent of shoreline trajectories may also be defined on the basis of changes in depositional style that can be correlated regionally. All stratal stacking patterns reflect the interplay of the same two fundamental variables, namely accommodation (the space available for potential sediment accumulation) and sediment supply. Deposits defined by specific stratal stacking patterns form the basic constituents of any sequence stratigraphic unit, from sequence to systems tract and parasequence. Changes in stratal stacking patterns define the position and timing of key sequence stratigraphic surfaces.Precisely which surfaces are selected as sequence boundaries varies as a function of which surfaces are best expressed within the context of the depositional setting and the preservation of facies relationships and stratal stacking patterns in that succession. The high degree of variability in the expression of sequence stratigraphic units and bounding surfaces in the rock record means ideally that the methodology used to analyze their depositional setting should be flexible from one sequence stratigraphi
- Published
- 2011
34. Are beds in shelf carbonates millennial-scale cycles? : an example from the mid-Carboniferous of northern England
- Author
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Tucker, Maurice E., Gallagher, James, Leng, Melanie, Tucker, Maurice E., Gallagher, James, and Leng, Melanie
- Abstract
The mid-Carboniferous strata of northern England are characterised by mixed clastic-carbonate cycles (Yoredale cycles), attributed here to the short eccentricity Milankovitch rhythm. In a typical cycle, transgressive normal-marine shelf carbonates are succeeded by marine shales, then highstand prodelta mudstones and delta front-delta top sandstones with local coals. A detailed study of one cycle, the Great Limestone Cyclothem of the northern Pennines (Alston Block), reveals that within the transgressive carbonates, the beds, averaging 75 cm in thickness and defined by mm-shale partings or cm-mudrock layers, form two thinning-upward to thickening-upward bed-sets. Individual beds and the bed-sets are regionally correlatable. Oxygen isotope and strontium trace element data also reveal patterns of increasing and decreasing values through the limestone, which broadly correspond to the bed-thickness cycles. The beds are interpreted as millennial-scale cycles, the result of high-frequency, arid-humid climatic fluctuations. The bed-sets are interpreted as the response to a longer term arid-humid climate and sea-level cycle, driven by the precession rhythm. It is postulated that millennial-scale climatic changes, which are a well-known feature of the Quaternary, and are here inferred for the Carboniferous, were responsible for the deposition of the beds that are a characteristic feature of many marine sedimentary successions in the geological record. The most likely over-riding control is fluctuations in solar output.
- Published
- 2009
35. Diagenesis and Geochemistry of Upper Muschelkalk (Triassic) buildups and associated facies in Catalonia (NE Spain): a paper dedicated to Francesc Calvet
- Author
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Tucker, Maurice, Marshall, Jim, Tucker, Maurice, and Marshall, Jim
- Abstract
Carbonate buildups are well developed in the Triassic Upper Muschelkalk of eastern Spain in the La Riba Unit, but they are completely dolomitised. These mud-mounds with reefal caps have well-developed fibrous and botryoidal marine cements which were probably high-Mg calcite and aragonite originally. The dolomite is fabric retentive indicating an early origin, but the d18O values are quite negative (average -3.¿), interpreted as indicating recrystallisation during shallow burial, but without fabric destruction. Low Sr and Na contents support this. The d13C signature is quite uniform (~ +1¿) and this is probably the inherited, original marine CaCO3 value. The Alcover Unit, deposited between and above the La Riba buildups after a sea-level fall terminated mound growth, is an organic-rich laminated dolomicrite with exquisitely-preserved fossils. The d18O signature (average ¿3.4¿) is similar to the La Riba dolomites, also interpreted as suggesting recrystallisation. The d13C values, however, show a stratigraphic trend of increasingly negative (to ¿5.5¿) and then more positive to marine values (~0¿), over a thickness of 10 metres. This is interpreted as a reflection of increasing stratification and developing anoxia, which would have led to the preservation of the special fossils, and then a return to conditions of more open-marine circulation. The dolomicrites of the Alcover unit may well have been formed on or close to the sea-floor. Recrystallisation of the dolomites took place during shallow to moderate burial, with the resetting of the d18O signatures and loss of Sr. The dolomitisation of the La Riba Unit is attributed to circulating seawater, probably driven by sea-level change, during deposition of the Alcover Unit or shortly thereafter.
- Published
- 2004
36. Sedimentary rocks in the field
- Author
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Tucker, Maurice E. and Tucker, Maurice E.
- Published
- 2003
37. Principles of Stratigraphic Analysis
- Author
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Tucker, Maurice E.
- Subjects
Principles of Stratigraphic Analysis (Book) -- Book reviews ,Books -- Book reviews ,Environmental issues ,Science and technology ,Zoology and wildlife conservation - Published
- 1991
38. HIGH-FREQUENCY CYCLES AND THEIR SEQUENCE STRATIGRAPHIC CONTEXT: ORBITAL FORCING AND TECTONIC CONTROLS ON DEVONIAN CYCLICITY, BELGIUM.
- Author
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TUCKER, Maurice and GARLAND, Joanna
- Subjects
- *
SEQUENCE stratigraphy , *LIMESTONE , *STRUCTURAL geology ,DEVONIAN stratigraphic geology - Abstract
The sequence stratigraphic approach has evolved into an important tool for stratigraphic analysis and does have an element of prediction. Several sequence models have been proposed and are in use, but there have been emotive discussions in the literature over these, as well as systems tracts and key surfaces. Metre-scale cycles (parasequences) are the building blocks of sequences and are an essential component of carbonate successions throughout the stratigraphic record. Their thickness and facies patterns, reflecting the longer-term changes in accommodation that affected deposition, enable the various systems tracts in a sequence to be recognised. There have been many arguments over the origin of parasequences with orbital forcing, tectonic and sedimentary mechanisms all having their proponents. Devonian carbonates of the Ardennes-Eifel-Aachen area are dominated by a suite of parasequence types deposited in ramp and shelf-interior locations. They show thickness patterns and trends in facies, which on a broad scale can be correlated across the region, whereas individual cycles cannot. Some packaging of cycles is seen, which could indicate an orbital-forcing control. However, there is clear evidence for a tectonic control on regional thickness patterns in some parts of the succession, as a result of deposition across syn-sedimentary extensional faults. As with many areas of Earth Science, explanation involves a combination of several hypotheses and here one mechanism does not seem to have been responsible for the Devonian cyclicity. [ABSTRACT FROM AUTHOR]
- Published
- 2010
39. Dated effort?
- Author
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Tucker, Maurice E., primary
- Published
- 1991
- Full Text
- View/download PDF
40. Facies-succession and architecture of the third-order sequences and their stratigraphic framework of the Devonian in Yunnan-Guizhou-Guangxi area, South China
- Author
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Mingxiang, Mei, Tucker, Maurice E., Yuan, Wang, and Min, Liu
- Subjects
sequence stratigraphy ,Devonian ,Yunnan-Guizhou-Guangxi area ,South China - Abstract
The Caledonian orogeny at the end of the Silurian resulted in great changes in the palaeogeography in the Yunnan-Guizhou-Guangxi area of South China; the continental area of the Early Paleozoic evolved into the extensive Dian-Qian-Gui Sea in the Late Paleozoic. Early in the Devonian, as a result of a major transgression, seawater encroached gradually from the south to the north and clastic facies were deposited. Carbonate deposition was then established in the Yunnan-Guizhou-Guangxi area, with a palaeogeography marked by attached platforms, isolated platforms and narrow basins. As a result of the Ziyun movement towards the end of the Devonian, the Upper Devonian strata are regressive and thin out from the open-sea to the land areas. A study of the nature and distribution of sedimentary facies in space and time recognises 13 third-order sequences in the Devonian strata in Yunnan-Guizhou-Guangxi area, and these form two second-order sequences. The strata of the Lower Devonian comprise 5 third-order sequences (SQ1 to SQ5), which are dominated by transgressive clastics. 4 third-order sequences (SQ6 to SQ9) in the Middle Devonian are characterized by alternations of transgressive clastics and highstand carbonates. In the Upper Devonian, carbonates constitute 4 third-order sequences (SQ10 to SQ13), which are generally marked by the transgressive limestones and highstand dolomites. On the basis of earlier biostratigraphic studies, sea-level changes represented by the third-order sequences with their different facies successions are explored, and the sequence stratigraphic framework is established. Therefore, the Devonian strata in the study area provide an example for further understanding of depositional trends within the sequence-stratigraphic framework.
- Full Text
- View/download PDF
41. Carbon isotope excursions in Precambrian/Cambrian boundary beds, Morocco.
- Author
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Tucker, Maurice E.
- Published
- 1986
- Full Text
- View/download PDF
42. Biomineralization of Monohydrocalcite Induced by the Halophile Halomonas Smyrnensis WMS-3.
- Author
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Pan, Juntong, Zhao, Hui, Tucker, Maurice E., Zhou, Jingxuan, Jiang, Mengzhen, Wang, Yapeng, Zhao, Yanyang, Sun, Bin, Han, Zuozhen, and Yan, Huaxiao
- Subjects
CALCIUM ions ,CARBONATE minerals ,BIOMINERALIZATION ,HIGH resolution electron microscopy ,SCANNING transmission electron microscopy ,DIFFERENTIAL scanning calorimetry ,CARBONIC anhydrase - Abstract
The halophilic bacterium Halomonas smyrnensis from a modern salt lake used in experiments to induce biomineralization has resulted in the precipitation of monohydrocalcite and other carbonate minerals. In this study, a Halomonas smyrnensis WMS-3 (GenBank:MH425323) strain was identified based on 16S rDNA homology comparison, and then cultured in mediums with 3% NaCl concentration to induce monohydrocalcite at different Mg/Ca molar ratios of 0, 2, 5, 7, and 9. The growth curve of WMS-3 bacteria, pH values, NH
4 + concentration, HCO3 − and CO3 2− concentration, carbonic anhydrase (CA) activity, and the changes in Ca2+ and Mg2+ ion concentration were determined to further explore the extracellular biomineralization mechanism. Moreover, the nucleation mechanism of monohydrocalcite on extracellular polymeric substances (EPS) was analyzed through studying ultrathin slices of the WMS-3 strain by High resolution transmission electron microscopy (HRTEM), Selected area election diffraction (SAED), Scanning transmission electron microscopy (STEM), and elemental mapping, besides this, amino acids in the EPS were also analyzed. The results show that pH increased to about 9.0 under the influence of ammonia and CA activity. The precipitation ratio (%, the ratio of the mass/volume concentration) of the Ca2+ ion was 64.32%, 62.20%, 60.22%, 59.57%, and 54.42% at Mg/Ca molar ratios of 0, 2, 5, 7, and 9, respectively, on the 21st day of the experiments, and 6.69%, 7.10%, 7.74%, 8.09% for the Mg2+ ion concentration at Mg/Ca molar ratios 2, 5, 7, and 9, respectively. The obtained minerals were calcite, Mg-rich calcite, aragonite, and hydromagnesite, in addition to the monohydrocalcite, as identified by X-ray diffraction (XRD) analyses. Monohydrocalcite had higher crystallinity when the Mg/Ca ratio increased from 7 to 9; thus, the stability of monohydrocalcite increased, also proven by the thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC) analyses. The C=O and C–O–C organic functional groups present in/on the minerals analyzed by Fourier transform infrared spectroscopy (FTIR), the various morphologies and the existence of P and S determined by scanning electron microscope-energy dispersive spectrometer (SEM-EDS), the relatively more negative stable carbon isotope values (−16.91‰ to −17.91‰) analyzed by a carbon isotope laser spectrometer, plus the typical surface chemistry by XPS, all support the biogenesis of these mineral precipitates. Moreover, Ca2+ ions were able to enter the bacterial cell to induce intracellular biomineralization. This study is useful to understand the mechanism of biomineralization further and may provide theoretical reference concerning the formation of monohydrocalcite in nature. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
- View/download PDF
43. Mechanism of Biomineralization Induced by Bacillus subtilis J2 and Characteristics of the Biominerals.
- Author
-
Han, Zuozhen, Wang, Jiajia, Zhao, Hui, Tucker, Maurice E., Zhao, Yanhong, Wu, Guangzhen, Zhou, Jingxuan, Yin, Junxiao, Zhang, Hucheng, Zhang, Xinkang, and Yan, Huaxiao
- Subjects
CALCITE ,BACILLUS subtilis ,CARBONATE minerals ,BIOMINERALIZATION ,MICROBIAL exopolysaccharides ,MINERALS ,CARBONIC anhydrase - Abstract
Biomineralization induced by microorganisms has become a hot spot in the field of carbonate sedimentology; however, the mechanisms involved still need to be explored. In this study, the bacterium Bacillus subtilis J2 (GenBank MG575432) was used to induce the precipitation of calcium carbonate minerals at Mg/Ca molar ratios of 0, 3, 6, 9, and 12. Bacillus subtilis J2 bacteria released ammonia to increase pH, but the ammonia released only made the pH increase to 8.25. Carbonic anhydrase was also produced to catalyze the hydration of carbon dioxide, and this process released carbonate and bicarbonate ions that not only increased pH but also elevated carbonate supersaturation. The biominerals formed at a Mg/Ca molar ratio of 0 were spherulitic, elongated, dumbbell-shaped, and irregularly rhombohedral calcite; at a Mg/Ca molar ratio of 3, the biominerals were calcite and aragonite, the weight ratio of calcite decreased from 26.7% to 15.6%, and that of aragonite increased from 73.3% to 84.4% with increasing incubation time. At higher Mg/Ca molar ratios, the biominerals were aragonite, and the crystallinity and thermal stability of aragonite decreased with increasing Mg/Ca molar ratios. FTIR results showed that many organic functional groups were present on/within the biominerals, such as C–O–C, N–H, C=O, O–H, and C–H. HRTEM-SAED examination of the ultra-thin slices of B. subtilis J2 bacteria showed that nano-sized minerals with poor crystal structure had grown or been adsorbed on the EPS coating. The EPS of the B. subtilis J2 strain contained abundant glutamic acid and aspartic acid, which could be deprotonated in an alkaline condition to adsorb Ca
2+ and Mg2+ ions; this made EPS act as the nucleation sites. This study may provide some references for further understanding of the mechanism of biomineralization induced by microorganisms. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
- View/download PDF
44. Construction of Wire Strain Gages for Engine Application
- Author
-
AIRCRAFT ENGINE RESEARCH LAB CLEVELAND OH, Nettles, J. C., Tucker, Maurice, AIRCRAFT ENGINE RESEARCH LAB CLEVELAND OH, Nettles, J. C., and Tucker, Maurice
- Published
- 1943
45. Combined Effect of Damping Screens and Stream Convergence on Turbulence
- Author
-
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON DC, Tucker, Maurice, NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON DC, and Tucker, Maurice
- Abstract
An analysis is presented of the combined effect of a series of damping screens followed by an axisymmetric-stream convergence (or divergence) upon the mean-square fluctuation-velocity intensities, scales, correlations, and one-dimensional spectra of a turbulence field convected by a main stream. The treatment is restricted to negligible turbulence decay and linearized by postulating small fluctuation velocities and velocity gradients, and absence of viscosity except as simulated by the idealized screen action. Compressibility of the main stream is allowed for during passage through the contracting section. The density fluctuations associated with the turbulence field are regarded as negligible. Numerical results for the statistical quantities describing the turbulence field downstream of a screen-contraction configuration are obtained for the case of upstream isotropic turbulence. The action of the damping screens and the stream convergence is to distort this initially isotropic field into a field of turbulence symmetric about the longitudinal direction with the lateral fluctuation velocities greater in magnitude than the longitudinal velocities. An approximate method of taking into account the effects of turbulence decay upon the mean-square fluctuation velocities obtained for the case of negligible decay is presented. This method of correction together with the tabulation of fluctuation-velocity ratios over an extensive range of conditions should prove useful for engineering applications.
- Published
- 1953
46. Sequence stratigraphy: methodology and nomenclature
- Author
-
Catuneanu, Octavian, Galloway, William E., Kendall, Christopher G. St. C., Miall, Andrew D., Posamentier, Henry W., Strasser, André, Tucker, Maurice E., Catuneanu, Octavian, Galloway, William E., Kendall, Christopher G. St. C., Miall, Andrew D., Posamentier, Henry W., Strasser, André, and Tucker, Maurice E.
- Abstract
The recurrence of the same types of sequence stratigraphic surface through geologic time defines cycles of change in accommodation or sediment supply, which correspond to sequences in the rock record. These cycles may be symmetrical or asymmetrical, and may or may not include all types of systems tracts that may be expected within a fully developed sequence. Depending on the scale of observation, sequences and their bounding surfaces may be ascribed to different hierarchical orders.Stratal stacking patterns combine to define trends in geometric character that include upstepping, forestepping, backstepping and downstepping, expressing three types of shoreline shift: forced regression (forestepping and downstepping at the shoreline), normal regression (forestepping and upstepping at the shoreline) and transgression (backstepping at the shoreline). Stacking patterns that are independent of shoreline trajectories may also be defined on the basis of changes in depositional style that can be correlated regionally. All stratal stacking patterns reflect the interplay of the same two fundamental variables, namely accommodation (the space available for potential sediment accumulation) and sediment supply. Deposits defined by specific stratal stacking patterns form the basic constituents of any sequence stratigraphic unit, from sequence to systems tract and parasequence. Changes in stratal stacking patterns define the position and timing of key sequence stratigraphic surfaces.Precisely which surfaces are selected as sequence boundaries varies as a function of which surfaces are best expressed within the context of the depositional setting and the preservation of facies relationships and stratal stacking patterns in that succession. The high degree of variability in the expression of sequence stratigraphic units and bounding surfaces in the rock record means ideally that the methodology used to analyze their depositional setting should be flexible from one sequence stratigraphi
47. Evidence of synsedimentary tectonic movements in the Triassic halite of Cheshire
- Author
-
Tucker, Roger M., primary and Tucker, Maurice E., additional
- Published
- 1981
- Full Text
- View/download PDF
48. Exfoliated pebbles and sheeting in the Triassic
- Author
-
TUCKER, MAURICE E., primary
- Published
- 1974
- Full Text
- View/download PDF
49. Precambrian dolomites: Petrographic and isotopic evidence that they differ from Phanerozoic dolomites
- Author
-
Tucker, Maurice E., primary
- Published
- 1982
- Full Text
- View/download PDF
50. The incorporation of Mg 2+ ions into aragonite during biomineralization: Implications for the dolomitization of aragonite.
- Author
-
Han Z, Meng R, Zhao H, Gao X, Zhao Y, Han Y, Liu F, Tucker ME, Deng J, and Yan H
- Abstract
Bacteria can facilitate the increase of Mg
2+ content in biotic aragonite, but the molecular mechanisms of the incorporation of Mg2+ ion into aragonite facilitated by bacteria are still unclear and the dolomitization of aragonite grains is rarely reported. In our laboratory experiments, the content of Mg2+ ions in biotic aragonite is higher than that in inorganically-precipitated aragonite and we hypothesize that the higher Mg content may enhance the subsequent dolomitization of aragonite. In this study, biotic aragonite was induced by Bacillus licheniformis Y1 at different Mg/Ca molar ratios. XRD data show that only aragonite was precipitated in the media with Mg/Ca molar ratios at 6, 9, and 12 after culturing for 25 days. The EDS and atomic absorption results show that the content of Mg2+ ions in biotic aragonite increased with rising Mg/Ca molar ratios. In addition, our analyses show that the EPS from the bacteria and the organics extracted from the interior of the biotic aragonite contain the same biomolecules, including Ala, Gly, Glu and hexadecanoic acid. The content of Mg2+ ions in the aragonite precipitates mediated by biomolecules is significantly higher than that in inorganically-precipitated aragonite. Additionally, compared with Ala and Gly, the increase of the Mg2+ ions content in aragonite promoted by Glu and hexadecanoic acid is more significant. The DFT (density functional theory) calculations reveal that the energy needed for Mg2+ ion incorporation into aragonite mediated by Glu, hexadecanoic acid, Gly and Ala increased gradually, but was lower than that without acidic biomolecules. The experiments also show that the Mg2+ ion content in the aragonite significantly increased with the increasing concentration of biomolecules. In a medium with high Mg2+ concentration and with bacteria, after 2 months, micron-sized dolomite rhombs were precipitated on the surfaces of the aragonite particles. This study may provide new insights into the important role played by biomolecules in the incorporation of the Mg2+ ions into aragonite. Moreover, these experiments may contribute towards our understanding of the dolomitization of aragonite in the presence of bacteria., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Han, Meng, Zhao, Gao, Zhao, Han, Liu, Tucker, Deng and Yan.)- Published
- 2023
- Full Text
- View/download PDF
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