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21.
ABSTRACT
The mineralogy and isotope geochemistry of carbonate minerals in the Coorong area are determined by the water chemistry of different depositional environments ranging from seawater to evaporitically modified continental water. The different isotopic compositions of coexisting calcite and dolomite suggest that each of the above two minerals was formed from water of composition and origin unique to that specific mineral. In addition, the dolomite was not formed by simple solid state cation exchange.
The occurrence of two types of dolomite was shown by isotope analysis and SEM observations. The dolomite, which is isotopically light (δ13 C = -1 to -2% 0 ; δ18 O=+3 to +5%0 ) and of fine grain size (˜ 0·5 μm) probably precipitated under the influence of evaporitically modified continental water. Coarser grained dolomite (up to 4 μm) is isotopically heavier (δ13 C=+3 to +4%0 ; δ18 O=+5 to + 6%0 ) contains Mg in excess of Ca and was formed in or close to equilibrium with atmospheric CO2 probably by the dolomitization of aragonite. 相似文献
The mineralogy and isotope geochemistry of carbonate minerals in the Coorong area are determined by the water chemistry of different depositional environments ranging from seawater to evaporitically modified continental water. The different isotopic compositions of coexisting calcite and dolomite suggest that each of the above two minerals was formed from water of composition and origin unique to that specific mineral. In addition, the dolomite was not formed by simple solid state cation exchange.
The occurrence of two types of dolomite was shown by isotope analysis and SEM observations. The dolomite, which is isotopically light (δ
22.
U-series Isotope Data on Lau Basin Glasses: the Role of Subduction-related Fluids during Melt Generation in Back-arc Basins 总被引:6,自引:2,他引:6
PEATE DAVID W.; KOKFELT THOMAS F.; HAWKESWORTH CHRIS J.; VAN CALSTEREN PETER W.; HERGT JANET M.; PEARCE JULIAN A. 《Journal of Petrology》2001,42(8):1449-1470
New thermal ionization mass spectrometry U-series disequilibriumdata are presented for 24 basaltic to dacitic glasses from activespreading centres in the back-arc Lau Basin (SW Pacific), togetherwith additional inductively coupled plasma mass spectrometrytrace element analyses and SrNdPb isotope data.Valu Fa Ridge samples, adjacent to the arc front, have highU/Th and (230Th/238U) <1, implying a recent (<<350ka) addition of a U-rich slab-derived fluid. The Valu Fa datacan be combined with existing 230Th238U data for theCentral Tonga arc to infer a fluid addition event at 相似文献
23.
The observation that the results of line and point counting analyses of the particle size distribution of the same sand are different leads to the conclusion that these results are biased by the sampling technique1 . The influence of the currently used sampling techniques on the numerical results of a particle size analysis is discussed. Evidence is presented to show that the use of line and point counting methods in granulometric analysis leads to results in which the influence of the sampling method is so strong that the practical value of these techniques is doubtful. It is therefore considered advisable to discontinue line and point counting techniques in granulometric analysis in favour of ribbon sampling methods. 相似文献
24.
A computer program(FEA)is presented for processing historical laboratory data.It performs on a list ofsample entries stored in a laboratory information management system.Using an algorithm which is basedon fuzzy set theory,FEA classifies the entries into a limited number of clusters called sample types.Theclassification is fully user-defined.The program transforms the historical data into a representation whichis more suitable for studying the performance of the laboratory or which can be used as preparation for asimulation project. 相似文献
25.
西昆仑山前冲断带晚新生代构造地貌特征 总被引:5,自引:0,他引:5
在卫片解译、DEM数据处理、地形图分析与剖面制作的基础上,结合野外构造地貌考察与观测,对西昆仑山前冲断带的构造地貌特征进行了定量、半定量的研究。沿山前发育系统的水系变化、冲积扇变化、不对称背斜、大规模正断裂、不对称河流阶地等典型的构造地貌,表明这条由南向北逆冲的冲断带在扩展过程中存在着由西向东迁移的特征。冲断带的东西分段以桑株河为界,以西发育固满背斜,其构造样式为向北的逆冲伴随向南的反冲;以东发育一系列不对称的背斜,表现出明显的由南向北逆冲的特征,地表无明显的反冲构造出现。利用生长地层和河流阶地估算了西昆仑山的隆升速率:晚上新世—早更新世以来的最低隆升速率为0.21~0.25mm/a,100ka以来的隆升速率为1.5mm/a。 相似文献
26.
The magneto-telluric and telluric-telluric profiling techniques are presented, and then a new method which combines these two techniques for mapping a parameter defined as the “apparent pseudo-resistivity”. The results obtained for the uranium structures in the Cluff Lake district (Saskatchewan Canada) indicate the use of these different techniques in the detection of zones of conduction for surface zones and for deeper zones, and demonstrate the advantages of these methods over the usual electrical methods in problems of structural research. 相似文献
27.
GERRIT J. VAN DER LINGEN 《Sedimentology》1979,26(5):731-735
Euhedral, tetragonal, dipyramidal crystals of weddellite, an authigenic calcium oxalate, occur in samples from the topmost core of Deep Sea Drilling Project Site 210 in the Coral Sea Basin. Opinions in the literature differ as to whether weddellite is formed in situ or during sample storage. Comparison of smear-slides made of samples after a 4 year storage period with shipboard smear-slides made immediately after core retrieval, indicates that weddellite was formed in situ. Possible further growth during storage is not obvious. The presence of many corroded crystals, and the absence of weddellite in deeper cores, suggest that weddellite is formed soon after deposition, but dissolves again in time and with increased burial, due to changing geochemical parameters. 相似文献
28.
R.A. VAN OVERMEEREN 《Geophysical Prospecting》1980,28(3):392-407
In the Andes mountains of North Chile seismic refraction measurements revealed the existence of a buried graben structure. The special geological environment permitted the deduction, by detailed analyses of diffraction patterns and delayed arrival times, of a low velocity layer underneath a high velocity ignimbritic sheet. The gravity method was chosen as an economic secondary aid to trace the course of the buried structure. This unusual combination of detailed gravity measurements following a general seismic survey was not only successful in detecting and tracing a buried structure, but also provided complementary data about the deeper subsurface conditions. 相似文献
29.
Spherular modern dolomite from the Coorong area, South Australia 总被引:1,自引:0,他引:1
Scanning electron micrographs show that the youngest and apparently least altered of the Coorong dolomite is in the form of spherular bodies about 0.2–1.0 μm in size which themselves are composed of spherules about 100 nm in diameter. Older and more lithified sediments show sharply defined dolomite crystals suggesting an origin as primary dolomite spherules followed by aggregation and diagenetic alteration to well crystallized dolomites. 相似文献
30.
KARL-DAG VORREN MAARTEN BLAAUW STEFAN WASTEGÅRD JOHANNES VAN DER PLICHT CHRISTIN JENSEN 《Boreas: An International Journal of Quaternary Research》2007,36(3):253-277
From the Sellevollmyra bog at Andøya, northern Norway, a 440‐cm long peat core covering the last c. 7000 calendar years was examined for humification, loss‐on‐ignition, microfossils, macrofossils and tephra. The age model was based on a Bayesian wiggle‐match of 35 14C dates and two historically anchored tephra layers. Based on changes in lithology and biostratigraphical climate proxies, several climatic changes were identified (periods of the most fundamental changes in italics): 6410–6380, 6230–6050, 5730–5640, 5470–5430, 5340–5310, 5270–5100, 4790–4710, 4890–4820, 4380–4320, 4220–4120, 4000–3810, 3610–3580, 3370–3340 (regionally 2850–2750; in Sellevollmyra a hiatus between 2960–2520), 2330–2220, 1950, 1530–1450, 1150–840, 730? and c. 600? cal. yr BP. Most of these climate changes are known from other investigations of different palaeoclimate proxies in northern and middle Europe. Some volcanic eruptions seemingly coincide with vegetation changes recorded in the peat, e.g. about 5760 cal. yr BP; however, the known climatic deterioration at the time of the Hekla‐4 tephra layer started some decades before the eruption event. 相似文献