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1.
刘季花  陈迎蓉 《沉积学报》1999,17(12):789-793
以５ｃｍ为间隔取得东太平洋５７９４岩心早中新世超微化石软泥须（２４．０６～２２．０６Ｍａ）的５５个样品,用同位素质谱仪、耦合等离子光谱仪和化学溶解当分别对尼中可溶碳酸盐组分的＾８７Ｓｒ／＾８６Ｓｒ、全岩的Ａｌ２Ｏ３和ＣａＣＯ３含量进行了测定。结果显示,＾８７Ｓｒ／＾８６Ｓｒ和ＣａＣＯ３呈反射发育了２个完整旋回和１个半旋回。＾８７Ｓｒ／８６Ｓｒ和ＣａＣＯ３短期旋回具有重要的古海洋学意义：（１）＾８７  相似文献   

2.
通过沉积作用及岩浆活动产物的特征，可以识别古边缘海的存在，沉积作用形成的沉积物主要为火山碎屑岩，深海浊积岩 岩浆活动的产物主要是玄武岩，其特征是具有高挥发组分，高气孔率，Ｋ，Ｒ和Ｂａ含量较高，Ｆｅ，Ｍｇ，Ｃｒ，Ｚｒ和Ｎｉ含量较低，ＬＩＬ／ＨＦＳ比值较高，Ｋ／Ｒｂ，Ｋ／Ｂａ和Ｚｒ／Ｎｂ比值较你，轻稀土富集中等偏高等。  相似文献   

3.
一个古元古代A型流纹岩   总被引：17，自引：2，他引：15  
于津海  王德滋 《地球化学》1998,27(6):549-558
山西吕梁群流纹岩是一个古元古代的弱碱性火山岩,它具有高ＳｉＯ２,Ｎａ２Ｏ＋Ｋ２Ｏ和Ｚｒ,Ｇａ等高场强元素和高ＦｅＯ＾＊／ＭｇＯ,Ｒｂ／Ｓｒ和Ｇａ／Ａｌ比值,以及低ＣａＯ,Ｓｒ和Ｅｕ／Ｅｕ＾＊的地球化学特征,相似于Ａ型花岗质岩石。它形成于大陆边缘裂谷环境,化学成分及同位素特征为高εＮｄ（ｔ）值,低（＾８７Ｓｒ／＾８６Ｓｒ）ｉ值,表明流纹岩的原始岩浆由下地壳晚太古代变质岩受裂谷岩浆和热流作用的影响部分  相似文献   

4.
莺歌海盆地上新统双壳类贝壳的锶含量及其意义   总被引：1，自引：0，他引：1  
王子玉  蓝秀 《地层学杂志》1998,22(2):149-153
锶（Ｓｒ）是碳酸盐沉积物及软体动物介壳中的重要微量元素之一,Ｓｒ含量和Ｓｒ／Ｃａ比值的变化明显受沉积相的控制。因此,锶作为地球化学指标具有一定的环境意义。通过对南海北部莺歌海盆地莺６井上新统双壳类贝壳中的Ｓｒ含量和Ｓｒ／Ｃａ比值的变化与环境、成岩作用关系的研究,发现莺歌海盆地上新世沉积环境为上陆坡→潮下带→潮间带,所得结论与双壳类的生态环境和地层沉积相的综合分析结果一致。  相似文献   

5.
李红春  陈文寄 《地质论评》1998,44(5):456-463
对采自北京西山石花洞内的石笋进行了δ＾１８Ｏ,δ＾１３Ｃ和Ｍｇ／Ｓｒ分析,获得分辨率为２５ａ的北京地区３０００ａ认来的古气候和古环境信息,以δ＾１８Ｏ和Ｄｍｇ／Ｃａ作为气候变化信息,证实石笋δ＾Ｃ反映了古气候变化对植被的影响,当石笋δ＾１３Ｃ植增大时,表示Ｃ３／Ｃ４植物比值降低,气候变干热,当石笋δ＾１３Ｃ值减小时,表示Ｃ３／Ｃ４植物比值升高,气候变湿冷,同时,笔者也发现了北京元大都建立以来对森林  相似文献   

6.
海南岛中元古代花岗岩地球化学及成因研究   总被引：16，自引：3，他引：16  
海南岛中元古代花岗岩岩体主要由二长花岗岩、花岗冈长岩等岩石组成，构成一个明显的 自花岗岩向花岗闪长岩和英云闪长岩的岩浆演化系列及钙碱性演化趋势。该岩体为一套板块碰撞 后隆起期原地一半原地过铝质花岗岩。是板块碰撞引起的地壳增厚升温和随之的玄武岩浆底侵加 热联合作用下，主要由抱板群变质沉积岩及斜长角闪片麻岩部分融熔、并在幔源物质的参与下形 成的，所形成的花岗质岩浆在“走滑扩容泵吸”机制驱动下沿戈枕剪切带上升、固结就位，因而具壳 幔二元混合成因特点。化学成分以高 ＳｉＯ２、Ｋ２Ｏ、Ｒｂ、Ｂａ、Ｔａ、Ｃｅ和贫Ｐ、Ｔｉ、Ｚｒ、Ｓｒ、Ｆｅ２Ｏ３＋ＦｅＯ、 ＭｇＯ、ＣａＯ为特征；元素比值Ｚｒ／Ｎｂ、Ｌａ／Ｎｂ、Ｂａ／Ｎｂ、Ｒｂ／Ｎｂ、Ｋ／Ｎｂ、Ｂａ／Ｌａ及Ｃｒ、Ｃｏ、Ｎｉ、Ｖ均接近 大陆中下地壳成分，Ｒｂ、Ｓｒ、Ｂａ、Ｔａ、Ｚｒ及比值Ｋ／Ｓｒ、Ｒｂ／Ｓｒ石ｒ／Ｂａ变化范围小，反映岩浆源区成分 或熔融方式上的一致性；轻重稀土较强分馏，负铕异常明显，稀土配分模式总体相似，呈左高右低 型，和抱板群变质沉积岩稀上元素组成基本一致；εＮｄ（ｔ）值普遍高于抱板群地层，（８７Ｓｒ／８６Ｓｒ）ｉ值变化 大，暗示幔源参与信息。结合抱板群变基性火山岩的  相似文献   

7.
中扬子台地北缘上震旦统碳酸盐岩沉积发育,可分为浅水台地和深水台盆两个相区和七种不同的相带。地球化学分析表明,该区碳酸盐岩中 Ｓｒ 和 Ｓｒ／ Ｃａ ×１０００ 的比值与沉积环境密切相关,由浅滩相向深水斜坡－ 盆地相明显增加。究其原因,一方面因不同沉积环境中碳酸盐矿物组分不同,影响了锶的分布;另一方面与沉积环境所决定的成岩环境有关。因此,利用微量元素锶的含量和 Ｓｒ／ Ｃａ ×１０００ 比值可以判别沉积相。  相似文献   

8.
泌阳凹陷核桃园组微量元素演化特征及其古气候意义   总被引：31，自引：6，他引：31  
泌阳凹陷下第三系核桃园组总体上表现为一个大的湖退体系，而其中的微量元素含量及有关元素比值却呈现出细微而明显的旋回变化特征。本文依据泥岩、页岩和碳酸盐岩中Ｔｉ、Ｓｒ、Ｂａ等十六种微量元素含量及Ｓｒ/Ｂａ、Ｆｅ/Ｍｎ、Ｓｒ/Ｃｕ等七种比值的变化特征，结合古盐度及岩相资料，对核桃园组沉积时的古气候作了系统的研究，基本上分出了温暖潮湿、干湿交替、炎热干旱、温热半干旱四类较为特征的古气候类型，以期为油气勘探提供依据。  相似文献   

9.
（古）盐度研究的一种重要工具——锶同位素   总被引：1，自引：0，他引：1  
本文详细地阐述了海水－陆表水双元体系中锶同位素的混合原理、混合水体中＾８７Ｓｒ／＾８６Ｓｒ值与盐度的定量关系。利用Ｓｒ同位素不随生物、何尝作用过程发生分馏作用及Ｓｒ与Ｃａ化学性质相似等特征,地层、沉积物中生物壳体和碳酸盐岩＾８７Ｓｒ／＾８６Ｓｒ值可作为沉积水体（古）盐度确定的一种有用工具。文中详细地综述了国内外在这方面的研究进展,并讨论了成岩后生作用对生物壳体和碳酸盐岩＾８７Ｓｒ／＾８６Ｓｒ原始值  相似文献   

10.
贵州织金地区晚二叠世的沉积环境分析   总被引：9，自引：0，他引：9  
黄昔容  陶述平 《贵州地质》1999,16(4):301-306
主要根据Ｂ,Ｂ／Ｇａ和Ｓｒ,Ｓｒ／Ｂａ的含量和比值大小来判断水的盐度,以及岩石类型和古生物组合,推断当时的沉积环境为过渡相偏海相的沉积特征。  相似文献   

11.
We reconstruct SST from coral Sr/Ca ratios measured at three coral cores taken from the lagoon of Tahiti (French Polynesia). Two coral cores were drilled from the same coral colony (one horizontally and one vertically), and a third core was drilled vertically from another coral growing at a different site. We evaluate several Sr/Ca records as proxies for regional SST variations: (1) the three single-core records from Tahiti, (2) an average Sr/Ca record computed from the two cores drilled from the same coral colony, (3) an average Sr/Ca record computed from all three Tahiti cores, and (4) an average Sr/Ca record computed from the three Tahiti cores and a fourth core taken from a different island (Rarotonga). On a monthly scale, the average Sr/Ca record including the four coral cores from Tahiti and Rarotonga shows the best correlation with regional SST. The variance of the SST reconstruction is very realistic and the residual SST is low. This suggests that reconstructing SST from average proxy records gives a better representation of regional SST variations. Of the three Tahiti cores, the one that was drilled horizontally shows the best correlation with grid-SST on an annual mean scale. All three Tahiti corals show much larger interannual SST variations than that indicated by grid-SST.  相似文献   

12.
文章采用全谱直读等离子体原子发射光谱(ICP-AES)的方法测定了1986~1996年海南岛东部海域滨珊瑚的Sr/Ca比值,建立了该海域月分辨率的Sr/Ca海水表面温度计方程:SST(℃)=170-16 (mmol/mol),n = 133,r=0.80,p=0.01, 此与韦刚健等在西沙海域建立的温度计方程:SST(℃)=169-16.7 (mmol/mol)一致,这表明南海中、北部海域也出现有相似的微量元素温度计。此外,文章还分析了在某些年月份SST的实测值和计算值出现的显著差别,探讨了可能造成的海洋气象环境因素。  相似文献   

13.
Sea surface temperatures (SSTs) have been inferred previously from the Sr/Ca ratios of coral aragonite. However, microanalytical studies have indicated that Sr in some coral skeletons is more heterogeneously distributed than expected from SST data. Strontium may exist in two skeletal phases, as Sr substituted for Ca in aragonite and as separate SrCO3 (strontianite) domains. Variations in the size, quantity, or both of these domains may account for small-scale Sr heterogeneity. Here, we use synchrotron X-ray fluorescence to map Sr/Ca variations in a Porites lobata skeleton at a 5 μm scale. Variations are large and unrelated to changes in local seawater temperature or composition. Selected area extended X-ray absorption fine structure (EXAFS) spectroscopy of low- and high-Sr areas indicates that Sr is present as a substitute ion in aragonite i.e., domains of Sr carbonate (strontianite) are absent or in minor abundance. Variations in strontianite abundance are not responsible for the Sr/Ca fluctuations observed in this sample. The Sr microdistribution is systematic and appears to correlate with the crystalline fabric of the coral skeleton, suggesting Sr heterogeneity may reflect nonequilibrium calcification processes. Nonequilibrium incorporation of Sr complicates the interpretation of Sr/Ca ratios in terms of SST, particularly in attempts to extend the temporal resolution of the technique. The micro-EXAFS technique may prove to be valuable, allowing the selection of coral microvolumes for Sr/Ca measurement where strontium is incorporated in a known structural environment.  相似文献   

14.
Massive corals in the Great Barrier Reef, analyzed at high-resolution for Sr/Ca (thermal ionization mass spectrometry) and trace elements such as Ba and Mn (laser ablation inductively coupled plasma mass spectrometry), can provide continuous proxy records of dissolved seawater concentrations, as well as sea surface temperature (SST). A 10-yr record (1989 to 1998) from Pandora Reef, an inshore reef regularly impacted by the freshwater plumes of the Burdekin River, is compared with an overlapping record from a midshelf reef, away from runoff influences. Surface seawater samples, taken away from river plumes, show little variability for Sr/Ca (8484 ± 10 μmol/mol) and Ba (33.7 ± 0.7 nmol/kg). Discrete Ba/Ca peaks in the inshore coral coincide with flood events. The magnitude of this Ba/Ca enrichment is most likely controlled by the amount of suspended sediments delivered to the estuary, which remains difficult to monitor. The maximum flow rate at peak river discharge is used here as a proxy for the sediment load and is shown to be strongly correlated with coral Ba/Ca (r = 0.97). After the wet summer of 1991, the coral Ba/Ca flood peak is followed by a plateau that lingers for several months after dissipation of plume waters, signifying an additional flux of Ba that may originate from submarine groundwater seeps and/or mangrove reservoirs. Both Mn and Y are enriched by a factor of ∼5 in inshore relative to midshelf corals. Mn/Ca ratios show a seasonal cycle that follows SST (r = 0.7), not river discharge, with an additional high variability in summer suggesting a link with biological activity. P and Cd show no significant seasonal variation and are at a low level at both inshore and midreef locations. However, leaching experiments suggest that part of the coral P is not lattice bound.  相似文献   

15.
The high precision measurement of the Sr/Ca ratio in corals has the potential for measuring past sea surface temperatures at very high accuracy. However, the veracity of the technique has been questioned on the basis that there is both a spatial and temporal variation in the Sr/Ca ratio of seawater, and that kinetic effects, such as the calcification rate, can affect the Sr/Ca ratio of corals, and produce inaccuracies of the order of 2-4 °C. In the present study, a number of cores of the massive hermatypic scleractinian coral Porites, from the central Great Barrier Reef, have been analyzed for Sr/Ca at weekly to monthly resolution. Results from a 24 year record from Myrmidon Reef show an overall variation from 22.7 °C to 30.4 °C. The record shows a warming/cooling trend with maximum warming centred on the 1986-1987 summer. While some bleaching was reported to have occurred at Myrmidon Reef in 1982, the Sr/Ca record indicates that subsequent summer temperatures were much higher. The 4.5 year record from Stanley Reef shows a maximum SST of 30 °C during the 1997-1998 El Niño event. The calibrations from Myrmidon and Stanley Reefs are in excellent agreement with previously published calibrations from nearby reefs. While corals do not calcify in equilibrium with seawater due to physiological control on the uptake of Sr and Ca into the lattice of coralline aragonite, it can be argued that, provided only a single genus such as Porites sp. is used, and that the coral is sampled along a major vertical growth axis, then the Sr/Ca ratio should vary uniformly with temperature. Similarly, objections based on the spatial and temporal variability of the Sr/Ca activity ratio of seawater can be countered on the basis that in most areas where coral reefs grow there is a uniformity in the Sr/Ca activity ratio, and there does not appear to be a change in this ratio over the growth period of the coral. Evidence from several corals in this study suggest that stress can be a major cause of the breakdown in the Sr/Ca-SST relationship. Thermal stress, resulting from either extremely warm or cool temperatures, can produce anomalously low Sr/Ca derived SSTs as a result of the breakdown of the biological control on Sr/Ca fractionation. It is considered that other stresses, such as increased nutrients and changes in light intensity, can also lead to a breakdown in the Sr/Ca-SST relationship. Two of the main issues affecting the reliability of the Sr/Ca method are the calibration of the Sr/Ca ratio with measured SST and the estimation of tropical last glacial maximum (LGM) palaeotemperatures. Instead of producing a constant calibration, just about every one published so far is different from the others. What is obvious is that for most calibrations while the slope of the calibration equation is similar, the intercepts are not. While the cause for this variation is still unknown, it would appear that corals from different localities around the world are responding to their own particular environment or that certain types of environments exert a control on the corals’ physiology. Sr/Ca derived SST estimates for the LGM and deglaciation of 5 °C-6 °C cooler than present are at odds with estimates of 2 °C-3 °C cooling by other climate proxies. The apparent lack of reef growth during the LGM suggests that SSTs were too cold in many parts of the tropics for reefs to develop. This would lend support to the idea that tropical SSTs were much cooler than what the CLIMAP data suggests.  相似文献   

16.
Coral proxy records of sea surface temperature (SST) and hydrological balance have become important tools in the field of tropical paleoclimatology. However, coral aragonite is subject to post-depositional diagenetic alteration in both the marine and vadose environments. To understand the impact of diagenesis on coral climate proxies, two mid-Holocene Porites corals from raised reefs on Muschu Island, Papua New Guinea, were analysed for Sr/Ca, δ18O, and δ13C along transects from 100% aragonite to 100% calcite. Thin-section analysis showed a characteristic vadose zone diagenetic sequence, beginning with leaching of primary aragonite and fine calcite overgrowths, transitional to calcite void filling and neomorphic, fabric selective replacement of the coral skeleton. Average calcite Sr/Ca and δ18O values were lower than those for coral aragonite, decreasing from 0.0088 to 0.0021 and −5.2 to −8.1‰, respectively. The relatively low Sr/Ca of the secondary calcite reflects the Sr/Ca of dissolving phases and the large difference between aragonite and calcite Sr/Ca partition coefficients. The decrease in δ18O of calcite relative to coral aragonite is a function of the δ18O of precipitation. Carbon-isotope ratios in secondary calcite are variable, though generally lower relative to aragonite, ranging from −2.5 to −10.4%. The variability of δ13C in secondary calcite reflects the amount of soil CO2 contributing 13C-depleted carbon to the precipitating fluids. Diagenesis has a greater impact on Sr/Ca than on δ18O; the calcite compositions reported here convert to SST anomalies of 115°C and 14°C, respectively. Based on calcite Sr/Ca compositions in this study and in the literature, the sensitivity of coral Sr/Ca-SST to vadose-zone calcite diagenesis is 1.1 to 1.5°C per percent calcite. In contrast, the rate of change in coral δ18O-SST is relatively small (−0.2 to 0.2°C per percent calcite). We show that large shifts in δ18O, reported for mid-Holocene and Last Interglacial corals with warmer than present Sr/Ca-SSTs, cannot be caused by calcite diagenesis. Low-level calcite diagenesis can be detected through X-ray diffraction techniques, thin section analysis, and high spatial resolution sampling of the coral skeleton and thus should not impede the production of accurate coral paleoclimate reconstructions.  相似文献   

17.
The integrity of coral-based reconstructions of past climate variability depends on a comprehensive knowledge of the effects of post-depositional alteration on coral skeletal geochemistry. Here we combine millimeter-scale and micro-scale coral Sr/Ca data, scanning electron microscopy (SEM) images, and X-ray diffraction with previously published δ18O records to investigate the effects of submarine and subaerial diagenesis on paleoclimate reconstructions in modern and young sub-fossil corals from the central tropical Pacific. In a 40-year-old modern coral, we find secondary aragonite is associated with relatively high coral δ18O and Sr/Ca, equivalent to sea-surface temperature (SST) artifacts as large as −3 and −5 °C, respectively. Secondary aragonite observed in a 350-year-old fossil coral is associated with relatively high δ18O and Sr/Ca, resulting in apparent paleo-SST offsets of up to −2 and −4 °C, respectively. Secondary Ion Mass Spectrometry (SIMS) analyses of secondary aragonite yield Sr/Ca ratios ranging from 10.78 to 12.39 mmol/mol, significantly higher compared to 9.15 ± 0.37 mmol/mol measured in more pristine sections of the same fossil coral. Widespread dissolution and secondary calcite observed in a 750-year-old fossil coral is associated with relatively low δ18O and Sr/Ca. SIMS Sr/Ca measurements of the secondary calcite (1.96-9.74 mmol/mol) are significantly lower and more variable than Sr/Ca values from more pristine portions of the same fossil coral (8.22 ± 0.13 mmol/mol). Our results indicate that while diagenesis has a much larger impact on Sr/Ca-based paleoclimate reconstructions than δ18O-based reconstructions at our site, SIMS analyses of relatively pristine skeletal elements in an altered coral may provide robust estimates of Sr/Ca which can be used to derive paleo-SSTs.  相似文献   

18.
《Chemical Geology》2007,236(3-4):339-349
We present a new high precision analytical method for the determination of Mg/Ca and Sr/Ca ratios in carbonates using an inductively coupled plasma quadrupole mass spectrometer (ICP-QMS) with a 650-W cold plasma technique and a desolvation introduction system. Signal intensities are detected in pulse-counting mode and Mg/Ca and Sr/Ca ratios are calculated directly from intensity ratios of 24Mg/43Ca and 86Sr/43Ca using external matrix-matched standards for every 4–5 samples to correct for instrumental mass discrimination and low-frequency ratio drift. Significant matrix effect of Ca content on Mg/Ca determination (− 0.018 Mg/Ca (mmol/mol)/[Ca] (ppm)), can be overcome by diluting [Ca] to 6–8 ppm in the sample solution or using an empirical correction. The Sr/Ca ratio affects the Mg/Ca determination, with a factor of − 0.32% Mg/Ca per mmol/mol. This is mainly caused by the influence of doubly charged 86Sr, which biases the intensity measurement of the 43Ca+ ion beam. This effect results in a trivial offset of less than 0.1% on Mg/Ca measurements for Quaternary foraminiferal and coral samples. The internal precision of our method ranges from 0.1 to 0.2%. Replicate measurements made on standards and samples show long-term external uncertainties (2σ) of Mg/Ca = 0.84% and Sr/Ca = 0.49%. The minimum sample size requirement is only 3.5 μg of carbonate. The application of this newly developed technique on the planktonic foraminifera Globigerinoides ruber from a core recovered in the southern South China Sea yields a glacial–interglacial difference in sea surface temperature (SST) of 3 °C. Three-year coral Sr/Ca data suggest that the seasonal SST ranged from 22.6–23.8 °C in winter to 26.9–27.9 °C in summer in Nanwan, south Taiwan, during 2000–2002. The coral-Sr/Ca inferred SSTs in 2002 match well with instrumental records, which demonstrates the validity of this ICP-QMS method.  相似文献   

19.
星罗棋布的热带珊瑚作为海洋环境的信息载体,具有分辨率高、时间跨度大、记录连续完整、体系封闭性好、蕴涵的信息丰富、可选择的代用指标多、测定简便和易于定年等特点。珊瑚有效地记录了全球环境变化的诸多信息,已成为研究过去（如末次间冰期以来）和近代（如数十至数百年以来）的气候—环境变率和可预测性（PAGES CLIVAR）领域重要的环境载体。以全球变化为背景,对近年来珊瑚环境代用指标的研究成果进行评述。重点讨论了珊瑚氧同位素和微量元素比值等指标在海表温度（SST）变化、海气交换程度、季风强弱、厄尔尼诺—南方涛动（ENSO）发生的频率和强度,以及它们之间的相互作用等全球变化的核心问题上的研究进展,并展望了南海珊瑚在高分辨率全球变化研究中的地位与方向。  相似文献   

20.
The geochemistry of coral skeletons may reflect seawater conditions at the time of deposition and the analysis of fossil skeletons offers a method to reconstruct past climate. However the precipitation of cements in the primary coral skeleton during diagenesis may significantly affect bulk skeletal geochemistry. We used secondary ion mass spectrometry (SIMS) to measure Sr, Mg, B, U and Ba concentrations in primary coral aragonite and aragonite and calcite cements in fossil Porites corals from submerged reefs around the Hawaiian Islands. Cement and primary coral geochemistry were significantly different in all corals. We estimate the effects of cement inclusion on climate estimates from drilled coral samples, which combine cements and primary coral aragonite. Secondary 1% calcite or ∼2% aragonite cement contamination significantly affects Sr/Ca SST estimates by +1 °C and −0.4 to −0.9 °C, respectively. Cement inclusion also significantly affects Mg/Ca, B/Ca and U/Ca SST estimates in some corals. X-ray diffraction (XRD) will not detect secondary aragonite cements and significant calcite contamination may be below the limit of detection (∼1%) of the technique. Thorough petrographic examination of fossils is therefore essential to confirm that they are pristine before bulk drilled samples are analysed. To confirm that the geochemistry of the original coral structures is not affected by the precipitation of cements in adjacent pore spaces we analysed the primary coral aragonite in cemented and uncemented areas of the skeleton. Sr/Ca, B/Ca and U/Ca of primary coral aragonite is not affected by the presence of cements in adjacent interskeletal pore spaces i.e. the coral structures maintain their original composition and selective SIMS analysis of these structures offers a route to the reconstruction of accurate SSTs from altered coral skeletons. However, Mg/Ca and Ba/Ca of primary coral aragonite are significantly higher in parts of skeletons infilled with high Mg calcite cement. We hypothesise this reflects cement infilling of intraskeletal pore spaces in the primary coral structure.  相似文献   

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