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Spectacularly developed lower Eocene chert in the Corones platform carbonates of the Spanish Pyrenees is concentrated within a restricted, brackish-water, laminated ostracod-rich facies, which also contains abundant sponge spicules. The chert occurs as nodular, bedded and mottled varieties, and four petrographic types of quartz are developed: microquartz; length-fast (LF) chalcedony; megaquartz; and microspheres. δ18 O values of chert range from 29·6‰ to 30·9‰ (SMOW), which correspond to a broad isotope rank common for biogenic and diagenetic replacement cherts. Calcian dolomite crystals with high Fe and Na are disseminated within the microquartz and LF-chalcedony, but are absent from the megaquartz and host carbonate. The chert is closely associated with desiccation cracks and with interstratal dewatering structures. Load casts are silicified, and laminae rich in sponge spicules are convoluted. Early cracks related to dewatering are filled by microquartz and quartz cements. Ostracod shells within chert are locally fractured; those in the host carbonate are commonly flattened. Late fractures are filled by LF-chalcedony and megaquartz. There is much evidence for the dissolution of sponge spicules and their calcitization in the carbonate host rock. Silica for the Corones cherts was derived from sponges during early diagenesis and shallow burial. Early mechanical compaction and sediment dewatering played a major role in sponge spicule dissolution, migration of silica-rich fluids and the consequent precipitation of chert. Quartz cements continued to be precipitated into the burial environment. 相似文献
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对海岛礁及周边包括海浪、潮汐、潮流、温度等在内的复杂环境要素及其特点进行了分析。针对海洋复杂要素的特点,提出了适用于海洋高动态的面向可细分对象的时空数据模型,能够有效地对高动态及交互性较强的对象进行建模。以舟山群岛附近海域为例,对海岛礁及周边复杂环境进行了动态三维建模,并在Geoglobe等平台上进行了验证。实验表明,该模型对海岛礁及周边复杂环境建模有较好的实用性。 相似文献
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提出了适合航空影像区域分割的水平集运算策略,将原始影像首先进行格网分类,对分类后的海岸线格网进行水平集运算提取精确海岛(礁)边缘,并采用多核编程策略提高运算效率。实验表明该方案效果理想,能够正确提取海岛(礁)区域。 相似文献
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A global inventory of coral reef stressors based on satellite observed nighttime lights 总被引:1,自引:0,他引:1
In this article, we present a satellite-based approach to gather information about the threat to coral reefs worldwide. Three chosen reef stressors – development, gas flaring and heavily lit fishing boat activity – are analysed using nighttime lights data derived from the Defense Meteorological Satellite Program (DMSP) produced at the National Oceanic & Atmospheric Administration, National Geophysical Data Center (NOAA/NGDC). Nighttime lights represent a direct threat to coral reef ecosystems and are an excellent proxy measure for associated human-caused stressors. A lights proximity index (LPI) is calculated, measuring the distance of coral reef sites to each of the stressors and incorporating the stressor's intensity. Colourized maps visualize the results on a global scale. Area rankings clarify the effects of artificial night lighting on coral reefs on a regional scale. The results should be very useful for reef managers and for state administrations to implement coral reef conservation projects and for the scientific world to conduct further research. 相似文献
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The Role of Isopod Crustaceans in the Reef Crest Community at Carrie Bow Cay, Belize 总被引:1,自引:0,他引:1
Abstract. The species composition and numbers of specimens of isopod crustaceans from the rubble of a Belizean reef crest were obtained. Four sets of 30 samples were taken from three rubble zones (rubble with algal turf, rubble between Thalassia plants, and pure rubble), in four different collecting periods. Twenty-four species of isopods were identified, sexed and counted. By means of a Likelihood Ratio Chi-square Contingency Table Analysis the presence of 13 species was shown to be positively correlated with habitat, 15 species with season, and nine species with habitat and season combined. From the spread of total numbers and of ovigerous females it is proposed that the isopods may be grouped into three patterns: a) those present and breeding in the reef crest rubble throughout the year, i. e. stress-tolerant species; b) those showing a breeding peak in summer and a population decrease in winter-spring, i. e. opportunist species; and c) those showing a breeding peak in the fall, and a second peak in spring, and a decrease or complete avoidance of the habitat, especially by ovigerous females, in the summer. The diversity of the Belizean reef crest isopod fauna is compared with the published report of the isopod fauna of a coral reef in Madagascar. Several similarities in composition are noted. The multiplicity of microhabitats is invoked as a possible explanation for the relatively high diversity of anthuridean isopods in coral reefs. 相似文献
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济南北部地热田地热资源类型属于层状裂隙岩溶型,热源是北部齐河-广饶断裂的沟通导热,盖层是第四系、新近系、石炭-二叠系、侏罗系.可利用的、具有开发价值的热储层为奥陶系灰岩热储,该热储层顶板埋深在700~2500m左右,热储层厚度由南向北逐渐增大,单井涌水量2000m3/d左右,孔口水温一般在38~57℃,地热田东部地热水矿化度1.4~3.5g/L左右,西部5.1~7.2g/L左右,地热水中富含氟、锶、偏硅酸等微量元素,具腐蚀性,结垢性弱,具较好的开发利用价值.经计算奥陶系热储层单井可采资源量为7.3×105m3/a,合理井间距为5000m. 相似文献
10.
海洋沉积体系的定量模拟可分为仿真和勘察式模拟,后者的目标是建立沉积特征的连续谱、凝练新的科学问题。本文提出一个勘察式模拟的方法论框架,即根据控制方程确定自变量的定义域,进而由模拟计算给出应变量的值域,并结合物质收支平衡原理和“圆台状环礁”几何模型,以此方法预估环礁及其海底阶地物质输运和堆积格局。环礁是珊瑚礁的独特类型,其礁盘区提供了礁体生长和礁外坡、海底阶地堆积的几乎全部物源。结果表明,环礁自身生长受控于生物碎屑生产,而海底阶地的范围和沉积速率不仅决定于离礁悬沙通量,而且受到环礁外水深和海盆环流的制约。悬沙输运和重力流过程形成常态沉降和水下滑坡的交替沉积。此模型所预测的环礁沉积体系高程-面积曲线与南海环礁的实际曲线相对照,可获得环礁演化的机制信息。模拟结果还提示了需进一步研究的科学问题,如环礁生长规模及其控制机制、环礁沉积体系中周期性沉积的时间尺度、环礁外坡由于珊瑚生长自组织机制形成的重力流事件与地震等极端事件的对比和机制识别、环礁群的海底阶地沉积记录多样性、海面变化对环礁演化的影响和沉积记录、环礁人居环境安全等。 相似文献