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钙质碳酸盐碎屑是热带海滩沉积物的重要组成部分,其物理特性与海滩中的石英颗粒差异明显。对海南岛东部文昌铜鼓角两侧海湾海滩砂样采用除钙和不除钙两种预处理方法,使用Mastersizer 2000激光粒度仪和筛析法进行粒度分析,结果表明:除钙以后粒度频率曲线主体朝细偏,但在粒度频率曲线细尾(4~9)会新增一小峰;去钙前后粒度参数存在明显的线性相关,平均粒径、分选系数和偏态的相关系数依次降低;粒度参数的组合变化以“平均粒径变细、分选系数变好、偏态朝细偏”为主,但仍存在其他的组合变化;在对类似于铜鼓岭周边环境的海滩进行沉积物粒度分析及动力环境研究时,需要了解钙质碎屑含量和颗粒组成。 相似文献
3.
Francis P. Shepard 《International Journal of Earth Sciences》1958,47(1):150-167
Six years of intensive study of the shallow water sediments of the northwestern Gulf of Mexico have indicated that there are many criteria by which ancient sediments deposited under similar conditions can be recognized. Thus the presence of echinoid fragments and of glauconite-filled Foraminifera tests favors marine shelf deposition over bay deposits; calcareous aggregates and grains of gypsum suggest high salinity bay deposits; abundance of wood fibers, high mica content, ferruginous aggregates, and well laminated sediments all are suggestive of deposition near river mouths; greater roundness distinguishes dunes from adjacent beach sands; and coarser grain size distinguishes beach sands from shallow shelf sands in the vicinity.Faunal assemblages of Foraminifera, Ostracoda, and Mollusca all serve to distinguish between bay and shelf deposits. Within the bays the faunas show a close relationship to salinity conditions whereas on the shelf the faunas are arranged in bands parallel to the shore and to the depth contours. Certain generalizations concerning the relation of faunas to environment can be made without detailed knowledge of the species.Contribution from the Scripps Institution of Oceanography, New Series No. 997. Investigation supported by a grant from American Petroleum Institute, Project 51. 相似文献
4.
钙质砂颗粒内孔隙的结构特征分析 总被引：3，自引：0，他引：3
钙质砂是一种碳酸钙含量达50%以上的海洋生物成因的颗粒状材料。从微观结构上来看,钙质砂颗粒棱角度高、形状不规则、强度低、易破碎,且颗粒含有内孔隙。内孔隙的存在深刻影响着钙质砂的压缩、剪切和破碎等力学性能。利用激光技术对南沙群岛永暑礁环礁泻湖的未胶结钙质砂颗粒进行飞秒切割,通过光学显微镜探查并获取了颗粒的内孔隙图像,借助MATLAB图像处理软件,对钙质砂颗粒的内孔隙进行了定量分析。结果表明：较大颗粒钙质砂的内孔隙断面孔隙度相对较大,小孔隙数量较多,而大孔隙所占空间则较大;对于1 mm以上的钙质砂,缝隙状内孔隙含量远低于等轴或不等轴孔隙,等轴与不等轴内孔数量大致相等。 相似文献
5.
A. Y. Kwarteng S. M. Al-Hatrushi W. K. Illenberger A. McLachlan 《Arabian Journal of Geosciences》2016,9(9):557
The nature of Al Batinah coast beach sediments in the Sultanate of Oman was investigated by the analysis of grain size and mineralogy. The beach sediments, mostly light-medium gray green, were predominantly fine sands, with the average grain size of all samples about 200 μm. Some of the particles were gravel (2–16 mm), and some were even larger pebble-size particles (16–256 mm). Some mud (sediment <63 μm) was present, mostly in the sub-tidal sediments. The majority of the samples were skewed to the coarse size with coarse tail partly due to the presence of shell fragments. Approximately 50 % of the beach sediments were quartz with different varieties based on shape and size. The second major component of beach sediment was calcium carbonate which varied from 10 to 65 %. The other components in decreasing order consisted of microbreccia, feldspar, pyroxene, igneous rock fragments, biotite flakes, and heavy minerals. The levels of carbonate were lower in NW Al Batinah coast from Harmul to Al Khaburah but were higher in the SE from Al Khaburah to Al Ghubrah. This could be attributed to either lower carbonate production or more sediment input by wadis along the north-western part of Al Batinah coast. The unique and complex nature of these sediments is largely due to the geology of the terrestrial source area in the Hajar Mountains which contains the famous Samail ophiolite complex and the weak sorting along the shoreline in these tide-modified beaches. 相似文献
6.
N. Stark R. Wilkens V. B. Ernstsen M. Lambers-Huesmann S. Stegmann A. Kopf 《Geotechnical and Geological Engineering》2012,30(1):1-14
The societal usage of coastal zones (including offshore wind energy plants, waterway deepening, beach conservation and restoration)
is of emerging importance. Sediment dynamics in these areas result in sandy deposits due to strong tidal and wave action,
which is difficult to simulate in laboratory geotechnical tests. Here, we present data from in situ penetrometer tests using
the lightweight, free-fall Nimrod penetrometer and complementary laboratory experiments to characterize the key physical properties of sandy seafloors in areas
dominated by quartzose (North Sea, Germany) and calcareous (Hawaii, USA) mineralogy. The carbonate sands have higher friction
angles (carbonate: 31–37°; quartz: 31–32°) and higher void ratios (carbonate: 1.10–1.40; quartz: 0.81–0.93) than their siliceous
counterparts, which have partly been attributed to the higher angularity of the coral-derived particles. During the in situ
tests, we consistently found higher sediment strength (expressed in deceleration as well as in estimated quasi-static bearing
capacity) in the carbonate sand (carbonate: 68–210 g; quartz: 25–85 g), which also showed a greater compressibility. Values
were additionally affected by seafloor inclination (e.g., along a sub-aqueous dune or a channel), or layering in areas of
sediment mobilization (by tides, shorebreak or currents). The study shows that the differences in in situ measured penetration
profiles between carbonate sands and quartz sands are supported by the laboratory results and provide crucial information
on mobile layers overlying sands of various physical properties. 相似文献
7.
Physical controls on sand composition and relative durability of detrital minerals during ultra‐long distance littoral and aeolian transport (Namibia and southern Angola) 
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下载免费PDF全文 Eduardo Garzanti Alberto Resentini Sergio Andò Giovanni Vezzoli Alcides Pereira Pieter Vermeesch 《Sedimentology》2015,62(4):971-996
Sediment in coastal Namibia to southern Angola is supplied dominantly from the Orange River with minor additional fluvial input and negligible modifications by chemical processes, which makes this a great test case for investigating physical controls on sand texture and composition. This study monitored textural, mineralogical and geochemical variability in beach and aeolian‐dune sands along a ca 1750 km stretch of the Atlantic coast of southern Africa by using an integrated set of techniques, including image analysis, laser granulometry, optical microscopy, Raman spectroscopy and bulk‐sediment geochemistry. These results contrast with previous reports that feldspars and volcanic detritus break down during transport, that sand grains are rounded rapidly in shallow‐marine environments, and that quartzose sands may be produced by physical processes. Mechanical wear is unable to modify the relative abundance of detrital components, including pyroxene and mafic volcanic rock fragments traditionally believed to be destroyed rapidly. The sole exceptions are poorly lithified or cleaved sedimentary/metasedimentary rock fragments, readily lost at the transition to the marine environment, and slow‐settling flaky micas, winnowed and deposited offshore. Coastal sediments tend to be depleted in relatively mobile amphibole, preferentially entrained offshore or re‐deposited in sheltered beaches, while less mobile garnet is retained onshore. No detrital mineral displays a significant increase in grain roundness after 300 to 350 km of longshore transport in high‐energy littoral environments from the Orange mouth to south of the Namib Erg, but all minerals get rapidly rounded after passing into the dunefield. Pyroxene and opaques get rounded faster than harder quartz and garnet, but sand mineralogy remains unchanged. Excepting strong transient selective‐entrainment effects, physical processes are unable to modify sand composition significantly. Selective mechanical breakdown can be largely neglected in quantitative provenance analysis of sand and sandstone even in the case of ultra‐long‐distance transport in high‐energy environments dominated by strong persistent winds and waves. 相似文献
8.
The sources of volcanic temper sands in prehistoric pottery found on low-lying raised-coral islands of Tonga have long been uncertain. The paucity of noncalcareous sand on most inhabited Tongan islands has led to the suggestion that temper was imported from the active magmatic are to the west, or even that most pottery was imported to Tonga from Fiji. The simple mineralogy of the tempers, which are composed almost exclusively of pyroxene and plagioclase mineral grains, volcanic rock fragments, and opaque ferro-magnesian oxide grains, is compatible with derivation from Tongan volcanics, but island volcanoes of Tonga lack deposits of rounded and well-sorted sands that are similar texturally to the tempers. Discovery of local placer deposits composed of volcanic sand on beaches otherwise composed of calcareous reef detritus within the Ha'apai Group of central Tonga provides a satisfactory local source for temper on the shorelines of several inhabited islands. The beach placer sands were apparently derived from reworking of thick tephra deposits that mantle the islands. Detailed compositional analysis of temper sands in numerous ancient Lapitoid potsherds from all the constituent island groups of Tonga implies that pottery making was once a widespread industry making use of locally available raw materials. Stylistically diagnostic protohistoric Fijian potsherds, found in small numbers on several islands in Tonga, can be distinguished from the older indigenous Lapitoid wares by their anomalous tempers, which contrast sharply with the Tongan volcanic temper sands. © 1996 John Wiley & Sons, Inc. 相似文献
9.
Cui Ming-Juan Zheng Jun-Jie Chu Jian Wu Chao-Chuan Lai Han-Jiang 《Acta Geotechnica》2021,16(5):1377-1389
Calcareous sands have abundant intraparticle pores and are prone to particle breakage. This often leads to poor engineering properties, which poses a challenge to coastal infrastructure construction. A study using bio-cementation to improve the engineering properties of calcareous sand is presented in this paper. The macro- and microscopic properties of bio-cemented calcareous sand were characterized by drained triaxial tests and scanning electron microscopy observations. Experimental results show that the precipitated calcium carbonate can effectively fill the intra- and interparticle pores and bond adjacent particles, thus enhancing the shear strength of calcareous sand. The special structures (e.g. abundant intraparticle pores and rough surface) and mineral components (i.e. calcium carbonate) of calcareous sand are beneficial for improving bacterial retention in soil, which leads to a relatively uniform and dense calcium carbonate distribution on the sand particle surface, exhibiting a layer-by-layer growth pattern. This growth pattern and the abundant interparticle pores would result in less effective calcium carbonate. The strength enhancement of bio-cemented calcareous sand is significantly lower than that of bio-cemented silica sand at the same calcium carbonate content, which may be caused by the differences in the following: (a) soil skeleton strength; (b) the amount of effective calcium carbonate; and (c) interparticle pore-filling of calcium carbonate.
相似文献10.
颗粒级配与形状对钙质砂渗透性的影响 总被引：1，自引：0，他引：1
钙质砂是富存于热带海洋环境（包括中国南海海域）中的一种特殊岩土介质,具有不同于陆源砂的水理性质。采用传统常水头渗流试验,首先探究了不同不均匀系数和曲率系数条件下级配对钙质砂渗透性的影响。针对钙质砂的颗粒形状特性,采用扫描电镜（SEM）与图像处理技术,引入球度 和圆度X的比值 从三维空间角度上对颗粒形状进行了定量描述。并在粒径区间、相对密实度相同的条件下,通过与福建标准砂、玻璃珠进行对比试验来考察钙质砂渗透特性,从而进一步探究颗粒形状对钙质砂渗透性的影响。试验结果表明,钙质砂渗透性随着颗粒粒径不均匀系数和曲率系数的增大而增大,符合级配对一般砂土渗透性的影响规律;钙质砂颗粒形状具有较强的结构性和不均匀性,同等密实度下钙质砂的渗透性小于陆源的石英砂。本研究获得的钙质砂渗透规律对今后南海岛礁填筑和海上平台基础工程设计具有一定的指导意义。 相似文献
11.
Dominique Ngan-Tillard Johan Haan David Laughton Arno Mulder Art Nooy van der Kolff 《Engineering Geology》2009,108(1-2):54-64
Carbonate sands undergo degradation when transported hydraulically from a dredging vessel to the reclamation site. Risks involved in the production of fines during hydraulic transport are a deterioration of the mechanical properties of the fill in certain areas of the reclamation area where these fines concentrate. In order to assess sand degradation in the concrete and road construction industry, the Micro-Deval test for fine aggregates was developed in France and Canada. During Micro-Deval testing, aggregates degrade when tumbled in a rotating steel drum with water and steel balls. In the Canadian standard, the steel charge is lower than in the French standard and balls have the diameter of the smallest balls used in the French test. During testing, the quantity of fines produced is measured. This makes the Micro-Deval test an option for assessing the degradation of sand during hydraulic transportation of slurries in the dredging industry. Three sands are tested: two shelly carbonate sands and one quartzic river sand for comparison. The carbonate sands were sampled on reclaimed land and had been subjected to hydraulic transportation in pipeline before artificial deposition. Due to differences in particle shape, the carbonate sands and the quartz sand have a different number of contacts with the steel charge in the drum of the Micro-Deval and are not exposed to the same degradation forces during testing. It was found that the quartzic sand suffers relatively much degradation as compared to the carbonate sands, despite its greater hardness and resistance to crushability. The French test appears to create turbulence that promotes floatation of the curved shells of the carbonate sands instead of shell grinding at the bottom of the drum by contact with the steel balls. Microscopic observations of sand samples before and after testing showed that the French Micro-Deval test is too destructive. The test leads to the fragmentation by impact of the quartz sands and the destruction of certain particle types that had survived hydraulic transportation. With respect to the Canadian test, microscopic examination of sand grains before and after testing shows there is still much fragmentation of quartz grains. A lower rotational speed combined with a limited steel charge made of uniform balls of a smaller diameter, reduces turbulence, shell floatability and last but not the least, impact forces. It produces the desired result: a high Micro-Deval loss for the carbonate sands in comparison to that for the quartz sands and a very limited fragmentation of the quartz grains. Once the slurry reaches its destination, the grain size distribution of the fines fraction will influence the mechanical behaviour of mixed sands. A procedure is proposed to measure the particle size distribution of the fines fraction produced during Micro-Deval testing.Field validation is needed to validate preliminary laboratory results. 相似文献
12.
Mark P. S. Krekeler Erin P. Argyilan Jill Lepp Lance E. Kearns 《Environmental Earth Sciences》2009,59(2):411-420
Constructed wetlands can be a low-cost, ecologically based technology to locally treat domestic wastewater prior to discharge.
Wetland systems implemented in the resort village of Akumal in the state of Quintana Roo, in the Yucatan Peninsula of Mexico
have been considered moderately successful over approximately 10 years of operation. Yet the wide-scale implementation of
constructed wetlands has not occurred in the region nor throughout Mexico due largely to the cost of the crushed aggregate
used in these systems. Variation in the geotechnical and mineralogical properties of 29 samples of local calcareous beach
sands collected from the tourist areas of Akumal and Tulum in the Yucatan, Mexico were analyzed and compared to those of crushed
aggregate currently used in constructed wetland systems in Akumal. Powder X-ray diffraction on beach sand samples from Akumal
and Tulum indicates that the proportion of aragonite varies from 24 to 84%, calcite varies from 7 to 38% and Mg-calcite varied
from 8 to 57% compared to crushed aggregate which consists of 0–25% aragonite and 75–100% calcite. Compared to crushed aggregate
beach sands are unimodal and have better uniformity coefficients, making them a better geotechnical choice than crushed sands
with respect to these properties. Grain-size of the beach sands is much smaller compared to that of the crushed aggregate
currently used in the constructed wetland systems in Akumal which should enhance the efficiency of the filtration of organic
matter and bacteria. The average hydraulic conductivity measurements of 0.010 and 0.016 cm/s for beach sands from Akumal and
Tulum, respectively are comparable or less than the average of 0.016 cm/s for crushed aggregate currently used in engineered
wetland systems. Yet a combination of high bulk porosity, intragranular pores, and the presence of Mg-calcite observed in
beach sands may likely result in higher dissolution rates versus the crushed aggregate. Preliminary assessment suggests that
the use of local sand may be a technical, economic, and perceptual enhancement to the systems. Still a careful and thorough
analysis of the potential environmental and aesthetic impacts of mining beach sands is necessary. 相似文献
13.
钙质砂抗剪强度特性的环剪试验 总被引：2，自引：0，他引：2
珊瑚礁沉积的钙质砂与石英砂的物理力学性质有较大差别。对取自南海岛礁的钙质砂进行了单次往返环剪试验以分析钙质砂的抗剪强度特性,试验中考虑了相对密实度和竖向应力对结果的影响,并与相同级配和试验条件下的石英砂进行对比分析。结果表明：钙质砂正向剪切时应力-位移曲线为软化型,具有明显的残余强度特性,而反向剪切时则表现为硬化型,正向和反向剪切强度基本一致;石英砂正向剪切和反向剪切均表现为软化型。钙质砂正向剪切和反向剪切残余强度与峰值强度的比值在0.75～0.93之间;石英砂正向剪切和反向剪切残余强度与对应峰值强度的比值在0.89～0.96之间。相同级配和试验条件下,钙质砂残余强度均大于石英砂,且强度比值基本保持在1.05～1.3之间。在100、200 kPa竖向荷载作用下,钙质砂0.5～2.0 mm的颗粒发生了破碎,破碎率分别为4%和6%。 相似文献
14.
Grain size and geochemical analyses have been carried out on 58 samples collected from different areas of mangrove environment
of the Egyptian Red Sea coast. The texture characteristics of mangrove sediments show that the mean size decreases in sediments
of coastal areas while increase in island sediments and the sediment type generally changes from sand to slightly gravelly
muddy sand. The sediments are composed mainly of poorly sorted, negatively nearly symmetrical and leptokurtic fine sands.
Cluster analysis showed that, distribution of gravel, sand and mud fractions is related to bottom facies and type of sediment
source. Generally, sand fraction is the main category among the three constituents. Geochemically the factor controlling the
carbonate content of studied sediments includes material supply of biogenic and terrigenous components. Therefore, sediments
of Hamata area, km 17 south Safaga, Wadi El-Gemal Island and Abu-Minqar Island are terrigenous sediments, while sediments
of km 37 north Quseir are highly carbonates. In general organic matter is higher in the mangrove sediments relative to adjacent
areas. The high organic matter in the mangrove sediments is primarily due to the high supply from primary productivity, terrestrial
and reworked sediments. Texture is the main controlling factor for the organic matter enrichment. Spatial variations in the
phosphorus content in the different studied localities are related to the sources of phosphorus to the area. In comparison,
cluster analysis indicates that phosphorus might be transported from terrestrial source to the sea through wadis draining
the excavated Upper Cretaceous phosphate rocks. Also, the abundance of phosphorus content may be attributed to phosphatization
of calcareous skeletons. Our observations provide knowledge on the physico-chemical effects and will be useful in the management
and suitable development of the areas under study. In addition it represent database in the future. 相似文献
15.
MICP联合纤维加筋改性钙质砂的动力特性研究 总被引：1，自引：0，他引：1
为了提高我国南海钙质砂地基的抗液化性能,提出利用微生物诱导碳酸钙沉积（MICP）技术联合纤维加筋技术对钙质砂进行改性处理。通过开展动三轴试验,对比分析了改性前后钙质砂试样的动应变、动孔压、应力−应变滞回曲线以及动弹性模量的发展规律和演化特征,并结合扫描电镜（SEM）试验探究了MICP和纤维加筋技术对钙质砂的联合改性机制。研究结果表明：（1）MICP技术可以明显改善钙质砂试样的抗变形与抗液化性能,相比于未胶结处理试样,仅MICP处理试样的动应变和动孔压分别降低了95.74% 和 92.46%;（2）纤维的掺入进一步提升了MICP的改性效果,相比于仅MICP处理试样,MICP和纤维加筋联合处理试样的动应变和动孔压分别降低了 74.32%和 74.18%;（3）MICP 和纤维加筋技术通过减轻试样在循环荷载作用下的循环活动强度和能量耗散、提高试样的动弹性模量和减小动弹性模量的衰减速率,从而实现试样抗变形与抗液化性能的显著提高;（4）SEM 试验分析结果表明,MICP 与纤维对钙质砂动力特性的改善具有协同作用。纤维的掺入为细菌提供了更多的附着场所,促进了碳酸钙晶体的生成量,该部分碳酸钙不仅增加了颗粒间的胶结强度,同时也将纤维固定在砂颗粒上增强了纤维网的约束作用。 相似文献
16.
混积岩一例--滇东震旦系陡山沱组砂质砂屑白云岩的成因 总被引：11，自引：2，他引：9
滇东震旦系陡山沱组顶部的砂质砂屑白云岩是一例典型的混积岩,即狭义的混合沉积。岩石中的石英砂分选好,圆度和球度高,它们时稀时密地呈“悬浮”状散布在白云石砂屑沉积物中。其产状及结构构造特征表明,它是当时的海滩砂在海进过程中被搬运到海洋中,并与白云石砂屑混合而形成的。 相似文献
17.
Samir M Zaid 《Journal of Earth System Science》2017,126(4):50
Texture, mineralogy, and major and trace element geochemistry of 26 coastal dune sand samples were studied to determine the provenance and tectonic environment of two dune fields close to the beaches of Safaga (SF) and Quseir (QS) at the Egyptian Red Sea coast. Onshore winds generate fine, moderate, moderately-well to well-sorted, coarse-skewed to near-symmetrical dune sands with mesokurtic distributions. Winds pick up and transport grains from nearby beach sands and alluvial deposits into a wide Red Sea coastal plain at the border of the beach. The mineralogical (Qt–Ft–Lt) and geochemical composition of the sands, indicate that SF and QS coastal dune sands are mature and influenced by quartz-rich sands. The average CIA values in SF and QS coastal dune sands are low relative to the range of the PAAS, suggesting an arid climate and a low intensity of chemical weathering. The SF and QS coastal dune sand samples are plotted in the recycled orogen and partly in craton interior fields suggesting recycled older sedimentary and partly metamorphic-plutonic sources. The high content of quartz with shell debris and carbonates in coastal dune sands support the recycled sedimentary beach and alluvial sand sources. The dominance of heavy minerals like amphiboles (hornblende) and biotite in the coastal dune sands also supports the effect of metamorphic-plutonic source rocks. The new tectonic discriminant-function diagrams suggest that the coastal dune sands were deposited in a passive margin of a synrift basin. The results provide a good evidence for the extension in the Red Sea rift system during Oligocene-post Pliocene, which is consistent with the general geology of Egypt. 相似文献
18.
钙质砂是一种海洋生物成因的特殊岩土介质,其颗粒形态与基本性质较一般陆源砂有很大的不同。一方面通过钙质砂及石英砂的显微镜三维成像试验,对比研究了钙质砂的三维颗粒形态特征。发现相比石英砂,钙质砂颗粒棱角更显著,轮廓趋于扁平。另一方面,对两砂进行一维压缩试验,分析了各粒组含量对钙质砂压缩特性的影响规律,并利用三维形态分析从细观上解释了钙质砂的压缩宏观特性。发现相同级配、密实度下,钙质砂的压缩性比石英砂高约60%～160%（以av1-2表征）,且粗粒组（5～1 mm）含量对钙质砂的压缩性影响最为显著;当粗粒组含量<25%,中、细粒组质量比值M一定时,存在最劣粗粒含量使钙质砂压缩性最大,且该值随着M的增大而减小,并提出了一个经验公式。 相似文献
19.
M. Mendieta-Lora R.O. Mejía-Ledezma J.J. Kasper-Zubillaga E. Arellano-Torres L.F. Álvarez Sánchez 《Chemie der Erde / Geochemistry》2018,78(3):323-339
Coastal dune (CD) and beach sand samples were mineralogically and chemically studied to assess the weathering rates in a coastal area surrounded by the Trans-Mexican Volcanic Belt (TMVB). The study area is a narrow coastal plain with sub-humid warm weather and vigorous coastal dynamics located in the Western Gulf of Mexico (WGM). Our results show that the grain size parameters remain homogeneous along nine CD and beach sites, probably due to the hydrodynamic mechanisms prevailing in the area, i.e. wind deflation, longshore currents, and waves. The minerals found in the CD and beach sands are enriched in recycled, highly corroded monocrystalline quartz (Qm), with loss of plagioclase (P) and olivine (ol), with ilmenite fractions (op) especially in the northern sites. The geochemical data show that the sands are controlled by the exhumation of the TMVB rocks composed of a high volcanic lithic content with lathwork, microlithic, and negligible vitric textures. These volcanic fractions are in agreement with the presence of lavas of calc alkaline, andesite, Na-alkaline lavas, and rhyolite tuffs derived from the TMVB. Significant Spearman Rank Correlations (SRCs) resulted from high silica, titanium, iron, magnesium, calcium, vanadium, chromium, cobalt, associated with the presence of Qm, ilmenite, clinopyroxene, shell fragments, and volcanic lithics. Monocrystalline quartz enrichments, compared to a quartz dilution effect (<Qm; < Qm) at the northern and southern beach sites, reflect the vigorous coastal dynamics. The presence of ilmenite lag deposits in the northern sites indicate that high energy hydrodynamic conditions prevail at the site. The rare earth element (REE) patterns support the mineralogical and compositional framework of the CD and beach sands as part of the TMVB exhumation. We used various chemical indices such as the Chemical Index of Alteration (CIA), the Chemical Index of Weathering (CIW), the Plagioclase Index of Alteration (PIA), and the Weathering Index of Plagioclase (WIP). The WIP values reflect the depletion of mobile elements such as Ca, Na, K, and enrichment of Qm at the northern beach sites, e.g. the Istirinchiá site. The CIA/WIP ratio of 2.13 indicates intermediate weathering under warm climatic conditions and recycling of CD and beach sands. 相似文献
20.
为了掌握南海钙质砂压缩变形特征及其微观机制,对3种不同粒组(S1:1.43~2mm、S2:0.5~1mm、S3:0.5~2mm)的钙质砂进行100~3200kPa压力范围的压缩试验,利用自制的砂土微观结构提取装置和图像处理软件(PCAS)获得并分析了钙质砂压缩过程中微观结构。结果表明:(1)钙质砂的大小、形状和级配对颗粒的破碎具有显著影响,当压力较低时(＜800kPa),粒径较大的S1组以砂颗粒棱角破碎为主;粒径较小的S2组没有明显破裂,相对规则的颗粒形态使S2粒组在该压力范围内主要因颗粒的滚动与重分布导致压缩;级配良好的S3组除部分低宽度断肢状颗粒外其余大小、形态颗粒无明显破裂。(2)当压力较大时(＞800kPa),S1组钙质砂逐渐转向以颗粒的整体破坏为主的破碎形式;S2、S3两组试样随着密实度的提高,砂颗粒的破坏以整体破碎为主。基于对破碎过程中试样微观结构变化的提取与分析,总结并提出了控制钙质砂颗粒破碎的4种接触模式:点-线接触、线-面接触、面-面接触和复合接触,可用于判断不同条件下的颗粒破碎形式。最后,讨论了钙质砂在破碎过程中颗粒几何参数的变化。 相似文献