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1.
Abstract. The occurrence, lithology, and stratigraphic setting of buried manganese deposits and associated host sediments in cores obtained on Legs 123–210 of the Ocean Drilling Program (ODP) are examined in order to establish the formative environment and conditions of preservation. Fossil manganese nodule and crusts are found to have formed or deposited throughout the period from 100 Ma to the present, with an additional example of formation near 137 Ma, suggesting that the deep-sea environment has been oxic and suitable for the formation of manganese nodules and crusts since the Cretaceous. Many manganese nodules and crusts occur on horizons corresponding to hiatuses in sedimentation or periods of slow sedimentation, consistent with the environment in which modern nodules form (sedimentation rate less than 10 m/m.y.). Sediments overlying the fossil nodules and crusts are oozes or biogenic sediments with sedimentation rates of 1–18 m/m.y. Low total organic carbon (<0.1 wt%) in the overlying sediments and high sulfate content (>25 mM) in interstitial water around the manganese horizon suggest that no strong reduction occurred within the overlying sediments. Coverage by biogenic sediments containing only small amounts of organic matter is therefore considered important for the preservation of manganese nodules and crusts. Manganese carbonate occurs sporadically as nodules, concretions or thin layers in various host sediments, including clay, calcareous ooze and siliceous ooze with sedimentation rates of 6–125 m/m.y. Hiatuses are rare around the host sediments of manganese carbonate. Higher total organic carbon (0.2–1.8 wt%) in the host sediments and lower sulfate content (0–25 mM) in interstitial water around the manganese carbonate horizon suggest that reduction in association with decomposition of organic matter would have proceeded in the host sediments. 相似文献
2.
Pascal Kindler 《Sedimentary Geology》1992,80(3-4):319-329
Sedimentological and petrographic study of Holocene deposits in the Eastern Bahamas shows that sedimentation occurred episodically during this period of continually rising sea-level.
The Holocene stratigraphic record exposed on the islands of San Salvador, Lee Stocking and Cat consists of two distinctive units separated by a paleosol: (1) 5000 year-old oolitic eolianites deposited when sea-level was lower than today, and (2) 3000 to 500 year-old bioclastic paleo-beaches and dunes that are congruent with the present stand of sea-level.
A five-stage model that reconciles intermittent sedimentation pattern with continuous sea-level rise is presented. Pre-Holocene topography and changes in the rate of the transgression seem to regulate local4 hydrodynamic conditions, which in turn control onset and offset of sedimentary processes.
This Holocene example of episodic sedimentation during an uninterrupted transgression should be considered when studying ancient discontinuities that are systematically interpreted in terms of relative sea-level fall. 相似文献
3.
湖南省锰矿资源丰富,类型多样,沉积型锰矿是最重要的类型,主要沉积成锰期集中在早南华世大塘坡期、中奥陶世烟溪期及晚二叠世孤峰期。通过对三个主要成锰期代表性锰矿石电子探针分析显示,三个主要成锰期所成锰矿床,矿石组分类似,组成矿石的锰矿物主要为锰的碳酸盐,包括菱锰矿、钙菱锰矿、镁菱锰矿、锰白云石、锰方解石等。三个主要成锰期代表性锰矿石及地层稀土元素地球化学标准化参数与配分模式显示,各成矿期含锰地层与锰矿石之间无显著差异,暗示了它们是相似的沉积环境下形成的产物,为正常沉积与热水沉积的复合。一方面,各成矿期岩、矿石稀土元素总量中等偏高,表现为正常沉积物的稀土元素特征。另一方面,在北美页岩标准化配分曲线上,呈现出水平或重稀土相对富集的左倾配分曲线,Ce的负异常,又是典型热水沉积成因呈现出的稀土元素地球化学特征。δCe异常特征,指示了成锰作用处于波动的缺氧还原/氧化沉积环境。 相似文献
4.
The English Channel and its Western Approaches constitute a 700 km long epicontinental sea located in a temperate environment and in a tectonic setting where subsidence is minimal. A sedimentological survey of this region reveals quite distinct provinces: a central sector (Western Channel) where predominantly bioclastic sediments are widely represented, bounded by two mainly terrigenous-rich zones, the outer terrace of the Celtic Sea and the Eastern Channel. Lateral sedimentary variations of decreasing grain size are interpreted in terms of current velocity patterns. The various types of such sequences may relate to the degree of mixing of older lithoclastic sediments with the Holocene bioclastic supply. A scenario for the evolution of the recent sedimentation of this epicontinental sea is presented. Starting from a permanent marine zone—at least since the Würm period—that bounds the Bay of Biscay, the Holocene transgression progressed over the English Channel. In the Western Channel earlier terrigenous deposits were gradually overlapped by bioclastic sediments that originated on the pre-Mesozoic rocky substratum and which were particularly extensive off the Armorican Massif. In the subsequently submerged Eastern Channel the pre-Holocene clastic source has undergone comparatively less modification and still crops out in most of the area. With the opening of the Straits of Dover, at about 9000 yr BP, submersion was complete and new hydrodynamic conditions developed as the eustatic level stabilized. The present sediment distribution is in harmony with the hydrodynamic setting except on the southern rise of the Celtic Sea where both morphology and sedimentary patterns still largely reflect pre-Holocene conditions. 相似文献
5.
在甘孜—理塘结合带内理塘县中木拉乡附近发现锰结核。通过地质填图和综合研究,该锰结核产于结合带内瓦能蛇绿混杂岩组中的黑色粉砂质板岩中。其沉积层序为玄武岩→硅质岩→含锰结核粉砂质板岩。锰结核主量元素具有高Mn、低Fe、Si、Ca的特点,其中Mn含量为42.19%,高出大洋锰结核平均值1.83倍,Mn/Fe值较高,达8.1。锰结核中除Cr高于大洋锰结核平均值2～7倍外,多数微量元素低于大洋锰结核平均值。稀土元素具有较明显的Ce正异常,稀土总量、轻重稀土分异程度、Eu异常特征与混杂岩中的砂岩、硅质岩近似,而与玄武岩差别较大。该锰结核产出于大陆边缘构造环境,火山活动微弱,代表甘孜—理塘洋扩张到最大程度时的沉积。其时甘孜—理塘洋规模仍是有限的。 相似文献
6.
南海北部陆坡高速堆积体沉积物稀土元素特征及其物源意义 总被引：2，自引：0，他引：2
对南海北部陆坡MD05-2905站9个沉积物样品稀土元素进行分析,结果显示MD05-2905站沉积物中稀土含量总量(ΣREE)变化范围较大,其分布范围为60.66×10-6～350.37×10-6,平均值为174.59×10-6,其中全新世样品的稀土含量总量明显低于末次冰期样品,其球粒陨石分布模式与上地壳基本一致。对比发现,其ΣREE平均值相对接近中国黄土和珠江口,而与深海粘土中稀土元素的丰度相差较大,说明其主体可能来自陆源。稀土元素分馏参数δEu和δCe以及富集因子(EF)和判别函数(DF)揭示南海北部MD05-2905站沉积物与黄土、珠江口和台湾浅滩都有联系,显示了多物源多传输方式的特征。另外发现富集因子(EF)和判别函数(DF)数值在末次冰期时期与全新世时期差别相对较大,末次冰期时期黄土、珠江口和台湾浅滩的DF值都远远小于全新世时期,这可能反映末次冰期时黄土、珠江口和台湾浅滩对南海北部的物源贡献更大,也反映末次冰期与全新世期间各个物源供给/传输方式可能发生变化。 相似文献
7.
E. S. Bazilevskaya 《Geology of Ore Deposits》2006,48(2):134-143
The current concepts of two competing sources of manganese deposited as oceanic Fe-Mn ore are reviewed and assessed critically. A new solution of this problem proposed in this paper is a further development of fundamental works by N.M. Strakhov in the light of new facts and with allowance for geological, geochemical, and geohistorical data. It has been concluded that terrigenous material removed from land serves as a main source of manganese fixed in oceanic Fe-Mn ore. The history of sedimentation and nodule formation in the World Ocean lasted for more than two billion years. Manganese has been supplied to recent bottom sediments from both present-day and older sources. The closed geochemical cycle of Mn circulation in the ocean is intimately related to its circulation in the hydrosphere. Seawater is oversaturated with Mn and serves as its immediate source for ore deposition and elevated concentrations in bottom sediments affected by hydrothermal solutions or other manifestations of endogenic activity. Seawater is a repository for Mn, where this element is retained during global cataclysms, which have repeatedly occurred in geological history. 相似文献
8.
前寒武纪时期铁矿形成过程中铁物质如何迁移的研究,已取得了众多科研成果,但仍有些问题未得到很好的解决。尤其是对陆壳来源性铁矿床(非Algoma类型)的成因,仍然具有诸多争议,焦点主要集中在铁迁移问题。笔者以朝鲜半岛龙渊铁矿床为例研究了铁介质形成和运输的问题。首先通过铁矿石的地球化学研究和前人研究结果的考察,发现此铁矿床不属于Algoma类型,而是在强酸性介质条件下陆壳物质风化、移动和沉积而形成的。那么为什么会出现如此强大的酸性环境条件呢？为了揭示这一点,对在当时环境下把水的性质能够变成酸性的物质进行了热力学计算。研究结果表明,当硫化物如黄铁矿风化时,形成了能够使铁源物质风化和迁移的介质。这些结果也符合这样一个事实,即目前从富含硫化物地层淋沥的水的pH值小于3.5,并且铁含量远高于非硫化物类型的地层。本次研究结果表明,陆壳来源的铁矿床形成过程中,不能忽视硫化物的风化作用。 相似文献
9.
云南开远地区中三叠统法郎组是区内唯一的含锰地层,含锰层主要位于法郎组一段和二段粉砂质泥岩内,主体呈北东走向,与地层产状一致,局部受构造运动影响发生变化,锰矿地质特征可与斗南锰矿进行对比。通过对区内法郎组地层、岩相古地理及锰矿成矿地质特征进行研究,初步总结了锰矿成因,认为区内锰矿受地层、构造、古地理环境及锰质来源等控制。锰质主要来源于海盆周围的古陆及火山活动,构造控制古地理环境,环境控制锰矿的形成与分布。 相似文献
10.
Iron and manganese oxide coatings are actively forming on stream substrates in the White Oak Creek watershed in East Tennessee. Although oxidizing conditions are required for Fe-Mn oxide precipitation, coatings accumulate only if dissolved iron and manganese exceed 50 μg/L. Below this, coatings are lost by abrasion as fast as or faster than they form. Annual rates of formation of 3 mg/g on substrate (gravel) were observed. Manganese is dissolved from coatings between Eh values of 100 to 300 mV and below 1 mg/L dissolved O2 at pH 6.5 to 7.5. Iron oxides can be precipitated under these conditions.Uncontaminated gravels with oxide coatings (composed of illite, quartz, and feldspar) adsorbed radionuclides rapidly from waters below MPC (Maximum Permissible Concentration) levels. Contaminated gravels placed in uncontaminated waters lost 60Co by abrasion in oxidizing conditions and by dissolution of manganese coatings in reducing conditions. Exchangeable 90Sr was completely lost after one month whereas nonexchangeable 90Sr was lost more slowly; 137Cs was totally retained by the gravels. Gravels such as these can be used to monitor the radionuclide content of waters in the environment. 相似文献
11.
A Holocene lake sediment record is presented from Lake N14 situated on Angissoq Island 15 km off the main coast of southern Greenland. The palaeoclimatic development has been interpreted on the basis of flux and percentage content of biogenic silica, clastic material, organic material and sulphur as well as sedimentation rate, moss content and magnetic susceptibility. A total of 43 radiocarbon dates has ensured a reliable chronology. It is argued that varying sediment composition mainly reflects changing precipitation. By analogy with the present meteorological conditions in southern Greenland, Holocene climate development is inferred. Between 11 550 and 9300 cal. yr BP temperature and precipitation increase markedly, but this period is climatically unstable. From 9300 yr BP conditions become more stable and a Holocene climatic optimum, characterised by warm and humid conditions, is observed from 8000 to 5000 cal. yr BP. From 4700 cal. yr BP the first signs of a climatic deterioration are observed, and from 3700 cal. yr BP the climate has become more dry and cold. Superimposed on the climatic long‐term trend is climate variability on a centennial time‐scale that increases in amplitude after 3700 cal. yr BP. A climatic scenario related to the strength and position of the Greenland high‐pressure cell and the Iceland low‐pressure cell is proposed to explain the Holocene centennial climate variability. A comparison of the Lake N14 record with a terrestrial as well as a marine record from the eastern North Atlantic Ocean suggests that the centennial climate variability was uniform over large areas at certain times. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
12.
13.
文章对内蒙古中部辉腾锡勒湖相沉积剖面及好鲁库风成砂-古土壤剖面全新世地层的沉积特征及~(14)C、OSL测年结果进行了综合论述,根据岩性特征及测年结果确定了全新统的底界。对内蒙古中部全新统沉积序列进行了系统分析,并将其划分为3段:全新统下部(开始于12.5~11.4 ka,结束于8.2~7.0 ka)辉腾锡勒为灰黑色黏土、粉砂质黏土,沉积特征指示由冲积相转变为湖相沉积,湖面开始上升;好鲁库沙丘主要为中粗砂,为风成砂堆积。全新统中部(开始于8.2~7.0 ka,结束于4.5~2.3 ka)辉腾锡勒为灰褐色粉砂质黏土,富含有机质及双壳和螺类化石,为典型湖泊相发育阶段;好鲁库沙丘发育黑色砂质古土壤,气候温暖湿润。全新统上部(开始于4.5~2.3 ka)辉腾锡勒为黏土质粉砂,含植物碎屑,为湖滨相沉积,指示湖泊开始退缩;好鲁库沙丘为灰黄色中粗砂,沙丘重新活化,气候干旱。 相似文献
14.
A gravity core collected from the upper slope of southwest of Quilon at a water depth of 776 m (Lat: 8°12′263″N, Long: 76°28′281″E)
was analysed for texture (carbonate free), calcium carbonate and organic carbon. Variation in silicic fraction seems to be
controlled by silt, i.e., enrichment from 15 ka BP to 10 ka BP and then constant in Holocene. Below 15 ka BP, the silicic
fraction gets depleted compared to the Holocene section with a minimum around 21 ka BP. Clay content remains nearly constant
except in the Holocene where it shows an enrichment. Carbonate content of less than 63 micron when computed by subtracting
coarse fraction content from the total carbonate suggests that the total carbonates are mainly concentrated in the finer fraction.
All these carbonate phases show an inverse relationship with silicic fraction except in Holocene. Below 15 ka BP, CaCO3 dominates in sediments comprising more than 65%, such an increase is also seen in the coarse fraction. Coarse fraction from
these sections contains abundant nodular type aggregates encrusting small forams. This period is marked by a high sedimentation
rate comparable to Holocene. These parameters suggest that the productivity and precipitation have increased in the Holocene
due to the intensification of the southwest monsoon. During the last glacial maximum and early deglacial period the high sedimentation
rate indicates redeposition of the carbonates from the existing carbonate lithofacies situated between Quilon and Cape Comorin
probably due to the slope instability. 相似文献
15.
A. M. Kos 《Australian Journal of Earth Sciences》2013,60(5):621-632
McEachern's Deathtrap Cave (G—49/50) is located in the Lower Glenelg region of southeastern Australia and records a Late Pleistocene to Holocene sedimentary record that has been directly influenced by surface processes during its formation. The sedimentary sequence contained within the cave is divided into lower, middle and upper sequences consisting of eight facies. The lower sequence represents the earliest phase of sedimentation, and groundwater fluctuations during the Last Interglacial period resulted in its erosion and redistribution deeper into the cave system. A decrease in the magnitude and frequency of flood events in the cave during the formation of the middle sequence indicates increasingly drier surface conditions prior to the Last Glacial Maximum. The middle sequence has a minimum age of 9840 ± 290 a BP. Moving sand sheets during the Last Glacial blocked the entrance to the cave allowing flowstones to develop on the cave floor. The surface environment surrounding the cave was probably not as dry as contemporaneous inland sites because sedimentation continued to be dominated by flowing water during this period. Holocene sedimentation is represented by the upper sequence and reflects wetter cave conditions between 7680 ± 160 a BP and 5700 ± 110 a BP. A major phase of sediment accretion occurs after 5700 a BP and correlates to a phase of dune instability in the Lower Glenelg region. Flowing water remodelled the sediment cone sometime after 2240 ± 100 a BP, which represents a period of increased surface runoff, although it is not clear whether this is due to climatic or anthropogenic influences. 相似文献
16.
Peter Houben Norbert Kühl Rainer Dambeck Jan Overath 《Boreas: An International Journal of Quaternary Research》2013,42(4):947-958
We document the Lateglacial to Holocene sedimentation and vegetation history of a small, infilled crater landform in the West‐Eifel Volcanic Field (WEVF; western Germany). We analysed geomorphological landform change, sedimentological and geochronological data, pollen, and plant macrofossils of a 16‐m‐long sediment core from the Eichholz Maar (EHM). The EHM erupted between ～20 and 15 ka ago (MIS 2). Lacustrine siliclastic infilling was completed about 7500 years ago. Lateglacial rates of sedimentation are generally 2 to 5 times higher than in other maar lakes of the WEVF. Local factors, therefore, overprint the relative efficacy of the climate‐controlled variance of sedimentation rates at the Lateglacial/Holocene transition. The predominance of local factors relates to inherent geomorphological process–response mechanisms that were triggered by the EHM eruption. Rapid crater infilling and its completion by the mid‐Holocene are attributed to a combination of small storage capacity and geomorphological activity. A late Boreal interval of significant lake‐level fall can, however, be attributed to a period of continental‐scale climate change as recorded in other European lacustrine settings. Our findings highlight the importance of utilizing geomorphological information to reveal the relative significance of local controls as opposed to climate control when investigating small‐sized lake settings with active sediment supply systems. 相似文献
17.
《Quaternary Science Reviews》1999,18(4-5):541-548
Three main stages can be distinguished in the sedimentary development and geomorphological formation of the present delta plains on the Aegean coast of Turkey. The Early Holocene is characterized by post-glacial transgression and dependent sedimentation. The Middle Holocene was the period when sea level reached the present level, and apart from small fluctuations, stopped rising. Alluviation and deltaic progradation were prevalent during this transition period from marine to terrestrial environments. As for the Late Holocene, deltaic progradation slowed down and delta plains were covered by floodplain sediments. These characteristics can be observed in the same sequence throughout the Aegean coast of Turkey. 相似文献
18.
广西宜州市龙头锰矿是我国石炭系锰矿的典型代表。2014~2016年,中国冶金地质总局广西地质勘查院在南丹-宜州地区开展矿产地质调查工作取得了新的突破,圈定了弄竹、塘岭找矿靶区。两个靶区经后续广西地勘资金勘查,在里苗-塘岭一带估算锰矿资源量达8000多万吨,成为我国石炭系最大的锰矿。为了揭示该矿床的成矿机制,本文从区域成矿地质背景、矿床地质特征、构造环境、岩相古地理、锰质来源、矿化富集规律等方面分析了其控矿因素,圈定了成锰盆地边界线,建立了成矿模式。认为里苗-塘岭锰矿床是受NE向同沉积断裂控制的海底热水沉积矿床,是走滑拉张断陷-含锰热水-台沟相沉积环境耦合作用的产物。 相似文献
19.
岱海两支岩芯独立的高分辨率代用指标序列揭示了季风/干旱过渡区全新世适宜期的气候环境特征。研究表明,在约7.9~3.5kaB.P.期间,岱海流域出现植被繁盛、生产力相对增强和降水丰富的状况,显示气候条件相当适宜;而在约10.0~7.6kaB.P. 期间,流域气候以相对干燥为特征。这与早先认为的岱海流域全新世初期为适宜期,且降水丰富的结果明显不同。比较岱海与鄂尔多斯-内蒙古高原中部其他湖沼记录,季风/干旱过渡区的气候适宜期基本集中在约8~3kaB.P.的全新世中期,尽管各记录在适宜期的起止时间、表现特征上存在一些差异。这些差异的产生,一方面可能体现了不同的局地地形、植被、水文条件等对区域水热条件的不同反馈,另一方面则可能暗示不同的沉积序列、测年材料之间难以进行精细的对比。沉积序列的连续性、稳定性及高分辨率、测年材料的适用性是进行全新世气候、环境特征研究的前提。 相似文献
20.
湘中奥陶纪沉积锰矿带位于湖南省安化县、桃江县、宁乡县境内,呈近EW向展布,矿带内锰矿以质量好而著称。该成矿带的成锰沉积盆地受控于加里东期张性断裂系统,为一断陷盆地。盆地内发育一组NW向同沉积断裂,形成了一系列断陷槽,控制了沉积岩相的分布。锰矿主要产于盆地中心亚相的黑色页岩夹碳酸锰矿微相内。据矿带中锰矿的地质和地球化学特征以及微量元素和碳、氧、锶同位素组成,笔者认为,该锰矿属于热水沉积成因。综合对比表明,该成矿带具有良好的成矿条件和值得注意的资源潜力,有可能发展为大型锰成矿带。 相似文献