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1.
程广芬 《中国海洋大学学报(自然科学版)》1988,(1)
厌氧沉积的有孔虫组合中,底栖有孔虫主要由Bolivina诸种和Buliminella tenuata组成,同时含有少量厌氧标志种Suggrunda eckisi;浮游有孔虫中以Globigerrina bulloides和G.quingueloba为数较多。底栖有孔虫与浮游有孔虫数量相比,浮游有孔虫数量很少。 相似文献
2.
湖泊沉积物年纹层的研究方法及其意义 总被引：12，自引：4，他引：8
文章总结了前人对湖泊沉积物年纹层类型的划分,并根据年纹层的形成过程和组分特征分为3个大类,即碎屑年纹层、生物成因年纹层(如硅藻年纹层等)和化学成因年纹层(如方解石年纹层、菱铁矿年纹层、黄铁矿年纹层、蒸发盐年纹层等)。介绍了目前应用于湖泊沉积物年纹层研究的主要方法和技术包括:1)新鲜沉积物表面照相、X射线照相技术;2)光学显微镜观察;3)数字化图像分析;4)扫描电子显微镜技术等。而岩相学大薄片是目前年纹层研究工作中应用非常广泛的材料,对目前制作大薄片比较普遍采用的快速冷冻-冷冻干燥和水-丙酮-环氧树脂交换这两种方法进行了介绍并比较了各自的优劣。湖泊沉积物年纹层研究的古环境意义主要体现在两个方面,一是提供了高精度的纹层年代学时间标尺,在诸如气候突变事件的时限、大气14C浓度变化、火山灰层定年、古地磁场长期变化主曲线重建等方面有重要意义;二是年纹层性质研究如年纹层厚度和年纹层微相变化本身所蕴藏的高分辨率古气候环境变化信息,在太阳活动周期、ENSO等气候事件的研究中也有重要意义。最后,文章简单介绍了我国东北龙岗火山区四海龙湾玛珥湖沉积物中年纹层的特征并展望了其研究潜力。 相似文献
3.
正1 Introduction Annually laminated(varve)sedimentary deposits are considered as one of the most important archives,since they offer precise temporal information(years)in combination with high time resolutions.Bottom sediments of the lakes contain detailed geochemical information on 相似文献
4.
对东北四海龙湾玛珥湖SHLF6孔纹层沉积物的137Cs放射性测量表明:137Cs比活度的最大值出现在55cm处,对应于1963年世界原子弹试爆高峰期。纹层计年表明0～6cm共有35个纹层层偶。从75cm到65cm,137Cs比活度从256±009dpm/g急剧增加到1868±017dpm/g,可能65cm对应于1954年。通过测量226Ra子核214Pb和214Bi（能量为295keV,352keV和609keV）放射的光子数获得226Ra比活度数据,然后求得过剩210Pb比活度（210Pbuns）。210Pbuns比活度随深度增加而呈指数衰减,其异常波动可能与人类活动以及沉积速率变化有关,例如55cm处210Pb比活度较高,与137Cs的峰值对应,这可能与1963年前后人工核实验的高峰有关,因为核试验不仅产生137Cs,而且可以产生208Pb和210Pb;45cm处210Pb比活度较低,而226Ra较高,可能与人类活动加剧,导致沉积速率增加有关。根据210PbunsCRS模式,SHLF6孔0～19cm的平均沉积速率为20mg/cm2·a,或约为011cm/a。210Pb测年数据与137Cs时标及纹层计年均有很好的一致性。四海龙湾玛珥湖发育的纹层为年纹层,可以建立高分辨率时间序列。 相似文献
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纹泥反映了湖相沉积物中特有的沉积韵律,是气候的季节变化和年际变化的产物。山西榆社张村地区上新世晚期的湖心相沉积中发育了极为完好的纹泥剖面。纹泥深浅相间形成清晰的纹理,分别代表夏秋和冬春。一深一浅组成一对,代表一年。纹泥层的单层厚度平均为0．12～0．25mm／条,薄者＜0．1mm／条,厚者可达0．3mm／条。暗色纹泥层的厚度大于浅色纹泥层。暗色纹泥的有机质含量丰富,木本植物孢粉占优势,同时CaO的含量低;浅色纹泥恰好相反。湖相纹泥具有建立高分辨率时间标尺和环境演化序列的特殊优越条件。 相似文献
6.
Accurate determination of the thicknesses of 2717 biogenic carbonate varves from a Swiss lake (Soppensee), spanning the period from about 9740 to 6870 calendar yr BP, allowed the computation of a power spectrum using classical FFT methods. The presence of pronounced peaks at 40-50 and 20-25 yr agrees with the results of other studies on varve thickness and D14C which have been interpreted as indicating an association between solar forcing and varve thickness. The presence in the Soppensee varve series of an additional peak at 10.9 yr, corresponding to the Schwabe sunspot cycle, lends further support to this hypothesis. Because the Soppensee varves are of biogenic rather than clastic origin, any influence fluctuations in solar irradiance may have had on sedimentation rates is likely to have been exerted via primary production. 相似文献
7.
衡阳市郊五马归槽始新世鱼化石保存在黑色湖相纹层中。根据纹层序列的对比,发现该地的鱼化石均为同一层位;根据鱼化石在纹层序列中的具体位置及鱼化石的保存状况,笔者推测鱼群的死亡并非由于季节更替,而是由气候干旱引起的湖水盐度升高所控制;黑白纹层的变化是由大气降雨所致。 相似文献
8.
The discovery of annually laminated sediments (varves) from shallow Sugan Lake in inland arid China and their paleoclimatic significance 总被引：1，自引：0，他引：1
Detailed examination of sedimentary cores retrieved from Sugan Lake in the northern Qaidam Basin of northwest China’s Tibetan Plateau reveal that fine laminated beddings form in the sediments where water depth exceeds 3 m. Seasonal surface sediments trapped at the bottom of the lake suggest that sediments deposited during summer and autumn are mainly light colored monohydrocalcites, while those deposited in winter are dark organic matter, indicating that varve layers form under modern limnological conditions. Continuous varve sediments comprising four types have accumulated in the upper 5.5 m of Core SG03I from the center of the lake. All types exhibit clear seasonality indicative of annual deposition. Varve counts correspondence with 210Pb dates on recent sediments in the upper core suggest the continuous varves of the upper 5.5 m of the core formed in the late Holocene (2670 a BP). The Sugan Lake varve sequence is the first demonstration of annually laminated sediments re-ported in arid western China. 相似文献
9.
Carbonate deposits, which unconformably overlie the Palaeozoic bedrocks, extensively occur in the base of the Tertiary lake succession in the half‐graben Shulu Sag, central Hebei Province, North China. This study focuses on the basal carbonate successions on the hinged western slope. Based on seismic, borehole and core data, nine facies are identified in the carbonate successions, and are further grouped into five facies associations: mid‐proximal alluvial fan, distal alluvial fan, fan fringe, moderately deep lake and deep lake. The first two facies associations constitute alluvial fans formed by debrisflows at the edge of lake and are dominated by mounded‐ to lobate‐shaped, matrix‐ to clast‐supported carbonate rudstones with minor calcretes in the lowermost rudstone units and basinward increase in interfingering with lacustrine carbonate facies. The fan fringe, moderately deep lake and deep lake associations are dominated by pebbly carbonate arenites (or rare carbonate arenites), calcisiltite‐calcilutites, and varve‐like calcilutites, calcareous shales and oil shales, respectively. Widespread occurrences of fine‐grained limestone packages containing varve‐like organic‐rich laminations, minor authigenic glauconite and pyrite, and planktonic and plant fossils suggest a meromictic, anoxic deep lake under a semi‐humid to humid climate, probably with a connection to marine basins. Similarities in lithology and fossil assemblages (e.g. trilobites) of lithoclasts with those of the Mid‐Upper Cambro‐Ordovician bedrock carbonates suggest that the clastic and dissolved carbonate loads were sourced from this Lower Palaeozoic catchment, and shed off the surrounding highlands into the basin. These carbonate facies associations represent the lake lowstand and transgressive deposits of the basal third‐order sequence (Ia) in which the highstand deposits are composed of lacustrine siliciclastics. During the lake lowstand stage (or initiation of basin‐filling) under an intermediate climate, carbonate alluvial fans occurred mostly subaerially at the bottom of the hinged slope with a narrow, shallow lake zone basinwards, and locally were perched within the palaeovalley on the mid‐upper slope. During the transgressive (deepening) stage under a semi‐humid to humid climate, carbonate alluvial fans became smaller in size and episodically stepped backwards upon the slope, with greatly expanded and deepened lake. Nevertheless, the carbonate system was switched to an exclusively siliciclastic system during the highstand stage. The exhumation and erosion of the Mid‐Lower Cambrian bedrock dominated by siliciclastics was probably the cause due to further uplift of the drainage basin. All these facts indicate that the carbonate deposition in the Shulu Sag was mostly controlled by the interactions of tectonics, climate and provenance. 相似文献
10.
年纹层发育的湖泊沉积物可以提供独立的、绝对定年的时间标尺,为重建高分辨率的区域古地磁场长期变化主曲线提供了难得的条件;基于长而连续的湖泊沉积物年纹层时间标尺建立的区域磁偏角和磁倾角长期变化参考曲线大大增强了岩芯对比和古地磁定年结果的精确性。此外,满足特定条件的湖泊沉积物还可以提供古地磁场强度长期变化的记录并有助于反映宇宙成因核素(如^14C、^10Be等)产生速率的变化、太阳活动等信息;目前,湖泊沉积物纹层年代学时间标尺及古地磁研究程度较高的主要是瑞典、芬兰和北美一些地区,区域古地磁场长期变化主曲线的地理分布并不均匀,因此在全球范围内寻找长序列的、连续的年纹层发育的湖泊进行古地磁研究可以更好地理解仪器观测记录以前的地磁场行为。 相似文献