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71.
In laboratory experiments, the influence of inflow and outflow sequences on the behavior of fine sedi-ment was investigated. The experimental set-up consisted of two interconnected rectangular basins, between which water was moved back and forth. Suspended sediment concentration in the main basin as well as the sediment exchange rates were derived from turbidity measurements.The suspended sediment ratio, SSR, and sediment exchange rates (influx sediment rate, ISR, and evacuated sediment rate, ESR) were measured. In twenty test runs, a parametric study on the magnitude and frequency of inflow and outflow cycles, the relative duration between inflow and outflow sequences, the initial sediment concentration, and the intake position was done. An initial test with stagnant water described the set-tling behavior of fine sediment and served as a reference scenario.The test results show that settling of fine particles near the intake/outlet structure can be considerably reduced by the nature of the inflow and outflow sequences. High cycle magnitude and frequency lead to maximum suspended sediment ratio in the system. For low discharges, the evolution of suspended sediment concentration cannot be directly correlated to the inflow and outflow cycles. However, compared to"no operation"conditions, the suspended sediment ratio could be increased by 10%to 40%locally. For high discharge, the evolution of suspended sediment concentration correlated with discharge cycles and suspended sediment ratios between 50%and 80%higher than for stagnant water could be achieved. Similar ratios could be obtained when the intake is located closer to the bottom or to the free water surface.Meanwhile, the overall sediment balance remained in equilibrium over the test period, indicating that the influx and evacuated sediment rates are not significantly influenced by the inflow and outflow cycles. 相似文献
72.
南迦巴瓦地震台网完整地记录了米林M6.9地震发生的全过程.本文利用南迦巴瓦地震台网的连续波形数据对米林地震序列进行了研究.南迦巴瓦台网的定位结果显示,米林主震位于29.89°N,95.04°E,震源深度为16.7km,余震序列呈NW向展布,分布在南迦巴瓦峰和加拉白垒峰连线的东北部靠近帕隆—旁辛断裂.经计算,本次地震的h值为1.26,b值为0.84,综合序列衰减情况分析,本次地震属于主震—余震型地震.米林地震前,南迦巴瓦峰地区地震活动表现出明显的时间不均匀性,自研究区1992年ML6.2地震以来,研究区每12年左右发生一次ML6.0级以上地震,2017年至米林地震前,研究区6月前与6月后的地震活动差异很大,6月后的地震活动在频度上要明显强于6月前.空间分布上,米林地震震中附近为研究区地震活动性最强的区域,属于雅鲁藏布江断裂和帕隆—旁辛断裂交汇区域. 相似文献
73.
首都圈东部地区震群序列性质判定 总被引:1,自引:1,他引:0
采用传统方法和数字地震学方法(视应力),对首都圈东部地区2009-2017年发生的震群序列性质进行分析,分析结果表明:①使用传统方法不能确定震群序列性质,可以利用视应力方法进一步分析,该方法能够反映每个震群应力场的变化特征,可以进行异常性质判别;②通过2种方法的对比分析,可以提高震群序列异常性质判定结果的科学性和可信度,为后续地震活动趋势提供有力的参考依据。对2种方法进行震例检验,可知后续地震一般为中等以上地震,在震群(具有异常性质)发生1-7个月后发震,发震位置在震源区附近。 相似文献
74.
恩平凹陷恩平组下段成岩过程分析与储层动态评价 总被引:1,自引:0,他引:1
恩平凹陷恩平组下段现今埋深超过3 800 m,处于中成岩B期,客观评价恩平组下段的勘探潜力及有利目标是深入勘探的重要前提。通过大量铸体薄片、普通薄片、扫描电镜等分析,划分了恩平凹陷恩平组的成岩序列,找出了影响储层物性的主控成岩作用,认为压实作用是孔喉衰减的主导因素,有机酸性流体溶蚀作用是孔隙度局部回升的主要原因。根据恩平凹陷埋藏史、地热史、成岩过程分析建立了恩平组的孔隙度演化模式,在关键时期恩平组下段处于中成岩A期的晚期,该时期的古孔隙度平均值约10%,孔喉已经比较细小,不利于酸性流体的改造和油气的大量充注。在上述工作的基础上,运用沉积相、成岩相结合的方法对恩平组下段储层进行了动态评价,处于凹陷南斜坡的PY14 5 1井附近地区压实较弱,物性较好,是油气运聚的有利区带,其它地区成岩强度较高,只能作为天然气勘探的目标。 相似文献
75.
76.
选择中国的黄土-古土壤序列的超磁细菌作为研究对象,以透射电镜、扫描电镜、生化实验和有机地球化学方法先后研究了从黄土地区陕西段家坡、甘肃西峰以及陕西洛川富集的趋磁细菌,结果表明,虽然趋磁细菌在黄土和古土壤层的形态有所差异,但它们均由细胞膜、细胞质和沿长轴排列的磁小体与气泡组成,在适宜的条件下它能生长出较多的磁小体。磁小体由氧化铁组成,并可从体内排出,使环境中部分Fe^2 转变为Fe^3 ,促使地层磁化率增高,尤其在古土壤层段,中国黄土剖面中趋磁细菌的产量是地表温度、湿度、pH、铁含量的函数,与湖沼中的趋磁菌相比,它在菌体形态、磁小体的数量与排列方式上有很大差距,因而中国西北黄土地区的趋磁细菌是典型的生态物种。 相似文献
77.
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79.
湘中下石炭统测水组沉积层序及幕式聚煤作用 总被引:11,自引:0,他引:11
下石炭统测水组是我国南方主要含煤地层之一,煤系及煤层在湘中地区发育最佳,该区测水组形成于碎屑滨岸障壁-泻湖沉积体系中。文中对测水组沉积层序及其所反映的海平面变化历史进行了分析,提出测水组上段底部砂岩是海侵背景下形成的障壁砂坝或障璧岛,其底部侵蚀面是海侵冲刷面(ravinement surface)。同时提出测水组下段三、五煤层的形成与受海平面变化控制的幕式聚煤作用(episodie coal accumulation)有关,后者系指海平面下降阶段横跨不同相区的区域性聚煤作用。 相似文献
80.
From river to shelf,anatomy of a high‐frequency depositional sequence: The Late Pleistocene to Holocene Tiber depositional sequence 下载免费PDF全文
Salvatore Milli Marco Mancini Massimiliano Moscatelli Francesco Stigliano Mattia Marini Gian Paolo Cavinato 《Sedimentology》2016,63(7):1886-1928
The Late Pleistocene/Holocene Tiber delta succession represents the most recent and one of the best preserved, high‐frequency/low‐rank depositional sequences developed along the Latium continental margin of the Italian peninsula. Several previous studies have established a robust data set from which it has been possible to describe the stratigraphic architecture of the entire Tiber depositional sequence from the landward to seaward sectors and over a distance of 60 km. The Tiber depositional sequence shows many characteristics found in other Late Pleistocene to Holocene deltaic and coastal successions of the Mediterranean area. The stratigraphic architecture of the Tiber depositional sequence is controlled mainly by glacioeustasy, although factors such as tectonic uplift, volcanism and subsidence, exert an influence at a local scale. The resulting depositional model allowed discussion of some important points such as: (1) the genesis of the Tiber mixed bedrock‐alluvial valley, extending from the coastal plain to the innermost portion of the shelf, recording (i) multiple episodes of incision during relative sea‐level fall, and (ii) a downstream increase of depth and width of the valley during the base‐level fall and the subsequent base‐level rise; (2) the different physical expression of the Tiber depositional sequence boundary from landward to seaward, and its diachronous and composite character; (3) the maximum depth reached by the Tiber early lowstand delta at the end of the sea‐level fall is estimated at ca 90 m below the present sea‐level and not at 120 m as suggested by previous works; (4) the backward position of the Tiber late lowstand delta relative to the deposit of early lowstand; (5) the change of the channel pattern and of the stacking pattern of fluvial deposits within the Lowstand Systems Tract, Transgressive Systems Tract and Highstand Systems Tract. All of these features indicate that the Late Pleistocene/Holocene Tiber delta succession, even if deposited in a short period of time from a geological point of view, represents the result of the close interaction among many autogenic and allogenic factors. However, global eustatic variations and sediment supply under the control of climatic changes can be considered the main factors responsible for the stratigraphic architecture of this sedimentary succession, which has been heavily modified by human activity only in the last 3000 years. 相似文献