海山对深水底流沉积过程及演化的影响研究进展

王星星, 蔡峰, 吴能友, 李清, 孙治雷, 吴林强

王星星, 蔡峰, 吴能友, 李清, 孙治雷, 吴林强. 海山对深水底流沉积过程及演化的影响研究进展[J]. 海洋地质与第四纪地质, 2020, 40(5): 68-78. DOI: 10.16562/j.cnki.0256-1492.2019111101
引用本文: 王星星, 蔡峰, 吴能友, 李清, 孙治雷, 吴林强. 海山对深水底流沉积过程及演化的影响研究进展[J]. 海洋地质与第四纪地质, 2020, 40(5): 68-78. DOI: 10.16562/j.cnki.0256-1492.2019111101
WANG Xingxing, CAI Feng, WU Nengyou, LI Qing, SUN Zhilei, WU Linqiang. Research progress in seamount influence on depositional processes and evolution of deep-water bottom currents[J]. Marine Geology & Quaternary Geology, 2020, 40(5): 68-78. DOI: 10.16562/j.cnki.0256-1492.2019111101
Citation: WANG Xingxing, CAI Feng, WU Nengyou, LI Qing, SUN Zhilei, WU Linqiang. Research progress in seamount influence on depositional processes and evolution of deep-water bottom currents[J]. Marine Geology & Quaternary Geology, 2020, 40(5): 68-78. DOI: 10.16562/j.cnki.0256-1492.2019111101

海山对深水底流沉积过程及演化的影响研究进展

基金项目: 国家重点研发计划“冷泉系统发育的地质条件及控制作用”(2018YFC0310001);国家自然科学基金重点项目“西太平洋地球系统多圈层相互作用”(91858208);中国地质调查局海洋地质调查专项项目(DD20190819)
详细信息
    作者简介:

    王星星(1991—),男,博士,主要从事深水沉积学方面的研究工作,E-mail: Xingx_Wang@hotmail.com

  • 中图分类号: P736.2

Research progress in seamount influence on depositional processes and evolution of deep-water bottom currents

  • 摘要: 海山是广泛分布于深水区的一种构造地貌类型,底流则是一种长期存在于深水区的沉积动力,故二者之间将会不可避免地发生相互作用,对深水沉积过程及其演化具有不可忽略的控制作用。通过归纳总结全球海山区底流沉积过程研究成果,指出在海山的直接或间接作用下,深水底流沉积动力受到影响,流动路径发生改变,产生次级底流沉积动力,同时也可影响生物群落分布,进而导致海山区沉积地貌及岩相表现出独特的平面展布特征。随着海山区底流沉积动力和沉积地貌背景的垂向演变,不同时期底流沉积过程及其响应也有所差异。因此,海山区底流沉积动力复杂且具特殊性,造就了不同于开阔陆坡背景下的底流沉积地貌和岩相特征及时空分布规律,其对深海盆地构造和古海洋演化的指示意义也与开阔陆坡底流沉积体系有所不同。目前有关海山与底流沉积过程之间的耦合关系研究程度还相对较低,极大地限制着深水资源勘探和地质灾害预测,这一问题有必要在未来深水沉积学研究中给予重点关注。
    Abstract: Seamount is a kind of tectonic geomorphological features widely distributed in the deep sea around the world, where bottom currents persistently exist, thus the interactions between seamounts and bottom currents are very common and will bring about non-negligible influence on deep-water sedimentation and their evolution. This study summarized the global researches on the deep water sedimentation by bottom currents around seamounts, suggesting that deep-water bottom-current hydrodynamics would change under the direct or indirect influence of seamounts, including the changing in flow paths, generation of secondary bottom currents, and variation in ecosystems. Consequently, deep-water sedimentary morphologies and lithofacies would display special distribution patterns. With the evolution of bottom-current hydrodynamics and sedimentary morphologies, deep water sedimentation processes and associated responses would change as well. In summary, bottom currents are complex and special around seamounts, resulting in sedimentary morphologies and lithofacies features as well as distribution patterns differing from those on the open slope. Thus, the sedimentary morphologies and lithofacies formed under bottom currents around seamounts have very particular implications for basin structures and palaeoceanography evolution. However, there is still lack of study concerning the coupling relationship between seamounts and deep water sedimentation processes, greatly limiting deep-sea resource exploration and geo-hazard study, thus more attention is required to be paid to the relationships in the future research of deep-water sedimentology.
  • 渤海湾含油气盆地是继大庆油田发现之后,在中国东部地区所发现的另一个重要的含油气盆地,可分为碎屑岩、古潜山变质岩、湖相碳酸盐岩、火山岩等4大岩石类型。其中,古潜山变质岩的勘探程度较低,已探明储量仅占总储量的20%[1]。因此,古潜山油气藏是渤海湾盆地主要的勘探目标[2]。BZ19-6气田是渤海湾盆地最大的凝析气田,探明储量超千亿方[3],主要目的层为太古界潜山地层,岩性主要为花岗片麻岩,夹少量侵入岩[4-5]。受印支期、燕山期和喜马拉雅期等多期次构造运动的影响,太古界变质花岗岩潜山发育溶蚀孔隙-裂缝型和裂缝型储层,其中裂缝是主要的储集空间和渗流通道[6-7]。因此,有效的裂缝识别方法对该区块未探明单元的油气勘探至关重要。

    目前,识别储层裂缝的方法有直接法和间接法。直接法是从露头、岩芯和成像测井中识别裂缝特征,可以直接反映储层裂缝,但其局限性强、价格昂贵、操作不易。间接法通过处理和分析常规测井资料、地震资料和动态生产资料识别裂缝,可以根据少量数据获得大面积内的裂缝特征,但其必须引入复杂的数学算法。近年来,随着计算机技术的迅速发展和数学理论基础的深入研究,许多学者将常规测井与数学方法相结合,间接地识别裂缝发育的位置和程度。例如,Xiao等[8]利用重标极差(R/S)分析法对不同岩性进行了裂缝识别,表明运用R/S分析方法识别储层的裂缝具有可行性;陈义国等[9]采用R/S分析方法对常规测井资料进行裂缝识别,发现裂缝识别参数与裂缝线密度呈良好的线性关系;Li等[10]通过R/S分析方法对北贵州地区下寒武统牛蹄塘组页岩储层的裂缝进行识别,表明R/S分析方法可以有效地区分裂缝与噪声信号;Zhang等[11]基于R/S分析方法识别裂缝,表明可通过计算裂缝与基质之间的比例来确定裂缝线密度,进而预测天然裂缝的发育程度和空间分布规律;Xiao等[12]利用R/S分析方法对致密砂岩储层的非均质性进行评估,认为R/S分析方法可定量评估储层的非均质性;Aghli等[13]基于R/S分析方法识别碳酸盐岩储层裂缝,表明R/S分析方法能定量反映裂缝参数;Ge等[14]探讨了火成岩多重分形参数与裂缝发育程度之间的关系,发现裂缝发育程度与多重分形特征呈负相关。研究成果显示,重标极差(R/S)分析与分形维数已广泛应用于天然裂缝的识别,但仍存在以下问题:①识别裂缝的尺度具有局限性;②对噪声和异常值较敏感,需要通过其他地质、地球物理等资料进行验证。

    将此方法用于该区块的裂缝识别,仍面临着巨大的挑战。首先,BZ19-6气田储层裂缝网络复杂,主要发育微裂缝,裂缝宽度集中分布于0.01~0.2 mm,且大多数裂缝被方解石、泥质等填充;其次,针对岩性更为复杂的花岗片麻岩储层,R/S分析方法识别裂缝的研究鲜见。鉴于此,本文基于R/S分析方法并结合测井、岩芯和薄片等资料,旨在:①研究R/S分析方法识别裂缝的最小尺度;②建立利用赫尔特指数识别花岗片麻岩储层裂缝发育程度分类标准;③分析岩性各向异性对R/S分析方法识别裂缝精度的影响。

    BZ19-6气田位于渤中凹陷西南部,东南方向为渤南低凸起,西部为埕北低凸起,呈洼中隆的构造格局(图1)。如图2所示(图1中DD′剖面),太古界潜山地层在近南北向发育的构造脊上是古隆起的背景下发育的、经过多期次的构造作用改造的、被一系列断层复杂化的断层背斜构造,构造整体南高北低[15-16],形态完整,圈闭面积较大,埋藏较深,次生断层、裂缝较为发育[17]

    图  1  研究区位置图
    Figure  1.  Location of study area
    图  2  太古界潜山气藏构造剖面图
    Figure  2.  Archean buried hill gas reservoir structure profile

    研究区太古界潜山与上部始新统孔店组呈不整合接触,潜山岩性主要为变质岩,局部可见闪长玢岩、辉绿岩等侵入岩,纵向上可划分为半风化带和潜山内部[18]。半风化带岩石颜色较浅,主要为石英及长石,少量暗色矿物,其中部分岩石呈灰黑色,发育孔隙-裂缝型和裂缝-孔隙型储层[19];半风化带上部溶蚀作用较强,缝孔洞较为发育,风化比较严重,长石大多已经风化为高岭土;而在下部,风化程度逐渐变弱。潜山内部则主要发育裂缝型储层和孔隙-裂缝型,溶蚀孔、洞较少或者不发育。潜山储层主要发育三期裂缝[20],第一期裂缝主要发育在印支期,受华北板块和扬子板块碰撞而产生的大量挤压构造裂缝;第二期裂缝主要发育在燕山期,郯庐断裂发生左旋走滑作用,导致岩石破碎作用强烈,形成大量碎裂岩和碎斑岩以及一系列动力破碎带,并派生出大量裂缝;第三期裂缝与新近纪太平洋俯冲和郯庐断裂发生的右旋走滑作用有关[21]

    天然裂缝按成因可分为构造裂缝、岩溶裂缝、热胀冷缩裂缝、干缩裂缝等[22],按充填情况可分为张开缝和充填缝两类[23]。通过对BZ19-6区块的112块岩芯的观察(图3中a、b是原始岩芯,c、d为其岩芯切面),岩性为花岗片麻岩,裂缝较发育,多见微缝(<0.1 mm)及小缝(0.1~0.5 mm),存在少量中缝(0.5~10 mm)。裂缝产状主要为中高角度,有少量的垂直缝和水平缝,裂缝多呈网状交叉,大多被充填-半充填。

    图  3  太古界天然裂缝岩芯图片
    Figure  3.  Core pictures of Archean natural fractures

    观察201份岩芯薄片后,发现薄片裂缝较为发育,主要为微裂缝和小缝,大多处于充填-半充填状态。裂缝主要被云母化泥质、铁质、碳酸盐岩和黄铁矿充填,但也可见少量未充填的裂缝。其中,部分薄片显示斜长石绢云母化普遍,钾长石高岭土化,常见铁白云石交代现象及被铁质或铁泥质充填的岩石微裂缝(图4a)。另外,部分薄片显示黑云母见后期白云石交代现象,见微小裂缝,宽度为0.01~0.15 mm,其内被白云石、铁白云石和方解石所致密充填(图4b、c)。此外,部分岩石内裂缝和颗粒裂隙也较为发育,缝宽为0.01~0.20 mm,见被黄铁矿充填的微裂缝,但也可见少量未充填的裂缝(图4d)。另有部分岩石内发育数条裂缝,缝宽为0.01~0.17 mm,部分被碳酸盐矿物充填,也可见未充填裂缝,缝宽约为0.01~0.03 mm(图4e)。还有部分岩石见两期裂缝发育,缝宽为0.02~0.05 mm,裂缝先被石英、白云石、方解石完全充填,后被铁质或铁白云石充填,微裂隙较为发育,微裂隙宽度为0.01 mm左右(图4f)。

    图  4  太古界岩石薄片
    Figure  4.  Rock slices of Archean strata

    测井资料处理解释过程中将裂缝分为天然裂缝和诱导缝。其中,天然裂缝可进一步分为高阻缝和高导缝,按裂缝的倾角又可分为高角度裂缝、中角度裂缝和低角度裂缝。为了进一步了解该区块的裂缝发育情况及特征,对该井进行了Microscope-HD随钻成像测井资料处理分析。结果显示,该区块发育高导缝(图5a)、高阻缝(图5b)、诱导缝(图5c)及线理(图5d)。其中,高导缝较为发育,走向主要有NW-SE和近E-W向(图5e),以中高角度为主,倾角集中在40°~70°,均值为48°左右(图5f)。裂缝宽度集中分布在0.001~0.1 mm,其中<0.1 mm的裂缝占比91.12%(图5g);裂缝密度为1~13条/m,1~8条/m占所有的96.22%,平均为2.3~4.32条/m(图5h)。区块高阻缝发育较少,走向为NNW-SSE,以中等角度为主。电成像测井只能识别到毫米级别的裂缝,埋深和充填情况都会降低其分辨率;而岩芯的分辨率可以达到亚毫米级别,可直接观察到岩石的构造和裂缝,但岩芯取样点不连续且难以覆盖整个井段。两者在识别裂缝的尺度上不统一,均难以识别研究区的微裂缝。因此,亟需一种更为精细、有效的裂缝评价方法。

    图  5  Microscope电成像图裂缝特征
    Figure  5.  Fracture characteristics of Microscope electrical imaging

    R/S分析,也称为重标极差分析,由Hurst在1951年提出,用于研究尼罗河水流量与库容之间的关系[24],后被众多学者证明它是分析一维分形变量的有效技术[25-27]。对于单一岩性的地层,天然裂缝的发育给测井所测得的物理性质带来很大的变化,增强了地层的非均质性,裂缝发育程度不同,其物理性质的改变情况有所不同[28]。因此,可以根据测井曲线上的突变点大致判断裂缝的位置,根据突变点的强弱分析裂缝的发育程度。

    通过分析某些测井参数的R(n)/S(n)(后文缩写为R/S)与测井采样点n的关系,预测裂缝的发育程度。如公式(1)、(2)、(3)所示,R(n)是最大累积偏差与最小累积偏差之差,代表测井序列的复杂性;S(n)是变化的平方根,代表时间序列的平均趋势;Z(i)是测井序列,每一个采样间隔点上的值;i、j、k是从0到n变化的常数,其中k大于等于iH表示赫尔特指数。

    $$\begin{split} R\left(n\right)=&\underset{0 < k < n}{\mathrm{max}}\left\{\sum _{i=1}^{k}Z\left(i\right)-\frac{k}{n}\sum _{j=1}^{n}Z\left(j\right)\right\}-\\&\underset{0 < k < n}{\mathrm{min}}\left\{\sum _{i=1}^{k}Z\left(i\right)-\frac{k}{n}\sum _{j=1}^{n}Z\left(j\right)\right\}\end{split}$$ (1)
    $$ S\left(n\right)={\left\{\frac{1}{n}\sum _{i=1}^{n}{Z\left(i\right)}^{2}-{\left[\frac{1}{n}\sum _{j=1}^{n}Z\left(j\right)\right]}^{2}\right\}}^{1/2}$$ (2)
    $$ H=\frac{\partial \mathrm{L}\mathrm{g}(R/S)}{\partial n} $$ (3)

    通过数值模拟,计算出RS的值,做Lg(R/S)与Lg(n)的散点图,其斜率就代表赫尔特指数,H的范围是0到2,可以通过H的大小判断裂缝的发育程度。再对Lg(R/S)的值进行牛顿差分运算,n阶差分如公式(4)所示:

    $$ {\Delta }^{n}{f}_{{i}}={\Delta }^{n-1}{f}_{{i}+1}-{\Delta }^{n-1}{f}_{{i}} $$ (4)

    对该区块12口井进行计算后发现,二阶差分模型对该区块的裂缝位置预测准确性较高,其模型如公式(5)所示:

    $$ {K=\Delta }^{2}{f}_{{i}}=\Delta {f}_{{i}+1}-\Delta {f}_{{i}}={f}_{{i}+2}-2{f}_{{i}+1}+{f}_{{i}} $$ (5)

    该区块随钻测井曲线包含井径曲线(CAL)、自然伽马曲线(GR)、冲洗带电阻率曲线(Rxo)、原状地层电阻率曲线(Rt)、密度曲线(RHOB)、中子曲线(TNPH)、声波时差曲线(DT)等,通过岩芯裂缝统计对比,选择对天然裂缝较为敏感的测井参数。TNPH曲线受岩性、钻井液等因素干扰严重;GR曲线主要反映岩性的变化,而泥质含量的变化和钻井液的变化会对GR值影响明显,从而掩盖或放大裂缝存在的信息,而花岗片麻岩地层较为致密,密度变化较小。相比之下,CAL、Rxo、DT三条测井曲线对裂缝更为敏感,而GR、RHOB、TNPH对裂缝的敏感度较低(图6)。通过实际处理,发现在Lg(n)=3.5左右的深度为4 882 m处,R/S曲线出现明显的下凹区间,表明测井响应在此处有较大的变化,结合电成像图显示,此段裂缝高度发育。因此,本文选择CAL、Rxo、DT三条测井曲线进行处理分析,以进一步分类识别该井的裂缝发育程度。

    图  6  R/S分析曲线
    Figure  6.  R/S analysis curve

    选取30个层段共150 m,经过R/S分析发现,在花岗片麻岩中利用R/S分析方法能够有效识别裂缝的发育情况。该方法的准确性也得到了电成像资料的验证。针对这30个层段的CAL、Rxo、DT三条测井曲线的R/S分析结果,分别用HCALHRxoHDT表示,并绘制了三维散点图(图7),发现分区性明显。因此,本文建立了针对花岗片麻岩储层的裂缝发育程度分类识别标准(表1)。

    图  7  赫尔特指数三维散点图
    Figure  7.  Three-dimensional scatter plot of Hurst index
    表  1  花岗片麻岩储层裂缝发育程度分类识别标准
    Table  1.  Classification and identification standard of fracture development degree of granite gneiss reservoir
    裂缝发育情况HCALHRxoHDT
    不发育>0.95>1.0>1.0
    较发育0.75<HCAL<0.950.7<HRxo<1.00.75<HDT<1.0
    发育<0.75<0.7<0.75
    下载: 导出CSV 
    | 显示表格

    R/S分析处理后的值采用牛顿差分的方法处理,经过对比后发现二阶差分对裂缝的位置识别较为准确,其中CAL、Rxo、DT曲线的二阶差分值分别用K-CAL、K-Rxo、K-DT表示。如图8所示,对电阻率Rxo曲线进行R/S分析,进一步采用牛顿差分的方法处理,得出以下结论:①定义R/S曲线明显下凹的部分为下凹区间,其二阶差分的值为正且大于0.0001,主要反映测井曲线的变化情况,对应裂缝发育段;②定义R/S曲线明显上凸的部分为上凸区间,其二阶差分的值为负,主要反映基岩段,其裂缝不发育或发育程度低。由式(5)计算的二阶差分K值与测井曲线分析的R/S曲线的下凹区间吻合较好,证明K值对识别曲线的下凹区间是有效的,进一步证明了识别裂缝发育位置的准确性。

    图  8  Lg(R/S)曲线的K值和凹区间对比
    Figure  8.  Comparison of K value and concave interval of Lg(R/S) curve

    表2显示,通过牛顿二阶差分K值与随钻Microscope-HD电成像图共识别出3个有效的区域类别:①井壁崩落区:K-CAL值较大,K-DT和K-Rxo值较小,因此K-CAL值可以明显预测井壁崩落的位置;②裂缝发育区:K-DT敏感程度强,从图像上也可以发现,裂缝发育的小层段,K-DT值都比较突出;③基岩区:K-Rxo值突出,成像图上显示特征为高阻亮色,裂缝不发育。对每一个区域类别的深入对比分析,可以得出以下结论:①K-CAL值可以区分井壁崩落区和裂缝发育区,井壁崩落区K-CAL>0.00003,裂缝发育区K-CAL<0.00003;②K-DT值对裂缝的发育位置识别较为准确,即裂缝越发育,K-DT越大;③K-Rxo值可以区分裂缝发育区和基岩区,裂缝发育区K-Rxo<0.00001,基岩区K-Rxo>0.00001。

    表  2  牛顿二阶差分K值与Microscope-HD电成像图对比
    Table  2.  Comparison of Newton ' s second-order difference K value and Microscope-HD electrical imaging map
    类别测井曲线特征参数特征
    井壁崩落区K-CAL>0.00003
    K-DT<0.00001
    K-Rxo<0.00001
    裂缝发育区K-CAL<0.00003
    K-DT>0.00001
    K-Rxo<0.00001
    基岩区K-CAL<0.00003
    K-DT>0.00001
    K-Rxo>0.00001
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    在裂缝发育区(K-Rxo<0.00001),为进一步识别裂缝的发育程度,除了应用前文的赫尔特指数H值之外,电成像解释的裂缝线密度与K-Rxo散点图 (图9)显示,裂缝线密度与K-Rxo值呈正相关,即裂缝线密度越大,K-Rxo值越大,其相关性R2=0.8895。因此,在裂缝发育区(K-Rxo<0.00001),K-Rxo值越大,裂缝线密度越大,裂缝越发育。

    图  9  裂缝线密度与K-Rxo散点图
    Figure  9.  Fracture line density and K-Rxo scatter plot

    裂缝是油气井初周日产量的主要影响因素之一,初周的日产气和日产液可间接验证研究区裂缝的发育程度与分形维数的预测效果。选取研究区裂缝较为发育的层段,其垂直深度在4 650~4 700 m,在研究区井位平面图上绘制裂缝发育层段DT曲线R/S分析曲线二阶差分K值的等值图,结合初周日产量与电成像图等资料,对BZ19-6气田的裂缝相对发育情况进行预测(图10)。由图可知,A7H井裂缝较发育,A3H井裂缝发育程度低。在其他各种因素相近的条件下,牛顿差分K值与油气井初周日产液产量间存在正相关性,裂缝相对发育区的产量明显高于裂缝相对不发育区。

    图  10  BZ19-6气田裂缝发育预测
    Figure  10.  Prediction of Fracture Development in BZ19-6 Gas Field

    计算结果表明,应用R/S分析结合二阶差分的方法进行裂缝识别和预测不仅具备坚实的理论基础,而且计算结果与成像测井所解释的裂缝信息具有较好的吻合度。客观地分析此方法识别裂缝精度存在误差的原因主要有以下3个方面:一是测井信息不仅包括裂缝信息,还包括母岩本身的纵向非均质性信息(如岩性、物性、电性、含水饱和度等),其势必会给裂缝识别带来一定的影响;且岩性从花岗片麻岩变为闪长玢岩(图11),而又有裂缝发育,其中K-DT值与K-Rxo值较小,因此对非花岗片麻岩储层中的裂缝K值预测效果欠佳。二是研究区天然裂缝中充填方解石、白云石、石英、黄铁矿和泥质等矿物,当裂缝被矿物充填时,测井响应特征不明显,因此对完全充填缝的识别较难。三是该区块的裂缝宽度集中分布在0.001~0.1 mm,大量数据表明此方法对裂缝宽度小于0.005 mm的微裂缝仍然有响应,但特征不明显,因此裂缝的宽度对识别效果有影响。

    图  11  非花岗片麻岩裂缝发育特征
    Figure  11.  Fracture development characteristics of non-granitic gneiss

    (1)将R/S分析和牛顿差分法相结合改进的裂缝识别方法,在变质岩储层裂缝评价中具有可行性,并建立了利用赫尔特指数识别花岗片麻岩储层裂缝发育程度分类标准。

    (2)此方法可识别宽度大于0.005 mm的裂缝,提高了裂缝识别的精度。此外,研究还发现,K-Rxo值与裂缝线密度呈正相关关系,且相关性较好。

    (3)岩性各向异性和裂缝充填情况影响常规测井曲线R/S分析方法识别裂缝的精度。

  • 图  1   全球底流沉积与底流年平均流速分布叠合图数字代表全球底流沉积统计实例序号,统计数据见文献[12]。

    Figure  1.   Global distribution of bottom currents superimposed with annually mean flow velocity The numbers indicate the sites for the case studies on bottom current around the world, modified from reference [12].

    图  2   对称海山附近底流流速平面分布(A)和垂直流向纵剖面(B)B中流速单位为m/s,黄色指示反向流速 (据文献[21]修改)。

    Figure  2.   Plan view(A)and vertical cross-channel section(B)for the flow velocity distribution of bottom currents flowing through the axisymmetric hill (The velocity unit in B is m/s, the yellow indicates negative velocity) (Modified from references [21]).

    图  3   流经海山的底流流场特征图ut代表随时间变化的实际流速,u0代表平均流速,f为科氏力参数,约为10−4/s,D为海山底部直径 (据文献[4, 19]修改)。

    Figure  3.   Diagrams showing the flow-field features of bottom currents flowing through seamounts utindicates the actual flow velocity varied with time, u0 indicates the mean flow velocity, f is the Coriolis parameter, ~10−4/s, D represents the seamount diameter at the seamount base (modified from references [4, 19]).

    图  4   南海北部地貌图(A)和南海北部海平面异常(SLA)与表层流速度平面分布图(B)及南海东沙陆坡地区TJ-A-1站位原位观测结果(C-F)[35]

    Figure  4.   (A) Bathymetric map for the northern South China Sea; (B) Map of sea level anomaly (SLA) with surface geostrophic current velocity; (C-F) In-situ observed results at the site TJ-A-1 on the Dongsha slope, South China Sea[35]

    图  5   流经海山区的中尺度涡旋所导致的底流的流场分布示意图

    A指示深入深层的表层涡旋情形,B指示底层涡旋情形 (据文献[7]修改)。

    Figure  5.   Diagram for the flow patterns influenced by mesoscale eddies passing through seamount

    A indicates the scenario dominated by surface deep-reaching eddy, B indicates the scenario dominated by bottom eddy (modified from reference [7]).

    图  6   海山附近底流沉积动力及沉积地貌分布模式图(A)和海山附近底流沉积地貌平面以及横、纵剖面示意图(B—D)[5]

    Figure  6.   (A)Schematic block diagram showing the distribution of sedimentary dynamics and the associated morphologies near seamount,(B-D)Horizontal, longitudinal and cross profiles showing the contourite morphologies near seamount[5]

    图  7   东沙陆坡海山区底流改造砂

    Figure  7.   Reworked sands under bottom currents around the seamount on the Dongsha Slope

    图  8   海山之上受水动力影响的生物群落补充过程示意图[51]

    Figure  8.   The diagram showing the hydrodynamics-influenced recruitment of species populations living on seamount[51]

    图  9   海山区底流沉积层序演化过程示意图[55]

    Figure  9.   Diagram showing the bottom current sequence evolution around a seamount[55]

    表  1   海山对底流沉积动力影响

    Table  1   Seamount influences on bottom-current dynamics

    影响因素 对底流沉积动力的影响
    海山形态、规模 (1)相比于圆锥形海山,伸长状海山更容易导致底流沉积动力增强,并且增强幅度与海山高度呈正相关[27]
    (2)底流沉积动力随坡度的增大而有所增强[14],故坡度较陡的海山受到的侵蚀作用更强;
    (3)当海山高程较大时,将导致海山周缘斜坡在垂向上受到不同底流的影响,所对应的底流沉积动力与沉积响应也有所差异;
    底流流向与伸长状
    海山走向的关系
    (1)垂直:迎流一侧底流强度更大,易于造成侵蚀;背流一侧易于激发内波作用继续向前传播[6]
    (2)平行:底流顺坡侵蚀,尤其在坡脚处底流强度相对较大,易于形成底流沟道[38]
    (3)斜交:底流流向易于发生改变,平行海山走向分量可沿斜坡走向进行侵蚀[38]
    海山群空间分布 随着海山间中心连线的距离和走向的改变,海山区底流沉积动力也随之发生改变。但是,目前该方面研究程度还相对较低,主要集中在早期的数值模拟研究方面[4],还需要展开进一步的研究。
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  • 收稿日期:  2019-11-10
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