Hein James R, Dowling Jennifer S, Schuetze Anthony, Lee Homa J
US Geological Survey, 345 Middlefield Road, MS999, Menlo Park, CA 94025, USA.
Mar Environ Res. 2003 Jul-Aug;56(1-2):79-102. doi: 10.1016/S0141-1136(02)00326-4.
Clay mineralogy is useful in determining the distribution, sources, and dispersal routes of fine-grained sediments. In addition, clay minerals, especially smectite, may control the degree to which contaminants are adsorbed by the sediment. We analyzed 250 shelf sediment samples, 24 river-suspended-sediment samples, and 12 river-bed samples for clay-mineral contents in the Southern California Borderland from Point Conception to the Mexico border. In addition, six samples were analyzed from the Palos Verdes Headland in order to characterize the clay minerals contributed to the offshore from that point source. The <2 microm-size fraction was isolated, Mg-saturated, and glycolated before analysis by X-ray diffraction. Semi-quantitative percentages of smectite, illite, and kaolinite plus chlorite were calculated using peak areas and standard weighting factors. Most fine-grained sediment is supplied to the shelf by rivers during major winter storms, especially during El Niño years. The largest sediment fluxes to the region are from the Santa Ynez and Santa Clara Rivers, which drain the Transverse Ranges. The mean clay-mineral suite for the entire shelf sediment data set (26% smectite, 50% illite, 24% kaolinite+chlorite) is closely comparable to that for the mean of all the rivers (31% smectite, 49% illite, 20% kaolinite+chlorite), indicating that the main source of shelf fine-grained sediments is the adjacent rivers. However, regional variations do exist and the shelf is divided into four provinces with characteristic clay-mineral suites. The means of the clay-mineral suites of the two southernmost provinces are within analytical error of the mineral suites of adjacent rivers. The next province to the north includes Santa Monica Bay and has a suite of clay minerals derived from mixing of fine-grained sediments from several sources, both from the north and south. The northernmost province clay-mineral suite matches moderately well that of the adjacent rivers, but does indicate some mixing from sources in adjacent provinces.
粘土矿物学对于确定细粒沉积物的分布、来源和扩散路径很有用。此外，粘土矿物，尤其是蒙脱石，可能会控制沉积物对污染物的吸附程度。我们分析了从康塞普申角到墨西哥边境的南加州边境地区的250个陆架沉积物样本、24个河流悬浮沉积物样本和12个河床样本的粘土矿物含量。此外，还对帕洛斯维德斯岬角的六个样本进行了分析，以表征从该点源输入近海的粘土矿物。在通过X射线衍射分析之前，分离出<2微米大小的部分，用镁饱和并进行乙二醇化处理。利用峰面积和标准加权因子计算蒙脱石、伊利石以及高岭石加绿泥石的半定量百分比。大部分细粒沉积物是在冬季主要风暴期间，特别是在厄尔尼诺年期间由河流输送到陆架的。该地区最大的沉积物通量来自圣伊内斯河和圣克拉拉河，它们流经横向山脉。整个陆架沉积物数据集的平均粘土矿物组合（26%蒙脱石、50%伊利石、24%高岭石+绿泥石）与所有河流平均值的组合（31%蒙脱石、49%伊利石、20%高岭石+绿泥石）非常相似，这表明陆架细粒沉积物的主要来源是相邻的河流。然而，区域差异确实存在，陆架被分为四个具有特征性粘土矿物组合的省份。最南端两个省份的粘土矿物组合平均值在相邻河流矿物组合的分析误差范围内。向北的下一个省份包括圣莫尼卡湾，其粘土矿物组合源自几个南北来源的细粒沉积物的混合。最北部省份的粘土矿物组合与相邻河流的组合适度匹配，但确实表明有来自相邻省份来源的一些混合。
