Variation of gypsum morphology along deep core SG-1, western Qaidam Basin (northeastern Tibetan Plateau) and its implication to depositional environments
Variation of gypsum morphology along deep core SG-1, western Qaidam Basin (northeastern Tibetan Plateau) and its implication to depositional environments
复制标题
柴达木盆地西部（青藏高原东北部）SG-1深部石膏形态变化及其沉积环境意义
DOI：
10.1016/j.quaint.2015.12.102
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发表时间：
2017-02-12
影响因子：
2.2
通讯作者：
Yang, Yibo
中科院分区：
文献类型：
--
作者：
Li, Jiao;Li, Minghui;Yang, Yibo
柴达木盆地位于青藏高原北方边缘，是一个干旱、封闭的山间盆地。在柴达木盆地西部获得了一个938.5m长的岩心（SG-1），其年龄介于2.8Ma-0.1Ma之间。石膏是岩芯中主要的蒸发矿物之一。选取了201个石膏样品，对其晶体形貌进行了研究。晶体习性有透镜状、棱柱状、板状、孪晶状、双晶状和聚集状。棱柱状晶体出现在723米以上，而透镜状晶体几乎完全存在于523米以上。片状晶体是最常见的形态。石膏晶体（包括板状、透镜状和棱柱状）的总丰度随深度的减小而增加。晶体习性与沉积环境之间的关系是复杂的，因为相同的形貌可以出现在不同的环境中，而不同的形貌也可以出现在相同的沉积环境中。然而，不同形貌的发生可以归因于附加阳离子的抑制作用引起的可变生长速率用X射线衍射法测得石膏晶胞参数为：a = 5.854-12.57埃; B = 9.654-16.231埃;和c = 5.163-14.024埃; β = 113.54-119.88度;体积= 601.55-712.65埃（3）。K+、Na+和Mg 2+取代Ca 2+使c轴变小，Sr 2+使a轴和B轴变小。a/c、B/c、a/B随K+、Na+和Mg 2+的增加而增加，随Sr 2+的增加而减小。石膏中Mg ~（2+）、Na ~+、K ~+和Sr ~（2+）的含量具有显著的变异性，K/Ca摩尔比在1.03 × 10 ~（-4）~ 32.08 × 10 ~（-4）之间变化，Mg/Ca摩尔比在0.0023 ~ 0.1629之间变化，Na/Ca摩尔比在0.031 ~ 0.575之间变化，Sr/Ca摩尔比为5.59 × 10 ~（-4）~ 19.67 × 10 ~（-4）。石膏中Sr ~（2+）、Mg ~（2+）、Na ~+和K ~+的浓度主要取决于生长速率和卤水浓度。(C)2016 Elsevier Ltd和INQUA。All rights reserved.
The Qaidam Basin is an arid, closed, intermontane basin located on the northern margins of the Tibetan Plateau in China. A 938.5 m-long core (SG-1), dated between similar to 2.8 Ma-0.1 Ma, was obtained from the western Qaidam Basin. Gypsum is one of major evaporative minerals in the core. A total of 201 gypsum samples were selected and their crystal morphologies were carefully investigated. The crystal habits are lenticular, prismatic, tabular, twinned, stubby, and aggregate. Prismatic crystals occur in the upper 723 m, while lenticular crystals exist almost entirely in the upper 523 m. Tabular crystals are the most common morphology. The total abundance of gypsum crystal (including tabular, lenticular, and prismatic forms) tends to increase with decreasing depth. The relationship between crystal habits and depositional environments is complex, because same morphology can appear in different environments, and different morphologies can also occur in the same depositional environment. However, the occurrence of different morphologies can be attributed to the variable growth rates caused by the inhibition effect of additional cations (e.g. Mg2+, Na+, K+ and Sr2+) on particular lattice parameters and the variation in precipitation experiments.The lattice parameters of the unit cell of gypsum, measured by X-ray diffraction method, are: a = 5.854-12.57 angstrom; b = 9.654-16.231 angstrom; and c = 5.163-14.024 angstrom; beta = 113.54-119.88 degrees; Volume = 601.55-712.65 angstrom(3). The substitution of K+, Na+ and Mg2+ for Ca2+ can reduce c-axis, while Sr2+ can reduce a and b axes. a/c, b/c, a/b tend to increase with K+, Na+ and Mg2+ and decrease with Sr2+. The Mg2+, Na+, K+ and Sr2+ contents in gypsum show significant variability, with K/Ca molar ratios varying from 1.03 x 10(-4) to 32.08 x 10(-4), Mg/Ca molar ratios from 0.0023 to 0.1629, Na/Ca molar ratios from 0.031 to 0.575, and Sr/Ca molar ratios from 5.59 x 10(-4) to 19.67 x 10(-4). Sr2+, Mg2+, Na+, and K+ concentrations in gypsum mainly depend on growth rate and brine concentration. (C) 2016 Elsevier Ltd and INQUA. All rights reserved.