Journal
QUATERNARY INTERNATIONAL
Volume 430, Issue -, Pages 71-81Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.quaint.2015.12.102
Keywords
Gypsum; Crystal morphology/habit; Co-precipitated ions; Lattice parameters; Depositional environment
Funding
- National Basic Research Program of China [2013CB956401]
- Strategic Priority Research Program of the Chinese Academy of Sciences [XDB03020400]
- National Natural Science Foundation of China [41271100, 41402156]
- China Postdoctoral Fund [2014M560122]
Ask authors/readers for more resources
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.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available