Preferred Orientation Patterns of Phyllosilicates in Surface Clays

Abstract

AbstractThe alignment of phyllosilicates in clays has received a lot of attention because it is a major cause of seismic anisotropy in the Earth’s crust. Thus far, all attention has been on shales where the orientation pattern has been attributed to compaction and observed to increase with burial depth and diagenetic processes. Here, for the first time, the same methods that were developed to quantify shale preferred orientation were applied to clays forming in surface environments, a seasonal streambed in Death Valley, California; a mudpool from mud volcanoes in Imperial Valley, California, close to the Salton Sea; and a glacial lake from Val Albigna in the Swiss Alps. Preferred orientation was analyzed quantitatively with high-energy synchrotron X-ray diffraction. All three samples showed strong alignment of phyllosilicates with (001) pole figure maxima 2–4 multiples of a random distribution, comparable to shales, and indicating that significant preferred orientation can be produced at surface conditions. The original alignment during sedimentation may be an important factor for the final microstructure in many shales.