The topics covered in this chapter can be summarized as follows:

Section Summary
9.1 Introduction to Structural Geology Visualizing layers of rocks as 3D forms is a fundamental skill for any geologist. Layers of rocks often form as planes, and the attitude of any plane can be described by specifying its dip and dip direction. Dip is the angle between 0° (horizontal) and 90° (vertical) measured from horizontal to the inclined plane. Dip direction refers to the direction of maximum dip, or the direction towards which water would flow if it was poured onto the dipping plane. In this course, we will use cardinal (e.g., W for west) and ordinal directions (e.g., SE for southeast) to describe dip direction.
9.2 Geological Maps Geological maps share many common cartographic elements with topographic maps. The legend on a geological map displays information about each unit, including map code, full unit name (e.g., formation name), age, and a brief description of lithology. Legends are formatted such that the oldest rocks are listed at the bottom, and the youngest rocks at the top. Map patterns of units on a geological map reflect the intersection of geology (i.e., the attitude of the strata) and topography.
9.3 Estimating Dip Direction from a Geological Map Determining the dip direction in a block model, where the top surface is perfectly flat, is straightforward. In real life, topography influences the map pattern of a unit. Some clues in map view can help estimate the dip and dip direction of strata: horizontal strata have contacts that are parallel to topographic contour lines, and vertical strata have contacts that appear to cut across contour lines at a high angle. For dipping units, the Rule of V’s provides a quick, visual method of estimating the dip direction by examining how a dipping contact is deflected across a stream or valley in map view.
Lab 9 Exercises Satellite imagery of areas with arid climates is often clear enough to distinguish different layers of bedrock where they are exposed at the Earth’s surface. In the same way that we can group together and map layers of rocks seen in satellite imagery based on common visible features (i.e., colour), geologists group together mappable units of rock to create a geological map. In arid areas where exposure of the bedrock is extensive, and visible differences between units are distinct, map patterns and dip direction can be determined using satellite imagery and the Rule of V’s.


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A Practical Guide to Introductory Geology Copyright © 2020 by Siobhan McGoldrick is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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