![]() Transfer the marks from your paper to a provided diagram.If they are not provided, use the Rule of V’s or the ages given to help determine the geologic structure. To determine this, use any strike and dip symbols. Position the marks in the direction you believe the rocks are dipping. At each geologic contact, make a mark on the scratch paper.Place the paper along the map where you want to draw a cross-section. Take a sheet of scrap (scratch) paper.Pay close attention to any strike and dip symbols, geologic contacts, and ages of the rock types. Locate the points between which you will be constructing a cross-section for.How Do I Construct a Geologic Cross-section?įollow these steps to successfully create your own geologic cross-section ( Figure 16.5): Table 16.2: General geologic map symbols. Table 16.1: General geologic age symbols. The explanations include descriptions with enough detail for any geologist to be able to recognize the units and learn how their ages were determined. The explanations of rock units often follow the map symbol on the map, but for very large maps are often given in a separate pamphlet that accompanies the map. The map legend also contains an explanation of the symbols shown on the map, such as the symbols for different types of faults and folds ( Table 16.2). The geologic age (typically the geologic period) is listed for each unit in the key and uses standard symbols ( Table 16.1). This allows the map reader to quickly assess the relative age of each unit. The symbols typically follow superposition and are stacked in an age sequence from oldest at the bottom to youngest at the top. The symbol for each formation, or unit, is shown in a box next to its name with a brief description. Figure 16.3: General formatting for the legend of a geologic map. The map legend to a geologic map is usually printed on the same page as the map and follows a customary format ( Figure 16.3). Figure 16.1: Simplified geologic map illustrating Mesozoic terranes in and around the Bay Area. ![]() Geologic maps are also vital in finding and developing geological resources, such as sediments, groundwater, fossil fuels, and minerals. Second, geologic maps are essential tools for practical applications such as zoning, engineering, and hazard assessment. First, as geologists make geologic maps and related explanations and cross-sections, they develop a theoretical understanding of the geology and geologic history of a given area. Geologic maps are important for two reasons. Geologic maps take practice to understand, since they display three-dimensional features, such as folds, on a two-dimensional surface. At each outcrop, geologists record information such as rock type, strike and dip of the rock layers, and relative age data. Geologists make these maps by making careful field observations at numerous outcrops (exposed rocks at the Earth’s surface) throughout the mapping area. These mappable units are shown as different colors or patterns on a base map (usually a topographic map), over which information about geologic contacts and strikes and dips are included. Generally, a mappable unit is a geologic formation. A mappable unit of rock or sediment is one that a geologist can consistently recognize, trace across a landscape, and describe so that other geologists may recognize and verify its presence and identity. Typically, a geologic map will depict mappable rock or sediment units. What Are Geologic Maps and Why Are They Important?Ī geologic map uses lines, symbols, and colors to illustrate information about the nature and distribution of rock units within an area ( Figure 16.1).
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