Lab 3 - Geologic Maps

Lab 3 - Geologic Maps - LAB 3 GEOLOGIC MAPS AND STRUCTURES...

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LAB # 3 - GEOLOGIC MAPS AND STRUCTURES Maps Used for Geological Studies You are probably familiar with topographic maps ; these depict the Earth's surface in three dimensions. They accomplish this by means of contour lines , brown lines drawn on standard topographic maps that connect points of equal elevation. In this lab, geologic maps will be especially utilized for interpreting Earth history. These show the surface distribution of rocks, often with with each geologic unit depicted by a unique color. Geologic cross sections show the distribution of rocks in vertical section. They use data from outcrops, subsurface lithologic logs or well logs to define the sedimentologic or structural trends across a given geographic region. These may be constructed in two- dimensions, or three-dimensional cross-sections (termed Fence Diagrams ) may be drawn. The "layer-cake"-type cross sections may be combined with geologic maps to form geologic block diagrams . These diagrams also yield three-dimensional figures, and are thus very useful for interpreting geologic history. There are also other maps that are useful for interpreting ancient facies and sedimentary environments. Structure-Contour Maps depict the elevations of the tops of economic deposits, key beds, formations, or prominent seismic reflectors. They are made by drawing contours that connect points of equal elevation above or below some datum, usually modern sea level. Structure-contour maps are used to map sedimentary basins, depositional facies, or subsurface structural features. They are used quite frequently for mapping economic deposits, such as hydrocarbon-bearing structural domes or anticlines. Isopach Maps show the thickness of a stratigraphic unit or units. They are also often times used to show the distribution and thickness of oil- and natural gas-bearing units, as thicker units potentially contain more economic deposits versus thinner units of the same type. Isopach maps are also used to interpret the size and shape of sedimentary basins, calculate ancient subsidence rates, and map centers of sediment deposition. Lithofacies and Biofacies Maps reveal the composition or texture of rocks, or map fossil distributions. They are often used to interpret depositional environments, for determining the source area of sediments ( provenance ), and are often used to determine the paleoecology of a region. Structural Geology Structural geology is the study of features formed due to rock deformation. In order to understand the structural history of an area, the attitude of the rock layers must be determined. The position and orientation of the rock layers is defined by means of their strike and dip.
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