Untitled Document

GEOLOGICAL MAPS

BY: AMBER SILVEY

[ Introduction] [ Principles] [ Conclusion] [Map Example ] [ Links]

Introduction

Understanding Geologic Maps

Geologic maps show the absolute ages of rock formations that outcrop on the surface. Each of the various rock layers are representing one of four major time units. These time units are defined as eras. Cenozoic is the most recent rock, Mesozoic is older than Cenozoic, even older than Mesozoic is Paleozoic, The oldest rock on earth are Precambrian. Geologic maps use vivid colors to held distinguish the layers of rock easily. An excellent example of this is found at Geologic mapping in Kansas

Information from ES 111 Lab book: Johnston, P., Aber, S.W., and Ye, H. (1996). Introduction to Earth Science Lab. Edina, MN: Burgess International Group, Inc.

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Principles

Principles for understanding features on Geological Maps

1) Law of Superposition- Each layer of rock is older than the layer above.

2) Principal of Horizontality- The acceptance that all rock sequences were originally deposited horizontally.

Information

Image scanned from: Thompson and Turke, G.R. and Turke,J. (1992). Earth Science and the Environment.

Orlando, FL: Harcourt Brace College Publishers. pp. 80

Image scanned from: Thompson and Turke, G.R. and Turke, J. (1992). Earth Science and the Environment.

Orlando, FL: Harcourt Brace College Publishers. pp. 81

The two principals above are accurate, but due to tectonics the position and appearance can change. A deformation in the Earth's crust may cause layers to be turned upside down or to be folded and faulted. A fold is a bend in the layers of rock. Faults are breaks in rock layers. Dikes and sills may intrude into rocks over time. Dikes are ingenious intrusions cutting across surrounding rock. Sills intrude parallel to the pre-existing rock layers.

Information from ES 111 Lab book: Johnston, P., Aber, S.W., and Ye, H. (1996). Introduction to Earth Science Lab. Edina, MN: Burgess International Group, Inc.

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Conclusion

Geologic Maps prove to be a vital tool in our everyday lives. As the map below colorfully demonstrates every type of bedrock (rock on the surface or just beneath the soil). Whether the rock is in sandstone, shale, or limestone, it is shown on these maps. It is very important that the content of the bedrock be known when building roadways, housing developments, and when laying underground pipe. When you are ready to build your dream home, look at a geologic map to determine the most stable location and a good site.

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