Geologic Maps

Descriptive information

1 Topographic information. If a geologic map is drawn with superimposed topographic lines and other information, then it may provide most or all of the information that a typical topographic map would provide. However, these maps are, in some cases, difficult to read because geologic information overlaps topographic information.

2 Types and locations of bedrock units of different ages.

3 Contacts between different rock units.

4 Types and locations of surficial deposits (glacial deposits, river sediments, floodplains).

5 Types and locations of faults and folds.

6 Trends and angles of rock layers

Interpretive information

1 Rock structures (folds and faults) beneath the ground surface (can be extrapolated from surface information).

2 Rock types, both at the surface and subsurface.

3 Rock durability and how difficult the rock may be to remove for mineral deposits.

4 Origin and type of material in surficial deposits.

5 Geologic history of an area.

Adapted from Spencer (1993).

the topographic information provides visible landmarks, which help geologists to orientate themselves. Geologic maps are particularly useful in dinosaur studies because they show the probable locations of outcrops of known or suspected fossil-bearing zones. However, outside of paleontology they are important for locating mineral deposits. Overall, the information conveyed by topographic and geologic maps is extensive (Table 4.2).

All maps, no matter how simple or complex, should have several important features:

A scale that shows the horizontal distances on the map, corresponding to the actual distances on the land; A legend, which is a key to all map symbols used; and An indicator of the direction of geographic north (the north pole of rotation for the Earth).

A global positioning system (GPS) device receives signals from satellites to calculate a position on the Earth's surface with regard to latitude, longitude, and elevation.

Magnetic north differs from geographic north because the Earth spins on an axis deviated slightly from where its magnetic field emanates. Consequently, a map should also show the amount of difference between the two norths (declination) in the area being explored. For example, a difference of 10 degrees from a compass bearing (which generally points to magnetic north) of geographic north can become a large difference over the course of a several kilometer hike to a dinosaur site.

Although this equipment list may sound old-fashioned, it is still recommended because these tools and their usefulness have been repeatedly tested by generations of geologists and paleontologists. Of course, the equipment list must be modified to meet personal preferences and needs, and should keep up with the development of new technology that makes fieldwork easier. A GPS (see box) can cross-check information on maps for the accuracy of either tool. Many GPS units are also capable of downloading geographical locality information into computers; the latter can then construct digital maps that can be compared to any previously printed maps. Digital maps can have layers of information stored in GIS (Geographic Information System) programs, such as the distribution of rock types, fossils found, and vegetation patterns. For this and other reasons, laptop computers are now part of the standard list of field equipment, and most are easily portable. Nevertheless, like personal digital assistants (PDAs), battery life is still a limiting factor in their extended use in the field. Some geologists circumvent this problem by using either solar panels or chargers connected to a field vehicle.

However inspiring the finding of a dinosaur fossil might be, the person who discovers it should first know more basic principles of geology. This can make the find more meaningful, especially in how it relates to the small picture of its local paleo-environment and the larger picture of the ancient global system. Attempting to collect a dinosaur fossil without further knowledge of its setting is risking the loss of valuable scientific information. Making a detailed description of the geologic setting of a dinosaur fossil in the field should precede preparing it for transportation.

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