U of M GEOL 3000 - Lab - Virtual Geologic Mapping

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Geol 3000 Lab 2 – Virtual Geologic Mapping 2/27-29/09 The purpose of this exercise is to give a sense of what information is collect from field observations, how those observations are recorded on base maps, what interpretations are then involved in creating a geologic map from those observations, and what story can be read from the geologic map. Procedure: Choose to work on one of the four geologic field areas (A, B, C, or D) The rock types corresponding to the different colored outcrops are: Map A B C D Granite Red Rose Red Red Diabase Blue Sandstone Yellow Yellow Yellow Yellow Shale White Violet Violet Limestone Green Green Green Green Dolomite Blue/Violet 1) OUTCROPS - As accurately as possible, record outcrop locations and shapes to your gridded base map using specific colors for specific rock types (though they need not be the same color as the outcrops). Darkly color your outcrops or outline them in pencil. 2) STRUCTURE – Show the approximate strike and dip (direction and approx. value) of planar geologic structures at a minimum of five locations on your map. Use the following symbols for the two main types of structures 45º Igneous Contact - Inclined - Vertical 45ºSedimentary Bedding 3) GEOLOGIC CONTACTS AND UNITS - Keying off outcrops with exposed contacts, infer where these contacts project through your map area by making dashed lines with a #2 pencil. Use the strike and dip measurements to guide you in how to trend your contact lines (on the horizontal surface of your map, geologic contact lines should approximately parallel the strike of your measurements). If you find that the outcrop geology requires that the contact curves in violation of the structure measurements, this may imply that a fault has offset the contact. Another clue to the existence offaults is that rivers tend to follow these zones of weakness. In the end, all outcrops of a certain rock type should be enclosed by geologic contacts or the margins of the map. Using the same colors as the outcrops, lightly shade the map units defined by the geologic contacts. 4) MAP LEGEND - First thing, give a title to your map (be creative, humorous, whatever) along with your name and the date (IMPORTANT). Next, determine the scale of your base map and record that value in the space below the map. Determine the number and relative ages of your geologic map units. On the map legend sheet, color and label them in stratigraphic order (i.e., oldest at the bottom, youngest at the top). Give them unique names if you like (e.g. the Bizzaro Formation), but indicate the major rock type that composes it. CAUTION – realize that it is possible to find the same rock type forming geologic units of different age; not all sandstones formed at the same time in earth history. Units separated by an unconformity, should be noted by a zig-zag line between the map unit boxes. Also on the legend, draw and define the map symbols you used on your map. 5) CROSS SECTION – Trace a line across your map area that generally traverses a right angle to the strike of your geologic units. Label the south end A and the north end A’. On graph paper, construct a geologic cross section of that traverse in the box provided (the length of your cross section will be shorter than the box unless your traverse line runs from corner to corner). Using the dip measurements you measured and a protractor, project your units into the subsurface to the base of the cross section box. 6) GEOLOGIC STORY – On a separate piece of paper, briefly tell the geologic story of your area. Using outline form is OK. Include depositional events, deformational events, and erosional


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U of M GEOL 3000 - Lab - Virtual Geologic Mapping

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