Portable outcrops First-experience mapping under ideal conditions Kurt Friehauf - Kutztown University of Pennsylvania http://faculty.kutztown.edu/friehauf
Background Geologic mapping is challenging because it requires rapid rock type identification, efficient strike and dip measurement, precise location on the map, and thoughtful visualization of the relationship between rock bodies, all given limited outcrop that can be less-than-perfect for measurements and lessthan-ideally located.
433350.000000
433400.000000
433450.000000
or email
[email protected]
4485120.000000
4485120.000000
Rickenback
Base map for students Geography department maintains a GIS database of the campus (surveyed by geography students in their classes). University also maintains an AutoCAD map of the campus. For the student version, I removed sidewalks, park benches, and other detailed landmarks to force students to triangulate their locations rather than eyeball. I also require students to show their triangulation work on their maps in light pencil.
4485080.000000
4485080.000000
deFrancesco
4485040.000000
4485040.000000
Temporary classrooms
Objective
MN
12°
4485000.000000
4485000.000000
Rohrbach Library
Learn how to make a geologic map given the ideal conditions of fortuitously-located outcrops with planar strike-dip surfaces and unweathered rock samples on level terrain.
Lytle Hall
Legend Buildings Asphalt
4484960.000000
4484960.000000
Concrete
433250.000000
433300.000000
Things that complicate geologic mapping
433350.000000
0
15
433400.000000
30
60
433450.000000
90
Gravel SportFields UTM Zone 18N, NAD 1983 Kutztown University September 2009
433500.000000
Kurt Friehauf - Field Geology
[email protected]
120 Meters
This exercise factor eliminated factor eliminated factor eliminated factor eliminated factor eliminated still wild card
Answer Key 433350.000000
? Map scale
1
3
1. Students must pass strike/dip quiz prior to participation in the exercise 2. Demonstrate triangulation technique with the group
30
Work out answer key using base map before turning off sidewalk layers (so don’t select outcrop locations on sidewalk where high traffic and cannot stake outcrops down) This example is more complex than the simple plunging syncline I ran last fall. The simple syncline was challenging enough for some students, and an “easy opening game win” for others. I’ll run this more complex example with 15 outcrops this fall, but run it as a 4-5 hour exercise rather than just 2 hours.
40
30
4485120.000000
2
deFrancesco
35
4
5 8
40
6
30
7
Temporary classrooms
40 strike/dip
45
MN
11 50
12°
60
quartz arenite
4485000.000000
10 50
calcareous shale
Rohrbach Library
13 50
Lytle Hall
12
Legend Buildings
50 4484960.000000
4484960.000000
55
433250.000000
433300.000000
433350.000000
0
15
30
433400.000000
60
90
433450.000000
120 Meters
433500.000000
na
fol
d
il d
ow
nf
lat
op ce r t tc rfa a u l o su f n p ow di d il a n
? Correct location of outcrops on map using
Gravel SportFields UTM Zone 18N, NAD 1983 Kutztown University September 2009
Kurt Friehauf - Field Geology
[email protected]
Fall 2009 cardboard box
Assessment
Asphalt Concrete
14 55 15
Outcrop
4485040.000000
9 4485040.000000
4485080.000000
4485080.000000
40
cu
t
t
cu
ld
fo
triangulation ? Correct location of geologic contacts plotted on map with interpolated contacts between outcrops ? Correct strike/dip orientation data plotted on map ? Identify geologic structure in 3-D based on 2-D map ? Extra credit o calculate amount of fault offset assuming only dip-slip movement
Follow-up Once students are relatively comfortable with the basic concept, we go out to map rocks “in the wild.”
masonite surface 1”x2” boards for legs
Fall 2010 hinge
approx. 20 inches 50 cm
outcrop dip surface
? Brunton compass
Pre-exercise
433500.000000
Rickenback
? Plexiglas map board ? Colored pencils + hard lead mechanical pencil
433450.000000
30
Student equipment ? Hand lens for rock identification
433400.000000
5
Preparation 1. Using a digital GIS map of campus as base map, sketch a geologic map of an ideal geologic structure (e.g., fold, fault, faulted fold) on a separate layer. 2. Identify key locations where outcrops would be necessary to define the geologic structure 3. Print the final geologic map for self. 4. Print map sans geology for students to use as base map. 5. Select hand specimens to represent each mapping unit (e.g., quartz arenite, calcareous shale, etc.). 6. Make portable outcrops a. First iteration (Fall 2009) i. Cut cardboard box corners to make outcrops ii. Label outcrop rock type (“Rock A,” “Rock B,” etc.) with marker on box b. Second iteration (Fall 2010 with Dr. Sarah Tindall) i. Cut tripods and surfaces from stakes and ply wood, respectively – hinge with brass hinges or Cordura/Nylon ii. Notify groundskeeper not to remove outcrops without instructor’s consent 7. Place portable outcrops in locations on campus corresponding to planned map, including samples of appropriate rock type at each station
433300.000000
Answer key
4485160.000000
4485160.000000
433250.000000
4485120.000000
Lack of outcrop Less-than-heuristic outcrop locations Outcrop weathered Outcrop highly irregular surfaces Outcrop difficult to access Bad weather
433500.000000 4485160.000000
433300.000000
4485160.000000
433250.000000
This exercise removes several of the variables that make mapping difficult so students can more fully focus on the underlying concept of mapping.
Variable
This is what I look like, so if you want to talk, please track me down!
student base map
4485000.000000
ickies t s w yello ster o e p s u e h e Pleas y on t l t c e ided r i v d o r e p t i rker a or wr m s e th ment m with o c ke to ma
irregular bottom so students don’t just line Brunton up with base
nylon cord holds tripod leg spacing
Portable outcrops Last year I made the outcrops by cutting up cardboard boxes from the recycling bin. I pegged the boxes down using some spare 6 inch nails. Cardboard flexed a bit when heavyhanded students leaned their Bruntons on the surface, creating a little more spread in the measurements than I’d like. This year I’ll be constructing sturdier outcrops with a tripod design using lumber discarded by the theater department (an old set) that I pulled from the dumpster last spring.
Comments, please!