Costa Rica Field Module - GSC 491L/499
Costa Rica Pacific Margin: Geomorphology and Tectonics
Dr.
Jeff Marshall & Dr. Jon Nourse
Geological Sciences Department
Required Assignments – Spring 2008
5. Playa Cedro Structural Geology Exercise,
Nicoya Peninsula
After completing our Nicoya Peninsula geologic mapping
project, we will conduct a structural analysis of highly deformed turbidite
beds of the Paleogene Cabo Blanco Formation. This unit is exposed on the
low-tide platform between Playa Cedro and Playa Cabuya. Using a Brunton
compass, you will record structural data from folds and faults in this unit
(e.g. strike/dip of bedding, axial planes, and faults; as well as trend/plunge
of fold hinges and slickenlines). Your instructors will indicate which data
types will be mot useful at this study site. In addition to the structural
data, you will also record GPS coordinates for each data location. You will
plot all data on a scale map of the field area. These data may also be plotted
on stereo-nets and used to interpret if the deformation is tectonic (oriented)
or soft-sediment related (chaotic). Your final report on the structural geology
exercise will include an excel table of your field data, a final map including
data from all students, stereo-nets, and a brief written description of your
observations and interpretations.
a.
Field Copy of Individual Structural Geology Map — (20 pts)
(Due in Costa Rica - March 30, 8 am)
Each student shall submit a professionally drafted
structural geology map of the Cabo Blanco Formation exposed on the Playa Cedro
shore platform. This map should display your own structural measurements and
other field observations. Use the base map and coordinate system we agreed upon
in the field. In addition to
mapping your structures with conventional symbols, include all the basic
supplementary information contained on any good geologic map. Be neat, precise and creative.
b.
Final Nicoya Peninsula Structural Geology Map and Report — (30 pts)
(Due at Cal Poly – Monday, April 14, 5 pm)
a. Submit an Excel spreadsheet of all observations
made during your 2-hour field exercise.
Include these columns: Waypoint #, UTM east, UTM north, strike, dip,
trend, plunge, and description.
Fill in the columns as appropriate.
b.
Transparencies of all student maps will be made available in the Geology office
beginning April 1. Use these
transparencies to create a vellum overlay that shows your structural
interpretation for the entire study area.
In particular, show all major and minor fold trends.
c. Write a description of this field area and
interpret its tectonic significance.
Type this out in one page or less, single-spaced. Your document should address the
following questions:
When were the turbidite
beds originally deposited, and at what orientation? What was the environment of
deposition?
What is the geometry and
structural style of deformation that has affected these beds? (or how is the
deformation manifested?)
How many deformational
events are preserved in this small area?
What is the age of
deformation(s)?
How do the structures we
mapped relate to the regional tectonic history of this particular part of the
Nicoya Peninsula? (What is the most plausible interpretation of these
structures and their field sequence?)