GSC 491L/499
- Geological Sciences Field Module
Spring 2008
Costa Rica Pacific Margin: Geomorphology and Tectonics
Dr. Jeff Marshall & Dr.
Jon Nourse
Geological Sciences Department
Required
Assignments:
1. Research Article Readings
& Group Discussion
Each student will be assigned 3 research articles related to our field area. You will be expected to read your articles in advance and develop a basic understanding of their content. On three different evenings during the trip, we will hold an informal group presentation and discussion session following dinner. Each session will have a different theme focusing on a particular set of articles. During each of these sessions, you will give a short (5 min) presentation summarizing the one article assigned to you for that evening. As a group, we will discuss the implications of each of these articles for understanding the geology and tectonics of our study area.
2. Field Notebook
Each student is expected to keep a field notebook that will be turned in at the end of the field module. Use your notebook to record your daily field activities, geologic data, GPS coordinates, field sketches, and descriptions of outcrops, mapping units, and samples. Be as complete and neat as possible.
3. Volcán Poás Exercise
We will visit the active summit crater of Poás volcano and walk along several short trails in the area. You should make a detailed sketch of the crater and its deposits as viewed from the observation platform overlooking the main crater. We will provide a geologic map and a topographic map of the summit area to aid in your interpretation. Compare your observations and sketch to the maps. Upon return to the hotel, you will construct a topographic profile and geologic cross section across the crater using the topo map, geologic map, and your sketch. You will submit your first drafts of these illustrations (field version) for grading while we are in Costa Rica. Final drafts (office version) will be submitted with your complete field module report due in early Spring Quarter.
4. Cerro Buenavista Geologic
Mapping Exercise
We will map geologic units exposed along the Cerro Buenavista Road between Playa Cedro and Delicias on the Nicoya Peninsula. Each student will be provided with a set of topographic maps of varying scale for use in the field. On our first day, we will visit key outcrops as a group to familiarize ourselves with the map units, ranging from Cretaceous oceanic basalts and Paleogene turbidites, to late Pleistocene marine terrace deposits and Holocene beach sands. We will also pay close attention to the marine terrace geomorphology, local faults, and the relationship between basement rocks and Quaternary units. Students will work in teams to complete the mapping on our second day. You will map on the topo sheets in the field, and will record location data using hand-held GPS. The GPS data will be used later to create an accurate final map with mapping/illustration software at Cal Poly. While in the field, you should also make careful lithologic descriptions of each mapping unit. Depending on progress, we may expand the field area to include other roads. In addition to a final field map, you will create a stratigraphic column and an accurate cross-section along the mapping transect. You will also create a correlation diagram linking marine terrace elevations to a late Pleistocene sea level curve. Your final field module report will include your field maps, final map, stratigraphic column, cross section, and sea level correlation, along with a written description of the geologic/tectonic history of our field site.
5. Playa Cabuya Structural
Geology Excercise
After completing our 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 at 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; and trend/plunge of fold hinges and slickenlines). Your instructors will indicate which data types will be mot useful at this study site. Later, this data will be recorded on stereo-nets and used to interpret if the deformation is tectonic (oriented) or soft-sediment related (chaotic). Your final field module report will include stereo-nets and a brief description of your interpretations.
6. Misc. Short Field Exercises
Throughout our trip, we may stop at interesting outcrops or geomorphic features that provide insight into regional geologic history. You may be asked to examine an outcrop or landform, and create a detailed sketch of important features. You will then be asked to interpret the geologic history or geomorphic processes effecting that outcrop or landform. As instructed, these short “outcrop vignettes” may also be required in your final report.