The First Field Trip: An introduction to sedimentation and stratigraphy

Upon completion of this trip the student will be able to:

1. Recognize sedimentary rocks and describe major stratigraphic units.
2. Determine the thicknesses the nature of contacts and the orientation of stratigraphic units.
3. Recognize periods of geologic time not represented in an outcrop.
4. Observe internal features fossils structures etc. of the rock units.
5. Construct a complete stratigraphic section including all the units.
6. Identify modern environments where these rocks are forming.
7. Apply stratigraphic principles and observation of an outcrop to create some hypotheses about the environments of deposition and a depositional history of the rocks.

This field trip was designed for Pescadero Point beach in northern California but could be adapted to any sedimentary rock outcrop that includes at least two sedimentary units with well exposed structures separated by an unconformity. The field trip is designed for introductory students as an introduction to sedimentary rocks and stratigraphic principles.

Field Trip Handout/Assignment (Microsoft Word 129kB Aug25 09)

This trip will likely take a full lab period (2-4 hours). When adapting for other outcrops some photos of appropriate modern sedimentary environments can replace the modern beach, or looking at fluvial units and a modern river.
Some other notes are mentioned on the last page of the exercise:
Discussion points:
Part II:
Based on the Principle of Superposition, what can you infer about the units in the cliff face?
Based on the Principle of Initial Horizontality, what can you infer about the lower units on the cliff face?
Based on the Principle of Cross Cutting Relationships, what can you infer about the relationship between the two units?
Part III:
Try to get the students to assemble their own list of things to look for and describe based on their readings and activities previous knowledge what they see and instructor guidance. Things to look for and describe include: thickness of beds nature of cross-bedding range of rock types fossils or trace fossils burrows feeding tracks etc. other sedimentary structures grain sizes shapes and sorting color other distinguishing features. Also discuss reasons why fossils occur in lenses why burrow holes are filled etc.
Part V: Go over the sequence of events in the field: what happened first 2nd etc. and then ask them to write about it.

Assessable products:

• Outcrop sketch and stratigraphic column (individual products - can consult other students)
   
• Answers to handout questions (can be done as pairs/groups)
   
• Geohistory (if gone over in the field, the order should be correct and the description should be the assessed)

Sources:

• Press F. and Siever R. 1998 Understanding Earth W.H. Freeman and Co.: New York 682 p.
• Steno N. 1669 De Solido Intra Solidium Naturaliter Contento Dissertationis Prodromus.