Tara Curtin

Geoscience Department, Hobart & William Smith Colleges

This several week long project is designed for an undergraduate course in sedimentology. I assume that students have completed one semester of physical geology prior to enrollment. There are anywhere between 9 and 16 students who enroll in this course.

By this time in the semester, students have learned to identify common minerals and rock fragments found in sedimentary rocks and sedimentary structures in different environments based on field observations and lab simulations. Students know how to identify siliciclastic and carbonate rocks. Students have also been introduced to proper use of a Brunton compass for mapping (pace and compass) and measuring a stratigraphic section with a Jacob staff.

This project is comprised of a sequence of field exercises that occurs during the middle portion of the course that spans five weeks. Each week, during the 3.5 hr long lab period, we visit different Devonian outcrops that are within 20-40 minutes of campus. We also take a required 3-day trip to the Catskills (4.5 hrs from campus) to explore different Devonian strata. Students are aware that this trip is required prior to enrollment in the class.

At each field locality, students, in groups of 2 or 3, will:

• measure stratigraphic section
• identify sedimentary rocks
• identify sedimentary structures and know how to measure paleocurrent direction and plot these data on rose diagrams or stereonets
• identify fossils and their taphonomy to determine the possible environmental of deposition (water depth, salinity, wave action)
• draw stratigraphic columns by hand that includes all of the above information

Back in the lab, each student will:

• plot paleocurrent data on rose diagrams or stereonets (first, by hand and later using a computer program) and
• draw neat stratigraphic columns by hand that includes all of the above information.

For this project, we visit five local outcrops and take one 3-day trip to the Catksills, NY region. Students have 8 stratigraphic columns to use for their paleoenvironmental analysis of Lower and Middle Devonian strata across New York State.

• determine lithofacies associations
• make process interpretations of sedimentary textures and structures, linking products to processes that we saw in the field or simulated in the lab during the first month of the course
• determine environment(s) of deposition of each formation
• correlate the stratigraphic sections across New York, especially the Hamilton Group, based on lithostratigraphy and then biostratigraphy
• create fence diagrams
• draw generalized facies maps for different time slices of the Lower and Middle Devonian across New York (with scant data)
• create generalized, annotated cross-sections that depict the basin highlands and lowland locations and sediment transport direction
• write a short paper that describes the geologic history of New York during the Lower and Middle Devonian that focuses on environments of deposition, periods of erosion and quiescence, and tectonism by synthesizing all of the above data

• work in groups of 2-3 students (teamwork)
  
• develop keen observation skills
• keep an accurate, legible, organized field notebook that separates observations from interpretations
• Excel and other computer programs
• use Brunton and Jacob staff to measure stratigraphic section
• use Brunton to measure paleocurrent directions
• plot stereonets and rose diagrams

The purpose of this project is to develop students' field skills by starting at the outcrop scale and then building on these experiences to create a regional picture of events by visiting multiple sites across NY. Students become proficient and efficient at measuring stratigraphic sections in teams after 5 weeks of field work. We visit eight outcrops within 5 weeks and measure detailed stratigraphic sections at each site. We begin by learning how to measure a detailed ~6 m thick stratigraphic section of siliciclastic rocks exposed in a local state park (that students visited during their introductory physical geology course) using a Jacob staff and Brunton. The outcrop is comprised of only 3 lithologies, but many sedimentary structures (bioturbation, flute casts, drag marks, groove casts, asymmetric ripples (plan view) and trough cross-beds). These lithofacies repeat several times even within the ~6 m measured section as these are turbidite deposits. We return to the lab after measuring the section and students work up their field data to construct a detailed, hand-drawn stratigraphic section for the first time. Students also make paleocurrent measurements in the field when possible and learn to plot these pooled class data during the next class meeting. For the other local sections, students perform the same field observations and measurements. At these locales, several formations crop out and students learn to recognize them based on their lithologic and paleontologic composition. Both carbonate and siliciclastic rocks occur at these sites. During the 3-day weekend field trip, students measure three stratigraphic sections of Lower Devonian through Middle Devonian strata and recognize that, for example, western NY lacks the Helderberg carbonate sequence and that the Oriskany Sandstone is thicker and laterally continuous in eastern NY rather than the lenses that crop out in central-western NY. Students also realize that the Hamilton Group changes character as they march across NY, building on their reading of Walther's Law in Boggs (2006) and their in-class stratigraphic correlation (lithostratigraphy, biostratigraphy) exercises from Fichter and Poche (2001) completed prior to the weekend field trip.

1. I collect field notebooks and make comments and suggestions on how to improve their work using large Post-It notes rather than writing in their notebook. Because I expect students to read these comments and use them to do a better job during the next field exercise, I collect their notebooks at the end of lab, and return them by the beginning of the next class meeting. Their graded work depends on the quality of their field notes. To grade the notebook and the work penalizes students twice.
2. I grade the hand-drawn stratigraphic sections as this is the basis of all other analyses. These are submitted each week.
3. I also grade any paleocurrent plots generated each week.
4. Each week, I pose a few questions before we go into the field to focus our work that day. I grade their responses each week.
5. As part of the culminating assignment, students submit facies maps and correlated stratigraphic columns for a grade and identify any stratigraphic pinchouts and unconformities that occur across the state as well as coarsening or fining upwards sequences.
6. The culminating exercise is to write a geologic history (~6 typed pages, single-spaced, not including figures) of New York during the Lower and Middle Devonian using all the data and figures already submitted and returned. All of their previously work (stratigraphic columns, stereonets, etc.) are re-submitted with the paper. I expect any errors in the figures, maps, and sections to be corrected in this final version.

• Boggs, S. Jr. 2006. Principles of Sedimentology and Stratigraphy, 4th edition, Prentice Hall, 662 p.
• Brett, C.E. and Ver Straeten, C.A. 1994. Stratigraphy and facies relationships of the Eifelian Onondaga Limestone (Middle Devonian) in western and western-central New York State. New York State Geological Association 66th Annual Meeting Field Trip Guidebook, p. 221-270.
• Compton, R.R. 1985. Geology in the Field. Wiley. 416 p.
• Fichter, L.S. and Poche, D.J. 2001. Ancient Environments and the Interpretation of Geologic History. Prentice Hall: Upper Saddle River, NJ. 310 p.
• Johnson, K.G. 1987. Strand-line facies of the Catskill Delta Complex (Middle and Upper Devonian) in eastern New York State: in Centennial Field Guide Volume 5, Roy, D.C. (ed.) Northeastern Section of the Geological Society of America, p. 129-132.
• Marshak, S. and Englender, T. 1987. Exposures of the Hudson Valley Fold-Thrust Belt, west of Catskill, NY: in Centennial Field Guide Volume 5, Roy, D.C. (ed.) Northeastern Section of the Geological Society of America, p. 123-128.
• Patchen, D.G., Avary, K.L., and Erwin, R.B. 1985. Correlation of Stratigraphic Units of North America (COSUNA) Project, Northern Appalachian Region: American Association of Petroleum Geologists. Chart. 1 sheet.
• Stow, D.A.V. 2005, Sedimentary Rocks in the Field: A Color Guide. Academic Press. 320 p.
• Tucker, M. 2003. Sedimentary Rocks in the Field. Wiley. 244 p.
• Woodrow, D.L. and Isley, A.M. 1983. Facies, topography, and sedimentary processes in the Catskill sea (Devonian), New York and Pennsylvania: Bulletin of the Geological Society of America. vol. 94. p. 459-470.
• Woodrow, D.L. 1983. Topography and sedimentary processes in an epicontinental sea: In, Stanley, D.J. and Moore, G.T. (eds.) The Shelfbreak: Critical Interface of Continental Margins, Society of Economic Paleontologists and Mineralogists, Special Publication. no. 33. p. 159-166.