IntroductionAs the final laboratory project in introductory historical geology, the class is divided into groups of 3 to 5 students to analyze a sedimentary rock core and associated geophysical log. Each group describes and interprets 24 feet of split core, along with a gamma log for the same interval (Fig. 1). Students use hand lenses, binocular microscopes, spray wash bottles, dilute HCl, a logging form (Fig. 2), and selected research papers on textures, structures, and fossils in the core, as well as papers on regional paleogeography, paleoceanography, and tectonics. Each group gives a 10-minute presentation to the class and submits a graphic log. All students turn in a 2-page report with their own observations and interpretations. Assessment is based on both the group presentation and individual report.

Student Goals• Learn to use a logging form to describe and interpret subsurface core• Correlate a geophysical log with rock types• Synthesize observations of rock type, texture, structures, fossils, and mineralogy• Formulate hypotheses about the sedimentary depositional environment• Work as a team to collect and interpret scientific data, and communicate results in a group presentation• Write a concise and scholarly individual report

AcknowledgmentsI thank Cindy Carr and John Conners for over a decade of assistance in the historical geology laboratory and with the monitoring well; Francye Hutchins for her vision of the core as part of an Earth Science Week celebration; Alcoa, Inc. and MHC Xploration for their generous donation of the well and core; Mike Miller of Geo Cam, Inc. for donating geophysical and video logs; and the Texas Bureau of Economic Geology for donating preparation of the core. Generous support for the project was also provided by Austin Community College.

Well Core and Geophysical LogCore for this project was taken from a water well donated to the college by a drilling company, MHC Xploration, and coal mine, Alcoa’s Sandow Mine. Splitting, facing and boxing of the core were donated by the state geological survey, the Bureau of Economic Geology, and the geophysical log was donated bya water-well logging company, Geo Cam, Inc. (Fig. 4). The college later purchased shelving to store the core (Fig. 5).

Potential sources for core and geophysical logs include:• Petroleum and mining companies• Geotechnical engineering firms• State geological surveys• USGS Core Research Center

(http://geology.cr.usgs.gov/crc)

This exercise could be modified to use well cuttings in place of core; With cuttings there would be more emphasis on textural trends, mineralogy, and possibly microfossil identification.

ConclusionsGroup presentations, individual papers, and student course evaluations for the past 10 years suggest that this is a meaningful learning experience for most students. The project combines the excitement of discovery (e.g. fossil shark’s teeth, wood fragments, and accretionary lapilli) in original scientific research with an integration of concepts of sedimentology, stratigraphy, paleontology, tectonics, and oceanography

Robert H. BlodgettDepartment of Physical Sciences, Austin Community College, 1212 Rio Grande, Austin, Texas 78701-1785

Figure 1. Student examining core with a hand lens, a logging form on his clipboard and geophysical log on the lab table.

Figure 3. Group presents results of their study of 24 feet of core. Student in the center uses a diagram that he made to explain how the accretionary lapilli in the core formed in a volcanic eruption cloud.

For further informationPlease contact rblodget@austincc.edu. More information on this project can be obtained at serc.carelton.edu/teachearth/ and www.austincc.edu/rblodget.

Figure 5. Core is stored at one campus and transported to others for historical geology classes. Cindy Carr, laboratory technician, stands next to shelving purchased for core storage.

Figure 4. a. Wax-coated cardboard box containing 3-inch diameter core of white, bioturbated fossiliferous chalk of the Cretaceous Atco Formation (left) overlying brown, organic-rich shale of the Eagle Ford Formation (right). b. The geophysical log for the well shows a spike in the gamma log for the cored interval in Figure 4a.

Tying it all together – A capstone project for historical geology

Gamma Log

Interval in core to left

Figure 2. Graphic logging form developed by Alan J. Scott and modified for description of the siliciclastic and carbonate sedimentary rocks found in the core. Students log the core at ascale of one inch on the form for each foot of core. A copy of the form can be downloaded from serc.carelton.edu/teachearth.

a. b.