Shape of gravel particles. What does it mean?

Patricia Manley
Middlebury College
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This is a lab assignment using three sets of gravel-size clasts. The purpose is to show how to measure gravel-size clasts and what their shape can discern about the environment they were formed in. This utilizes real data sets, hands-on investigation and statistical methods of analyses.

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Undergraduate course in sedimentary rocks

Skills and concepts that students must have mastered

The students need to be able to use a vernier caliper and use EXCEL spreadsheet to do calculations and graph data.

How the activity is situated in the course

This a stand-alone exercise. However, it can easily be changed to be a part of a series of exercises focusing on a particular research question.


Content/concepts goals for this activity

The exercise is aimed at showing how the shape of gravel particles can yield the environmental history of the sediment.

Higher order thinking skills goals for this activity

The assignment involves the measuring of clasts to determine look at four elements of shape (form, sphericity, roundness and surface texture). These are determined both subjective and quantitatively. Final analysis is to use all acquired data to determine the deposition site of the data sets.

Other skills goals for this activity

The exercise requires working in groups.

Description of the activity/assignment

Students need to do initial background reading on particle size analyses and in particular for this assignment Gale and Hoare (1991). In class, students work in groups measuring three sets of clasts. From the measurement of the relative lengths of the three orthogonal axes, the students calculate various shape elements. The activity continues by generating various shape plots and interpreting the data in the context of where the clast set came from (beach, glacial, fluvial or alluvial fan deposits).

Determining whether students have met the goals

The student must write up the lab exercise with all appropriate graphs, data sets and final interpretations.

More information about assessment tools and techniques.

Teaching materials and tips

Other Materials

Supporting references/URLs

Boulton, G.S., 1978, Boulder shapes and grain-size distributions of debris as indicators of transport paths through a glacier and till genesis, Sedimentology, 25, 773-799.

Dobkins, J.E. and R.L. Folk, 1970, Shape development on Tahiti-Nui. Journal of Sedimentary Petrology, 40, 1167-1203.

Dowdeswell, J.A., Hambrey, M.J. and W. Ruitang, 1985, A comparison of clast fabric and shape in Late Precambrian and modern glacigenic sediments., Journal of Sedimentary Petrology, 55, 691-704.

Gale, S. J., 1990, The shape of beach gravels, Journal of Sedimentary Petrology, 60, 787-789.

Gale, S.J. and P.G. Hoare, 1991, Quaternary Sediments, Petrographic Methods for the Study of Unlithified Rocks, Belhaven Press, p. 101-125.** required reading for the assignment.

Krumbein, W.C., 1941, Measurement and geological significance of shape and roundness of sedimentary particles, Journal of Sedimentary Petrology, 11, 64-72.

Sneed, E.D. and R.L. Folk, 1958, Pebbles in the lower Colorado River, Texas a study in particle morphogenesis, The Journal of Geology, 66, 114-150.

Stratten, T. 1974, Notes on the application of shape parameters to differentiate between beach and river deposits in southern Africa, Transactions of the Geological Society of South Africa, 77, 59-64.