Modeling Sea Level: Lateral and Vertical Facies Changes

Kate Pound

Earth & Atmospheric Sciences Dept., St. Cloud State University

I use the Large Class Demonstration version in a large-enrollment General Education geology Class. I also use it in smaller (20-40 person) classes to pre-teach or further develop concepts before and sfter going into the field. I use it in Introductory -level geology classes, and as a review in more advanced undergraduate-level classes (Field Geology, Sedimentology, Stratigraphy). We have used it in upper elementary and high-school level (Grades 6-12) as a way to bookend the field work / field trip. I use the small (Lab / Classroom version) once I have introduced the Large version.

Be able to follow directions/instructions. .
Difference in sediment graion size. Concept that different sedimentary settings display different grain-size characteristics which are related to distance from source. Ohn and don't spill the beads on the floor unless you want to pick them up.

I have used it to pre-teach concepts, but I much prefer using it as a follow-on to the Field trip. That way the students concentrate on observing and thinking about what they can observe (collecting data) in the field, and are not worried about understanding the Big picture. Then they can start to place the sedimentary rocks they saw in the field into the big picture once they have collected and reviewed their observations. I do always have a couple of leading questions in the field-based exercise so that big-picture thinkers are already being poked and prodded when they are in the field.

Inquiry
Earth Science

Modeling the effect of sea-level change in lateral and vertical facies changes in a sedimentary basin.
Understanding Walthers Law. Being able to look at a fence diagram and draw a hypothetical sea-level curve. Critical evaluation of a model

Using observations to interpret and predict outcomes in unfamiliar situations (sedimentary basin architecture / facies patterns)
Critical evaluation of model.

Recording simple data. Drawing very simple schematic stratigraphic columns with a key. Learning to predict and interpret

I introduce a simplified series of depositional settings (Figure 1), which are: Stream, Beach, Shelf & Continental Slope, and Ocean Basin (siliciclastic) and Ocean Basin (carbonate). Coarser sediment is deposited closer to source (fluvial), finer sediment deposited farther from source. Farthest from source, where essentially no siliciclastic terriginous material is available carbonate sediment is deposited. The 'position' that it is easiest to track is the transition between the stream sediments and the fluvial sediments; this transition is assumed to mark the position of sea level. I do NOT use a horizontal line to mark sea level because it gets into so many problems; firstly there is no slope to the basement surface (I deliberately set it up like this; I want them to see Walther's Law in action; it also gives them something to critique about the model). Students need to grasp the fact that the sedimentary settings will 'move' with sea-level, and that the settings in Figure 1 shift as sea level position changes, and the sediments deposited consequently change too (i.e. we are seeing Walther's Law in action).

Most importantly, in smaller (less than 20) classes I try to make sure I hear each of the explaining what is happening. Especially if they are doing some peer-teaching in small groups. In terms of grading/evaluating I look for the following:

1. Whether they have been able to draw a sea-level curve for the Paleozoic sedimentary sequence of SE Minnesota.

2. Whether they have correctly interpreted the sea-level history for the 'mystery basin'

3. Whether they have indicated the 'correct' shoreline / sea-level movement on the table in the handout.

4. Whether they can answer the 'write-in question' - this is usually a problem that it is clear they are having that I try to deal with by asking a problem-specific question on the handout sheet.