UGA Stratigraphy Lab

The data is in the strata

Backstrip 1.1 Instructions

Overview

You can backstrip a section in three steps. First, make a data file using TeachText and save it as backstrip.dat. Next, double-click on the backstrip program and it will automatically open your data file, as long as the data file is in the same folder/location as the backstrip program. The program will show you the results as it runs, which might take a while for large data sets. The program will automatically save your results in a file called backstrip.res. Finally, you can open your output file in any program like Excel to plot it.

Making a data file

Use TeachText to make your data file. You must save it as backstrip.dat. Any other name will not work and it must be typed entirely lowercase.

Enter your data starting with the uppermost layer and ending with the bottom layer. Your data set will run correctly only if it is in stratigraphic order (youngest at the top, oldest at the bottom). After the last set of data, be sure to press return, or it won't read the last line of data.

For each layer, type the following in order on one line:
- thickness (in meters, including a decimal point)
- a blank space
- water depth (in meters, including a decimal point)
- a blank space
- the lithologic code (no decimal point).

Your data should look something like this:
50.0 2.0 1
0.0 0.0 1
21.5 25.0 2
34.5 10.0 2
0.0 0.0 1
20.0 25.0 2
52.5 10.0 2
38.0 10.0 2
37.1 25.0 2
1.0 2.0 1

You should note several things. The youngest layer is at the top; the oldest layer is at the bottom. In the actual data file, I would make sure to press return after the last (oldest) layer. The youngest layer is 50.0 meters thick, was deposited in 2.0 meters of water, and has a lithology code of 1, indicating that it is a sandstone (see below). Note that every thickness and water depth has a decimal point, and that no lithologic code has a decimal point.

Lithology codes:
1: Sandstone
2: Shale
3: Limestone

Count the number of lines of data you have and write this down somewhere. Save your file when you're finished, and quit TeachText.

Running the program

Make sure your backstrip.dat data file is in the same location/folder as the backstrip program. Double-click on the backstrip program to run it. It will automatically read your data, calculate the backstripping, then display a table of the results. It will also save your data as backstrip.res and this file will be located in the same location/folder as the backstrip program.

Watch the program as it runs to see its progress. After it reads your data it will first write how many lines of data you have. Verify that this matches what you wrote down. Next, it will write the data to the screen; you should verify that the numbers and sequence make sense. When the program says "Beginning calculations...", be patient as this step may take several minutes for large data sets.

The program will then show what it is printing to the output file. The output is in the same order that you typed it: oldest at the bottom, youngest at the top. The first three columns of output are your data, the last column is the total accomodation space accumulated by the end of that layer. In most cases, the a-space column will monotonically increase over time, although it can decrease in some situations. Once the program is finished, press return and the program will automatically quit.

Viewing your results

You can open your data file in Excel or a similar program. Column labels are not included in the output file, but from left to right, the columns are: thickness, water depth, lithology, cumulative accomodation space. Note that this last column is not the space created in any given time step, but the total amount of accommodation space made to that point in time.

Based on your research, assign a numerical data corresponding to the end of each layer, and then you can plot the a-space column on the y-axis and the age on the x-axis. A-space should increase downwards on your plots, and time should proceed from left to right (i.e., oldest on the left, youngest on the right). This may take some fiddling to get your particular program to do this right.

Update notes - version 1.1

This modification eliminates certain rare conditions under which the model would fail to converge and enter an infinite loop. These modifications also speed execution time in all cases.

August 1998
Steven Holland