4.0 Simulating Sealevel Changes

A `sealevel file' (filename.sea) defining a eustatic sealevel curve can be input or a simple function can be specified. There are two types of sealevel files: Points or Waves. Point sealevel files linearly interpolate sealevel between given elevation points. Wave sealevel files define sine waves that oscillate around the `datum for sealevel oscillation' set below. If none is used for sealevel file, then the sealevel character can be set in the other sealevel parameters.

4.1 Simple Sinusoidal Sealevel Functions

A simple eustatic sealevel curve can be added to the model by adding values to the lines in the Sealevel Group File and leaving sealevel file as none. Figure 6.b shows the dramatic change in geometry that results from setting `sealevel oscillation amplitude' to 50 (meters) in comparrison to Figure 6.a which has no sealevel change incorporated.

Figure 6.a & figure 6.b Model run without eustatic sea level change (runex.dat with skip lines 3) and a model run using a eustatic sea level curve with amplitude = 50 meters, period = 8 million years (runex_eu50.dat with skip lines set to 3).

4.2 Wave Sealevel Files

A wave sealevel file allows the user to use multiple sealevel sine waves that can have different amplitudes and periods applied over different time intervals.

Example of simple wave sealevel file (sealevel.sea):

Wave sealevel file notes:
1) The first line must be the word `Waves'
2) The first and second columns set the ages that the sine wave will contribute to sealevel
3) The third column is the amplitude, the fourth column is the period and the fifth column is the offset of the sealevel sine wave

The file sealevel.sea specifies the two waves which are to be summed over the range of the simulation. Both sealevel curves act over the range 0 to 20 million years, however, a higher frequency, lower amplitude wave has been added to the 50 meter, 8 million year frequency curve. This can be seen by clicking in plotbasin. If the scroll bar is pulled to the bottom and the window stretched to fit the screen, the user will see the diagram in Figure 7. The composite sealevel curve from the wave sealevel file sealevel.sea can be seen on the right of Figure 7.

Figure 7:Wheeler diagram display illustrating the result of using a user-defined eustatic curve file (specified in line 1 of the setbasin Sealevel window). The setbasin library file used to generate this model run is sealevel.dat. The sealevel file sealevel.sea (shown above) was the wave file used to create the sealevel curve.

4.3 Point Sealevel Files

Point sealevel files linearly interpolate sealevel between known points. Example of point sealevel file:

Point sealevel file notes:
1) The first line must be the word `Points'
2) The first column is the age
3) The second column is the sealevel elevation

4.4 Haq's Exxon Sealevel Curve

Another option is to use the built-in sea-level curve from Haq et. al (1987). We give an example run (Figure 8) from 100 - 80 ma below, using the sealevel file exxon.sea.

Figure 8: Model run using the Exxon sea level curve (exxon.sea) beginning 100 ma. The library file used for this run is exxon_ex.dat with skip lines set to 2 and a vertical exaggeration of 75.

Note the method of using the Haq (1987) sea-level curve in this model is a bit non-intuitive due to the format of Haq's curve file. In this example it was necessary to 1) specify `sealevel file' as exxon.sea, and 2) set the time to start eustatic curve file (`time offset') at -100e6. This has the effect of starting the simulation with the sea level curve at 100 ma and forward modeling from that point in time (i.e. if it is a 20 m.y. simulation, the model will use the Haq (1987) curve from 100 to 80 ma).

Last Modified: 01:47pm EST, February 22, 1996 - Steven E. Nelson