6.07 Exercising the SEDPAK EDIT Menu - 0pening a File to Edit

To become familiar with the SEDPAK EDIT menu, turn to Chapter 3 of the manual. Read Section 4.1, then load VailClast.db. To load this file, select Open from the File pull-down menu on the SEDPAK EDIT panel (Section 2.06). This used in a manner similar to the File option of the SEDPAK EXEC menu.

Note: Every time a file is modified with the EDIT menu, it should be saved (pull down File to Save or Save As...) before loading and restarting this file for execution of the SEDPAK program.

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6.08 Comments

Read Section 3.01 and write some comments in the Comments box on the SEDPAK EDIT menu. Don't forget to use the Save As... and change the file name if comments are to be saved.

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6.09 Constants

Read Section 3.02.

• € Purpose: Try out the various SEDPAK Constants by experimenting with each of the buttons on the Constants dialog.
  -Turn buttons "on" and "off."
  -Save the file.
  -Execute the file by Loading and Restarting from the EXEC menu.

The Balloon Help explains the use of this option and each button within this option.

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6.10 Setup

This menu determines the general dimensions of the simulation output. Read Section 3.03 and then edit the various Setup parameters.

Duration of Time Step:

• € Purpose: To investigate effect of changing the number of time steps in a simulation.

• € Exercise:

-Load Demo_VailClast.db from SEDPAK EXEC or EDIT. Watch the simulation closely.
-Go to the SEDPAK EDIT window.
-Click on Set up.
-Now change the Duration of Time Steps from "0.04" to "1".
-Click Apply; notice the change in Number of time steps (from 50 to 20).
-Click OK.
-Save the file as VailClast_your name_.db.
-Load the file VailClast_your name_.db from the SEDPAK EXEC menu.
What are the differences between VailClast.db and VailClast_your name_.db?
-Try to decrease the Duration of time steps and see what happens.
What can be concluded from this exercise?

Width of Column

• € Exercise:

-Load Demo_VailClast.db. Watch the simulation carefully.
-Change the width of column by clicking on Setup on EDIT menu.
-Multiply the number of column by two.
-Save the file and Load and Restart.
What is the difference between smaller and bigger width of column?
-Try to reduce the width of column, too.

Sea Level Offset

• € Purpose: To place the zero axis of the sea level curve at the most reasonable "depth" for a simulation run.

• € Exercise:

-Load Demo_VailClast.db. Watch closely where the sea level intersects the basin margin.
-Open Setup window and change the sea level offset by typing 50.
-Save, Load and Restart the simulation.
What does sea level have to do with the sediment geometries?
-Try to increase the sea level offset and see how it is changes the simulation output.

Note: Remember that if the Sea Level Offset parameter is changed by too much, the sea level will leave the field of view and the program may exit with a Shore Error (see Exercise 6.11 below). Pay special attention to the discussion in Section 7.01 about shore errors and on aliasing effects related to too few time steps and/or columns in Section 7.02.

Wave Base

• € Purpose: This function defines the boundary between shallow and deep water.

• € Exercise:

-Load Ex_WaveBase.db. Watch the simulation carefully.
-Open Setup and change the Wave Base to 200 meters.
-Save, Load and Restart.
-Try to decrease the Wave Base and see the differences.
What conclusion(s) can be made about lower and higher Wave Base position?

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6.11 Understanding Shore Error

Read Sections 1.11 and 3.05 to become familiar with the causes of a Shore Error and how to avoid this effect.

Shore Error occurs when:

No accommodation space is provided for sediment deposition.
Sea level does not intersect the basin surface.

• € Purpose: To become familiar with the causes of Shore Error

• € Exercise :

-Load file Ex_Shore-error1.db.
When did the shore error occur?
Why did it occur?
-Try to fix the shore error.

• € Exercise :

-Load file Ex_Shore-error2.db.
-When did the shore error occur?
-Why did it occur?
-Try to fix the shore error.

6.12 Basin Surface and Deus ex Machina Surfaces

This parameter allows users to define the initial basin surface and unconformity surfaces. Read Section 3.04 on the Basin Surface.

• € Purpose: To become familiar with creating Basin Surfaces on plotters and data sheets, and use Surface Snapshot and Simplify curves.

Initial Basin Surface

• € Exercise:

Creating an initial Basin Surface.
-Load Ex_NewFile1.db from SEDPAK EDIT menu.
-Click Basin Surface.
-Click Options and Show Datasheet.
-Insert distance 20 and 50, depth 75 and 170, respectively.
-Try to create the basin geometry using both the datasheet and the plotter.

Unconformity

• € Exercise:

Creating an Unconformity (Figure 6.12.1 and 6.12.2)
-Load Ex_MakeCanyon.db to the SEDPAK EXEC menu.
-To make an unconformity surface at -2.8 Ma: Pause the simulation at 2.8 Ma.
-Pull down File on the EXEC menu.
-Click on Surface Snapshot which activates a File dialog.
-Type in MC28.sur and click OK. This step creates a surface (.sur) file.
-Click Basin Surface.
-Click Load and open MC28.sur.
-Now the coordinates of the surface of -2.8 Ma will be transferred to the simulation file.
-Pulldown curves and activate Simplify and edit the curve by reducing the points.
-Add new points to make canyons.
-Do the same for creating an unconformity at -10.8 Ma

The capability to prescribe the quantity of erosion at a sediment surface enables the creation of subaerial erosion surface associated with sea level drops, and also the development of sharp submarine erosional scarps along the basin margin. The sediment removed by this deus ex machina function has no further involvement with the simulation.

Although the geometries associated with this erosion may be correct, the filling of this submarine valley within the simulation is accomplished by processes acting along the plane of section. This oversimplification obviously does not match the processes that fill valleys in nature. However, it is possible to vary the rate of filling to match the natural fill of a valley, and so create realistic sediment geometries.

Note that the basin surfaces are identified by age, and the "initial" basin surface is identified as the curve which corresponds to the start time of the run. Any other curves are unconformity surfaces or deus ex machina events.

Summary: These exercises demonstrate that the removal of all sediment above a plane create a new basin surface at different times. This mimics the erosion both downslope and out of the plane of section. Following the erosion, sediment fills the resulting valley (Figure 6.12.2).

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6.13 Sea Level

Read Section 3.05 and note that editing both the plotter and data sheet for the digitized Sea Level curve is similar to editing the Basin Surface plotter and data sheet.

• € Purpose: Creating a sea level curve

Digital Sea Level Curve

• € Exercise:

- Load Ex_Sealevel.db.
-Click Sea Level and choose Digitized curves.
-Click on Options and show datasheet.
-Make a new curve and name it "1," thereby giving the curve an ID number.
-Type in :

Time	Depth
-20	-240
-15	-200
-10	-150
-5	-130
0	-140

-Click OK and Save the file.
-Run the program. The output should look like Figure 6.13.1.

Creating sinusoidal Sea Level curve

• € Exercise:

-Open the Sea Level plotter menu from the EDIT menu and create and name a new curve.
-Click Option, open the datasheet.
-Click Create Range at the base of the data sheet.
-Input increments of 0.5 and click OK.
-Click Calculator on the datasheet and select the depth column.
-Click Cycle Description.
-Type in Amplitude = 25 and Period = 5.
-Click on Sine and depress the + button.
-Click Apply on the Sea Level Calculator.
-Now add -250 to all the depths on the datasheet.
-Click OK in the Sea Level Calculator.
-Save the file.
-Run the simulation. The output should look like Figure 6.13.2.
What is the difference between the first and the second simulation?

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6.14 Subsidence, Faulting, and Salt Tectonics

Read Section 3.06 and practice editing the Subsidence plotter and datasheet.

• € Purpose:

-To create a Subsidence curve for a location in the basin
-To create a fault.

Keep in mind that SEDPAK is only capable of modeling vertical faults and faults that deform the basement.

Subsidence curves can be constructed in two ways:

-Manually inputting the rate of subsidence using the worksheet or plotter
-Using the Backstripping Calculator

Creating a fault.

• € Exercise:

-Open Ex_Faulting.db.
-Study the fault development in the simulation.
-Open subsidence menu by clicking Subsidence option in SEDPAK menu.
-Choose View Curves on the plotter.
-Using Copy Current Curve create a fault between kms 220 and 224, so that the area between kms 100 and 200 is a graben. The output should look similar to Figure 6.14.1.

The Backstripping dialog is used to determine subsidence rates during sediment deposition. For the exercise below a Backstripping file has been created to test and use the Backstripping Calculator.

Backstripping Calculator

€ Purpose: Become familiar with the function of the Backstripping Calculator.
Backstripping is an inverse modeling scheme to reconstruct the local subsidence behavior using well data. Once sediment thickness, age, lithology, and paleobathymetry have been inserted into SEDPAK's Backstripping Calculator, the subsidence curve for a particular location can be determined.

• Exercise:

This exercise provides a well data set to enter into the Backstripping Calculator to determine the correct subsidence history for a simulation.

-Load Ex_Backstripping.db file into the EXEC menu.

For better display:
-Turn off surface lines under Display Controls.
-Under View option:
Select well position to 250.
Turn Well Position on.
-Activate the Zoom function and enter the coordinates of the area of interest for this exercise.
Left 150
Top 300
Right 400
Bottom -500

In file Ex_Backstripping.db, the subsidence rate at distance 0 m and 500 m are constant throughout the simulation, at 0 m/Ka and -0.02 m/Ka, respectively. In this exercise, we will incorporate well information located at 250 m to define the subsidence curve at location 250 m using the Backstripping Calculator.

-Click on Subsidence on the Edit Menu.
-Select Backstripping Calculator and enter the well information provided below:

-Click Save and name the file Backstripping250.bkstr.
-To create a subsidence curve from this chart, click OK and locate the curve. In this exercise, type 250.
-Save the file and run the simulation.

The result is shown in Figure 6.14.2. Note that the basin surface of the new file is slightly improved by entering the well information.

To Load a Backstripping file (.bkstr) that already exists

• € Exercise:

-Click on Subsidence.
-Click on Backstripping Calculator.
-Load Backstripping250.bkstr created from previous exercise and the file will be transferred to SEDPAK.
-To activate this, click Apply and a dialog asking for the location of this curve is initiated.
-Type in 250 for the location.
-Close the Backstripping Calculator window and run the program.

Try to locate any errors in the input. When the corrections are made, follow the aforementioned steps for saving the new curve. Do not forget to remove the old subsidence curve at location 250. The answer key to this exercise is Ans_Backstripping.db (Figures 6.14.1 and 2), the correct Backstripping Calculator file for this exercise is BackstrippingExer.bkstr.

Salt Diapirs

Salt tectonics can be modeled using the Subsidence parameter. Salt diapirs can be created in one of two ways: 1) the surface may be uplifted at the location where the diapir is to form, or 2) the Subsidence curve(s) for the diapir may be set to zero while the surface around it subsides.

• € Purpose: Creating Salt Diapirs

• € Exercise:

-Open Ex_SaltDiapir.db
-Watch the development of the diapir.
-Open Subsidence menu on SEDPAK EDIT.
-Create another salt diapir between the 43 and 49 km columns, stops the diapir intruding at around -1.4 Ma. The result should look like Figure 6.14.5.

Chapter 6, Section 15

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