The Exercises

The exercises below involve the analysis of parasequence using outcrops. The parasequences are seperated from each other using major surfaces that include TS (transgressive surfaces), mfs (Maximum Flooding Surface), and SB (sequence boundary). This is followed by the examination of the stacking patterns of the parasequences.

An analysis of parasequences should the lead to the interpretation of the depositional settings of the lithologies that are enveloped by the surfaces listed above. Finally the parasequence sets can be used to identify potential acquifers, acquicludes, hydrocarbon source rocks, reservoirs and seals.

EXERCISES 1-3

Exercise 1 - Introduction to clastic parasequence identification in outcrop

Click on thumb nails to expand images.

The interpretation process is divided into two steps:

If you intend to apply the techniques you have learnt in this exercise to other successions you should realize that the marine flooding surface often forms the maximum flooding surface (mfs), which marks the boundary between the prograding Highstand System Tract and the top of the Transgressive System Tract. The mfs is also often characterized by the presence of radioactive and often organic rich shales, glauconite, hardgrounds and burrows, and widespread thin-bedded concentrations of fauna (condensed sections) with high abundance and diversity. An mfs can often be the only portion of a sedimentary cycle which is rich in fauna. Often in a landward direction the maximum flooding surface may match the underlying trangressive surface formed during or just after the inital transgressive phase that immediately follow sea level lowstands. In this case glossifungites burrows may occur within this surface and the surface may be cemented by carbonates.

In the case of this exercise each of these particular parasequences is a shoaling upward cycle that is bounded by a maximum flooding surface. As a result the lower surface of the parasequences cycle will be the base of the deeper lithofacies layer which overlies the top of a shallowing upward cycle. The upper boundary is the top of a shallower lithofacies layer that is overlain by a deeper lithofacies layer. You can mark each cycle with a triangle that narrows in the direction of the finer grain size. Alternatively you can use a curved arrow to indicate the grain size variation and so it's shoaling upward character. An arrow that moves to the left indicates that the grain size is coarser and so the water is becoming shallower. Patterns of the stacking of parasequence sets are used in conjunction with bounding surfaces and their position within a sequence to define system tracts (Van Wagoner et al., 1988). Note the solution this exercise use the triangle to track variations in the grain size of each parasequence and the maximum flooding surface (mfs) is assumed to lie at this boundary marked by the sharp change in grain size (Exercise #1 Solution).

Exercise # 1 - Kennilworth Section to the North East of Helper in the Book Cliffs:

Approximate location. Lithofacies. Solution.

If you are confused in this exercise you should work you way through the descriptions in the Introduction to high frequency clastic parasequences.

 

Exercise 2 - Correlate measured sections on the basis of lithofacies and parasequences

Exercise 2
The objective of this exercise is to continue learning how to identify vertical sets of parasequences in clastic sections while extending this to use these parasequences to correlate the three measured sections located in the Book Cliffs (Exercise #2 diagram linked below).

As in the exercise above the sections provided in this exercise were previously described by Van Wagoner et al, (1999). For this exercise you should combine the interpretation of the Exercise #2 diagram what you did with the Exercise #1 diagram, the block diagram of a clastic shoreline (Figure 5 ), the photographs of Coe et al, 2003 (Figure 6 ) and Table 1. As in Exercise #1 the interpretation process begins with the two steps of Exercise #1 and now includes a third step which involves the correlation of the parasequences you have identified in the three measured sections:

As before examine the block diagram (Figure 5 ) see how hierarchies of sedimentary structures match depositional setting. Use these associations to subdivide the sediments of the three measured sections into their depositional settings. Now use a combination of this subdivision, and abrupt changes in grain size and/or sedimentary structures to identify parasequence boundaries in the sections.

Now identify marine flooding surfaces in the three sections and use these to separate parasequence from each other. Mark each of the parasequences either with triangles that broaden in the directions of coaser grain size or arrows so an arrow that moves to the left indicates that the grain size is coarser and so the water is becoming shallower. As in Exercise #1 each of the parasequences in the three sections is a shoaling upward cycle bounded by a marine flooding surface. Thus the lower surface of each of the parasequences cycle is the base of the deeper lithofacies layer that overlies the top of a shallowing upward cycle. The upper boundary is the top of a shallower lithofacies layer that is overlain by a deeper lithofacies layer. You should mark each cycle with a curved arrow to indicates the grain size variation and so its shoaling upward character. An arrow that moves to the left indicates that the grain ize is coarser and so the water is becoming shallower. Patterns of the stacking of parasequence sets are used in conjunction with bounding surfaces and their position within a sequence to define system tracts (Van Wagoner et al., 1988).

Two bounding surfaces are provided as a framework on which to base the correlation three measured sections of Exercise #2. Correlate the parasequences and make a regional sequence stratigraphic interpretation of facies geometries between the surfaces you have identified, establishing the lithofacies, and the high-frequency sequence stacking pattern and truncation within the section.

Exercise # 2 - Tie sections from Panther Canyon, Kennilworth and Coal Canyon in the Book Cliffs:

Approximate location. Lithofacies. Solution.

You will find that correlation of the shales is the key to understanding the depositional geometries of each of the parasequences (see the solution). The question you should ask yourself is: "Are these parasequences aggrading, prograding or retrograding?" To answer this question you should refer to the section in the terminology to determine what the requisite geometries are for each of these processes.

Exercise 3 -Regional sequence stratigraphic interpretation

Exercise 3
The objective of this exercise is to continue learning how to identify vertical sets of parasequences in clastic sections while extending this to use these parasequences to correlate the twelve measured sections in the Book Cliffs.

As in the two earlier exercises associated with outcrops the sections provided in this exercise were previously described by Van Wagoner et al, (1999). For this exercise you should combine the interpretation of the Exercise #3 diagram with what you did with the Exercise #2 and #1 diagram and the block diagram of a clastic shoreline Figure5. There is now a difference. Previously all the parasequences of the three sections built out over each other. Now you should find evidence of updip erosion to the West. You should ask yourself "What is the evidence of this erosion and what is initiating it?"Again use Figure 5 to help your interpretation.

As in Exercise #1 and Exercise #2 the interpretation process begins with the two steps of Exercise #1 and the third step of the correlation of the parasequences you have identified in the twelve measured sections. As before examine the block diagram (Figure 5 ) that matches hierarchies of sedimentary structures and depositional setting. Use these associations to subdivide the sediments of the twelve measured sections into their depositional settings. Now use a combination of this subdivision, and abrupt changes in grain size and/or sedimentary structures to identify parasequence boundaries in the sections. As before identify marine flooding surfaces in the sections and use these to separate parasequences from each other. Look for evidence of updip and westward erosion.

As in Exercise #1 each of parasequences in the lower portions of the sections is shoaling upward cycle bounded by a marine flooding surfaces. Thus the lower surface of each of the parasequences cycle is the base of the deeper lithofacies layer that overlies the top of a shallowing upward cycle. The upper boundary is the top of a shallower lithofacies layer that is overlain by a deeper lithofacies layer. As before you should mark each cycle with either a triangle or a curved arrow to indicate the grain size variation and so its shoaling upward character. In the sections to the east the arrow that moves to the left indicates that the grain size is coarser and so the water is becoming shallower (ask the question are these a shoreline represented by a beach, stacked beachs, a delta or tidal flat). However in the upper portions of the nine sections to west the arrow that moves to the right and indicates that the grain size is finer. In this case the water is still becoming shallower but the reduced grain size reflects a setting (either tidal flat, estuarine channels, or fluvial over bank) protected from the winnowing effects of waves. As before the patterns of the stacking of parasequence sets are used in conjunction with bounding surfaces and their position within a sequence to define system tracts(Van Wagoner et al., 1988).

Two bounding surfaces are provided as a framework on which to base the correlation twelve measured sections of Exercise #2. Correlate the parasequences and make a regional sequence stratigraphic interpretation of facies geometries between the surfaces you have identified, establishing the lithofacies, and the high-frequency sequence stacking pattern and truncation within the section. You will find that correlation of the shales is the key to understanding the depositional geometries of each of the parasequences. Note the updip westward erosion of the upper parts of the sections.

Exercise # 3 - Tie sections from Gilson Gulch to Coal Canyon in the Book Cliffs:

Approximate location. Lithofacies. Solution.

As in Exercise #2 the question you should ask yourself is: "Are these parasequences aggrading, prograding or retrograding?" To answer this question you should refer to the section in the terminology to determine what the requisite geometries are for each of these processes.

For more detailed discussion of high frequency sequence analysis of the Book Cliff escarpment on which this exercise is based examine the references at the base of the Introduction to high frequency clastic parasequences in outcrop.