Geology Tools: How to make a Jacob staff

Tutorial prepared by Daniel G. Koehl, senior geology student in the Dept of Earth Sciences, TTU. 

One of the simplest and most useful tools in geology is the Jacob staff. More robust than a tape measure or meter stick, the Jacob staff is used to measure bed thicknesses on an outcrop. The staff is usually 1.0-1.5 m and solid enough to be held perpendicular to bedding in areas of steep dip without collapsing or bending. (Click here to learn about apparent vs. true thicknesses.) The top of the staff can be designed to hold a Brunton compass, which is then used to ensure the staff is truly perpendicular to bedding. To learn more about the history of the Jacob staff as a surveying tool, click here.

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Tennessee Tech students Sidney Huskey and Kayla Hillis adjust Jacob staffs to be perpendicular to bedding, which is dipping to the east (right) in this photo. Multiple staffs are used to trace beds while they measure stratigraphic sections in the Fort Payne Formation of Tennessee.

 

This tutorial shows how to construct a simple and lightweight Jacob staff using materials that can be purchased at your local hardware store. The total cost is $10-$20, much less than professional models. While some staffs have a fixed attachment for a Brunton compass, this student version is best used as a measuring tool and photographic aid. It is an ideal design for a university-level field geology course.

MATERIALS

  • measuring tape in metric units
  • marker
  • electric tape
  • PVC glue
  • 5 ft. or 10 ft. length of 3/4-inch diameter PVC pipe (to be cut down)
  • two 3/4-inch diameter PVC caps
  • PVC pipe cutter [*Optional. Local hardware stores or your university machinery shop may be able to cut the pipe down for you.]

 

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Materials to make a Jacob staff. In this example, the PVC pipe is cut to 1.0 m.

 

CONSTRUCTION

Step 1. Decide what length you would like the staff to be: 1.0 m or 1.5 m. Both are useful in the field. In the images below, we will make a 1.0 m. Jacob staff to use in the Tennessee Tech sedimentary geology lab.

Step 2. Cut the pipe to be 1 cm LESS than your desired length. This allows enough space to attach the end caps. You can use a PVC pipe cutter, or you may be able to have your local hardware store or university machine shop cut the pipe for you.

Step 3. Place the PVC end caps on either end of the pipe. Use a tape measure to verify that the pipe is the correct total length with the caps in place. Then, use the PVC glue to attach the end caps.

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Once you verify the pipe is the correct length (1.0 or 1.5 m), attach the end caps using PVC glue.

Step 4. Use the marker and tape measure to mark the pipe at 10 cm increments.

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Careful to use metric units, not inches.

Step 5. At alternate intervals on the staff, wrap electrical tape between the notches. For this staff, 1.0 m, we taped five notches total, including one end with a cap.

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The sharp contrast between black electrical tape and the white PVC makes a great photographic aid in the field.

Nice work – – the completed staff should look like the one below. The next step is to take it into the field to measure section!

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1.0 m Jacob staff make of PVC pipe and electric tape.

 

 

 

 

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Students use dGB’s OpendTect software to interpret North Sea seismic data

Undergraduates in this semester’s Sedimentation and Stratigraphy course broke new ground in learning seismic sequence stratigraphy. Rather than using traditional 2D line exercises, the class utilized dGB’s OpendTect software package to interpret seismic data. This new educational approach is a product of collaboration between the TTU Earth Science Department, dGB OpendTect developers and geologists at Marathon Oil Company.**

In a two-hour lab session, students used OpendTect to view seismic data in 3D space, learning the software alongside basic geophysical survey concepts such as inlines and crosslines. Once comfortable with navigating the 3D seismic cube, students characterized reflector geometries using the HorizonCube tool. From there, it was a short mental hop to picking sequence boundaries and flooding surfaces in the North Sea dataset. The final product of the lab assignment was an interpretation using the Sequence Stratigraphic Interpretation System (SSIS).

Students use the HorizonCube tool.

Students use the HorizonCube tool.

OpendTect is an open-source seismic interpretation package, meaning that students could use the software in the classroom as well as on their own computers (if desired). Data for the exercise came from dGB’s Seismic Data Repository, a growing database of free seismic data to be used for education.

Discussing sequence boundaries and flooding surfaces in the North Sea dataset.

Discussing sequence boundaries and flooding surfaces in the North Sea dataset.

** To learn more about teaching sequence stratigraphy in 3D, please visit the OpendTect website, contact J. Wolak or attend our poster presentation at the 2013 AAPG Annual Conference and Exhibition: A new era in seismic sequence stratigraphy: Computational seismic stratigraphy in the undergraduate classroom

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Field Trip: Foreland Basin Deposits of East Tennessee

On Saturday, Nov. 3rd, students in the Sedimentation and Stratigraphy class loaded up into vans to visit the Sevier Basin in east Tennessee.

Field trip route to the Sevier Basin from Cookeville, TN

Deposits in the Sevier Basin are fascinating because they record the sedimentary response to one of the earliest episodes of mountain building in the eastern US. This mountain-building event is called the Taconic Orogeny and began approximately 472 million years ago. To get an idea of Tennessee paleogeography at this time, check out these amazing maps by Ron Blakey.

The Taconic Orogeny resulted from a series of small islands colliding with the eastern margin of Laurentia. As the islands accreted, they loaded the crust and caused concave-up flexure of the lithosphere. This resulted in a foreland basin – – the Sevier Basin.

The first stop of the day was at the Lighthouse Pointe Marina, where rocks of the Mosheim Member (Lenoir Formation) are exposed on the north side of Douglas Lake. In general, the thick limestone bedding strikes east-west and dips steeply (55-65) to the south. The rocks are dominantly carbonate – – micrites and grainstones with veins of sparry calcite. Dolomite is also common. To the north, an unconformity between the Knox Dolomite and the overlying Lenoir Formation crops out. Ages based on conodonts and graptolites put deposition of the Lenoir Formation beginning around 472 Ma.

Breaking in a new rock hammer on micrite.

Outcrops of the Lenoir Formation on the north shore of Douglas Lake, TN.

From the Marina, students could see the difference between the Lenoir Formation on the north shores of Douglas Lake and the Blockhouse Formation on the southern shores. The second stop was in Crescent Bend, a new subdivision with fantastic (and highly deformed) exposures of the Blockhouse shale. Students ate lunch in the shade of thinly-bedded siltstones and lime mudstones of the Blockhouse. The abrupt lithology change across Douglas Lake is due to the rapid subsidence of the Sevier Basin as it was tectonically loaded.

This diagram, from Ettensohn (1994) and Ettensohn (2008) shows the typical sequence of rocks that fill a foreland basin. In the case of the Sevier Basin: (1) the unconformity at the base would be the top of the Knox Dolomite; (2) the limestone above the unconformity would be the Lenoir Formation; and (3) the shales and siltstones would be the Blockhouse and Sevier Formations.

After lunch, the group drove south and west to Sevierville, with a brief stop at the Bush’s Beans Factory at Chestnut Hills, TN.

Mmmm… geologists love beans!

The final stop of the day was an exercise measuring stratigraphic sections in the Blockhouse Formation on Highway 66. Students fanned out across a 100m outcrop and worked in groups to characterize the interbedded lime muds, siltstones and fine sandstones. Each group measured stratigraphic sections, and the completed column showed a general coarsening-upward trend characterized by increasing silt and sandstone beds. Sedimentary structures included horizontal, silt-filled burrows found by Audrey and clay injection features identified by Bryant.

Measuring section in the Blockhouse Formation of the Sevier Basin, TN.

In addition to checking out foreland basin deposits, students worked their way through a vertical series of changing depositional environments, predicting the overlying lithologies using Walther’s Law. It was a productive and exciting day in the field.

Stay tuned for future sedimentary adventures in the Sevier Basin of east Tennessee.

References:

Ettensohn, F.R., 2008. The Appalachian Foreland Basin in Eastern United States. In: Sedimentary Basins of the World, vol. 5. Elsevier, The Netherlands. P. 106-162.

Shanmugam, G. and Walker, K.R., 1980. Sedimentation, subsidence, and evolution of a foredeep basin in the Middle Ordovician, Southeastern Appalachians. American Journal of Science, v. 280, p. 479-496.

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