Constructing Fence Diagrams
Fence diagrams allow greater illumination of facies relationships through the connections of several measured
sections. The sections could be surface sections, subsurface sections constructed from well data, or a
combination of the two. Each section of the fence is termed a panel.
Assignment
Construct a fence diagram using the descriptions provided below.
Procedures
1. Mark the locations of each section on your paper as if it was a map. For this exercise, start by placing
point for C1 about 1 inch from the base of the paper and ¼ inch from the lower right hand side of the
paper. C2 is located approximately 60 miles along a trend of N20W from C1, C3 is located 40 miles
west from C2, C4 is located 30 miles from C3, and C1 is located 40 miles S80W from C4. Use a
horizontal scale of 1”= 10 miles to separate the column localities. Assume that the longer margins of
your paper are exactly N-S.
2. Determine total thickness of columns
3. Determine the scale to draw the length of the column. We will use 1”=100’
4. Draw a vertical line representing the length of the section, and you mark off the stratigraphic boundaries
along the line. The descriptions below are from oldest to youngest lithologies.
5. The next step is to choose pairs of sections between which to draw the “fence” or panels, i.e. the facies
and stratigraphic relationships. The selection of panels should be based on the relative locations of
sections and the lithologic and stratigraphic variations. Where a choice is possible between several
sections, select those which will present the panel in the most advantageous orientation and will show
the widest variation in lithologic and stratigraphic relationships. Most sections will be connected to two
other sections with panels. Some will be connected to three and those on the edges may be connected to
only one. In cases were a section is connected to three others, one of the panels will be partially hidden
behind another one We will make a fence diagram linking C1 to C2, C2to C3, C3-C4, and C4 to C1
6. Use generalized lithologic symbols for columns. Need not be detailed, but must capture the general
lithologic description
7. Each lithologic description provided for each locality is for an individual formation
C1
Granite—25”+. Unconformity separates granite from overlying sedimentary sequence
Sandstone—100’ thick, coarse to medium grained sandstone, texturally and compositionally immature, 30%
feldspar, 50% quartz, 20% lithic fragments, asymmetrical ripples, crossbeds, channel scours filled with
conglomerate and sandstone, lacks fossils. Color light blue
Sandstone, 50” thick, fine grained, compositionally and texturally supermature, large-scale multidirectional
crossbeds, inverse grading in sand comprising crossbeds, some plant fragments and root casts. Color light
yellow
Shale—25’ thick black, leaves impressions, some siltstone and sandstone laminations with cross laminations
and symmetrical ripples on parting surfaces, minor evaporates, some large tracks of animals in places. Color
light green
4” ash layer marks the top of shale.
C2
Granite—25”+. Unconformity separates granite from overlying sedimentary sequence
Interbedded Sandstone and conglomerates/breccia—300’, Conglomerate beds up to 20’ thick and both paraand polymictic conglomerates/breccias represented, with normal and inverse grading, logs and plant fragments,
poorly to moderately defined, red interstitial matrix of clay and sandstone. Some large scale scours. Color light
red
Sandstone-very coarse, texturally and compositionally immature, 50% lithic fragments, 40% quartz, 10%
quartz, hornblende, unidirectional cross beds, large scours.
2’ thick ash layer in sandstone in 150’ up in section with geochemical signature similar to that encountered in
C1.
C3
Granite—25”+. Unconformity separates granite from overlying sedimentary sequence
Sandstone—25’ thick, coarse to medium grained sandstone, texturally and compositionally immature, 30%
feldspar, 50% quartz, 20% lithic fragments, asymmetrical ripples, crossbeds, channel scours filled with
conglomerate and sandstone, lacks fossils
Sandstone, 50” thick, fine grained, compositionally and texturally supermature, large-scale multidirectional
crossbeds, inverse grading in sand comprising crossbeds, some plant fragments and root casts.
Shale—50’ thick, black, leaves impressions, some siltstone and sandstone laminations with cross laminations
and symmetrical ripples on parting surfaces, minor evaporates, some large tracks of animals in places. 4” ash
layer marks the top of shale
Sandstone, 50” thick, fine grained, compositionally and texturally supermature, large-scale multidirectional
crossbeds, inverse grading in sand comprising crossbeds, some plant fragments and root casts.
Shale—100’ thick, black, leaf impressions, some siltstone and sandstone laminations with cross laminations and
symmetrical ripples on parting surfaces, minor evaporates, some large tracks of animals in places.
4” ash layer marks the top of shale
C4
Granite—25”+. Unconformity separates granite from overlying sedimentary sequence
Shale-300’ thick—Dark, fish scales and fossils, fissile, lacks bioturbation,
2’ thick ash layer in sandstone in 200’ up in section with geochemical signature similar to that encountered in
C1.
Questions
1. What is the depositional environment(s) represented by each formation. You may group formations if they
represent similar depositional environments. Explain why you made these interpretations.
2. Where was the source area located? Use arrow on fence diagram and label source area to indicate
provenance direction.
3.What is the likely provenance for the rocks?
4.Construct a simplified facies block model, much like you did for the first class exercise showing the lateral
relationships between the depositional environments.
Why would it be very useful to measure more sections, especially between panels C2 & C3, and panels C1 and
C4?
Example of fence diagram.