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This section exposes a
1000' vertical succession of steeply dipping turbidite strata in the middle Jackfork Group.
These strata record repeated cycles of turbidite sedimentation in a deep marine basin.
The rocks are exposed along two spillway walls that are approximately 300' apart.
The overall vertical sequence grades upward from thin-bedded sandstone and shale at the base,
through thicker-bedded sandstone, into massive pebbly sandstone and conglomerate at the top.
Major cycles of sandstone deposition are separated by 10' - 30' thick shales of hemipelagic
or debris flow origin.
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 Click for Larger View. Steeply dipping sandstone turbidite beds along west spillway wall.
 Click for Larger View. Alternating distal and proximal turbidite packages. Each bedding plane separates an individual depositional episode. | ||
 Click for Larger View. Mainly sandstone beds - typical of proximal turbidites at North end of section.  Click for Larger View. Thin beds of sandstone and shale typical of uppermost beds (distal beds) in turbidite package. | ||
 Click for Larger View. Chaotic deposit separates 2 major cycles of sandstone deposition.  Click for Larger View. Francois gets closer look at turbidite beds. | ||
 Click for Larger View. Stephanie provides scale for sandstone float with scour marks.  Click for Larger View. Another chaotic deposit between 2 major cycles of sandstone deposition. | ||
 Click for Larger View. Channel-fill overlying chaotic deposit and heralding beginning (?) of a major sandstone deposition cycle.  Click for Larger View. Sam zeroes in on the muddy sandstone channel-fill and its contact with thick overlying sandstone beds. | ||
 Click for Larger View. Unconformity - Cretaceous (Tokio Gravel) overlying Pennsylvanian (Jackfork Sandstone) - just north of DeGray spillway. | |
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