Emmett Evanoff describing the Fountain formation at Stop #1 of field trip (3/15/2003, 9:30 a.m.). The Fountain a mixture of conglomerates with dark red arkosic sandstone layers. It easy to see the broad trough crossbeds with truncated surfaces. The Fountain formation has a high feldspar content.
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Fountain formation: alternating layers of dark red and white are differing iron content. The white (or light) areas are more permeable and the iron has been leached out and reduced, leaving a lighter colored material. The dark red areas more muddy and are far less permeable. They still contain high levels of iron oxides. Note that these are not the original color of the rock. It is all the result of weathering and water intrusion.
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Fountain formation: arkosic sandstone and conglomerates.
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Fountain formation: Notice dark red layers are abruptly pinched out (as in lower center of image).
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Warning: Huge image (795 KB). Panoramic image looking at face of Fountain formation. Vertical image composed of 9 seperate images. These were then stitched together.
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Fountain formation. 1 of 9 images to make vertical panoramic image. (#1 is bottom, of formation, #9 is the top). The Fountain is not alluvial fan deposits as was previously thought. The Ancestral Rockies were nearby to the west were the deposition source. The layering and structure indicate that it was probably a braided stream, not a meandering river. The braided streams flowed east and dumped into the inland sea of the Pennsyvanian Epoch.
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Fountain formation. 2 of 9 images to make vertical panoramic image. (#1 is bottom, of formation, #9 is the top). There are no ripples present because it is too coarse.
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Fountain formation. 3 of 9 images to make vertical panoramic image. (#1 is bottom, of formation, #9 is the top)
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Fountain formation. 4 of 9 images to make vertical panoramic image. (#1 is bottom, of formation, #9 is the top)
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Fountain formation. 5 of 9 images to make vertical panoramic image. (#1 is bottom, of formation, #9 is the top)
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Fountain formation. 6 of 9 images to make vertical panoramic image. (#1 is bottom, of formation, #9 is the top)
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Fountain formation. 7 of 9 images to make vertical panoramic image. (#1 is bottom, of formation, #9 is the top)
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Fountain formation. 8 of 9 images to make vertical panoramic image. (#1 is bottom, of formation, #9 is the top)
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Fountain formation. 9 of 9 images to make vertical panoramic image. (#1 is bottom, of formation, #9 is the top)
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Notice cracks that are NOT on the bedding plane. These are exfoliation joints caused by weathering and the formation being brought back to the surface. The rock was under extreme pressure at depth. As it came up and weathered, these surface layers are popping off perpendicular to the bedding planes.
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Iron oxides have been leached out and reduced in the white bands. They are more permeable than the muddy red bands.
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Scours, tiny channels, developed and were later filled with sand.
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Scours, tiny channels, developed and were later filled with sand. Notice cross beds near top with truncated surfaces.
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More alternating banding. Colors are not original - the sands were originally gray. Water intrusion is the source of the iron oxides. The dark red muds have high porostity, but low permeability, meaning the pores aren't connected. Water is absorbed, but it doesn't pass through easily.
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