Implications
of a sand volcano in the Late Cretaceous Upper Member of the
Wahweap Formation
Wolf, Hannah
L., Simpson,
Edward L., Storm,
Lauren P., Tindall,
Sarah E., Wizevich, Michael C., and Simpson, Wendy S., 2008, Implications
of
a
sand volcano in the Late Cretaceous Upper Member of the Wahweap
Formation [abs]: Cordilleran Section (104th Annual) and Rocky
Mountain Section (60th Annual) Joint Meeting (19–21 March 2008),
Geological Society of America Abstracts with Programs, Vol. 40, No.
1, p. 40.
A
vertical slice through a well-preserved sand volcano was discovered
1.8 meters above the base of the Late Cretaceous upper member of the
Wahweap Formation at the Gut in Grand Staircase – Escalante National
Monument, Utah. The internal structure of the sand volcano permits
the reconstruction of the vertical fluid flow pathways and
interpretation of seismogenesis during local faulting.
The 1.3 meter long conduit for the sand volcano cuts across eight
beds composed of lithic sandstone. In its lower reaches the conduit
is a narrow dike-like feature cross cutting a low-permeability
fine-grained sandstone seal. Above the seal, the pipe widens and the
pipe edges are more diffuse in high permeability sandstone, whereas
the pipe contracts in diameter through lower permeability
sandstones. The change in character of the pipe and the
structureless sandstone near the pipe indicates that lateral flow to
the conduit was greater in the high permeability zones. Within the
pipe a winnowed concentration of pebbles 30 cm below the vent
indicates that vertical fluid flow was of suffucient velocity to
elutriate fine sand forming the surface sand volcano. The internally
massive, cone-shaped surface volcano is slightly asymmetrical
measuring ~120 cm in apparent diameter and ~20 cm in height. The
volcano onlaps the lee face of a fluvial dune.
Modern sand volcanoes often develop with high magnitude seismic
events proximal to faults. This sand volcano is in close proximity
to a series of normal faults with preserved syntectonic deposits in
the Waheap Formation indicating that the fault slip history included
some intense high magnitude seismic activity.