Pleasanton sandstone exposed during construction at I-70 and Hwy N in St. Louis
Fluvial sandstone at the base of the Pleasanton Group
construction on the interchange at I-70 and Highway N. The "massive"
appearing sandstone is actually cross-bedded, and was deposited in
the channel of a meandering river. Thinner-bedded (and cross-bedded)
point bar deposits overlie the channel sandstone. The arrow points to a
"lag gravel" consisting of reworked limestone clasts and marine fossils
eroded from bedrock that was deposited in this area prior to development
of the river system. Beneath the gravel is an inconspicuous very thin
layer of dark gray marine shale containing conodonts, and then mudstone
(slight brownish cast) with a paleosol (neutral gray) developed on top.
These are the highest Pennsylvanian beds in Missouri east of the
western outcrop belt.
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