Page 203 - Carbonate Facies in Geologic History

190 Pennsylvanian-Lower Permian Shelf Margin Facies

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MISSOURI
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Fig, VI-1S. Generalized paleogeography of Upper Pennsylvanian sea during limestone phase
of cyclic deposition in midcontinent North America. From Heckel (1972c, Fig,l)
ing wave action in shallow water. One mound flank dips westward 15° and at
least 50 m of relief is indicated, The normal dip into the neritic shelf, however, was
probably more on the order of 1 0, The open carbonate shelf sediments northwest
of the buildups are of burrowed argillaceous bioclastic wackestone with fenes-
trates, other bryozoans, brachiopods, sponges, and echinoderms,
The same types of flat lenses of micritic phylloid algal buildups are common
across the Pennsylvanian outcrops of north central Texas. As in Kansas, these
represent low carbonate banks occurring in the shelf lagoon between sandstone
channels and clay mud ponds, It is significant that Chico Ridge near Bridgeport,
Texas appears to represent oolitic lime sand accretion into a channel lying south
of a platy algal mound oriented north-south; this situation is probably a duplica-
tion of the Kansas mound-channel relations described by Heckel.