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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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The Starved Rock Member of the St. Peter Sandstone has been described as a clean, medium-grained sandstone that was deposited in a broad band across northern Illinois. This deposit displays a sequence of sedimentary structures that indicates deposition in shallow water. From the base upward the structures include (1) massive beds; (2) small-scale trough cross
-strata; (3) high-angle tabular
cross
strata; (4) large-scale trough
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cross
strata; (5) alternating beds of horizontal, burrowed laminae and small-scale trough
cross
strata; and (6) massive and burrowed beds.
Tabular cross
strata and small-scale trough
cross
strata show a consistent northwest orientation, whereas the large-scale trough
cross
strata show no preferred orientation. Both tabular and large-scale trough
cross
strata consist of medium-coarse sand, whereas the small-scale trough
cross
strata and horizontal laminae are of medium sand. Discontinuous horizontal laminae, present at irregular vertical intervals in the
section
, consist of interlaminated medium to fine sand and silt.
Recently, the sand waves of the North Sea have been proposed as an analog for the St. Peter environment in Wisconsin, because of the presence of such sedimentary structures as very large-scale tabular cross
strata. However, the sedimentary structures, directional data, and textures observed in the Starved Rock Member resemble more closely those developed on nonbarred coasts, like that of Oregon. The presence of inferred deeper water sediments within the St. Peter, landward of the Starved Rock Member, indicates that this sand body may have been deposited as an offshore shoal.
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