Abstract

Toroidal, radially ripple marked sedimentary structures in the Early Mississippian Napoleon Sandstone of southern Michigan are herein named rippled toroids. These objects are considered to be sand fillings (casts) of small depressions formed in unconsolidated, inner sublittoral marine sands. The field occurrence of rippled toroids, observation of similar structures in Recent sediments, and experimental evidence support the conclusion that the original toroidal depressions were produced by vortex currents, probably along the margins of rip currents or at the intersection of opposed longshore currents.

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