Grains at the margins of Ordovician and Silurian Skolithos were oriented significantly parallel to the trace in vertical section, and tangential to the margin in horizontal section. Control analyses showed no similar orientations developed away from the traces. Microprobe analyses of the same traces showed anomalous concentrations of cations at trace margins. Similar analyses of impregnated Holocene burrows suggest that these cation concentration gradients are not diagenetic. Control analyses of various inorganic sedimentary structures showed that the chemical anomalies are biologically produced. Similar petrographic and geochemical studies on structures of questionable origin in the Huronian Bar River Formation produced identical results to the Recent, Silurian, and Ordovician examples. These techniques allow objective criteria to be employed to differentiate between organic and inorganic sedimentary structures.

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