A COMPLEX, VERTICAL TRACE FOSSIL FROM THE UPPER CAMBRIAN GALESVILLE SANDSTONE NEAR BARABOO, WISCONSIN

Vertical trace fossils commonly occur in quartz arenites throughout the Phanerozoic. In Upper Cambrian strata, vertical traces tend to be simple straight or U-shaped tubes that penetrate only a few centimeters. Such is the case in an outcrop of the Upper Cambrian Galesville Sandstone southwest of Baraboo, Wisconsin, where 2- to 6-cm-long specimens of Skolithos are common and 4-cm-long specimens of Arenicolites are rare. The distribution of Skolithos at the top of trough-cross-stratified layers suggests episodic sedimentation. The cross-stratification along with the texture (very clean, medium-grained, well-rounded and well-sorted quartz sands) of the Galesville are consistent with the interpretation that the trace makers were suspension feeders.

A single, enigmatic vertical trace occurs in the uppermost layer of the Galesville, just below the Upper Cambrian Tunnel City Formation. The trace consists of at least two 2- to 3-mm-wide, sub-parallel, unlined shafts that branch downward at a depth of 10 cm. The branching results in the expansion of the width of the trace to 7 cm at its maximum depth of 20 cm. The trace resembles a miniature yarn mop with handles and mop head of about equal length. The complexity and depth of penetration of this trace stand in sharp contrast to other traces in adjacent strata and in other lower Paleozoic strata described in the literature.