PRODUCING AND PRESERVING CLIMACTICHNITES

Most Climactichnites represent epifaunal trackways of an unknown, soft-bodied, Late Cambrian animal. Infaunal burrows made by the Climactichnites trackmaker are similar, but often better preserved. They exhibit fine striations atop transverse bars, lack lateral ridges, and like many Cruziana and Rusophycus, are preserved by overlying sediment sealing them from erosion. Modern gastropods, including Bullia digitalis and Polinices duplicatus make subaqueous and subaerial trackways similar to epifaunal Climactichnites and are the best analogue for understanding Climactichnites production and preservation.

To test the hypothesis that epifaunal Climactichnites were preserved by mucus, experiments using the aquatic gastropod Viviparus intertextus were conducted. Although copious amounts of mucus were secreted, it was insufficient to preserve Viviparus trackways. When trackways were submerged, mucus floated to the surface and agitation by waves mobilized the surrounding sand, thus undermining the trackway. Field observations of intertidal gastropods support experimental observations; agitation of sand by waves mobilizes the bed surface and completely obliterates trackways. In the Late Cambrian Elk Mound Group of Wisconsin, delicate arthropod trackways occur on the same medium-coarse grained bed surfaces as Climactichnites; these are not undertracks nor are they produced by mucus-secreting animals. Thus, other non-mucus mechanisms must be responsible for the preservation of Climactichnites surface traces. Rapid burial can be rejected because many traces are blanketed by fine-grained beds deposited under low-energy hydraulic regimes. Even more perplexing are coarse sand beds and tidal channels directly above Climactichnites trackways that are not eroded. Together, these suggest an alternative preservational hypothesis: microbial biofilms stabilized track surfaces on which many epifaunal Climactichnites were made. In support of this hypothesis, microbial sedimentary structures, such as domal sand buildups (i.e., sand stromatolites), are cross-cut by, and grow over some epifaunal Climactichnites trackways, and elsewhere in studied sections, other microbial structures are common.