Abstract The Blackberry Hill quarries in Wisconsin, USA, expose the tidal flat facies of the middle to late Cambrian Elk Mound Group. The mature quartz sandstone of this succession is known for its rich ichnofauna recording the earliest animals conquering dry land. Microbial mats were abundant, forming a great variety of sedimentary structures on the ancient tidal flats. The fossil microbial structures reflect the paleoenvironmental conditions that existed by the time of burial. Erosional remnants and pockets, multidirectional ripple marks, and large mat clasts record episodic storms. This is supported by imprints of stranded medusae. Tattered surfaces constitute ancient microbial mats that disintegrated and released abundant mat chips at the end of a growth season, possibly pointing towards seasonality of the paleoclimate. Wide-spaced exposure of the heterogenous distribution of invertebrate trace fossils allows a glimpse into the local paleoecology and the influence of microbial mats. Trace fossils show that ancient mollusks remained in subtidal and intertidal areas. However, they may have ventured into the lower supratidal zone during spring high tides, where the mollusks bulldozed through thin-layered microbial mats in erosional pockets, but avoided thick, epibenthic mats of erosional remnants. Possibly during subaerial exposure, arthropods crossed upper intertidal and lower supratidal flat surfaces but appear to have not left behind any traces on thick, epibenthic mats of the lower supratidal zone. Wormlike trace fossils are restricted to shallow tidal channels of the lower intertidal zone, where no mats colonize.
Noffke et al. (Thu,) studied this question.