ABSTRACT

This study documents the association of glauconitic pellets and trace fossils at two Cambrian sites: the Reno Member, Lone Rock Formation, in southern Wisconsin and the Lion Mountain Member, Upper Riley Formation, in central Texas. Each site reflects a marine paleoenvironment on the Cambrian Laurentian margin rich in marine life that was affected by shifts in shoreline and wavebase. Both units contain abundant glauconitic fecal pellets, which were mixed with terrigenous quartz, and ichnofauna that characterize siliciclastic sublittoral marine environments of variable energy. This combination of ichnologic features is suggestive of multiphase depositional histories. Initial stages are represented by intense invertebrate feeding and pelletizing large quantities of seafloor sediment. Glauconitization of the pellets in relatively quiet-water environments represents intermediate stages. Burrowing of the units rich in relict glauconitic pellets in high-energy settings represents the final episode at each site. Findings demonstrate a major shift in benthic paleoecology in response to a changing paleoenvironment. The glauconitic pellets were sufficiently resistant to survive processes associated with a shallowing marine environment, as they were incorporated into primary sedimentary structures (ripplemarks and crossbeds) and biogenic structures (burrows). The combined ichnologic, mineralogic and sedimentologic observations offer insight for depositional interpretation.

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