FECAL PELLETS, GLAUCONITE, REGRESSING SHORELINES, AND BURROWING ORGANISMS INDICATE DYNAMIC MARINE ENVIRONMENTS IN THE LATE CAMBRIAN OF TEXAS AND WISCONSIN

An important aspect of biodeposition involves the activity of organisms concentrating sediment in the form of fecal pellets. Abundant fecal pellets on the seafloor indicate an intense level of metabolic activity, and abundant glauconitic pellets, originating as fecal material, imply a thriving benthic community. The broad tropical epicratonic seas of the Late Cambrian must have been ideal for intense invertebrate feeding and pelletizing large quantities of seafloor sediment, because they commonly are characterized by abundant glauconitic pellets.

This study documents the coprolithoid (fecal-related) nature of glauconitic pellets and associated trace fossils at two Cambrian sites in Texas and Wisconsin and offers insights for depositional interpretation. Ichnologic evidence suggests a multi-stage depositional history for such deposits. Production of fecal pellets by benthic organisms represents the initial stage, glauconitization of the pellets represents an intermediate stage, and burrowing of the units rich in relict glauconitic pellets represents the final episode at each site.

Each study site contains abundant glauconitic fecal pellets that were mixed with terrigenous quartz grains, and the resident ichnofauna characterize siliciclastic sublittoral marine environments of variable energy. The glauconitic pellets were incorporated into primary sedimentary structures (ripplemarks and crossbeds) and biogenic structures (burrows). Shoreline regression is evident at both study sites. The presence of relict glauconitic fecal pellets in a high energy setting implies a dynamic depositional history that brought shallow marine ichnotaxa in association with deeper water glauconitic pellets.