HAVE YOU SEEN ME? ‘RIBBON STRUCTURES’ FROM THE CARBON CANYON MEMBER OF THE LATE TONIAN CHUAR GROUP

Macroscopic ribbon-like structures occur in the ca. 755 Ma Carbon Canyon Member of the Chuar Group in the Grand Canyon, Arizona. Compared to fossils known from this interval, ribbons are large – averaging ~1 cm wide, ~1 mm thick, and up to 17 cm long. Ribbons deform one another and exhibit evidence of flexure and twisting, suggesting that they were pliable prior to deposition. Ribbons are preserved in three dimensions as corrugated dolomicrite clasts that lack carbonaceous material within or on their margins. Ribbons were transported and are preserved on bedding planes, often stacked atop one another. Although their affinity is unknown, ribbons are ornamented by longitudinal striations and are similar to certain fossilized seagrasses and seaweeds, but could also be an anachronistic sedimentary structure. Like crystal fans in cap carbonates or soft-bodied organisms in coarse arenites, ribbon structures could represent another search image for earth scientists to use to decipher characteristics of Precambrian paleoenvironments.