Lower Cambrian trace fossils of the White-Inyo Mountains, eastern California: Engineering an ecological revolution

The objective of this research was to gain an understanding of the early stages of the Cambrian transition from "matground" to "mixground" substrates by examining the Lower Cambrian succession in the White-Inyo Mountains, eastern California. Lower Cambrian siliciclastic strata in this succession represent a range of depositional environments and contain abundant horizontal and limited vertical bioturbation. Although macroscopic microbially-mediated sedimentary structures are common on bedding-plane surfaces, x-radiography and petrography of studied samples revealed no microscopic evidence for microbial influence. Planolites, a simple horizontal trace fossil, is the dominant type of bioturbation throughout, although x-rays and thin sections of samples reveal the presence of rare vertical bioturbation. Subtle patterns in bedding-plane bioturbation indices and diameters of Planolites traces primarily reflect slight variations in environmental conditions rather than large-scale evolutionary trends. However, an overall trend toward increasing quantities of horizontal bioturbation up-section may reflect a combination of environmental variation and evolutionary innovation.