LOWER CAMBRIAN ANEMONE BURROWS FROM THE UPPER MEMBER OF THE WOOD CANYON FORMATION, DEATH VALLEY REGION, UNITED STATES: PALEOECOLOGICAL AND PALEOENVIRONMENTAL SIGNIFICANCE

Abstract

Large (up to 7 cm in diameter) and deep-penetrating (up to 30 cm) vertical burrows are described from the lower Cambrian Wood Canyon Formation of the Death Valley region, United States, and their paleoenvironmental and paleoecological implications are addressed. Trace fossils occur as dense populations that precede the earliest occurrences of Skolithos pipe rock in the region. These trace fossils are assigned to the ichnogenera Bergaueria, Conichnus, and Dolopichnus, and each represents the burrowing behavior of an anemone-like organism. These ichnotaxa occur within oolitic and sandy dolostones of a flood-tidal delta and lagoonal environment, respectively, and burrow fill is dominated by echinoderm ossicles. Ichnofabric indices of 4–5 and a tidally influenced position place these ichnotaxa within the same nearshore locus of bioturbation as Skolithos pipe rock; however, unlike Skolithos pipe rock, the tracemaker of these trace fossils can be identified. This study reveals that anemone-like animals were responsible for extensive modification of the marine substrate and this style of deep-penetrating bioturbation appears first in nearshore environments. This is in accord with the observation that many evolutionary novelties originate in nearshore environments, and specifically that deep-penetrating bioturbation originated nearshore before expanding offshore. This study also provides insight into the paleoecology of earliest Cambrian noncalcified cnidarians and their behavior and paleoenvironmental distribution during the Cambrian radiation.