LARGE EARLY CAMBRIAN SEA ANEMONE BURROWS FROM THE UPPER MEMBER OF THE WOOD CANYON FORMATION, DEATH VALLEY REGION, UNITED STATES
The upper member of the Wood Canyon Formation is a mixed carbonate-siliciclastic succession that represents deposition within a tidal inlet complex. Five facies are recognized: 1) interbedded siltstone and hummocky cross-stratified sandstone of the offshore transition; 2) amalgamated hummocky cross-stratified sandstone of the lower shoreface; 3) planar laminated and small-scale bidirectional trough cross-stratified sandstone of an ebb-tidal delta; 4) medium-scale trough and tabular cross-stratified oolite with reactivation surfaces of a flood tidal delta; and 5) sandy dolostone and dolomitic sandstone of a back-barrier lagoon.
The three recognized ichnogenera Bergaueria, Conichnus, and Dolopichnus are found within flood-tidal delta and lagoonal environments and all represent the behavior of sea anemones. Bergaueria is interpreted as a shallow-penetrating resting or dwelling trace. Conichnus is also interpreted as a resting or dwelling trace; however, deflected funnel laminae likely reflect the added component of escape or equilibration. Dolopichnus preserves active burrowing by the anemone, and a basal swell at the terminus of the burrow represents the expanded physa of the burrowing anemone, acting as an anchor.
This study reveals that sea anemones were responsible for extensive modification of the marine substrate, and this style of deep-penetrating bioturbation originated in onshore environments. This fits with the notion that evolutionary novelties originate in onshore environments; specifically, that deep-penetrating bioturbation originated onshore before expanding offshore. This study also provides insight into the paleoecology of earliest Cambrian non-calcified cnidarians and their paleoecological behavior and paleoenvironmental distribution during the Cambrian radiation.