CHARACTERIZATION OF BURGESS SHALE TYPE BIOFACIES FROM THE WHEELER SHALE, UTAH

As probably the best known example of Konservat Lagerstätten (fossil assemblages of unusually well preserved remains), the Burgess Shale records a very rare image of both the typical hard part remains, and the almost exclusively absent soft parts remains of life in the aftermath of the Cambrian Explosion. The fauna of the Burgess Shale is well preserved in similar equivalent Burgess Shale Type (BST) deposits around the world, and has recently been characterized with a biofacies model (Gaines and Droser, 2005). One of the better known BST's is the Wheeler Shale. A multi-proxy analysis high resolution examination of the Upper Wheeler Shale of the Drum Mountains, Utah may provide new insight on the currently accepted model of Cambrian environments and the conditions that led to such wonderful preservation. The present model assumes the world has had relatively uniform environmental tolerances of benthic organisms since the early Cambrian. However, a potentially new biofacies below the predicted anoxic boundary could imply that life in the Cambrian did not comply with the assumptions of the model, and was indeed very different than previously acknowledged. Presently, there are three biofacies in the model based upon trace fossils seen similarly in younger and modern assemblages of fauna found in each: Oxic, Dysoxic, and Anoxic. The biofacies, which is characterized by an in situ diminutive fauna, is between the actual dysoxic/anoxic boundary and the last occurrence of benthic burrowers. The hypothesis is that the biofacies is a previously un-described biofacies that will either refute or refine the model for the progression of biofacies in equivalent faunas by application of independent proxies and detailed faunal study. The site includes all three previously recognized biofacies in succession with this new unit included in context. This interval could on a very practical scale serve as a good microcosm for BST's and depositional sequences around the world.