New Approaches to Understanding the Mechanics of Burgess Shale-type Deposits: From the Micron Scale to the Global Picture

Abstract

ABSTRACT Cambrian Burgess Shale-type (BST) deposits are among the most significant deposits forunderstanding the “Cambrian explosion” because they contain the fossilized tissues ofnonmineralized organisms and provide a substantially different window on the radiationof the Metazoa than is afforded by the more “typical” fossil record of skeletal parts ofbiomineralized organisms.Despite nearly a century of research,BST deposits remainpoorly investigated as sedimentologic entities largely because they comprise fine-grainedmudrocks.Here,we describe a new,integrative approach to understanding a single BSTdeposit,the middle Cambrian Wheeler Formation of Utah,which reveals a dynamicinterplay of paleoenvironmental,paleoecologic,and sedimentologic/diagentic factorswithin a superficially homogeneous lithofacies.This millimeter-scale microstratigraphicand paleontologic approach is augmented by both outcrop and microscopic study.Thesetypes of data are applicable to issues of quite different scales,including micron-scale dia-genetic processes involved in fossil preservation,organism-environment interactions andpaleoecology of the early Metazoa,and regional and global controls on the distributionof BST deposits.