2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 338-2
Presentation Time: 1:45 PM


BOAG, Thomas H., Department of Geological Sciences, Stanford University, 450 Serra Mall Bldg. 320, Palo Alto, CA 94305, DARROCH, Simon A.F., Earth and Environmental Sciences, Vanderbilt University, PMB 351805 2301 Vanderbilt Place, Nashville, TN 37235-1805 and LAFLAMME, Marc, Department of Chemical and Physical Sciences, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON L5L 1C6, Canada, tomboag@stanford.edu

The latest Ediacaran (~579-542 Ma) is characterized by globally distributed marine soft-bodied organisms of unclear phylogenetic affinities colloquially called the ‘Ediacara biota’. In the absence of systematic agreement, previous workers have tested for underlying biogeographic, ecological, and paleoenvironmental factors that may control the occurrence of Ediacaran macrofossils in stratigraphic space and time. Three taxonomically distinct ‘assemblages’, termed the Avalon, White Sea, and Nama were subsequently identified and incorporated into Ediacaran biostratigraphy. After ~15 years of new fossil discoveries and taxonomic revision, we test the validity of these assemblages using a comprehensive database of Ediacaran fossil occurrences. Using multivariate analysis, we also test the degree to which taphonomy, time (evolution), and paleoenvironment (bathymetry) explain the taxonomic composition of these assemblages. We find that: 1) the three ‘assemblages’ remain distinct groupings after incorporating new fossil discoveries, localities, and taxonomic re-identification; 2) there is little support for a large-scale taphonomic bias present in the Ediacaran; and, 3) there is significant biostratigraphic overlap between the Avalon and White Sea. This suggests that these taxonomically and geographically distinct assemblages were temporally coeval at least during the Avalon-White Sea transition ca. 560-559 Ma. Furthermore, both assemblages are constrained to narrow bathymetric ranges, reinforcing that they were paleoenvironmental-ecological biotopes that were spatially restricted in marine settings. Meanwhile, the terminal Ediacaran Nama appears to be a unique faunal stage, defined by a global loss of diversity, coincident with a noted expansion of bathymetrically unrestricted, long-ranging taxa. These data re-assert that bathymetry plays a first order control on the distribution of Avalon and White Sea assemblages. As such, studies of global biodiversity or stratigraphic ranges of representative taxa must first statistically account for this varying likelihood of preservation at a local-scale in order to aggregate the Ediacaran macrofossil record into a global biostratigraphic context.