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

Paper No. 225-2
Presentation Time: 9:00 AM-6:30 PM


PEHR, Kelden1, LOVE, Gordon D.1, KUZNETSOV, Anton2, BEKKER, Andrey1 and PODKOVYROV, Victor2, (1)Department of Earth Sciences, University of California, Riverside, 900 University Avenue, Riverside, CA 92521, (2)Institute of Precambrian Geology and Geochronology, RAS, nab. Makarova 2, St Petersburg, 199034, Russia, kpehr001@ucr.edu

The earliest lipid biomarker evidence of metazoans (in the form of demosponge biomarker 24-isopropylcholestane) is found in thermally immature sedimentary strata from South Oman Salt Basin dating back to >635 Myr ago (Love et al., 2009), yet prolific fossil evidence of metazoans does not appear later until the Ediacaran-Cambrian boundary. This transition from the first arrival of metazoans towards complex eukaryotic dominated basins has been poorly constrained, due partly to a sampling and preservation bias of organic rich samples. Organic-rich deposits are frequently targeted for biomarker analysis due to their increased chances of preserving enough extractable molecules for gas chromatography-mass spectrometry detection however ancient organic-lean deposits can also preserve biomarker lipids if they have avoided thermal and pressure stresses. Here we show that Late Neoproterozoic to Early Cambrian samples from the East European Platform record oligotrophic conditions in a shallow-marine shelf setting.

Samples from a suite of drill cores covering the Late Ediacaran to Early Cambrian transition across the East European Platform were selected for analysis. Our preliminary data show high hopane/sterane ratios indicative of bacterially dominated microbial communities within these shallow marine environments. This is in contrast to abundant algal steranes found in organic-rich rocks deposited during this time interval (Dutta et al., 2013). Similar to the organic-rich samples however C29 sterane remained the dominant sterane in our samples indicative of green algae being dominant within the eukaryotic phytoplankton population. Despite the low total organic carbon (TOC) (<0.3 weight % of TOC) we detected remnants of the 17β,21β(H)- biological stereochemistry consistent with these rocks having undergone a very mild thermal history and as such being ideal for organic geochemical investigation. We will discuss the details of the rich biomarker assemblages detected with respect to source biota and changing marine ecology through Late Ediacaran and Early Cambrian time.

Love et al. (2009) Nature 457, 718-722.

Dutta et al. (2013) Organic Geochemistry 56, 68–80.