Publication Date:
2022-05-25
Description:
Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 437 (2016): 76-88, doi:10.1016/j.epsl.2015.12.040.
Description:
High concentrations of extraterrestrial iridium have been reported in terminal Sturtian and
Marinoan glacial marine sediments and are used to argue for long (likely 3-12 Myr) durations of
these Cryogenian glaciations. Reanalysis of the Marinoan sedimentary rocks used in the original
study, supplemented by sedimentary rocks from additional terminal Marinoan sections, however,
does not confirm the initial report. New platinum group element concentrations, and 187Os/188Os and 3He/4He signatures are consistent with crustal origin and minimal extraterrestrial
contributions. The discrepancy is likely caused by different sample masses used in the two
studies, with this study being based on much larger samples that better capture the stochastic
distribution of extraterrestrial particles in marine sediments. Strong enrichment of redox-sensitive elements, particularly rhenium, up-section in the basal postglacial cap carbonates, may
indicate a return to more fully oxygenated seawater in the aftermath of the Marinoan snowball
earth. Sections dominated by hydrogenous osmium indicate increasing submarine hydrothermal
sources and/or continental inputs that are increasingly dominated by young mantle-derived rocks
after deglaciation. Sedimentation rate estimates for the basal cap carbonates yield surprisingly
slow rates of a few centimeters per thousand years. This study highlights the importance of
using sedimentary rock samples that represent sufficiently large area-time products to properly
sample extraterrestrial particles representatively, and demonstrates the value of using multiple
tracers of extraterrestrial matter.
Description:
We are grateful for support from a 2008 WHOI Summer Student Fellowship for CAW. BPE
acknowledges financial support from WHOI’s Ocean and Climate Change Institute (CH11320)
and U.S. NSF SGER grant EAR-0821878. Fieldwork in NW Canada was licensed by the Aurora
Research Institute and supported by a grant to PFH from the Astrobiology Institute of the US
National Aeronautics and Space Administration (NASA). Fieldwork in NW Canada and
Namibia was supported by grants EAR-9905495 and EAR-0417422 (to PFH) from the US NSF.
We thank Jon Husson (Harvard University) and Ricardo Trindade (University of São Paulo,
Brazil) for excellent support during fieldwork in Namibia in August of 2005.
Keywords:
Snowball earth
;
Osmium isotopes
;
Iridium
;
Helium isotopes
;
Extraterrestrial matter
;
Cap carbonate
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Permalink
