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U-Pb and Re-Os geochronology tracks stratigraphic condensation in the Sturtian snowball Earth aftermath

Alan D. Rooney, Chuan Yang, Daniel J. Condon, Zhu Maoyan and Francis A. Macdonald
U-Pb and Re-Os geochronology tracks stratigraphic condensation in the Sturtian snowball Earth aftermath
Geology (Boulder) (April 2020) 48 (6): 625-629


The snowball Earth hypothesis predicts a strong hysteresis resulting in discrete multimillion-year glaciations followed by globally synchronous deglaciation. Here we present new U-Pb zircon and Re-Os sedimentary rock geochronology and Os isotope chemostratigraphy from post-Sturtian sequences in south China to test the synchroneity of deglaciation. High-precision chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-IDTIMS) U-Pb zircon dates refine the minimum age of deglaciation to 660.98+ or -0.74 Ma, which is approximately 2 m.y. older than previously reported. We also provide a new maximum age constraint on the onset of the Marinoan glaciation of 657.17+ or -0.78 Ma. A global compilation of new Os isotope chemostratigraphy reveals a large and systematic trend to unradiogenic values over <1 m of stratigraphy. Together, these data indicate that the Mn-carbonates in south China are not cap carbonates that formed as a response to post-snowball alkalinity, but are authigenic carbonates that formed millions of years after deglaciation. Sturtian cap carbonates tend to be absent or more condensed than their younger Marinoan counterparts. We suggest that this reflects a combination of enhanced accommodation space in early Cryogenian underfilled rift basins, stronger hysteresis, larger ice volume, and/or higher CO2 levels needed for deglaciation of the longer Sturtian glaciation. Further, our findings indicate that the apparent diachroneity of deglaciation can be explained readily as a consequence of stratigraphic condensation, itself due to the large post-Sturtian glacioeustatic transgressive sequence that outpaced shallow-water carbonate deposition.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 48
Serial Issue: 6
Title: U-Pb and Re-Os geochronology tracks stratigraphic condensation in the Sturtian snowball Earth aftermath
Affiliation: Yale University, Department of Geology and Geophysics, New Haven, CT, United States
Pages: 625-629
Published: 20200413
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 32
Accession Number: 2020-039364
Categories: StratigraphyIsotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2020184
Illustration Description: illus. incl. geol. sketch map
N20°00'00" - N53°00'00", E74°00'00" - E135°00'00"
Secondary Affiliation: British Geological Surve, GBR, United KingdomChinese Academy of Sciences, Nanjing Institute of Geology and Palaeontology, CHN, ChinaUniversity of California-Santa Barbara, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 202025
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