Dodging snowballs: Geochronology of the Gaskiers glaciation and the first appearance of the Ediacaran biota

Abstract

The snowball Earth hypothesis predicts that low-latitude glaciation lasted millions of years while CO 2 built up to critical levels to culminate in catastrophic deglaciation in a supergreenhouse climate. The Gaskiers Formation of eastern Newfoundland (Canada) has been attributed to a snowball glaciation event, but the lack of robust paleomagnetic data and precise geochronological constraints has precluded tests of the hypothesis. Here we present high-precision U-Pb zircon geochronology (chemical abrasion-isotope dilution-thermal ionization mass spectrometry) from eight tuffs from multiple distant stratigraphic sections that bracket glacial diamictites and the first appearance of large Ediacaran fossils. Including internal error, deposition of the Gaskiers diamictite on the Avalon Peninsula is constrained to have been between 580.90 ± 0.40 and 579.88 ± 0.44 Ma, and the Trinity diamictite on Bonavista Peninsula was deposited between 579.63 ± 0.15 and 579.24 ± 0.17 Ma. Assuming approximately synchronous deglaciation, these results imply a maximum duration for deposition of the Trinity diamictite of ≤340 k.y.; this is inconsistent with the multimillion year duration predicted by the snowball Earth hypothesis. Our geochronologic data also constrain the first appearance datum of Ediacaran fossils to <9.5 m.y. after the Gaskiers glaciation. Thus, despite existing paleomagnetic constraints that indicate that marine ice sheets extended to low to middle latitudes, it appears that Earth narrowly escaped a third Neoproterozoic snowball glaciation just prior to the late Ediacaran expansion of metazoan ecosystems.

Ice, Fire, or Fizzle: The Climate Footprint of Earth's Supercontinental Cycles

“…The protracted Sturtian (717–659 Ma) and relatively short Marinoan (645–635 Ma) global glaciations mark the cold Cryogenian period that was terminated as Earth entered the Ediacaran period (Hoffman & Li, ; Hoffman et al, ). This period is initially marked by an advance of polar ice to potentially midlatitudes (60°– 40° S, Trindade & Macouin, ) during the relatively short‐lived 340‐kyr‐long Gaskiers event at 580 Ma (Hoffman & Li, ; Ivanov et al, ; Pu et al, ; Trindade & Macouin, ), possibly less than 10 million years before the abrupt rise of complex animals (see Hoffman et al, ; Knoll, ; Pu et al, , and references therein) and Earth's transition to the nonglacial Cambrian period at 541 Ma.…”

Animal origins and the Tonian Earth system

“…In this scenario, multiple eukaryotic lineages possessed the [44,56,63], Ascomycota [64], Basidiomycota [64], Embryophytes [65][66][67], and Laminarialeans [68]. References for and biomarkers earliest fossils: Metazoans [57,69,70], Florideophytes ([71] -though see [42]), Ascomycota [72], Basidiomycota [73], Embryophytes [74,75] and Laminarialeans [76].…”

The “Dirty Ice” of the McMurdo Ice Shelf: Analogues for biological oases during the Cryogenian

“…Sedimentary biomarker hydrocarbons derived from algae and demosponges provide further evidence for the presence of a productive biosphere during the Cryogenian Epoch (Grosjean, Love, Stalvies, Fike, & Summons, ; Love et al., ). Molecular clock data suggest that animal phyla, and specifically sponges, appeared in the time window just prior to the Snowball Earth Epoch (Dohrmann & Wörheide, ; Erwin, ) and well before the Doushantuo embryos which comprise the earliest body fossil evidence for metazoans, dated to about 600 Ma, and which precede the earliest documented Ediacaran biota of ~571 Ma (Erwin, ; Pu et al., ). If so, there must have been refugia capable of supporting complex ecosystems during Cryogenian times.…”