Emplacement of the Franklin large igneous province and initiation of the Sturtian Snowball Earth

Abstract

During the Cryogenian (720 to 635 Ma ago) Snowball Earth glaciations, ice extended to sea level near the equator. The cause of this catastrophic failure of Earth’s thermostat has been unclear, but previous geochronology has suggested a rough coincidence of glacial onset with one of the largest magmatic episodes in the geological record, the Franklin large igneous province. U-Pb geochronology on zircon and baddeleyite from sills associated with the paleo-equatorial Franklin large igneous province in Arctic Canada record rapid emplacement between 719.86 ± 0.21 and 718.61 ± 0.30 Ma ago, 0.9 to 1.6 Ma before the onset of widespread glaciation. Geologic observations and (U-Th)/He dates on Franklin sills are compatible with major post–Franklin exhumation, possibly due to development of mafic volcanic highlands on windward equatorial Laurentia and increased global weatherability. After a transient magmatic CO 2 flux, long-term carbon sequestration associated with increased weatherability could have nudged Earth over the threshold for runaway ice-albedo feedback.

Detrital zircon geochronology and provenance of the Mesoproterozoic Husky Creek Formation: a fluvial sandstone recording the waning stages of one of Earth's largest magmatic episodes

“…), this study (Husky Creek Fm. ), and the Franklin Igneous Event (Pu et al 2022). with generally high dispersion and no significant variation with stratigraphic position.…”

“…An erosional unconformity between Sequence A and Sequence B reflects a tectonic disturbance coinciding with the amalgamation of supercontinent Rodinia at 1200-1000 Ma (Rainbird et al 1996(Rainbird et al , 2017. The Sequences B-C boundary reflects rifting and magmatism (Franklin Igneous Event) associated with the breakup of Rodinia at about 720 Ma (Heaman et al 1992;Shellnut et al 2004;Pu et al 2022). Sequences A and B are preserved in a series of inliers located along the northern Canadian mainland and Arctic islands, as well as in the northern Cordillera (Young et al 1979;Rainbird et al 1994Rainbird et al , 1996 (Fig.…”

The Cambrian Explosion: macroevolution and biomineralization

“…In a mismatch between "rocks and clocks", the molecular clock age of animal origins has been estimated at Tonian Period or Cryogenian Period age (850-650 Ma), whereas the animalian fossil record begins only at around 580 Ma [1]. A recent reinterpretation of putative keratose sponge fossils and thrombolites from the 890 Ma Little Dal reefs of the Stone Knife Formation, Canada, as metazoan trace fossils [2] implies an origin of animals well before the Sturtian Snowball Earth glaciation of 720-635 Ma [3]. In the Kris and McMenamin [2] interpretation, the microburrows and burrow clotting in thrombolites are the earliest evidence for eumetazoan animal (and, any animal, for that matter) life.…”

Impact-induced initiation of Snowball Earth: A model study

“…While we do not dismiss these mechanisms, we note that any mechanism that calls for Snowball initiation via the lowering of atmospheric CO 2 through biological or tectonic changes must explain how the proposed mechanism contends with and overcomes the stabilizing effect of the silicate weathering feedback ( 24 , 25 ), which is suggested to have maintained habitable conditions over much of Earth history. On the other hand, it is possible that weathering played an indirect role by cooling the climate and lowering the threshold for Snowball initiation in response to volcanism or impacts; the latter mechanism is the topic of this paper ( 19 ).…”

“…Additional suggestions for Snowball initiation appeal to variations in volcanic outgassing ( 16 ), changing continental configuration and composition ( 17 – 19 ), evolution of the biosphere ( 20 , 21 ), or the collapse of a methane greenhouse ( 22 , 23 ). While we do not dismiss these mechanisms, we note that any mechanism that calls for Snowball initiation via the lowering of atmospheric CO 2 through biological or tectonic changes must explain how the proposed mechanism contends with and overcomes the stabilizing effect of the silicate weathering feedback ( 24 , 25 ), which is suggested to have maintained habitable conditions over much of Earth history.…”