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Tillites: rocks from glacial till (poorly sorted) Dropstones (coarse particles emplaced into fine-grained mud by sea ice

Tillites: rocks from glacial till (poorly sorted) Dropstones (coarse particles emplaced into fine-grained mud by sea ice) Glacial striations: erosional features. Huronian glaciation. Named for Huronian Supergroup in Canada, paleolatitude of 3 o

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Tillites: rocks from glacial till (poorly sorted) Dropstones (coarse particles emplaced into fine-grained mud by sea ice

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  1. Tillites: rocks from glacial till (poorly sorted) • Dropstones (coarse particles emplaced into fine-grained mud by sea ice) • Glacial striations: erosional features

  2. Huronian glaciation • Named for Huronian Supergroup in Canada, • paleolatitude of 3o • Contains glacial dropstones in laminated sediments, • glacially scoured rocks • Linked to: Rise of atmospheric oxygen and methane • oxidation? • Flood basalts in North America (Hearst dike swarm)

  3. Neo-Proterozoic Glaciation:“The SnowballEarth”- 750 and 600 MYr- Tillites- Glacial scour- Dropstones, even in BIFs!

  4. Snowball Earth Hypotheses • Driven by oliquity variations • Driven by continental configuration • Driven by changes in C-cycle Must Explain • Timing • Geology (ap carbonates and BIFS)

  5. Obliquity: Tilt of Earth’s rotational axis - Cause change in solar distribution such that poles receive more heat than equator; equatorial glaciation

  6. Wilson or Supercontinent Cycles J T Wilson, 1966.

  7. Wilson Cycle Stages • Max. Dispersal • Assembly • Supercontinent • Fragmentation

  8. Snowball earth linked to assembly and breakup of supercontinents?

  9. Steps to a snowball Earth fA in the BLAG model Continental land masses positioned at equator • A positive feedback via methanogenesis? • Positive Albedo feedback

  10. Tectonic Cycles: Emplacement of land at equator • Leads to high rates of continental weathering, CO2 drawdown, burial of organic matter • Continued weathering at equator during growth of high-latitude ice sheets • High OM buildup: leads to localized anoxia: BIFs • OM buildup supports methanogenesis, supports weathering? • Runaway albedo and weathering feedbacks during glaciation • Glacial buildup of CO2 to ~350 time modern levels initiates ice melting • Ensuing rapid weathering floods oceans with chemical weathering products: cap carbonates

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