Research ArticleCLIMATOLOGY

Geologic evidence for an icehouse Earth before the Sturtian global glaciation

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Science Advances  10 Jun 2020:
Vol. 6, no. 24, eaay6647
DOI: 10.1126/sciadv.aay6647
  • Fig. 1 Geological map of the study area and rhyolite eruption age estimates from within the Konnarock Formation.

    (A) Geological map of the study area with samples depicted as colored circles. Coordinates are in Universal Transverse Mercator zone 17N [World Geodetic System (WGS) 84]. A geological map placing the study area in a broader context is available in fig. S1. (B) Example of a coarse gravel-sized granite dropstone in laminated diamictite of the Konnarock Formation (Fm.) collected along strike west of the mapped area. (C) Bayesian eruption age probability distributions for the three dated rhyolite samples. Eruption age modes and 95% credible intervals are displayed. Photo credit: Scott MacLennan, Princeton University.

  • Fig. 2 Map of Laurentia with paleolatitudinal constraints on the Konnarock Formation.

    (A) Paleogeographic map of Laurentia (Mercator projection), with the location of the Konnarock Formation shown by the yellow star. The location of paleomagnetic sites (colored circles) and their paleo-equators (2125) is depicted. Ages for paleomagnetic poles derived from the Kwagunt and Galeros Formations have been updated based on new geochronologic and paleomagnetic data (25, 38). The extent of basement rocks involved in the Grenville orogeny (GRO) is shown in gray. (B) Latitudinal distance between the Konnarock Formation depositional area and available paleo-equators between 780 and 710 Ma ago. The timing of Konnarock Formation deposition and initiation of the Sturtian Snowball Earth are shown by dashed red lines.

  • Fig. 3 Plot of potential paleo-altitudes of the Konnarock Formation and implied tropical SST.

    Relationship between tropical STT and altitude of the tropical snow line. Modern/LGM (52) and Cretaceous (39) SSTs are shown, along with the dry (9.8°C/km), LGM (6.7°C/km) (41), and humid (5.5°C/km) lapse rates. Red, light blue, and dark blue areas respectively correspond to the climate conditions needed for tropical ice during the Cretaceous, LGM, and a hypothetical colder climate. Tropical SST at Snowball initiation estimated using the average LGM (52) latitudinal temperature gradient as a lower bound. The elevation of major East African Rift lakes is shown by gray lines.

Supplementary Materials

  • Supplementary Materials

    Geologic evidence for an icehouse Earth before the Sturtian global glaciation

    Scott A. MacLennan, Michael P. Eddy, Arthur J. Merschat, Akshay K. Mehra, Peter W. Crockford, Adam C. Maloof, C. Scott Southworth, Blair Schoene

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    • Supplementary materials and methods
    • Figs. S1 to S19
    • Tables S1 and S2
    • References

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