Glacial incisions of the snowball Earth

There are surprisingly few lines of geological evidence for glacial incisions associated with a snowball Earth scale event that are not controversial. A recent article published by members of the Earth Dynamics Research Group reports multiple lines of geological field evidence for deep but variable glacial erosion during the Sturtian glaciation (ca. 717‐659 million years ago, Ma).

Unlike current-day glaciers, which only occur in the mid-to-high latitudes, several Precambrian glaciations show an affinity for “snowball Earth” conditions (where the polar ice caps potentially extended into the tropics to meet at the equator). While the snowball Earth hypothesis has gained favor in recent years, there is little consensus on the erosion rates during the glaciation period. In this publication, the heterogeneity in snowball glacial incisions (reported here and elsewhere) were likely  associated with the breakup of supercontinent Rodinia.

Geological map of the Arkaroola area (modified from Coats, 1973) indicating three measured stratigraphic sections: (A and B) the Wooltana Volcanics and (C) the Merinjina Formation. Sections A and B constitute a composite section of the entire exposed Wooltana Volcanics, supported by magnetic susceptibility measurements (Figure 6a). Section C is Tillite Gorge (Figure 5). Both deep and shallow glacial troughs are interpreted (a and b), respectively. Thick solid lines, faults; thin solid lines, geological boundaries; dashed lines, roads and tracks.

(a) Schematic cross section of glacial troughs on either side of the Paralana Fault, illustrating how incision appears to be significantly increased by tectonic uplift. Sedimentary thicknesses (except that of the thin Copley Quartzite) and glacial incisions are shown to scale. Fault offset unknown. Although depicted in (a) as apparently two glacial troughs, the two incisions documented here actually represent the same glacial trough (Figure above) with variable depths of incision, as depicted in the block diagram (b). According to the interpretation of a single trough, equal ice mass flux at both incisions is depicted by their equal cross‐sectional areas.

Contact person: Ross Mitchell, Earth Dynamics Research Group, Curtin University.

Relevant publication:

Ross N. Mitchell, Thomas M. Gernon, Adam Nordsvan, Grant M. Cox, Zheng‐Xiang Li, Paul F. Hoffman, Hit or miss: Glacial incisions of snowball Earth. Terra Nova, Volume 31, pages 381– 389 (2019).; doi.org/10.1111/ter.12400.