Here are teaching slides for "Timing
and extent of Proterozoic glaciation". You can see a full-size version
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Ice extent at Present and at the Last Glacial Maximum, and the secular
in oxygen isotopes (δ18O) of bottom-dwelling foraminifera
(proxy for the global volume of non-floating ice) over the last 450 kyr
Paleogeographic extent of continental ice sheets and permanent sea ice
over the last 800 million years. Red lines indicate major mass extinctions.
Snowball Earth episodes correlate broadly with major turning points in
the chemical history of seawater and the evolution of life.
Rise in atmospheric oxygen over geological time and its relationship
ages (blue bars) and biological innovations.
Histogram of papers relating to Precambrian glacials and glaciation by
year of publication
(445 papers) from 1930 to 2005.
Stratigraphic setting of the three glacial and glacial-marine formations
in the Paleoproterozoic
(2450-2220 Ma) Huronian Supergroup, north shore of Lake Huron, Ontario,
Present global distribution of older (“Sturtian”) Cryogenian
(ca 720-700 Ma) glacial and glacial-marine deposits. Red dots indicate
include banded iron or iron-manganese formations (BIF).
Present global distribution of younger (“Marinoan”) Cryogenian
(ca 660-635 Ma) glacial and glacial-marine deposits. Red dots indicate
that include banded iron or iron-manganese formations (BIF).
Present global distribution of Ediacaran (635-542 Ma) glacial and glacial-marine
Present global distribution of Sturtian, Marinoan and Ediacaran glacial
deposits (left), and secular variation in the carbon isotopic composition
(δ13C) of marine carbonates (right) from 860 to 490 Ma
(modified after Halverson et al., 2005) and their relation to the three
and early faunal diversification (after Knoll and Carroll, 1999). Note
the generally elevated δ13C values before the Marinoan
glaciation and major negative δ13C anomalies informally
named after formations in which they were originally documented: B (Bitter
Springs, Australia), M (Maieberg,
Namibia), R (Rasthof, Namibia), S (Shuram, Oman), and T (Trezona, Australia).
The R, T and M anomalies suggest that the Sturtian and Marinoan glaciations
were globally synchronous.
The Australian Antarctic explorer and geologist Sir Douglas Mawson (1882-1958)
was an early advocate of global Neoproterozoic glaciation, based on the
mistaken belief that continents were fixed in location, and therefore that
glacial deposits now near the equator originated at low latitude.
The English geologist and stratigrapher Brian W. Harland (1917-2004) marshaled
evidence for a “great infra-Cambrian glaciation” in the context
of continental drift. He argued for the existence of low-latitude ice sheets
on the basis of climate-dependent sedimentological indicators and primitive
This outcrop near Biggenjarga on the Varanger Peninsula of northern Norway
interpreted as a sub-glacial pavement, grooved by ice movement (red arrow),
overlain by boulder-claystone (tillite) of glacial origin by Hans Reusch
of the Geological Survey of Norway in 1891. The tillite belongs to the
Smalfjord Formation, which is tentatively correlated with the younger Cryogenian
(Marinoan) glaciation, and was apparently deposited at a middle latitude.
The hammer handle (circled) is 33 cm long.
A useful criterion for glacial action is the presence in tillites (diamictites)
of pebbles that were faceted and multiply-scratched by entrainment at the
base of a moving glacier or ice sheet. This example is from the Jbéliat
Formation in the Taoudeni Basin in Mauritania (West Africa), which is tentatively
correlated with the younger Cryogenian (Marinoan) glaciation.
A Neoproterozoic carbonate platform (Otavi Group) containing both Cryogenian
glacial horizons is spectacularly exposed on the Great Western Escarpment
of southern Africa in Namibia. The escarpment rises from the hyper-arid
coastal sand sea (Namib Desert).
Bedrock tectonic elements of central and northwestern Namibia. The Damara
separates the Kalahari paleocontinent to the south and the Congo paleocontinent
to the north, and their respective continental-margin successions exposed
in the Witvlei and Otavi fold belts.
Geological map of the Otavi fold belt showing the Neoproterozoic carbonate-dominated
succession (Otavi Group) and the foreslope-platform facies change.
Composite stratigraphically-restored cross-section of the western Otavi
showing relations between the platform and southern foreslope. Representative
carbon isotope (δ13C) records are shown for Otavi Group
Stratigraphic architecture, generalized sedimentary facies, U-Pb ages of
volcanic zircons and composite carbon isotope profile for the Otavi Group,
projected onto a north-south cross-section of the carbonate platform and
its southern foreslope. Note rift-drift transition at the base of the Ombaatjie
Formation. The 635-Ma Ghaub glaciation occurred after the rift-drift transition
and the older Chuos glaciation before it.
Marine tillite (diamictite) from the younger Cryogenian glaciation (Ghaub
in the Otavi Group, Namibia. Both the large clasts and fine-grained matrix
are composed entirely of detrital carbonate, dolostone (tan color) or limestone
(grey-black). The tillite-bearing Ghaub Formation has been mapped for >600
km along the outer arc of the Otavi fold belt.
Stratified proglacial carbonate with ice-rafted debris (dolostone and limestone)
the top of the Ghaub Formation on the southern foreslope. Of the Otavi
Ice-rafted “dropstone” within stratified proglacial carbonate
near the top of the Ghaub Formation on the southern foreslope of the Otavi
Group, Namibia. Diameter of all coins is 2 cm.
Ice-rafted dropstone (oolitic limestone) within stratified proglacial carbonate
near the base of the Ghaub Formation on the southern foreslope of the Otavi
Representative glacial marine sediments on the southern foreslope of the
Otavi Group, Namibia.
Nature of host strata (carbonate, mixed, or terrigenous) for Neoproterozoic
glacial deposits (inverted triangles) in different regions.
Theoretical distribution of carbonates and glacial deposits on earth-like
planets with high and low orbital obliquities. Obliquities >54 degrees
result in a reversed meridional temperature gradient (i.e., poles warmer
than the equator).