ES 331/767 Exercise III
GLACIATIONS THROUGHOUT
EARTH HISTORY

James S. Aber

Table of Contents

Major glaciations Huronian ice age
Stuartian ice age Andean ice age
Karoo ice age Holarctic ice age
Exercise References

Major glaciations in Earth history

At least five major ice ages along with other glaciations are documented during the history of the Earth, for which a rock and fossil record of ancient environments exists (GE fig. 1.7). Each of these ice ages lasted 10s to 100s of millions of years. Each was marked by multiple glacier expansions and contractions, which were individually millennia in duration.

All manner of large terrestrial and marine ice sheets, smaller ice caps, and alpine glaciers developed during these ice ages. For the most part these glaciations took place in mid- to high-latitude, continental settings. The five major ice ages are summarized below beginning with the oldest. This summary is based primarily on Habicht (1979), Hambrey and Harland (1981), and Harland (1983).

Huronian Ice Age

Known mainly from Canada and the United States in North America, where dated rocks range from 2500 to 2100 million years old. The Gowgonda Formation of Ontario is especially noteworthy for its excellent preservation of glaciogenic strata dated about 2300 million years old. Other glacial deposits are found in Wyoming, Michigan, Quebec, and the Northwest Territories. These rocks record extensive Early Proterozoic continental glaciation through a time span of about 400 million years, during which three or more glacial expansions took place. The configuration of the continents during this time is highly speculative.

Stuartian-Varangian Ice Age

This Late Proterozoic ice age was apparently the greatest of all. Glacial strata are known from all modern continents (except Antarctica) with an overall time range of about 950 to 600 million years old. Glacial strata from several intervals during this time are well preserved in Africa, China, Australia, Europe, Arabia, North America, and elsewhere. Multiple glaciations are the rule. In Scotland and Ireland, for example, three glacial episodes took place between 700 and 580 million years ago (McCay et al. 2006). Glaciations that are particularly well known and dated are listed in Table III-1.

Table III-1. Major phases of
late Proterozoic glaciation.
Region Age (million years)
Lower Congo region, Africa 950-750 and 620-600
Stuartian glaciation, Australia 800-780
Sinian glaciation, China 800-760, 740-700, 600
Western Canada/U.S.A. 850-800
Saharan region, Africa 730-650
Marinoan glaciation, Australia 690-680
Varangian glaciation, Norway about 650

The Late Proterozoic glaciation presents a paradox, because paleomagnetic evidence suggests that many of the glaciated continents were located in low paleolatitude positions. This results in a chaotic arrangement of paleoclimates--see Fig. III-1. Several possible explanations have been offered to explain this confusing situation (based on Chumakov and Elston 1989).

  1. Diamictites are nonglacial. Possibly true in some cases, but overwhelming evidence is that most are true tillites.

  2. Near global glaciation. All continents (except Antarctica, India, and Siberia) have glacial strata, but evidence for tropical or arid climates is also widespread with no obvious latitudinal zonation.

  3. Earth's axis more tilted. Would lead to greater seasonality of climate, but otherwise does not explain mixed distribution of climatic indicators.

  4. Equatorial shading by icy ring. Possible, but does not explain mixed distribution of climatic indicators.

  5. Earth's magnetic field different. Weaker, unstable, drifting magnetic field would invalidate paleomagnetic latitude reconstructions. Difficult to evaluate overall, but Africa was most likely in high southern latitudes throughout late Proterozoic and Paleozoic times.

  6. Fast-moving plates. Glaciation in high (southern) latitudes--see Fig. III-2, followed by rapid continental drift to lower latitudes, where paleomagnetism was set (or overprinted) during later orogenies. Note: this explanation is favored by your instructor and is supported by a great deal of tectonic evidence.

Some geologists and climatologists lately have proposed that Earth was locked in a global ice age, in which all oceans were frozen over and ice sheets covered nearly all continents--a snowball earth (Hoffman and Schrag 2000). This is an important hypothesis, as it bears on the potential for radical climatic conditions and their potential impact on life. However, this extreme climatic model ignores widespread evidence for tropical sediments and fossils as well as desert conditions that existed during the same period of the late Proterozoic.

Several other scientists have stressed evidence that late Proterozoic glaciations and oceans were essentially similar to late Cenozoic glaciations and oceans--multiple glacial centers and asynchronous ice-sheet growth and decay in various parts of the world (Leather et al. 2002; Kendall et al. 2006). Note: your instructor does not accept the premises that the Earth's surface was totally frozen and that most life became extinct in the late Proterozoic.

Andean-Saharan Ice Age

Glaciation is known from Arabia, central Sahara, western Africa, the lower Amazon of Brazil, and the Andes of western South America. Spectacular erosion of underlying rocks took place over large areas of the Sahara; whereas a good sedimentary record is preserved in Arabia. Continental ice sheets were developed in Africa and eastern Brazil, while alpine glaciers formed in the Andes region. The center of glaciation appears to have migrated through time: Ordovician (450-440 Ma) in Sahara, and Silurian in South America (Brazil 440-430 Ma, and Andes 430-420 Ma). The two continents were joined as parts of Gondwana, which was located over the South Pole--see Fig. III-3.

Note: Ma = million years old.

Karoo Ice Age

Glaciation is known from all continents that were once part of Gondwana, including: Africa, South America, Antarctica, India, Arabia and Australia. Glaciation began in the early Carboniferous (360 Ma), reached a peak in late Carboniferous, continued into early Permian, and mostly came to an end by late Permian (260 Ma) time, thus spanning 100 million years. Multiple glacial centers were active; each experienced repeated glacier advances and retreats. Particularly well-known glacial strata include the Dwyka Tillite (Karoo basin) in South Africa, Talchir Boulder Beds in India, and Wynyard Formation of Tasmania. Overall, two major glacial cycles took place. Both expanded gradually over periods of about 20 million years each to reach their maximum extents in late Pennsylvanian and early Permian times. Each major cycle then ended abruptly during only 1-10 thousand years (Gastaldo et al. 1996).

Although precise dating is not possible for many of the Gondwana glacial deposits, a general migration of glaciation through time is apparent. Carboniferous glaciation took place mainly in South America, southern Africa, India, and western Antarctica; whereas Permian glaciation was located mostly in Australia and eastern Antarctica. This migration corresponded to the drifting of Gondwana over the South Pole--see Fig. III-4.

The Karoo ice age is marked by cyclothems, cyclic sedimentary sequences in continental areas that were located in low latitudes. Pennsylvanian and Permian cyclothems are well known throughout the mid-continent of the United States, particularly eastern Kansas. The cyclothems were created by repeated marine transgressions and regressions over a stable continental platform. These cycles are interpreted as results of frequent changes in global sea level associated with glaciation in Gondwana. Glacial cycles and variations in sea level are documented in oxygen-isotope variations within fossils of Pennsylvanian cyclothems--see Fig. III-5. Late Pennsylvanian sea-level fluctuations were at least 80 m and likely greater than 100 m in amplitude (Soreghan and Giles 1999).

More on Permian cyclothems of the Flint Hills, Kansas.

Holarctic-Antarctic Ice Age

This late Cenozoic ice age began at least 30 million years ago in Antarctica; it expanded to Arctic regions of southern Alaska, Greenland, Iceland, and Svalbard between 10 and 3 million years ago. Glaciers and ice sheets in these areas have been relatively stable, more-or-less permanent features during the past few million years.

During the last one million years, large ice sheets developed in North America, Eurasia, the Andes, and elsewhere. These ice masses were unstable, growing and self-destructing in cycles averaging about 100,000 years, which correspond to eccentricity in the Earth's orbit around the Sun (Mangerud et al. 1996). The most recent great ice sheets disappeared only 10,000 years ago, but the Holarctic-Antarctic Ice Age still continues in regions of stable glaciation.

Exercise

Major glaciations have taken place several times during the history of the Earth. These ice-age periods have lasted 10s to 100s of millions of years. The solid Earth is about 4½ billion years old. The oldest surviving crustal rocks are nearly four billion years old, and good fossil evidence is found in sedimentary strata for early life as much as 3½ billion years ago.

The vast time spans represented by these past events in Earth history are almost incomprehensible to most people. Much more is known about relatively young events in geology than is known about earlier Earth history. For this reason, most geologic time scales are expanded for younger eras and compressed for earlier periods--see Kansas Geologic Timetable (also see GSA timescale from lecture 1). In many cases, the first 4 billion years of the Earth are given less space on time scales than are the last 600 million years! This common bias gives the impression that little of importance happened early in the Earth's history. Quite to the contrary, some of the most important events, including major ice ages, took place early in the Earth's existence.

In order to better comprehend the time dimension of ancient glaciations, you will construct various graphical time scales on which past ice ages can be shown. The information you need about times and places of ancient glaciations can be found mainly in this exercise, course lectures, and your textbook (GE). Your time scales should include the following key events--see Table III-2, and more information is presented for the last billion years in Table III-3.

Table III-2. Major life/rock developments and approximate ages (billions of years before present).
Event Age
Origin of solid Earth 4.5
Oldest crustal rocks 3.9
First fossil algae/bacteria 3.5
Appearance of stable continents 2.6
Massive banded iron formation 2.5
Terrestrial red beds begin 1.9
Sexual reproduction appears 0.9
Multicellular/metazoan life 0.7
Abundant fossil invertebrates 0.6
First land vegetation 0.4
Beginning age of reptiles 0.3
Beginning age of mammals 0.06

You should experiment with at least two time scales, linear and logarithmic, and you may try other scales. Number forward (time zero = beginning of Earth) or backward (time zero = now). Think of ways to depict better the magnitude of numbers shown on your scales--pie diagrams, spiral graphs, rolled charts, etc.

Turn in one time scale you like best. Briefly describe any patterns, cycles, or other such features that are apparent on your time scale, and discuss those factors that may be related to long-term development of ice-age climates.

Table III-3. Last billion years of Earth history (not to scale). Based on many sources.
Major Orogenies Major Ocean Rifting
Major Sea-level Rise1 		Major Glaciations2
Andean/Cordilleran and
Alpine/Himalayan (0-40 Ma) 		Late Cenozoic: North America, Antarctica,
Eurasia, Greenland (0-25 Ma)
N. Atlantic Ocean Tejas (65 Ma) Climatic cooling begins (70 Ma)
Atlantic/Indian3 Zuni (80 Ma)
Deserts worldwide (200-250 Ma)
Appalachian/Uralian4 (260-320 Ma) Absaroka5 (280 Ma)
Kaskaskia (350 Ma) 		Gondwana: Africa, South America, India,
Australia, Antarctica, Arabia (260-360 Ma)
Acadian/Caledonian6 (360-400 Ma)
Taconic: N. America (440-460 Ma) Tippecanoe (440 Ma) Andean-Saharan: South America, Africa,
Arabia (420-450 Ma)
Iapetus Ocean7 Sauk (520 Ma)
Avalonian: N. America8 (600-700 Ma) Late Proterozoic: Africa, Australia, Greenland,
China, North America, Europe (600-950 Ma)
Grenville: N. America9 (900-1000 Ma)

Ma = millions of years before present; all ages approximate.

Notes:

  1. Major marine transgressions on North America with peak date.
  2. Except as noted, Earth's climate has been mild to tropical.
  3. Breakup of Pangaea, rapid sea-floor spreading.
  4. Creation of Pangaea, the latest supercontinent.
  5. Characterized by cyclothems = frequent sea-level fluctuation.
  6. Collision of North America and Europe.
  7. Breakup of supercontinent, rapid sea-floor spreading.
  8. Creation of supercontinent Rodinia.
  9. Creation of supercontinent Kanatia.

References

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ES 331/767 © by J.S. Aber (2008).