Paleogeography and Geology of the Quaternary:
Single most important geological phenomenon of the Quaternary: the Quaternary Ice Ages (sometimes called the "Pleistocene Ice Ages" (even though the Holocene is part of the ordinary cyclity, too) or "late Neogene Ice Ages" (back when the Neogene extended to the present...)

Possible causes/contributing factors:

• Closure of the Isthmus of Panama
  • Start of the Oceanic Conveyer Belt and thermohaline circulation:
    • Chills northern waters, allowing build up of polar ice cap and of northern continental glaciers
• Continued erosion of Himalayas:
  • Buries more carbon
    • CO₂ levels (greenhouse gasses) fall, reducing planetary temperature
• ?Change in solar output:
  • Very hypothetical, although known for Sol-type stars

Climate dries in general throughout late Cenozoic.

Late Neogene Ice Ages once thought to be a series of four advances and four retreats; now known to be very complex set of advances and retreats of varying magnitudes:

• Alternates between glacials and interglacials
• During glacials (or glacial maxima):
  • Continental glaciers advance equatorward; alpine glaciers advance downslope
  • Large scale scouring and erosion due to advance
  • Eustatic regression (sea water trapped in glaciers), up to 100 m, out to the edge of the continental slope
  • In response, rivers carve deep channels along edge of continents
  • Land surface is depressed under up to 3 km depth of ice
  • Migration of animal and plant species
  • In tropical regions and many higher latitudes: climate dries even more, deserts expand, forests and rainforests contract
  • In western North America and a few other locations, deflected weather patterns actually make things WETTER: huge lakes
  • Episodes last for 5-20 kyr
• During deglaciations:
  • Heinrich events: massive discharge of icebergs releasing sediment into the sea
  • Glacial lakes form along edges of continental glaciers. These and other large lakes often overflowed (burst through ice dams, etc.), leaving large outwash plains. Extreme example is the Channeled Scablands
  • Deglaciations are now known to be VERY rapid: several degrees rise in less than 10 years!
• During interglacials (or glacial minima):
  • Glaciers retreat
  • Isostatic rebound in continental regions
  • Sea level rise, up to 30 m higher than present at maximum
  • Coastal river valleys flood to form estuaries
  • Animal and plant migrations poleward
  • Also last for 5-20 kyr

Glacial-Interglacial cycles seem to be controlled by orbital parameters of the Earth (the Milankovtich Cycle).

This cycle is (in principle) still ongoing. The end of the Last Glacial Maximum (at around 11-10 ka), which marks the beginning of the Holocene, is not the last glacial advance. During the Holocene there have been several more smaller fluctuations (Medieval Warm Period, Little Ice Age, etc.). In a sense, the Holocene is not a distinct Epoch, but only the latest major interglacial.

Animation of the global deglaciation from the LGM to the present and into the near future.

The GSSP for the Holocene officially begins with a climate shift marked in the NGRIP2 Greenland ice core (and seen many other places). It is dated to approximately 11,700 yr b2k (Before 2000 CE; unlike radiocarbon dates -- in which the "present" is defined as 1950, the new ice core dates are relative to 2000 AD/CE), with a plus/minus 50 yr uncertainty. Thus, the Holocene begins at something close to 9700 BCE.

Marine Life of the Paleogene:
Recovery from K-T extinction event. Coccolithophorids survive, but never recover old diversity. Foraminiferans, however, radiate greatly.

Nummulitids: giant disc-shaped forams from the Early and Middle Eocene of the Tethys.

Seagrass radiation in the Eocene: not true grass, but a marine (the ONLY marine) group of angiosperms, with representatives going back to the mid-Cretaceous (c. 100 Ma). In Eocene, however, spread across coastlines of world.

Hexacoral reefs begin again in latest Eocene, with switch to aragonite seas.

Sand dollars (VERY irregular echinoderms): evolved from sea biscuits (typical irregular burrowing echinoids). Evolution of sand dollars (Clypseasteroidea) was fairly rapid (during Early Eocene).

Giant predatory sharks (and shark radiation in general): some forms (up to 14 m long) replace the vanished marine reptiles as the top predators in the sea.

Continued diversification of teleosts. During Early Eocene, huge radiation of spiny-finned (acanthomorph) teleosts, including the perch family.

First penguins.

Origin of several lineages of marine mammals:

• Whales (Cetacea):
  • Marine members of the even-toed hoofed mammals (artiodactyls), closest living relatives are hippos
  • Descendants of hoofed carnivores
  • Arose in Eocene
  • Early whales still capable of coming on land
  • Ancestrally were fish eaters; planktonivory arose in Neogene
  • Most fully aquatic of all marine mammals: deepest divers, found out in deep water, etc.
• Manatees & sea cows (Sirenia):
  • Marine ungulates, closest living relatives are elephants
  • Also arose in Early Eocene
  • Sea grass eaters, fully aquatic but stay in shallow water
• Desmostylians (Desmostylia):
  • Marine ungulates, close relatives of sirenians and elephants
  • Known only from Late Oligocene and Miocene of the northern Pacific Rim
  • Could come on land to breed (like pinnipeds)
  • ?Plant eaters.
• Seals & sea lions (Pinnipedia):
  • Marine carnivorans, close relatives of bears
  • Primarily fish-eaters
  • Appear in latest Oligocene and radiate throughout Neogene.

Marine Life of the Neogene:
Recovery of foram diversity after the late Eocene extinctions.

Radiation of baleen whales (plankton eaters).

With the beginnings of the ocean conveyer belt and thermohaline circulation, a major shift in marine ecosystems in terms of diversity:

• Drop in species numbers of most groups
• Loss of the giant predatory sharks (replaced by killer whales)

Freshwater Life of the Cenozoic:

Radiation of freshwater teleosts during Eocene.

Appearance of freshwater diatoms.

Plant Life of the Cenozoic:
Paleocene floras very similar to Cretaceous, with increasing abundance of angiosperms.

During Eocene, increased diversity of grasses (grow by stems along ground; silica in the leaves; grow from base rather than tip, so can be grazed without great damage). Tend to form deep, rich soils that hold moisture and sequester carbon. Do quite well with fire: in fact, fire favors spread of grasses at the expense of trees and shrubs. By Oligocene, large grasslands in South America. During Miocene, grasslands sweep into Africa, North America, and Eurasia, causing a MAJOR change in the fauna.

At beginning of Miocene: origin and radiation of the composits (Compositae, sometimes called the Asteracea), the family of herbs containing most "garden plants" and weeds (daisies, asters, sunflowers, lettuces, etc., etc.). Generally the first to colonize cleared ground, but do not do well at retaining it. May have diversified as a response to the spread of grasslands (with grasslands comes grass fires, which periodically clear ground).

Between 7 and 6 Ma, the shift from C₃ to C₄ grasses (use different physiological pathway). C₄ grasses have about 5 times the amount of silica in their tissue. Became a selective pressure on grazers.

With the rise of continental glaciation in the Northern Hemisphere during the late Pliocene: rise of tundra biome. Throughout Pleistocene tundra region was more productive, and different (more diverse) plant and animal diversity, than today: the mammoth steppe:

• Mammoths, woolly rhinos, and other giant Arctic animals ripped holes in matted vegetation, and redeposited lots of nutrients as waste
• This mobilized nutrients and created new spots for plants to colonize
• More nutrients and more diverse plants supported more diverse small- and medium-sized herbivores
• Extinction of giant Arctic animals allowed vegetation mats to cover tundra, and stopped the presence of nutrient-rich giant mammal waste
• Reduced nutrient availability and growing spots led to reduced mammalian diversity, producing today's tundra.

Some of the major trends in Cenozoic climate, tectonics, and biotic evolution.

To Next Lecture.
To Previous Lecture.
To Syllabus.

Last modified: 9 March 2011