Quaternary Notes

The Quaternary Period is a term retained from the 1700s-1800s when rocks and time were divided into Primary, Secondary, Tertiary, and Quaternary.
Primary and Secondary were abandoned in favor of Paleozoic and Mesozoic eras and periods.

The Quaternary is divided into the Pleistocene (2.58 Ma - 11.7 Ka) and the Holocene (11.7 Ka - present).
We currently live in the Holocene.
Some stratigraphers have proposed a new third division, the Anthropocene, with the lower boundary debated but often placed in the mid-20th century.

Icehouse: Continental ice sheets are present and vary through glacial/interglacial cycles; greenhouse gas levels are low; temperature is low.
*Late Paleozoic
*Current began 34 mya
Greenhouse: No continental glaciers exist on Earth; $CO_2$ and other greenhouse gas levels are high; temperature is high (sea surface temperature ~0-28°C/32-83°F).
Most of Earth's history has been spent in greenhouse conditions.
Icehouse/greenhouse cycles are mainly driven by tectonic cycles, but the transitions are not well understood.

Shorter climate cycles, involving repeated cooling and warming, are driven by variations in Earth’s orbit around the sun.
These cycles result in a series of glacial/interglacial climate states within an icehouse period.
These cycles are documented by oxygen isotopes in ice cores spanning the last ~1 million years and older records from oxygen isotopes in cyclically deposited sediments.

During the glacial maximum, approximately 1/3 of all land mass was covered by ice, totaling around $40 \times 10^6 km^3$ of snow and ice.
Sea level fell by 75+ meters during the glacial maximum.

Low sea levels formed a land bridge between Siberia and Alaska across the Bering Strait.
Glaciers carved landscapes.
Climate zones shifted southward ahead of the ice sheet.

Till: Unsorted or poorly sorted clasts ranging in size from clay to boulders, deposited by glacial melting.
Erratic: Large, non-indigenous rocks deposited by glacial melting.
Stratified drift: Well-sorted sediments deposited by meltwater flows.
Loess: Windblown silt (rock flour ground by glaciers).
Moraines: Mounds of till deposited by glaciers (lateral, recessional, terminal).

The valleys of the Missouri and Ohio rivers approximate the maximum extent of glaciers.
The flow of rivers before glaciation was different; for example, the Ohio River didn’t exist, and the Missouri River had multiple segments.
Glaciation created temporary lakes and floods and shaped the modern courses of the rivers.

The Great Lakes formed in dry lowland depressions in a failed midcontinent rift prior to glaciation.
Glaciers carved these lowlands deeper.
Meltwater collected in the depressions to form the modern Great Lakes, starting around 14 Ka.
Areas south of the Great Lakes are dominated by kettles, which are small glacial meltwater lakes in depressions.

*Post-glacial sea level rise occurred as ice sheets melted.
*Meltwater Pulse 1A
*Last Glacial Maximum

The Washington Scablands are a key area in discussions of gradualism versus catastrophism.
Gradualism: Small changes accumulate over time.
Catastrophism: Major change occurs suddenly.
The Scablands resulted from massive ice age floods south of the Cordilleran Ice Sheet.

Meltwater pooled in a temporary lake the size of Rhode Island.
This lake drained like an overflowing tub into the Columbia River Gorge.
Floodwaters carved the Grand Coulee Canyon, which is 3 miles wide, with walls up to 1000 feet tall; rocks as big as houses were moved, and megaripples formed in the landscape.