Regional Geomorphology of the United States: Midterm

Fundamentals Concepts of Geomorphology

Lyell’s Uniformitarianim (4 Types)

+ Uniformity of Law: the laws of science have not changed over time.

+ Uniformity of Process: the natural processes going on, on earth today have always operated.

+ Uniformity of Rate: the processes affecting the earth have always operated at the same

gradual rates and same intensities.

+ Uniformity of State: the earth has not changes overall.

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Importance of Structure (Configuration of rock layers)

-Think anticline & syncline (types of folding), horizontal, vertical.

Importance of Process

One Cycle – 1 cycle

Multi-Cyclic – many cycles

Polyclimatic – man climate cycles

Davisian Cycle of Erosion (influenced by Darwin)

1.) Youth 2.) Maturity 3.)Old age

Base-level – (dominant in all streams) Elevation below which

a stream cannot erode. Can be rejuvenated (uplift, change in

sea level).

Empirical Geomorphology – observation/measurement (G.K. Gilbert)

Catastophism - theory that the Earth has been affected in the

past by sudden, short-lived, violent events, possibly worldwide

in scope. (asteroids, volcanoes, floods, etc.)

Quaternary Dating Methods

Law of Superposition: in any sequence of sediments or rocks that has not been overturned, the

youngest sediments or rocks are at the top of the sequence and the oldest are at the bottom.

Unconformity: change from one rock type to another. (wavy)

contact surface between younger and older rocks representing a

discontinuity in the geological record. Most commonly it represents

an erosional surface

Conformity: change from one rock type to another. (stratified)

Disconformity: lack of conformity, rock layers are parallel.

Relative Age Dating: formation of 14

C (Radiocarbon)

3 isotopes: 12

C, 13

C (both of which are STABLE), and 14

C (which is radioactive; enriched w-

nitrogen from the atmosphere; UNSTABLE)

Libby Half Life (5,730 years = 1 half life)

Contamination in 14

C

Reservoir Effect: between the 12

C and 14

C variation in the ratio. Some place carbon can be stored

(water, air, variations across space; NOT PREDICTABLE).

-There is a difference in the ratio of time 12

C, 13

C, and 14

C fractions.

-Fotosintesis plays a role.

-PDB Standard, we know its stable isotope

composition. All ratios are based off the

comparison of the PDB Standard.

PDB- “Protein Data Bank”

In C2, C3, C4 plants, PDB tells us the type of vegetation of the time period maintained.

Industrial Bomb Effects (1947)

Wacked out the radiocarbon (14

C) levels!!! Now dates calculated in ‘y BP’ are based off from

1947.

Cecular Effects

Variation in radiocarbon (14

C), which is produced over time.

Tree rings (represent time) have gotten radiocarbon dated in specific rings. This represents the

variation in radiocarbon and calendar time!

Calendar Time (linear) Radiocarbon Time (non-linear)

1,500 ± CAL yrs BP = a correct calendar date.

14

C = YRS BP (1947*) 1,500 ± 100 YRS BP (NOT corrected in calendar time!)

1σ = 68% correctness σ = Standard Deviations (affects correctness)

2 σ = 95% correctness

Radiocarbon 14

C Corrections: 1947 base date, Cecular Effects, Standard Deviation Correctness

Optical Stimulated Luminescence (OSL ) Dating

Quartz Grains – small microscopic fissures

Gamma rays from surrounding feldspars penetrate tiny cracks in quartz grains and are thus stored

until exposed to light.

Need: Dose Rate (bag of sand) & Sample (in a tube, not exposed to light)

Atlantic & Gulf Coastal Plain

Post dates the Mid-Atlantic Ridge

Fall Line- line that separates the Coastal Plain from

the Piedmont. (rapids, elevation)

Coastal Plain Sediment = marine and eroded sediments from the Appalachian Mountains.

Igneous & Metamorphic Basement, Sedimentary Cap, Fluvial/Marine Sediments on top

35 million y BP, Impact Crater in the Southern Chesapeake Bay = Breccia

Notice how streams diverge into the crater, still evident today!

Dendritic Drainage Pattern

- Uniform sediment composition (fluvial/marine)

- Time (older time period)

-Allows Atlantic Coastal streams to parallel the coast.

Continental Shelf

-Subaerial (above) – water tied up in glaciers (glaciations).

-Subaquis (below) – below water, current, etc.

Oxygen Isotope Ratios

-95% of earth = H2O

16 (lighter, easily evaporated)

-5% of earth = H2O

18

-16

O is stored in glaciers during glaciations

Ice Core

-Layers of ice/marine sediments, that change in ratio between O16

and O18

,

can see when glaciations and inter-glacials occurred.

-Stage 1: non-glacial period (10,000 - NOW)

-Stage 2: glaciations (Wisconsin; ratio is more negative) (70,000 – 10,000 y BP)

-Stage 3: Sangamon inter-glacial (120,000 – 70,000 y BP)

-Stage 4:glaciations (Illinoisian; ratio is more negative) (120,000 y BP+)

Appalachian Mountains

Piedmont

- formed prior to the coastal plain

-1.2 Billion year old rocks (Igneous/Metamorphic)

-Were exposed after sea levels fell

-Uplifted during the Alleghany Orogeny

-Has gently rolling terrain, and a few Igneous intrusions

Blue Ridge (Thrust Fault)

- Grenville Orogeny aged (1.2 Billion y BP)

-Single ridge you can trace near much of the east coast

-Intrusion of plutons (uplifted)

-Thrust faulting over Paleozoic rocks

-20 miles in width, hundreds of miles in length.

Ridge and Valley (Folding)

-Northeast Pennsylvania (heart of PA) and Tennessee

-Boundary between the Blue Ridge/Ridge and Valley

-Shenandoah Valley

-Deformed by the uplift of the Blue Ridge

-Streams cross the Ridge and Valley terrain

-Formed during the Alleghany Orogeny (250 million)

when the North American and African plates collided

Appalachian Plateau (Uplift)

-Cambrian (500-300 million y BP) aged rocks (Sedimentary)

-Undulated (hilly/eroded); created by streams (dissected)

-Coal laden (eastern portion; West Virginia, Maryland, Pennsylvania)

-Horizontal structure

-“Uplift” caused stream dissection to take place

-Allegany Escarpment = western edge of the Appalachian Plateau

Grenville Orogeny – 1.2 Billion y BP, Canada, Collision of Continents

Taconic Orogeny – 0.5 Billion y BP, Collision of Continents (again) Volcanic Mountain

Building, Birth of the Appalacians.

Acadian Orogeny – 400-360 million y BP, Nova Scotia, Continental Collision, Faulting/Folding

Allegheny Orogeny – 330-250 million y BP, Southern Appalachians, Thrust Faulting

Hurricanes largely impact the Appalachian Mountains via Weathering & Mud-Slides.

Anticline & Syncline Topography

-High spots are NOT generally Anticlines because;

-Rock Type

-Region

-Climate

-Etc.

-Typically consist of Sedimentary Rock

Water Gaps in the Appalachian Mountains

Wind Gaps – breaches in structure where no streams occur. Stream once went through the gap,

but got pirated.

Water Gaps – breaches in structure where streams occur.

1.) Uplift

Streams changed their orientation, “Stream Piracy”, caused different drainage patterns of present

day streams.

Consequent Streams – who’s coarse is a direct consequence of the “Original Slope” of the

surface uponwhich its developed. Streams that follow the slope of the original landscape.

Subsequent Streams – who’s coarse has been determined by selective headwater erosion along

weak strata. Original relief of the land and generally follow the path determined by the

weak rock belts.

2.) Superimposed – High ocean levels on the coastal plain cause penaplains and produce coastal

plain sediments. Streams then cut through ridges!

NOT LIKELY; extremely high ocean levels.

Superimposed Streams – gradually lower themselves into astructure.

3.) Antecedent- Stream was already established, land uplifted, streams cut through ridges!

LIKELY; today jointing has helped.

Antecedent Streams- Older than the rock structure evolve as streams develop.

North American Craton (Canadian Shield)

-Foundation to the North American Continent

-Pre-Cambrian, Igneous/Metamorphic rocks (basement)

-North: exposed at the surface, rocks stripped away by

multiple glaciations

-South: buried by sedimentary rocks!

-Exposed in the US: Catskills, New York and the Superior Upland

-Stable for 600 million years!

-Central Lowlands, hold a lot of evidence of the Querternary!

Last Glacial Maximum (LGM) – 20,000 – 18,000 y BP

Laurentide Ice Sheet: Laurentide Mountains and Labrador = Source Areas

Cordilleran Ice Sheet: west, alpine glacier, coalesced during the LGM.

MICHIGAN

-Ice advanced from the northeast into Michigan.

-300 foot of ice (1/4 mile) covered Michigan!

-Last Glaciation: Wisconsin Glaciation (25-10,000 y BP)

Traditional Glacial Theory

Nebraskian Glaciation: 1.2 million y BP

Kansasian Glaciation: 600,000 y BP

Illisnoisian Glaciation: 135,000 y BP

Wisconsin Glaciation: 20-18,000 y BP (LGM)

There is a much more complete record during the Quaternary (2.588 million y BP)

20+ Glaciations!!! (Ice Core & Ocean Sediment Records)

- 18

O and 16

O

- 18

O is high = Glaciation (16

O is contained in the glacier)

- 16

O is high = Inter-Glacial

-Glaciations tend to last 80,000-90,000 years

-Inter-Glacials tend to last 20,000 years

-TOGETHER the cycle lasts about 100,000 years.

Orbital Cycle (Milankovitch Hypothesis)

+ Spherical shape of Earth’s orbit around the sun (100,000 year cycle) (eccentricity/odd)

+Earth’s wobble (20,000 year cycle)

+Earth’s tilt (40,000 year cycle)

-24.5o – 22.1

o

-last glaciation was tilted at 22o, 100,000 y BP = COLDER!

-now positioned at a higher tilt 24-23.5o = WARMER!

PALIMPSEST MORAINE – moraine that existed before an advance, then the ice over-road it.

END MORAINE - Formed at the end of the Glacial Margin Till, unsorted, unstratified drift

normally.

GROUND MORAINE - "UNDER THE ICE", between recessional moraines, "NOT HILLY",

low, rolling Till Dominated - "TILL PLAIN".

TERMINAL MORAINE - Location where the Glacier advanced the furthest, NONE in Michigan.

RECESSIONAL MORAINE - Moraines formed during the recession of the terminal position.

INTERLOBATE MORAINE - Moraine formed between 2 Ice Lobes, A lot of meltwater, burying

a lot of "Outwash!"

MICHIGAN BASIN

-Consists of soft SHALES where the Great Lakes currently are. (Carved out by glaciers)

-Sedimentary Rocks from top to bottom.

-More resistant DOLOMITE forms peninsulas and cliffs in areas, such as Wisconsin’s Door

Peninsula, Michigan’s UP Garden Peninsula, Ontario’s Georgia Island/Peninsula, and Niagara

Falls.

Hinge Line – area that separates “Rebounding” (north) and

“Stability” / “Subsidence” (south)

Today we know that Isostatic Rebound effected/s northerly regions

more than in the southern basin. 14

C dates allow us to know this!

Late Pleistocene History of the Great Lakes

21,000 y BP

The maximum of the Wisconsin Glaciation, produced a

Terminal Moraine in southern Indiana, Illinois, Ohio, etc.

21,000-14,000 y BP

Glacier started to retreat northerly as the climate started

to warm. The land sloped “away” from the glacial margin,

resulting in outwash plains, NOT glacial lakes.

14,000-12,500 y BP

As the glaciers retreated over the eroded

shale carved by the glacial advance,

water started to pool. The land now in

locations sloped “toward” the ice margin.

This produced Lakes “Chicago”,

“Maumee”, and “Saginaw”. Drainage

during this time period exited via an

ancestral Mississippi River system.

12,500 y BP-10,000 y BP

The glacial front proceeded to push northward,

enlarging the size of the proglacial lakes. As the

margin passed the Straights of Mackinaw, “Lake

Algonquin” was formed (coalesced Lake Chicago

and Lake Saginaw). Lake levels continued to rise as

melt water entered the basin.

When the glacial front passed the subsided “North

Bay” outlet, Lake Algonquin catastrophically drained

via the lower outlet. Causing much lower lake stages.

Holocene History of the Great Lakes

10,000-8,500 y BP

Lake Chippewa – Present day Lake Michigan

Lake Stanley – Present day Lake Huron

Lake Minong – Present day Lake Superior

Early Lake Erie = LOW

Early Lake Ontario = HIGH

The opening of the glacially subsided “North

Bay” outlet in central Ontario and the rebounding

unglaciated south allowed for lower lake levels

in lake’s Michigan, Huron, and Erie. An excess of

water flowed in the St. Lawrence Lowland.

Nipissing Transgression: 8,500-5,000 y BP

The “North Bay outlet in central Ontario slowly

rebounded as the glacier was no longer over it. As

the outlet rose, so did lake levels. This continual

rise in lake levels is known as the “Nipissing

Transgression”, which continued until about

5,000 y BP when the max. Nipissing phase fell.

5,000 y BP-Present Day

The erosion of outlets, such as St. Clair, Detroit,

St. Marys, last North Bay drainage allowed the

Nipissing level to fall to the “Algoma Stage” (also

known as Nipissing II.Lake levels continued to fall

to their modern levelsfluctuating between 175 and 173 meters.

MAJOR FACTORS THAT INFLUENCE LAKE LEVELS

-Isostatic Rebound

-Outlet Changes

-Climate

-Glacial Advances/Retreat

SAND DUNES

Need 3 things!

-SAND

-WIND

-FETCH (distance of open water)

High Perched Dunes

-Glacial Sediments (Wisconsin Glaciation; around 13,000 y Bp)

-Sand dunes on top of High Perched Dunes

-Paleosol = stability during the Chippewa low

-Manistee, MI and northward

Low Perched Dunes

-Dunes are stabilizing because of;

low lake levels & less windy conditions

-Manistee, MI and southward

-Noticeably Late Holocene Paleosols, but also older.

-Paleosol = periods of stability (lake sediments), covered by dune sands (unstable periods)

Formation of paleosols in Sand Dunes

Great Plains

Deposition of loess;

Larger grained (sands) are deposited near the source area (heavy; harder to transport)

Smaller grained (silts/clays) are deposited further away from the source (lighter; easier to

transport)

Loess in North America: Mid-latitudes (Jet-Stream driven), High in carbonates, small particle

size (compact)

Source Areas: Rivers, Lakes, Outwash Plains, Sandstone (during dry windy times), essentially

anything with sand, silts, and clays!!!

EUSTIS ASH PIT, IOWA

Peoria Loess: (Peoria, Ill) Wisconsin

Glaciation (Stage 2; 20-10,000 y BP).1.5

meters every 1,000 years!Seasonal?

(laminations, oxidized pine needles found)

Gilman Canyon Formation: (20-30,000

y BP; Stage 2) First accumulation of loess

in Wisconsin Glaciation. Organics = deco-

mposed prairie grasses. Soil formation

slower, less loess deposits, allows soil to

keep forming. NOT RAPID LOESS DEPO-

SITS like the Peoria Loess.

Overlain by the Sangamon

Paleosol Sangamon Interglacial (Stage 3).

Looks like an “Ultisol”(deeply weathered,

wet, warmer).

Loveland Loess: (Loveland,IA)

Illinoisian Glaciation (Stage 4)

Yellowstone Ash: 600,000 y BP

maximum limiting date.

NEBRASKA

Brady Paleosol: (9-10,000 y BP)

Brief period of stability, wet, warmer?

Bignell Loess: (8-5,000 y BP)

Warmer, drier, earth’s tilt was maxed

out at 24o. Not everywhere, patchy,

“Alti-Thermal” (warm climate)

Loess thickness in Nebraska decreases from

Northwest to Southeast.

Long time believed: Source was the Nebraska

Sand Hills.

Current Hypothesis: White River Group

(Badlands; sandstones), blown threw the Sand Hills

during a period with drier/strong winds conditions. (Mason)

DUNES OF THE GREAT PLAINS

Holocene in age!!!! (10,000 year and less in age; mostly late Holocene)

NOT Pleistocene, which was previously thought.

Great Bend Sand Dunes, Kansas (Arbogast)

Source: the Arkansas River, which Al identified by looking

at the decrease of calcium in samples further away from

the river bank.

Loess: warm dry period (700 y BP – Present)

Paleosol: wet/ cool period (710 y BP)

Eolian Sand: warm dry period (5,370-1,000 y BP)

Silty/Sandy/Clay: cool climate, wet, gleyed. On

account of the Jet Stream being further south during

the Wisconsin Glaciation. (16,670- 5,370 y BP)

RELATE THIS WITH DUNE BUILDING IN GEORGIA!!!

Medieval Warm Period

-Last 1,000 y BP

-Warmer and Drier

-Dune Building in the Plains!

-2-3o warmer than today!

WISCONSIN LOESS

Southwestern Source:

Mississippi River

Northeastern Source:

Glacial, Outwash Plains (Schaetzl)

Crazy Glacial Winds!