GL102 midterm

Physical Geology

examines the materials composing earth to gain an understanding of the many processes that operate both on and beneath earth

Relative Dating

events are placed in their proper sequence or order without knowing their age in years

• geologic time scale

• before radiometric dating

Law of Superposition

states that in layers of sedimentary rocks or lava flows, youngest layer is always on top and oldest at the bottom

Geologic Time Scale

time scale divides the 4.6 billion years of earth into

• Eons

• Eras

• Periods

• Epochs

What are the two principle divisions of Earth’s surface?

Continents and Ocean basins

Continental Shelf

Boundary between the land and ocean, where the sea is relatively shallow compared to the deep ocean floor.

Ring of fire/ Circum-Pacific belt

region surrounding the Pacific Ocean, includes the mountains of the western americas and continued into western pacific in the form of volcanic island arcs

• island arcs are active mountainous regions composed largely of deformed volcanic rocks

  • in the Aleutian Islands, Japan, the Philippines, New Guinea

alpide belt

extends eastward from Alps though Iran and the Himalayas, bends southwards into Indonesia

What are stable interiors of continents?

unlike young mountain belts, the interiors of continents have been geologically stable for over 100 million years

Shields

are expansive, flat regions with stable interiors, composed of igneous and metamorphic rocks

where is the Canadian Shield located?

is exposed in much of the northeastern part of North America

When were shields formed?

during the Precambrian era, more than 1 billion years ago

Ocean Basin floor

has a wide diversity of features including linear chains of volcanoes, deep canyons and large plateaus

Oceanic Ridge system

a prominent feature of ocean basin

forming a continuous belt for more than 70,000 km and consists of layers upon layers of volcanic rock that has been fractured and uplifted,

Deep Ocean Trenches

narrow, extremely deep depressions that can exceed 11,000 meters below sea level,

Weathering

the process of breaking down rocks through physical, chemical or biological means

What are Earth’s External Processes

processes that occur at or near Earth’s surface, powered by the sun or gravity

include

• weathering - breaking down rock

• mass wasting - downslope of movement of rock and soil

• erosion - removal of rock by water, wind or ice

What are the 3 types of weathering?

1. mechanical weathering

2. chemical weathering

3. biological weathering

Weathering

physical breakdown and chemical alteration of rock

Mass Wasting

transfer of rock and soil downslope by gravity

Erosion

physical removal of material by water, ice or wind

Mechanical Weathering

physcial breakdown of rocks into smaller pieces without altering its compositon

• increases surface area which enhances chemical weathering

What are the three main processes of mechanical weathering?

1. frost wedging - water expands when it freezes, breaks rock apart

2. sheeting (unloading) - rocks expand and fracture as overlaying layers are removed

3. biological activity - roots, burrowing animals and microorganisms break down rocks

Frost Wedging

When water enters cracks in rock and freezes, it expands by 9% causing the rock to break apart after repeated freeze-thaw cycles

Sheeting (Unloading)

where large igneous rock bodies break into onion-like layers due to pressure release when overlying rock is removed

• can create exfoliation domes like Half dome in Yosemite

Biological Activity

• plant roots grow into cracks, breaking rock apart

• lichens and mosses produce acids that weaken rock

• burrowing animals move rock fragments, exposing them to weathering

Chemical Weathering

decomposition of rock due to chemical reaction between minerals and environment. water is the most important agent of this weathering

3 main processes of Chemical Weathering

1. dissolution - rock dissolves in acidic water

2. oxidation - iron reacts with oxygen, forming rust

3. hydrolysis - water reacts with mineral to form clay minerals

Dissolution

form of chemical weathering where minerals dissolve in water

• ex: limestone dissolving in acid rain

• produces hard water in regions with calcium carbonate

oxidation

chemical reaction where oxygen combines with iron to form oxide (rust)

• occurs faster in moist environments

• ex: red-coloured rocks in Lake Superior, caused by hematite formation

Hydrolysis

process where minerals react with water and acids, forming new minerals like clay

• example: granite weathers into clay minerals, releasing quartz grains

Spheroidal Weathering

a process where sharp rock edges become rounded as water penetrates joints, breaking minerals down

• over time, layers may peel off like an onion

How does climate affect weathering rates?

• warm, wet climates → rapid chemical weathering

• cold, dry climates → slow chemical weathering

• freeze-thaw cycles → more frost wedging

why do some rocks weather faster than others?

1. rock composition - some minerals (e.q quartz) resist weathering better than other (e.g. calcite)

2. texture & fractures - more joints and cracks → faster weathering

3. climate - more moisture and warmth → more chemical weathering

Differential Weathering

the process where rocks weather at different rates due to mineral composition, texture and fractures. Creates unique landforms like

• ridges and pinnacles

• steep cliffs

• rock arches

Mass Wasting

downslope movement of rock and soil due to gravity, without the aid of wind, water or ice

what is Erosion and how is it different from weathering?

• erosion is the physical removal of material by water, ice or wind.

• weathering breaks rocks down, erosion transports fragments away

examples of Differential Weathering?

• Al-Naslaa rock formation (Saudi Arabia)

  • sandstone split by natural weathering

• Bryce Canyon (Utah, USA)

  • Hoodoos formed by differential erosion

How does weathering impact human-made structures?

• acid rain accelerates weathering of buildings and monuments

• freeze-thaw cycles damage roads and sidewalks

• differential weathering affects stability of cliffs and slopes

How does weathering contribute to soil formation

• breaks rocks into smaller particles

• produces clay minerals (from chemical weathering)

• organic material mixes with minerals to form soil

What is Soil and why is it important?

Soil is a combination of mineral and organic matter, water and air that supports plan growth.

• It forms at the interface where the geosphere, atmosphere, hydrosphere and biosphere

What is important in soil formation?

Weathering

Why is soil considered an interface in the Earth System?

because its where the geosphere (rock), atmosphere (air), hydrosphere (water) and biosphere (living things) interact

• crucial for earths ecosystems

4 main components of soil

1. mineral matter - disintegrated rock (~45%)

2. organic matter (Humus) - decomposed plant and animal material (~5%)

3. water - essential for chemical reactions and nutrient transport (~25%)

4. air - supplies oxygen and carbon dioxide for microorganisms (~25%)

Humus

a dark organic material formed from decomposed plant and animal matter, essential for soil fertility.

5 main factors that control soil formation

1. Parent Material - type of rock or sediment soil forms from

2. Time - older soils are more developed

3. Climate - influences weathering and organic activity

4. Plants and Animals - contribute organic materials and acids

5. Topography - Affects water drainage and erosion rates

What is Parent Material

source material from which soil develops

• when material is bedrock - Residual Soils, when materialis transported - Transported Soils.

Residual Soil

formed from the weathering of underlying bedrock, remaining in place where it originated.

Transported soil

developed from sediments that have been moved from their original location by water, wind, or ice.

How does time influence soil development?

• young soils resemble parent material

• over time, climate and organisms shape soil characteristics

• older soils are thicker and less like the original rock

How does Parent Material influence soils

• type of parent material will affect the rate of weathering and thus, the rate of soil formation.

  • unconsolidated deposits develop into soil faster than bedrock because they are already partially weathered and have a greater surface area

    • greater SA → faster reactions, easier to break down

• chemical composition of parent material plays a major role in soil fertility because it determines

  • types of minerals available

    • when rocks weather they release nutrients into soil

  • nutrient availability for plants

why is climate the most influential factor in soil formation?

it determines

1. weathering type

   • chemical weathering will dominate in warm, wet climates

   • mechanical weathering dominates in cold, dry climates

2. soil depth

   • more precipitation = deeper soils

3. leaching

   • high precipitation removes nutrients, affecting soil fertility

How do plants and animals contribute to soil formation?

• they supply organic material (humus) to the soil

  • influences soil fertility

• decay of plant and animal remains causes the formation of various acids that speed up the process of weathering

• aids water retention

• microorganisms break down organic matter and enhance nutrient cycling in the soil.

• earthworms and burrowing animals mix soil, improving aeration and drainage

How does topography impact soil development?

• steep slopes → thin, poorly developed soils due to erosion

  • little water soaks in, the moisture content of the soil may be insufficient for plant growth

• flat areas → deep, well developed soils

  • provides food drainage, minimum erosion

• lowlands → thick, dark soils rich in organic matter that accumlates

  • due to water accumulation, poor drainage system

What is a Soil Profile?

vertical section through different soil layers (horizons), revealing variations in composition, texture and structure over depth as time passes

what are the 5 main soil horizons

O horizon (organic layer), A horizon (topsoil), E horizon (eluviation layer), B horizon (subsoil), and C horizon (parent material).

• These horizons represent distinct layers that vary in composition, texture, and biological activity.

O horizon

the organic layer composed of decomposed plant material and organic matter.

A horizon

topsoil mineral matter mixed with some humus

E horizon

the eluviation layer where leaching occurs, removing minerals and nutrients.

B horizon

the subsoil layer containing minerals (like clay) leached from above and some organic material.

• also called zone of accumulation - where minerals are deposited.

• minerals such as clay help in the absorption for water

C horizon

partially altered parent material that serves as the source for soil formation.

Eluviation

the process of leaching minerals and nutrients from the upper soil layers.

Leaching

the process by which soluble substances are washed out of soil, often through water movement.

What are the 3 main soil types based on climate?

1. pedalfer → develops in humid temperate regions, rich in iron & aluminum (forests)

2. pedocal → develops in drier regions, rich in calcium carbonate (grasslands)

3. laterite → develops in tropical climates, heavily leached, infertile soil

Pedalfer soil

• found in humid temperate climates (pacific, southeast Canada, eastern Canada)

• high in iron oxides and aluminum rich clays in the subsoil (B horizon)

• rainfall sufficient to leach soluble minerals from upper layer, leaving a rusty brown coloured B-horizon

• organic rich, best developed in forest vegetation

  • acid condition are best produced here for leaching

Pedocal Soil

• found in dry regions (prairies Canada, western US)

• rich in calcium carbonate (alkaline)

• water contained in soil is drawn upwards and evaporated, causing the precipitation of calcium carbonate near the surface

• best developed in grassland vegetation

Laterite Soil

• found in hot, wet tropical climates

• chemical weathering is much more intense under these condtions

  • soils are deeper and denser

• highly leached, poor in nutrients

• rich in iron and aluminum oxides, giving it a red colour

• low humus, making it infertile for crops

What is Soil Erosion and why is it a problem?

removal of soil particles by water, wind or gravity

• accelerated by human activity (deforestation, overgrazing, poor farming)

• leads to loss of fertile land, lower crop yields and desertification

3 main types of soil erosion?

1. sheet erosion

2. rill erosion

3. gully erosion

sheet erosion

thin layers of dislodged soil removed by water

Rill erosion

small channels form as water cuts into soil

gully erosion

large channels develop, making land unusable due to significant soil loss and water runoff.

What was the Dust Bowl, and what caused it?

severe wind erosion event in 1930s, affecting Canadian parries and US Great Plains

• caused by drought, over-farming and lack of vegetation

• resulted in massive soil loss, crop failure and economic hardship

What is a Sedimentary Rock?

type of rock formed by weathered materials (rock fragments, minerals or dissolved ions) that are then transported though means of wind, water, ice or gravity and are deposited. Loose sediment becomes lithified turning into a rock

• these rocks cover 75% of Earth’s surface but make up 5% of the crusts volume

• relatively thin and discontinuous layer in the uppermost portion of crust

What are the 3 steps in turning sediment into sedimentary rock?

1. Deposition - sediments settle in layers

2. Diagenesis - chemical, physical and biological changes occur after deposition but before metamorphism

3. Lithification - compaction and cementation turn loose sediment into solid rock

What is diagenesis?

chemical, physical and biological changes that occur after deposition but before metamorphism of sediment (rock fully developing)

• the process that turns sediments into rocks

What are the two main lithification processes?

1. Compaction

2. Cementation

Compaction

the process where sediments are pressed together under pressure, reducing pore space, driving water out and increasing density.

• deeper the sediment is buried, the more compact it comes

• is most significant as lithification process in fine-grained sedimentary rocks

Cementation

the most important process by which sediments are converted to sedimentary rock

• minerals precipitate between sediment grains (acting as cement), binding them together

• common cements: calcite, silica, iron oxide

What are sedimentary environments?

geographic setting where sediment accumulates

• determines sediment type, deposition process and eventual rock formation

What are the 3 types of sedimentary environments?

1. Continental - on land (rivers, deserts, glaciers)

2. Transitional (shoreline) - coastal areas (deltas, beaches, tidal flats)

3. Marine - oceanic (shallow marine and deep marine environments)

What is a Continental Environment?

A geographic setting on land where sediments are deposited

• rivers - transport sediment, sorting it by size

• glaciers - carry a mix of sediments, leaving poorly sorted deposits

• deserts - wind moves fine grains, creating sand dunes

What are transitional environments and how do the form?

Transitional environments are coastal areas where sediment accumulation occurs between land and marine settings.

• form through

  • deltas - forms when rivers slow down, depositing sediments

  • beaches - wave action sorts sediments into sand and gravel

  • tidal flats and lagoons - fine sediments settle in calm water

Deltas

are landforms created at the mouth of rivers where they deposit sediments as they slow down, often resulting in a fan-shaped area.

Tidal Flats

are coastal wetlands that form at the interface between land and sea, characterized by the regular flooding and exposure to tides, allowing for the accumulation of fine sediments.

What is a marine environment?

A marine environment is a vast ecosystem that includes oceans, seas, and coastal areas, characterized by saltwater and diverse marine life such as fish, invertebrates, and aquatic plants.

what are the 2 types of marine environments?

1. shallow marine (0-200 m) - sand, mud and limestone from coral reefs form here

2. deep marine (>200m) - fine sediments settle slowly; turbidity currents bring coarser material

3 types of sedimentary rocks

• Detrital (Clastic) - made from rock fragments

  • sandstone, shale, conglomerate

• Chemical - form from precipitated minerals (limestone, rock salt)

• Organic - made from biological materials (coal)

what are detrital sedimentary rocks and how are they classified?

formed from solid rock fragments that are transported and deposited

classified by grain size

• mud rocks (smallest grains, shale, siltstone)

• sandstone (medium grains, quartz sandstone)

• conglomerate and breccia (largest grains, rounded vs angular)

Mudrocks

include shale, mudstone and siltstone

• consist of clay to silt sized particles that account for more than 50% of all sedimentary rocks

• particles in these rocks are small, and hard to identify

• typically deposited in quiet, low-energy environments such as lakes and deep ocean floors.

Sandstone

composed of sand sized particles

• after shale, sandstone is the second most abundant sedimentary rock, accounting for proxy 20% of the entire group

• quartz is the predominant mineral in most sandstones

• and commonly forms in environments like beaches and deserts.

Conglomerate

consist of largely rounded pebbles and cobbles, which can range from large boulders to small peas

• usually large enough to be able to distinguish

• poorly sorted because the spaces between large gravel contain trapped sand or mud

  • moved pretty far, causing the round edges of the pebbles

Breccia

similar to conglomerate except

• edges are angular instead of rounded

• indication that particles did not travel far from their source area before being deposited

What is a chemical sedimentary rock and how does it form?

forms when dissolved minerals predicate form solution. includes

• limestone (from calcium carbonate)

• dolostone (magnesium replaces calcium in limestone)

• evaporites (rock salt, gypsum)

Organic Precipitation

processes where aquatic organisms form chemical sediments of biochemical origin

Inorganic precipitation

process such as evaporation and chemical activity

How do organic sedimentary rocks form?

from biological material accumulating overtime

• coal - forms compressed plant material in swamps

• chalk - made from microscopic marine organisms

• coral reefs and fossil limestone - built from calcium carbonate skeletons of marine life

How do inorganic sedimentary rocks form?

from the accumulation of mineral particles and chemical precipitates, often through processes like evaporation or precipitation from water.

• inorganic limestones - form when chemical changes, high water temp or microbial activity increases concentration of calcium carbonate

inorganic limestone

a type of inorganic sedimentary rock formed from chemical changes that increase calcium carbonate concentration, often in warm water conditions.

dolostone

composed of calcium magnesium carbonate mineral dolomite

• often formed from the alteration of limestone through magnesium-rich fluids.

• less prone to being dissolved by acidic rainwater

• prominent in the Niagara Escaprment