GEOL 1303.002 - Lectures Part 2: Weathering, Sediments & Soils

Exam November, 8th

What is Weathering

The physical breakdown and chemical alteration of Earth's materials as they are exposed to the atmosphere, hydrosphere, and biosphere.

Parent Material

The original rocks and minerals that are weathered

Erosion

The removal of weathered material away from the location of the original parent material

Differential Weathering

Rocks are not homogeneous, therefore they may weather at a varying rate

Mechanical Weathering

• Physical forces break apart Earth materials to make smaller fragments

• The product is different sizes and shape but same composition as the parent material

Mechanical Weathering: Chemical Weathering

• Decomposition and alteration of the composition of Earth materials Decomposition and alteration of the composition of Earth materials
• Product is a different composition than the parent material

Mechanical Weathering: Fluvial weathering

• Water volume
• Water velocity
• Water composition
• Terrain slope

Mechanical Weathering: Eolian weathering

• Wind Velocity
• Wind Density
• Moisture content of sediment

Mechanical Weathering: Coastal (tidal / wave) weathering

• Wave amplitude
• Wavelength
• Water composition/density

Mechanical Weathering: Crystal wedging

• Frost Wedging
• Salt Wedging
• Gypsum Wedging

Mechanical Weathering: Expansion / Contraction weathering

• Pressure Release
  • Sheet joints
  • Exfoliation domes

  • Thermal
  • Hydration

Mechanical Weathering: Biological weathering

• Animals (burrowing, digging, etc.)
• Plants (roots)
• Lichens
• Bacteria

Mechanical Weathering: Anthropogenic weathering:

• Construction
• Mining
• Recreation

Chemical Weathering: Mineral Stability

• Minerals are in equilibrium with the environment in which they are formed.
• Quartz is stable at Earth's surface conditions.
• Olivine is unstable at Earth's surface condition

Chemical Weathering: Solution weathering:

• The dissociation of elements in water to produce ions
• Carbonates (CaCO3, CaMg(CO3)2)
• Evaporites (CaSO4, NaCl)

Chemical Weathering: Oxidation:

• The addition of oxygen to a compound in an oxic environment
• Iron (Fe) plus oxygen (O2) react to form hematite (Fe2O3)

Chemical Weathering: Reduction

• The removal of oxygen from a compound in an anoxic environment
• Sulfate (CaSO4) is reduced to form sulfide (H2S)
• Hematite (Fe2O3) is reduced to form pyrite (FeS2)

What is Sediment?

• solid material that has settled down from a state of suspension in a liquid
• solid fragmental material transported and deposited by wind, water, or ice, chemically precipitated from solution or secreted by organisms, and that forms in layers in its unconsolidated form.

Sediment Size

Surface area determines the rate of weathering

Sediment Shape

• Angular
• Subangular
• Subrounded
• Rounded

Sediment Transport

Mechanisms of transport are effectively the same as the mechanisms that induce mechanical weathering, including:
• Fluvial
• Eolian
• Wave
• Wind
• Gravity
• Biological
• Anthropogenic

What is Soil?

Unconsolidated association of regolith, humus, and water

Regolith

• Weathered bedrock

Humus:

• Carbon derived from the decay of organic material

Residual Soils

• Soil that forms in place by the decomposition of the underlying bedrock

Transported Soils:

Soils that form from sediments that have been transported away from the area of their source bedrock

Controls on Soil Formation

• The primary driver of soil formation is climate
• Factors that control soil development, include:
• 1) Host rock composition, 2) Moisture, 3) Temperature, 4) Fluid Content, 5) Biology, 6) Topography (Slope & Orientation)

Soil Horizons

• Not all soil horizons are present in every soil profile
• The degree of development is dependent upon physical and environmental parameters
• Climate is the major driver behind development of individual soil horizons

Pedalfer Soil

• Develops in moist climates
• Moderate O horizon
• Moderate A horizon, well-leached
• Dispersed B horizon, because most leached material is transported out of the system
• Extensive C horizon

Laterite Soil

• Develops in tropical climates
• Well-developed O horizon
• Extensive A horizon that is completely well-leached
• Extensive B horizon, but most material is leached out of system completely
• Extensive C horizon, with accumulations of Fe and Al

Physical Deterioration Erosion:

The loss of soil from vegetation change can cause significant degradation, by both wind and water

Physical Deterioration Sheet Erosion

Thin, uniform layers are removed from the entire surface

Physical Deterioration Rill Erosion

Soil is removed along preferential, channelized flow paths

Rills

small-scale erosion

Gullies

large-scale erosion

Physical Deterioration Compaction

cattle and machinery

Chemical Deterioration Degradation

of soils by the alteration of the composition such that they can no longer sustain desired vegetation
• Overuse depletes soils of nutrients
• Salinization from saline waters used in irrigation
• Chemical pollution – accumulation of industrial and agricultural products

Prevention:

• Crop rotation
• Contour plowing
• Terrace construction
• No-till farming
• Environmental regulations
• Location, Location, Location

What is Soil?

Unconsolidated association of regolith, humus, and water

Controls on Soil Formation

• The primary driver of soil formation is climate
• Factors that control soil development, include:
• 1) Host rock composition, 2) Moisture, 3) Temperature, 4) Fluid Content, 5) Biology, 6) Topography (Slope & Orientation)

Soil Horizons

• Not all soil horizons are present in every soil profile
• The degree of development is dependent upon physical and environmental parameters
• Climate is the major driver behind the development of individual soil horizons

Pedalfer Soil: Soil types 1

• Develops in moist climates
• Moderate O horizon
• Moderate A horizon, well-leached
• Dispersed B horizon, because most leached material is transported out of the system
• Extensive C horizon

Pedocal Soil: Soil types 2

Develops in arid climates
• Thin O horizon
• Thin A horizon, poorly leached
• Moderate B horizon, with dense colic (caliche) and gypsic deposits.
• Moderate C horizon

Laterite Soil: Soil types 3

• Develops in tropical climates
• Well-developed O horizon
• Extensive A horizon that is completely well-leached
• Extensive B horizon, but most material is leached out of the system completely
• Extensive C horizon, with accumulations of Fe and Al

Soil Degradation I Physical Deterioration:

• Erosion:
• The loss of soil from vegetation change can cause significant degradation, by both wind and water
• Sheet Erosion:
• Thin, uniform layers are removed from the entire surface
• Rill Erosion:
• Soil is removed along preferential, channelized flow paths
• Rills – small-scale erosion
• Gullies – large-scale erosion
• Compaction: cattle and machinery

Soil Degradation II: Chemical Deterioration:

Degradation of soils by the alteration of the composition such that they can no longer sustain desired vegetation
• Overuse depletes soils of nutrients
• Salinization from saline waters used in irrigation
• Chemical pollution – accumulation of industrial and agricultural products

Soil Degradation III: Prevention

• Crop rotation
• Contour plowing
• Terrace construction
• No-till farming
• Environmental regulations
• Location, Location, Location

What is a Sedimentary Rock?

1. solid material that has settled down from a state of suspension in a liquid;
2. solid fragmental material transported and deposited by wind, water, or ice, chemically precipitated from solution or secreted by organisms, and that forms in layers in its unconsolidated form

Sediment Size

• Clay: <0.002 mm
• Silt: 0.002 mm to 0.0625 mm
• Sand: 0.0625 mm to 2 mm
• Pebble: 2 mm to 64 mm
• Cobble: 64 mm to 256 mm
• Boulder: >256 mm

Conglomerate

composed of rounded clast

Breccia

composed of angular clasts

Lithification

• Sedimentary Rocks are created through lithification/consolidation.
• Process through which unconsolidated sediments are converted into a consolidated mass, through various processes, generally associated with burial diagenesis.
• Compaction
• Dewatering
• Cementation

Clastic Sedimentary Rocks

sedimentary rocks composed primarily of fragments derived from the weathering of preexisting rocks and transported to their place of deposition

Sandstone

• Quartz Sandstone – >50% Quartz
• Arkose Sandstone – >50% Feldspar
• Lithic Sandstone – >50% Lithics

Mudrock:

• Mudstone – Clay content ≈ Silt content
• Claystone – Clay content > Silt content
• Siltstone – Silt content > Clay content
• Sandstone – >90% Sand
• Shale = mudstone & claystone

Gravel

clast size > pebble

Conglomerate Gravel

composed of rounded clasts that are pebble size or larger

Breccia Gravel

composed of angular clasts that are pebble size or larger

Clastic Rocks Aqueous Sedimentation

clastic sediments deposited in a liquid environment as a result of fluid flow; subaqueous deposition (rivers, streams, and oceans)

Clastic Rocks Eolian Sedimentation

clastic sediments deposited and modified by wind processes; subaerial deposition

Clastic Rock Glacial Sedimentation

clastic sediments resulting from glacial modifications to the Earth surface

Clastic Rock Gravitational Sedimentation

clastic sediments, subaerial or subaqueous, deposited primarily as a result of collapse or slope failure

Coal

A readily combustible rock that contains >50% by weight and >70% by volume of carbonaceous material, formed from the compaction of altered plant materials such as peat.

Peat

compressed organic material containing ~50% carbon

Lignite

low-grade coal containing~70% carbon – dull black or brown coloration.

Bituminous

mid-grade coal containing ~80% carbon – dark coloration.

Anthracite

metamorphosed coal containing >90% carbon – dark black coloration.

Biochemical Sedimentary Rocks:

sedimentary rocks formed by direct secretion from organisms or as a result of changes in the environment resulting from environmental modification by organisms

Aragonite

CaCO3 : limestone

Calcite

CaCO3 : limestone

Dolomite

Ca0.5Mg0.5CO3 : dolomite

Biochemical Sedimentary Rocks: General Terms:

• Skeletal grain – shells of calcareous organisms
• Carbonate Mud – clay-size particles
• Coquina – shell hash
• Ooid – concentrically banded, spherical grains
• Peloid (pellet) – spherical grains (usually feces)

Carbonate Reefs:

a ridge-like or domal structure built by the accumulation of calcareous organisms, which generally exhibits High biodiversity

Carbonate Mound

a domed structure built by the accumulation of calcareous organisms, which generally exhibits low biodiversity.

Carbonate Shoals:

calcareous deposition in relatively shallow water forming a ridge, bank or bar of unconsolidated material

Chert

Chert / Microcrystalline Quartz – SiO2 :
• Accumulation of siliceous shells, usually in deep water
• Carbonates dissolve at ~1.8 km depth
(carbonate compensation depth)

Chert Types

• Flint: dark coloration due to organics
• Jasper: red coloration due to iron oxides

Dunham Carbonate Rock Classification

Mudstone, Wackestone, Packstone, Grainstone and Boundstone

Chemical Sedimentary Rocks

sedimentary rocks formed by direct chemical precipitation from solution.

Chemical sed. Rocks

• Calcite – CaCO3 : limestone
• Dolomite – Ca0.5Mg0.5CO3 : dolomite
• Potash – K2CO3
• Halite – NaCl : rock salt
• Sylvite – KCl : bitter salt
• Gypsum (Anydrite) – CaSO4·2H2O (CaSO4)

Sabkha

supratidal environment of deposition in arid or semiarid regions, characterized by high evaporation rates and evaporate deposit

Salina:

environment of deposition with restricted circulation and high evaporation rates; salt pond or playakake

Secondary Precipitates:

broad group of minerals that precipitate inorganically as a result of changes in the physical and chemical environment.

Strata / Beds

distinct layers of sediment / sedimentary rock representing:
• Consistent sedimentation
• Periods of environmental stability
• Individual storm events

Ripple Marks

small ridges separated by small trough

Current ripple marks:

asymmetrical features formed by flow in one direction

Wave ripple marks

symmetrical features formed by flow in two directions

Cross-Bedding

layers angled downward from the surface they were deposited in, which indicates the direction of flow (fluvial or eolian layers angled downward from the surface they were deposited in, which indicates
direction of flow (fluvial or eolian

Graded Bedding

upward decrease in grain size as a result of deposition

Mudcracks:

Desiccation features formed by the contraction of sediments during dewatering

Imprints

Indentations on surfaces created by objects walking, crawling, or being drug across the surface, including both animate and inanimate objects.

Sedimentary Facies I

Sedimentary Facies represent environments of deposition, which are characterized by distinct physical, chemical, and biological attributes

Marine Transgression

• Relative rise in sea level related to subsidence, rise in sea level or a combination
• Inland shift in facies environments

Marine Regression:

The relative drop in sea level related to uplift, drop in sea level, or a combination
• Seaward shift in facies environments

Fossil:

the remains or traces once living organisms preserved in rock

Modes of Preservation

• Unaltered Remains

• Freezing
• Desiccation
• Permineralization
• Replacement
• Carbonization
• Molds & Casts
• Trace fossils

Natural Resources I

Aggregate:
• All rocks can be used as sources of building materials
• Unconsolidated sediments are often used in concrete as aggregate filler Building Stone:
• Many sedimentary rocks naturally break along bedding planes making them ideal for construction
Ceramics:
• Pure clays are mined as source material for ceramics and bricks

Natural Resources II

Hydrocarbons:
• Petroleum (both liquid and gas) is associated with the maturation of organic molecules trapped in sedimentary rocks during deposition and diagenesis
• Source rocks contain the original organic carbon
• Reservoir rocks store the mature hydrocarbon products
• Oil Shale contains tightly sealed hydrocarbons
• Tar Sand contains highly viscous hydrocarbon

Natural Resources III

Coal:
• Coal has been mined for millennia as a source of energy
• Most electricity in the United States is generated from the combustion of coal (primarily lignite)
Coke:
• Fused ash from coal combustion that is used in steel refining

Natural Resources IV

evaporites:
• Halite: mined for salt, both table and deicing salt for roadways
• Sylvite & Potash: mined for phosphates that are used as fertilizers
Phosphates:
• Apatite: mined like some evaporites for phosphates that are used as fertilizers