PRINCIPAL OF FAUNAL SUCCESSION

i. Recognizes that life has changed throughout time.

ii. As one group of organisms disappears from the fossil record it is replaced with new ones.

iii. The same form is never exactly duplicated

iv. This allows fossils to be put in chronological order based on their appearance in the strata and the fossil record.

INDEX FOSSILS

v. A fossil that occurred geographically wide, but for a very brief time period.

vi. Abundantly preserved in rocks

vii. Easily identified in the field

CORRELATION

viii. The use of index fossils and the other methods of reading fossils to make it possible to compare rocks that have been exposed in two locations.

10. Give the definition of Weathering. List the factors that influence weathering. Describe the types of weathering.

Weathering is the process of alteration and fragmentation by the joined action of atmosphere, water and living organisms. Weathering itself involves little or no movement of the decomposed rocks and minerals. This material accumulates where it forms and overlies unweathered bedrock.

Weathering is influenced by:

• Atmospheric agents;

• Solar radiation;

• Surface water;

• Animals and plants.

Weathering types:

• Mechanical Weathering (Physical Weathering)

• Chemical Weathering

Mechanical weatheringis the process by which rocks are broken down into smaller pieces by external conditions, such as the freezing of water in cracks in the rock.

The rock is chemically weatheredwhen it reacts with rain, water, and the atmosphere to destroy chemical and mineralogical bonds and form new minerals.

11. Describe mechanical weathering. Explain the major processes which cause mechanical weathering.

It’s the breakdown of rocks and minerals into small-sized particles through physical forces.

Mechanical weatheringis the process by which rocks are broken down into smaller pieces by external conditions, such as the freezing of water in cracks in the rock.

• Five major processes cause mechanical weathering:

1. pressure-release fracturing:In pressure release, also known as unloading, overlying materials (not necessarily rocks) are removed (by erosion, or other processes), which causes underlying rocks to expand and fracture parallel to the surface.
2. frost wedging: Frost wedging is a type of mechanical weathering caused by frost and ice.ice wedging - water enters a crack or edge, freezes and then expands. Then the rock breaks.
3. abrasion: the wearing down of rocks by particles by solid/wind. (solid particles carried by the wind) - cold wet climate
4. organic activity:Plants (root pry) Animals (burrowing)
5. thermal expansion and contraction: Temperature changes: heating and cooling at fast rates. Generally occurs in desert

Two additional processes—salt cracking and hydrolysis expansion—result from combinations of mechanical and chemical processes.

12. Describe chemical weathering in detail. What are the consequences of chemical and mechanical processes operating together?

Chemical weathering: It’s the breakdown of rocks through chemical reactions causing changes in their mineral composition. e.g.: Hydrolysis, Oxidation, Carbonation and Dissolution

CHEMICAL AND MECHANICAL WEATHERING OPERATING TOGETHER:

• Salt Cracking: In environments where ground water is salty, salt water seeps into cracks in bedrock. When the water evaporates, the dissolved salts crystallize. The growing crystals exert tremendous forces, enough to widen a crack and fracture a rock, a process called salt cracking.

• Exfoliation (frequently explained by pressure-release fracturing)

Granite commonly fractures by exfoliation, a process in which large plates or shells split away like the layers of an onion.

13. Describe weather crust and types. What kind of mineral deposits are related to weathered crust?

Weathered Crust [Crust of weathering]– a collection of rocks of the upper lithosphere, which were formed due to the destruction and transformation of primary rocks under the influence of physical, chemical and biochemical processes.

Geologists identify 2 major morphogenetic types among the weathered crust:

• Areal weathered crust isdeveloped as a cover or a shield and spreads to vast areas of hundreds of square kilometers, and represents various tectonically-quiet surface topography.

• Linear weathered crust has a linear distribution in the layout and is related to zones of fracturing, faulting and contacts of rocks of different composition and genesis. In these conditions, as a result, more free water and dissolved reactive components are penetrated which causes intense chemical weathering process.

· The ancient weathered crustswere formed at different stages of geological history, coinciding with major sedimentation breaks.

Formation of large mineral deposits, such as:

• Bauxite
• Iron
• Kaolin
• Manganese
• Nickel
• Cobalt

14. Soil and soil formation. Soil Profile. Soil forming factors. Soil types.

Soil is a mixture of mineral and organic matter lacking any inherited rock structure.

• Engineering definition: Anything that can be removed without blasting

• The layers of weathered particles of earth material that contain organic matter and can support vegetation are defined as soil. Soil can be all or just part of the sedimentary material that covers the bedrock.

• It can take hundreds of thousands years to form soil

• Soil contains mostly quartz and clay particles of varying sizes

- quartz and sand keep the soil porous

- clay particles hold water and nutrients

• Loamcontains sand, silt, and clay with abundant organic material.

• Topsoilis the upper part of a section of loam, has the highest organic content, and is considered to be the most fertile layer.

• The rocky subsoilunderlies the topsoil and contains less organic material.

Types of Soil:

• Residual soil and transported soil. When soil isdeveloped from the weathering of the underlying bedrock it is called residual soil.

• Transportedsoil is deposited by agents such as ice and water and is not derived from the underlying bedrock. Examples include sand left by retreating glaciers and the mud that is left after a flood.

SOIL HORIZONS

– 0 horizon (humus)

– A horizon (uppermost layer)

– B horizon (middle layer)

– C horizon (the lowest layer)

Soil Profile:

Over time different levels of a soil can differentiate into distinct horizons that create soil profiles.

• Chemical reactions and formation of secondary minerals (clays).

• Leaching by infiltrating water.

• Deposition and accumulation of material leached from higher levels in the soil.

Factors of soil formation:

Climate

• Temperature and precipitation

• Indirect controls (e.g., types of plants)

• Weathering rates

The greater the rainfall amount, the more rapid the rate of both weathering and erosion.

Organisms

• Types of native vegetation

• Weathering is dependent of plant growth

• Plant and animal activity produces humic acids that are powerful weathering agents.

• Plants can physically as well as chemically break down rocks.

• Plants stabilize soil profiles, Animals (including humans) tend to increase erosion.

Parent Material:

• Chemistry

• Mineralogy

• Grain size

Topography:

• Ground slope

• Elevation

• Aspect (e.g., north facing vs. south facing slopes)

Time

• Development and destruction of soil profiles

• Typical reaction rates are slow, the longer a rock unit has been exposed, the more likely it is to be weathered.

15. Describe Eolian processes in detail. Explain all terms related to wind processes.

Date: 2015-12-11; view: 879