Depositional Environments, Landforms, and Waterforms

erosion

is a geological process in which earth materials are weathered and transported. Erosional agents such as water, wind, ice, or animals and humans are responsible for transporting these materials.

deposition

These earth materials are then “added” to an environment or landform in a process called

There are many types of depositional environments, but they can be classified into three main types:

Terrestial Environments, Transitional Environments, and Marine Environments

Terrestrial Environments

Land and water forms in this environment can be found on land and usually involve freshwater. Here are some depositional environments that fall under this category:

• Fluvial: rivers and streams

• Eolian: deserts and arid environments 

• Alluvial: mountainous environments

• Glacial: ice caps and glaciers

• Lacustrine: lakes

Associated landforms and waterforms:

• Mountains – These are elevated (more than 2,000 ft) areas of land, usually resulting from tectonic forces. Hills are similar to mountains but with lesser steepness (below 2,000 ft).

• Plains – These are relatively flat expanses of land that lie above sea level. Plains can occur between two mountains as a valley. A plateau is a plain that is relatively elevated than the surrounding land.

• Desserts – These areas receive little rainfall and have high evaporation rates. Despite this, the most dominant agent of erosion in these areas is running water, followed by wind.

• Glacial environments – These are areas where the most dominant erosional agent is ice. Glaciers are large masses of moving ice over land. Ice sheets are also large masses covering an extensive land area (more than 50,000 km²).

• Rivers – Long bodies of water that originate from high elevation (such as mountains or hills) and flow down to lower elevation (such as plains, mountain slopes, etc.). Rivers are usually supplied with water from rainfall, melted ice, or natural springs from underground in areas called drainage basins.

Transitional Environments represent the interface between land and sea. It is here where freshwater meets with seawater.

Here are some depositional environments that fall under transitional environments:

• Beach: where land meets the sea in shallow waters

• Deltaic: where the river flows into the sea; freshwater mixes with seawater

• Tidal flat: low-lying areas affected by tides

• Lagoonal: a small body of water closed off from a larger body of water (the ocean)

Associated landforms and waterforms:

• Deltas are areas at the end of the mouth of a river where freshwater mixes with seawater.

• Wetlands are areas near rivers or coastlines where soils are saturated or submerged in water. Swamps are wetlands where trees dominate plant life. Marshes are wetlands where moss and soft-stemmed vegetation are most prominent. 

Marine Environments

These environments can be found in the open waters, from the shallow depths to the deepest portions of the ocean.

Here are examples of marine environments:

• Shallow marine/reefal: a region where sunlight penetrates the water; high energy environment and teeming with life

• Continental shelf: extensions of continental crust submerged by water

• Continental slope: steep slope between the shallow continental shelf and the deep ocean basin

• Deep marine: a region where sunlight does not reach; low energy environment

Associated landforms and waterforms:

• Oceans – These are large bodies of water that surround continents. Seas are smaller bodies of saltwater enclosed or partially enclosed by land and are connected to the ocean.

• Atolls are rings or partial rings of coral that usually form around a volcanic island or volcano that has receded or been eroded.

• Guyots are elevated platforms with flat tops formed by volcanic activity near the ocean floor. These can be massive and reach heights of up to more than 600 m. They are also known as seamounts.

What does stratigraphy study?

studies rock layers or strata and their relationship to time.

Who is considered the Father of English Geology?

William Smith.

Who formulated the basic principles of stratigraphy?

Nicolaus Steno.

What does the Law of Superposition state?

In an undisturbed sequence, the bottom layers are the oldest, and the upper layers are younger.

What does the Law of Lateral Continuity state?

Strata extend laterally until they encounter a barrier or obstacle.

What does the Law of Original Horizontality state?

Strata are deposited in horizontal layers.

What does the Law of Cross-Cutting Relationships state?

A geologic feature that cuts through strata is younger than the strata it cuts.

What principle states that fossil sequences in strata are predictable and consistent?

The Principle of Faunal Succession.

What is an unconformity in a rock sequence?

A gap or break in the rock record.

What is a disconformity?

A missing layer due to erosion or non-deposition between parallel strata.

What is a nonconformity?

Sedimentary rocks deposited on top of igneous or metamorphic rocks.

What is an angular unconformity?

Horizontal strata deposited on tilted or folded layers.

What is relative dating?

A method that determines the sequence of events without exact dates.

What is absolute dating?

A method to determine the numerical or exact age of rocks.

What is radiometric dating?

A method of dating rocks using the decay of radioactive isotopes.

What is a parent isotope?

A radioactive isotope that decays into a more stable daughter isotope.

What is a daughter isotope?

The stable product of the decay of a parent isotope.

What is a half-life?

The time it takes for half of a radioactive substance to decay.