Sedimentary Environments and Landforms

Question 1

Clastic Sediment

Answer 1

Origin: Formed from fragments (clasts) of pre-existing rocks.

Process: Weathering and erosion break down rocks, then the particles are transported and deposited.

Examples: Sand, silt, clay, gravel.

Question 2

Chemical Sediment

Answer 2

Origin: Formed when dissolved minerals precipitate out of a solution.

Process: Often occurs in evaporating bodies of water (like salt flats).

Examples: Rock salt (halite), gypsum, some types of limestone.

Question 3

Biogenic Sediment

Answer 3

Origin: Formed from the remains of living organisms.

Process: Accumulation of biological material like shells, plants, or bones.

Examples: Coal (from plant material), chalk and some limestones (from shell fragments or microorganisms).

Question 4

What is needed for long term storage of sediment and conversion into sedimentary rock.

Answer 4

Space is needed (accommodation) which is generated by subsidence.
Sediment then needs to be transported to and deposited in this environment (sedimentary basins).

Question 5

Is the deep ocean considered a sedimentary basin?

Answer 5

No as sediment can get out into the deep ocean easily.

Question 6

What are the main depositional geomorphic elements associated with fluvial systems?

Answer 6

1. Floodplains (Broad, flat areas adjacent to rivers that flood periodically.)
2. Levees (Natural embankments along riverbanks.)
3. Point Bars (Curved deposits on the inside bends of meandering rivers.)
4. Deltas (Triangular or fan-shaped deposits at the mouth of a river.)

Question 7

Floodplain formation

Answer 7

During floods, rivers overflow and deposit fine sediment (silt and clay) over the land, gradually building up the floodplain.

Question 8

Levee formation

Answer 8

When rivers flood, coarser sediment (like sand) is deposited closest to the channel, building up ridges over time.

Question 9

Point bar formation

Answer 9

As water slows on the inside of a meander, sediment drops out and accumulates.

Question 10

Delta formation

Answer 10

As rivers enter standing water (like lakes or oceans), their velocity drops, and sediment settles out causing the flow to divert round the deposited material. This fans out into a lobed shape.

Question 11

What are the main depositional geomorphic elements associated with aeolian (Wind) systems?

Answer 11

1. Dunes (Hills or ridges of sand shaped by wind.)
2. Loess Deposits (Extensive blankets of fine, wind-blown silt.)
3. Sand Sheets (Flat or gently undulating surfaces covered with sand.)

Question 12

Dune formation

Answer 12

Wind picks up loose sand and drops it when it slows down, creating various dune shapes depending on wind direction and sediment supply.

Question 13

Loess formation

Answer 13

Wind transports silt from glacial outwash plains or deserts and deposits it far from the source. Loess is often very fertile.

Question 14

Sand sheets formation

Answer 14

Occur where windblown sand is evenly deposited without enough energy to form dunes.

Question 15

What shape do fluvial dominated coastlines have?

Answer 15

Deltas which stick out from the coast.

Question 16

What shape and features do wave dominated coastlines have?

Answer 16

Linear coasts where wave strike is not perpendicular to coast due to long shore drift. Spits and bars may form with lagoons behind.

Question 17

What shape and features do tide dominated coastlines have?

Answer 17

Estuaries (opposite of deltas) ‘trumpet’ morphology that sticks into the land as well as tide flats.

Question 18

How is sediment transported and deposited in deep marine settings?

Answer 18

Sediment is transported and deposited by gravity-driven flows, suspension settling, and biogenic activity.

Question 19

What is continental shelf?

Answer 19

Submarine continental rock that then steeply drops off to true oceanic rock. The width of this shelf can vary.

Question 20

What are the main depositional geomorphic elements associated with deep water systems?

Answer 20

1.Submarine Fans (Large fan-shaped deposits at the base of continental slopes.)

2. Submarine Canyons (Steep-sided valleys cut into the continental slope.)
3. Continental Rise (A gently sloping area at the base of the continental slope, between the slope and abyssal plain.)
4. Abyssal Plains (Vast, flat regions of the deep ocean floor, often over 4,000 meters deep.)

Question 21

Submarine fan formation

Answer 21

Created by turbidity currents—dense, sediment-laden flows that rush down submarine canyons. As these flows slow, they deposit layers of sediment, coarsest first (graded bedding).

Question 22

Submarine canyon formation

Answer 22

Carved backwards into the continental shelf by turbidity currents or submarine landslides. They act as conduits for transporting sediment from shallow to deep water.

Question 23

Continental rise formation

Answer 23

Accumulation of sediment from turbidity currents and submarine landslides, forming thick sequences of graded beds and muds.

Question 24

Abyssal plain formation

Answer 24

Sediment slowly settles out of suspension over time—pelagic sedimentation (e.g., clay, microscopic shells from plankton like radiolarians and foraminifera).

Question 25

What are the categories of biogenic sediment?

Answer 25

1. Soft Parts – “Organic” Sediments 2. Hard Parts – “Carbonate” Biogenic Sediments

Question 26

Organic sediments

Answer 26

Origin: From the soft tissues of plants and animals. Composition: Rich in organic carbon, hydrogen, and other elements. Common Forms: 1) Peat – partially decayed plant matter in wetlands. 2) Coal – formed from buried and compacted plant material. 3) Oil Shales – fine-grained rocks with high organic content. 4) Marine organic-rich muds – can lead to source rocks for petroleum. Environment: Typically found in low-oxygen environments (like swamps, lakes, or ocean basins) where decomposition is slowed and organic matter can accumulate.

Question 27

Carbonate sediments

Answer 27

Origin: From the skeletal remains or shells of marine organisms. Composition: Mostly calcium carbonate (CaCO₃), but also includes silica (SiO₂) in some cases. Common Forms: 1) Shell fragments – from organisms like molluscs, corals, foraminifera. 2) Coral reefs and limestones – built largely from calcium carbonate skeletons. 3)Chalk – formed from microscopic plankton shells (coccolithophores). 4) Biogenic oozes – accumulate on the deep seafloor (e.g., calcareous ooze, siliceous ooze). Environment: Warm, shallow marine settings are ideal for carbonate sedimentation, but carbonate oozes also accumulate in deeper ocean settings (as long as they’re above the carbonate compensation depth, where CaCO₃ can dissolve).

Question 28

What are the 2 factors that control the deposition sedimentary organic matter?

Answer 28

1) The rate of organic production 2) The rate of organic decay

Question 29

Peat Formation

Answer 29

Conditions Needed: -High Plant Productivity -Waterlogged Conditions (limits oxygen supply) -Low Rates of Decomposition -Acidic Environment (deduces microbial activity) -Cool to Temperate Climate

Question 30

Organic Muds Formation

Answer 30

Conditions Needed: -High Organic Productivity (Common in upwelling zones or nutrient-rich coastal waters.) -Low Oxygen (Anoxic or Dysoxic) Bottom Waters (Can occur in stratified water bodies where bottom water doesn’t mix with oxygen-rich surface water.) e.g. Kimmeridge clay -Rapid Burial by Fine Sediment -Low Energy Environment

Question 31

What is a polymorph and give and example?

Answer 31

A mineral with the same chemical composition but a different internal structure. Aragonite and calcite are polymorphs – both contain calcium carbonate (CaCO3) but have different internal structures.

Question 32

What are necessary for the formation of carbonates?

Answer 32

1. Warm, Shallow Marine Water (Calcium carbonate is less soluble in warm water, making precipitation more likely.) 2. Clear, Sunlit Water (Supports photosynthetic organisms (like algae and coral symbionts) that aid in carbonate production.) 3. High Biological Productivity (Many carbonates come from the skeletal remains of marine organisms) 4. Warm, Alkaline, Low-Nutrient Water 5. Low Input of Terrigenous Clastics (Carbonate environments don’t mix well with a lot of sand, silt, or clay from land as they reduce light penetration.) 6. Stable, Subsiding Platforms or Shelves (Provides room for continuous carbonate accumulation without being eroded or drowned.

Question 33

What are the 3 environments of carbonate production?

Answer 33

Rimmed shelves, Isolated platforms and Ramps.

Question 34

Rimmed shelves

Answer 34

-Production is high -Water is warm, clear and salinity is normal Morphology: -Attached to land -Flat top with distinct barrier reef -Lagoon located behind -Steep slope in front of reef into deep waters

Question 35

Isolated platforms (Atolls)

Answer 35

-Production is high -Warm, clear and salinity is normal -Often form around volcanic islands Morphology: -Not attached to land -Flat top with distinct barrier reef -a Lagoon in the middle -Steep slope to true deep water

Question 36

Carbonate ramps

Answer 36

-Production is lower -Water is cooler, contaminated or hypersaline Morphology: -A ramps that dips uniformly into deeper water -No barrier reef, only local patches -Sediment is more readily reworked and moved away

Question 37

What are evaporite sediments?

Answer 37

Evaporites are chemical sedimentary rocks or deposits that form when water evaporates, and the dissolved salts and minerals precipitate out of the solution. Such as calcite, dolomite, gypsum and the salt group.

Question 38

Conditions Necessary for Evaporite Deposition

Answer 38

1. High Evaporation Rates (hyper salinity) 2. Restricted Water Bodies (Limited connection to the open ocean or an enclosed basin which prevents fresh water from diluting the ion-rich water.) 3. Warm, Arid Climate (Hot temperatures and dry conditions speed up evaporation.) 4. Steady Supply of Saline Water (To build thick evaporite deposits, the basin must be refilled periodically with new water.)

Question 39

Why are evaporite deposits valuable?

Answer 39

-They are good paleoclimate indicators. -Economic value