Depositional enviroments

Question 1

What are tides?

Answer 1

Tides occur in open ocean shallow marine tidal environments. There is no force strong enough to make it happen in a lake.

tides are caused by the moon (and sun) pulling earths gravity

Ocean tides are measured in the vertical direction (the rise and fall of sea level) but they are caused by currents = a horizontal flow.
The water tries to hunt the point where gravity pulls, but Corriolis and the point moving makes the complex system of tides

Question 2

How are ocean tides measured?

Answer 2

Ocean tides are measured in the vertical direction, the rise and fall of sea level, but they are caused by currents, a horizontal flow.

They are divided into three groups, from how the tides affect different lattitudes.
Diurnal: high lattitudes, has one high tide and one low tide during the day
Semidurnal: equator, has two high tides and two low tides during the day
Mixed semidurnal: has two high tides and two low tides, but they are not the same. One high and low are higher than the other high and low.

Question 3

What determines how tides affect a location?

Answer 3

Placement on Earth determines how one is affected by tides.

Question 4

What is the difference between diurnal and semidiurnal tides?

Answer 4

Diurnal tides expect a high tide followed by a low tide 12 hours later.
Semidiurnal tides have two high tides in 24 hours.

Question 5

What are the main depositional environments?

Answer 5

Continental environments: fluvial, alluvial, desert, glacial, and lacustrine.

Transitional environments: marine deltaic, estuarine, lagoonal, and littoral.

Marine environments: shallow siliciclastic seas, shallow-marine carbonate seas, pelagic, and deep clastic.

volcanic

Question 6

What is the difference between cold and temperate glaciers?

Answer 6

A cold glacier is frozen to the bedrock and moves by sheer movement, eroding less. A temperate glacier has water between the bedrock and ice, allowing faster movement and more erosion.

Question 7

How can we recognize dropstones in ancient sedimentary sequences?

Answer 7

Dropstones are much bigger stones than surrounding sediment, often misplaced, indicating they were transported by ice.

Ice has the greatest power of transportation. Dropstones comes from big rocks being transported in the ice, when it reaches the water the ice floats, but as it melts, it drops the rocks.

Question 8

Why is the Sahara an arid place?

Answer 8

The Sahara is arid due to the ITCZ, where water condenses and rains before reaching the region, leaving dry air.

Question 9

What are the different types of sand dunes?

Answer 9

Sand dunes include ripples, dunes, and draa, formed by wind which can only move sand-sized particles.

Question 10

What are the geomorphologic differences between meandering and braided river systems?

Answer 10

Meandering rivers have a single route, eroding on the outer side (cut bank) and depositing on the inner side (point bar). Braided rivers occur in softer sediment, flowing in smaller channels.

In general, braided rivers tend to occur in more proximal areas and meandering rivers occur further downstream. As the water goes down the slope decreases and the velocity too. That Results in erosion at the top and deposition at the bottom of the system.

Geomorphological is looking from above at the river, stratigraphically you look at the sediments deposited. Here you can see the difference in amalgamated (braided) or non-amalgamated (meander).

Question 11

What are point bars?

Answer 11

Point bars are created by deposition on the inner side of a river bend, while erosion occurs on the opposite cut bank.

Meandering rivers

Question 12

What are calcrete nodules?

Answer 12

Calcrete nodules are formed from plant roots in semi-arid environments, causing chemical reactions that break down chalk in the ground.

Question 13

What separates the shoreface from offshore zones?

Answer 13

The fair-weather wave base separates the shoreface from offshore zones.

Question 14

Describe a shallowing-upward wave-dominated siliciclastic sequence.

Answer 14

It usually starts with mud and silt, followed by alternating sand and mud layers, transitioning to predominantly sand beds, firstly crossstratification, then low angle crosstratification.

This relates to lower offshore, upper offshore, lower shoreface, uppershoreface and foreshore.-
shallowing-upward indicates a regression, the coast has mooved towards the water.

Question 15

What is the difference between photozoan and heterozoan organisms?

the two type of Carbonate factories

Answer 15

Photozoan organisms need light for photosynthesis, while heterozoan organisms require nutrients. Heterozoans can survive in deeper, colder waters where light doesnt reach.

Question 16

What is a drowning surface?

Answer 16

In geology, a drowning surface is a layer in sedimentary rocks that shows a sudden and permanent shift from shallow-water to deep-water conditions. This happens when the sea level rises quickly, or the land sinks, making the area too deep for the sediments and organisms typical of shallow water.

For example, you might see a transition from sandstones or reef limestone (shallow water) to deep-water mudstones or shale above this surface. It’s like a marker showing when the environment “drowned” and became much deeper.

Question 17

What is the difference between a delta and an estuary?

Answer 17

A delta is progradational, with the river moving towards the ocean, while an estuary is retrogradational, with the ocean moving toward the river.

Question 18

What is a beach berm?

Answer 18

A beach berm is sand deposited from high tide waves, characterized by a dip on either side.

Question 19

What characterizes lagoonal facies?

Answer 19

Lagoonal facies are characterized by mud deposits from low energy zones, with minimal wave action.

Question 20

What is the difference between density flows and turbiditic currents?

Answer 20

Density flows are gravity-driven flows caused by density differences, while turbiditic currents are a specific type of density flow driven by suspended sediment.

Question 21

What is the carbonate compensation depth?

Answer 21

The carbonate compensation depth (CCD) is the ocean depth where the rate of calcium carbonate supply matches the rate of solvation.

Below the CCD carbonate precipitation is not favored = shells dissolve

Question 22

How does the CCD affect pelagic sediments?

Answer 22

Below the CCD, carbonate particles dissolve, resulting in pelagic sediments primarily consisting of ooze with a slow sedimentation rate.

Question 23

Name the different types of delta and estuary?

Answer 23

Tide dominated and wave dominated Estuary
Tide dominated, wave dominated and river dominated Delta

Estuaries CAN NOT be river dominated, because then it would become a DELTA.

Question 24

What is the difference between the Delta front and the Delta top

Answer 24

The delta top is where you have the river.
The delta front is where it enters the ocean.

Question 25

what is a Delta?

Answer 25

A delta is always a progradational feature, with fluvial sediments capping marine deposits! A river that arrives in the sea. When it goes from shallow marine to foreshore (like a normal regression) but then has fluvial deposit on top, you know you have a delta!

Question 26

What is an Estuary?

Answer 26

An estuary is always a retrogradational feature, with marine deposits atop fluvial sediments The sea portion of a drowned valley system which receives sediment from both fluvial and marine sources and which contains facies influenced by tides, waves and fluvial processes.

Question 27

What is a lagoon?

Answer 27

A shallow body of water partly or completely separated from a larger body of water by a barrier, which can be a bioconstructed reef, a clastic beach barrier or hard rocks ridge

Question 28

Which three portions can an Estuary be divided into?

Answer 28

An outer, marine-dominated portion, a relatively low-energy central zone and an inner, river-dominated (but marine-influenced) part

Question 29

What are the main sedimentological differences between a carbonate ramp and a rimmed shelf?

Answer 29

A carbonate ramp is a gently sloping depositional surface with no significant barrier, where sediments transition gradually from shallow, high-energy areas to deeper, low-energy zones. It is characterized by a smooth energy gradient and widespread sediment dispersal. A rimmed shelf is a flat platform with a pronounced margin, such as a reef or shoal, that separates high-energy outer environments from low-energy, restricted lagoons. The rim acts as a barrier, creating distinct sedimentary zones. ## Footnote Carbonate ramp is shallow water with circulation Rimmed shelf protects a lagoon and divides two zones on either side

Question 30

What is the Bouma sequence?

Answer 30

At the base there is an eroded surface. Big energy erodes the surface. A: graded upward granules to sand B: horizontal lamination = Planar lamination. C: ripples and convolute lamination. D: planar lamination E: Above and below there is pelagic mud. This is the normal sedimentation in the environment. Mud comes after the turbidity flow when the water settles to normal conditions. ## Footnote A and B are deposited in the upper flow regime UFR C and D are from the lower flow regime LFR

Question 31

what is a turbidite?

Answer 31

A turbidite is an underwater flow, an underwater avalanche.

Question 32

what can cause a turbidity currents?

Answer 32

Storms, an increased sedimentsupply on the slope, a vulcanic eruption or an earthquake.

Question 33

what is contourites?

Answer 33

the products of continuous flow along the sea floor parallel to, or nearly parallel to, the bathymetric contours of the continental margin may be sheets of fine muddy and silty sediment

Question 34

What is Hummocky cross stratification a sign of in a profile?

Answer 34

Hummocky cross stratification = storm deposition. It forms in the lower shoreface during storm.

Question 35

What is an oxbow lake? ## Footnote Hesteskosø på dansk

Answer 35

When a meandering river gets "too big", sometimes it is easier for the water to skip the meander and just cut straight through, this leaves behing a piece of the old river, now forming an oxbow lake. ## Footnote Water will choose the easiest route to save energy.