Deposited Sediments and Sedimentary Rocks

Question 1

What features can deposited sediments have?

Answer 1

Sedimentary structures: small, 3D features that can form in a sediment during or after deposition as result of how and where the sediment is deposited, or from the activities of plants and animals

Question 2

Primary sedimentary structures:

Answer 2

form as the sediment is being deposited, most common type is strata which hare nearly horizontal layers of sediment which form as sediment accumulates over time. Layers > 1cm thick called beds, < 1cm layers are called laminations.

Question 3

A graded bed is a special type of

Answer 3

bed, normal grading: grain fine upwards, reverse grading: grains coarsen upwards

Question 4

If the strata are inclined, we call the layers:

Answer 4

cross-beds or cross-lamination

Question 5

Cross-bedding is the result of deposition on:

Answer 5

inclined surfaces such as ripples (small) and dunes (large), which are produced by flowing water or wind

Question 6

Symmetrical ripples:

Answer 6

form in areas of oscillating waves (beach)

Question 7

Asymmetrical ripples:

Answer 7

form in areas of unidirectional fluid flow (rivers and deserts)

Question 8

Imbricated pebbles:

Answer 8

form when flat pebbles overlap because flowing water in rivers pushes them all over to point downstream

Question 9

Sole marks are grooves and indents the form either as objects are dragged across sediment by:

Answer 9

a current, or back-current eddies scour out patches of sediment

Question 10

Secondary sedimentary structures

Answer 10

form after a sediment has been deposited

Question 11

Mudcracks:

Answer 11

form when water dries up and clay minerals contract

Question 12

Bioturbation:

Answer 12

result of animals, insects, and plant roots churning up sediment and erasing primary sedimentary structures

Question 13

Soft sediment deformation:

Answer 13

occurs when sediment is loaded onto waterlogged sediments. Compression may cause water to squeeze out, deforming the original horizontal bedding

Question 14

How do sediments turn to stone?

Answer 14

Lithification

Question 15

What is lithification?

Answer 15

describes the processes that turns sediment into stone

• Compaction: due to burial
• Cementation: precipitation of chemical sediments between clasts

Question 16

Cements like silica or carbonate minerals precipitate out of solution:

Answer 16

bind grains together.

Question 17

Compactions reduces pore space (voids or space between grains) by

Answer 17

forcing grains and matrix closer together. Helps to consolidate the grains (hold clasts together).

Question 18

Sedimentary rocks type is based on:

Answer 18

• Texture (clastic or crystalline)

- Composition (the type of sediment it is made of)

Question 19

Siliciclastic sedimentary rocks are distinguished by:

Answer 19

• Grain size and shape (texture)
• In sandstones, also specify grain type (relative proportion of quartz, feldspar, lithics, and clay)
• Gravel = conglomerate or breccia
• Sand = sandstone
• Silt = siltstone
• Clay and slit = shale (fissile) or mudstone (massive)

Question 20

Chemical sedimentary rocks are distinguished by:

Answer 20

Crystal type (carbonate, halite, microcrystalline quartz)

Question 21

Bioclastic sedimentary rocks are distinguished by:

Answer 21

• Grain size and shape (texture)

- Grain type (chemical sediments like shells, or organic sediments like plants)

Question 22

Naming Clastic Sedimentary Rocks Based on Grain Size

Answer 22

Clast name + rock name = name of rock

Question 23

Clast names of clastic sedimentary rocks

Answer 23

Conglomerate (rounded clasts) or Breccia (angular clasts) for sizes: boulder to granule
Sandstone for very coarse sand to very fine sand
Siltstone/Mudstone/Shale for microscopic grain sizes

Question 24

Naming Sandstones (for very coarse sand to very fine sand sedimentary rocks!!!!)

Answer 24

Feldspathic arenite, quartz arenite, lithic (rock) arenite INCLUDE GRAIN SIZE MODIFIER

Question 25

Classification of Carbonate Rocks

Answer 25

• Use Dunham classification of limestones diagram
• All have modifier i.e oolitic or fossiliferous or dolomitic if including dolomite/calcite followed by type of stone: mudstone, wackestone, packstone, grainstone, or boundstone