Sedimentary Rocks

Question 1

Sediments

Answer 1

Loose grains and chemical residues of Earth materials including rock fragments, mineral grains, parts of plants or animals, and rust. All sediments have a source where they were produced by the biochemical processes of plants or animals, or by chemical and physical weathering of rocks.

Question 2

Chemical weathering

Answer 2

decomposition or dissolution of Earth materials. Ex: halite (sodium chloride) dissolves to form salt water.

Question 3

Physical (aka mechanical) weathering

Answer 3

Cracking, scratching, crushing, abrasion or other physical disintegration of Earth materials. This process causes big rocks to be disintegrated into clasts, including rock fragments and mineral grains. It causes the breakdown of animal shells

Question 4

Clasts

Answer 4

Broken pieces - including rock fragments and mineral grains.

Question 5

Lithification

Answer 5

The hardening of sediment/clasts to produce rocks. This process occurs as layers of sediment are compacted (pressure hardened), or cemented (glued together by tiny crystals or chemical residues precipitated from fluids in the pores of sediment)

Question 6

Precipitation of minerals

Answer 6

It’s possible to form a dense hard mass of inter-grown crystals directly, as they precipitate from an aqueous solution.

Question 7

Ocean water

Answer 7

The most common aqueous solution and variety of salt water on Earth. As it evaporates, a variety of minerals precipitate in a sequence. First to form is aragonite (calcium carbonate. Gypsum forms when 50-75% of ocean water has evaporated. Halite (table salt) forms when 90% has evaporated.

Question 8

Sedimentary Rocks

Answer 8

Broken into different classifications based on what type of material they are made of (composition). The composition of a sediment or sedimentary rock is a description of the types and abundance of the grains it’s made of. There are 3 main types: detrital, biochemical and chemical.

Question 9

Detrital Rocks

Answer 9

Detrital sedimentary rocks contain clasts. These are fragments or pieces of rock or minerals. The composition of clastic sedimentary rocks is divided into three types - clay/silt, sand and gravel.

Question 10

Biochemical rocks

Answer 10

Biochemical sediments and rocks are composed mostly of the remains of organisms, such as shells, plant fragments and carbon.

Question 11

Chemical Rocks

Answer 11

Chemical sediments and rocks are composed mostly of intergrown mineral crystals precipitated from aqueous solutions and chemical residues.

Question 12

Textures of sediments and sedimentary rocks

Answer 12

The texture of a sediment or sedimentary rock is a description of it’s constituent parts and their sizes, shapes and arrangement. The texture is a small-scale property of a rock, but determined many of it large-scale properties, such as the density, porosity or permeability.

Question 13

Clastic texture

Answer 13

Clastic texture means a rock consists of clasts. In detrital rocks, it is called siliciclastic and the clasts are rock fragments. In biochemical rocks it is called bioclastic and the clasts are fragments/shells of organisms. The size and form of the clasts can be used to determine the velocity and direction of current in the sedimentary environment the rock was formed. Fine, calcareous mud settles in quiet water. Gravel and larger clasts are only deposited by fast-moving water.

Question 14

Matrix or cement

Answer 14

Between the clasts of the rock can be composed of a matrix or cement (cement can be crystals or precipitated minerals).

Question 15

calcareous

Answer 15

from old English cealc “calk, soft white limestone, lime, plaster, pebble. Possibly borrowed. from Latin: calcarius - of or pertaining to lime

Question 16

Clay and silt

Answer 16

Less than 1/16 mm. Clasts are not visible to the unaided eye.

Question 17

Sand

Answer 17

clasts between 1/16 and 2 mm in size

Question 18

Sediment size

Answer 18

Gravel is greater than 2 mm. For context - 1 mm is the size of a pencil lead. 2 mm is the coloring surface of a crayon. 5 mm is a pencil eraser. The 1/16 mm is the boundary between silt and sand, and divides particles visible to the human eye (sand) and particles that are too small to be recognized in the field (silt and clay).

Question 19

Sorting (well or poorly)

Answer 19

distribution of grain sizes for different rock types. When all clasts are generally the same size the rock is ‘well-sorted’, when there is a large difference between grain size the rock is ‘poorly sorted.’

Question 20

Chemical texture

Answer 20

Crystalline and microcrystalline textures. Sedimentary rocks that form when crystals precipitate from aqueous solutions have a crystalline texture, either clearly visible or microcrystalline (too small to identify). As crystals grow, they interfere with each other and form an intergrown and inter-locking texture that holds the rock together

Question 21

HCl

Answer 21

Hydrochloric acid is used to test whether a rock is calcareous or not. Calcareous rocks effervesce in HCl

Question 22

Sedimentary Structures

Answer 22

a variety of structures formed at the time of deposition or by physical processes, or by activities of plants and animals. Sedimentary structures can be used as indicators of the environments where they normally form today. (Think Rift Valley and how we can extrapolate the environment Australopithecus lived in)

Question 23

Layering of sediments

Answer 23

Sediments and sedimentary detrital rocks are characterized by bedding or stratification, which occurs when layers of sediment, or beds, with different particle sizes or compositions, are deposited on top of one another. These beds range from millimeters or centimeters thick to meters or many meters. most bedding is relatively horizontal, though some form at high angle relative to horizontal.

Question 24

Cross bedding

Answer 24

consists of beds deposited by wind or water and inclined at ranges of as much as 35 degrees from horizontal. Cross-beds form when sediment particles are deposited on the steeper, downcurrent (leeward) slopes of sand dunes on land or sandbars in rivers and on the seafloor. Cross-betting patterns in wind-deposited