Chapter 6

Question 1

Arkose

Answer 1

A type of sandstone containing abundant feldspar, indicating minimal weathering and quick burial after deposition.

Question 2

Bed

Answer 2

A single layer of sediment or sedimentary rock with a distinct boundary, often from changes in deposition conditions.

Question 3

Biochemical Sedimentary Rock

Answer 3

Rock formed from the accumulation of organic material, typically from shells or skeletons of organisms, such as limestone.

Question 4

Breccia

Answer 4

A clastic sedimentary rock composed of large, angular fragments cemented together, indicating deposition close to the source of the fragments.

Question 5

Cementation

Answer 5

The process where minerals precipitate from water and fill the spaces between sediment grains, binding them into solid rock.

Question 6

Chemical Sedimentary Rock

Answer 6

Rock formed by the precipitation of minerals from water solutions, such as evaporites and travertine.

Question 7

Clastic Sedimentary Rock

Answer 7

Rock composed of fragments (clasts) of pre-existing rocks, bound together by natural cement.

Question 8

Clast

Answer 8

Individual grain or fragment within a clastic sedimentary rock.

Question 9

Coal

Answer 9

An organic sedimentary rock formed primarily from plant material, buried, compressed, and lithified over millions of years.

Question 10

Compaction

Answer 10

The process of sediments being pressed together under the weight of overlying material, reducing pore space.

Question 11

Conglomerate

Answer 11

A clastic sedimentary rock consisting of rounded, gravel-sized particles, indicating water transport and some distance from the source.

Question 12

Cross Bed

Answer 12

Slanted layers within a bed of sediment, formed by wind or water currents, indicating a direction of flow.

Question 13

Delta

Answer 13

A landform at the mouth of a river where sediment is deposited as water flow slows, forming layers of sedimentary material.

Question 14

Deposition

Answer 14

The settling and accumulation of sediment, often after transportation by water, wind, or ice.

Question 15

Depositional Environment

Answer 15

The specific location or setting where sediment accumulates, such as rivers, lakes, or deserts, affecting sediment characteristics.

Question 16

Detritus

Answer 16

Loose fragments or particles derived from weathering of pre-existing rocks.

Question 17

Diagenesis

Answer 17

All physical, chemical, and biological processes that transform sediment into sedimentary rock, occurring after deposition.

Question 18

Dolostone

Answer 18

A carbonate rock composed primarily of dolomite, typically formed by alteration of limestone.

Question 19

Erosion

Answer 19

The removal and transport of rock or sediment by natural forces like water, wind, or ice.

Question 20

Geologic Map

Answer 20

A map showing the distribution, nature, and age relationships of rock formations at Earth’s surface.

Question 20

Graded Bed

Answer 20

A sedimentary layer with a vertical change in particle size, typically coarser at the bottom, indicating settling from a turbidity current.

Question 20

Evaporite

Answer 20

A type of chemical sedimentary rock formed by precipitation of minerals from evaporating water, such as gypsum or halite.

Question 21

Limestone

Answer 21

A biochemical or chemical sedimentary rock composed primarily of calcite, often formed in marine environments from shells or coral.

Question 22

Lithification

Answer 22

The transformation of loose sediment into solid rock through compaction and cementation

Question 23

Mudstone

Answer 23

A fine-grained clastic rock composed of silt and clay particles, lacking distinct layering.

Question 24

Organic Sedimentary Rock

Answer 24

Rock formed from the accumulation of organic material, like coal, typically derived from plant remains.

Question 25

Regression

Answer 25

A geological process where sea level falls, exposing previously submerged areas and shifting depositional environments seaward.

Question 26

Ripple Mark

Answer 26

Small ridges formed on a sediment surface by water or wind flow, often preserved in sedimentary rock.

Question 27

Sandstone

Answer 27

A clastic sedimentary rock composed primarily of sand-sized particles, often formed in environments like rivers or beaches.

Question 28

Sedimentary Basin

Answer 28

A low-lying area where sediment accumulates over time, often resulting from subsidence.

Question 29

Sedimentary Rock

Answer 29

Rock formed from the accumulation and lithification of sediment, or from precipitation from solution.

Question 30

Sedimentary Structure

Answer 30

Features within sedimentary rocks, such as bedding, ripple marks, or cross-bedding, formed during or shortly after deposition.

Question 31

Shale

Answer 31

A fine-grained, clastic sedimentary rock composed mostly of clay, with thin, parallel layers that split easily.

Question 32

Siltstone

Answer 32

A fine-grained clastic sedimentary rock composed mostly of silt-sized particles, intermediate between sandstone and shale.

Question 33

Sorting

Answer 33

The degree to which sediment grains are uniform in size, indicating transport distance and energy of the depositional environment.

Question 34

Strata

Answer 34

Layers of sedimentary rock that differ from one another in composition, grain size, or other characteristics.

Question 35

Stratigraphic Formation

Answer 35

A recognizable, mappable unit of rock with distinct characteristics, representing a specific depositional environment.

Question 36

Subsidence

Answer 36

The gradual sinking of an area of Earth’s crust, often leading to sediment accumulation in sedimentary basins.

Question 37

Transgression

Answer 37

A process where sea level rises, flooding previously dry land and shifting depositional environments landward.

Question 38

Travertine

Answer 38

A chemical sedimentary rock formed from calcium carbonate, often found near hot springs or limestone caves.

Question 39

Turbidity Current

Answer 39

A fast-moving, sediment-laden current that flows down a slope underwater, depositing graded beds as it slows.

Question 40

Describe how a clastic sedimentary rock forms from its unweathered parent rock

Answer 40

Clastic sedimentary rocks form through weathering and erosion of parent rock, transporting the sediment, deposition in a basin, compaction of layers, and cementation where minerals precipitate and bind grains together.

Question 41

Explain how biochemical sedimentary rocks form.

Answer 41

Biochemical sedimentary rocks form from the accumulation of material from living organisms, such as shells or skeletons, which then compact and lithify into rock like limestone.

Question 41

How do grain size and shape, sorting, sphericity, and angularity change as sediments move downstream?

Answer 41

As sediments move downstream, grain size decreases, shape becomes rounder, sorting improves (grains become more similar in size), and sphericity increases due to continued abrasion and transport.

Question 42

Describe the two different kinds of chert. How are they similar? How are they different?

Answer 42

Biochemical chert forms from silica-rich remains of marine organisms, while chemical chert forms from silica precipitation in groundwater. Both are composed of microcrystalline quartz, but they form under different conditions and sources of silica.

Question 43

Do all chemical sedimentary rocks have the same composition? What conditions produce evaporites?

Answer 43

No, chemical sedimentary rocks vary in composition depending on the minerals that precipitate from solution. Evaporites form in arid environments where water evaporation concentrates dissolved minerals, causing them to crystallize.

Question 44

How does dolostone differ from limestone, and how does dolostone form?

Answer 44

Dolostone contains the mineral dolomite rather than calcite, as found in limestone. It forms when magnesium-rich water alters limestone, converting calcite to dolomite.

Question 45

What are cross beds, and how do they form? How can you read the current direction from cross beds?

Answer 45

Cross beds are slanted layers within a horizontal bed, forming from wind or water moving sediment in a particular direction. The slope of the cross beds indicates the flow direction.

Question 46

Describe how a turbidity current forms and moves. How does it produce graded bedding?

Answer 46

A turbidity current is a fast, sediment-laden underwater flow triggered by slope failure, which slows down and deposits material as it moves, creating graded bedding with coarser sediment settling first.

Question 47

Compare deposits of an alluvial fan with those of a deep-marine deposit.

Answer 47

Alluvial fan deposits are coarse, poorly sorted, and angular, forming near mountains, while deep-marine deposits are fine-grained, well-sorted, and often layered, reflecting gradual sedimentation on the ocean floor.

Question 48

Why don’t sediments accumulate everywhere? What types of tectonic conditions are required to create basins?

Answer 48

Sediments need low-lying areas to accumulate, which form in tectonic settings like rift zones, foreland basins, or passive margins where the crust subsides, creating space for sediment deposition.

Question 49

How is it possible for sandstone derived from sediment deposited in a beach environment to comprise a formation that blankets a broad region?

Answer 49

Shifting sea levels during transgression can spread beach sand over vast areas, creating a widespread sandstone layer as part of a larger sedimentary formation.