Post Depositional Structures

Question 1

the structures formed during deposition

Answer 1

Primary sedimentary structures

Question 2

• is the general term for changes to the fabric and layering of beds of recently deposited sediment.

Answer 2

Soft-sediment deformation

Question 3

is the process of whereby a granular material is converted from a static solid like state to a dynamic fluid like state

Answer 3

Fluidization

Question 4

is a process for separating particles based on their size, shape and density, using a stream of gas or liquid flowing in a direction usually opposite to the direction of sedimentation

Answer 4

Process of elutriation

Question 5

• is a shorter-term process that happens when a mass of saturated sediment is affected by a shock, such as an earthquake, and becomes momentarily liquid, behaving like a viscous fluid

Answer 5

Liquefaction

Question 6

are deformed into layers that will typically show a fold structure with the noses of the anticlines oriented in the downslope direction

Answer 6

Slumped Beds

Question 7

The surface left as the slumped material is removed and is preserved when later sedimentation subsequently fills in the scar

Answer 7

Slumped Scars

Question 8

synsedimentary extensional faults that initiate and evolve at the margins of continental plates. They extend parallel to passive margins that have high sediment supply.

Answer 8

Growth Faults

Question 9

• are concave disruptions to the layering in sediments a few centimeters to tens of centimeters across formed by the upward movement of fluid

Answer 9

Dish

Question 10

• also known as elutriation pipes, are vertical water-escape channels that can be simple tubes or have a vertical sheet-like form.

Answer 10

Pillar

Question 11

• Fluidisation of a large body of sediment in the subsurface and can result in elutriation of sediment and the formation of vertical structure centimetres to tens of centimetres across

Answer 11

Clastic Dykes

Question 12

are formed from the extruded liquefied sediment brought to the surface in isolated pipes

Answer 12

Sand Volcanoes

Question 13

sand brought up to the surface through clastic dykes that are spread out on the surface in thin sheet like
structure

Answer 13

Extruded Sheet

Question 14

form where the higher density sand has partially sunk into the underlying mud to form downward-facing,
bulbous structures

Answer 14

Load Cast

Question 15

the mud may also become forced up into the overlying sand bed

Answer 15

Flame Structure

Question 16

are masses of clastic sediment that take the form of isolated pillows or protruding ball structures

Answer 16

Ball and Pillow Structures

Question 17

where the instability due to density differences
between layers of unconsolidated sediment results in
movements of material on a large scale

Answer 17

Diapirism

Question 18

occurs where a layer of sediment has a high

porosity and its density is reduced due to the presence of a high proportion of water mixed with the sediment

Answer 18

Mud Diapirs

Question 19

The physical and chemical changes that alter the characteristics of sediment after deposition
These processes occur at relatively low temperatures, typically below 250° and at depths of about 5000m

Answer 19

Diagenesis

Question 20

is the process of transforming sediment into sedimentary rock, and involves both chemical and
physical changes that take place at any time after initial
deposition

Answer 20

Lithifaction

Question 21

happens when sediments are deeply buried, placing them under pressure because of the weight of overlying layers. This squashes the grains together more tightly

Answer 21

Compaction

Question 22

occurs as one part of a sediment pile compacts more than the part adjacent to it

Answer 22

Differential Compaction

Question 23

subjected to very little overburden pressure the clasts will be in contact mainly at the point where they touch

Answer 23

Point Contacts

Question 24

grains are rotated and pushed closer together, and pore space is reduced

Answer 24

Long Contacts

Question 25

softer grains are compacted around harder ones, and grains start to dissolve in the pore waters at their contacts

Answer 25

Concavo-Convex Contacts

Question 26

irregular grain boundaries

Answer 26

Sutured Contacts

Question 27

-is a deformation mechanism that involves the dissolution of minerals at grain-to-grain contacts into an aqueous pore fluid in areas of relatively high stress

Answer 27

Pressure Solution

Question 28

– forms very soon after deposition

Answer 28

Eogenetic Cement

Question 29

chemical changes occur in sediment that is buried and saturated with pore waters

Answer 29

Mesogenic Cements

Question 30

cement formation occurs during uplift

Answer 30

Telogenic Cementation

Question 31

The nucleation and growth of crystals within pore spaces in sediments

Answer 31

Cementation

Question 32

are minerals precipitated within pore spaces during diagenesis

Answer 32

Cement

Question 33

Cement growth is in optical continuity with the adjacent grain

Answer 33

Overgrowth Cement

Question 34

Grains are enveloped in large crystals of cement

Answer 34

Poikilotopic Cement

Question 35

Cystals of cement grow uniformly into pores

Answer 35

Isopachous Cement

Question 36

Cement develops from drops of pore water attached to grains

Answer 36

Meniscus Cement

Question 37

mineral deposit formed by chemical processes that dissolve a rock and deposit a new assemblage of minerals in its place

Answer 37

Replacement

Question 38

- The introduction of, or replacement by, silica, generally resulting in the formation of fine-grained quartz, chalcedony, or opal, which may fill pores and replace existing minerals.

Answer 38

Silicification

Question 39

is a mass, or lump of a mineral or mineral aggregate that typically has a contrasting composition,. Forms as irregular cemented patches

Answer 39

Nodules

Question 40

Large nodules are referred as

Answer 40

Doggers

Question 41

- form as minerals within a rock and begins to precipitate within cracks and cavities. It has a symmetrical, round or discoid features

Answer 41

Concretions

Question 42

The interiors of some carbonate concretions in mudstones display an array of cracks that are often filled with sparry calcite. "turtle-back" appearance.

Answer 42

Septarian Concretions

Question 43

Chert form directly from siliceous ooze deposited on the sea floor.

Answer 43

Primary Chert

Question 44

may also form in concretions or nodules as a result of the concentration of silica during diagenesis

Answer 44

Secondary Chert

Question 45

is the specific name given to nodules of chert formed in the Cretaceous Chalk

Answer 45

Flint

Question 46

nonmarine calcite cement that forms above the water table

Answer 46

Vadose Zone

Question 47

Calcite cement that forms on aquifers

Answer 47

Phreatic Zone

Question 48

The diagenetic replacement of a mineral by a different crystal form of the same mineral

Answer 48

Neomorphism

Question 49

Cement that forms in Phreatic Zone

Answer 49

Meniscus Cement

Question 50

The process by which limestone is altered into dolomite

Answer 50

Dolomitization

Question 51

Carbonate cement that form in vadose zone

Answer 51

Isopachous Cement

Question 52

triggered by an evaporation phase in lagoonal and/or shallow marine settings

Answer 52

Reflux Model

Question 53

proposes that where fresh water mixes with marine waters then dolomitisation would occur

Answer 53

Mixing-Zone Model

Question 54

–involves prime mechanism which is the dewatering of basinal mud rocks due to compaction and removal of Mg-rich fluids into neighboring shelf edge.

Answer 54

Burial Model

Question 55

Thermally driven circulation, either by a geothermal heat source or by temperature differences between the interior of a platform and seawater

Answer 55

Seawater Model

Question 56

The process in which magnesium is removed from the mineral dolomite

Answer 56

Dedolomitization

Question 57

waterlogged areas of accumulation of organic material

Answer 57

Mires

Question 58

coal formed in areas where most of the input of water is from rainfall

Answer 58

Ombotrophic Mires or Bogs

Question 59

coal formed in places where there is a through-flow of groundwater

Answer 59

Rheotrophi Mire Or Swamps

Question 60

rheotrophic mires that have an input of clastic sediment, and these are referred to as

Answer 60

Marshes

Question 61

Coals that originate as peat deposits are known as

Answer 61

Humic Coals

Question 62

deposits of aquatic algae that accumulate in the bottoms of lakes are known as

Answer 62

Sapropelic Coal