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GEOLOGY BOARD EXAM REVIEWER > Sedimentary Structures > Flashcards

Sedimentary Structures Flashcards

1
Q

Produced by erosion or scouring of muddy sediment, forming “scoop-shaped” depressions

A

Flute Marks / Flute Casts

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2
Q

Commonly preserved as bulbous or mammilla natural casts on the bottoms of sandstone beds

A

Flute Marks/ Flute Casts

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3
Q

They can be used to determine paleo-current directions

A

Flute Marks / Flute Casts

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4
Q

Elongated ridges on bed undersurfaces that maybe parallel to each other or show vairation in trend formed by filling of grooves

A

Groove Casts

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5
Q

Produced as “tools” (object such as sticks, shells, bones or pebbles) carried by current bounce skip, roll or drag along the sediment surface

A

Tool Marks

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6
Q

Commonly preserved on lower surfaces of sandstone beds as thin ridges

A

Tool Marks

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7
Q

Generally aligned parallel to the direction of current movement

A

Tool Marks

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8
Q

Small-scale erosional structure less than a meter across, cutting down several centimeters and occurring on the base of or within a bed elongate in the current direction with sharp and irregular with some relief but can be smooth

A

Scour Marks / Scoured Surfaces

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9
Q

Larger structures that are sites of sediment transport for relatively long periods of time, concave up in cross section and their fills may form elongate (shoestring) sediment bodies

A

Channels

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10
Q

Stratification thicker than 1cm produced by changes in the pattern of sedimentation

A

Bedding

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11
Q

Sharply defined upper and lower surfaces enclosing or bounding beds

A

Bedding Plane

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12
Q

Indicator of the depositional conditions under which the bed formed

A

Bed Shape

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13
Q

Stratification thinner than 1cm produced by changes in the pattern of sedimentation

A

Lamination

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14
Q

Sets of beds in which they are genetically related to one another

A

Bedsets

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15
Q

Refers to finely-interbedded grain sizes, such as sand and mud, and can occur at a variety of scales

A

Heterolithic Bedding

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16
Q

Washed-out ripples produced at the boundary between lower and upper flow regime

A

Planar beds

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17
Q

0.5 to 3.0 cm in height with wavelength of 5 to 40 cm

A

Ripples

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18
Q

Typically found under low to moderate flow velocities in sand that is less than 0.7mm in diameter

A

Ripples

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19
Q

Formed by the action of waves of non-cohesive sediment, typically symmetrical in shape, asymmetrical when one direction of wave motion is stronger than the other may be difficult to distinguish from straight-crested current ripples

A

Wave-formed ripples

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20
Q

Produced by unidirectional currents, making them asymmetric with steep lee-side (downstream) and gentle stoss-side (upstream)

A

Current Ripples

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21
Q

Over 3.0 cm in height with wavelengths of at least 40 cm

A

Dunes

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22
Q

Typically formed under moderate to high flow velocities in relatively deep water and sand that is more than 0.2 mm in diameter

A

Dunes

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23
Q

Dune height and spacing is related to __________

A

water depth

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24
Q

Typically have long, straight, parallel crests with bifurcations, ripple index is high and rarely preserved

A

Wind Ripples

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25
Q

Type of aeolian dune with a single prevailing wind direction, and limited sand supply, forming a crescent shaped dune

A

Barchan Dunes

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26
Q

Type of aeolian dune with a single prevailing wind direction, and a good supply, forming wavy- shaped dunes

A

Transverse Dunes

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27
Q

Type of aeolian dune with two prevailing winds crossing in a single direction, forming linear-shaped dunes

A

Seif Dunes / Linerar Dunes

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28
Q

Type of aeolian dune with multiple prevailing winds from multiple directions, forming star-shaped dunes

A

Star dunes

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29
Q

Internal sedimentary structure of many sand-grade, and coarser sedimentary rocks and consists of stratification at an angle to the principal bedding direction, with a height of > 6cm, and thickness of 1cm or more

A

Cross-bedding

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30
Q

Internal sedimentary structure of many sand-grade and coarser, sedimentary rocks and consists of stratification at an angle to the principal bedding direction, with a height of <6cm, and thickness of only a few mm

A

Cross-lamination

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31
Q

Cross-stratification where the inter-set boundaries are generally planar and produced by straight-crested bedforms (ripples in cross lamination and sandwaves or dunes in cross bedding)

A

Tabular Cross-bedding

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32
Q

Cross-stratification where the inter-set boundaries are scoop-shaped from curve-crested bedforms (linguoid ripples in cross-lamination and lunate and sinous dunes in cross bedding)

A

Trough Cross-bedding

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33
Q

Forms when ripples are migrating and much sediment is being deposited out of suspension, ripples will climb up the backs of those downcurrent to form climbing-ripple cross-lamination

A

Climbing Ripples / Ripple drift

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34
Q

Commonly, the laminae are not concordant with the ripple profile, and distinguished from current ripple by irregular and undulating lower set boundaries and draping foreset laminae

A

Wave-formed cross lamination

35
Q

Cross bedding where cross-beds dips of adjacent sets oriented in opposite directions produced by reversals of currents

A

Herringbone Cross bedding

36
Q

Cross-stratification where cross-laminated sand contains mud streak, usually the ripple troughs

A

Flaser bedding

37
Q

Cross-stratification where mud dominates and the cross-laminated sand occurs in lenses

A

Lenticular bedding

38
Q

Cross-stratification where thin-ripple cross-laminated sandstones alternate with mudrock

A

Wavy bedding

39
Q

Results of storm waves and deposition in the outer shoreface or transition zone between fair weather wave-based and storm wave-base and includes hummocky cross-stratification, swaley cross-stratification and tempestites

A

Storm bedding

40
Q

Cross-stratification characterized by gently undulating low angle (1-5 degrees) cross-lamination with the convex upward part of the hummock and concave-downward part of the swale

A

Hummocky Cross-stratification

41
Q

Cross-stratification where hummocks are rare and the bedding mostly consists of broad concave-up laminae

A

Swaley Cross-stratification

42
Q

Low angle planar cross-stratification formed by wave swash and backwash commonly possess primary current lineation

A

Beach Cross-bedding

43
Q

Produced by wind action and generally forms sets which are much thicker, and the cross-beds themselves dip at higher angles (>30 degrees) and reach up to 30m high

A

Aeolian Cross bedding

44
Q

Large-scale low angle bedding, oriented normal to medium/smaller scale cross-stratification formed through lateral accretion of point bars generally 1m or more in height and continue laterally for several meters to more than 10m

A

Epsilon Cross-bedding

45
Q

Typical of meandering river channel sandstones but can occur in delta distributary and tidal channel deposits

A

Lateral Accretion

46
Q

Formed when deltas build into lakes or lagoons often referred as Gilbert-type deltas, occur as wedge or fan in marginal-lacustrine or marginal-marine

A

Small delta cross-bedding

47
Q

Large-scale that represents prograding front of the delta

A

Fan-delta cross-bedding

48
Q

Referred to at least 50m thick commonly developed at carbonate platform margins and adjacent to reefs where the dipping beds will be made of shallow water material, reef fragments; angle of dip varies from few degrees to 30 degrees

A

Very large-scale cross strata and clinoforms

49
Q

Low amplitude bedforms sand-grade which migrate upstream throughout deposition of the sediment on the upstream-facing slope of the bedroom

A

Antidune cross-bedding

50
Q

Where the coarsest particle at the base give way to finer particles higher up

A

Normal grading

51
Q

Where there are several graded units within one bed

A

Composite or multiple graded-bedding

52
Q

Where the grain size increases upwards

A

Reverse or inverse grading

53
Q

Have no apparent internal structure during deposition or depositional structure was destroyed by bioturbation, recrystallization, dolomitization or dewatering or formed through rapid sedimentation or “dumping”

A

Massive beds

54
Q

Found in fine-grained rocks that form through desiccation on exposure common in marine and lacustrine shorelines and river floodplains

A

Shrinkage cracks/ Mudcracks

54
Q

Form when strong current flows elongate and discoidal pebble can become oriented with in upstream dip

A

Imbrications

55
Q

Incomplete polygonal patterns that form through dewatering from salinity changes or osmotic effects and occur in shallow sublittoral lacustrine deposits

A

Synresis cracks

56
Q

May develop in carbonate sediments through early cementation and expansion of the surface crust

A

Polygonal cracks

57
Q

Small depressions with rims, formed through the impact of rain on the soft exposed surface of fine-grained sediments

A

Rainspots

58
Q

Cavities filled with internal sediment and sparry calcite cement

A

Geopetal Structure

59
Q

Continuous cavities either parallel or cutting the bedding, vary considerably in size

A

Sheet Cracks/ Neptunian dykes

60
Q

Formed by cracking of the lithified or partially lithified sediment and opening up the cavities, or through penecontemporaneous tectonic movements, early compaction and settling or slight lateral movement

A

Sheet Cracks/ Neptunian dykes

61
Q

Formed through subaerial exposure and meteoric dissolution of a limestone surface generally under humid conditions, usually have irregular topography, with potholes or cracks

A

Paleokarstic surfaces

62
Q

Present in limestones where there has been synsedimentary cementation so that sediment was partly or wholly lithified on the seafloor

A

Hardgrounds

63
Q

Forms when cemented surface layer can expand and crack into polygonal pattern as a result of sedimentary cementation of carbonate sediments and can develop in shallow subtidal sediments but commonly in tidal-flat carbonates

A

Tepee structures

64
Q

Biogenic laminated structures which have a great variety of growth forms developed through trapping and binding of carbonate particles by surficial microbial mat (algal mat composed of blue-green algae) and biochemical precipitation of carbonate

A

Stromatolites

65
Q

A mass of sediment transported downslope where there is little internal deformation of the sediment mass, meters to kilometers in size

A

Slide

66
Q

Used for deposits of large blocks, result of fault activity during deposition and erosion of fault scarps or collapse of carbonate platform

A

Megabreccia

67
Q

Occurs when a sediment mass is internally deformed during downslope movement, typically shows folding, with recumbent folds, asymmetric anticlines, and synclines and thrust folds being common, found in meters to kilometers in size

A

Slump

68
Q

Typically occurs in cross-laminated sediments, with the lamination deformed into rolls, small anticlines and sharp synclines, convolutions commonly asymmetric and overturned in paleocurrent direction

A

Convolute bedding

69
Q

Consist of concave-up laminae (dishes), few cm across which may be separated by structureless zones (pillars)

A

Dish-and-pillars structures

70
Q

Common on the soles of sandstone bed overlying mudrock occurring as bulbous, rounded structures, generally without any preferred orientation

A

Load casts

71
Q

Form when mud is injected up into the sand

A

Flame structures

72
Q

Forms as a result of loading, bed or usually of sand, can sink into underlying mud and break up into discrete masses

A

Ball-and-pillow structure

73
Q

Local patches of cementation that form in sediments after deposition.

A

Nodules / Concretions

74
Q

Nodules can either be (1)________ or (2)_________

A
  1. Diagenetic nodules
  2. Pedogenic nodules
75
Q

Composed of fibrous crystals of calcite in fanning or conical pattern, that develops in organic-rich mudrocks during burial, and may relate to crystal growth under high pre-fluid pressure during compaction

A

Cone-in-cone structure

76
Q

Develop within the soil of semi-arid environments where evaporation exceeds precipitation, typically found in red-bed successions in floodplain mudrocks or marine clastic sediments

A

Calcrete

77
Q

Sutured type which are generally bedding-parallel, although they can be at high angles to the bedding too and may occur as a single sutured planes or as zones or swarms

A

Stylolites

78
Q

Strange patterns, usually found on bedding planes resulting from precipitation of manganese and iron oxides/hydroxides and generally black that look like fossil leaves

A

Dendrites

79
Q

Refers to the disruption of sediment by the activity of organisms and plants

A

Bioturbation

80
Q

A type of trace fossil that is more complicated surface trails, found in symmetrical or ordered pattern, either coiled, radial, meandering, and mostly made by detritus feeders

A

Grazing trails

81
Q

A type of trace fossil that is found to be simple to complex burrow systems but no suggestion of systematic working of sediment, and can be clay-lined or pelleted, with some made by suspension feeder

A

Dwelling Burrow

82
Q

A type of trace fossil that is a simple to complex burrow system, often well-organized with defined branching pattern indicating systematic reworking of sediment by detritus feeders

A

Feeding Burrow

83
Q

A type of trace fossil made by organisms in a hard substrate - cemented sediment, pebbles or fossils

A

Boring

GEOLOGY BOARD EXAM REVIEWER (17 decks)

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