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SedPet > Conglomerates > Flashcards

Conglomerates Flashcards

1
Q

Siliciclastic sedimentary rocks made up of

A

gravel-size (>2 mm) clasts.

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2
Q

Conglomerates A.K.A.:??

A

Rudites

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3
Q

Sedimentary rock composed of Gravel size sediments or

A

30% clast composition

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4
Q

Common in stratigraphic sequences of all ages but **less than ** of sedimentary rock mass

A

1 % of the total weight

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5
Q

Useful due to:

A
  • tectonic and provenance analysis
  • has specialized depositional environments
  • reservoir rocks of oil and gas
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6
Q

Folk
- ???? = <30 % Gravel
-????= >30% Gravel

A
  • gravelly mud/gravelly sand
    Gravel
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7
Q
  • Gilbert
    25-50% gravel-size clasts
    >50% gravel size clasts
    <25% gravel size clasts
A

Conglomeratic Sandstones or Conglomeratic Mudstones;
Conglomerate ;
Pebbly SST/Pebbly MST;

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8
Q

Non sorted - Poorly Sorted w/ larger particles of any size in a muddy matrix

A

Diamictite

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9
Q

poorly sorted sedimentary rock made up of dispersed pebbles in an abundant MST matrix

A

Pebbly SST

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10
Q
  • Mud/Sand Matrix abundant
  • Clasts does not form a supporting framework
A

Matrix Supported

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11
Q
  • Little Mud/Sand Matrix
  • gravel sized framework in contact, forming a supporting framework
A

Clast Supported

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12
Q
  • Aggregates of Angular, gravel size fragments
  • distinguished from breccias as sharp edged and unworn cornered clasts
  • Can also be non sedimentary in origin (ie. volcanic and tectonic breccias)
A

Breccias

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13
Q
  • Extraformational : Clasts originating from outside the formation
  • Epiclastic : Generated by breakdown of older rocks via processes of weathering and erosion
A

Extraformational, Epiclastic CGL + BRC

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14
Q
  • formed by penecontemporaneous fragmentation of weakly consolidated beds and subsequent redeposition of fragments w/in the same depositional unit
  • processes usually involve short term events (few hours or days) such as storm waves, mass flows which bring clast fragmentation and redeposition
  • occur as thin units and generally localized
  • well rounded to angular - depends on amount of transpo + rework
A
  • Intraformational CGL + BRC
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15
Q
  • flat/disc-shaped clasts
A

Flat Pebble CGL

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16
Q

flat/disc-shaped clasts stacked virtually on edge

A

Edgewise CGL

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17
Q
  • Formed by Primary Volcanic Processes
  • Explosive Volcanism
  • Autobrecciation of partially congealed lavas
  • Quench Fragmentation of Hot Magmas
A

Volcanic Breccia

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18
Q
  • formed via cataclasis/collapse
A

Cataclastic Breccias

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19
Q

soluble rock dissolution, leaving behind insoluble gravel size residues

A

Solution Breccia

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20
Q
  • stable CGL
  • single clast type
    -composed of clasts from a single source/mineralogy/petrology
A
  • Oligomict Conglomerate
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21
Q

assortment of clasts

A

Polymict Conglomerate

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22
Q

a type of polymict that is made up of unstable/metastable clasts

A

Petromict Conglomerates

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23
Q
  • Not Recycled from an older gen of CGL
  • Some are enriched from quartzose due to source rocks being quartzite, qtz, arenite or chert nodule LST
  • Other came from mixed parent-rock sources w/ less stable rock types
  • Continued Recycling can cause selective destruction of unstable clasts and concentration of stable ones
  • Petromict and Oligomict composed of weak clasts, both of which are more likely to be first-cycle deposits
A

First Cycle Deposits

24
Q

For CGL
can remove fine size detritus and deposit gravels w/ little sand/mud matrix

A

High Energy processes (fluvial or beach)

25
Q

Glacial transport and sediment-gravity flow yields ????
- May contain more muddy matrix than framework clasts

A

gravel with abundant matrix

26
Q

CGL w/o matric (unfilled voids among pebbles)
- Uncommon compared to SST w/ open pores
- Two Size Modes
- Gravel size range (framework)
- Mud size range (matrix)

A

Openwork Conglomerate

27
Q
  • Shallow, Braided Streams
  • Steam Energy high
  • Episodic Discharge
  • Dominantly Clast supported
  • Non graded beds but with vertical facies having a fining upward trend
  • Clasts
    • upstream dipping imbrication
    • Transverse long axis orientation
A

Sheetflood (braided stream)

28
Q
  • Deeper Fluvial Channels
  • Clast Supported
  • Silts/Sand Matrix rare to abundant
  • Clasts
    • unimodal orientation
    • dominant upstream imbrication dips
    • transverse long-axis orientation
    • fair size sorting
A

Streamflow

29
Q

Nearshore environment
- Sufficient wave energy to transport and rework gravels supplied via fluvial or coastal erosion
- Constant reworking in surf zone produces well sorted + rounded gravel deposits
- Clast supported
- Clasts
- may appear as thin gravel deposits in sandy beaches
- disc shape, good sorting
- well developed
- seaward dipping imbrication
- seaward stratification

A

Wave Worked (beach face)

30
Q
  • deposited in shoreface and shelf
  • poor to moderate sorting
  • fabric ranges from clast to matrix supported
  • Structures:
    • sharp-based
    • beds more than 1 m thickness
    • cross beds, normal grading or imbricated in lower parts
  • Clasts
    • bimodal dip directions
  • Shoreface deposits gravel dominated or;
  • Consists of sand w/ interbedding gravelly layers
A

Wave-, storm-, and current worked (shoreface and shelf)

31
Q

not well represented in the ancient sed record
- Matrix supported but some are clast supported
- Clasts
- moderate-poorly sorted
- rounded to well rounded
- Grading
- variable
- Tabular to trough cross bedding
- Fining upward trend
- diminishing upward in size + abundance

A

Tide-Worked

32
Q
  • Deposited Subareally
  • Materials dropped by melting of grounded glaciers
  • poorly sorted
  • matrix rich gravelly deposits; called till/glacial diamictite
  • Clast
    • meter size boulders
    • faceted or striated
    • long dimension parallel to ice-flow direction
    • little or no imbrication
  • massive but has lenses of better sorted material
A

Meltout/Lodgement

33
Q
  • AKA aquatillites
  • lacustrine/marine environment
  • due to deposition from melting, gravel-charged ice
  • Deposition occur as traction carpet
    • from dense meltwater underflows from subglacial tunnels
    • or meltout of ice rafted material from floating ice
  • Matrix supported
  • Poorly sorted
  • Clasts
    • angular to well rounded
    • striated, polished and faceted
  • Random Dropstone orientation unless reworked by bottom currents
  • Traction underflow deposits
    • parallel-to-current-flow long axis trend
    • up current imbrication dips
A

Subaqueous meltout

34
Q

from land debris flows
- alluvial dans and proglacial outwash fans
- sediment gravity flows
- gravel sized particles
- presence of cohesive matrix of clay and sand particles
- capable of tranpo mats of varying sizes
- deposits are matrix supported
- poorly sorted
- Non graded
- show no preferred orientation
- no preferred internal stratification
- Cgl units maybe capped by a thin later of gravel overlain by sts

A

Subaerial Debris Flow

35
Q

Retransportation of previously fluvial, lacustrine, coastal, or shelf to deep water environments
- Can occur via massflow process
- subaqueous debris flows,
- marine and lacustrine, also seen in glacially influenced envi
- density-modified grain flows, and
- high-density turbidity currents.
- Both subaqueous debris flows and grain flows can likely evolve into fully turbulent turbidity currents with downslope mixing and dilution

A

Resedimented

36
Q

Pyroclastics @ 2-64 mm

A

Lapili

37
Q

Pyroclastics > 64 mm =

A

Blocks (angular); bombs (round)

38
Q
  • lithified deposits from coarse pyroclastic particles are called
A

lapillistone, pyroclastic breccia, and agglomerate (bombs).

39
Q

Angular fragments from lava-water induced granulation or lava shattering

A

Hyaloclastites

40
Q
  • Thick sequences of cgl implies that
A
  • preserved and accumulated metastable clasts
    • rapid erosion of sharply elevated highlands or areas with active volcanism
    • Alternatively,
      • Clasts may form from glacial processes such as LST conglo
41
Q
  • consists dominantly of metaquartzite, vein-qtz or chert clasts
  • derived from metaseds, seds, and some igni rocks
  • residuum concentrated by destruction of a larger rock volume
A

Quartzose conglomerates

42
Q

Less Stable Metaseds

A

-like argillite, slate and schist
- from weathered, eroded and sed transpo

43
Q
  • Concentration of Vein-Qtz clasts in qtzose cgl
A
  • implies destruction of large igni/met bodies
44
Q
  • Concentration of chert clasts
A
  • destruction of large chert nodules in a lst
    • may also be derived from erosion of bedded cherts
45
Q

Since Qtz are a small part of source rocks, an enrichment of these in cgl implies that

A

extreme chemical weathering or vigorous transpo
- More than one cycle is involved
- Source rocks likely come from orogen or continental block provenances

46
Q

Two Groups of Clasts by stabilityy

A
  • Ultrastable Clasts
  • Metastable Clasts
47
Q
  • Two CGL based on stability
A
  • Quartzose CGL
  • Petromict CGL
48
Q

framework grains with more than 90% ultrastable clasts

A

Quartzose CGL

49
Q
  • less than 90% ultrastable clasts; more metastables
  • common use for cgl with abundant un/metastable clasts
A

Petromict CGL

50
Q

Elongated Gravel size clasts orientation

A
  • Orients transverse to current flow
51
Q

Sand Size clast orientation

A

oriented parallel to current flow

52
Q

Tabular and Elongated ones

A

can be imbricated/shingled under unidirectional currents

53
Q
  • Clasts in a fluvial CGL is
A

well rounded

54
Q

Fissile fabric are likely to release

A

tabular or disc shaped fragments

55
Q

Massive rocks tend to be

A

more equant

56
Q

Debris flow type of deposition may have matrix supported, with rapid erosion

A

Fanglomerate

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