Sed+Strat Class

Front 1

Sedimentary Rock

Back 1

Those which consist of recycled rock material: wear or break it down, move it to lowland, deposit, lithify

Front 2

Physical Weathering

Back 2

cracks (aka joints) develop and grow until they are extensive enough to fully detach the rock into moveable blocks

Front 3

Freeze Thaw Weathering

Back 3

water retained in joints and fissures expands during freezing, acts as wedges

Front 4

Roots Wedging

Back 4

Trees rooting in joints, cracks, and fissures grow to diameters which force rock material apart

Front 5

Salt Weathering

Back 5

similar to root wedging, high temperature desert environments promote growth of salt crystals in pore spaces and fractures

Front 6

Isolation Weathering

Back 6

differential heating of rock surface expands outermost rock relative to interior, and cracks rock along grain boundaries

Front 7

Wet-dry weathering

Back 7

repeated cycles of heavy wetting then extended drying of (ex.) loosely lithified mudstone or shale can make joints in the rock, often rectiliniar

Front 8

Spheroidal weathering

Back 8

in sandstones, what begins with breakdown in cubic joints in sandstone becomes more spheriod with time, eventually having the appearance of skins or weathering rinds. Common in sandstones which have had concretionary lithification history

Front 9

Exfoliation weathering

Back 9

intrusive rocks develop convex sheet like texture, jointing follows concentric zoning of its cooling history (oblate-shaped intrusion cooling from outside in) as removal of overburden decreases pressure

Front 10

Stress release weathering

Back 10

similar to exfoliation, but for rock types other than intrusive. Removal of overburden reduces pressure, rock rebounds in layers or sheets

Front 11

What are the three categories of weathering products

Back 11

1. source rock residues
2. secondary minerals
3. soluble materials

Front 12

Source Rock Residues

Back 12

the in-situ remains of jointed, cracked, or broken bedrock which retain (for the most part) the original composition

Front 13

Secondary Minerals

Back 13

Products of the weathering, after leached or dissolved (partly dissolved) components recombine with other elements to form crystalline additions to the rock detritus

Front 14

Soluble Materials

Back 14

Those water-borne ion-scale (solute) products of the weathering, which have been removed from the site of weathering. That is they are enroute to the nearest basin (somewhere in the river, lake, or an ocean system far from the weathering site)

Front 15

Soils

Back 15

Source rock residues which have been broken down, at least partly, to gravel-sized grains and which have experienced significant rainfall, plus incorporated some organic materials for are capable of growing vegetation

Front 16

Erosion

Back 16

the process of removing (ie transporting) material, usually from highland areas (source regions) to lowland areas (basins); in arid regions can happen just by wind alone

Front 17

Proximal Deposit

Back 17

material that is deposited close to its source

Front 18

Distal Deposit

Back 18

material which has traveled far before being deposited

Front 19

What are the characteristics of a proximal deposit?

Back 19

larger clasts, poor sorting and angular (non worn) faces/edges

Front 20

What are the characteristics of a distal deposit?

Back 20

finer grained, well sorted, tends to have a higher percentage of quartz grains making them compositionally mature

Front 21

Compositionally Mature

Back 21

A rock that contains a high percentage of quartz grains

Front 22

Mud

Back 22

The name you use in the field when you are unable to discern between silt or clay

Front 23

Sorting

Back 23

Grain distribution

Front 24

What 3 things is sorting a function of?

Back 24

1. input (was it like sized before?)
2. Transport medium (air vs water)
3. Distance traveled

Front 25

Poorly sorted

Back 25

the rock contains grains spanning 3 or more of the grain size classes

Front 26

moderately sorted

Back 26

the rock contains grains spanning 2 of the grain size classes

Front 27

well sorted

Back 27

the rock consists entirely of grains within one grain size class

Front 28

PHI (ᶲ)

Back 28

An alternative measure of grain size which we use if we need a precise < statistically derived description for sorting

Front 29

Grain Shape

Back 29

The combination of form, roundness, and texture

Front 30

Roundness

Back 30

A description of grain edges (not overall shape) and reflects the degree to which transport of the grain has worn or torn off its formerly angular faces

Front 31

What is the assumption we are making when determining roundness and what is the implication of this?

Back 31

that weathering produces blocky or rectilinear grains the implication being that well rounded grain has traveled further or at a higher NRG then an angular grain

Front 32

Surface Texture

Back 32

a description of smoothness of the grain faces

Front 33

Maturity

Back 33

provides an estimate of how long material has been traveling from its source or “weathering” site to its point of deposition, it is a function of both texture (which is in large part dependent of wear during travel),and on composition

Front 34

Arenite

Back 34

composed mostly of quartz, making it compositionally mature

Front 35

Arkose

Back 35

composed of at least 25% feldspars, making it compositionally immature

Front 36

Fabric

Back 36

indicated the NRG level and type of transport medium that the sediment was deposited in
EX. a constantly moving stream will arrange the grains that line its bed according to the flow rate and flow depth

Front 37

Orientation

Back 37

long-axis of a grain is usually parallel to the current (stream) direction

Front 38

Imbrication

Back 38

when grains pack with their long axis parallel to each other and with overlap, so that rows or planes interlock with each other

Front 39

Porosity

Back 39

the amount of pore space between grains → the better sorting the higher porosity

Front 40

laminar

Back 40

straight, unidirectional; a "solid stream"

Front 41

What does the Hjulstrom Diagram illustrate

Back 41

the minimum force (current velocity) required to move quartz grains on a planar bed at 1m water

Front 42

What are the three categories of grain transport that entrained sediment flows downstream by?

Back 42

1. Bedload
2. Suspended Load
3. Wash-Load

Front 43

Bed Load

Back 43

(usually) coarse particles which travel along or very near to the river bed (ie stream bottom)

Front 44

Traction

Back 44

particles larger than sand-size which are in continuous traction with (ie sliding and shoving along) the stream bed

Front 45

Saltation

Back 45

grains “hop” along the river bottom, where”hop”means short-lived entrainment into the water column, to a height up to a few times their diameter

Front 46

Suspended Load

Back 46

(usually) finer material carried higher up in the water column, which remains in continuous suspension until water velocity falls significantly after which they are deposite

Front 47

Intermittent Suspension

Back 47

Occurs commonly for fine to medium grained sand, for which grains of sand may from time to time be dropped/re-entrained

Front 48

Wash Load

Back 48

(extra-fine material, clay) very low particle size results in very low settling velocity. can include material re-eroded from river bank, as well as chemically weathered source material

Front 49

Basin

Back 49

a standing body of water which acts as a sink for sediment (A lake, ocean). Water can not be moving unidirectionally on it, so a “pit” or low point in a river cannot be called a basin, these are called pools

Front 50

Long System Sediment Transport

Back 50

Materials that transport FAR→ALL the way down a river system to a basin a long distance away

Front 51

Short System Sediment Transport

Back 51

transport in which the basins are very near to (or immediately adjacent to) highland areas

Front 52

What are 4 transport mechanisms?

Back 52

1. Water (Fluvial)
2. Wind (Aeolian)
3. Ice (Glacial)
4. Mud (Alluvial)

Front 53

Colluvial

Back 53

applies to the material moved by gravity. The unconsolidated (loose, non-lithified) material is called colluvium (or talus)

Front 54

Alluvial

Back 54

applies to the material moved en-masse by gravity with the aid of some water

Front 55

Fluvial

Back 55

applies to material entrained and carried entirely by water (streams), this is the dominant method of both short and long distance sediment travel

Front 56

Glacial

Back 56

deposits are those which are transported by ice and are dropped (deposited) when it melts

Front 57

Coastal

Back 57

deposits are those caused by wave action in large bodies of water (oceans, large lakes), this includes creation of beaches, reworking of beach sediments by prevailing currents (splits, bars, ect.)

Front 58

Aeolian

Back 58

deposits are moved by wind, gravity need not play a major role

Front 59

Original Horizontality

Back 59

means that deposition of sediment in water is done so in horizontal to sub-horizontal layers, each layer is called a bed

Front 60

Superposition

Back 60

refers to the intuitive concept that beds on the bottom of the stack were deposited first, therefore a stack of sedimentary beds youngs upwards

Front 61

Ripple Marks

Back 61

are indicative of wave action on the surface of the bed
Small ridges formed on the surface of sediment layer by moving water or wind, oriented perpendicular to the wave motion

Front 62

Cross Bedding

Back 62

indicates prograde deposition of one seasonal (deltaic) or tidal (coastal) cycle
A feature of sandstone deposited on steep local slopes (ie large dunges), a series of thin, inclined layers within a larger bed of rock
A feature of sand dunes, sand ridges deposited by ocean currents on the sea floor, sediment bars in river channels, and deltas

Front 63

Fossils and burrows

Back 63

on or near the tops of bedforms
record biogenic activity of soft-bodied life which itself will not leave a fossil (no shell)
identify the species, know the environment!

Front 64

Mud Cracks

Back 64

indicate prolonged absence of water, sub-aerial setting
A shallow lake which dries up in the summer
A desert environment that received a pulse of water

Front 65

Graded Bedding

Back 65

systematic change in grain size from bottom to top
overload of sediment at depo-site early in event
waning energy or current later = finer clasts at top
typical of storm event or slope-failure (wet climate) event or turbidity current

Front 66

Marker Beds

Back 66

Are those which contain something that permits correlation of units in time across a large distance
A coal seam, a specific short lived fossil, something with distinct coloration, an ash bed containing datable minerals from a volcanic eruption

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Back 67

lenticular linear (shoestring)

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Back 68

lenticular lobate (elliptical)

Front 69

Back 69

lobate wedge

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Back 70

inclined sheet

Front 71

Back 71

(flat) tabular sheet

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Back 72

lobate to irregular sheet

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Back 73

planar bedding

Front 74

Back 74

wavy bedding

Front 75

Back 75

lenticular bedding

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Back 76

domal bedding

Front 77

Back 77

parabolic trough cross bedding (lenticular)

Front 78

Back 78

irregular (nodular) bedding

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Back 79

graded bedding

Front 80

Back 80

tabular planar cross bedding

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Back 81

convolute bedding

Front 82

Diagenesis

Back 82

the process by which the sediments are changed into rocks. The individual clasts or grains are bound to one another so that the deposited material behaves as a single unit

Front 83

What are teh two steps of diagenesis? Describe them

Back 83

1. Compaction
- weight compresses the sediments to push the grains into contact with one another
- usually this occurs through addition of more material, sequential deposition
2. Cementation
- Secondary minerals form along grain contacts and act as “glue” to bind the grains
-- quartz and calcite are the most common cementing minerals
-- hematite is also a good cement but is less common

Front 84

compositionally mature

Back 84

rock composed mostly of quartz (arenite)

Front 85

compositionally immature

Back 85

contains at least 25% feldspars (arkose)

Front 86

What are the 2 main categories of the composition of sedimentary rocks

Back 86

1. siliclastic
2. chemical

Front 87

Limestone

Back 87

consists of calcite, is the most common rock composition (either inorganic precipitate or bioclastic → shell remains, macro or microscopic)

Front 88

Coal

Back 88

composed of plant remains

Front 89

Chert

Back 89

is a siliceous rock (SiO2) which is actually a precipitate

Front 90

What are the 4 root categories siliclastic (detrital) rocks fall into based on texture?

Back 90

1. Breccia
2. Conglomerate
3. Sandstone
4. Mudstone

Front 91

Breccia

Back 91

angular fragments
usually poor sorting and with immature matrix (v. proximal)
largest fragment must exceed sand size

Front 92

Conglomerate

Back 92

similar to breccia, except clasts have partly rounded to well-rounded faces/edges
rounding happens by mechanical wear during transport
implies water-aided transport mechanism

Front 93

Sandstone

Back 93

can not contain fragment larger than sand
compositional maturity viable

Front 94

mudstone

Back 94

Fragments smaller than sand
Assign name based on largest size or fragment, such as, siltstone, or shale if discernable

Front 95

Major Minerals

Back 95

>2% volume of the rock - quartz, feldspar, clay minerals
ex. average sandstone (sst) = 65% quartz, average shale = 50% quartz

Front 96

Accessory Minerals

Back 96

< 2% volume of the rock - micas (biotite, more rarely muscovite), heavy minerals (ex. zircon, hornblende, garnet, apatite)
can break down into stable and unstable (table 5.1) to aid with assessment of maturity

Front 97

Rock Fragments

Back 97

if present - grains that are not singular mineral crystals but rather represent a piece of intact former rock, however small
list in the rock description (but not the name) as rock type (sedimentary, igneous, metamorphic)

Front 98

What are 3 important cementing minerals

Back 98

1. hematite
2. quartz
3. calcite

Front 99

What are the first and second most abundant sedimentary rock types

Back 99

1. siliclastics
2. carbonates

Front 100

Limestone

Back 100

calcite dominant mineral

Front 101

dolostones

Back 101

dolomite, in which Mg may replace for some or much of the Ca

Front 102

Calcite

Back 102

- Calcite Group
- Rhombohedral
- CaCO3
- Dominant mineral of limestone, especially in rocks older then the tertiary

Front 103

Magnesite

Back 103

- Calcite Group
- Rhombohedral
- MgCO3
- Uncommon in sedimentary rocks but occurs in some evaporite deposits

Front 104

Rhondochrosite

Back 104

- Calcite Group
- Rhombohedral
- MnCO3
- Uncommon in sedimentary rocks, may occur in Mn-rich sediments associated with siderite and Fe-silicates

Front 105

Siderite

Back 105

- Calcite Group
- Rhombohedral
- FeCO3
- Occurs as cements and concentrations in shales and sandstones, common in ironstone deposits, also in carbonate rocks altered by Fe-bearing solutions

Front 106

Smithsorite

Back 106

- Calcite Group
- Rhombohedral
- ZnCO3
- Uncommon in sedimentary rocks, occur in association with Zn ores in limestones

Front 107

Dolomite

Back 107

- Dolomite Group
- Rhomobohedral
- CaMg(CO3)2
- Dominant mineral in dolomite, commonly associated with calcite or evaporite minerals

Front 108

Ankerite

Back 108

- Dolomite Group
- Rhombohedral
- Ca(Mg,Fe,Mn)(CO3)2
- Much less common then dolomite, occurs in Fe-rich sediments as disseminated grains or concentrations

Front 109

Aragonite

Back 109

- Aragonite Group
- Orthorhombic
- CaCO3
- Common mineral in recent carbonate sediments, alters readily to calcite

Front 110

Cerussite

Back 110

- Aragonite group
- Orthorhombic
- PbCO3
- Occurs in supergene lead ores

Front 111

Strontionite

Back 111

- Aragonite group
- SrCO3
- Occurs in veins in some limestones

Front 112

Witherite

Back 112

- Aragonite group
- Orthorhombic
- BaCO3
- Occurs in veins associated with galena ore

Front 113

Back 113

clasts in sparry calcite: intrasparite to intrasparudite
clasts might or might not be carbonate in chemistry, the dominant mineral in this case telling us of depositional environment (marine) = abundant sparry cement (note the lack of compaction)

Front 114

Back 114

Clasts in sparry ccalcite: intrasparite to intrasparudite (relatively rare)
Increased packing and poorer sorting vs sparite

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Back 115

biosparite (fossils with sparite matrix)
A rock with fossil-content this high which was not microscopic in scale would be called a fossiliferous limestone

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Back 116

Oosparite (ooids in a sparry matrix)
ooids have radial zonation, form by rollin in calcium rich sediments

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Back 117

radial ooids in sparry calcite (white) and micrite (dark) cement
ooids have radial zonation, form by rollin in calcium rich sediments

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Back 118

Pellets (peloid texture) in sparry calcite cement
Pellets = of the fecal variety, the bottom of your fish tank (in detail) 10 000 years later

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Back 119

Planar Euhedral
- most dolomite crystals are euhedral rhombs, crystal-supported with intercrystalline areas filled with another mineral or unfilled (porus)

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Back 120

planar subhedral
- subhedral to anhedral dolomite crystals with low porosity and/or low intercrystalline matrix, straight compromise boundaries are common and many of the crystals have preserved crystal-face junctions

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Back 121

planar void-filling
- euhedral dolomite crystals lining large pores and vugs or surrounding patches of another mineral such as gypsum or calcite

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Back 122

planar-porphyrotopic
- euhedral dolomite crystals floating in a limestone matrix, crystals are matrix supported

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Back 123

Nonplanar Anhedral
- Tightly packed anhedral dolomite crystals with mostly curved, oblate, serrated, indistinct, or otherwise irrgular intercrystalline boundaries, pre-crystal face junctions rare, crystals commonly have undulatory extinction

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Back 124

Nonplanar Void-filling
- Pore-lining, saddle-shaped, or baroque (irregular) dolomite crystals characterized by scimitar-like termination, as viewed in thin section, sweeping extinction

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Back 125

Nonplanar-Porphytopic
- Single anhedral dolomite crystals or patches of anhedral dolomite crystals floating in a limestone matrix, crystals commonly have undulatory extinction

Front 126

What are the 3 stages of diagenesis

Back 126

1. Eogenesis
2. Mesogenesis
3. telogenesis

Front 127

Eogenesis

Back 127

BURIAL
- Organic reworking (bioturbation): destruction of primary sedimentary structures, formation of mottled bedding and other traces
- Cementation and replacement: Formation of pyrite (reducing environment) or iron oxides (oxidizing environment), precipitation of quartz and feldspar overgrowths, carbonate cements, kaolinite, or chlorite

Front 128

Mesogenesis

Back 128

BURIAL
- Physical Compaction: tighter grain packing, porosity reduction, and bed thinning
- Chemical compaction (partial solution): precipitation of carbonate (calcite) and silica (quartz) cements with accompanying porosity reduction
- Dissolution by Pore Fluids: Solution removal of carbonate cements and silica framework grains, creation of new (secondary) porosity by preferential destruction of less stable minerals
- Mineral Replacement: Partial to complete replacement of some silicate grains and clay minerals by new minerals (ex. replacement of feldspars by calcite)
- Clay mineral authigenesis: Alteration of one kind of clay mineral to another (ex. smectite to ilite or chlorite, kaolinite to ilite)

Front 129

Telogenesis

Back 129

UPLIFT
- Dissolution, replacement, oxidation: solution of carbonate cements, alteration of feldspars to clay minerals, oxidation of iron carbonate minerals to iron oxides, oxidation of pyrite to gypsum, solution of less stable minerals (ex. pyroxenes, amphiboles)

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Back 130

Plastic and Ductile Grain Deformation
- Combination of rigid and soft materials (sand grains in silt or clay) result in overall rearrangement of the softer material into all the void spaces

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Back 131

Flexible Grain Deformation
- A semi-rigid grain which was "roofing" a void space looses coherence, collapse into the former void space (settlement)

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Back 132

Pressure Solution
1. Concavo-convex contact
2. Sutured Contact
3. Long Contact
- Contacts of grains where overpressured, release of Si and O2 ions which immediately reprecipitate in adjacent void-spaces (become cement)

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Back 133

Marl

Front 134

Back 134

Coquina

Front 135

What 3 carbonate rock names are detrital casts or shells of marine organisms for which diagenetic process is not similar to the bulk of carbonate rocks which are chemically precipitated?

Back 135

1. Coquina
2. Chalk
3. Marl

Front 136

Coquina

Back 136

An agglomeration of reasonably well sorted, partly abraded shell material

Front 137

Chalk

Back 137

Fine grained (well sorted) loosely consolidated (soft) material consisting of microorganic calcite "tests" (exoskeletons) such as foraminifers

Front 138

Marl

Back 138

A loosley consolidated fine-grained mixture of siliclastic and calcitic materials (clay and calcite)

Front 139

Why are foraminifers useful?

Back 139

rapid speciation results in short duration of cast type which in turn means very good for dating

Front 140

Evaporites

Back 140

an important group which produces, amongst other things, our major source for ingestible salts (halite) and crop fertilizer (potash)

Front 141

Cherts

Back 141

microcrystalline quartz, make up a relatively minor but important part of the sedimentary rock record (useful for paleocurrent/paleogeography)

Front 142

Iron bearing sedimentary rocks

Back 142

>15% Fe, small fraction of sed-rock record, but economically important as ores

Front 143

Phosphorites

Back 143

>15% P2O5 (=,> 6.5% P), limiting range, volumetrically minor

Front 144

carbonaceous sedimentary rocks

Back 144

coal, oil, oil-shales, bitumen

Front 145

What are the three mineral classes that marine based precipitate minerals with form into?

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1. Chlorides (mostly halite and sylvite)
2. Sulfates (mostly anhydrite and gypsum)
3. Carbonates (calcite and dolomite)

Front 146

Why do non-marine evaporite rocks precipitate different minerals then marine evaporites?

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1. They are not yet in the “big sink of all time” (the ocean) that contains all chemically weathered material and/or atmospheric material that became absorbed into the hydrosphere
2. They can contain higher bicarbonate and/or higher magnesium
3. mostly, sparse to absent chlorine

Front 147

Coastal Sabkhas

Back 147

are similarly broad and flat, to dune dominated regions adjacent or proximal to shorelines, but receive more saline water (different mineral assemblage)

Front 148

Sabkhas

Back 148

are salt flats, sub-aerial remains of broad flats (Ex. Utah)

Front 149

Salinas

Back 149

are shallow subaqueous environments

Front 150

What are the two main categories of chert?

Back 150

1. Bedded Cherts
2. Nodular Cherts

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What are the 4 categories bedded chert is divided up into?

Back 151

divided based on types of organism
1. Diatomaceous
2. Radiolarian Chert
3. Spicularite (usually sponge parts)
4. skeletal-poor cherts

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What are the three types of phosphorite deposits?

Back 152

1. Bedded
2. Bioclastic
3. Nodular

Front 153

What are the three graphical methods for presenting grain size data?

Back 153

1. Histogram (grain size plotted against individual weight percent)
2. Frequency curve
3. Cumulative Curve (most useful of the three plots)

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Mode

Back 154

diameter of the modal size corresponds to the diameter of grains represented by the steepest point on a cumulative curve

Front 155

Median

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Midpoint of the grain size distribution, half of grains by weight are larger and half smaller

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Mean

Back 156

arithmetic average of all particle sizes in the sample

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Standard Deviation

Back 157

mathematical expression of sorting

Front 158

Skewness

Back 158

asymmetry of the curve shape, reflects sorting in the "tails" of a grain size population

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Kurtosis

Back 159

Degree of peakedness, or the grain size frequencies various degree of sharpness or peakedness

Front 160

What does Reynolds Number represent

Back 160

the relationship of inertial forces (related to the scale and velocity of fluids in motion and tend to cause fluid turbulence)

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Inertial Forces

Back 161

related to the scale and velocity of fluids in motion and tend to cause fluid turbulence

Front 162

Viscous Forces

Back 162

increase with increasing viscosity of a fluid, resist deformation of a fluid and tend to suppress turbulence

Front 163

Froude Number

Back 163

Accounts for the addition of gravity influence, along viscosity and inertial forces. It is the ration between inertial and gravity forces

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Boundary Layer

Back 164

A zone of retardation where, fluid flow over a solid surface such as a streambed, flow in the immediate vicinity of the boundary is retarded by the frictional resistance of the boundary

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Hydraulically Smooth

Back 165

sediments on the stream bed are so small that they lie within the viscous sublayer, the near-bed flow is dominated by viscous forces

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Hydraulically rough

Back 166

grains are large enough that they exceed the thickness of the viscous sublayer and thus protrude into the turbulent part of flow

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Critical Threshold

Back 167

shear stress increases, larger grains are put into motion until finally grain motion is common everywhere on the bed. For grain movement is a direct function of several variables including boundary shear stress, fluid viscosity and particle size, shape and density. It is also an indirect function of the velocity of flow.

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Drag Force

Back 168

Acts parallel to the bed and is related to boundary shear stress

Front 169

Alkali Feldspars

Back 169

constitute a group of minerals in which chemical composition can range through complete solid solution series, potassium rich feldspars are common in this group

Front 170

Plagioclase Feldspars

Back 170

form a complex solid solution series ranging in composition from albite through anorthite, can be distinguished from alkali on basis of optical properties

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Overgrowths

Back 171

quartz cement that is chemically attached to the crystal lattice of existing quartz grains forming rims of cement

Front 172

Compositional Maturity

Back 172

refers to the relative abundance of stable and unstable framework grains in a sandstone (quartz=mature, feldspars or others=immature)

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Textural Maturity

Back 173

determined by the relative abundance of a matrix and the degree of rounding and sorting of framework grains, can range from immature (much clay, framework grains poorly sorted and poorly rounded) to supermature (little or no clay, framework grains well sorted and well rounded)

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Quartz Arenites

Back 174

Composed of more than 90% silicious grains
commonly white or light grey (may be stained by iron oxides)
generally well lithified and well cemented
typically occur in association with assemblages of rocks deposited in stable cratonic environments such as aeolian, beach, and shelf environments, therefore tend to be interbedded with shallow water carbonates
most are texturally mature to super mature
cross bedding particularly characteristic of these and ripple marks are moderately common
rarely contain fossils

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Feldspathic Arenites

Back 175

contain less than 90% quartz, more feldspar then unstable rock fragments, and minor amounts of other minerals such as mica and heavy minerals
some are colored pink or red because of presence of potassium feldspar or iron oxides, and others are grey to white
Typically medium to coarse grained and may contain high percentages of subangular to angular grains
Matrix content may range from trace amounts to more than 15% and sorting of framework grains can range from moderately well to poorly sorted
commonly texturally immature or submature (they are wackes)
Not characterized by any particular type of sedimentary structures
bedding may range from essentially structureless to parallel laminated or cross laminated
Fossils may be present, especially in marine beds
typically occur in cratonic or stable shelf settings, where they may be associated with conglomerates, shallow water quartz arenites or lithic arenites, carbonate rocks, or evaporites
Less commonly can occur in sedimentary successions that were deposited in unstable basins or other deep water, mobile belt settings
commonly matrix rich (called feldspathic graywackes)

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Lithic Arenites

Back 176

extremely diverse group of rock
characterized by generally high content of unstable rock fragments such as volcanic and metamorphic clasts
contain less than 90% quartzose grains and more unstable rock fragments than feldspars
colors may range from light grey (Salt and Pepper like) to uniform medium to dark grey
many are poorly sorted, however the sorting ranges from well-poorly sorted
generally poorly rounded
tend to contain substantial amounts of matrix
texturally immature to submature
range from irregular bedding, laterally restricted, cross stratified fluvial units to evenly bedded laterally extensive, graded, marine turbidite units
may occur in association with fluvial conglomerates and other fluvial deposits or in association with deeper water marine conglomerates, pelagic shales, cherts, and submarine basalts
typically compositionally immature
originate under conditions favoring the production and deposition of large volumes of relatively unstable materials
may be deposited in non marine settings in proximal alluvial fans

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Volcaniclastic Sandstones

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special type of lithic arenite composed primarily of volcanic detritus
may be made up largely of pyroclastic materials that have been transported and reworked or they may contain volcanic detritus derived from the weathering of old volcanic rocks
characterized by the presence of euhedral feldspars, pumice fragments, glass shards, and volcanic rock fragments
generally have very low quartz content

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Epiclastic Congomerates

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which form by breakdown of older rocks through the process of weathering and erosion

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Clast Supported Conglomerates

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so rich in gravel-size framework grains that the gravel size grains touch and form a supporting framework

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Matrix Supported Conglomerates

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cast poor conglomerates that consist of sparse gravels supported in a mud/sand matrix

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diamictites

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matrix supported conglomerates

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Quartzose (oligomict) conglomerate

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tend to occur as thin, pebbly layers or lenses of pebbles in dominantly sandstone units
may be either clast or matrix supported
most appear to be of fluvial origin

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Intraformational Conglomerates

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composed of clasts of sediments believed to have formed within depositional basins
commonly form thin beds a few cms to a meter in thickness

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Rimmed Carbonate Shelves

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Shallow platforms marked at their outer edges (margins) by a pronounced break in slope into deeper water

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Unrimmed Platform

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no pronounced marginal barrier
occur today on leeward side of large tropical banks and in all cool water carbonate settings

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Ramp Platform

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a gently sloping unrimmed platform on which shallow-water deposits pass downslope with only a slight break in slope into deeper water facies

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Isolated Platform

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shallow water platforms tens to 100’s km wide
commonly located offshore from shallow continental shelves surrounded by deep water

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Epeiric Platform

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no modern examples exist so we are only able to guess at the processes that form these, likely connected to the open sea and storms and winds may have strongly affected water circulation

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what are the three major realms that diagenesis occurs at

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1. Marine Realm
2. Meteoric Realm
3. Subsurface Realm

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Marine Realm

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include the seafloor and the very shallow marine subsurface
characterized by seawater temperatures and marine waters of normal salinity
principle diagenetic process in this environment involve bioturbation of sediments, modification of carbonate shells and other grains by boring organisms, and cementation of grains in warm water areas

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Meteoric Realm

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may be brought from seafloor to here in 2 way: (1) by falling sea level and (2) by progressive sediment filling of a shallow carbonate basin
Characterized by presence of freshwater, it includes unsaturated vadose zone above the water table and the phreatic zone below the water table
waters in this zone are typically highly charged with CO2 and thus are chemically acidic

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Subsurface Realm

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after an initial period of diagenesis on the seafloor and possibly meteoric realm carbonate sediments are gradually buried and subjected to increased pressures, higher temps, and compositionally changed pore fluids
under these changed conditions carbonate sediments may undergo physical compaction, chemical compaction and additional chemical or mineralogical changes that may include dissolution, cementation, aragonite-to-calcite transformation and replacement of calcite by another mineral such as dolomite

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What are the 6 major diagenetic processes and changes

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(1) Biogenic Alteration
(2) Cementation
(3) Dissolution
(4) Neomorphism
(5) Replacment
(6) Physical and Chemical Compaction

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Biogenic Alteration

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organisms in carbonate depositional environments rework sediment by boring, burrowing, and sediment ingesting activities, these may destroy primary sedimentary structures in carbonate sediment and leave behind mottled bedding and various kinds of organic traces

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neomorphism

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covers the combined processes of inversion (ex. transformation of aragonite to calcite) and recrystallization
inversion refers to the change of one mineral to its polymorph
strictly speaking inversion takes place only in the solid (dry) state
may occur in all three realms but particularly important in meteoric and subsurface

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Replacement

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involves the dissolution of one mineral and the nearly simultaneous precipitation of another mineral of different composition in its place

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What are the 5 basic type of carbonate grains

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1. carbonate clasts
2. skeletal particles
3. ooids
4. peloids
5. aggregate grains

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Extraclasts

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Carbonate clasts that are derived from older limestone present in land sources located outside of the depositional basin

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ooids

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applied as a general name to coated carbonate grains that contain a nucleus of some kind ( a shell fragment, pellet, or quartz grain) surrounded by one or more thin layers or coatings consisting of fine calcite or aragonite crystals

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micrite

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microcrystalline calcite