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Sediments and Sedimentary Rocks. Geology Today Barbara W. Murck & Brian J. Skinner. LAYERED ROCKS, PARIS CANYON, ARIZONA. © Houghton Mifflin 1998; N. Lindsley-Griffin, 1999. Rock Cycle Weathering, Erosion, Deposition.

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sediments and sedimentary rocks

Sediments and Sedimentary Rocks

Geology Today

Barbara W. Murck & Brian J. Skinner

LAYERED ROCKS, PARIS CANYON, ARIZONA

© Houghton Mifflin 1998; N. Lindsley-Griffin, 1999.

slide2

Rock CycleWeathering, Erosion, Deposition

Sedimentsunconsolidated particles created by weathering of rock by chemical and mechanical means

J. R. Griffin, 1999

slide3

Rock CycleDeposition, Compaction, Lithification

Sedimentary rock

Rock formed from weathered products of pre-existing rocks,

plus or minus fossils that have been transported, deposited and lithified

J. R. Griffin, 1999

sediments

Sediments

Bedding is the best clue that a rock is sedimentary.

Also termed strata, layering. (Fig. 8.2, p. 219)

Capital Reef National Park, Utah

N. Lindsley-Griffin, 1999.

slide5

Lithification

Lithification - loose sediment changes to sedimentary rock: grains in matrix, cement.

COMPACTION - pore space decreases, water forced out

CEMENTATION - dissolved ions precipitate between grains

RECRYSTALLIZATION - less stable minerals change to more stable forms

(Figs. 8.4B, p. 221; 8.9, p. 225)

N. Lindsley-Griffin, 1999.

slide6

Clastic Sediments

The SIZE of the particle

transported depends on the density and speed of the transporting medium and the slope angle....

Buffalo, WY

N. Lindsley-Griffin, 1999.

slide7

Clastic Sediments

Sorting - the range

in clast sizes.

Poorly sorted = great size variation.

Well-sorted = grains all about the same size.

Fig. 8.4, p. 221

N. Lindsley-Griffin, 1999.

sphericity how equidimensional are the grains round vs angular how sharp are the corners

Clastic Sediments

Sphericity - how equidimensional are the grains?

Round vs. angular - how sharp are the corners?

Fig. 8.4, p. 221

N. Lindsley-Griffin, 1999.

clastic sediments

Clastic Sediments

Size of clast or fragment:

gravel(pea size and larger) -- CONGLOMERATE

sand (pin head) -- SANDSTONE

silt (grain of table salt) -- SILTSTONE

clay (particle of flour) -- SHALE, CLAYSTONE

Mud is a mixture of clay and silt -- MUDSTONE

Fig. 8.3, p. 220

N. Lindsley-Griffin, 1999.

slide10

Clastic Sediments

BRECCIA

Angular fragments of rock

in finer-grained matrix

CONGLOMERATE

Rounded pebbles of rock

in finer-grained matrix

These are lithicclasts

Houghton Mifflin 1998; N. Lindsley-Griffin, 1999

slide11

Clastic Sediments

Clast size, sorting, roundness, and sphericity suggest:

how far it traveled

nature of transporting medium

how sediment was deposited

Glacial Till, Matanuska Glacier, AK (Fig. 8.4A, p. 221)

Quartz sand, St. Peter Sandstone, WI (Fig. 8.4B, p. 221)

N. Lindsley-Griffin, 1999.

slide12

Clastic Sediments

COMPOSITION of the clastic particle depends on source:

white coral sand, Bora Bora

green olivine sand, Hawaii

N. Lindsley-Griffin, 1999.

slide13

Clastic Sediments

COMPOSITION of the clastic particle depends on

strength of particle vs. distance traveled

basalt weathers quickly, is found only close to its source

quartz travels long distances

Quartz sand, Oregon

Basalt sand, Hawaii

N. Lindsley-Griffin, 1999.

sand can be any composition
SAND can be any composition...
  • but most is quartz because it is:
    • durable
    • chemically stable

N. Lindsley-Griffin, 1999.

slide15

Chemical Sediments

Precipitated from dissolved matter in sea or lake water:

- through activities of plants and animals (but not their remains)

- through evaporation of water containing dissolved ions

Banded Iron Formation, western Australia (Fig. 8.10, p. 225)

N. Lindsley-Griffin, 1999.

slide17

Chemical Sediments

Great Salt Lake, Utah

Evaporites:

Least soluble carbonates (limestones) precipitate first

Sulfates (anhydrite, gypsum) precipitate next

Most soluble halides (rock salt) precipitate last

N. Lindsley-Griffin, 1999.

slide19

Biogenic Sediments

Composed of the remains of plants and animals.

Bioclastic sediments consist of broken clasts of remains.

Coquina - shells and shell fragments (Fig. 8.8, p. 225)

N. Lindsley-Griffin, 1999.

slide20

Biogenic Sediments

Coral reefs, where most limestones form, require certain conditions:

Shallow water where light penetrates

Warm water - tropical or temperate

Little land-derived detritus

N. Lindsley-Griffin, 1999.

slide21

Biogenic Sediments

Coral reefs support a complex ecosystem that develops around the coral framework.

Algae form a symbiotic relationship with corals

N. Lindsley-Griffin, 1999.

slide22

Biogenic Sediments

Sediment in the lagoon (quiet water behind reef) is biogenic calcareous mud which will form limestone

N. Lindsley-Griffin, 1999.

slide23

Biogenic Sediments

Deep ocean biogenic sediments are mostly microscopic fossil shells:

Calcareous (foraminifers, nannofossils) - CHALK

Siliceous (radiolarians, diatoms, sponges) - CHERT

N. Lindsley-Griffin, 1999.

sedimentary rock names

Sedimentary Rock Names

Clastic sediments clastic rocks = siliciclastic rocks

conglomerate, breccia,

sandstone, siltstone,

mudstone, shale, claystoneChemical sediments chemical sedimentary rocks

gypsum, rock salt, phosphorite

banded iron formation

(a few limestones)

Biogenic sediments biogenic rocks

limestone, dolostone = carbonate rocks

chert

peat, coal

N. Lindsley-Griffin, 2000.

sedimentary structures

Sedimentary Structures

(Fig. 8.6, p. 223)

Graded bedding:

coarse grains at sharp base.

Grains gradually become smaller upwards.

N. Lindsley-Griffin, 1999.

sedimentary structures26

Sedimentary Structures

Turbidites form in deep ocean.

- rhythmic layering

- graded bedding

(Fig. 8.17, p. 237)

N. Lindsley-Griffin, 1999.

sedimentary structures27

Sedimentary Structures

Ripple marks on bedding surfaces:

sediments were deposited in water, usually shallow, with waves or currents.

Sharp crests point upwards, rounded troughs point downwards.

(Fig. 8.11, p. 230)

N. Lindsley-Griffin, 1999.

sedimentary structures28

Sedimentary Structures

Mudcracks:

sediments on drying mud flats or lake bottoms.

Cracks polygonal, narrow to “V” downwards. (Fig. 8.11, p. 230)

N. Lindsley-Griffin, 1999.

slide29

Sedimentary Environments

Interpreted from composition, texture, structures

Alluvium (left): sorted layers, rounding, mixed clasts

Lahar (above): no layers, angular, volcanic clasts

N. Lindsley-Griffin, 1999.

sedimentary environments

Sedimentary Environments

Turbidites (right): beds graded from sand up to clay size

Beach(below): steep cross bedding, very well sorted quartz sand, fossil seashells

N. Lindsley-Griffin, 1999.

sedimentary environments31

Sedimentary Environments

Loess, an eolian sediment:

uniform silt size

massive - no structures

deposited by wind

common all over Nebraska

- both field trips

(Fig. 8.15, p. 235)

N. Lindsley-Griffin, 1999.

sedimentary environments32

Sedimentary Environments

Eolian cross bedding, formed in sand dunes, preserves the steep front face (downwind)

gentle back face (upwind)

Fig. 8.7, p. 224

N. Lindsley-Griffin, 1999.

sedimentary environments33

Sedimentary Environments

Varves record annual cycles (usually glacial lakes):

light silt deposited in warm months,

dark clay-rich layers in winter months.

Fig. 8.5, p. 222

N. Lindsley-Griffin, 1999.

sedimentary environments34

Sedimentary Environments

Fig. 8.14, p. 233

N. Lindsley-Griffin, 1999.