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Sedimentary Rocks. John Day Fossil Beds Natl. Mon.,Oregon. Sedimentary rocks  composed of sediment (particles derived by weathering). Detrital sediments  particles derived by physical weathering

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sedimentary rocks

Sedimentary Rocks

John Day Fossil Beds Natl. Mon.,Oregon

slide2
Sedimentary rocks composed of sediment

(particles derived by weathering)

slide3
Detrital sediments particles derived by physical weathering
  • Non-detrital sediments minerals precipitated from solution by inorganic chem. processes or activities of organisms

Classification of Sedimentary Particles

SizeSediment Name

>2 mm gravel

1/16-2 mm sand

1/256-1/16 mm silt

<1/256 mm clay

why should you study sedimentary rocks
Why Should You Study Sedimentary Rocks?
  • Sediments are the most common Earth materials.
  • Rock Features record environmental conditions at the time sediment was deposited. (impt. in deciphering Earth history)
  • Fossils knowledge of pre-existent life preserved in sedimentary rocks
  • Some sed. rocks contain resources (i.e. water, petroleum, natural gas, etc.).
transport deposition
Transport & Deposition

Ice

-- carries particles of any size.

Wind

-- transports sand & smaller particles.

Water (most prolific agent)

Larger particles require more vigorous current for transport.

  • Depositional environment geographic area where sediment accumulates
slide6
well-rounded, poor-sorted gravel

angular, poor-sorted gravel

  • Rounding -- abrasion during transport reduces particle size & smoothes sharp corners
  • Sorting -- variety of particle sizes present in sediment or sed. rock (influenced by transport & depositional processes)
slide7
Processes (Physical, chemical, & biological) operating in the depositional environment impart distinctive charac. to accumulating sediment.
how are sediments transformed into sedimentary rocks
How Are Sediments Transformed into Sedimentary Rocks?

Compaction

  • due to weight of overlying sediment
  • particles pack more closely & pore space is reduced
  • deposit’svolume reduced

Cementation

  • binds one particle to anotherby chemical precipitation of minerals in sediment pore space.
  • {Common cements include quartz, calcite, & hematite.}

Lithification

  • involves compaction & cementation
  • converts sediments to sedimentary rocks
slide9
Detrital sedimentary rocks

comprised of solid particles derived from parent material by phys. weathering

Classification of Detrital Sed. Rocks

Based on:

Sediment Size

Composition

slide10
Conglomerate = rounded gravel (>2 mm)

Breccia = angular gravel

A

B

slide11
Sandstone = sand-size (1/16 - 2 mm) particles
  • classified by mineralogy

Quartz sandstone most common

Arkose sandstone 25% feldspar

slide12
Mudrock any combination of silt & clay

Siltstone silt (1/16 – 1 / 256 mm)

Claystone clay (< 1 / 256 mm)

  • Shale is fissile clay. (splits along many closely spaced planes)
  • Mudrocks = most common sed. rock (quiet-water environ)

shale

slide13
Chemical sedimentary rocks

 ions taken into soln by weathering of parent material **crystalline texture (interlocking mineral grains)

Biochemical sedimentary rocks Organisms aid in the precipitation of minerals.

Classification of Chemical Sed. Rocks

Based on:

Mineral composition

Texture

slide14
Evaporites formed by precipitation of minerals from evaporating water

\

Rock salt{halite (NaCl)} (A) & Rock gypsum{gypsum (CaSO4. 2H2O)}(B) are most common.

B

A

slide15
Limestones

composed of Calcite (CaCO3)

contains much pore space

Coquina

Clastic texture

 shell fragments

Fossiliferouslimestone

skeletal fragments of marine invertebrates

-- pores filled w/ cement & mud --

slide16
Coal

crystalline texture

carbon

(compressed, altered plant remains that occupied swamps & bogs)

A

B

Chert

crystalline texture

silica

(layers of microscopic shells of marine organisms)

sedimentary facies
Strata (beds)layers differ in color, texture, & comp. from rock layers above & below. Sedimentary Facies

-- sets of sed. rock w/ distinct attributes imparted by their depositional environment

Coastal areas facies accumulate simultaneously on various areas of seafloor (w/ unique charac.).

slide18
1

Regression(seaward shift in the shoreline)

  • Drop in sea level

Nearshore deposits overlie offshore deposits.

2

3

slide19
Transgression (landward shift in shoreline)
  • Rise in sea level

Nearshore seds overlie old land surfaces, & offshoreseds are stacked on top.

determining the depositional environment
Determining the Depositional Environment

Grand Canyon

Muav Limestone (offshore)

Bright Angel Shale

Tapeats Sandstone (onshore)

(deposition record of laterally adjacent environ.)

Transgression Sed structures, fossils & ripple marks

slide21
Sedimentary Structures

- formed by physical processes at the time of deposition

  • Cross bedding
  • Graded bedding
  • Oscillation ripple marks
  • Current ripple marks
  • Mudcracks
slide22
Cross bedding
  • inclined layers w/in a bed
  • Formed by wind or water
  • slopes downward in flow direction
slide23
Graded bedding
  • upward decrease in grain size w/in a bed

{deposits of turbidity currents}

slide24
Ripple marks

-- small ridges separated by intervening troughs

Oscillation ripple marks(A) symmetric cross-sections generated by the back-&-forth motion of waves.

A

B

Current ripple marks(B) asymmetriccross- sections record flow in one direction (i.e., streams).

slide25
Mudcracks

 shrinkage (polygonal patterns of intersecting fractures)

  • clay-rich sediment
  • depositional environ. periodic drying (i.e., a river floodplain, lake shore, or tidal flat)
slide26
Fossilsare NOTSedimentary Structures.  remains or traces of ancient organisms

Morphology of organisms reveals info about environment the organisms lived in.

  • Heavy-shelled clams = shallow-water, turbulent
  • Thin, fragile-shelled clams = low-energy
  • Filter-feeding organisms (corals) = clear seawater (suspended sediment clogs their feeding organs.)
resources in sedimentary rocks
Resources in Sedimentary Rocks?
  • Sand & gravel building & road construction
  • Limestone cement
  • Gypsum wallboard/plaster
  • Phosphate-bearing sedimentary rock fertilizer
  • Sand-sizedquartz glass
  • Carnotite(uranium mineral) fuels nuclear reactors [assoc w/ plant remains in sandstones formed in ancient stream channels]
  • Hematite & magnetite (banded iron formations)  iron ores
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