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Sediments and Diagenesis

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Sediments and Diagenesis The Rock Cycle is a group of changes. It is an ongoing process. Igneous rock can change into sedimentary rock or into metamorphic rock. – PowerPoint PPT presentation

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Title: Sediments and Diagenesis


1
Sediments and Diagenesis
The Rock Cycle is a group of changes. It is an
ongoing process. Igneous rock can change into
sedimentary rock or into metamorphic
rock. Sedimentary rock can change into
metamorphic rock or into igneous rock.
Metamorphic rock can change into igneous or
sedimentary rock.
2
Sediments and Diagenesis
Sediment Diagenesis 75 of all the rocks
exposed at the Earths land surface (only 5 of
Earths outer 10 miles - so mostly at the
surface) I. Sediment Rock fragments created by
weathering and erosion Accumulates
everywhereoceans, beaches, lakes, rivers,
deserts, swamps, caves, base of glaciers
3
Sediments and Diagenesis
  • Classified based on its origin.
  • Detrital composed of transported solid fragments
    (detritus) of preexisting rocks
  • 2. Chemical forms when previously dissolved
    minerals either precipitate from solution or are
    extracted from water by living organisms and
    converted to shells/skeletons

4
Sediments and Diagenesis
5
Sediments
  • B. Sediment Transport and Deposition
  • Detrital
  • Generally move from high ground to low ground by
    the pull of gravity (assisted by water, wind, or
    glacial ice)
  • Deposited when the carrying material loses its
    capacity to carry the sediment
  • 2. Chemical
  • Ions remain in solution until theres a change in
    the waters temperature, pressure, or chemical
    composition and then the ions precipitate

6
Sediments
C. Sediment Texture Detrital sediment and
chemical sediment are classified based on
composition. 1. Grain size Grain composition -
some minerals are stronger than others. a.
Distance - smaller grains travel longer
distances. b. Energy of the transportation
medium - high energy environment moves larger
grains.
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Sediments
8
Sediments
2. Grain shape a. Distance transported - over far
distances, grained become more rounded. b.
Transportation medium High energy river, wind
produce rounded grains Middle of glacier,
mudflow, debris flow preserve angular grains
not enough distance to round grains
9
Sediments
C. Sediment Texture detrital sediment and
chemical sediment are classified based on
composition. 3. Sorting Related to the carrying
capacity of the transport medium Well sorted
wind Medium - well sorting waves Medium - poor
sorting streams Poorly sorted glaciers,
debris flows
10
Sediments
11
Sediments and Diagenesis
II. Turning sediments into rock Eventually
accumulated sediment turns into rock A.
Diagenesis All the chemical, physical, and
biological changes that take place after
sediments are deposited. Burial Alteration by
groundwater Recrystallization regrowth of less
stable minerals into more stable
ones. Lithification occurs within the upper few
kilometers of the crust at temperatures lt 200?C
(400?F)
12
Sediments and Diagenesis
  • II. Turning sediments into rock
  • B. Lithification the process by which
    unconsolidated sediments are transformed into
    solid sedimentary rocks (part of diagensis)
  • Compaction pressure (from overlying sediment)
    reduces the volume of sediment
  • Compaction forces out air and water and packs
    grains together.

13
Sediments and Diagenesis
II. Turning sediments into rock B.
Lithification 2. Cementation Cements grains
together - ions dissolved in water by chemical
weathering may be deposited by groundwater
circulating through the sediment. Calcium
carbonate CaCO3 Calcium ions plus CO2 and
H2O Silica SiO2 is produced by chemical
weathering of silicate igneous rocks Iron oxide
Fe2O3
14
Sediments and Diagenesis
III. Types of Sedimentary rocks A. Detrital
Sedimentary rocks made of sediment that is
transported as solid particles Particle size is
the primary basis for distinguishing various
detrital sedimentary rocks. Particle size
indicates environment of deposition Water and
air currents sort by size. Stronger current
larger grain sizes
15
Sediments and Diagenesis
  • III. Types of Sedimentary rocks
  • A. Detrital Sedimentary rocks made of sediment
    that is transported as solid particles
  • 1. Shale (mudstone, siltstone)
  • gt50 of all sedimentary rocks
  • Silt and clay
  • Small grain size settling from quiet,
    non-turbulent water
  • Silt and class form in lakes, lagoons, swamps,
    deep ocean.
  • Need quiet water depositional setting

16
  • III. Types of Sedimentary rocks
  • A. Detrital Sedimentary rocks
  • 2. Sandstone sand sized particles (1/16 2
    millimeters)
  • 25 of all sedimentary rocks
  • Windblown dunes, some rivers, and beaches
  • Shape and sorting important for determining
    depositional environment.
  • Sorting well sorted wind waves poorly sorted
    streams
  • Shape well rounded water or wind transported
    over long distances
  • Angular glacier or debris flow
  • Transported over short distances

Sediments and Diagenesis
17
  • III. Types of Sedimentary rocks
  • Detrital Sedimentary rocks
  • 2. Sandstone sand sized particles (1/16 2
    millimeters) (
  • 25 of all sedimentary rocks
  • Windblown dunes, some rivers, and beaches
  • Shape and sorting important for determining
    depositional environment.
  • Sorting well sorted wind waves poorly sorted
    streams
  • Shape well rounded water or wind transported
    over long distances
  • Angular glacier
  • Transported over short distances

Sediments and Diagenesis
18
  • III. Types of Sedimentary rocks
  • Detrital Sedimentary rocks
  • 2. Sandstone sand sized particles (1/16 2
    millimeters) (
  • 25 of all sedimentary rocks
  • Windblown dunes, some rivers, and beaches
  • Shape and sorting important for determining
    depositional environment.
  • Sorting well sorted wind waves poorly
    sorted streams
  • Shape well rounded transported over long
    distances (water)
  • Angular transported over short distances
    (glacier)

Sediments and Diagenesis
19
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21
Sediments and Diagenesis
  • III. Types of Sedimentary rocks
  • Detrital Sedimentary rocks
  • 3. Conglomerate and Breccia
  • Composed of gravels (pea to large boulders, gt2
    mm)
  • Conglomerate composed of rounded grains of
    difference sizes.
  • Formed in energetic mountain streams or coasts
    (storm deposits)
  • Breccia composed of angular pieces.
  • Did not travel far glaciers, landslides

22
Sediments and Diagenesis
  • III. Types of Sedimentary rocks
  • Detrital Sedimentary rocks
  • 3. Conglomerate and Breccia
  • Composed of gravels (pea to large boulders, gt2
    mm)
  • Conglomerate composed of rounded grains of
    difference sizes.
  • Formed in energetic mountain streams or coasts
    (storm deposits)
  • Breccia composed of angular pieces.
  • Did not travel far glaciers, landslides, (close
    to source)
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