Download Sediment

Chapter 8: From Sediment to
Sedimentary Rock
Carbonate reef off coast of the Bahamas
© 2012 John Wiley & Sons, Inc. All rights reserved.
Learning Objectives
Sediment
• Describe the three major types of sediment and
their formation.
Transport and deposition of sediment
• Describe the process of deposition, including
where and how it takes place.
Sedimentary rock
• Discuss the lithification of sediment into different
types of rock.
How plate tectonics affects sedimentation
• Contrast what happens to sediment in different
plate tectonics settings.
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sediment
Sediment is separated into three broad categories:
• Clastic
• Chemical
• Biogenic
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sediment
Figure 8.1 From clasts to rocks
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sediment
Clastic Sediment
Clastic sediment
•
•
•
Sediment formed from fragmented rock and
mineral debris
Produced by weathering and erosion
Described by particle shape, angularity, and size
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sediment
Figure 8.2a Sorting
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sediment
Figure 8.2b Roundness
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sediment
Figure 8.2c Till, poorly sorted
Figure 8.2d Well-sorted quartz sand
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sediment
Clastic Sediment
•
•
Clasts: grains of mineral
or rock fragments
Volcaniclastic sediments
• Volcanic in origin
• Pyroclasts are
distinguished by size:
• Bombs
• Lapilli
• Ash
Figure 6.1 Volcanoclasts
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sediment
Chemical and Biogenic Sediment
Chemical sediment
• Sediment formed by the
precipitation of minerals
dissolved in lake water,
river water, or sea water.
• Plants and animals alter
chemical balance:
• Limestone deposits
• Shallow sea water
evaporation causes
dissolved salts to
precipitate.
Figure 8.3a Chemical Sediment
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sediment
Chemical and Biogenic Sediment
Biogenic sediment
• Sediment that is
primarily composed of
plant or animal remains
• Shells, bones, teeth
• Wood, roots, leaves
• Or, sediment
precipitates as a result
of biologic processes
Figure 8.3b Biogenic sediments
© 2012 John Wiley & Sons, Inc. All rights reserved.
Transport and Deposition of
Sediment
Transportation of
sediment by:
• Water
• Wind
• Ice
• Mass wasting
Figure 8.4 Transport of sediment
© 2012 John Wiley & Sons, Inc. All rights reserved.
Transport and Deposition of
Sediment
Deposition
• The laying
down of
sediment
Figure 8.5 Depositional environments
© 2012 John Wiley & Sons, Inc. All rights reserved.
Transport and Deposition of
Sediment
Figure 8.5, part 3 Delta
Figure 8.5, part 4 Playa
© 2012 John Wiley & Sons, Inc. All rights reserved.
Transport and Deposition of
Sediment
Figure 8.5, part 5 Sand dunes
© 2012 John Wiley & Sons, Inc. All rights reserved.
Transport and Deposition of
Sediment
Depositional Environments on Land
Streams
Lakes
Glaciers
Wind
• Eolian
sediment
Figure 8.6 Soil from the last Ice Age
© 2012 John Wiley & Sons, Inc. All rights reserved.
Transport and Deposition of
Sediment
Depositional Environments in and Near the
Ocean
Deltas and estuaries
• Estuary: Semi-enclosed body of coastal water, in
which fresh water mixes with seawater
Beaches
Shelves
Carbonate platforms and reefs
© 2012 John Wiley & Sons, Inc. All rights reserved.
Depositional Environments in and Near the
Ocean
Figure 8.7a Delta
Figure 8.7b Beach
© 2012 John Wiley & Sons, Inc. All rights reserved.
Transport and Deposition of
Sediment
Depositional Environments in and Near the
Ocean
Turbidity current
•A turbulent, gravity-driven flow consisting of a
mixture of sediment and water
•Conveys sediment from the continental shelf to the
deep sea
Seafloor is rich in nutrients:
•Calcareous ooze
•Siliceous ooze
© 2012 John Wiley & Sons, Inc. All rights reserved.
Depositional Environments in and Near the
Ocean
Figure 8.7c Carbonate reef
Figure 8.7d Deep-sea turbidites
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sedimentary Rock
Rock Beds
Lithification
• The processes by which
loose sediment is
transformed into
sedimentary rock
Bedding
• The layered arrangement
of strata in
sediment/sedimentary rock
Bedding surface
• The top or bottom surface
of a rock stratum or bed
Figure 8.8 Layers of rock: bedding
© 2012 John Wiley & Sons, Inc. All rights reserved.
Rock Beds
Figure 8.9 Clues to bed’s origin
© 2012 John Wiley & Sons, Inc. All rights reserved.
Rock Beds
Figure 8.9 Clues to bed’s origin
© 2012 John Wiley & Sons, Inc. All rights reserved.
Rock Beds
Ancient dunes
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sedimentary Rock
Lithification
Compaction
• Reduction of pore space in
a sediment as a result of
the weight of overlying
sediments
Cementation
• Substances dissolved in
pore water precipitate out
and form a matrix in
which grains of sediments
are joined together
Figure 8.10 Lithification
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sedimentary Rock
Lithification
Recrystallization
• The formation of new crystalline mineral grains
Figure 8.10 Recrystallization
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sedimentary Rock
Types of Sedimentary Rocks
Clastic sedimentary rock
•
•
•
•
Conglomerate has large fragments in a finer-grained
matrix.
Sandstone is medium-grained, where clasts are
typically, but not necessarily, dominated by quartz
grains.
Mudstone is a very fine-grained sedimentary rock of
the same composition as shale but without fissility.
Shale is a very fine-grained fissile or laminated
sedimentary rock, consisting primarily of clay-sized
particles.
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sedimentary or Igneous?
Sedimentary or Igneous?
Sedimentary or Igneous?
How do you know?
How do you know?
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sedimentary Rock
Types of Sedimentary Rocks
Chemical sedimentary rocks
•
•
Evaporite
• Formed by the evaporation of lake water or sea
water, followed by lithification of the resulting
salt deposit
Banded iron formation
• A type of chemical sedimentary rock rich in iron
minerals or silica
© 2012 John Wiley & Sons, Inc. All rights reserved.
Types of Sedimentary Rocks
What a Geologist Sees: A Change in the Atmosphere
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sedimentary Rock
Types of Sedimentary Rocks
Biogenic sedimentary rocks
•Limestone
• A sedimentary rock that consists primarily of the
mineral calcite
•Peat
• Formed from the accumulation and compaction
of plant remains
•Coal
• A combustible rock formed from the lithification
of plant-rich sediment
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sedimentary Rock
Interpreting Environmental Clues
Figure 8.12a Ripples
Figure 8.12b Ripple marks
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sedimentary Rock
Interpreting Environmental Clues
Figure 8.12c Mudcracks
Figure 8.12d Mudcracks preserved in rocks
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sedimentary Rock
Interpreting Environmental Clues
Figure 8.13 Seagull footprints
Figure 8.13 Fossilized
footprints
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sedimentary Rock
Interpreting Environmental Clues
Figure 8.14 Fossil fern found in Greenland from the Triassic Period
© 2012 John Wiley & Sons, Inc. All rights reserved.
Sedimentary Facies
Figure 8.15 One sedimentary environment changes over time
© 2012 John Wiley & Sons, Inc. All rights reserved.
How Plate Tectonics
Affect Sedimentation
Divergent plate boundaries
• Rift valleys
• A linear, fault-bounded valley
along a divergent plate
boundary or spreading center
Convergent plate boundaries
• Collisional type
• Subduction type
• Back-arc basin
• Accretionary wedges
• Ophiolites
© 2012 John Wiley & Sons, Inc. All rights reserved.
How Plate Tectonics Affects
Sedimentation
Figure 8.17 Accretionary wedge
© 2012 John Wiley & Sons, Inc. All rights reserved.
Critical Thinking
• If oxygen from cyanobacteria caused iron to
precipitate billions of years ago, then what is your
hypothesis as to why silica precipitated?
• Estuaries are generally shallow, yet there are thick
accumulations of estuarine sediments in the
geologic record. What hypothesis can you suggest
to explain this?
© 2012 John Wiley & Sons, Inc. All rights reserved.