4. What is a sedimentary rock?
• Sedimentary rocks result from mechanical
and chemical weathering
• Comprise ~ 5% of Earth’s upper crust
• About 75% of exposed rocks
• Contain evidence of past environments
• Record how sediment is transported
• Often contain fossils
5. Fossil Fish - 50 Million Year Old Lakes in southern Wyoming
These fish tell us the Wyoming climate
50 million years ago.
Sedimentary Rock made of fine-grained mudstone.
6. Overview
► sediment production
► types of sediment and sedimentary
rocks
► sediment transport and deposition
► depositional systems
► stratigraphic architecture and basins
► chrono-, bio-, chemo-, and sequence
stratigraphy
► Earth history
7. Sedimentary rocks are the
creation
product of the creation,
transport, deposition, and
diagenesis of detritus and
solutes
solutes derived from preexisting rocks.
8. Steps Involved in Formation
of Clastic Sedimentary Rock
Weathering
Erosion
Transport
Deposition
Lithification
--Compaction
--Cementation
12. Ions weather out of rock,
are transported by
groundwater to sediment
layers below
6_11
Ions transported
to lake or
Water enters pore
ocean
spaces between
sediment grains
Ion-rich
groundwater
Dissolved ions precipitate
to form cement between
sediment grains
13.
14. Diagenesis includes:
Recrystallization – growth of stable
minerals from less stable ones
Lithification – loose sediment is
transformed into solid rock by
compaction and cementation
Natural cements: calcite, silica, and
iron oxide. Formed from ions in
solution in water.
15. ► Diagenesis – chemical and physical changes
that take place after sediments are deposited
► Diagenesis varies with composition
16. Lithification
► Compaction: As more sediments are piled on
top, compaction drives out the excess water.
► Cementation: Precipitation of chemicals
dissolved in water binds grains of a sediment
together.
► Remember where the dissolved chemicals
come from?
19. ►
Source area - the locality from which the
sediment was derived: factors used to evaluate
source area include rock type, environment of
deposition, direction (paleocurrents) and distance
from source area
20. ►
Depositional environment – where sediment
is deposited. It can be determined by looking at
sedimentary structures (including fossils), the
bed shape and vertical sequences within the
sedimentary layers, and grain composition
21. Sedimentary environments & plate tectonic
settings
Convergent boundaries – coarse-grained clastic
sediments with abundant volcaniclastic and felsic
material
22. Sedimentary environments & plate tectonic
settings
Divergent boundaries - thick wedges of gravel and
coarse sand along margins,with lake bed deposits
and associated evaporite rocks possible in bottoms
of rift valleys
23. What is the economic importance
of sedimentary rocks?
►
They are important for economic reasons
Remember this
because they contain
when we talk about
►Coal
►Petroleum and natural gas
correlation. Note
how beds pinch out
or are offset by
faults
►Iron, aluminum, uranium and manganese
►Geologists use them to read Earth’s history
24. SEDIMENTARY ROCKS
► WEATHERING PROCESSES BREAK
ROCK INTO PIECES, SEDIMENT, READY
FOR TRANSPORTATION DEPOSITION
BURIAL LITHIFICATION INTO NEW
ROCKS.
25. CLASSIFYING SEDIMENTARY
ROCKS
►
►
►
►
THREE SOURCES
Detrital (or clastic) sediment is composed of
transported solid fragments (or detritus) of pre-existing
igneous, sedimentary or metamorphic rocks
Chemical sediment forms from previously dissolved
minerals that either precipitated from solution in water , or
were extracted from water by living organisms
Organic sedimentary rock consisting mainly of plant
remains
27. SHALES
► SHALES:
finest-grained – composed of
very small particles (from <0.004-0.063 mm)
50% of all sedimentary rocks are Shales
Consist largely of Clay minerals
Subcategories: Claystones; Siltstones;
Mudstones
Economic value: building material; china
and ceramics; spark plug housings
28. SANDSTONES
► SANDSTONES: medium-grained; particle-size
(0.063-2 mm)
► 25% of all sedimentary rocks fall into this
category
► Three major kinds of Sandstone, based on
mineral composition and appearance:
Quartz Arenite: >90% quartz grains
Arkoses : more Feldspar minerals
Graywackes :quartz and feldspar grains, and
volcanics
► Economic value: glass; natural reservoirs for oil,
gas, and groundwater
29. CONGLOMERATES BRECCIAS
► CONGLOMERATES
AND BRECCIAS :
► The coarsest of all the detrital sedimentary
rocks
► Composed of particles >2 mm in diameter
Conglomerate - the particles are rounded
Breccia - the particles are angular
31. INORGANIC CHEMICAL
SEDIMENTARY ROCKS
► Formed when dissolved products of
chemical weathering precipitate from
solution
► Most common types:
Inorganic limestones and cherts: precipitates
directly from seawater and fresh water
Evaporites: precipitates when ion-rich water
evaporates
Dolostones: Origin is still in debate
32. INORGANIC - LIMESTONES
► Limestones
- account for 10% - 15% of all
sedimentary rocks formed from Calcite or Calcium
Carbonate (CaCO3).
►
Formed as pure carbonate muds accumulate on the sea floor
►
Also formed on land:
Tufa - a soft spongy inorganic limestone that forms where underground
water surfaces
Travertine - forms in caves when droplets of carbonate-rich water on the
ceiling, walls and floors precipitate a carbonate rock
33. ORGANIC LIMESTONES
►
Formed with calcite from marine environment: CaCO 3 shells and
internal/external skeletons of marine animals
►
Coquina - “crushed” shell fragments cemented with CaCO3
Chalk - made from billions of microscopic carbonate-secreting
organisms
Coral Reefs - Formed from the skeletons of millions of tiny
invertebrate animals who secrete a calcite-rich
material. Live “condo” style while algae acts
as the cement to create the large structures
called “reefs”.
Organic Chert - formed when silica-secreting microscopic marine
organisms die (radiolaria {single-celled animals} and
diatoms {skeletons of singled-celled plants})
Flint - an example of an Organic Chert
►
►
►
►
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34. ORGANIC SEDIMENTARY
ROCKS
►
►
Coal - Organic sedimentary rock consisting mainly of plant
remains
Formation:
Burial of decaying vegetation;
Increasing pressure from the overlying layers expels water, CO2
and other gases;
Carbon accumulates.
►
►
►
►
Peat
- formed early in the process, when the original plant structure
can still be distinguished.
Lignite
- a more hardened form of Peat
Bituminous - more pressure and more heat produce this moderately
hard coal.
Anthracite - the hardest coal - formed from metamorphic processes
under extreme heat and pressure - Hard - Shiny - the most
desired as an energy resource.
36. SEDIMENTARY
PROCESSES
► LITHIFICATION :
►
As sediment is buried several kilometers beneath the surface, heated from
below, pressure from overlying layers and chemically-active water
converts the loose sediment into solid sedimentary rock
►
Compaction - volume of a sediment is reduced by
application of pressure
Cementation - sediment grains are bound to each other
by materials originally dissolved during chemical
weathering of preexisting rocks
►
typical chemicals include silica and calcium carbonate.
