Download 06 Chapter 6_Sedimentary Rocks

Engineering Geology
CVL 3315
Chapter 6
Sedimentary Rocks
Dr. Sari Abusharar
University of Palestine
Faculty of Applied Engineering and Urban Planning
Civil Engineering Department
2nd Semester 2014-2015
1
Outline of Presentation
What is a sedimentary rock?
Types of sedimentary rocks
Detrital Sedimentary Rocks
Chemical Sedimentary Rocks
Turning sediment into rock
Classification of sedimentary rocks
Sedimentary environments
Sedimentary structures
Fossils: Evidence of past life
2
What is a sedimentary rock?
Sedimentary rocks are products of
mechanical and chemical weathering
They account for about 5 percent (by
volume) of Earth’s crust
Contain evidence of past environments
• Provide information about sediment
transport
• Often contain fossils
What is a sedimentary rock?
Sedimentary rocks are important for
economic considerations because they
may contain
• Coal
• Petroleum and natural gas
• Sources of iron, aluminum, and
manganese
• Reservoirs for water
Types of sedimentary rocks
Sediment originates from mechanical
and/or chemical weathering
Rock types are based on the source of the
material
• Detrital rocks ‫ –صخور فتاتية‬transported
sediment as solid particles
• Chemical rocks – sediment that was once
in solution
Detrital sedimentary rocks
The chief constituents of detrital rocks
include
• Clay minerals
• Quartz
• Feldspars
• Micas
Detrital sedimentary rocks
Particle size is used to distinguish among
the various types of detrital rocks
‫جلمود‬
‫جرول‬
‫كونجلومرات‬
‫زلط‬
‫حصاة‬
‫حبيبة‬
‫بريشيا‬
Detrital sedimentary rocks
Particle size is used to distinguish among
the various types of detrital rocks
‫حجر رملي‬
‫ حجر‬،‫طفل‬
‫طيني أو‬
‫حجر الغرين‬
Detrital sedimentary rocks
Common detrital sedimentary rocks (in
order of increasing particle size)
• Shale ‫الطفل‬
– Mud-sized particles (less than 1/16 mm) in
thin layers that are called lamina ‫صفيحة‬
– Most common sedimentary rock
– They exhibit fissility ‫(التفسخ‬can be split)
Shale containing plant remains
Detrital sedimentary rocks
• Mudstone ‫الحجر الطيني‬
– If the rock is form by fine-grained sediment
but it split into chunks or blocks it is called a
mudstone.
Detrital sedimentary rocks
• Sandstone
– Composed of sand-sized particles
– Forms in a variety of environments
– After shale, sandstone is the most abundant
sedimentary rock, accounting for approximately
20 percent of the entire group
– Sorting, shape, and composition of the grains can
be used to interpret the rock’s history
Quartz Sandstone
Sorting
Detrital rocks commonly have a variety of different size clasts.
Sorting ‫ فرز الحبيبات‬is the degree of similarity in particle size in a
sedimentary rock.
Particle Shape
Geologists describe a particle’s shape in terms of its angularity
(degree to which the clast’s edges and corners are rounded) and
sphericity (how close the shape of the clast is to a sphere).
Transportation reduces the size and angularity of clasts but does
not change their general shape.
Detrital sedimentary rocks
Composition: The composition represents
transportation history of the sediment
the
• Mostly quartz (quartz sandstone) long transportation.
• When a sandstone contains appreciable quantities of feldspar
(More than 25%) the rock is called arkose ‫أركوز‬, poorly sorted
and more angular, represents a granitic source rocks, which
suggests short-distance transport.
• A third variety of sandstone with a similar composition but
more than 15% is matrix (silt- and clay-size particles found in
spaces between larger sand grains) is called graywacke
‫جرايواكى‬. The poor sorting and angular grains characteristic of
graywacke suggest that the particles were transported only a
relatively short distance.
Detrital sedimentary rocks
• Conglomerate and breccia
– Both are composed of particles greater than 2mm in
diameter
- Conglomerate
consists largely of
rounded gravels
- Breccia is composed
mainly of large
angular particles
Chemical sedimentary rocks
Consist of precipitated (‫ )مترسب‬material that
was once in solution
Precipitation of material occurs in two
ways
• Inorganic processes (such as evaporation
and chemical activity)
• Organic processes of water-dwelling‫تعيش‬
organisms also form chemical sediments
(biochemical origin)
Chemical sedimentary rocks
Common chemical sedimentary rocks
• Limestone
– Representing about 10 percent of the total volume
of all sedimentary rocks
– Most abundant chemical rock
– Composed chiefly of the mineral calcite (CaCO3)
Marine biochemical limestones form as coral
reefs ‫الشعب المرجانية‬, coquina ‫(صدف‬broken shells),
and chalk (microscopic organisms)
Inorganic limestones include travertine ‫راسب‬
‫كربوناتي‬and oolitic limestone ‫الحجر الجيري العويني‬
Chemical sedimentary rocks
Common chemical sedimentary rocks
• Dolostone ‫حجر الدولوميت‬
–Typically formed secondarily from limestone
– A rock composed of the calcium-magnesium
carbonate dolomite [CaMg(CO3)2].
–Dolostone and limestone sometimes closely resemble
one another, they can be easily distinguished by
observing their reaction to dilute hydrochloric acid.
–When a drop of acid is placed on limestone, the
reaction (fizzing ‫ )فوران‬is obvious. However, unless
dolostone is powdered, it will not visibly react to the
acid.
Chemical sedimentary rocks
Common chemical sedimentary rocks
• Chert ‫الصوان‬
– Very compact and hard rocks made of
microcrystalline ‫ دقيق التبلور‬quartz (SiO2)
– Varieties include flint ‫ ظر‬, jasper ‫ جاسبار‬and
banded form is called agate‫عقيق‬
– Like glass, most chert has a conchoidal
fracture.
Chert
Three examples are shown
here.
A. Agate is the banded
variety. B. The dark color
of flint results from organic
matter. C. The red variety,
called jasper, gets its color
from iron oxide. D. Native
Americans frequently made
arrowheads and sharp tools
from chert.
Chemical sedimentary rocks
Common chemical sedimentary rocks
• Evaporites ‫متبخرات‬
– Evaporation triggers deposition of chemical
precipitates
– Examples include rock salt and rock gypsum
Evaporites
Chemical sedimentary rocks
Common chemical sedimentary rocks
• Coal
– Different from other rocks because it is
composed of organic material
– Stages in coal formation (in order)
– 1. Plant material
– 2. Peat ‫الخث‬
– 3. Lignite (‫فحم بني )اللجونيت‬
– 4. Bituminous ‫الفحم البيتوميني‬
– 5. Anthracite ‫األنثراثيت‬
Stages of coal
formation
Turning sediment into Sedimentary
rock
Many changes occur to sediment after it
is deposited
Diagenesis ‫( تغيرات ما بعد الترسيب‬dia = change,
genesis = origin)-all of the chemical,
physical, and biological changes that take
place after sediments are deposited
• Occurs within the upper few kilometers of
Earth’s crust at temperatures that are
generally less than 150° to 200° C.
Turning sediment into rock
Diagenesis includes
– Recrystallization ‫ – إعادة التبلور‬development of
more stable minerals from less stable ones
– Lithification ‫( التصخر‬lithos = stone, fic = making)
– unconsolidated sediments are transformed
into solid sedimentary rock by compaction and
cementation ‫الكبس والتالحم‬
– Natural cements include calcite, silica, and iron
oxide
Classification of sedimentary rocks
Sedimentary rocks are classified according
to the type of material
Two major groups
• Detrital
• Chemical and Organic
Classification of sedimentary rocks
Two major textures are used in the
classification of sedimentary rocks
• Clastic ‫(فتاتي‬taken from a Greek word meaning
“broken.”)
– Discrete fragments and particles
– All detrital rocks have a clastic texture
• Nonclastic ‫غير فاتي‬
– Pattern of interlocking crystals
– May resemble an igneous rock
Classification of Sedimentary Rocks
Classification of Sedimentary Rocks
rock salt
Like other
evaporites, this
sample of rock salt
is said to have a
nonclastic
(crystalline)
texture because it
is composed of
intergrown
(interlocking)
crystals.
Sedimentary environments
Sedimentary environments is simply a
geographic setting where sediment is
accumulating.
Determines the nature of the sediments
that accumulate (grain size, grain shape,
etc.)
Sedimentary environments
Types of sedimentary environments
• Continental
– Dominated by erosion and deposition
associated with streams
– Glacial
– Wind
• Marine
– Shallow (to about 200 meters)
– Deep (seaward of continental shelves)
Sedimentary environments
Types of sedimentary environments
• Transitional (shoreline)
– Tidal flats ‫مسطحات المد والجزر‬
– Lagoons ‫بحيرات شاطئية‬
– Deltas
Continental (left) and marine (right)
depositional environments
Marine
depositional
environments
‫المراوح‬
‫الطميية‬
‫الرواسب‬
‫الثلجية‬
Continental (left) and marine (right)
depositional environments
‫مستنقعات‬
‫عذبة‬
Continental
depositional
environments
Sedimentary environments
Sedimentary facies ‫السحنات الرسوبية‬
• Different sediments often accumulate
adjacent to one another at the same time
• Each unit (called a facies) possesses a
distinctive set of characteristics reflecting
the conditions in a particular environment
• The merging of adjacent facies tends to be
a gradual transition
Sedimentary facies
Sedimentary structures
‫التركيبات الرسوبية‬
Provide information useful in the
interpretation of Earth history
Types of sedimentary structures
• Strata, or beds (most characteristic of
sedimentary rocks)
• Bedding planes ‫مستويات التطبق‬that separate
strata
• Cross-bedding ‫التطبق المتقطع‬
Strata
Cross-Bedding in Sandstone
Sedimentary structures
Types of sedimentary structures
• Graded beds ‫طبقات متدرجة‬
Turbidity currents are generally associated with graded beds
• Ripple marks ‫عالمات التموج‬
• Mud cracks ‫شقوق طينية‬
• Fossils ‫الحفريات‬
Graded beds
Ripple Marks
Mud Cracks
Fossils
Fossils: Evidence of past life
By definition, fossils are the traces or
remains of prehistoric life now preserved
in rock
Fossils are generally found in sediment or
sedimentary rock (rarely in metamorphic
and never in igneous rock)
Fossils: Evidence of past life
Geologically fossils are important for
several reasons
• Aid in interpretation of the geologic past
• Serve as important time indicators
• Allow for correlation of rocks from
different places
Dinosaur footprint in limestone
End of Chapter 6