SEDIMENTARY ROCKS,
METAMORPHIC ROCKS,
AND AGE
DETERMINATION
SED-MET ROCKS-AGE
• Sedimentary rock family
• Definition and Explanation
• comprised of sediments
• accumulated from physical and or
chemical processes mostly in large
bodies of water
• consolidated through lithification
SED-MET ROCKS-AGE
• Factors and concepts related to rock
formation
• weathering--”breaking down” of rock
materials at or near surface of Earth
• chemical--decomposition of materials
and formation of new substances
through removal of or additions to the
weathered material
• physical or mechanical--disintegration
of materials with no new substances
forming
SED-MET ROCKS-AGE
• Erosion
• removal or transportation of material by
stream water, glacial ice, wind, and
gravity
• eroded materials may eventually
accumulate in large amounts
• Lithification
• compaction and cementation of
sediments to become rocks
SED-MET ROCKS-AGE
• Stratification
• accumulations in layers (strata or beds)
and is the most common occurrence of
this family of rock
• Law of superposition
• in a series of strata, each layer is older
than the one above and younger than the
one below--this reflects a relative age
relationship between layers
Stratification in Sedimentary Rocks
SED-MET ROCKS-AGE
• Sedimentary rock types
• three types based on the way they form;
clastic (detrital), chemical inorganic, and
organic
• clastic
• sediments accumulated primarily by
physical processes as deposits from
stream water, glacial ice, wind, etc. then
lithified to rock
SED-MET ROCKS-AGE
• Wentworth’s sediment size classification
is used to name the specific clastic rock
in the detrital class
Wentworth’s Scale of
Sedimentary Particles
Different colors of beach sand in the world
CLASTIC ROCKS
Detrital (Clastic) Sedimentary Rocks
Larger grained
Conglomerate
Breccia
Detrital (clastic) Sedimentary Sandstones
Graywacke
Arkose
Quartz Sandstone
Detrital (clastic) Sedimentary Rocks
Smaller Grained
Claystone
Siltstone
Shale
SED-MET ROCKS-AGE
• biological (organic) rocks
• accumulation of animal shells or plant
material then lithified--particle size is
not important in naming biological rocks
SED-MET ROCKS-AGE
BIOLOGICAL OR ORGANIC ROCKS
SED-MET ROCKS-AGE
White Cliffs of Dover
COAL SERIES
buried plants
Peat
bituminous
lignite
anthracite
methane
coal gas
SED-MET ROCKS-AGE
Biological (organic) formed chert
SED-MET ROCKS-AGE
• chemical (inorganic) rocks
• formed from chemical reactions in the
oceans or large bodies of water
CHEMICAL OR INORGANIC ROCKS
Lakes formed from Glaciation
Lake Bonneville
Evaporite deposits in Death Valley, California
SED-MET ROCKS-AGE
Chemically (inorganic) formed chert---nodules of
chert caused by replacement of silica for bedrock—is
present in the local Burlington limestone bedrock in
this area
SED-MET ROCKS-AGE
• Some special features in sedimentary rocks
• cross bedding
• relatively thin layers inclined at an
angle to the main bedding
• formed by currents in water or wind
Cross bedding
SED-MET ROCKS-AGE
• graded bedding
• a sedimentary layer characterized by a
decrease in sediment size from bottom
to top
• ripple marks
• small waves of sand that develop on
surface of sedimentary layer by the
action of moving water or wind
Ripple marks
SED-MET ROCKS-AGE
• Significance of sedimentary rocks
• only family of rock containing an
abundant record of life forms and the
changes in life forms throughout geologic
time
• only family of rock in which natural gas,
petroleum and coal are formed and found
• used as building materials, tombstones and
some limestones are used as a source of
lime
Groundwater
Coal
Petroleum and Natural Gas
Cement from Limestone
Uranium
Salt
SED-MET ROCKS-AGE
• Metamorphic rock family
• Definition and explanation
• formed primarily through action of
temperature and/or pressure on
preexisting rocks
• little or no melting during process
• time is also an important factor
• rocks will loose evidence of fossils or
other features present before the change
SED-MET ROCKS- AGE
• Types of metamorphism
• contact or thermal
• usually forms with intrusions of
smaller rock bodies as stocks in
country rocks
• temperature associated with the
intrusive body is the prime
metamorphic agent—lower
temperatures would form lower grade
of metamorphic rocks
SED-MET ROCKS-AGE
• regional metamorphism
• usually forms with intrusions of larger
bodies like batholiths or laccoliths
• temperature and pressure are equally
important in the metamorphic process
and includes a much larger area of
metamorphism—higher temperatures
would form a higher grade of
metamorphic rock
SED-MET ROCKS-AGE
• Kinds of metamorphic rocks
• all but one rock is comprised of silicate
minerals
• foliated
• minerals are aligned in a pattern
Foliated metamorphic rocks
Foliated or Lineated Metamorphic Rocks
Gneiss
Slate
Schist
Gneiss
Phyllite
Nonfoliated metamorphic rocks
Non foliated Metamorphic Rocks
Quartzite
(from arkose)
Marble
SED-MET ROCKS-AGE
• Important uses
• building materials and tombstones
• marble can be used in art as a
sculpturing material
SED-MET ROCKS-AGE
• Age determination (geologic age)
• important concepts used
• relative age concepts
• crosscutting and intrusive nature of
igneous rocks
• law of superposition pertaining to
sedimentary rocks
• absolute age dating
• determination of amounts of
radioactive parent and stable daughter
Relative Age dating
SED-MET ROCKS-AGE
• Age determination method
• relative and absolute age determination
methods are used together to establish
the absolute age of rocks which cannot
themselves be dated
• igneous rocks are the best rock family to
use in absolute age determinations
• Index fossils are used to facilitate the
determination of the age of sedimentary
rocks
Determine the absolute age of sedimentary bed , B given:
1. igneous intrusive, V dated at 2.15 million years old
2. lava flow, P dated at 2.25 million years old (both V
and P were dated using the absolute age determination method we discussed in the mineral section)
Correlation of Index Fossils
From 2 Different Areas