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 • c

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 chemicalformation of new substances through

removal of or additions to the weathered material

• physical or mechanical disintegration of physical or mechanicalmaterials with no new substances forming

• 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

Siltstone

Claystone

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

BIOLOGICAL OR ORGANIC ROCKSSED-MET ROCKS-AGE

White Cliffs of Dover

SED-MET ROCKS-AGE

Peat

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

Cross bedding

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 Petroleum and Natural Gas

Coal

Cement from Limestone Salt

Uranium

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

of metamorphic rocks

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

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 determin- ation method we discussed in the mineral section)

Correlation of Index Fossils From 2 Different Areas