Transcript Sedimentary Rocks

WHAT HAPPENS TO THE PRODUCTS OF
ROCK WEATHERING
Weathering
Transport
Deposition
II. Sedimentary Rocks
WHY STUDY SEDIMENTARY ROCKS?
1) Cover over 70% of Earth’s Land Surface
These are the rocks you see most often.
2) Economically Important!!
 Contain all oil & gas deposits
 Important source of mineral resources like iron, salt,
aluminum; of agricultural fertilizer; of construction
materials like gypsum for drywall.
 Sedimentary rocks form important aquifers – sources
of fresh drinking water.
WHY STUDY SEDIMENTARY ROCKS?
3) They retain information about how and where they
formed. Important clues to Earth’s ancient environments!
4) They contain fossils. Important information on the
history and evolution of life!!
WHY STUDY SEDIMENTARY ROCKS?
They can be incredibly beautiful!!
II. Sedimentary Rocks: Two Types
a) Clastic: Rocks that form from the lithification
(compaction and cementation) of the weathered
and eroded products of pre-existing rocks.
b) Chemical: Rocks that form from the
crystallization of minerals out of water (usually
sea water).
Clastic Sedimentary Rocks
Rock names are based on the size of the particles that form the rock.
or Breccia
Siltstone
Shale
CONGLOMERATE
SANDSTONE
SHALE
Chemical Sedimentary Rocks
Can be chemical or biochemical precipitates
1) Limestone (CaCO3) – Composed of the
mineral calcite. Several different varieties.
a) Fossiliferous limestone
b) Lithographic limestone
c) Oolitic Limestone
d) Coquina
e) Travertine
2) Dolostone (CaMg(CO3)2) – Compsed of the
mineral dolomite.
Fossiliferous Limestone
Coquina – Fossil Hash
Travertine Deposits
Chert Nodules in Limestone
Chemical Sedimentary Rocks
3) Chert – microcrystalline quartz.
4) Evaporites – halite, gypsum, annhydrite
Devil’s Golf Course – Salt Crystals, Death Valley, CA
INTERPRETING SEDIMENTARY ENVIRONMENTS:
Rocks contain a complex and beautiful story about the Earth’s history. To
unravel this story we must learn to read the language of geology.
Clues To Interpreting Sedimentary Rocks
1) Transport History
Clues To Interpreting Sedimentary Rocks
2) Sedimentary Structures
A) Ripple Marks – modern beach
Ripple Marks in Sandstone – Rock was formed on an
ancient beach
2) Sedimentary Structures
B) Cross Beds – the inside of Ripple Marks
Checkerboard Mesa – Zion National Park, Utah
2) Sedimentary Structures
C) Mud Cracks – Environment that periodically dries out
2) Sedimentary Structures
D) Graded Bedding – Which way is up?
Kissing Camels – Garden of the Gods, Colorado