Download Sedimentary Rocks I

Sedimentary Rocks
Copyright © 2008 Joe Marx.
Vocabulary
• Cementation: minerals fill the spaces between
sediments and act as glue.
• Compaction: sediments are pressurized to
become rock.
• Breccia: sharp rocks (or sediments) cemented
together to form one rock
• Conglomerate: rocks cemented together to form
one rock (rounded edges).
Topics for This Lecture
•
•
•
•
What is sediment?
What are sedimentary rocks?
What are the different kinds of sedimentary rock?
What are sedimentary structures and how are they
produced?
• In what environments do sedimentary rocks form?
◄ Edge of Athabasca Glacier, Jasper
National Park, Alberta, Canada, August,
2006.
Sedimentary Rocks
Image courtesy of Wikimedia Commons.
Page 3
What is Sediment?
• Solid material that accumulates on Earth’s surface,
generally forming layers.
• Four main classes of sediment:
– Detritus: Solid fragments of rock or mineral matter
that have weathered out of pre-existing rock.
– Inorganic precipitates from natural waters.
– Shells, often microscopic, that were secreted by
plants or animals.
– Buried plant remains.
Silty and sandy sediment, Canyon
Largo, New Mexico. ►
Sedimentary Rocks
Image courtesy of U.S.Geological Survey.
Page 4
What is Sedimentary Rock?
• Rock formed, under moderate pressure, from
accumulated layers of sediment.
• There are four main classes of sedimentary rock,
corresponding to the four classes of sediment:
–
–
–
–
Clastic or detrital rock, from detritus.
Chemical rock, from inorganic precipitates.
Biochemical rock, from plant and animal shells.
Organic rock, from plant remains.
◄ Jonesboro Limestone, a chemical rock that
occurs within Great Smoky Mountains
National Park, Tennessee.
Sedimentary Rocks
Image courtesy of U.S.Geological Survey.
Page 5
Clastic Sedimentary Rock
• A clast is an individual mineral grain or rock
fragment—one piece of detritus.
• After chemically and physically weathering out of
pre-existing rock, clasts are transported by wind,
water, ice or gravity to a site of deposition.
• Clastic (or detrital) sedimentary rock is composed
of compacted and cemented detritus.
Limestone breccia, Titus Canyon,
Death Valley National Park,
California. ►
Sedimentary Rocks
Image courtesy of U.S.Geological Survey.
Page 6
Principal Clastic Rocks
• Clastic rocks are classified based on mineral
content, grain size, and grain shape.
• Sandstone and shale are the principal clastic rocks.
• Others include conglomerate and breccia.
Sandstone
Sedimentary Rocks
Shale
Conglomerate
Images courtesy of Oxford Earth Sciences Image Store.
Page 7
Chemical Rock
• Composed primarily of mineral crystals
inorganically precipitated from natural water.
• Principal chemical rocks include limestone
deposited in warm or running water, and evaporites,
such as rock gypsum and rock salt, left behind when
salty water evaporates.
Oolitic Limestone
Sedimentary Rocks
Rock Gypsum
Left-hand image courtesy of Oxford Earth Sciences Image Store. Righthand image courtesy of U.S.Geological Survey.
Page 8
Biochemical Rock
• Formed from shells—crystalline masses
precipitated by living organisms.
• The principal biochemical rock is biogenic
limestone.
Fossiliferous Limestone
Sedimentary Rocks
Chalk
Images courtesy of Oxford Earth Sciences Image Store.
Page 9
Organic Rock
• Formed by the compaction and anaerobic
distillation (carbon purification) of plant remains.
• The principal organic rock is coal.
Strip mine, Coalmont district, Jackson County, Colorado,
1940.
Sedimentary Rocks
Image courtesy of U.S. Geological Survey.
Page 10
Sedimentary Structure
• A distinctive arrangement of grains within a
sedimentary rock.
• Bedding describes the layers
◄ Banded iron formation,
Dales Gorge, Western
Australia.
Sedimentary Rocks
Image copyright © Society for Sedimentary Geology, courtesy of Earth
Science World Image Bank.
Page 11
Bedding or Stratification
• The arrangement of sedimentary rock in layers of
varying thickness and character.
Thin-bedded limestone of the Tomstown Formation,
near Rohersville, Maryland.
Sedimentary Rocks
Image courtesy of U.S. Geological Survey.
Page 12
Graded Bed
• Characterized by distinct vertical gradations in
grain size, generally from coarse at the base to fine
at the top.
• Produced when grains drop gradually from wind or
water currents. Finer grains take longer to settle.
◄ Graded Pleistocene
sediments, near
Lafayette, Indiana.
Graded bedding in
turbidites, Delaware
Basin, New Mexico. ►
Sedimentary Rocks
Images copyright © Bruce Molnia, Terra Photographics, courtesy of Earth
Science World Image Bank.
Page 13
Ripple Marks
• Alternating ridges and hollows produced by the
movement of wind or water across a granular
surface.
Ripples on gypsum sand dune, White
Sands National Monument, New
Mexico.
Sedimentary Rocks
Ripple marks in Tertiary sandstone, Point
Lobos State Park, California.
Left-hand image copyright © Larry Fellows, Arizona Geological Survey.
Right-hand image copyright © Bruce Molnia, Terra Photographics. Both
courtesy of Earth Science World Image Bank.
Page 14
Cross Bed
• A bed inclined at an angle
to the main plane of
stratification.
• Produced as dunes or
ripples deposited by a
current of wind or water.
Cross bedding in the Navajo Sandstone,
Zion National Park, Utah. ►
Sedimentary Rocks
Image copyright © Marli Miller, University of Oregon, courtesy of Earth
Science World Image Bank.
Page 15
Mud Cracks
• Surface fractures, arranged in rough polygons,
caused by the shrinkage of drying clay, silt or mud.
Ancient mud cracks in Arizona. ►
◄ Modern mud cracks in Utah.
Sedimentary Rocks
Left-hand image copyright © Bruce Molnia, Terra Photographics, courtesy
of Earth Science World Image Bank.
Right-hand
image courtesy of U.S. Geological Survey.
Page 16
Sedimentary Environment
• The type of locale in which deposition occurs.
• May be terrestrial or marine.
• Each sedimentary environment produces a facies,
or a set of characteristic sedimentary rocks and
structures.
• Geologists study facies to determine past
sedimentary environments.
River delta, Puget
Sound, Washington. ►
Sedimentary Rocks
Image courtesy of U.S.Geological Survey.
Page 17
Glacial Environment
Pit dug into glacial till, Rocky Mountain
National Park, Colorado.
Sedimentary Rocks
Meter-square cross section of a slab of
Precambrian tillite from India.
Images courtesy of U.S. Geological Survey.
Page 18
Mountain Stream Environment
Big Hunting Creek, Frederick County,
Maryland.
Enon Conglomerate, road cut near
Port Elizabeth, South Africa.
Sedimentary Rocks
Right-hand image copyright © Society for Sedimentary Geology, courtesy
of Earth Science World Image Bank.
Page 19
Mountain Front Environment
Black Mountains, Death Valley, California.
Sedimentary Rocks
Conglomerate of carbonate clasts in red
siltstone matrix, Leesburg Member of the
Bull Run Formation, Loudoun County,
Virginia.
Left-hand image copyright © Marli Miller, University of Oregon, courtesy
of Earth Science World Image Bank. Right-hand image courtesy of U.S.
Geological Survey.
Page 20
Sand Dune Environment
Great Sand Dunes National Park,
Colorado.
Sedimentary Rocks
Cross bedding in the Navajo Sandstone, Zion
National Park, Utah.
Left-hand image courtesy of National Park Service. Right-hand image
courtesy of U.S. Geological Survey.
Page 21
Lake or Lacustrine Environment
Farewell Lake, southwest Alaska.
Lacustrine shale, British Columbia. ►
Sedimentary Rocks
Left-hand image courtesy of National Climatic Data Center. Right-hand
image courtesy of Agriculture and Agri-Food Canada.
Page 22
River or Fluvial Environment
Kicking Horse River, near
Field, British Columbia.
Sedimentary Rocks
Gravel channel fill in bedded fluvial sands, near
Mexico, Indiana.
Left-hand image copyright © Society for Sedimentary Geology. Right-hand
image copyright © Bruce Molnia, Terra Photographics. Both images
courtesy of Earth Science World Image Bank.
Page 23
Delta Environment
Delta deposited by glacial
meltwater into Bow Lake, Banff
National Park, Alberta, Canada.
Sedimentary Rocks
Foreset beds in a glaciomarine delta, Lake
Auburn, Maine.
Left-hand image copyright © Society for Sedimentary Geology, courtesy of
Earth Science World Image Bank. Right-hand image by Woodrow B.
Thompson, used with permission of www.maine.gov.
Page 24
Beach or Tidal Environment
Trench cut into beach
overwash deposits, Core
Banks, North Carolina.
Sedimentary Rocks
Ancient tidal flat
deposits, Summerville
Formation, southeastern Utah.
Left-hand image copyright © Society for Sedimentary Geology, courtesy of
Earth Science World ImageBank.
Page 25
Shallow Marine Environment
Healthy modern coral reef, Kerama
Islands, near Okinawa.
Permian reef limestone, Carlsbad Caverns
National Park, New Mexico. ►
Sedimentary Rocks
Left-hand image courtesy of U.S. Geological Survey. Right-hand image
copyright © Bruce Molnia, Terra Photographics, courtesy of Earth Science
World Image Bank.
Page 26
Deep Marine Environment
• Turbidity Current
– Bottom-flowing current, laden with suspended
sediment, moving rapidly down a submarine slope.
– Produces distinctive patterns of graded bedding.
◄ Turbidite, Santa Paula,
California.
Sedimentary Rocks
Image copyright © Roger Slatt, University of Oklahoma, courtesy of Earth
Science World Image Bank.
Page 27
Sedimentary Basin
• Tectonically produced low area in Earth’s crust
where thick sediments accumulate.
• Basins form where the lithosphere has been
stretched or where nearby belts of thrusted crust
weight it down.
Sedimentary Rocks
Images courtesy of U.S. Geological Survey.
Page 28
Changes of Sea Level
• Sea level varies over time as continental glaciers
and mid-ocean ridges grow and shrink.
• During a transgression, the sea level rises and the
coastline moves inland.
• During a regression, the sea level drops and the
coastline moves seaward.
• Alternating transgressions and regressions are
often recorded in sedimentary basins.
Trees killed by sea-level rise,
Blackwater National Wildlife
Refuge, Maryland. ►
Sedimentary Rocks
Image courtesy of U.S. Fish and Wildlife Service.
Page 29