Transcript Sedimentary_MS

Sedimentary
Rocks
PRESSURE!
If You Are Going to be a Sedimentary Rock
…… Four Things Happen to You*
You - the clast or
particle will be:
1. Weathered
2. Transported
3. Deposited
4. Lithified
Perhaps several
times
+Unless
you precipitate (which we’ll get to later…..)
Weathered Chemically or Physically
Broken Away
Transported
By what agents of transportation?
How do they differ in what they
carry?
Gravity!
http://www.geo.duke.edu/geo41/geo41.htm
Deposited
“Low” - basin accumulates
sediment (preserved)
Go with gravity!
http://www.geo.duke.edu/geo41/geo41.htm
Buried and Lithified into Rock
• Uncompacted (loose)
sediment slowly becomes
rock through biological,
chemical and physical
changes.
• Diagenesis = Changes
from pressure, heat, chem.
– Physical - Compaction
– Chemical - Cementation
– <300°F (150°C)
– ~10-12 kilometers deep
Sediment & Sedimentary Rocks
Clastic Sedimentary Rocks
Sediment particles (skeletal, rock
fragment, mineral, plant
particles) derived from erosion
(breakdown / transport) of rock.
Carbonate /
Other Sedimentary Rocks
Press and Siever, 2000
Sediment & Sedimentary Rocks
• Sediment - loose
sedimentary particles
• Sedimentary Rock lithified (cemented,
compacted,
crystallization)
Press and Siever, 2000
Clasts - particles
Matrix - finer grained filler - deposited at same time
Cement - chemical precip.; crystalline - after deposition
• Rivers, wind, glaciers
weather and transport
sediment (erosion).
• When the transport agent
can no longer carry the
material, it is dropped or
deposited.
• The sediment has the
signature of the transport
agent and the environment
of deposition.
• Other sedimentary rocks
are produced by
organisms or precipitated
by physical processes.
Clastic
Sedimentary
Rocks
Clastic Sedimentary Rocks - Texture
– Size
– Sorting
– Shape
– Surface Texture
Provides clues to transportation and deposition history
Press and Siever, 2000
Texture - Size
Conglomerate - Boulder to granule (> 2 mm)
sized material - cemented by minerals or finer
particles. Rounded clasts (versus breccia).
Sandstone - Sand sized material cemented by
minerals or finer particles. 20% sed rx.
Siltstone - Silt-size material (1/256 - 1/16 mm);
can barely see grains - looks like mud / clay;
slightly rough to touch, gritty to taste;
commonly thin layers
Claystone or Shale - Finest mud-sized grains
(<1/256 mm) - can't see, feel, or taste grains
Claystones = no layers
Shales = split into layers (slate = meta)
Texture - Size
What was the
energy of the
transporting
agent?
Parent material may determine what is
available to transport
Press and Siever, 2000
Texture - Sorting
How much are all of the grains
the same?
• How was it transported /
deposited?
• How consistent was the
energy?
Press and Siever, 2000
http://www.science.ubc.ca/~geol202/sed/sili/sedstructures.html
Texture - Shape
Roundness - how
smooth are the edges?
Sphericity - how close is
it to a sphere?
How long was it in
transport?
Composition
Clasts:
• quartz (clear gray)
• feldspars (pink or white)
• olivine (green - igneous!)
• shell fragments (white - fizz)
• Rock fragments - PARENT!
Matrix
– May be too fine to determine
– Cement
• Calcite - fizzes
• Silica - hard, clear-ish
Maturity
• With time in transport - becomes more
texturally and compositionally mature:
• Textural Maturity - Grains become more
rounded, spherical, sorted – SMALLER!
• Mineralogical Maturity - Less durable
grains are broken down; more durable
grains remain
Sediment & Sedimentary Rocks
Clastic Sedimentary Rocks
Sediment particles (skeletal, rock
fragment, mineral, plant
particles) derived from erosion
(breakdown / transport) of rock.
Carbonate /
Other Sedimentary Rocks
Chemical precipitates (halite) or
biologically - produced
(organic) material (shell
fragments). In-situ.
Press and Siever, 2000
• Carbonate Rocks = chemical
or biological ppt; clastic or
crystalline - water
• Evaporites = chemical,
crystalline rocks formed by
precipitation of dissolved salts
during evaporation
• Miscellaneous = biologic
origin
What you have tells you
about the
environment of
deposition
Classification of Sediment & Sedimentary Rocks
Carbonate Rocks
Calcium carbonate dominant
constituent
Limestone - calcite or aragonite
(CaCO3) - usually from shell,
skeleton, or algae; inorganic
precipitation rare
• Fizzes with HCl / Vinegar
• Name from material (bioclastic
limestone, coquina, chalk,
micrite, oolite)
http://www.uky.edu/KGS/coal/webrokmn/pages/limestone.html
A Few Special Little Guys
• Chalk
– White Cliffs of Dover
– Coccoliths - carbonate
• Calcareous Ocean Deposits
• Foraminifers - single celled zooplankton
A Few Special Little Guys
• Diatomites / Cherts - silica
What Do
Carbonate
Rocks Tell You
About the
Environment?
Evaporites
Crystal precipitation
during evaporation
of salty water halite, gypsum,
anhydrite
http://www.dc.peachnet.edu/~pgore/geology/geo101/sedrx.htm#Silica
http://darkwing.uoregon.edu/~millerm/evaporite.html
http://www.emporia.edu/earthsci/museum/salt.htm
What Do Evaporites Tell You
About the Environment?
Coals
Coal = > 50% plantderived carbon and
silt or clay.
May see traces of
plants (roots, leaves,
etc)
What Do Coals Tell You
About the Environment?
Identify Away!
Weathering
Transport
Deposition
Lithification
What sedimentary rocks are where