Sediments and
Sedimentary Rocks
Tom Bean/DRK
L - 6: cd/EM - E
Sedimentary rocks
• 5 % by volume of the upper crust
• 75% by area of continental areas
• Often the only record of geologic
events:
e.g. The Himalayas will someday be
sandstone
Sedimentary Stages in the Rock Cycle
2 KINDS OF SEDIMENTARY
ROCKS
A. DETRITAL & CLASTIC - Rock
resulting from the consolidation of
loose sediment that has been
derived from previously existing
rocks and accumulated in layers
B. CHEMICAL - Rock formed by the
precipitation of minerals from
solution by either organic or
inorganic processes
Transport and deposition
of clastic sediments
• Movement of sediment by wind,
ice or water (GEOLOGIC
AGENTS).
• Mode of transport produces
distinctive deposits.
• Deposit as layers - beds/strata
Transport affects the
sediment in several ways Sorting:
measure of the variation in the
range of grain sizes in a clastic rock or
sediment
• Well-sorted sediments indicate that they have
been subjected to prolonged water or wind
action.
• Poorly-sorted sediments are either not farremoved from their source or deposited by
glaciers.
Sorting
Well-sorted
Poorly-sorted
Well-sorted Sand
Rex Elliott
Poorly-sorted Sand
Rex Elliott
Transport affects the sediment in
several ways - SHAPE
Roundness: measure of how
rounded the corners are
Sphericity: measure of how much it
is like a sphere
* Sorting, roundness, and
sphericity all increase with
LENGTH of transport.
Sorting
Roundness
Types of detrital rocks
Largely based on the size of the
particles, which may be anything.
•
•
•
•
•
•
Conglomerate (poorly sorted/round)
Breccia (poorly sort/angular)
Sandstone
(quartzite, arkose, greywacke)
Mudstone
Siltstone
Shale - most common rock on continents
Conglomerate
Breck Kent
Sandstone
Breck Kent
Shale
D. Cavagnaro/Visuals Unlimited
SEDIMENTARY ROCKS
CHEMICAL ROCK- Rock formed
by the precipitation of
minerals from solution by
either organic or inorganic
processes
Types of chemical
sedimentary rocks
Limestone
CaCO3
Chert
SiO2
Salt
NaCl, KCl
Gypsum
CaSO4 • 2H2O
Coal
altered organic debris
Limestone
Breck Kent
Halite
Breck Kent
Chert
Breck Kent
Fossiliferous Limestone
Peter Kresan
Chemical environments: Evaporites
Restricted environments such as
Mediterranean Sea & Texas coast
Minerals precipitate according to solubility.
Gypsum
CaSO4 •2H2O
Halite
NaCl
One Model for the
Formation of Evaporites
Chemical environments: Carbonates
Clear water — away from big rivers
(or volcanoes)
Warm water — subtropical to tropical
Shallow water -- two reasons:
Organic: sunlight only penetrates to
about 100 m
Inorganic: CCD so carbonates
dissolve
Foraminifer in the Eye of a
Needle
Chevron Corporation
Coral Reef Surrounding
Volcanic Island
Jean-Marc Truchet/Tony Stone Worldwide
Common Sedimentary Environments
Clues to interpreting
sedimentary depositional
environments
• Sedimentary structures
• Sorting, roundness, sphericity
• Sequence & kinds of beds
Sedimentary structures
Particular structural features can give
information about the environment
of deposition.
Structures also help determine if a
bed is right-side-up — important in
deformed rocks
Cross-bedded Sandstone
Peter Kresan
Varves record annual cycles in
glacial lakes
Turbidity currents
S. C. Porter
Modern Rippled Sand
Raymond Seiver
Ancient Ripple-marked Sandstone
Reg Morrison/Auscape
Fig. 7.9
Mudcracks
MODERN
ANCIENT
Bioturbation Tracks and Tunnels
Chip Clark
From Peat to Coal
The end