2. Intro to Sedimentary Rocks
• Produced from weathering products of pre-existing
rocks or accumulated biological matter
– Detrital (clastic) rocks produced from rock fragments
– Chemical rocks produced by precipitation of
dissolved ions in water
– Organic rocks produced by accumulation of biological
debris, such as in swamps or bogs
• Sedimentary rock types and sedimentary structures
within the rocks give clues to past environments
• Fossils in sedimentary rocks give clues to the history of
life
• Important resources (coal, oil) are found in sedimentary
rocks
3. Sediment
• Sediment - loose, solid particles originating
from:
– Weathering and erosion of pre-existing rocks
– Chemical precipitation from solution, including
secretion by organisms in water
• Classified by particle size
– Boulder - >256 mm
– Cobble - 64 to 256 mm
– Pebble - 2 to 64 mm
– Sand - 1/16 to 2 mm
– Silt - 1/256 to 1/16 mm
– Clay - <1/256 mm
4. From Sediment to
Sedimentary Rock
• Transportation
– Movement of sediment away from its source, typically by
water, wind, or ice
– Rounding of particles occurs due to abrasion during
transport
– Sorting occurs as sediment is separated according to
grain size by transport agents, especially running water
– Sediment size decreases with increased transport
distance
5. • Deposition
– Settling and coming to rest of transported
material
– Accumulation of chemical or organic sediments,
typically in water
– Environment of deposition is the location in which
deposition occurs
• Deep sea floor
• Beach
• Desert dunes
• River channel
• Lake bottom
From Sediment to
Sedimentary Rock
6. • Preservation
– Sediment must be preserved, as by burial with additional
sediments, in order to become a sedimentary rock
• Lithification
– General term for processes converting loose sediment into
sedimentary rock
– Combination of compaction and cementation
From Sediment to
Sedimentary Rock
7. Types of Sedimentary Rocks
• Detrital (clastic) sedimentary
rocks
– Most common sedimentary rock
type
– Form from cemented sediment
grains that come from pre-existing
rocks
• Chemical sedimentary rocks
– Have crystalline textures
– Form by precipitation of minerals
from solution
• Organic sedimentary rocks
– Accumulate from remains of
8. Sandstones
Conglomerate
s
Breccia
Shale/mudsto
nes
TYPES OF SEDIMENTARY ROCKS
Clastic rocks Chemical & Organic rocks
Evaporitic rocks
These rocks are formed
due to evaporation of
saline water (sea water)
eg. Gypsum, Halit
(rock salt)
Carbonate rocks
Form basically from
CaCO3 – both by
chemical leaching
and by organic
source
(biochemical) eg.
Limestone; dolomite
Organic rocks
Form due to
decomposition of
organic remains
under
temperature and
pressure eg.
Coal/Lignite etc.
9. formed from broken rock fragments
weathered and eroded by river, glacier,
wind and sea waves. These clastic
sediments are found deposited on
floodplains, beaches, in desert and on the
sea floors.
CLASTIC ROCKS
Clastic rockssolidify
• Clastic rocks are classified on the
basis of the grain size: conglomerate,
sandstone, shale etc.
10. Gravel
>256-2 mm
Sand
2- 0.062 mm
Clay
<0.004
mm
Silt
0.062-0.004 mm
Boulder: >256mm
Cobble: 64-256 mm
Pebble: 4-64 mm
Granule: 2-4mm
Fine gravel
11. Clastic rocks
mainly comprise
broken fragment
of older rock –
they are also know
as Terrigenous rocks
12. Any rock fragment
(size is > 4 mm=Pebble)
Fine-gravel/
Granule
(size <4mm)
Matrix:
is the finer
grains or
material that
surrounds the
larger clasts. It
consist of either
clay, silt and
sand.
Cement:
dissolved
substance
that
bounds the
sediments.
1. Calcareou
s
2. siliceous
13. Degree of roundness helps in knowing the distance of transportation
•Angular clasts- short distance transport from the source
•Rounded clasts- long distance transport
14. When clastic fragments are
cemented or undergo
consolidation they are called
CONGLOMERATES
Similarly when angular clasts
undergo consolidation they
are called BRECCIA
15. Sorting of the sediments also suggest the mode of deposition and
transportation.
Long distance transport= well-rounded and well-sorted
sediments,
Short distance transport = poorly sorted angular grains.
Also helps in knowing the energy conditions of the river.
17. Examples of clastic sedimentary rocks include
CONGLOMERATE
BRECCIA
SANDSTONESHALE
18. Clastic Sedimentary Rocks
• Breccia and Conglomerate
– Coarse-grained clastic sedimentary rocks
– The individual grains are larger than 2 mm
– Sedimentary breccia composed of coarse,
angular rock fragments cemented together
– Conglomerate composed of rounded gravel
cemented together
• Sandstone
– Medium-grained clastic sedimentary rock
– The individual grains of sandstone ranges from
0.062 to 2 mm
– Types determined by composition
• Quartz sandstone - >90% quartz grains
• Arkose - mostly feldspar and quartz grains
• Graywacke - sand grains surrounded by dark, fine-
grained matrix, often clay-rich
19. Clastic Sedimentary Rocks
• Shale
– Fine-grained clastic sedimentary rock
– Splits into thin layers (fissile)
– Silt- and clay-sized grains
– Sediment deposited in lake bottoms, river
deltas, floodplains, and on deep ocean
floor
• Siltstone
– Slightly coarser-grained than shales
– Lacks fissility
• Claystone
– Predominantly clay-sized grains; non-
fissile
• Mudstone
– Silt- and clay-sized grains;
massive/blocky
20. 2. Non-Clastic contain 2 types:
chemical and biochemical
CHEMICAL Sedimentary Rocks are made from mineral crystals
that formed from chemicals dissolved in water.
Here’s How They Form:
•The water in the oceans, lakes, and
underground is often full of dissolved
minerals like halite and calcite.
•Water evaporates leaving the solids
behind: rock salt is formed when salt
is left after evaporation and limestone
is formed when calcite is left behind
21. Limestone Cave
Chemical Sedimentary Rocks are also formed in caves where
mineral-rich water drips from the ceiling, creating stalactites
and stalagmites made out of limestone
Limestone
Examples of chemical
sedimentary rocks include
limestone and rock salt
22. BIOCHEMICAL OR ORGANIC Sedimentary Rocks are made
from remains of once-living plants or animals (organic matter)
COQUINA
Made from
shells
CHALK
Made from dead animals
Biochemical sedimentary rocks include: coquina, chalk, coal
and limestone
•this is the sedimentary rock type with the most fossils
•will be found near areas of lots of biological activity
COAL
Made from dead
plants LIMESTONE
with
fossils in it
23. Chemical Sedimentary Rocks
• Carbonates
– Contain CO3 as part of their chemical
composition
– Limestone is composed mainly of calcite
• Most are biochemical, but can be inorganic
• Often contain easily recognizable fossils
• Chemical alteration of limestone in Mg-rich water
solutions can produce dolomite
• Chert
– Hard, compact, fine-grained, formed almost
entirely of silica
– Can occur as layers or as lumpy nodules within
other sedimentary rocks, especially limestones
• Evaporites
– Form from evaporating saline waters (lake,
ocean)
– Common examples are rock gypsum, rock salt
24. Organics in Sedimentary Rocks
• Coal
– Sedimentary rock forming from compaction
of partially decayed plant material
– Organic material deposited in water with low
oxygen content (i.e., stagnant)
• Oil and natural gas
– Originate from organic matter in marine
sediment
– Subsurface “cooking” can change organic
solids to oil and natural gas
– Can accumulate in porous overlying rocks
25. Sedimentary Structures
• Bedding
• Cross-bedding
• Ripple marks
• Graded bedding
• Mud cracks
• Sedimentary structures
– Features within sedimentary
rocks produced during or
just after sediment
deposition
– Provide clues to how and
where deposition of
sediments occurred
26. • Bedding
• Layers in sedimentary rocks, caused by changes in
composition or grain size.
27. Sedimentary Structures
• Cross-bedding
– Series of thin, inclined layers within a
horizontal bed of rock
– Common in sandstones
– Indicative of deposition in ripples, bars,
dunes, deltas
28. • Ripple marks
– Small ridges formed on surface of sediment layer by moving wind or
water
29. • Graded bedding
– Progressive decrease in grain size from bottom to top of a bed
30. • Mud cracks
– Polygonal cracks formed in fine grained muddy sediments when they
dried.
– They are preserved when new sediments are deposited in these
cracks
31. Sedimentary Rock Interpretation
• Sedimentary rocks give important clues to the
geologic history of an area
• Source area
– Locality that eroded and provided sediment
– Sediment composition, shape, size and
sorting are indicators of source rock type
and relative location
• Depositional environment
– Location where sediment came to rest
– Sediment characteristics and sedimentary
structures (including fossils) are indicators
– Examples: glacial valleys, alluvial fans,
river channels and floodplains, lakes,
deltas, beaches, dunes, shallow marine,
reefs, deep marine
32. Plate Tectonics and
Sedimentary Rocks
• Tectonic setting plays key
role in the distribution of
sedimentary rocks
• Occurrence of specific
sedimentary rock types
can be used to
reconstruct past plate-
tectonic settings
• Erosion rates and
depositional
characteristics give clues
to each type of tectonic
