8. Types of sedimentary rocks
Chemical rocks – sediment
from ions that were once in
solution
Detrital rocks –sediment
transported as solid particles
9. Detrital sedimentary rocks
Constituents of detrital rocks can
include
Clay minerals
Quartz
Feldspars
Micas
Particle size is used to distinguish
among the various types of detrital
rocks
10. Detrital sedimentary rocks
Mudrocks: grains less than .06 mm
1. Mud: small particles easily kept in
suspension
Settles only in quiet water
Rock types include Shale: mud-sized particles
<.004 mm deposited in thin bedding layers
called laminae
The most common sedimentary rock
2. Larger mudrock grains called silts
silt-sized particles .004-.06 mm
Gritty grains can be felt
12. Detrital sedimentary rocks
Sandstones
Made of sand-sized particles .064 – 2
mm … Sand is a size!
Forms in a variety of environments
Sorting, angularity and composition
of grains can be used to interpret the
rock’s history
Quartz is the predominant mineral
(due to its durable nature)
14. Classifying Sandstones
Photomicrograph of quartz rich sandstone (Arenite)
Grains subangular to subrounded, sandstone is poorly sorted
Plagioclase grain
Making thin sections
15. Types of Sandstone
Quartz Arenite >90% quartz grains
Beach and dune deposits
Arkoses >25% feldspar, angular, poor
sort.
Transform boundaries; exposed granites
Any felsic rock eroded, not transported far
Graywackes Quartz, feldspar, volcanics
Port sorted, angular
Erosion of Island Arcs
Rift Valley Sediments
16. Detrital sedimentary rocks
Conglomerate and breccia
Both composed of particles > 2mm in
diameter
Conglomerate consists largely of
rounded clasts
Breccia is composed of large angular
particles
19. Energy
Coarse sediments are deposited in high
energy (fast water) environments such as
under breaking waves at the beach, or in
the beds of fast streams.
Fine sediments are deposited in low
energy environments, e.g. the slow water
of deep lagoons, the abyssal plain, etc.
20. Outcrop of conglomerate
with cobble-sized clasts
interbedded with sandstone
Conglomerates are fastwater sediments
“High Energy”
K.E. = 1/2mv2
In fast water, smaller sizes
swept away
21. Chemical sedimentary rocks
Precipitated material once in solution
Precipitation of material occurs two
ways:
Inorganic processes: the minerals
precipitate out of water
Organic processes: animals and plants
precipitate the minerals to use as shells
or skeletons
A foraminiferan,
a type of microfossil
http://www.ucmp.berkeley.edu/collections/micro.html
22. Common chemical sedimentary rocks
Limestone
Most abundant chemical rock
Made of the mineral calcite CaCO3
Marine biochemical limestones form
as coral reefs, coquina (broken
shells), and chalk (microscopic
organisms)
Inorganic limestones include
travertine (caves) and oolitic
limestone (Bahamas)
27. Other chemical sedimentary rocks
Chert
Made of microcrystalline quartz
Usually deposited as siliceous ooze in deep
oceans (can be diatomaceous)
chert
Diatomaceous chert
28. Other chemical sedimentary rocks
Dolostone (made of mineral Dolomite)
Like Calcite, but some Ca is replaced by Mg
The Dolomites, sediments thrust up when the Alps formed
29. Evaporation
How to make Dolomite
6_19
Limestone
Seawater enriched
in Mg2+
Mg2+ -rich seawater circulates
Dolostone
through porous limestone
Mg2+ replaces some of the
Ca2+ in limestone
31. Chemical sedimentary rocks
Common chemical sedimentary rocks
Coal
Different from other rocks because
it is composed of organic material
Stages in coal formation (in order)
1. Plant material
2. Peat
3. Lignite
4. Bituminous
33. Sedimentary Environment
Is the geographic setting where
sediment accumulates
Determines nature of sediment that
accumulates (grain size, shape, etc.)
34. Character of detrital sediments depends on time, distance,
and energy. For 6_5
example, in streams:
Particles are large and
irregular, and consist of
a variety of lithologies,
including the least
resistant.
Particles are mid-sized
and of intermediate
sphericity, and include
resistant and nonresistant
lithologies.
HIGHLANDS
LOWLANDS
Particles are small and
nearly spherical, and
consist mainly of the
most resistant lithologies,
such as quartz.
NEAR-COASTAL
36. Sediment Maturity
Sediment Maturity is
indicated by decreasing
clay content, increasing
degree of size sorting,
and increasing rounding
of grains within the
deposit
Poorly sorted
Well sorted
Sorting refers to the range
of particle sizes in the
sediment
Well-sorted - uniform grain
size
Poorly-sorted - mixture of
grain sizes
immature
OCNG 251
mature
Texas A&M University
Oceanography
37. We can recognize past floods
Floods change the local
conditions
6_6
Fine-grained sediment
on floodplain
Older sediment
1
Pre-flood
Bounders on
bottom, sands
and muds
suspended
Flood water
Erosion of uppermost
fine-grained sediment
2 Flood stage
Flood: One source of
Graded Bedding
3
Post-flood
Fining-upward
flood deposit
Bedding plane is an
erosional surface
38. Types of sedimentary environments
Continental
Streams
cross beds from ripples, fine mud w/ cracks
on floodplain
Lakes – Fine parallel lamellae - Varves
Wind (dunes) well sorted, frosted grains
Glacial Ice: Poorly sorted, unstratified
Marine
Shallow (< 200 meters deep) carbonate-rich
sands, muds
Deep (seaward of continental shelves)
microfossils, volcanic ash, turbidites
39. Types of sedimentary environments
Transitional (shoreline)
Tidal flat Sands w/ symmetrical ripples
Lenses of tidal creek muds
Lagoons – including Bays behind Barrier
Islands.
Organic rich black muds and sands
Deltas
Complex, e.g. Sandstones w/ large
foresets at seaward face
40. A picture glossary of sedimentary
Turbidite: underwater landslide
= graded bedding
environments
41. Sedimentary Facies
Different sediments accumulate
next to each other at same time
Each unit (called a facies) possesses
a distinctive characteristics
reflecting the conditions in a
particular environment
The merging of adjacent facies
tends to be a gradual transition
42. Some facies in an oversimplified drawing
Abyssal Ooze
Stillwater muds
Nearshore sands
43. Sedimentary structures
Tell us something about past
environments
Types of sedimentary structures
Strata, or beds (most
characteristic of sedimentary
rocks)
-bedding planes that separate
strata caused by variation in
deposition
46. Recognizable Sedimentary Structures
Types of sedimentary structures 1
Graded beds: waning flow (flood, turbidite)
Sediments become coarser upward
Determines “Right side up”
47. Graded Beds – grains fine upward
Note: Beds were tilted from horizontal after deposition
48. Recognizable Sedimentary Structures
Ripples
Irregularities in bottom sediment lead to
ripples
Asymmetric types indicate flow
direction.
Symmetric types formed in tidal areas
49. Cross Beds – ripples in cross section
In cross section these look like lines
at an angle to the horizontal – “cross
beds”
Form determined by velocity and size
of particles.
51. Cross bedding in Sand Dune deposits
Navaho Sandstone
Sand Dune? Look for Frosted Grains
Shoreline of
an interior
seaway
Sandstone deposited
in ancient sand dunes
Frosted Grains
55. Sedimentary Environments
Sediments are formed in many different
environments
Each have characteristic appearance
today, features that allow them to be
recognized in the geologic record
56. Fresh Water Facies
Streams (includes big Rivers), with
floodplains and levees, called fluviatile. The
Point Bar Sequence is typical for meandering
streams. Cutoffs generate Oxbow deposits.
•
High gradient streams with high sediment
load are Braided.
• Lake deposits called lacustrine, generally
still waters, often varved deposits if winters cold
http://hays.outcrop.org/gallery/rivers/arid_meander?full=1
59. Terms for Marine (i.e. Ocean) Environments
6_27
and some characteristic sediment facies
Continental
shelf
Shallo
w
marin
e
Continental
slope
Abyssal
Plain
Dee
p ma
rine
Submarine
volcanoes
60. Facies changes due to rising sea level - water getting deeper everywhere
River
6_29
Direction
of migration
of shoreline, and landward
shift of sedimentary facies
Time B
Shoreline at
time B
Time A
Shoreline at
time A
Shallow
marine
Beach
River
Sea level
rising
Deep
marine
Shallow
marine
Beach
Comparison of sediments deposited
Deep
marine
Shallow
marine
Deposited
at time A
Deposited
at time B
REMEMBER: the facies
follow the shoreline
61. Fossils: Evidence of past life
By definition, fossils are the traces or
remains of prehistoric life now preserved in
rock
Fossils are generally found in sediment or
sedimentary rock (very rarely in
metamorphic or igneous rocks)
62. Fossils: Evidence of past life
Geologically fossils are important for
several reasons
Aid in interpretation of the geologic past
Serve as important time and environment
indicators
Allow for correlation of rocks from different
places
63. 3 Billion Year Old Algal Mounds (Stromatolites) Australia
CO2 in
O2 out
