CHAPTER 5—THE SEDIMENTARY ARCHIVES
CHAPTER OVERVIEW
The title of this chapter emphasizes the historical significance of sedimentary rocks as indicators of past
environments. When interpreting sedimentary rocks, it is important to consider the tectonic elements of a
continent as well as particular areas such as cratons, orogenic belts, shields, and platforms. These
tectonic settings determine the type of depositional environments, for example, marine, continental, or
transitional. These listed environments of deposition are associated with specific types of sandstones,
shales, limestones, and other sedimentary rocks. Some positive general indicators relate to color, grain
size, sorting, textural maturity, and sedimentary structure. The field of stratigraphy is introduced using
examples of how it is applied to the geologic column and world wide correlations. This chapter concludes
with a description of the different types of maps used by geologists and the economic resources found in
sedimentary rocks.
LEARNING OBJECTIVES
By reading and completing information within this chapter, you should gain an understanding of the
following concepts:
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Explain how the tectonic setting is reflective of the different kinds of sedimentary rocks.
Describe the different kinds of tectonic settings and how each is reflective of the size and
shape of clastic particles.
Define the principle elements of a continent, including cratons, shields, platforms and mobile
belts.
Describe the different kinds of environments of deposition (marine, continental, and
transitional) and characters of each.
Discuss how sedimentary rock color is indicative of some of the different environments.
Discuss the types of sedimentary rocks and how each is interpretative of different
environments: sandstones, shales, and carbonates.
Discuss how the sedimentary rock record is interpretative through rock units, facies, sea level
changes, correlation, and unconformities.
Describe the different types of mapping used in environmental interpretation including
geologic maps, paleogeographic maps, isopoch maps, and lithofacies maps.
CHAPTER OUTLINE
I.
Tectonic Setting is the Biggest Factor in Sediment Deposition
A. Depositional Basins
B. Cratons, Shields, Platforms, and Orogenic Belts
II.
Environments Where Deposition Occurs
A. Marine Depositional Environments
1. Shallow Marine (Continental Shelf) Environment
2. Continental Slope Environment
3. Deep Marine Environment
B. Continental Depositional Environments
1. Stream Deposits
2. Alluvial Fans
3. Lake Deposits (Lacustrine)
4. Glacial Deposits
5. Wind Deposits
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Page 1
C. Transitional Depositional Environments
1. Deltas
2. Barrier Islands, Lagoons, Tidal Flats, and Estuaries
III.
What Rock Color Tells Us
A. Shades of Black
B. Hues of Red and Other Colors
IV.
What Rock Texture Tells Us
A. Grain Size and Sorting
B. The Shape of Grains
C. Orientation of Grains
V.
What Sedimentary Structures Tell Us
VI.
What Four Sandstone Types Reveal About Tectonic Settings
A. Maturity
B. Quartz Sandstone
C. Arkose
D. Graywacke
E. Lithic Sandstone
VII.
Limestones and How They Form
VIII.
Organizing Strata to Solve Geologic Problems
A. Rock Units (Formally Called Lithostratigraphic Units)
B. How We Name Rock Units: Geography + Rock Type
C. What Are Facies
IX.
Sea-Level Change Means Dramatic Environmental Change
X.
Stratigraphy and the Correlating of Rock Bodies
A. Correlating Rock Bodies
B. Correlation Methods
C. Using Lithostratigraphic Correlation
D. Using Chronostratigraphic Correlation
XI.
Unconformities: Something is Missing
XII.
Depicting the Past
A. Geologic Columns and Cross-Sections
B. Geologic Maps
C. Paleogeographic Maps
D. Lithofacies Maps
Chapter 1— The Sedimentary Archives
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KEY TERMS (pages are given in parentheses)
angular unconformity (110): An unconformity below which older strata dip at a different angle (usually
steeper) than the overlying strata.
alluvial fan (86): The result of abrupt deposition when stream-transported materials accumulate quickly
where a rapidly flowing river emerges from a mountainous area onto a flat plain.
arkose (99): Sandstones containing 25% or more of feldspar (derived from erosion of a granitic source
area).
barrier island (89): A transitional (between marine and non-marine) environment builds islands parallel
to shorelines by wave and current action.
biofacies (104): When a facies can be distinguished because of biologic (rather than lithologic)
differences, it can be designated a biofacies. Fossil assemblages differ allowing for the recognition of
different environments.
biostratigraphic correlation (108): The correlation of rock units by the use of its fossil content.
cement (in clastic sedimentary rock) (91): A chemical precipitate that crystallizes in the voids between
grains following deposition. Some cements include silica (SiO 2), and calcium carbonates (CaCO3).
chronostratigraphic correlation (108): Correlation that links units by age equivalences as determined
by fossils or radioactive dating methods.
clast (82): An individual grain, fragment, or constituent of detrital sediment or sedimentary rock produced
by physical breakdown of a larger mass.
continental shelf (84): Oceanic topographic regions included in the shallow marine realm. They are
nearly flat, smooth surfaces that fringe the continents in widths that range from only a few kilometers to
about 300 km at depths that ranges from low tide to about 100 meters. They resemble continents in their
structure and composition.
continental slope (85): Those areas of the ocean floor that extend from the seaward edge of the
continental shelves down to the ocean depths. The surface is inclined from 3 to 6 degrees.
correlation (107): Determination of the equivalence of rock bodies in different locations.
craton (82): The long-stable region of a continent, commonly with Precambrian rock, either at the surface
or only thinly covered with younger sedimentary rocks.
cross-bedding (94, 96): An arrangement of laminae or thin beds traverse to the planes of stratification.
The inclined laminae are usually at inclinations of less than 30 degrees and may be either straight or
concave.
delta (82): Transitional environments (between marine and non-marine) form deltas when streams enter
bodies of standing water, undergo an abrupt loss of velocity, and drop their load of sediment.
discharge (of stream) (86): The rate of stream flow at a given instant expressed in terms of volume per
unit of time.
disconformity (110): A variety of unconformity in which bedding planes above and below the plane of
erosion or non-deposition are parallel.
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eolian environment (88): Environment in which wind is an important agent of sediment transport and
deposition.
epicontinental sea (107): In the geologic past, there have been repeated advances of the sea into lowlying regions of the interiors of continents. The resulting inland sea is termed epeiric, meaning “a sea over
a continent.”
estuary (89): The seaward mouth of rivers that are engulfed by the sea. Freshwater from streams and
saltwater from the ocean are brought together. Mixing may occur, and typically, the lighter freshwater will
flow seaward above the denser saltwater.
facies (104): A particular aspect of sedimentary rocks that is a direct consequence of sedimentation in a
particular depositional environment. It allows identification of the environment of deposition.
ferric (91): The combination of two iron atoms with three oxygen atoms. Ferric minerals include hematite
and tend to color the rock red, brown, or purple.
ferrous (91): Occurs when oxygen is in short supply such as stagnant lake or ocean where the iron
atoms have lost only two electrons.
formation (103): A mapable, lithologically distinct body of rock having recognizable contacts with
adjacent rock units.
geologic map (103): Map showing the distribution of rocks of different kinds and ages that lie directly
beneath the loose rocks and soil covering most areas of the surface.
graded bedding (95): Consists of repeated beds, each of which has the coarsest grains at the base and
successively finer grains nearer the top.
graywacke (99): Immature sandstone consisting of significant quantities of dark, very fine-grained
material (usually clay, chlorite, micas, and silt). There is little or no cement, and the sand-sized grains are
not in close contact because they are separated by the finer matrix particles. The matrix constitutes about
30% of the rock, with the remaining coarser grains consisting of quartz, feldspar, and rock particles.
group (104): The combination of formations into larger units.
hematite (90): Ferric mineral that tends to color the rock red, brown, or purple.
isopach map (113): A map depicting the thickness of a sedimentary unit.
lacustrine deposit (86): Pertaining to lakes, as in lacustrine sediments (lake sediments). Sediments that
are deposited in lakes.
lagoon (89): Water-filled area found between the mainland and a barrier island. Represents a transitional
environment (between marine and non-marine).
lithic sandstone (99): A rock that has a more transitional composition and texture is termed a lithic
sandstone. Feldspars are relatively scarce, whereas quartz, muscovite, chert, and rock fragments are
abundant. Fine-grained detrital matrix does not exceed 15% and the remaining voids are filled with
mineral cement or clay. Quartz grains are better rounded and more abundant, the sorting is better, and
the quantity of matrix is lower than in greywacke.
lithofacies (104): When the differentiating characteristics are lithologic (rather than biologic), facies can
be designated as lithofacies.
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lithostratigrapic correlation (115): Bodies of rock identified by their distinctive lithologic and structural
features without regard to time boundaries. Features used include texture, grain size, clastic or
crystalline, color, composition, thickness, type of bedding, nature of organic remains, and appearance of
the unit in surface exposure.
matrix (in clastic sedimentary rock) (98): A category of bonding material that consists of finer clastic
particles (often clay) that were deposited at the same time as the larger grains and that fill the crevices
between them.
maturity (of sandstone) (98): Aggregates of well-rounded, well-sorted, highly stable minerals (such as
quartz).
member (104): Distinctive smaller units within formations.
mud cracks (94, 97): Indicate drying after deposition. Developed by shrinkage of mud or clay on drying
and are most abundant in the subaerial environment.
nonconformity (111): An unconformity developed between sedimentary rocks and older plutons or
massive metamorphic rocks that had been exposed to erosion before the overlying sedimentary rocks
were deposited.
offlap sequence (104): A sequence of sediments resulting from a marine regression and characterized
by an upward progression from offshore marine sediments (often limestone) to shales and finally
sandstones (above which will follow an unconformity).
onlap sequence (104): A sequence of sediments resulting from a marine transgression. Normally, the
sequence begins with a conglomerate or sandstone deposited over an erosional unconformity and
followed upward in the vertical section by progressively more offshore sediments.
orogenic belt (83): Great linear tracts of deformed rocks, primarily developed near continental margins
by compressional forces accompanying mountain building.
paleogeographic map (113): A map showing the geography of a region or area at some specific time in
the geologic past.
paraconformity (111): Recognized as a type of unconformity only by missing fossil zones.
platform (83): That part of a craton covered thinly by layered sedimentary rocks and characterized by
relatively stable tectonic conditions.
quartz sandstone (98): Characterized by the dominance of quartz with little or no feldspar, mica, or fine
clastic matrix. Quartz grains are well sorted and well rounded. Commonly held together by such cements
as calcite and silica.
red beds (90): Prevailing red, usually clastic sedimentary deposits.
ripple marks (95): Commonly seen sedimentary features that develop along the surface of bedding
planes. Symmetric ripple marks are formed by the oscillatory motion of water beneath waves. Asymmetric
ripple marks are formed by air or water currents and are useful in indicating the direction of movement of
currents.
rock unit (= lithostratigraphic unit) (103): Bodies of rock identified by their distinctive lithologic and
structural features without regard to time boundaries. Features used include texture, grain size, clastic or
crystalline, color, composition, thickness, type of bedding, nature of organic remains, and appearance of
the unit in surface exposure.
Chapter 1— The Sedimentary Archives
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Page 5
rounding (of sedimentary particles) (93): A particle becomes rounded by having sharp corners and
edges removed by impact with other particles. The roundness can be used to infer the history of abrasion.
It reflects the distance the particles had traveled, the transporting medium, and the rigor of transport.
Wind is the best transport medium.
scour marks (97): A mark produced by the cutting or scouring action of a current flowing over the bottom
of a river or body of water.
shield (82): Large areas of exposed ancient crystalline rocks; a component of cratons.
sorting (91): A measure of the uniformity of the sizes of particles in a sediment or sedimentary rock.
sphericity (of sedimentary particles) (93): A descriptive term regarding shape of a particle and how
closely the grain approaches the shape of a sphere.
stratigraphy (107): The science of rock strata; concerned with all characters and attributes of rock as
strata, and their interpretation in terms of mode of origin and geologic history.
stream deposits (86): Sand, silt, and clay along the banks, bars, and floodplains of streams. Discharge
will alter water velocity and type of sediment being transported.
structural cross-section (113): A cross-section showing the features transected by a vertical plane. It is
a level line that is parallel to sea level.
tectonics (82): The structural behavior of a region of the Earth’s crust.
tidal flat (89): Represents a transitional environment (between marine and non-marine). Mud-covered
flats that are alternately inundated and drained of water by tides.
turbidite (86): Sediment deposited from a turbidity current and characterized by graded bedding and
moderate to poor sorting.
turbidity current (86): A mass of moving water that is denser than surrounding water because of its
content of suspended sediment and that flows along slopes of the sea floor as a result of that higher
density.
unconformity (110): An erosional gap or hiatus in a rock record. A surface separating an overlying
younger rock formation from underlying formations and representing an episode of erosion or
nondeposition.
Walther’s Principle (106): Walther recognized onlap and offlap patterns of sedimentations. He observed
that the succession of facies occurring laterally is also seen in vertical succession of facies. This
relationship, in which the vertical succession of facies corresponds to the lateral succession, is known as
Walther’s Principle.
Chapter 1— The Sedimentary Archives
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Page 6
MULTIPLE-CHOICE QUESTIONS
1.
The term used for the central, topographically subdued region of a continent is
a. orogenic syncline.
c. craton.
b. crustal trench.
d. tectonic subduction zone.
2.
What is the proper order of these clastic rocks from coarsest to finest texture?
a. sandstone, shale, siltstone, claystone
b. sandstone, siltstone, shale, claystone
c. shale, sandstone, siltstone, claystone
d. siltstone, claystone, sandstone, shale
3.
What is the smallest particle size found in sedimentary rocks?
a. silt
c. fine sand
b. clay
d. granules
4.
Which of the following sedimentary rock types does not fit within the clastic grouping?
a. shale
c. limestone
b. sandstone
d. conglomerate
5.
Which of the following is not a primary sedimentary structure?
a. mud cracks
c. folds
b. cross bedding
d. ripple marks
6.
The three major types of environments of deposition are
a. continental slopes, rises, shelves.
b. continental slopes, marine, nonmarine.
c. transitional, marine, nonmarine.
d. continental slopes, marine, lagoonal.
7.
The characteristic appearance or aspect of a rock from which its environment of deposition can be
determined is
a. biolithic zone.
c. facies.
b. isopach zone.
d. paleoclimatic zone.
8.
Transitional sandstone in which feldspars are relatively scarce and quartz muscovite and chert are
abundant; the quartz grains that are more rounded and abundant are called
a. arkoses.
c. graywackes.
b. orthoquartzites.
d. subgraywackes (lithic sandstone).
9.
What are immature sandstones consisting of significant quantities of dark, very fine-grained
materials with a fine matrix that consists of clay, chorite, micas and silt?
a. arkoses
c. graywackes
b. orthoquartzites
d. subgraywackes
10.
A type of sandstone that may develop as a basal sandstone derived from the erosion of granitic
coastal area experiencing an advance of the sea or in adjacent areas adjacent to granite mountains
is
a. arkoses.
c. orthoquartzite.
b. subgraywacke.
d. graywacke.
11.
A map showing the geography of a region or area at some specific time in the geologic past is
a. a paleogeographic map.
c. an isopach map.
b. a geologic interval map.
d. a lithofacies map.
Chapter 1— The Sedimentary Archives
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Page 7
12.
Lithofacies maps are useful in determining changes mostly in which of the following areas?
a. sea floor spreading
b. geosyncline formation
c. zones of tectonic instability
d. aerial variation in the overall lithologic character of a given stratigraphic unit
13.
A map prepared by geologists to illustrate changes in the thickness of a formation or time rock unit
is a (an)
a. paleoclimatic map.
c. lithofacies map.
b. paleogeographic map.
d. isopach map.
14.
This method of correlation links rock units by age equivalences, determined by fossils or radioactive
dating.
a. lithostratigraphic
c. chronostratigraphic
b. biostratigraphic
d. paleostratigraphic
15.
Spherical grains of concentric laminated calcium carbonate which are formed in shallow, saline
marine conditions are called
a. crinoids.
c. blastoids.
b. ooid.
d. septarian nodules.
16.
This type of unconformity is characterized by stratified sedimentary rocks resting on older igneous
or metamorphic rocks.
a. angular unconformity
c. disconformity
b. nonconformity
d. paraconformity
17.
A ferric mineral that tends to color rock red, brown, or purple and are dubbed “red beds.”
a. hematite
c. graywacke
b. micrite
d. orthoclase feldspar
18.
Lithostratigraphic units are bodies of rock having distinctive features without regard to time
boundaries.
a. time-rock unit
c. rock units
b. formation
d. lithofacies unit
19.
Four sedimentary structures are formed during or after deposition, but before lithification. Which
one of the following would not be included?
a. mud cracks
c. graded-bedding
b. cross-bedding
d. scour marks
20.
A body of rock that can be recognized wherever it occurs by the characteristics of composition,
texture, or color is
a. time rock.
c. formation.
b. rock interval.
d. rock unit.
Chapter 1— The Sedimentary Archives
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Page 8
FILL IN THE BLANK
1.
The study of the deformation or structural behavior of a large area of the Earth’s crust over a long
period of time is
.
2.
Hues of brown, red, and green often occur in sedimentary rocks as a result of their ________
content.
3.
Geologists designate strata colored in shades of red, brown, or purple by ferric iron as _____
.
4.
The size, shape, and arrangement of mineral and rock grains in a rock constitute its
.
5. One category of bonding material that consists of finer clastic particles (often clay) that were
deposited at the same time as the larger grains and that fill the crevices between them is called
6.
An expression of the range of particle sizes deviating from the average size is
.
7.
The sandstones that are clastic rocks characterized by a dominance of quartz with little or no
feldspar, mica, or fine clastic matrix are
.
8.
The immature sandstones that consist of significant quantities of dark, very fine-grained material
are
.
9.
Quartz sandstone, arkose, and graywacke are rather distinct kinds of sandstones. A rock that has
a more transitional composition and texture is termed a
.
10.
The general appearance or aspect of a rock from which its environment of deposition can be
inferred is a sedimentary
.
11.
A map showing the geography of a region or area at some specific time in the geologic past is
termed a
map.
12.
Maps prepared by geologists to illustrate changes in the thickness of a formation or timestratigraphic unit are called
maps.
13.
_____________________ ____________________ form a shallow ocean environment near the
shore.
14.
During an __________ ___________ world temperatures drop and more of the planet’s water
becomes frozen in glaciers and polar ice caps.
15.
_____________ ______________ form when fast-moving currents begin to slow, dropping larger
particles (cobbles then pebbles) followed by progressively finer grains (sand, then salt, then clay).
Chapter 1— The Sedimentary Archives
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.
Page 9
TRUE/FALSE
1.
The three major environments of deposition are marine, continental, and fluvial.
2.
Small-scale, wave-like structures on bedding planes produced by running water are called
flute casts.
3.
A rock unit deposited during a marine transgression becomes younger in a seaward direction.
4.
Sedimentary rocks represent the material record of environments that once existed on the
earth.
5.
Alluvial fans occur when streams enter bodies of standing water, undergo an abrupt loss of
velocity, and drop their load of sediment.
6.
A time-rock unit differs from a rock unit in that the time-rock unit is an assemblage of strata
deposited within a particular interval of time.
7.
Lacustrine deposits are accumulations of sediment that form where a stream flows into
relatively quiet water.
8.
On the landward side of lagoons are almost featureless, low-lying plains called tidal flats.
9.
Deltas are the seaward mouths of rivers drowned by the sea.
10.
Sorting is a geologic term for the degree to which sediment and particles in sedimentary
rocks are uniform by particle size.
Chapter 1— The Sedimentary Archives
© 2013 JOHN WILEY & SONS, INC. ALL RIGHTS RESERVED.
Page 10
ANSWER KEY
Multiple Choice
1. c
2. b
3. b
4. c
5. c
6. c
7. c
8. d
9. c
10. a
11. a
12. d
13. d
14. c
15. b
16. b
17. a
18. c
19. d
20. d
Fill Ins
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
tectonics
iron oxide
red beds
texture
matrix
sorting
quartz
graywacke
lithic (subgraywacke)
facies
Paleogeographic
isopach
Continental shelves
Ice Age
Graded beds
Chapter 1— The Sedimentary Archives
© 2013 JOHN WILEY & SONS, INC. ALL RIGHTS RESERVED.
True/False
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
F
F
F
T
F
T
F
T
F
T
Page 11
Chapter 5—The Sedimentary Archives
RESPONSES TO QUESTIONS ACCOMPANYING SELECTED FIGURES
FIGURE 5–2 (p. 84) Fossils would be the most diagnostic feature. One would look for fossils of nonmarine crustaceans, mollusks, freshwater fish, and insects. There would be an absence of marine
invertebrates. Other clues might be desiccation features such as mudcracks and finely laminated (varved)
shales.
FIGURE 5–5 (p. 86) Graywacke (immature sandstone) is characteristic of deep-sea fan deposits.
FIGURE 5–6 (p. 87) Quartz and feldspar would be abundant in the debris produced by the weathering of
granite. Clay, which also is silicate mineral, is another product of the weathering of granite.
FIGURE 5–9 (p. 88) A delta would cease to prograde if wave current action removed sediment faster than
it could be supplied by the stream. Progradation also might cease if the supply of sediment from the
stream diminished.
FIGURE 5–10 (p. 89) Coarser sediments occur along the windward side of the barrier island because
wave action removes finer particles, leaving the heavier material to accumulate.
FIGURE 5–12 (p. 92) Graywacke is an immature sandstone.
FIGURE 5–15 (p. 94) Multiple impacts during transport cause feldspar grains to break along cleavage
planes, imparting angularity. Quartz has no cleavage and is harder.
FIGURE 5–17 (p. 95) The walls of mudcracks converge downward so as to form a V profile, and the point
of the V indicates the downward direction.
FIGURE 5–18 (p. 96) Current flowed from right to left, as indicated by the flattening of the inclined
laminae at the bottom of the beds.
FIGURE 5–21 (p. 97) Asymmetric ripple marks are formed by currents. They are commonly formed in
shallow near-shore sandy deposits worked by currents, but they also may occur in deep parts of the
ocean as a consequence of turbidity current deposition.
FIGURE 5–23 (p. 98) Overturned beds are common in orogenic belts around the world.
FIGURE 5–25 (p.101) As a result of wave action, the sands are likely to exhibit ripple marks in addition to
having such textural features as good sorting and good rounding.
FIGURE 5–25 (p. 101) Arkose has poor sorting. Because of the clay and other fine particles between the
larger grains, fluids would not pass through this rock readily, and it is unlikely to have good permeability.
FIGURE 5–44 (p. 112) An onlap or marine transgression is indicated by the fining upward sequence of
quartzite (formerly sandstone), followed upward by shale, siltstone, and finally limestone.
FIGURE 5–46 (p. 114) The oldest rock unit seen at the surface along A-A’ is the sandstone. The siltstone
is the youngest rock unit.
FIGURE 5–51 (p. 117) Ash from volcanic eruption may be spread across a wide area in what amounts to
a “geologic instant.” As a result, it is the same age wherever it occurs, and its age can be ascertained
through the use of isotopic radioactive dating methods.
Chapter 1— The Sedimentary Archives
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