Chapter 5—The Sedimentary Archives
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: i.e. cratons,
orogenic belts, shields and platforms. These tectonic settings determine the type of
depositional environments, i.e. 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:








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, 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, lithofacies maps.
CHAPTER OUTLINE
I.
Tectonic Settings 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
Chapter 5—The Sedimentary Archives
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 5—The Sedimentary Archives
KEY TERMS
(Pages 77–117)
angular unconformity (106): An unconformity below which older strata dip at a
different angle (usually steeper) than the overlying strata.
alluvial fan (82): 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 (95): Sandstones containing 25% or more of feldspar (derived from erosion of a
granitic source area).
barrier island (85): A transitional (between marine and non-marine) environment
builds islands parallel to shorelines by wave and current action.
biofacies (100): 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 (104): The correlation of rock units by the use of its fossil
content.
cement (in clastic sedimentary rock) (87): A chemical precipitate that crystallizes in
the voids between grains following deposition. Some cements include silica (SiO2), and
calcium carbonates (CaCO3).
clast (80,87): An individual grain, fragment, or constituent of detrital sediment or
sedimentary rock produced by physical breakdown of a larger mass.
continental shelf (80): 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 (82): 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 ٱ‬to 6‫ٱ‬.
chronostratigraphic correlation (104): Correlation that links units by age
equivalences as determined by fossils or radioactive dating methods.
craton (79): 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 (91, 94): 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 (83): 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) (82): The rate of stream flow at a given instant expressed in
terms of volume per unit of time.
disconformity (106): A variety of unconformity in which bedding planes above and
below the plane of erosion or non-deposition are parallel.
eolian environment (83): Environment in which wind is an important agent of
sediment transport and deposition.
Chapter 5—The Sedimentary Archives
epicontinental (epeiric sea) (103): In the geologic past, there have been repeated
advances of the sea into low-lying regions of the interiors of continents. The resulting
inland sea is termed epeiric, meaning “a sea over a continent.”
estuary (86): 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 (100): 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 iron oxide (86): 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 (86): Occurs when oxygen is in short supply such as stagnant lake or ocean
where the iron atoms have lost only two electrons.
formation (99): A mapable, lithologically distinct body of rock having recognizable
contacts with adjacent rock units.
geologic map (107): 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 (91, 94): Consists of repeated beds, each of which has the coarsest
grains at the base and successively finer grains nearer the top.
graywacke (95): 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 (100): The combination of formations into larger units.
hematite (86): Ferric mineral that tends to color the rock red, brown, or purple.
isopach map (114): A map depicting the thickness of a sedimentary unit.
lacustrine deposit (83): Pertaining to lakes, as in lacustrine sediments (lake
sediments). Sediments that are deposited in lakes.
lagoon (85): Water-filled area found between the mainland and a barrier island.
Represents a transitional environment (between marine and non-marine).
lithic sandstone (97): 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 (100): When the differentiating characteristics are lithologic (rather than
biologic), facies can be designated as lithofacies.
lithostratigrapic correlation (104): 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 5—The Sedimentary Archives
matrix (in clastic sedimentary rock) (87): 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) (95): Aggregates of well-rounded, well-sorted, highly stable
minerals (such as quartz).
member (100): Distinctive smaller units within formations.
mud cracks (91, 94): Indicate drying after deposition. Developed by shrinkage of mud
or clay on drying and are most abundant in the subaerial environment.
nonconformity (106): 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 (100): 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 (100): 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 (79): 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.
platform (79): That part of a craton covered thinly by layered sedimentary rocks and
characterized by relatively stable tectonic conditions.
quartz sandstone (95): 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 (86): Prevailing red, usually clastic sedimentary deposits.
ripple marks (93): 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) (99): 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.
rounding (of sedimentary particles) (89): 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 (94): A mark produced by the cutting or scouring action of a current
flowing over the bottom of a river or body of water.
shield (79): Large areas of exposed ancient crystalline rocks. A component of cratons.
Chapter 5—The Sedimentary Archives
sorting (88): A measure of the uniformity of the sizes of particles in a sediment or
sedimentary rock.
sphericity (of sedimentary particles) (89): A descriptive term regarding shape of a
particle and how closely the grain approaches the shape of a sphere.
stratigraphy (103): 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 (82): 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 (107): A cross-section showing the features transected by a
vertical plane. It is a level line that is parallel to sea level.
tectonics (78): The structural behavior of a region of the Earth’s crust.
tidal flat (85): Represents a transitional environment (between marine and nonmarine). Mud-covered flats that are alternately inundated and drained of water by tides.
till (83): Unconsolidated, unsorted, unstratified glacial debris.
turbidite (82): Sediment deposited from a turbidity current and characterized by
graded bedding and moderate to poor sorting.
turbidity current (82): 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 (105): 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 (101): 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 5—The Sedimentary Archives
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. greywacke.
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 5—The Sedimentary Archives
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
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 Correlation
c. Chronostratigraphic
Correlation
b. Biostratigraphic Correlation
d. Paleostratigraphic Correlation
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 5—The Sedimentary Archives
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 finegrained 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 time-stratigraphic 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 5—The Sedimentary Archives
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 5—The Sedimentary Archives
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
True/False
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
F
F
F
T
F
T
F
T
F
T
Chapter 5—The Sedimentary Archives
RESPONSES TO QUESTIONS ACCOMPANYING SELECTED FIGURES
FIGURE 5–2 (p. 80) Fossils would be the most diagnostic feature. One would look for fossils of nonmarine crustaceans, mollusks, freshwater fish, and insects. There would be an ansence of marine
invertebrates. Other clues might be dessication features such as mudcracks and finely laminated (varved)
shales.
FIGURE 5–5 (p. 82) Graywacke (immature sandstone) is characteristic of deep-sea fan deposits.
FIGURE 5–9 (p. 85) 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. 85) Coarser sediments occur along the windward side of the barrier island because
wave action removes finer particles, leaving the heavier material to accumulate.
FIGURE 5–6 (p. 83) 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 5–12 (p.88) Graywacke is an immature sandstone.
FIGURE 5–15 (p. 90) 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. 91) 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. 92) 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. 93) 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. 94) Overturned beds are common in orogenic belts around the world.
FIGURE 5–25 (p. 97) 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 3–25 (p. 78) The 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 3–33 (p. 82) Dolomite rocks are composed of more than 50 percent of the mineral dolomite
[CaMg(CO3)2]. Limestones are composed primarily of CaCO3, with less than 50 percent magnesium
carbonate.
FIGURE 3–42 (p. 88) There are two major episodes of sea-level rising, each having many minor
oscillations within it.
FIGURE 5–44 (p. 108) 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. 112) 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. 115) 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 radioisotopic dating methods.