1. The Sedimentary Archives
Chapter 5
The Sedimentary Archives
REPLACE FIGURE
(Chapter opening art)

2. Factors affecting Sedimentary Characteristics
Tectonic setting
Physical, chemical, and biological processes in the depositional environment
Method of sediment transport

3. Rocks in the source area from which the sediment is derived
Climate (and its effect on weathering)
Post-depositional processes of lithification (cementation, compaction)
Time

4. Tectonics
The forces controlling deformation or structural behavior of a large area of the Earth's crust over a long period of time.

5. Structural Behavior Tectonically stable - midwestern U.S.
Subsiding (sinking) - New Orleans or Mexico City
Rising gently - New England and parts of Canada after glacial retreat
Rising actively to produce mountains and plateaus - parts of Oregon in the Cascade mountains

6. tectonic elements of a continent
Principle
tectonic elements of a continent
REPLACE FIGURE
(Fig. 5-1)
Craton
- Shield
- Platform
Orogenic belt

7. Principle tectonic elements of a continent – the craton
Craton – the stable interior of a continent.
Shields - Large areas of exposed crystalline rocks.
Platforms - Ancient crystalline rocks covered by flat-lying or gently warped sedimentary rocks.

8. Principle tectonic elements of a continent
Orogenic belts - Elongated regions bordering the craton which have been deformed by compression since Precambrian. Orogenic belts are mountain belts.

9. Depositional Environments
All of the physical, chemical, biological and geographic conditions under which sediments are deposited.
By comparing modern sedimentary deposits with ancient sedimentary rocks, the depositional conditions can be interpreted.

10. Depositional Environments
Sediments and sedimentary rocks may be:
Extrabasinal in origin - formed from the weathering of pre-existing rocks outside the basin, and transported to the environment of deposition.
Intrabasinal in origin - formed inside the basin; includes chemical precipitates, most carbonate rocks, and coal.

11. Depositional Environments
There are three broad categories of depositional environments:
Marine environments (ocean)
Transitional environments (along contact between ocean and land)
Continental environments (on land)

12. Depositional Environments
REPLACE FIGURE
(Fig. 5-2)

13. Marine Depositional Environments
Continental shelf
Continental slope
Continental rise
Abyssal plain

14. Marine Depositional Environments
REPLACE FIGURE
(Fig. 5-5)

15. Continental Shelf
The flooded edge of the continent. Flooding occurred when the glaciers melted about 10,000 years ago.
Relatively flat (slope < 0.1o)
Shallow water (less than 200 m deep)
May be up to 300 km wide (averages 80 km wide)
Exposed to waves, tides, and currents

16. Continental Shelf – cont'd
Covered by sand, silt, and clay
Larger sedimentary grains are deposited closer to shore.
Locally cut by submarine canyons (eroded by rivers during Ice Age low sea level stand)
Coral reefs and carbonate sediments may accumulate in tropical areas

17. Continental Slope The steeper slope at edge of the continent.
Located seaward of the continental shelf
Boundary between continental and oceanic crust
May be about 20 km wide

18. Continental Slope – cont'd
Deeper water
More steeply inclined (3 - 6o)
Rapid sediment transport down the slope by dense, muddy turbidity currents
Passes seaward into the continental rise

19. Continental Rise At the base of the continental slope.
More gradual slope
May be hundreds of km wide
Water depths of 1400 to 3200 m
Submarine fans form off submarine canyons
Turbidity currents transport sediment downslope from continental shelf (turbidites)
Passes seaward into the abyssal plain

20. Deep Marine Realm The deep ocean floor. Nearly flat
Water depths of 3 to 5 km + (2 - 3 miles +)
Covered by very fine-grained sediment and shells of microscopic organisms
Clay
Volcanic ash
Foraminifera (calcareous)
Radiolarians (siliceous)
Diatoms (siliceous)

21. Transitional Depositional Environments
Environments at or near the transition between the land and the sea.
Deltas
Beaches and barrier Islands
Lagoons
Tidal flats
Estuaries

22. Deltas Fan-shaped accumulations of sediment
Formed where a river flows into a standing body of water, such as a lake or the sea
Coarser sediment (sand) tends to be deposited near the mouth of the river; finer sediment is carried seaward and deposited in deeper water.
The delta builds seaward (or progrades) as sediment is deposited at the river mouth.

23. Deltas Mississippi River delta Niger River delta REPLACE FIGURE

24. Beaches and Barrier Islands
REPLACE FIGURE
(Fig. 5-10)
Shoreline deposits
Exposed to wave
energy
c. Dominated by sand

25. Beaches and Barrier Islands
Marine fauna
A few km or less in width but may be more than 100 km long
Separated from the mainland by a lagoon (or salt marsh)
May be associated with tidal flat deposits

26. Lagoons Bodies of water on the landward side of barrier islands
Protected from the pounding of the ocean waves by barrier islands
Contain finer sediment than the beaches (usually silt and clay)
Lagoons are also present behind reefs, or in the center of atolls.

27. Tidal flats
Nearly flat, low relief areas that border lagoons, shorelines, and estuaries
Periodically flooded and exposed by tides (usually twice each day)
May be cut by meandering tidal channels
May be marshy, muddy, sandy or mixed sediment types (terrigenous or carbonate)

28. Tidal flats Laminations and ripples are common
Sediments are intensely burrowed
Stromatolites may be present (if conditions are appropriate)

29. Estuaries Mouth of a river drowned by the sea
Brackish water (mixture of fresh and salt)
May trap large volumes of sediment
Sand, silt, and clay may be deposited depending on energy level
Many estuaries formed due to sea level rise as glaciers melted at end of last Ice Age
Some formed due to tectonic subsidence, allowing sea water to migrate upstream

30. Continental Environments
Rivers or fluvial environments
Alluvial fans
Lakes (or lacustrine environments)
Glacial environments
Eolian environments

31. Fluvial Environments Braided and meandering river and stream systems
River channels, bars, levees, and floodplains are subenvironments
Channel deposits are coarse, rounded gravel, and sand.
Bars are sand or gravel.
Levees are fine sand or silt.
Floodplains are covered by silt and clay.

32. Alluvial Fans Fan-shaped deposits at base of mountains.
Most common in arid and semi-arid regions with rapid erosion.
Sediment is coarse, poorly- sorted gravel and sand.
REPLACE FIGURE
(Fig. 5-6)

33. Lacustrine Environments (Lakes)
May be large or small
May be shallow or deep
Filled with terrigenous, carbonate, or evaporitic sediments
Sediments are typically fine grained but may be coarse near the edges
Fine sediment and organic matter settling in some lakes produced laminated oil shales
Playa lakes are shallow, temporary lakes that form in arid regions They periodically dry up as a result of evaporation

34. Glacial Environments
Sediment is eroded, transported, and deposited by ice (glaciers)
Glacial deposits called till contain large volumes of unsorted mixtures of boulders, gravel, sand and clay
REPLACE FIGURE
(Fig. 5-7a)

35. Eolian Environments
REPLACE FIGURE
(Fig. 5-8)
Wind is the agent of sediment transport and deposition
Dominated by sand and silt
Common in many desert regions

36. Color of Sedimentary Rocks
Black and dark gray coloration in sedimentary rocks generally indicates the presence of organic carbon and/or iron.
Organic carbon in sedimentary requires anoxic environmental conditions.

37. Color of Sedimentary Rocks
Red coloration in sedimentary rocks indicates the presence of iron oxides.
Red beds typically indicate deposition in well-oxygenated continental sedimentary environments. May also be transitional or marine.
REPLACE FIGURE
(Fig. 5-11)

38. Color of Sedimentary Rocks
Green and gray coloration in sedimentary rocks indicates the presence of iron, but in a reduced (rather than an oxidized) state.
Ferrous iron (Fe+2) generally occurs in oxygen-deficient environments.

39. Textural Interpretation of Clastic Sedimentary Rocks
Texture = size, shape, sorting, and arrangement of grains in a sedimentary rock.
The texture of a sedimentary rock can provide clues to the depositional environment.
Fine-grained textures typically indicate deposition in quiet water.
In general, it takes higher energy to transport larger grains.

40. Three "textural components" to most clastic sedimentary rocks:
Clasts - the larger grains in the rock (gravel, sand, silt)
Matrix - the fine-grained material surrounding clasts (often clay)
Cement - the "glue" that holds the rocks together
Silica (quartz, SiO2)
Calcite (CaCO3)
Iron oxide
Other minerals

41. Grain Size
Sedimentary grains are categorized according to size using the Wentworth Scale.
Gravel
> 2 mm
Sand
1/ mm
Silt
1/ /16 mm
Clay
< 1/256 mm

42. Sorting Sorting refers to the distribution of grain sizes in a rock.
The range of grain sizes in a sedimentary rock can provide clues to help interpret the depositional environment.
For example, turbulence from waves will winnow out finer grain sizes such as silt and clay, leaving sands on the beach.

43. Sorting
If all of the grains are the same size, the rock is "well sorted."
If there is a mixture of grain sizes, such as sand and clay, or gravel and sand, the rock is "poorly sorted."
REPLACE FIGURE
(Fig. 5-12)

44. Sorting
Well-sorted sands tend to have higher porosity and permeability than poorly-sorted sands (if they are not tightly cemented), and may be good reservoirs for petroleum and natural gas, or good aquifers.

45. Sorting
Poor sorting is the result of rapid deposition of sediment without sorting by currents. Examples of poorly-sorted sediment include alluvial fan deposits and glacial till.

46. Grain Shape
Grain shape is described in terms of rounding of grain edges and sphericity (equal dimensions, or how close it is to a sphere).
REPLACE FIGURE
(Fig. 5-15)

47. Rounding
Rounding results from abrasion against other particles and grain impact during transport.
Very well rounded sand grains suggest that a sand may have been recycled from older sandstones.
REPLACE FIGURE
(Fig. 5-14)

48. Sedimentary Structures
Some sedimentary structures are created by the water or wind which moves the sediment. Other sedimentary structures form after deposition - such as footprints, worm trails, or mudcracks.

49. Sedimentary Structures
Sedimentary structures can provide information about the environmental conditions under which the sediment was deposited.
Some structures form in quiet water under low energy conditions, whereas others form in moving water or high energy conditions.

50. Sedimentary Structures
Stratification (= layering or bedding) is the most obvious feature of sedimentary rocks. The layers (or beds or strata) are visible because of differences in the color, texture, or composition of adjacent beds.
REPLACE FIGURE
(From chapter opening art)

51. Graded Bedding
The grain size in a graded bed is coarser at the bottom and finer at the top.
Graded bedding results when a sediment-laden current (such as a turbidity current) begins to slow down.
REPLACE FIGURE
(Fig. 5-20)

52. Cross-bedding or cross-stratification
An arrangement of beds or laminations in which one set of layers is inclined relative to the others.
(From Fig. 5-18b; add arrow
REPLACE FIGURE
text on top of figure)
water flow
direction

53. Ripple marks
Undulations of the sediment surface produced as wind or water moves across sand.
Symmetric ripple marks are produced by waves
REPLACE FIGURE
(Upper part of Fig.
5-22)

54. Ripple marks
Asymmetric ripples form in unidirectional currents (such as in streams or rivers).
REPLACE FIGURE
(Lower part of Fig.
5-22

55. Mud cracks
A polygonal pattern of cracks produced on the surface of mud as it dries.
(Repositioned parts of Fig. 5-17)
REPLACE FIGURES
Modern mudcracks Fossil mudcracks

56. Determining "up direction"
Rocks can be overturned by tectonic forces. Examine sedimentary structures to determine "up direction."
Symmetrical ripples
Stromatolites
Burrows
Tracks
Graded beds
Cross beds
Mudcracks
Scour marks

57. Sands and Sandstones
Sandstone classification is based on the composition of the grains.
Quartz
Feldspar
Rock fragments

58. Major types of sandstone
Quartz sandstone - dominated by quartz
Arkose - 25% or more feldspar
Graywacke – about 30% dark fine-grained matrix
Lithic sandstone - quartz, muscovite, chert, and rock fragments. Less than 15% matrix.

59. Sandstone Interpretation
Minerals provide information on the amount of weathering and transport of sand grains.
Intense weathering and long transport produce sandstone dominated by quartz.
Sandstones with abundant feldspars, and ferromagnesian minerals indicate relatively little weathering and transport.

60. Sandstone Environmental Interpretation
Quartz sandstone
Long time in the depositional basin
Tectonically stable setting
Shallow-water environments
REPLACE FIGURE
(Fig. 5-25a)

61. Sandstone Environmental Interpretation
Arkose
Short time in the depositional basin
Rapid erosion
Arid climate
Tectonic activity
REPLACE FIGURE
(Fig. 5-25b)

62. Sandstone Environmental Interpretation
Graywacke
Tectonically active source area & basin
Rapid erosion
REPLACE FIGURE
(Fig. 5-25c)

63. Sandstone Environmental Interpretation
Lithic sandstone
Deltaic coastal plains
Nearshore marine environments
Swamps or marshes
REPLACE FIGURE
(Fig. 5-25d)

64. Carbonate Rocks and Sediments
Carbonate rocks are chemical or biochemical in origin.
Limestone
Calcite (CaCO3)
Aragonite (CaCO3)
Dolostone (or Dolomite)
Dolomite (CaMg (CO3)2)

65. Carbonate Rocks and Sediments
Most carbonate rocks form in the shallow marine environment.
Some form in lakes, caves and hot springs.
Most limestones are the direct or indirect result of biologic activity.

66. Characteristics of most marine carbonate environments
Warm water
Shallow water (less than 200 m deep)
Tropical climate (30 ° N - 30 ° S of equator)
Clear water (low to no terrigenous input)
Sunlight required for photosynthesis by algae

67. Origin of carbonate sediments
Much lime mud forms from the disintegration of calcareous algae
REPLACE FIGURE
(Fig. 5-29)

68. Origin of carbonate sediments
When calcareous algae die, their skeletons disintegrate, producing aragonite needle muds. Lime mud lithifies to form fine-grained limestone.

69. Origin of Oöids
Oöids are tiny spheres composed of concentrically laminated calcium carbonate.
Oöids form in warm shallow water with constant wave agitation.
REPLACE FIGURE
(Fig. 5-30b)

70. Origin of carbonate sediments
Microscopic shells of marine organisms
Abrasion of shells
Precipitation of calcium carbonate from seawater as a result of biologic activity
REPLACE FIGURE
(Fig. 5-29)

71. Dolomite A calcium-magnesium carbonate mineral (CaMg(CO3)2).
Makes up sedimentary rock dolostone. (Sometimes the rock is also called dolomite.)
Forms when magnesium in sea water replaces calcium in calcium carbonate in a limestone.
Dolomite (or high magnesium calcite) only forms in a few areas of the world where intense evaporation of seawater concentrates the magnesium.

72. Clay The word "clay" has two definitions: A grain size term
A layered silicate mineral which behaves plastically when wet and hardens upon drying or firing.

73. Clay Minerals
Clay minerals are complex hydrous aluminosilicates with atoms arranged in layered or sheet structures.
Kaolinites - Weathering product of feldspars.
Smectites - May contain magnesium, calcium, and/or sodium ions. Smectites swell when wet.
Illites - The major clay mineral in ancient shales.

74. Deposition of clays
Because of its fine grain size, clay tends to remain suspended in the water column. It will settle out of still, quiet water, given enough time.
Clays and shales typically indicate low energy environments, sheltered from waves and currents. They are commonly found in lacustrine, lagoon, and deeper water marine deposits.

75. Shale A very fine-grained rock composed of clay, mud, and silt.
REPLACE FIGURE
(Fig. A from chap. 15
enrichment box
titled “Oil Shale”)
A very fine-grained rock composed of clay, mud, and silt.
Shale is fissile - splits readily into thin, flat layers.

76. Claystone
A very fine-grained rock composed of tiny (less than 1/256 mm) clay minerals, mica, and quartz grains.
Individual grains are too small to see with the naked eye or a hand lens.
Feels smooth to the touch (not gritty).
Not fissile; it breaks irregularly.

77. Lithostratigraphic unit
A body of sedimentary, extrusive igneous, metasedimentary, or metavolcanic rock distinguished on the basis of lithologic characteristics (texture, color, composition, etc.) and stratigraphic position.
The smallest lithostratigraphic rock unit is the bed.

78. Formations Lithologically homogeneous
Distinct and different from rock units above and below.
Traceable from exposure to exposure, and of sufficient thickness to be mappable
Named for a geographic locality where well exposed.

79. Other lithostratigraphic units
Subdivisions within formations are called members.
A set of similar or related formations is called a group.

80. Virtually all lithostratigraphic units are "time transgressive" or diachronous (they, or their contacts, cut across time lines).
REPLACE FIGURE
(Fig )
Red lines G and O are time lines.

81. Facies
The characteristics of a particular rock unit, which we can use to interpret the depositional environment.
Every depositional environment puts a distinctive imprint on the sediment, making a particular facies.

82. Facies Change
Each depositional environment grades laterally into other depositional environments.
REPLACE FIGURE
(Fig. 5-33)

83. Facies and sea level changes
A sea level rise is called a transgression.
A transgression produces a fining-upward (deepening-upward) sequence of facies.
Finer-grained (deeper water) facies overlie coarser-grained (shallower water) facies.
Sometimes called an onlap sequence.

84. Sedimentation during a transgression produces an onlap sequence.
REPLACE FIGURE
(Fig. 5-34)

85. Causes of Transgressions
Melting of polar ice caps
Displacement of ocean water by undersea volcanism
Localized sinking or subsidence of the land in coastal areas.

86. Regressions A sea level drop is called a regression.
A regression produces a coarsening upward (shallowing-upward) sequence of facies.
Coarser-grained (shallower water) facies overlie finer-grained (deeper water) facies.
This is sometimes called an offlap sequence.

87. Sedimentation during a regression produces an offlap sequence.
REPLACE FIGURE
(Fig. 5-35)

88. Causes of Regressions Buildup of ice in the polar ice caps
Formation of glaciers
Localized uplift of the land in coastal areas

89. Walther's Law
Sedimentary environments that started out side-by-side will end up overlapping one another over time due to sea level change.
The vertical sequence of facies mirrors the original lateral distribution of sedimentary environments.
REPLACE FIGURE
(Fig. 5-36)

90. Correlation
Lithostratigraphic correlation - Matching up rock units on the basis of lithology and stratigraphic position.
Biostratigraphic correlation - Matching up rock units on the basis of fossils they contain.
Chronostratigraphic correlation - Matching up rock units on the basis of age equivalence, as determined by radioactive dating methods or fossils.

91. Lithostratigraphic correlation
REPLACE FIGURE
(Fig. 5-38)
Demonstration of lithostratigraphic correlation from one exposure to another.

92. Contacts between Rock Units
There are two basic types of contacts between rock units:
Conformable
Unconformable

93. Conformable Contacts
Conformable contacts between beds of sedimentary rocks may be either:
Abrupt or
Gradational
Most abrupt contacts are bedding planes resulting from sudden minor changes in depositional conditions.
Gradational contacts represent more gradual changes in depositional conditions.

94. Unconformities
Unconformable contacts (or unconformities) are surfaces which represent a gap in the geologic record, because of either:
Erosion or
Nondeposition
The time represented by this gap can vary widely, ranging from millions of years to hundreds of millions of years

95. Types of unconformities
REPLACE FIGURE
(Fig. 5-40)
Angular unconformity
Nonconformity
Disconformity

96. Depicting the Past
Various ways in which the distribution of rocks can be depicted:
Geologic columns
Stratigraphic cross-sections
Structural cross-sections
Geologic maps
Paleogeographic maps
Isopach maps
Lithofacies maps

97. Stratigraphic Cross-sections
They correlate geologic columns from different locations to show how rock units change in thickness, lithology, and fossil content in a given area.
REPLACE FIGURE
(Fig. 5-44)

98. Structural Cross-sections
They show the timing of tilting, folding, and faulting of rock units. Tops and bottoms of rock units are plotted by elevation. Folds and faults are depicted clearly.
REPLACE FIGURE
(Fig. 5-45)

99. Geologic Maps
REPLACE FIGURE
(Fig. 5-46, parts C, D,
and E only)
Geologic maps show the distribution of various layers and types of rocks in an area.
Map symbols indicate structural features (folds, faults, etc.) and formation names.

100. Paleogeographic Maps
REPLACE FIGURE
(Fig. 5-47)
Interpretive maps which depict the geography of an area at some time in the past.

101. Isopach Maps
Isopach maps show the thickness of formations or other units in an area.
REPLACE FIGURE
(Fig. 5-49)

102. Lithofacies Maps
They show the distribution of lithofacies that existed at a given time over an area.
REPLACE FIGURE
(Fig. 5-52)