IV. Sedimentary Rocks

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IV. Sedimentary Rocks

• A. Sediment Source and History
• B. Formation and Classification of
• Sedimentary Rocks
• C. Sedimentary Structures and
• Environments

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Weathering Sediments
Sediments
Weathering
Biotite
Quartz
Na Feldspar
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Clastic Particle Sizes
Kehew, Table 5.3
Gravel

• X .
• Example (mm) f
• Bowling Ball 256 -8
• Pool Ball 64 -6
• Buck Shot 2 -1
• Powder 1/16 4
• 1/256 8

Boulder Cobble Pebble Sand Silt Clay
Sand
Wentworth (Phi) Scale f -log2(X)
Mud
very small particles are usually clay minerals
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Fig. 7-3, p. 147
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Sediment History
Fig. 7.4c
Fig. 7.4a
Talus slopes Mtn. Streams Beaches
Oceans ?Alluvial Fans?
Rivers Delta
(Plains)
Transport and weathering effects (opposite of
grading) 1) Size, 2) Sorting, 3) Rounding, and
4) Composition
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Derital Sediment Characteristics Indicate source
and history
Immature Mature
Compo- sition . Rock and mineral fragments Small particles of stable minerals (e.g., qtz fld)
Rounding Size Angular Gravel Rounded Sand
Sorting Poorly Sorted (large and small) Well Sorted (uniform sand)
Wheres the rest?
Clay Deposited in deep lakes, seas and
oceans Ions Form evaporites (salts) and lime mud
(limestone)
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Talus Slopes

• Gravel
• (boulders, cobbles etc.)
• Poorly sorted
• Angular
• Fragments of rocks and minerals

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Mountain Stream (Upstream)

• Fast Flows?
• (high energy)
• Washes out mud
• Leaves course sand and gravel
• Rounds Sediment particles

Fig. 7-1, p. 146
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Mountain Stream (Upstream)

• Gravel
• (Cobbles, Pebbles etc.)
• Poorly sorted
• Sub-angular
• (Somewhat rounded)
• Fragments of Rocks and minerals

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Mountain Stream (Downstream)

• Gravel
• (Cobbles, Pebbles etc.)
• Poorly sorted
• Rounded
• Fragments of Rocks and minerals

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Depositional Environments

• Breccia
• Mountains, bases of cliffs, I.e., Talus slopes
• Conglomerate
• Mountain streams
• Beach cliffs

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Sedimentary Rocks from Gravel

• Breccia
• Angular gravel
• Poorly sorted
• Rock Fragments
• Conglomerate
• Rounded gravel
• Poorly sorted
• Rock Fragments

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Alluvial Fans

• Sand
• Poorly Sorted
• Sub-angular
• Many minerals
• See Fig. 6.11

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River in the Plains

• Sand
• Somewhat Sorted
• Sub-angular
• Many minerals

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Quartz Sandstone From Beaches and/or Dunes
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Sandstones

• Quartz Sandstone?
• Quartz
• Rounded
• Well sorted
• Arkose ?
• Many minerals
• Angular
• Poorly sorted
• Graywacke ?
• Many minerals
• Angular
• V. Poorly sorted

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Environments of Deposition

• Quartz sandstone
• Beach and
• Dunes
• Arkose
• Rivers and
• Alluvial fans
• Graywacke
• Turbidity currents and
• Submarine fans

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Delta

• Silt and Clay
• i.e., Mud
• Deep Sea
• (Lakes, Oceans)
• Clay
• Fig. 10.30 Clay minerals and quartz

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Graywackey From Turbidity Currents

• Fig 6.13

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Depositional Environments
Fig. 7-5, p. 149
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Depositional Environments

• Breccia Mountain Cliffs, (Talus Slopes)
• Conglomerate Mountain Streams
• Arkose Alluvial Fans and rivers near mountains
• Quartz Sandstone Beach and Dune
• Mudstone Delta, Lagoon, Tidal Flat
• Shale Deep Lake, Sea, Ocean
• Limestone Organic Reef, Shallow Tropical Sea

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Reading the Rocks from Depositional Environments
Limestone
Sandstone
Breccia
Conglomerate
Shale (Mudstone Claystone)
Sandstone
Graywacke
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Southwest US 470mya
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Sedimentary Structures

• Bedding Sediments are deposited in
• Horizontal layers (original horizontality)
• Deeper rocks are older (superposition)

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Tilted Sedimentary Rock Layers

• La Castilla, Peru

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What is this?

• Sand blasted wood?
• Laminated chocolate?
• Mountains in Arizona?
• Sedimentary Rocks on Mars?

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Cross Bedding

• Indicates current
• and direction Fig. 6.28
• Wind
• Water

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Graded Bedding
Fig. 7-11a, p. 156
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Sedimentary Structures

• Other information preserved in sedimentary rocks
• Cross Bedding (Dunes)
• Graded Bedding (Turbidity Currents)

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Figure 1, p. 158
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Ripple Marks
Fig. 7-12, p. 157
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Fig. 7-12e, p. 157
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Fig. 7-13, p. 159
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Fig. 7-14a, p. 159
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Fig. 7-14b, p. 159
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Structure of Our Continent
B
A
A
B
Virginia / Penn.
Canada
Ohio Michigan
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Deciphering the Geology of OhioUsing Stenos
Principles
Sandstone
Shale
Limestone

• By characterizing the sequence of sedimentary
  rocks found in Ohio, we can decipher the geologic
  history preserved in the rocks using the basic
  principles of geology

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Deciphering the Geology of OhioUsing Stenos
Principles (1650s)

• Uniformitarianism
• Original Horizontality
• Original Continuity
• Superposition

Sandstone Shale
Limestone
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Sedimentary Rocks of Ohio Demonstrate the Use
of Stenos principles

• Generalized sequence of rocks and ages in
  millions of years
• Principle of Uniformitarianism
• Principle of Original Horizontality
• Principle of Original Continuity
• Principle of Superposition

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Sedimentary Rocks of Ohio

• Uplift during the Tertiary period (26 mya)

Erosion
Sandstone
350
Shale
380
Limestone
450
Regional Uplift
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Sedimentary Rocks of Ohio

• Exposed older rocks in central and western Ohio

Erosion
Sandstone
350
Shale
380
Limestone
450
Regional Uplift
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Sedimentary Rocks of Ohio

• Forming the Findley Arch (with east flank in
  eastern Ohio)

Erosion
Sandstone
350
Shale
380
Limestone
450
Regional Uplift
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Sedimentary Rocks of Ohio

• And the pattern of rocks found across Ohio

Erosion
Sandstone
350
Shale
380
Limestone
450
Regional Uplift
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Sedimentary Rocks of Ohio

• The oldest rocks are found in southwestern Ohio
  (along the axis of the Findley Arch)

Erosion
Sandstone
350
Shale
380
Limestone
450
Regional Uplift
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Sedimentary Rocks of Ohio
Sandstone
350
Shale
380
Limestone
450
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Sedimentary Rocks of Ohio
Sandstone
350
Shale
380
Limestone
450
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Sedimentary Rocks of Ohio
Sandstone
350
Shale
380
Limestone
450
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Sedimentary Rocks of Ohio
Sandstone
350
Shale
380
Limestone
450
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Sedimentary Rocks of Ohio

• Sandstone Shale
  Limestone

Sandstone
350
Shale
380
Limestone
450
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Sedimentary Rocks of Ohio

• Sandstone Shale
  Limestone

Sandstone
350
Shale
380
Limestone
450
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Sedimentary Rocks of Ohio
Sandstone (325 my)
Limestone (400 my)
Shale

• Thus rocks are younger and change lithology (rock
  type) as you go west or east from Ottawa County

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The Geologic Record in the Rocks
Sandstone
Shale
Limestone
Gneiss
Granite
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Reading the Grand Canyon
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The Grand Canyon
The Grand Staircase
5. Coconino Sandstone
4. Redwall Limestone
Sedimentary Rocks
Intrusive Igneous
Metamorphic
3. Bright Angel Shale
2. Grand Canyon Pink Granite
1. Vishnu Schist (and gneiss)
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The Grand Staircase
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Eastern Zion National Park
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Checkerboard Butte Zion National Park
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Vishnu Schist and Pink Granite