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Stratigraphy
• Principles of Stratigraphy
• Types of Stratigraphy
• Contacts
• Unconformities
Text: Manual p. 29-35
Stratigraphy
“Stratigraphy can be defined as the complete triumph of terminology over facts and common sense.”
Attributed to P.D. Krynine by J. Ferm in Burton et al., 1987.
Stratigraphy
Stratigraphy: the study of the 3-D spatial and temporal relationships among rocks
Stratigraphy
• Principles of Stratigraphy
• Types of Stratigraphy
• Contacts
• Unconformities
Text: Manual p. 29-35
The oldest rocks are found on the bottom and the youngest rocks on the top.
youngest
oldest
Principles of Stratigraphy
1. Superposition
youngest? oldest?
Principles of Stratigraphy
older
younger
Principles of Stratigraphy
sediments are deposited at the earth’s surface in flat layers
Principles of Stratigraphy
2. Original Horizontality
Principles of Stratigraphy
Principles of Stratigraphy
cross-bedding
a bed will extend laterally until:
Principles of Stratigraphy
3. Lateral Continuity
1. Pinches out.
2. Abuts against older rock.
3. Truncated by erosion.
4. Cut by fault.
Principles of Stratigraphy
Rock that are cut by another geologic feature are older than the feature that cuts them.
Principles of Stratigraphy
4. Cross-Cutting Relationships
FaultErosion
IgneousIntrusion
If pieces of rock A are included in rock B, rock A formed before rock B.
Principles of Stratigraphy
5. Rule of Inclusions
A
B
6. Faunal Succession
Systematic sequence of fossils with time. Extinct fossils do not reappear in younger rocks.
Principles of Stratigraphy
http://www.geo.utexas.edu/courses/401/
Stratigraphy
Text: Manual p. 29-35
• Principles of Stratigraphy
• Types of Stratigraphy
• Contacts
• Unconformities
Types of Stratigraphy
Lithostratigraphy Lithostratigraphic Unit Lithology
Pedostratigraphy Pedostratigraphic Unit Buried Soils
Biostratigraphy Bio Zones Fossil Content
Chronostratigraphy Chronostratigraphic Units
(Period, Epoch, Age)
Time Relationships
Geochronostratigraphy Geochronostratigraphic Unit
(System, Series, Stage)
Time Relationships
Magnetostratigraphy Magnetic Reversals, Chrons Magnetic Polarity
Chemostratigraphy Isotope Zones Chemical Characteristics
Sequence Stratigraphy Allostratigraphic Units unconformity-bounded packages
Type Subdivisions Property
Types of Stratigraphy - Allostratigraphy
Types of Stratigraphy
Lithostratigraphy Lithostratigraphic Unit Lithology
Pedostratigraphy Pedostratigraphic Unit Buried Soils
Biostratigraphy Bio Zones Fossil Content
Chronostratigraphy Chronostratigraphic Units
(Period, Epoch, Age)
Time Relationships
Geochronostratigraphy Geochronostratigraphic Unit
(System, Series, Stage)
Time Relationships
Magnetostratigraphy Magnetic Reversals, Chrons Magnetic Polarity
Chemostratigraphy Isotope Zones Chemical Characteristics
Sequence Stratigraphy Allostratigraphic Units unconformity-bounded packages
Type Subdivisions Property
Types of Stratigraphy - Lithostratigraphy
Super Group
Group
*Formation
Member / Tongue / Lentil
Bed / Flow
*Formation: distinct, mappable rock body with definable boundaries
Types of Stratigraphy
Lithostratigraphic Units
lens / lentil
(E. McBride)
Stratigraphy
Text: Manual p. 29-35
• Principles of Stratigraphy
• Types of Stratigraphy
• Contacts
• Unconformities
Types of Contacts
• Intrusive
• Fault
• Depositional
- Conformable Contact
- Unconformity
Types of Contacts (Depositional)
Ve
rtic
al C
on
tac
ts
Lateral Contacts
pinchout
intertonguing
gradation
inte
rca
late
dg
rad
ua
la
bru
pt
(Boggs, p. 453)
Types of Contacts (Depositional)
Lateral Contacts
(E. McBride)
Stratigraphy
Text: Manual p. 29-35
• Principles of Stratigraphy
• Types of Stratigraphy
• Contacts
• Unconformities
Unconformities
Unconformity: buried surface of erosion; missing rock / time
Hiatus: amount of missing time
Diastem: small amount of missing rock / time
vs
vs
Uplift of Land
Erosion – Mechanical, Chemical, Biological
Drop in Sea Level
Unconformities
Unconformities
Calvert Bluff / Alluvium Contact (Field Trip 1)
Unconformities
Types:
1. Disconformity
2. Paraconformity
3. Nonconformity
4. Angular Unconformity
1. Disconformity – sediments on sediments (same orientation) with obvious erosion
Unconformities
Redwall Limestone
Supai Group
Muav Limestone150 million years
20 million years
Disconformity
Unconformities
Unconformities
2. Paraconformity – sediments on sediments (same orientation) no obvious erosion surface
(Boggs, p. 456)
3. Angular unconformity – sediments on sediments (different orientations)
Unconformities
250 million years
Angular Unconformity
Unconformities
Angular Unconformity
Unconformities
Wyoming
Angular Unconformity
Unconformities
(E. McBride)
4. Nonconformity – sediments on crystalline igneous or metamorphic rocks
Unconformities
Erosional Surface
Uplift, Erosion, Deposition
1800 million years
550 million years
Unconformities
Nonconformity
Canadian Shield
Nonconformity in Progress
Enchanted Rock
Unconformities
