Stratigraphy

Stratigraphy

• Principles of Stratigraphy

• Types of Stratigraphy

• Contacts

• Unconformities

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



• Contacts

• Unconformities

The oldest rocks are found on the bottom and the youngest rocks on the top.

youngest

oldest

Principles of Stratigraphy

1. Superposition

youngest? oldest?


older

younger


sediments are deposited at the earth’s surface in flat layers


2. Original Horizontality



cross-bedding

a bed will extend laterally until:


3. Lateral Continuity

1. Pinches out.

1. Abuts against older rock.

1. Truncated by erosion.

1. Cut by fault.


Rock that are cut by another geologic feature are older than the feature that cuts them.


4. Cross-Cutting Relationships

FaultErosion

IgneousIntrusion

If pieces of rock A are included in rock B, rock A formed before rock B.


5. Rule of Inclusions

A

B

6. Faunal Succession

Systematic sequence of fossils with time. Extinct fossils do not reappear in younger rocks.


http://www.geo.utexas.edu/courses/401/

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


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


Lithostratigraphic Units

lens / lentil

(E. McBride)

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



• 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:

• Disconformity

• Paraconformity

• Nonconformity

• Angular Unconformity

• 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


Unconformities

Wyoming


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

Documents

Stratigraphy