Download No Slide Title

Proterozoic
Quaternary
Cretaceous
The Geologic Column
[Fig. 3.8, p. 64]
N. Lindsley-Griffin, 1999
Dating the Geologic Time Scale
Sedimentary rocks
not easily dated
radiometrically
Radiometric
ages added to
geologic time
scale by:
1. Cross-cutting
relationships
2. Bracketing
© Houghton Mifflin 1998. All rights reserved
Relative Age - Principles
Unconformities:
Gaps in the rock
record - recognized
by an erosional
surface
Signifies a major
break in deposition
Columbia River Gorge, OR-WA
N. Lindsley-Griffin, 1999
Relative Age - Principles
Original horizontality
Superposition
Cross-cutting relationships
Horizontal sedimentary rocks
Youngest
sedimentary rock
Dike cuts strata
- dike is younger
Fault cuts dike and strata
- fault is youngest
Oldest
sedimentary rock
© Houghton Mifflin 1998. All rights reserved
Dating the Geologic Time Scale
Radiometric dating and cross-cutting relationships
bracket ages of sedimentary rocks
Radiometric age of
intrusion Y is 350 m.y.
Radiometric age of
intrusion X is 400 m.y.
Devonian strata (B) must be
older than 350 m.y. and
younger than 400 m.y.
Mississippian strata are
younger than 350 m.y.
© Houghton Mifflin 1998. All rights reserved
Silurian strata are older than
both Devonian and 400 m.y.
Angular unconformity - younger layers
over tilted layers - Grand Canyon, AZ
N. Lindsley-Griffin, 1998
Angular unconformity - younger layers
over tilted layers - Grand Canyon, AZ
N. Lindsley-Griffin, 1998
Disconformity
Time gap without angular relationship
N. Lindsley-Griffin, 1998
Angular Unconformity
Time gap after folding, faulting
Disconformity
Time gap without angular relationship
N. Lindsley-Griffin, 1998
Angular Unconformity
Time gap after folding, faulting
“Baked zone” - soil formed on older lava
flow before being covered and cooked by a
new lava flow - Disconformity
N. Lindsley-Griffin, 1998
“Baked zone” - soil formed on older lava
flow before being covered and cooked by a
new lava flow - Disconformity
N. Lindsley-Griffin, 1998