MondayNovember 29, 2010

(Unconformities)

The Launch PadMonday, 11/29/10

What are “inclusions”, and what do they tell us about rock layers in their

area? Inclusions are pieces of one rock unit that are contained within another.

The rock mass adjacent to the one containing the inclusion must have been there first in order to

provide the rock fragments.

Therefore, the rock mass containing inclusions is the younger of the two.

Announcements??

Assignment Currently Open Pages Date of Notes

on Website Date Issued Date Due

Five Multiple Choice

Questions on Plate Tectonics

11/11 11/12

Project – Decade

Volcanoes11/15 11/19

Project – Killer Earthquakes 11/17 12/1

Project – Greatest

Mountains11/19 12/3

Relative Dating An unconformity represents a long period during which deposition ceased, erosion

removed previously formed rocks, and then deposition resumed.

In other words, it’s a break in the rock record.There are three basic types of unconformities:

Angular UnconformitiesDisconformities

Nonconformities

Relative Dating Angular

UnconformitiesAn angular unconformity consists

of tilted or folded sedimentary rocks that are overlain by

younger, more flat lying strata.

An angular unconformity indicates that during the pause in

deposition, a period of deformation (folding or tilting)

and erosion occurred.

Relative Dating Disconformities

In a disconformity, the strata on either side are essentially parallel.

Relative Dating Disconformities

In a disconformity, the strata on either side are essentially parallel.

Relative Dating NonconformitiesIn a nonconformity, the break separates older

metamorphic or intrusive igneous rocks from

younger sedimentary strata.

Here, younger strata rest upon older, metamorphic

or igneous rocks.

Relative Dating NonconformitiesIn a nonconformity, the break separates older

metamorphic or intrusive igneous rocks from

younger sedimentary strata.

Here, younger strata rest upon older, metamorphic

or igneous rocks.

Relative Dating

The three basic types of

unconformities illustrated in the Grand Canyon.

Geologic Cross - Section of a Hypothetical Region

Figure 11.10 (bottom)