Question: How to tell which rock units are older … or younger … than other rock units?
A FEW PRINCIPLES
· Earth is dynamic LINK
· The present is the key to the past; the past is the key to the present. Lots of keys! LINK
· Geologic time is deep time . LINK
And ties to human geography LINK - IHC facilities of 1990s
· Older versus Younger … generalizations LINK
Old bedrock, Young landforms LINK
Older underneath Younger (superposition) LINK
Datable materials LINK
Tilted younger than what tilted LINK
What cuts is younger than what is cut (cross-cutting relationship) LINK
Surfaces... lots of them! Distinguish cross-cutting surfaces from others (such as between layers of rock).
Cross-cutting surfaces to appreciate for Analysis of Utah Landforms.
(a) MOST PERVASIVE and MOST OBVIOUS and MOST easy to be oblivious to... EROSIONAL SURFACES.
LINK to image of UofU and Wasatch Front
LINK to image of cross section of Basin and Range
(b) fault... surface across which movement happens between large (really large) crustal masses.
(c) contacts... between LAYERED rock units -- conformable if no time lost across the surface; unconformable if a time gap such as the gap between units tilted by tectonics and those deposited across them.. And contacts between intrusive rock units such as granite magma that intruded and then crystallized as huge mass(es) into the bedrock now found in Little Cottonwood Canyon; or salt that intrudes the bedrock that underlies Moab, UT.
BINGHAM COPPER MINE… what it took to have our world class copper ore. LINK