GEOL 102 Historical Geology

Spring Semester 2018
Every Rock is a Record of History: Historical Approaches to Lithology

Proterozoic granite weathering into sediment in the Wind River Canyon, Wyoming

The three main types of rock (igneous, metamorphic, sedimentary) all represent genetic (origin-based) classes.
Can think of these as three ways of forming rock, rather than three types of rock:

Each type of rock gives some evidence of its history.
Thus, Every Rock is a Record of History.

Within igneous rocks:

Within metamorphic rocks:

Within sedimentary rocks there is considerable information concerning the surficial environments (including fossils), so we will spend a lot of time in class and lab looking at them.

The Rock Cycle: any rock can be transformed to any other major class of rock, because rocks are classified by the process in which they are formed. So if you melt an igneous, metamorphic, or sedimentary rock, and it cools down, you form a new igneous rock; if you recrystallize an ingneous, metamorphic, or sedimentary rock, you form a new metamorphic rock; and if you erode an igneous, metamorphic, or sedimentary rock and deposit the sediment from it, you form a new sedimentary rock.

Because sedimentary rocks form where animals and plants lived and died, these are the rocks in which fossils are common. One of the main categories of information sedimentary rock contain is the paleoenvironment (the conditions that existed when that rock was formed). The different environments of deposition represent different paleoenvironments. Some of the clues to discover paleoenvironments:

To Lecture Notes.

Last modified: 18 January 2018

Proterozoic granite (pink) intruding into Archean gneiss (grey)