THE GEOLOGIC HISTORY
OF SUCIA
Jessica Hiedemann
The earth's crust is made up of three basic types of rock. Igneous, sedimentary, and metamorphic. Sucia Island is made up of sedimentary rocks. These rocks were once an ancient river system, which deposited sand, gravel and mud in layeres. The part of layers are refered to as bedding. The sediments are deposited one on top of the other, making the top layers the youngest. Also when these sediments are deposited, they are originally horizontal, or are laying flat on top of one another. Later the land was compressed due to huge tectonic plates colliding with one another. This causes waves in the land. These waves are called folds. The crest of the fold is referred to as an anticline, the trough of the fold is called a syncline. Due to more plate action these folds can be tilted or even overturned If the folds are tilted they are considered to be plunging. When you are determining whether what you are looking at is an anticline or a syncline, It's necessary to determine if the layers are overturned or upright. There is a number of ways to do this.
1) Look at the grading of the rock, When rock (or anything) settles the larger pieces fall to the bottom and the smaller pieces are on top.
2) Look at the cross-bedding of the rock. These are the lines running through the rock. The rock you are looking at is an old stream bed. When water runs over sand, ripples are created. If the current grows stronger or changes direction the tops of those ridges are truncated (cut off).
Another thing you can do is to stand in the center of your structure and note the direction the rock is tilting. If the rock is all sloping away from you then you are probably looking at an anticline, If they are sloping in towards you then you are probably looking at a syncline.
OBJECITIVE
Sucia Island is made up of rock from the Chuckanant Formation. In this formation sandstone was deposited on top of shale on top of sandstone. Using the information given and your own observations... .....
---------> Determine whether Sucia 'is an anticline or a syncline. <---------
*Keep in mind that Sucia has broken off of the main formation and the Island may not be "idealized", and there are other factor in play that I haven't talked about. Some of your findings may contradict what you have learned.**