Earth Science Outside – y2018-2019 – Via SLDistrict
Homework 3 – We did this in class and on the bus.
Goal: apply the 3 ‘rules’ of relative age… DONE! CONGRATULATIONS!
Superposition – what is on top, literally, of something else is younger than that it is on top of. We saw this. You all got it, Check!!
Cross-cutting relationships – that which cuts something else is younger than that which it cuts. We saw this. Examples include faults by the University of Utah and at the mouth of Little Cottonwood Canyon. We also saw erosional surfaces cutting today’s topography everywhere we went. Every surface we see today crosses what it is on. For example, the erosional surfaces of the Wasatch Range cut the bedrock of the Wasatch Range. That surface, today’s surface, is much much younger than the bedrock erosion cuts via wind, water, ground failure, glaciers, or by human activity. Everyone recognized the obvious (competence). To test your comprehension, examine your school yard for older than – younger than relationships. Check!!
And, number 3, original horizontality: most sedimentary sequences begin as layers that are virtually horizontal. When one sees a series of bedrock layers that are tilted, assume tectonics (some exceptions). We saw this. I’m less confident for you all on this one because it has a few steps: see the layers; recognize the extent of tilting. You all did well, keep practicing.
Geology is cumulative. First, recognize patterns in bedrock. Then use “simple” rules to figure out the relative age of rock units. Fossils can help.
ADD a nifty image here.