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The lower sandstone layer is disrupted by two faults, so we can infer that the faults are younger than that layer.But the faults do not appear to continue into the coal seam, and they certainly do not continue into the upper sandstone.So, let's imagine for a second that you have a 3-layered cake. So, by definition, the oldest layer of cake would be chocolate, as it was put there first. Now all of a sudden the big tower of cookies running through the middle of your cake is the youngest feature, as the other three layers in order for it to be there.Your 3 layers will consist of a chocolate cake, a vanilla cake, and a cheesecake, because you're crazy and your cake doesn't have to conform to standards. On your plate, you put the chocolate cake on bottom, or the first layer. Then vanilla and cheesecake are the second and third oldest, respectively. Now that I've gotten you all hungry for cake and cookies let's talk about rocks instead.
The Permian through Jurassic stratigraphy of the Colorado Plateau area of southeastern Utah is a great example of Original Horizontality and the Law of Superposition, two important ideas used in relative dating.
For example, a xenolith in an igneous rock or a clast in sedimentary rock must be older than the rock that includes it (Figure 8.6).
Figure 8.6a A xenolith of diorite incorporated into a basalt lava flow, Mauna Kea volcano, Hawaii.
These strata make up much of the famous prominent rock formations in widely spaced protected areas such as Capitol Reef National Park and Canyonlands National Park.
From top to bottom: Rounded tan domes of the Navajo Sandstone, layered red Kayenta Formation, cliff-forming, vertically jointed, red Wingate Sandstone, slope-forming, purplish Chinle Formation, layered, lighter-red Moenkopi Formation, and white, layered Cutler Formation sandstone.
(The near-vertical stripes are blasting drill holes.