g. Reddish-gray, very fine-grained, detrital rock, e h. Dark gray ck that looks
ID: 154040 • Letter: G
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g. Reddish-gray, very fine-grained, detrital rock, e h. Dark gray ck that looks somewhat like basalt, but with a hand lens, the texture appears to be clastic, not crystalline. Some white is too fine to recognize anything. One sam- hednagos in abology k most intcresding when you examine a whole serics of rocks deposited in layers one on top of the other because feldspar grains are present, as are dark grains of something unidentifiable; the matrix ple has thin beds that show a progressive decrease in grain size going from bottom to 2 I you a story. On a hike up a long hill you find the following succession of horizontal rock layers: (1) A are gray shales containing plant fossils and a thin laver of coal. (2) Then comes a transition to a quartz sandstone displaying some ripple marks. The grains are medium-sized at the base but become fine near the top. (3) This is fol- to more shales, but no plant fossils are visible and there is no coal. Instead, there are ancient seashells of various at the top of the hill come various layers of gray and licht tan limestones, some of which display various marine fos- like pages in a book, they tell you a story abundant cross-beds and even sils, including abundant corals. How cause these changes? did the environments of deposition change at this locality? What one thing could have occurred toExplanation / Answer
The above 5 condition suggest there was a quiet ,low energy environ ment which gradually distubed by marine intracalatin ,more specifically marine transgression .
At first the environment was humitropical and low energy condition with static water which led to the deposition of coal and fine grained shale .Followed by this there was an increase in fluvial condition and energy was high which led to the formation sand stone and ripple marks.After that there low energy cndition followed by marine transgression which leads to the deposition of limestone.
So marine transgression was there.It shows there is a gradual shift from fluvial to marine condition.
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