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D) When the rocks were deposited, side D was the highest (it was on top).E) The rocks were formed from lava flows far down in the Earth, and were not deposited.Feedback: This is a cliff in the Grand Canyon. The picture was taken and then turned on its side. Originally, the muds of side D were deposited on a floodplain, a mud crack formed and sand fell into it (the red arrows) as the sand-dune rocks of side B were deposited on top.Points Earned:1.0/1.0Correct Answer(s):B6.
Look at the picture above, which shows a small section of a “fossil” sand dune (a sanddune in which the grains have been “glued” together by hard-water deposits). When the dune was first deposited, which was up (which letter is closest to the arrow that is pointing in the direction you would have looked to see the sky when the dune was deposited)?A) AB) BC) CD) DFeedback: Just to the right of the letter “D” there is a small unconformity. The layers farther to the right are cut along that surface. Layers must exist to be cut, so the left-hand layers are younger, the right-hand layers are older, and “up” was to the left.Points Earned:1.0/1.0Correct Answer(s):D
7.The above picture shows a region a bit under a foot across, in a cliff in Red Canyon, just west of Bryce Canyon National Park. The rocks in the picture are the same as the rocks at the bottom of the beautiful Bryce Formation, the pastel rocks in Bryce Canyon. The red arrows surround a very interesting, reddish clast. What is the geological interpretation of this picture?A) A landslide made everything we see.B) Many older rocks, some with interesting histories, were rounded in a river, thenmixed with sand and glued together by hard-water deposits, then ground up in a big earthquake fault.C) A glacier picked up a range of rocks, carried them, then piled them up in a moraine, then a landslide happened to put those rocks with others, and then an earthquake fault ground up the rocks.D) Many older rocks, some with interesting histories, were rounded in a river, thenmixed with sand and glued together by hard-water deposits; the resulting rock layer was broken into pieces, which were rounded in a stream, mixed with other rocks and sand and glued together by hard-water deposits, and the resulting rock layer was raised out of the river, and eroded to yield the modern outcrop.
E) A glacier delivered the rock; glaciers can carry all different sizes of rocks, as seen here.Feedback: The story is even longer than D indicates, because of all the things that happened to make the various clasts in the reddish conglomerate clast, because thosevarious clasts include sandstones made of pieces of still-older rocks. Glaciers can carrymany sizes, as can landslides, but landslides don’t round the pieces, and glaciers knock off corners but make flat, striated faces. Earthquake faults also make flat surfaces with scratches on them.