SUPPOSE YOU FIND TWO DIFFERENT SEDIMENTARY ROCKS. ONE IS COMPOSED OF ROUNDED PEBBLES CEMENTED TOGETHER. THE OTHER IS SIMILAR, BUT THE PEBBLES COMPOSING THE SECOND ROCK ARE SHARP AND ANGULAR. WHAT CAN YOU CONCLUDE ABOUT THE CONDITIONS UNDER WHICH EACH OF THESE ROCKS FORMED?"
2006-09-26 10:48:19 · 6 answers · asked by phoenix 1 in Science & Mathematics ➔ Earth Sciences & Geology
Angular pebbles become rounded in an environment where there is more weathering usually due to a higher level of movement. One would expect that the rounded pebbles were most likely in a rapidly moving river where they were in motion and subject to the sharper edges being knocked off. Another place where you commonly find rounded sediments would be on a coastline where the sediments are subject to wave action. Any movement that would cause the sediments to have the sharper edges removed could be possible. The angular pieces were for whatever reason not subjected to the same level of weathering most likely because they were not in an area that caused a high amount of weathering.
2006-09-26 10:59:17 · answer #1 · answered by Anonymous · 0⤊ 0⤋
The rounded pebbles are a conglomerate and have had some time to weather and are at some distance from the source. The sharp and angular clasts in the other are a breccia and have had little time to weather and are close to the source.
2006-09-27 17:06:46 · answer #2 · answered by Amphibolite 7 · 0⤊ 0⤋
Ok, so what do you think would cause the pebbles to become rounded? Where have you seen (in nature) pebbles like that?
Now do the same for the angular ones.
2006-09-26 17:51:52 · answer #3 · answered by Anonymous · 0⤊ 0⤋
the rounded one suggests weathering or rounding via saltation before final deposition. the other could be from frost cracking or other earthly weathering. the component of the rounded sample could be seen as being older due to the degree of rounding of the grains. this assumes that the grains in the samples are chemically similar though. if the rouned grains are a sofet mineral and the angular ones, say a granite, i dont know what to conclude without further info.
2006-09-26 17:54:37 · answer #4 · answered by frankiethebear2002 2 · 0⤊ 0⤋
The one with the rounded pebbles is a conglomerate. The other one with the angular pebbles is a breccia. Please see the wikpedia articles for a description of each type of rock.
2006-09-26 17:54:12 · answer #5 · answered by Anonymous · 0⤊ 0⤋
Rounded pebbles got that way from the erosion from water.
2006-09-26 17:53:38 · answer #6 · answered by DanE 7 · 0⤊ 0⤋