Question

<Chapter 7: Sedimentary Rocks 12 of 29 Item 12 Instructions for Part A: 1. Zoom into the portion of the Gigapan image highlighted below. 2. Observe the grain size/texture the white layers of rock. Part A Grain Size Patterns

NOTE: I already chose the first option and it was incorrect.

Sedimentary structures are patterns in sedimentary rock that form near the time of deposition before the sediments become lithified into rock. One common type of sedimentary structure is grain size patterns. Examine the above highlighted portion of the Gigapan image. Are the grain sizes uniform, variable, or do they exhibit a trend, such as gradually changing from small to large in size, or vice versa, within the layers? There are several ways to help you identify sediment grains in the outcrop and determine their size: Look for rounded to angular-edged particles resting against one another, perhaps even tightly packed together with their boundaries touching. If you can see entire particles and their edges, then they are relatively large in size (e.g., small pebbles down to sand or more generally called coarse). If you cannot make out the individual particles and their boundaries, and they tend to blend in with the matrix (the material surrounding the grains), then they are likely rather small (e.g., silt and mud or more generally called fine). Choose the interpreted sketch that best indicates the direction of fining in grain size (i.e., the direction in which grain size goes from coarse [large] to fine [small] on the highlighted portion of the rock outcrop above).

Answer 1

In order to comment upon the size of individual grains the best way is to look for the sample in the field as in field the grains can be easily identified. If we see the figure in the fourth figure the grains are showing the trend in which the size is going from coarse to fine shown and it’s the most appropriate option for the question because other options shown variation in other grain size in other directions.