Activity 11A: Concept Sketches and Sedimentary Processes

Concept Sketches and Sedimentary Processes

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Alternatively, you may draw the concept sketches in another program (like PowerPoint, Illustrator, or others) and upload them here. See the rubric below of what to include in your concept sketch.

1. 1. Imagine a mountain composed of granite: what does the resulting sediments’ journey via a river to the ocean look like? After reading the background information provided, draw a concept sketch for “The Journey of a Pebble”. Labels should be short sentences explaining the relationships between geologic features and processes.

   The Journey of a Pebble

   As the granite mountain is weathered, it is broken down into clasts of varying sizes. Larger, jagged clasts remain nearby and retain the composition of the original granite minerals (quartz, potassium feldspar, muscovite, Na-rich plagioclase feldspar). Clasts that continue their journey, perhaps by a fast-moving river, are changed. During transportation, clasts collide with one another becoming progressively smaller and more rounded. As the topography flattens, the river’s velocity begins to slow, triggering deposition of larger clasts, while smaller clasts continue to be transported. As the river meets the beach and ocean, velocity will continue to slow down, depositing smaller and smaller sediments, until nothing is left. Throughout this journey, clasts will also undergo chemical weathering, fundamentally altering the original mineralogy of the granite. Feldspars and micas are transformed into clay-minerals, like kaolinite or montmorillonite, and the iron-bearing minerals alter to hematite. The only mineral that does not chemically change is quartz.