Chapter 4. Sedimentary Rocks
Exercises on Sedimentary Rocks
Adapted by Lyndsay R. Hauber & Joyce M. McBeth (2018) University of Saskatchewan from Deline B, Harris R & Tefend K. (2015) “Laboratory Manual for Introductory Geology”. First Edition. Chapter 10 “Sedimentary Rocks” by Bradley Deline, CC BY-SA 4.0. View source. Last edited: 8 Jan 2020
Note: much of the overview material for this chapter is replicated in this exercise section for your reference as you complete the lab. You will NOT have access to your lab book or notes for the rock and mineral exam!
Name: _______________
NSID and student number: ____________
Date and lab section time: _____________
TAs’ names: _______________ __________________
Your TAs will check that you have completed the questions at the end of the lab. Please hold on to your lab notes to help you prepare for the rock and mineral quiz and your lab final exam.
4.2 WEATHERING AND EROSION
Sedimentary rocks are formed by the weathering, erosion, deposition, and lithification of sediments. Sedimentary rocks are composed of pieces of other rocks, which are broken down by a process called weathering. There are two basic ways that weathering occurs in nature. First, rocks can be physically broken into smaller pieces (e.g. hitting a rock with a hammer), which is called mechanical weathering. Alternatively, rocks can be broken down and altered at the atomic level (e.g. dissolving salt in water), which is called chemical weathering. There are multiple ways each type of weathering can occur and, therefore, both the rate the rock breaks down and how it breaks down varies dramatically depending on the area and environment.
The most prevalent type of mechanical weathering is the collision, breaking, and grinding of rock by the movement of a fluid, either water or air. The size of the carried sediment depends on the type of fluid and speed of the movement. A fast fluid (e.g. a rapidly flowing river) can carry large particles and cause immense amounts of weathering, while a slow fluid (e.g. a calm stream) would hardly cause any weathering. The density of the fluid also controls the size of particle that can be transported; for instance, a denser fluid, like water, can carry larger particles than a less dense fluid, like air. Another common method of mechanical weathering is called frost wedging, which occurs when water seeps into cracks in the rock and freezes. Water expands when frozen, which puts pressure on the rock and can potentially split boulders. The addition and subtraction of heat or pressure can also cause rock to break, which can cause rocks to shatter when cooled very quickly or immense pressure is released. Finally, plants, animals, and humans can cause significant amounts of weathering. These sediments then undergo erosion, which is the transport of sediment from where it is weathered to where it will be deposited and turned into a rock.
Rocks can also be chemically weathered, most commonly by one of three processes. Th