Exam (elaborations)
ESS 101 B Lab 5 Quiz: Sedimentary Rocks
- Course
- ESS 101
- Institution
- University Of Washington
ESS 101 Introduction to Geology | ESS 101 B Lab 5 Quiz: Sedimentary Rocks
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3/9/24, 3:23 PM Lab 5: Sedimentary Rocks: ESS 101 B Wi 24: Introduction To Geology And Societal ImpactsLab 5: Sedimentary Rocks
Due Feb 18 at 11:59pm
Points 15
Questions 20
Available Feb 9 at 9am - Feb 18 at 11:59pm
Time Limit None
Allowed Attempts 4
Instructions
There are 3 prelab videos linked below to help you prepare for
this lab.
ESS101 Lab 5: Sedimentary rocks
Link to Whidbey Beach Walk (Sediment 1) (https://www.youtube.com/watch?v=la7gN6qYuA0)
(https://www.youtube.com/watch?v=la7gN6qYuA0)
Link to Whidbey Beach Walk (Sediment 2) (https://www.youtube.com/watch?v=LZjRgpvDcJA)
,3/9/24, 3:23 PM Lab 5: Sedimentary Rocks: ESS 101 B Wi 24: Introduction To Geology And Societal Impacts
(https://www.youtube.com/watch?v=LZjRgpvDcJA)
This quiz was locked Feb 18 at 11:59pm.
Attempt History
Attempt Time Score
LATEST Attempt 1 73 minutes 14.92 out of 15
Score for this attempt: 14.92 out of 15
Submitted Feb 9 at 2:04pm
This attempt took 73 minutes.
Introduction
In the igneous rock lab, we focused on tectonic processes that influence rock formation inside of the
earth’s crust. Now we will turn to the earth’s surface, where rock weathers into smaller rock fragments
and minerals. The solid particles and dissolved ions (charged atoms and molecules) freed by
weathering processes are transported by water, wind, gravity, and glaciers from their source (that is, the
original rock) to depositional basins (the places where sediment accumulates). This collection of
loosely packed, unconsolidated mineral or rock fragments is called sediment. In time, sediment is buried
and lithified to form sedimentary rock. Careful examination of the mineral composition and texture of
many sedimentary rocks provides clues to the:
(1) original source of the sediment (provenance);
(2) type and extent of the weathering processes by which the source rock was broken down;
(3) agent (water, wind, gravity, or ice) that transported the sediment and, in some cases, the duration
of transport;
(4) physical, chemical, and biological environment in which the sediment was deposited, and;
(5) changes that may have occurred after deposition (diagenesis).
Sedimentary rocks are a window into ancient environments. They contain traces of evidence that reflect
what the earth was once like. For example, fossilized bones in some sedimentary rocks show that
dinosaurs once roamed the earth. Therefore, the characteristics of a sedimentary rock reflect the
environment in which that rock formed.
The texture, size and shape of sedimentary clasts (or rock fragments) can tell us about the
environment in which a sedimentary rock formed. For example, if the clasts that make up a
sedimentary rock look like rounded river rocks, then we might conclude that that sedimentary rock
,3/9/24, 3:23 PM Lab 5: Sedimentary Rocks: ESS 101 B Wi 24: Introduction To Geology And Societal Impacts
formed in a riverbed (Figure 5-1).
Figure 5-1 Rounded rocks in a conglomerate, a type of sedimentary rock that usually forms in a river
environment.
The mineral composition of sedimentary clasts can tell us where the clasts came from
(provenance). For example, if sedimentary rocks in Oregon contain clasts that are mineralogically
identical to igneous rocks in British Columbia, then we could infer that a river or some other transport
mechanism once connected the two locations.
Sedimentary rocks can be divided into three different categories,
depending on what type of sediment(s) they are made of:
1. Clastic (or detrital), composed of clasts (broken pieces) of other rocks.
2. Chemical and biochemical, formed by the precipitation of ions.
3. Organic, composed of organic materials.
Section 1: Weathering
Weathering is a family of rock breakdown processes that occur at or near the earth’s
surface. Mechanical weathering (also called physical weathering) is when rock physically breaks into
smaller pieces. Chemical weathering is when chemical reactions, such as oxidation or hydrolysis,
dissolve or alter minerals.
Mechanical Weathering
, 3/9/24, 3:23 PM Lab 5: Sedimentary Rocks: ESS 101 B Wi 24: Introduction To Geology And Societal Impacts
Mechanical weathering (also called physical weathering) is when rock physically breaks into smaller
pieces. Plate tectonics and gravity forces cause igneous rocks to crack and break. Gravity then pulls
fragments downhill on slopes and in rivers, leading to rock-on-rock collisions and rock fragmentation.
Mechanical weathering in often facilitated by the action of water.
Chemical Weathering
Chemical weathering transforms existing minerals into new minerals, and releases ions into the
environment. For example, the hydrolysis reaction CaAl 2Si2O8 + H2CO3 + ½O2 → Al2Si2O5(OH)4 +
Ca2+ + CO32- turns plagioclase into kaolinite, a clay mineral. Kaolinite lacks calcium in its structure, so
the leftover calcium from plagioclase enters surface waters as a Ca2+ ion. Note that K-feldspar and Na
Plagioclase can also weather to produce kaolinite clay. Think about what ions will be dissolved and
enter surface waters when these minerals weather.
Question 1
1..25 pts
Identify the eight minerals commonly found in sedimentary rocks displayed on the following page. You
have identified all of these minerals in Lab 3B. Refer to your mineral identification charts (Appendices A-
1 (https://canvas.uw.edu/courses/1699809/files/113584328/download) , A-2
(https://canvas.uw.edu/courses/1699809/files/113584462/download) , and A-3
(https://canvas.uw.edu/courses/1699809/files/113584326/download) ) and the diagnostic properties of
sedimentary rock-forming minerals (Table 5-2).
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