GEOL101 Lab 6
pdf
keyboard_arrow_up
School
CUNY College of Staten Island *
*We aren’t endorsed by this school
Course
100
Subject
Geology
Date
Apr 3, 2024
Type
Pages
10
Uploaded by ChancellorBoar4201
Introduction:
Defined by their formation process, sedimentary rocks are the result of particles,
minerals, and organic materials settling in basins, lakes, oceans, and riverbeds. These rocks are
unique in that sand, silt, clay, and gravel sediments accumulate, compact, and cement - often in
layers in processes such as erosion, deposition, and lithification. While identifying sedimentary
rocks in this lab, it is valuable to note that they are clastic sedimentary rocks, which means the
rocks are composed of solid, individual fragments of materials that were transported and
deposited by geological processes. However, there are also chemical sedimentary rocks, forming
from the precipitation of minerals from water, and organic sedimentary rocks, primarily made of
organic materials such as plant debris or marine organisms. Additionally, while identifying grain
size will be important in this lab, the grain roundness types - very angular, subangular,
subrounded, and well-rounded - will provide more information on the distance and heights a
particular sediment has endured.
Activity 6.3: Sedimentary Rock Inquiry
A)
1.
Composition: Rock fragments, pebbles, cobbles
Texture:
Grain-size: Mostly gravel-sized
Grain-shape: Rounded
Grain arrangement: Poorly sorted
Sedimentary Rock: Conglomerate
2.
Composition: Calcite, shells, deposited in the ocean (tropical sea, shallow sea)
Texture:
Grain-size: Mostly gravel-sized
Grain shape: Angular
Grain arrangement: Poorly sorted
Sedimentary Rock: Coquina
3.
Composition: Halite, Sodium Chloride (NaCl)
Texture:
Grain-size: Crystallized
Grain shape: Angular, cubic
Grain arrangement: Uniform
Sedimentary Rock: Rock salt (Halite)
4.
Composition: Clay minerals
Note: Does not fizz in acid
Texture:
Grain-size: Silt, clay
Grain-shape: Well-rounded
Grain-arrangement: Well-sorted
Sedimentary Rock: Shale
5.
Composition: Fossil of a leaf, clay, mud
Note: Fizzes in acid
Texture:
Grain-size: Silt, sand-sized
Grain-shape: Well-rounded
Grain-arrangement: Well-sorted
Sedimentary Rock: Fossiliferous limestone
6.
Composition:
Note: Does not fizz in acid, grayish color
Texture:
Grain-size: Silt sized
Grain-shape: Well-rounded
Grain-arrangement: Well-sorted
Sedimentary Rock: Siltstone
B) Reflect and Discuss: Based on my observations and descriptions of sedimentary rocks in Part
A, I would classify rock specimens into logical groups by understanding that sedimentary rocks
form from the gradual accumulation and compression of sediments; therefore, while solidified
and compacted, they can either be clastic (composed of mineral fragments), chemical (formed by
mineral precipitation), or organic (composed of organic matter). To help narrow down
sedimentary rocks into this category, an observer can consider the size and arrangement of the
sediments, as well as if the rock contains any biological material, such as shells, or has traces of
fossils. While color and layering may be distinguishable characteristics for each sedimentary
rock, an observer could also reference if the rock fizzes in acid to determine if it is a Carbonate
Sedimentary Rock, meaning it fizzes in dilute hydrochloric acid, or if it is a Siliclastic
Sedimentary Rock, in which it does not react with HCl. Furthermore, to learn more about a
sedimentary rock's origin, an observer could consider the sedimentary structure to determine the
environment the rock could have developed. For instance, sedimentary rocks can have
symmetrical ripple marks, indicating an environment with high winds or water traveling in one
direction, such as rivers, ocean currents, or sand dunes.
Activity 6.4: Sediment from Source to Sink
1A) Grain size classes (including dirt) in Photo B: clay, silt, sand, gravel, boulders
1B) The sedimentary grains of the rockfall deposit are poorly sorted as all of the classes are
represented in their natural arrangement.
1C) The shape of the sedimentary grains in the rockfall deposit is angular as there was nothing to
round them off.
1D) If the sediments in the rockfall deposit were lithified together without any further movement
downslope, they would form Breccia, as the photo features angular to sub angular gravel-sized
grains surrounded by finer grains - there are various silicates and rock segments.
2A) I expect grain sizes of silt, clay, and sand to be carried in the water based on the turbulence
of the mountain stream.
2B) I expect pebbles and gravels to be rolling, sliding, or resting at the bottom of the channel.
2C) The shape of the sedimentary grains seen in the stream bank can be described as sub-round
with a mixture of rounded grains.
3A) The Merced River in Photo D would also include grain sizes of silt, clay, and sand; there
may be a few gravel-sized grains.
3B) The sedimentary grains in the stream bank are still poorly sorted.
3C) The sedimentary grains are more rounded; however, some grains remain sub-round as they
have edges to them that aren’t completely rounded out.
3D) If the sediments in the stream bank were lithified, they would create a Conglomerate given
that the grains are rounded to subrounded gravel-size grains containing rock fragments.
3E) To describe the change of sediments between the tributary streams and the Merced River, the
sediments are evidently more rounded out, and even though they remain poorly sorted, there is
some evidence of better sorting taking place. In general, even the boulders are smaller than they
were before.
4A) The grain sizes that are most likely to deposit in Lake McClure from the erosion of the
Yosemite Valley would be clay and silt with a potential for some sand-sized grains. These grain
sizes would be most common given the distance traveled and the large change in elevation for
the traveling gravel (weathering and erosion).
4B) The composition of most of the Yosemite Valley grains would be quartz (broken down into
different sizes) and clay minerals as they remain in the sediment load.
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
B) Reflect and Discuss: The clastic sediment traveling downstream from Yosemite Valley to
Lake McClure will change because the river is carrying eroded sediments across a 65 km
distance and an elevation that ranges from 1,200 meters to 250 meters. During this travel, the
sediments will experience abstraction, disintegration, and potential corrosion; nevertheless,
erosion will transform the sediments to be sand-sized. Depending on the distance traveled, more
angular, larger sediments will transform into rounded, smaller sediments; Quartz and Feldspar
can be used in observations to approximately determine how long a sediment load has traveled
for. These observations can be applied to describe clastic rocks in general as they require the
observation of the clasts' size, shape, and arrangement, as well as if there is the presence of
biological material or fossils. Furthermore, examining a clastic rock’s physical features can go
hand in hand with its physical environment because the environment influences sedimentary
structures, such as bedding planes, ripple marks, or mud cracks.
Activity 6.5: Sediment Analysis, Classification, and Interpretation
Sample A:
1.
Grain size range in mm: Approximately 0.5 - 1 mm
2.
Percent of each Wentworth size class:
Clay: 0 % | Silt: 10 % | Sand: 90 % | Gravel: 0 %
3.
Grain sorting: Well-sorted
4.
Grain roundness: Well-rounded
5.
Sediment composition: Bioclastic
6.
This sediment is found in coastal marine environments with moderate wave movement.
Sample B:
1.
Grain size range in mm: 0.5 - 2 mm
2.
Percent of each Wentworth size class:
Clay: 5 % | Silt: 20 % | Sand: 70 % | Gravel: 5 %
3.
Grain sorting: Moderate sorting
4.
Grain roundness: Sub-angular
5.
Sediment composition: Siliciclastic
6.
This sediment is found in an environment of high movement, such as rivers or one with
high winds, considering the Quartz is subround and has undergone a degree of erosion.
Sample C:
1.
Grain size range in mm: 1 - 10 mm
2.
Percent of each Wentworth size class:
Clay: 10 % | Silt: 20 % | Sand: 35 % | Gravel: 35 %
3.
Grain sorting: Poorly sorted
4.
Grain roundness: Angular
5.
Sediment composition: Bioclastic
6.
This sediment is found in a shallow marine environment given the presence of shells and
various fossils and is formed through the deposition of minerals.
B. Reflect and Discuss: Sample C sediments would be the least diagnostic of an ancient
environment as the seashells and similar sediments are organic substances that are more prone to
breaking down, dissolving, or recrystallizing in comparison to Sample B, Quartz. Additionally,
while not always true, seashells are typically found in marine environments, which means that
their presence would be telling of some sort of body of water, such as oceans or seas. On the
contrary, Quartz is abiotic and can be more telling of its geological history if analyzed for its
grain size, shape, and overall composition. Lastly, Sample C appears to have the largest mix of
grain sizes; therefore, it would be much harder for an observer to conclude from what ONE
specific environment the sediments are from.
Activity 6.6: Hand Sample Analysis and Interpretation
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
Activity 6.9: Using the Present to Imagine the Past - Cape Cod to Kansas
A1) The modern environment (Photograph Y) and Kansas rock (Photograph X) are similar as
they both feature clay, silt, and sand-sized grains (even though the key informs that Photograph
Y has mostly sand-sized grains). Furthermore, Photograph X has fossilized shells, starfish, and
other fossils indicating a marine environment. Photograph Y also has living starfish and smaller
organisms within a marine environment.
A2) The modern environment is different from Kansas Rock as it has fewer fossils located within
the grains. Photograph X represents an environment from 290 million years ago, while
Photograph Y captures a more modern marine environment. It is important to note the
geographical location of Photograph X Kansas, while Photograph Y is from Cape Code,
Massachusetts. In regards to the sediment, Photograph X has sand-sized fossil fragments and
rocks that are made of fossil shells, whereas Photograph Y features a mixture of sediments, such
as clastic sediment, bioclasts, and living starfish. While the depth of Photograph X is unknown,
Photograph Y is 40 meters deep which could still be identified as a shallow marine environment.
A3)If the area in Photograph X is now rolling hills and farm fields, then 290 million years ago
(when North America was part of Pangea, a supercontinent) this environment had to be a seaway
that eventually through sediment deposition, erosion, tectonic movement, and changes in sea
level, new landforms were created. As more and more sediments would accumulate, they would
be compacted and lithified to form rock, contributing to the development of fields and hills.
Reflect and Discuss: For sediment to turn into sedimentary rock, lithification would have to
occur. Lithification is the process of compaction and cementation of loose sediments to form a
rock. When sediments are deposited into a particular area, the weight of the overlaying layers
increases and this pressure pushes out air and water from the space between the sediments. As
this compaction continues to occur, minerals can fill the spaces between the sediment particles,
allowing for everything to bind together. Lastly, with time, the minerals that contribute to
holding the sediments together form crystals that bind the sediment particles even more.
Eventually, a solid rock will develop.
Conclusion:
While exploring sedimentary rocks in this lab, I learned that there are two main
categories of mineral composition, silicates and carbonates. To elaborate, silicate sedimentary
rocks have a dominant contents in silicate minerals, such as quartz, feldspar, and clay. Quartz in
particular is interesting as it is the most resistant to weathering; therefore, based on its physical
appearance, one can learn about the geological location and time period it derives from.
Moreover, carbonate sedimentary rocks are largely made of carbonate minerals, including
aragonite, calcite, and dolomite. In addition to the mineral composition, I learned a new word,
“fissility,” meaning that rock breaks easily along irregular, approximately parallel surfaces. I was
able to identify fissility in the mudstone, shale. Lastly, I was very intrigued by how the
sedimentary structures, for example, raindrop impressions, mud cracks, or ripple marks, resulted
from their environments. To elaborate, ripple marks are caused by environments where wind or
water travels in one direction for some time, such as rivers, ocean currents, or on sand dunes.
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
Overall, sedimentary rocks capture the intricate history of Earth’s surface environments, the
process that shaped them, and helps geologist better understand the changing landscape.