2-2- Milestone One-Geologic Analysis
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Leticia Pollard-Torres
PHY 103-Lynda Folts
2-2 Final Project Milestone One:
Geologic Analysi
s
Rock
Stratigraphy:
List the various rock types, in order, from the surface (A) downward.
Identify subtypes (detrital, extrusive, etc.) of each rock layer.
In geology, stratigraphy is the study of the order and position of the strata as well as the
relationship between those strata and the geological time scale. There are three types of rocks in
various layers, and these are: Igneous, metamorphic, and sedimentary rocks. Igneous rocks form
as magma or lava cools and crystallizes (Lutgens et al., 2021). Igneous rocks classified as
extrusive or volcanic are formed when molten lava solidifies at the surface. Nevertheless, magma
that solidifies under the earth's surface is referred to as intrusive or plutonic rocks. Unless the
crust is uplifted and the overlying rocks are eroded, intrusive rocks will remain deep
underground. It is important to note that there are many types of igneous rocks with different
textures and characteristics, but they all originate from either intrusive or extrusive sources. The
next type of rock is sedimentary. Upon exposure to the surface, rocks undergo a process known
as weathering. Sedimentary rocks are formed by the accumulation of sediments, such as mud,
sand, and gravel, over time. These sediments are often derived from the weathering and erosion
of pre-existing rocks like in the case of extrusive rocks. the particles of the rock are broken down
furthermore during the process of erosion and gravity (when they move downward from higher
elevation in a mountaing for example. Following deposition, this sediment may become lithified,
or “turned to rock" (Lutgens et al., 2021). Sedimentary rocks are classified by their texture,
composition, and how they are formed. Finally, we have the metamorphic rocks. These rocks
formed when the sedimentary rock is buried deep in the soil and exposed to great heat and
pressure. This process is called metamorphism (Lutgens et al., 2021). It is known that the
metamorphic rock has been under great pressure when it is foliated, and the mineral grains are
flat. A rock that is non-foliated will not align its grains regardless of how much pressure it is
placed under.
According to the diagram given to us, the layers are as follows:
Layer A
: Limestone- Is a chemical sedimentary rock. This rock is composed of mineral calcite
(CaCO2).
Layer B
: Sandstones - Detrital sedimentary rock composed of very small pieces of rock.
Layer C
: Limestone - chemical sedimentary rock. Calcite is the main component.
Layer D
: Coal- Organic chemical sedimentary rock consisting mostly of organic matter.
Layer E
: Siltstone - Clastic sedimentary rock composed of large silt-size grains mixed with clay-
size sediment.
Layer F
: Coal-Organic chemical sedimentary rock consisting mostly of organic matter.
Layer G
: Sandstone-detrital sedimentary rock
Layer H
: Schist- strongly foliated metamorphic rock formed by regional metamorphism.
Layer I
: Granite - an intrusive igneous rock formed by silica-rich magma solidifying slowly.
Volcano and Vent
: Andesite-extrusive igneous rock that can be fine grained or have a
porphyritic texture.
Relative Dating:
From the oldest to youngest the layers are organized as follows: H, G, F, E,
D, C, B, I, A, Volcano and Vent
Towards the bottom, the rock is the oldest, and the layers will gradually form horizontally. In this
pattern, additional sediment layers accumulate over time, layer by layer. According to the
stratigraphic reference shared with us, layer I cuts through almost all older layers and ends at
layer B, indicating that this layer was formed after layer B. Finally, the volcano and vent cut
through all the layers, making this the youngest layer.
Geologic Features
: Based on the stratigraphic reference, there is a clear presence of a fault
line in the diagram. There is a possibility that this fault is the result of the movement of
tectonic plates in depth or volcanic activity. This fault can be observed in Layer I go through
Layer B. This means that the volcanic pressure and heat exerted on the rock underneath
caused the cracks which then allowed magma to escape to the surface.
Depositional Analysis
: As we go down in the layers, we see that the first rock in Layers A
and C is limestone which is composed of mineral calcite (CaCO2). Nearly 90 percent of
limestone is formed from bio-chemical sediments secreted by marine organisms (Lutgens et
al., 2021). Next is the Sandstone in Layers B and G and these types of rocks are formed when
sandy sediment is compacted and lithified. Most sandstones are rich in quartz, so they are
referred to quartz sandstone but if they contain more than 25% of the mineral feldspar, is
called arkose (Lutgens et al.,2021). Going down to Layers D and F we have coal which is
formed from the carbon remains of dead plants from swamps. Swaps are the ideal
environment that allows the plant to accumulate in the bottom of the body of water (Lutgens
et al., 2021). In Layer E we have Siltstone It forms where water, wind, or ice deposit silt, and
the silt is then compacted and cemented into rocks (King, n.d.) Layer H is Schist which is a
metamorphic rock that goes under great pressure and heat. Its parent rock is shale, mudstone,
or siltstone (Lutgens et al., 2021). Lastly is Layer I and consists of Granite. Granite is a type
of intrusive igneous rock that forms where large masses of silica-rich magma slowly solidify
at depth (Lutgens et al., 2021).
Soils:
Based on the topography of the area in the map we see that these two mountains are
part of the Appalachian Mountains system in the Northeastern of the United States. The
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Appalachian Mountains form a natural barrier between the Coastal plains and the interior
territories in the United States. This natural barrier is a result of millions of years of erosion,
which has sculpted the landscape of the region (Dykeman, 2023). The Appalachian
Mountains are also home to a wide variety of wildlife and plants. As the third highest peak in
New Hampshire, Mt. Jefferson is named after the third President of the United States. As
with its neighbors in the picturesque Northern Peaks of the Presidential Range, it boasts a
large area of rare eastern above-timberline terrain, and weather that rapidly becomes near-
Antarctic (
Mount Jefferson - Peakbagger.com
, n.d.). The Appalachian Mountains also include
Mount Washington. There are three rivers that flow out of Mount Washington: the
Androscoggin River, the Connecticut River, and the Saco River (The Editors of
Encyclopaedia Britannica, 2023). As we have discussed in previous topics, runoff and
erosion may occur after rainfall recedes down the mountains. Limestone is part of the first
few layers, closest to the surface, and is a product of chemical weathering, so it may also
indicate a high erosion rate.
Surface Impacts
: It is crucial that the underlying geology of the area be understood in order
to facilitate the development and growth of the population. In areas of flooding zones,
structural instability may occur, and erosion of the soil can eventually cause the collapse of
structures. To ensure the safety of inhabitants, geological surveys should be conducted to
identify any potential risks. Local governments should also invest in preventive measures to
reduce the impact of natural disasters. Finally, detailed regulations and restrictions should be
put in place to limit the development of areas with high geologic risk. By doing so, many
human lives will be saved. The government is responsible for ensuring that no structures are
constructed in these areas.
References:
Lutgens, F. K., Tarbuck, E. J., & Tasa, D. G. (2021). Foundations of Earth Science (9th ed.).
Pearson Education (US).
https://mbsdirect.vitalsource.com/books/9780135851616
National Geographic Society (
2022
). Sedimentary rocks
. (n.d.-b).
https://education.nationalgeographic.org/resource/sedimentary-rock/
King, H. M. (n.d.).
Siltstone: A sedimentary rock made up of silt-size particles
.
https://geology.com/rocks/siltstone.shtml
Mount Jefferson - Peakbagger.com
. (n.d.).
https://www.peakbagger.com/peak.aspx?pid=6955
Britannica, T. Editors of Encyclopaedia (2023, July 11). Mount Washington. Encyclopedia
Britannica.
https://www.britannica.com/place/Mount-Washington
Dykeman, W. (2023, June 14). Appalachian Mountains. Encyclopedia Britannica.
https://www.britannica.com/place/Appalachian-Mountains