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07036-Final.docxRunning head: GEOLOGY 1
GEOLOGY 9
Geology
Name
Institution
Affiliation
Abstract
New York was once under the rule of the Dutch but the English people took over changing its name form New Amsterdam as initial name to New York City as it is famously known. New York City is one of the most populous cities in the world and is known to be the location as the world's most famous park (Central Park). The rock formation processes became a favorable aspect of the location of Central Park. Central Park may look attractive at a first glance as it is dominated by a single rock type called a schist which is a metamorphic rock type with a sedimentary protolith. Central Park sits on significant sections of the Manhattan Formation and some parts of the Hartland formation which slightly overlaps forming a point of the Cameron’s line that could likely be susceptible to earthquakes. Geologists have previously indicated that from their study of the park, it is clear that there is evidence of glacial movement in the past. This study hence seeks to answer three research questions which include; if rocks in Central Park belong to a single or multiple rock formation, what was the direction of the principal stresses during the folding processes and finally what was the direction glaciers were moving in the last glaciation process.
Introduction
New York is the United States' largest city with a population of about nine million people making it not only the largest city but also the most populous city in the United States of America. New York sits on about nine hundred and fifty square kilometers of land located towards the south of the state of New York. The area covered by New York City as above mentioned is both the dry masses of land and regions where surface water runs such as rivers that are considered within the state’s boundaries. New York's geographical position is one of the world's largest natural harbors (Baskerville, 1982). New York is located at River Hudson’s mouth that runs along the southeastern region of the state. The New York harbor is privileged to have sheltered bays and deep-running waters that have significantly contributed towards the enormous growth of New York City.
The origin of New York City as one of the world’s most renowned and largest cities in the world traces back to when the English claimed the land from the Dutch giving it its current name. New York was once a trading post while under the command of the Dutch but was made the capital of the United States of America when it came under the command of English.
After the English established their rule on the land (New York), settlements expanded northward hitting as hard bedrock in the region of the New England Upland. Valleys of Bronx and Manhattan became laid out (Puffer, Benimoff & Steiner, 2010). The hilly areas of Manhattan that were hilly became parks with Central Park is one of these parks. From a physiographic view, geologists have established from their previous research that New York covers three physiographic units which are; the New England Upland towards the Northwest were part of Staten Island, Bronx and Manhattan lie, the Atlantic Coastal Plain towards the Southeast and the Triassic Lowland towards the Southwest. Significant parts of Long Island and the Staten Island lie with the Atlantic Coastal Plain and the Triassic Lowland.
Background of the problem
According to the U.S geological survey, New York’s basic foundation is a sequence of Proterozoic Z and Paleozoic crystalline rocks. This paper seeks to analyze and discuss the geology and geographical aspects of Central Park. Historically, the site for the location of the Central Park was selected in the year 1853 when a bill was passed allowing the City of New York to take over the unarable land in Manhattan whose terrain was rocky. Central Park is located at N29oE which is approximately 4 kilometers long and about 0.8 kilometers wide (Baskerville, 1982).
The geology has been the main contributor to the landscape and design of the parks in the city. The shaping of the central park has been determined by the natural schist outcropping that were taken advantage of by both modern just as much earlier personnel that were responsible for designing parks (Merguerian, 1996). Designers had to put into consideration of geologic elements in their designs, particularly for the Central Park. New York has a number of significantly sized bedrock features most of which is rather evident in parks.
Research questions
From the geological aspect, many scientists have attributed that Central Park shows evidence of metamorphosed bedrocks. The rocks show signs of polydeformed rocks under ductile conditions with recrystallization and shearing and subsequent folding, metamorphosis and brittle faulting. For this paper, in this assignment, there are a few research questions whose answers aim to be sought after. The study aims to find out:
1. If the rocks belong to a single or multiple rock formations,
2. What was the direction of the principal stresses during folding
3. In what directions the glaciers were moving during the last glaciation.
Hypothesis
For any study, it is important to have carefully thought speculations of the answers to the drawn research questions stated above. The study will hence revolve around the drawn hypothesis and determining their truth in relation to the study. The hypothesizes for this study are:
1. That the rocks in Central Park belong to the same rock formation and not multiple different rock formations.
1. It also appears that the principal stress direction may have been about 140o
2. According to the data collected at Central Park, it may be evident that the glaciers could have been moving in a North to South direction.
Objectives
This study was guided by objectives to answer the previously stated research questions. This study was guided by the following objectives:
1. To determine if the rocks at Central Park belong to single or multiple rock formation
2. To determine the direction of the principal stresses during folding
3. To determine the directions that the glaciers were moving during the last glaciation
METHOD
For this study, it was prudent that a reasonable amount of data relevant to the study be collected to help to answer the drafted research questions and assert the truth the hypothesizes mentioned in previous parts of this paper. The map for the region of study (The Central Park) came in handy in the collection of data as it acted as a guide for the data collection for the study.
Outcrops were drawn on the base map by the use of pace and compass techniques. Each outcrop forms a line along which bending occurred. Other structural features were also mapped whereby these form lines and stratigraphic contacts were interlinked connected outcrops hence producing a map pattern. Linear structural features, as well as planar structural features, were measured, recorded.
The mode of selecting the outcrops to be used for the study was selected by sampling. Sampling entails a random selection of points out of the total to represent the whole population or area. Sampling is done randomly to eradicate the possibility of bias in the study. For this study, samples collected meant to represent the outcrops in the central park were collected for analysis.
As a test of Taterka’s placement of the Cameron's line through the center of the park, there would be samples that would fall to the north of the north park and about half would fall to the south. One of the most sensible reasons why it would be prudent to find the Cameron’s line would be as a way to find the fault line along which earthquakes are likely to occur along. New York City is not quite susceptible to earthquakes but there are as well not extremely unheard of. Sampling for this study was only restricted to schists which are the major component of the bedrock upon which New York City rests on (Merguerian, 1996).
RESULTS
From the results it may be anticipated that from the samples collected, any that would fall in the northern half were likely to be Manhattan Schist which may show some evidence of geochemical distinction and those in the southern half were like to be Hartland Schist which would least likely show a great distinction in geochemical composition.
It was rather impressive that Olmstead and Vaux’s Greensward plan left natural exposures in Central Park as geological sentinels.
The results were as recorded in the tables below.
|
Area |
Azimuth mean (*) |
Azimuth standard deviation |
|
1 |
67 |
60.3844824 |
|
2 |
99.45 |
55.38427955 |
|
3 |
131.4 |
6.11373681 |
|
4 |
128.7 |
7.902882737 |
|
5 |
132.7142857 |
42.94847411 |
|
6 |
109.6666667 |
61.07468909 |
|
7 |
56.4 |
46.1427736 |
|
8 |
91.9 |
59.39594075 |
Geology of the Bronx River
Mapping in New York delineates two culminating episodes of superposed isoclinal and shear folds resulting in the formation of the bedrock units. Since this deformation, the rocks where Central Park lies have been affected by the three almost weak open folding episodes. Foliated rocks of the Sauk, Taconic and the Tippecance have been imbricated along syntectonic ductile thrust faults which have been intruded by the late syntectonic calc-alkaline plutons. Shearing along the Cameron’s line and the later recrystallization produced an annealed highly laminated mylonitic textures along fault lines ((Merguerian, 2010). During the Pleistocene Epoch, the city was significantly affected as it experienced approximately four glaciations. Valleys across the path of flow of the glacier were filled in. the glacier began to retreat causing an abundance in meltwater. Water cascading through the ice eroded potholes. Distal margins of the glacier blocked local reaches of the pre-existing pre-glacial valleys blocking rivers from flowing.
Below are the data tables attached to show the movement of the glacier.
|
Course |
Avg. ELEV form Total Station Data (ft) |
Adj. ELEV （ft） |
|
7-8 |
0.33 |
0.31 |
|
8-9 |
0.42 |
0.40 |
|
9-10 |
-0.17 |
-0.19 |
|
10-11 |
-0.08 |
-0.10 |
|
11-12 |
-0.05 |
-0.07 |
|
12-7 |
-0.01 |
-0.03 |
|
|
0.11 |
0.32 |
Geochemical results
Approximately half the sample collected in the course of the study particularly in Manhattan were collected at locations that had been previously mapped by several authors as Hartland formation while the other half were collected from locations that were mapped as Manhattan formation. As previously stated, if the schist samples used for the study were collected from the northern half were Manhattan Schist, there would have been a high probability that they would display a geochemical distinction as compared to the Hartland Schist which would have been more likely been found on the southern half (Merguerian, 1996).
Sedimentary rock samples collected from the study form well defined tectonic settings were plotted onto a discrimination diagram. The results were plotted potassium oxide and sodium oxides against silicon oxide. The test showed that the samples were successfully separated into three different sections with a next to insignificant overlap. Recycled quartz sediments dominate the sediments which are mainly derived from adjacent continental terrains (Merguerian & Merguerian, 2010). The active continental margin is similar to the other tectonic models which define the sedimentation after the Taconic Orogeny which includes the Eastern North American cross-sections.
The graphs below show the geochemical samples of the rocks collected from the Central Park
DISCUSSION
The depth of the bedrock is a more than significant factor when one is considering to build huge buildings, particularly in New York City. The bedrock is not too far away from the surface in regions around midtown and the southern tip of skyscrapers that have been previously built there. Manhattan is hence situated within the metamorphosed marine Paleozoic sedimentary rock region commonly referred to as the Manhattan Prong. The Manhattan Prong has been overlying gneiss complex that is estimated to be about a billion years old whereby to the northeastern belt is the Hudson River (Merguerian & Merguerian, 2010).
New York City’s tectono-stratigraphic column is said to be influenced by the complicated depositional series and tectonic events. The bedrock at Central Park's geographical location is a metamorphosed sedimentary and volcanic rocks (Puffer, Benimoff & Steiner, 2010). These rocks were previously deposited all through the Ordovician time in a marine environment which is in close proximity to the Eastern Continental Margin of the northern part of America. Rocks were subjected to thrust faulting as a result of the closing of the ocean basin during the Ordovician Taconian which as well underwent metamorphism.
The Manhattan Formation is said to be a distal face of the Lowerre Quartzite which was as a result of the deposition of the continental slope-rise in the Northern part of America. On the other hand, geologists believe that the Hartland formation may have been deposited onto the oceanic crust on the eastward side of the site where the Manhattan formation was deposited then trusted forward to the west across the autochthonous and allochthonous rocks which lie across the Cameron’s line where earthquakes are much more likely to occur along (Puffer, Benimoff & Steiner, 2010). It is then clear that the Cameron’s line cuts down through the stratigraphic column which is set side by side with the Hartland formation down to the basement.
The autochthonous wallomsac schist overlie Manhattan and west Bronx’s basement-cover sequence in a rather uncomfortable position. The autochthonous wallomsac schist unit is mainly composed of brown to rusty weathering which is medium textured, massive which contains graphite, kyanite, pyrite, and quartz schist. The basement bedrock further contains calcite, diopside, tremolite and marble rocks that are significantly thick with layers measuring from centimeters to meters of thickness (Merguerian & Merguerian, 2010).
The wallomsac schist and the Inwood marble naturally, are overlain structurally by the Manhattan schist which can be geographically observed as it forms a bulk of exposed schist on Manhattan Island. The three previously mentioned and discussed mappable units of the Manhattan Island schist essentially represent the coeval foreland basin fill, deep water, and transitional slope or rise when the northern America edge was viewed in consideration of the closure of the proto-Atlantic ocean during the Taconic orogeny. In New York City, all allochthonous Manhattan Formation lies above the autochthonous rocks of the Wallomsac and the Cameron’s line is an indication of the regional ductile contact between the allochthonous and the deep oceanic type both being on the Taconic strata. From the study, it hence has been determined that the bedrock that sits the Central Park is mainly the Manhattan Formation and smaller parts of the Hartland formation (Puffer, Benimoff & Steiner, 2010).
Conclusion
References
Baskerville, C. A. (1982). The foundation geology of New York City. reviews in Engineering Geology, 5. Retrieved from https://books.google.co.ke/books?hl=en&lr=&id=ryBmEiYEHasC&oi=fnd&pg=PA95&dq=%22central+park%22+%22geology%22&ots=SaoCgkwF_g&sig=Gec01DohcqqoyJIbayqhEJKEjP8&redir_esc=y#v=onepage&q=%22central%20park%22%20%22geology%22&f=false
Merguerian, C. (1996). STRATIGRAPHY, STRUCTURAL GEOLOGY, AND DUCTILE- AND BRITTLE FAULTS OF NEW YORK CITY (Unpublished doctoral dissertation). Hofstra University, Hempstead, NY.
Merguerian, C. (2010). Diversion of the Bronx River in New York City-Evidence For Postglacial Surface Faulting? Retrieved from (https://dspace.sunyconnect.suny.edu/bitstream/handle/1951/48026/MERGU200.pdf?sequence =1)
Merguerian, C., & Merguerian, M. (2010). Geology of Central Park-From rocks to ice. Retrieved from (https://dspace.sunyconnect.suny.edu/bitstream/handle/1951/47759/Merguerians2004.pdf)
Puffer, J. H., Benimoff, A. I., & Steiner, J. (2010). Geochemical characterization of New York City schist formations. New York State Geological Association.
Taterka, B. D. (1987). Bedrock geology of Central Park, New York City (Unpublished master's thesis). University of Massachusetts, Amherst, MS.
Azimuth Mean Striation
0 0 60.384482396437861 55.384279548014639 6.1137368096588665 7.902882737049536 42.948474112259532 61.074689086878074 46.142773600592712 59.395940751685863 60.384482396437861 55.384279548014639 6.1137368096588665 7.902882737049536 42.948474112259532 61.074689086878074 46.142773600592712 59.395940751685863 1 2 3 4 5 6 7 8 67 99.45 131.4 128.69999999999999 132.71428571428572 109.66666666666667 56.4 91.9
Field Area Number
Striation Azimuth Mean
Number of Measurements for each Azimuth Direction
Area 1 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100 100-110 110-120 120-130 130-140 140-150 150-160 160-170 170-180 0 2 2 1 0 0 0 0 0 0 0 0 0 2 0 1 0 0 0 Area 2 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100 100-110 110-120 120-130 130-140 140-150 150-160 160-170 170-180 0 1 4 2 0 0 0 0 0 0 0 0 4 4 4 0 0 1 0 Area 3 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100 100-110 110-120 120-130 130-140 140-150 150-160 160-170 170-180 0 0 0 0 0 0 0 0 0 0 0 0 4 5 1 0 0 0 0 Area 4 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100 100-110 110-120 120-130 130-140 140-150 150-160 160-170 170-180 0 0 0 0 0 0 0 0 0 0 0 2 4 4 0 0 0 0 0 Area 5 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100 100-110 110-120 120-130 130-140 140-150 150-160 160-170 170-180 0 0 0 1 0 0 0 0 0 0 0 0 0 1 3 2 0 0 0 Area 6 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100 100-110 110-120 120-130 130-140 140-150 150-160 160-170 170-180 0 3 1 0 2 0 0 0 0 0 0 0 1 1 5 2 3 0 0 Area 7 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100 100-110 110-120 120-130 130-140 140-150 150-160 160-170 170-180 0 0 2 3 3 0 0 0 0 0 0 0 0 0 2 0 0 0 0 Area 8 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100 100-110 110-120 120-130 130-140 140-150 150-160 160-170 170-180 1 0 2 1 0 0 0 0 0 0 0 1 1 3 0 0 1 0 0
Glacial Striation Azimuth
Number Of Measurments
