analysis of core samples and stratigraphic sections in light of the glacial geology of long island
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Analysis of Stratigraphic Sections and a Core Sample
In Light of the Glacial Geology of Long Island
Gloria Gill
104451458
Stratigraphy Graduate Paper
Introduction:
Numerous geologic events influenced the current geologic state of Long Island, New
York. The most significant of which are the glacial episodes involving the advance & retreat
of a continental ice sheet during the late Pleistocene Epoch. The Pleistocene Epoch (~2
million‐10,000 years ago) is characterized by drastic climate changes and sea level
fluctuations. (Stoffer & Messina, 1996) Sea level change was a result of the several glacial
advances that took place over 10,000‐100,000 year intervals. Glaciation periods are
usually separated by a short warmer period, where the rate of melting is faster than the
rate of freezing, this is known as an interglacial period. (Stoffer & Messina, 1996)
According to Fuller (1914), the following six stages arranged in a chronological order from
youngest to oldest, have constructed Long Island’s current stratigraphy. These stages are:
the Holocene Postglacial Age, the Late Pleistocene Wisconsin Stage, the Sangamon
Interglacial Age, the Kansan Stage, the Interglacial and the Early Pleistocene Nebraskan
Stage.
A glacier acts like a bulldozer, it deforms the material underneath it, reworking and
picking up older deposits and which are then transported before being re‐deposited.
(Martini, 2001) Therefore, during the advancement of the continental ice sheet this
powerful debris flow transforms topography while plucking large boulders and cobbles
from the bedrock in its path. (Stoffer & Messina, 1996) As boulders and cobbles are
dragged along the base of the glacier they are eroded and destroyed, thus deeming a glacier
a silt‐depositing machine. However, boulders and cobbles within the ice are protected
from erosion and can be transported thousands of miles without erosion before deposited,
along with gravels, pebbles and silt, as unsorted diamicts when the ice melts. In addition to
direct glacial deposition, glacial systems include fluvial, eolean, lacustrine, and marine
depositional environments. Therefore, glacial advance and retreat left behind distinct
features that make Long Island unique. These features include but are not limited to
moraines, kettles, tunnel valleys, and outwash plains. (Bennington, 2003)
On long Island there are three well‐defined moraines, the Harbor Hill moraine, the
Ronkonkoma moraine, and Roanoke Point moraine (Bennington, 2003). Moraines are
sediment build ups at or near the margins of glaciers. They are either terminal, which
indicates the glacier’s maximum advance, or recessional, which indicates a glacier’s
temporary pause throughout its retreat (Martini, 2001). Figure 1 illustrates the locations
of these different moraines and their elevations, which provides more insight to their
glacial origin (Hanson, 2002).
Figure 1. Digital elevation model (DEM), Long Island, New York. Glacial features: Ronkonkoma Moraine (Rm), Roanoke Point Moraine (Rpm), Harbor Hill Moraine (HHm), kame deltas (kd).
The current model, which was first proposed by Fuller (1914), explains that the
Ronkonkoma moraine and the Roanoke Point moraine have developed from the same
glacial advance and retreat (Bennington, 2003). On the other hand, unlike previously
thought, the Harbor Hill moraine is not a recessional moraine. It is a younger terminal
moraine that was produced by a second glacial advance and retreat. (Bennington, 2003)
Extending south from the Harbor Hill Moraine is the slightly elevated outwash plain.
(Bennington, 2003) An outwash plain forms because of glacial melt water, in the form of
braided streams, transports large volumes of sediment and debris. (Martini, 2001) In
addition, tunnel valleys, developed by subglacial melt water, also contribute to the
sedimentology of the area. (Bennington, 2003) These features on the North shore of Long
Island (figure 2) are the focus of this study, as I attempt to support the hypothesis that if
Long Island is a composite of depositional environments indicative of glacial activity, then a
core analysis and a study of an exposed section on Stony Brook University Campus will
yield supporting data.
Figure 2. Harbor Hill Moraine (HHm) in Huntington‐Northport area. Glacial features: Tunnel valleys (dashed lines), outwash channels (oc), outwash plain (op). Cold Spring Harbor (CSH).
Experimental Design:
In order to study the stratigraphy data at Stony Brook University campus, two
methods were employed. First a detail stratigraphic section was drawn at three locations
within an exposed section near the stream valley (figure 3). Second, stratigraphic data was
complied using drilling techniques included a hollow stem auger and a geoprobe in the
Research and Development Park located west of the main campus. (figure 4) These
machines allow for core sample collection and core analysis. The Hollow‐Stem Auger Drill
is quick and easy to use but is only for shallow digging. It does not result in a neat core
sample. The Geoprobe drill us a direct push sampling device and is applicable for drilling
20 – 25 feet below the surface. This drill is easy to maneuver into tight spaces and creates
small holes, which minimize surface damage. The center of the Geoprobe drill is hollow like
a straw and thereby in capsules soil samples in five‐foot long plastic tubes. Yet, this type of
sampling results in a compacted core that distorts the actual increments. This can lead to
slight depth miscalculations. The soil samples were transported to the Earth Space &
Science building for examination. This transportation also could of slightly disturbed data.
Figure 4:
Location of Drill Site, marked by D. SB Research and Development Park
Figure 3: Location of Stream Valley, Stony Brook University Main Campus
Observations/Results:
Along the exposed sections of the Creek Valley wall, we used a small spade and
shovel to uncover approximately 4 feet of strata over 25 to 30 lateral feet. The stratigraphic
sections in figures 5‐7 illustrate the data observed on the Creek Valley wall. The stratum
includes organic, loess, clay, sand, and gravel layers, as well as iron and manganese layers.
We can see a trend in clay layering as well as the gravely sand layer of outwash throughout
the area. The stratigraphic sections (figures 5 ‐ 7) also note consistent, dark layers of
manganese and iron. This is seen clearly in the photo of section F (figure 8). These layers
formed in anaerobic conditions when the layer was far below the surface. Well‐defined
boundaries between rock layers often represent breaks in sedimentation. These breaks can
characterize a loss of information over long periods of erosion or none deposition, called
unconformities.
Figure 5: Stratigraphic column for exposed section (A), image complied with the held of Dina Zakaria.
Figure 7: Stratigraphic column for exposed section (F), image complied with the held of Dina Zakaria.
Figure 6: Stratigraphic column for exposed section (C), image compiled with the help of Dina Zakaria.
Figure 8: Photograph of Section F.
On November 12, 2009, with the help of Mr. Baldwin from Land, Air and Water
Environmental Services, we obtained a 25 ft long core sample from the Stony Brook
Research and Development Park, using a Hollow‐Stem auger Drill and a Geoprobe. The
technician drilled the upper 5 feet with the augur. This section consists of glacial till and
some sand‐gravel mix. The first few inches of the sample are silty sand and brown in color.
At a depth of 3 inches, the soil was more gravely sand and lighter in color. The sediment at
this level is poorly sorted. At a depth of 3‐5 feet, the sediment is a rusty colored gravely
sand. From 5 to 24 feet deep, I used the soil chart in figure 9 to hand‐draw the core sample
data, in figure 10, that has alternating series of gravely sand and silty sand. This trend of
layers is indicative of the glacial outwash stream channels, which will be discuss further in
the conclusion. The core sample also has areas of missing sediment due to compaction of
the sediment during the drilling process. This adds an aspect of approximation to the
sample intervals.
Figure 9: Soil Chart: This Chart shows the categorizing of different soils, their symbols and descriptions.
Figure 10: Hand‐drawn core data (sorry my scanner was not working properly.)
Data Analysis:
The sediments found in the core sample and the exposed sections at the Creek
Valley wall are indicative of glacial activity. The creek stratum has layers of clay whereas
the core sample does not. This is due to the presence of water at the creek, which runs
along a glacial tunnel valley. A tunnel valley is cut into drift and other loose material, or into
bedrock, by subglacial streams system. ( Maritni 2001) Wind blown material, better known
as loess, found in the Creek Valley section occurred after the cooling period known as
Younger Dryas, approximately 12,320+/‐ 1,290 years ago. Loess sediment deposits are
typically from near‐by sources and can have components of clay or sand. The low elevation
of this tunnel valley enabled it to collect thick layers of loess since once the wind blown
material was draped along the valley walls, it was protected from being swept back out.
The core sample, on the other hand, is from an area with preserved outwash layers
made mostly of diamictite. Sand and gravel are components of glacial outwash that runs off
melting glaciers in braided stream channels. This is evident by the alternation of sand and
gravel layers. This Donjek‐type sequence of variable scale represents deposition at
different levels within channel or different locations as channels migrate. (Class notes)
Here, the sand is deposited in bars and the gravel deposited at the base of the channel until
avulsion, or channel migration occurs. Avulsion occurs when sediment deposition chokes
the channel and the water finds a new path. We find evidence of glacial outwash
approximately 4 to 5 feet below the surface till. Till is the rocky, unsorted material pushed
up from under the glacier and left on the surface. The advancing glacier pushes material up
before the glacier goes over it forming fold and thrust belts and till is then deposited on top
of these folds and faults.
Conclusion:
The purpose of this research was to find evidence of glacial activity in the
stratigraphic exposures and core samples on Stony Brook University, along. Both the
exposed section and core data can be logically interpreted using the glacial advance and
retreat model. The most important finding that this exercise demonstrates is that although
the stratigraphy at stream valley differs greatly from the core sample, they both still have
the same environmental significance. Without the backdrop of extensive research
conducted in this area, environmental correlation would not of been possible based on the
small amount of data that was collected during this experiment. This is a prime example of
the complexity of the study of stratigraphy and the fact that one must combine multiple
techniques and technologies in order to make any concrete conclusions.
Works Cited
Bennington, J Bret. New observations on the glacial geomorphology of Long Island from a digital elevation model (DEM). Long Island Geologists Conference, Stony Brook, New York, April 2003.
Fuller, M. L., 1914, The geology of Long Island, New York. United States Geological Survey
Professional Paper 82, 231 p. Hanson, G. N., 2002, Evaluation of Geomorphology of the Stony Brook-Setauket-Port
Jefferson Area Based on Digital Elevation Models, Available: http://pbisotopes.ess.sunysb.edu/reports/dem_2/ [2003, March 10].
Martini, Peter I. Glacial Geomorphology and Geology. Prentice Hall, Upper Saddle River NJ, 2001
"New York State's Central Pine Barrens." Geologic Overview. 08/1996. Central Pine Barrens
Joint Planning and Policy Commission , Web. 10 Dec 2009. <http://pb.state.ny.us/cpb_plan_vol2/vol2_chapter02.htm>.