NOTES ABOUT THE
SPARKILL/PIERMONT REGION
TO ACCOMPANY
“WANDERING THE WATERSHED”
GEOLOGICAL SETTING
The region in
which we will be paddling has a very interesting and not entirely clear geologic
history, one that has been extensively studied for decades without reaching
consensus.
The dominant features are the igneous rocks forming the Palisades of
the Newark Lowlands on the western side of the Hudson River and the much older
metamorphic rocks of the Manhattan Prong on the eastern side. The Sparkill Gap,
from which we set out, is one of the largest breaks in the Palisades.
But beneath
such simplicity lie many questions. What is the connection between the Sparkill
Gap and the river? Why are the tops of the Palisades south of the Gap much
smoother than north of the Gap? What is the relationship between the Paleozoic
and Precambrian rocks in Westchester and the Mesozoic rocks in Rockland? What
were the effects of Pleistocene glaciation?
Many of these questions have been explored during field excursions sponsored by
the New York State Geological Association. Three guidebooks in particular are of
use for studying this region, and should be consulted for more details:
40th Meeting (1968) Queens College, CUNY
47th Meeting (1975) Hofstra University
52nd Meeting (1980) Rutgers-Newark
More information about the
availability of these and other volumes is found at
www.nysgaonline.com.
Here are some
excerpts from some of the write-ups of relevance in the area we are exploring
today. (Note: References have generally been omitted, but some dates for
publications have been provided for historical interest.)
1968 “Trip C: The Triassic
Rocks of the Northern Newark Basin” by E. Lynn Savage, Brooklyn College, with
“Road Log” by F.B. Van Houten and E.L. Savage
p. 81: Sparkill
(formerly Overpeck) Creek in the gorge is the only stream that flows eastward
across the Palisade Sill into the Hudson River. Presumably it flows along a
cross-fault (such as seen at Lincoln Tunnel plaza) that has offset the sill more
than 900 feet westward on the north side.
According to Johnson (1931) the Hudson River originally flowed
southwestward on the Schooley erosion surface above the position of the sill,
was superimposed on it and cut a water gap. (Figure 17) Later a subsequent
stream flowing on relatively non-resistant rocks east of the sill captured the
ancient Hudson drainage by headward erosion. Overpeck Creek then reversed the
original drainage direction. This explanation does not account for the
coincidence of the gap and a cross-fault.
Between Piermont and Nyack beach State Park, there are many outcrops
and abandoned quarries of “brownstone” which was
used extensively for building-stone more than 50 years ago. Most of the rock is
a dark brown to reddish-brown well-sorted medium to fine-grained arkose,
commonly interbedded with reddish brown mudstone. Some of the lighter colored
arkose is coarser grained, but conglomerate is rare. Presumably these deposits
are a gradational sequence between the uppermost part of the Stockton Formation
and the lower part of the Brunswick Formation, and differ in heavy mineral
content, sedimentary-metamorphic rock content, and dispersal direction from
those in the upper part of the Stockton Formation.
1975 Trip A-2 “Structure
and Form of the Triassic Basalts in North Central New Jersey” by Michael
Sichko, Jr.
p. 1 “The Palisadian Igneous Province”
The igneous rocks and their counterparts in the
other Triassic basins record the emplacement of basic magma on an enormous
scale, 1,000 miles in length and about 200 miles wide. Significantly, they
correlate broadly with the vast Karoo dolerites and equivalent basic rocks in
the Southern Hemisphere, and like them, apparently were emplaced during an
episode of tension attending the widening of the Atlantic.
[The Palisades Sill intrudes the Stockton Formation, consisting of
gray to red arkosic sandstone, conglomerate, and red shale.] The age of he
Palisades sill has been determined by Erickson and Kulp (1961) at 190 +/- 5 m.y.
by a K-Ar determination on biotite from dolerite at Fort Lee.
It has been established that the Palisades Sill is a multiple
intrusion comprising at least two magma phases, into which later-stage dikes
intruded after the main phases consolidated. This seems reasonable, as the
contemporaneous Watchung basalt flows, with three main basaltic successions,
show that igneous activity at the time was protracted and comprised a number of
phases.
The differentiation of the sill is a complex one of interacting
processes, both mechanical and chemical. The conditions and processes
responsible for the differentiation of the sill are outlined below:
1.
temperature
2.
pressure
3.
magma composition
4.
settling by gravity
5.
upward displacement of the liquid phase
6.
gas streaming
7.
convection
8.
flow differentiation
9.
filter pressing
10.
partial pressure of oxygen
11.
volatile content, particularly water
1980 “Late Wisconsin-Holocene History of the Lower Hudson
region: New Evidence from the Hackensack and Hudson River Valleys” by Stephen P.
Averill, Richard R. Pardi, Walter S. Newman, and Robert J. Dineen
p. 162 “Sparkill Gap Seismic Study”
Sparkill Gap has been most important to the
late and postglacial of the Hackensack. It breaches the otherwise continuous
wall of the Palisades that extends from Jersey City, New Jersey to Haverstraw,
New York. Because of the northward glacially induced isostatic crustal tilt, it
served as the drainage for the Hackensack River on several occasions.
Sparkill Gap is underlain by the Triassic Palisades Formation. These
sandstones and shales are cut by several northeast-southwest trending normal
faults. Sparkill Gap is on the north end of a +180 ft. to +200 ft. above sea
level terrace that was eroded by the southwest-flowing preglacial Hudson River.
The preglacial Hudson was consequent on a graben that broke the crest line of
the Palisades ridge. The Tappan and Sparkill Moraines lie west of the Gap; these
moraines were deposited by ice lying in the valley between Orangeburg and Mt.
Nebo. Stratifies drift (outwash) lies between the two moraines.
The Gap is filled by over 60 ft. of glacial drift, based on test
borings and water wells.
p. 175 “The Piermont Tidal Marsh”
The Piermont estuarine tidal marsh fringe abuts
the Palisades ridge along the west shore of the Hudson Estuary between the
Piermont Pier on the north and Sneden Landing on the south (Fig. 2a). The marsh
exactly spans the 3 kilometer wide Sparkill Gap. The marsh is about 0.6
kilometers wide at its northern end and tapers to a feather edge at its southern
terminus. Although examination of the Nyack 7-1/2 minute quadrangle sheet
suggests that the marsh developed as the delta of Sparkill Creek in the apex
bounded by the Palisades Ridge on the west and the Piermont Pier on the north,
our boring program within the marsh indicates that a portion of the marsh has
been in existence for at least several thousand years. The Piermont Pier was
built as the eastern terminus of the Erie Railroad in 1841. An 188 map of the
area, when compared with the most recent topographic map of the area, indicates
that the marsh has gained about 25% in area during a 73 year inter
According to Lehr (1967), the Piermont tidal marsh contains the most
northerly concentration of true halophytes in the Hudson estuary. Adjacent to
the road at the base of the Palisades escarpment, the marsh is dominated by
cattail while the marsh adjacent to the estuary is covered with Spartina spp.
with minor amounts of other salt marsh halophytes. … The marsh surface
appears essentially in equilibrium with contemporary sea level and forms a
convenient reference datum.
… Concluding the section, the sea level data obtained from the
Piermont Marsh demonstrates that the Hudson Estuary has been in existence for at
least 7,000 radiocarbon years and has witnessed a generally transgressive mode
for much of this interval. Paradoxically, our micropaleontological data suggest
that the estuary is perhaps less saline today than it was during mid-Holocene
times. We believe that the valley has been shoaling more rapidly that the sea
has been rising thus reducing the cross-sectional area of the estuary and
attenuating the penetration of the salt-water wedge intrusion upstream
*****
Robin Elizabeth Bell, Dorothy Peteet, and
others of the LDEO Hudson River Group have made extensive investigations into
many aspects of the river in recent years. These were the theme for the March
2002 E2C Workshop and resources in that section of the web site should also be
consulted.
From the “Hudson River Research at Columbia”
portion of the LDEO “Research” web pages (www.ldeo.columbia.edu),
two abstracts are of interest here.
“Rapid Late-glacial Climate Change in Hudson Watershed”
Principal investigators: Dorothy Peteet and Linda Heusser
After ice sheet retreat atop the
Palisades of the Hudson River, Alpine Swamp, Alpine New Jersey (41 N 74 W)
records a 12,500 C-14 year history of vegetational and climatic change. The
first arrival of trees to the area included spruce, which was followed by
deciduous hardwoods, and the forest became a mixture of boreal and deciduous
species around 11,000 years ago. A dramatic cold event called the Younger Dryas
ensued, lasting until about 10,000 years ago. This cold reversal was marked in
the Hudson region by an expansion of the boreal forest (spruce, paper birch,
fir, alder) and the decline of the warmth-loving trees (oak, ash, white pine).
The return of the warm trees at 10,000 years ago was extremely rapid, and the
boreal trees died out within a century. The timing of this event is synchronous
with the same cold event in Europe, Greenland, and the North Atlantic. [Peteet,
D., et al, 1993, “Late-glacial pollen, macrofossils, and fish remains in
northeastern USA—the Younger Dryas oscillation. Quaternary Science Reviews 12:
597-612.]
“Environmental History of the Piermont Marsh, Hudson River,
NY” Principal Investigators: Dorothy Peteet and Jennifer Wong.
An 11-meter core from Piermont
Marsh, New York, was retrieved from the northern mid-marsh region and dates to
about 4,200 C-14 years. The rate of deposition in the marsh is about 0.26 cm/yr
throughout. A low-resolution profile of pollen, plant macrofossils, and charcoal
reveals major changes in vegetation throughout the marsh history. Earliest
samples reveal a dominance of hemlock, while about 3,000 years ago, the profiles
are dominated by pine. Most recent sediments show anthropogenic influence with
the dominance of giant reed (Phragmites) seeds replacing the cattail marsh (Typha).
Foraminifera macrofossils reveal a history of oscillations between low and high
marsh environments. Further high-resolution research is ongoing. [Wong, J., and
Peteet, D., 1998, “Environmental history of Piermont Marsh, Hudson River, NY.
Section III, 30. In W.C. Nieder and J.R. Waldman (eds.), Final Reports of the
Tibor T. Polgar Fellowship Program, Hudson River Foundation.]
Tides and River Structure
Strictly speaking, this portion of the Hudson
is not a “river,” but rather a “tidal estuary.” Rivers flow from their head to
their mouth, either joining another river or lake, or entering the ocean. Many
streams also have steep to gentle gradients as they drop from their source to
their outlet. But the Hudson from Albany southward is basically at sea level and
experiences twice-daily tidal flows of more than a meter.
Predicted tidal information—times for high and low tides and
expected heights above datum level—can be found at
www.nos.noaa.gov. For example, on May 11, 2002, the predictions for
Tarrytown (about two miles north across the river) are:
4:23 a.m. Low 0.2 feet above datum level
10:11 a.m. High 3.4
4:24 p.m. Low 0.2
10:15 p.m. High 3.9
As the New Moon phase is on May 12,
these are close to “spring tide” variations. As a consequence of these tidal
flows, surface currents in the river need to be understood by paddlers. They can
be strong enough to impede or enhance a trip greatly, although at other times be
negligible.
NOTE: THE IMAGES ACCOMPANYING THIS 2002 TRIP
DEMONSTRATE THE IMPACT OF TRYING TO PADDLE IN THIS AREA AT SPRING LOW TIDE. AS
ONE PARTICIPANT SAID WHEN EVERYONE WAS SAFELY OUT OF THE MUCK, "ANYONE CAN TAKE
US KAYAKING, BUT YOU GAVE US AN ADVENTURE!"
For the portion from about Kingston southward,
the river also has a two-layer structure involving an upper freshwater layer and
a lower saltwater layer. The location of this “saltwater wedge” varies depending
on precipitation and other factors. The salt front is defined as 100 mg/L
chloride concentration, so droughts and heavy rainfall can easily affect the
location. Current position can be found through the US Geological Survey “Salt
Front” data (http://ny.usgs.gov/htdocs/dialer_plots/saltfront.html)
The
approximate location at that time was near Tellers Point, about 6 miles north of
the Tappan Zee Bridge and 33 miles above the Battery. During the past decade,
the position has fluctuated from less than 15 miles above the Battery to more
than 80, placing it north of Poughkeepsie. (http://ny.usgs.gov/htdocs/dialer_plots/rmdvall.HTM).
Because of the tidal nature, streamflow records
are not kept for this portion of the river system, although other data are. On
May 8, water temperatures at Hastings-on-Hudson (almost directly across from the
Piermont Marsh) was 15.8 deg C (about 60 deg F.) This indicates recent warming,
as only a week earlier, water temperatures below 12 C were recorded (http://waterdata.usgs.gov/ny/nwis/uv/?site_no=01376304&PARAmeter_cd=00065,00060,72020,00010)
Water Quality and Other Parameters
The U.S. Environmental Protection Administration’s (E.P.A.) “Surf
Your Watershed” (http://www.epa.gov/surf/)
contains vast amounts of valuable resources about the hydrology of our country.
The “Lower Hudson” watershed can be found at
http://cfpub.epa.gov/surf/huc.cfm?huc_code=02030101. Surprisingly, the Index
of Watershed Indicators classifies the water in this region as “2—Better
Quality/High Vulnerability” on a 6-point scale. You can learn about many other
hydrologic variables from this web site, as well as make comparisons with
adjacent or distant watershed.
. We hope these notes will stimulate you to
learn more about the area, whether or not you are observing it while paddling or
on-shore. Many other questions can be developed that could serve as the basis
for future investigations by you and your students. Just remember, “The real
classroom is outside—get into it!”
Michael J. Passow
May 2002
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