BOUGUER GRAVITY ANOMALY MAP OF NEW JERSEY
By
William E. Bonini
Associate Professor
Department of Geological Engineering
Princeton University
STATE OF NEW JERSEY
Richard J. Hughes, Governor
Department of Conservation and Economic Development
Robert A. Roe_ Commissioner
Division of Resource Development
Kenneth ft. Creveling,
Director
Bureau of Geology and Topography
Kemble Widmer, State Geologist
Trenton, New Jersey
1965
CONTENTS
Abstract
....................
Introduction
i
...................
Acknowledgements
1
.................
2
Gravity Data ...................
2
Significance
4
Detailed
of Gravity Anomalies ............
Surveys and Summaries of Results
.........
6
I
Regional Features
.................
8
Literature
.................
9
Cited
ILLUSTRATIONS
(Plates are in pocket)
Figure 1
Cross-section
from Phillipsburg to Barnegat Bay
showing Trans-New Jersey Gravity High ........
Plate I
Bouguer Gravity Anomaly Contour Map of New Jersey,
scale 1:250,000.
Plate II
Bouguer Gravity Anomaly Contour Map of New Jersey,
scale approximately 1:1,000_000.
Plate [II
Geologic Map of New Jersey,
I: 1,OOO,O00.
iii
scale
approximately
7
BOUGUERGRAVITY _:_OMALYMAP OF NEWJERSEY
By
Williom E. Bonini
AssociateProfessor
Deportment of Geological
Engineering
Princeton University
ABSTRACT
A Bouguer
is based
Gravity
Anomaly
on over 4000 gravity
tour interval
the State
is 5 milligals
Geologic
Map.
given with Boaguerand
marked
positive
density
excess.
Georgia
to Vermont
Map of New Jersey
observations,
half of which
and the map is translucent,
A cross-section
isostatic
Bouguer
and
The trans-New
and generally
is presented.
It
previously
unpublished.
Con-
New Jersey,
The trans-New
and is related
to Baruegat
Jersey
gravity
to basement
high is part of a series
associated
1:250,000)
so that it can be used as an overlay
shown.
anomaly
Jersey
were
from Philiipsburg,
anomalies
isostatic
(scale
with the Piedmont
on
Bay is
high is a
or sub-basement
of gravity
highs
running
from
Province
south
of New Jersey•
INTRODUCTION
Scope
and Purpose
Over 4000 gravity
observations
New York and Pennsylvania.
1000 stations
detailed
G. P. Woollard
of the middle
Connecticut,
southern
gravity
Atlantic
New York,
survey
Bay and Phillipsburg,
a gravity
study
of the Courtlandt
(1944)
on 700 stations.
have
added
measurements
(Bonini,
have
1949; Meier,
been
reported
which
New Jersey.
Complex
published
covered
a regional
He further
observations
Steenland
the results
wide section
based
on 185 stations.
of Phillipsburg_
University
in the Department
data.
1962; Vreeland,
About
of Geological
of a
the results
New Jersey,
in unpublished
on
between
New York,
in six theses
1
reports
report
to this published
1956; Stewart,
as Delaware,
(1952)
map of an a/'ea west
of
map based
as well
in a 5-mile
observations
1949; Johnson,
gravity
areas
and Woollurd
near Peekskill,
at Princeton
and in nearby
New Jersey,
Pennsylvania.
of 700 gravity
and students
2000 new gravity
been made in New Jersey
(1943a)
and eastern
has made a gravity
Faculty
over
states
consisting
Barnegat
J. B. ttersey
have
detailed
of
based
studies
1700 of these
new
Engineering
1965; and Wofford,
1962).
The purpose
New Jersey
those
and surrounding
not familiar
pretation
of this geologic
area
with gravity
report
compiled
anomalies,
is to present
the revised
from both the published
there
gravity
anomaly
and unpublished
is a brief section
on anomalies
map of
data.
For
and their inter-
in New Jersey.
ACKNOWLEDGEMENTS
George
supplied
P. Woollard,
Director_
a copy of his revised
at Princeton
the gravity
University,
map.
work.
The Higgins
partial
support
Kemble
1943 data.
provided
Princeton
Institute
John E. Hardaway
considerable
University
work and office
Widmer, New Jersey
State Geologist,
University
and John H. Vreeland,
and gravity
and the National
compilation
of the data.
The writer
overlay
while
students
of
for the field
Foundation
with respect
as a translucent
kindly
and in preparation
instrument
Science
for his encouragement
its publication
of Hawaii,
both in the field
the vehicle
University
for the field
possible
assistance
supplied
Fund of Princeton
of the map and for making
of Geophysics,
provided
is grateful
to
to preparation
for the State
Geologic
Map.
GRAVITYDATA
This
(1943a),
section
refers
and Steenland
only to the Princeton
and Woollard
(1952),
University
have
covered
data,
since
the following
Hersey
items
(1944),
Woollard
with respect
to their
observations.
Observed
Gravity
Values
Values
for observed
ter of Room 142 , Guyot Hall,
Guyot
Hall value
tion in Washington,
has
been
gravity
Princeton
established
D. C., by Bonini
are based
on the absolute
University,
and all field
by measurements
and Woollard
between
value
(980.1776
stations
gals) 1 in the cen-
are tied to this
it and the fundamental
value.
The
gravity
sta-
(1957).
1) The gal is the unit of gravitational
acceleration
and is equal to an acceleration
of one
centimeter
per second squared.
The milligal (regal) is one-thousandth
of a galand
is the
most frequently
used unit.
9) In 1964 this room was converted
into a corridor to permit access
to a new wing. The original site is otherwise
unchanged
.and is in the center of the corridor in the old part of the
building between Rooms 13 and 15.
2
The general
plan of gravity
to Guyot Hall by measuring
made relative
observations
short-time
to the field bases,
closed
was to establish
loops
with station
between
field
them.
reoccupations
every
base
Local
stations
related
observations
two to four hours
were then
for instrumental
drift control.
Elevation
and Position
Elevations
Control
were determined
from U. S. Geological
elevation
errors
anomalies
sheets
topographic
are estimated
caused
by pace
errors
or based
values
national
Gravity
and free
air correction
a density
Formula
of less
between
producing
than 0.3 regal.
from such
known
or by interpolation
on a 20 foot interval.
five feet,
an estimated
Stations
points.
In general,
error in the gravity
were located
On traverses
the
on topographic
by foot, positions
points.
where
Instruments
of gravity
at sea level
(U. S. Coast
and Geodetic
value,
of 2.67 gm/cc
stations
0.06 mgal/ft
for material
the effect
above
above
was greater
were determined
Survey,
1942).
sea level,
sea level.
was
Terrain
according
to the 1930 Inter-
The combined
Bouguer
used for all reductions
corrections
were applied
(mass)
assuming
only to
than 0.4 mgal.
and Calibration
A Worden Gra_cimeter,
and Meier (1949),
determined
on which
by comparison
The Humble
calibration
pendulum
stations
Accuracy
of Gravity
Observed
within
contoured
than
on mileage
and compass
tied to benchmarks,
Reductions
Theoretical
values,
by altimeters
maps
to be less
by elevation
at known points,
were located
Data
Survey
either
W-57, was used
the Humble
X-type
with pendulum
was determined
in the eastern
United
for all measurements
meter
was
and gravimeter
by comparison
States
employed.
data
except
those
of Bonini
(1949)
The Worden calibration
by others
with U. S. Coast
(see
Bonini,
and Geodetic
1963,
was
fig. l).
Survey
in 1948.
Data
gravity
in which observed
values
gravity,
are considered
latitude,
to be accurate
and elevation
0.5 regal.
3
to 0.2 regal.
are important,
Bouguer
should
anomaly
be accurate
• The Gravity
Anomaly
Bouguer
stations
gravity
indicated.
E. Hardaway
questionable
overlay
studies,
data.
(both
as an overlay
data
are contoured
on a 5 mgal interval
is nlade to the sources
is derived
from Woollard
and John H. Vreeland
A small
scales
a large
anomalies
Reference
most of the regional
by John
Map
geologic
approximately
on the New Jersey
(1943a),
of Princeton
included.
Geologic
and regional
further
regional
University
map of New Jersey
1:1,000,000)
gr_;vity map is also
of detailed
in areas
and an abbreviated
are provided
Although
stations
were added
of poor control
gravity
of 1:250,000,
can be purchased
of the
data.
in the rear pocket.
It is drawn on a scale
Map which
on the basis
for $3.00
anomaly
or
map
"For more detailed
and is suitable
from the following
source'.
Map and Publication
Sales Office
P. O. Box 1889
Trenton,
SIGNIFICANCE
New Jersey
08625
OF GRAVITY
ANOMALIES
General
The gravityanomaly at a given locationis the differencebetween the value observed
at that point and the predictedtheoreticalvalue. In the calculationof a theoreticalgravityvalue
two thingsmust be considered: (1)the latitudeof the stationand (i_)
itselevationwith respect to
sea level.
The theoreticalvalue of gravityat sea level at a given latitudeis determined according
to the 1930 International
Gravity Formula (U. S. Coast and Geodetic Survey, 1942),which considers
thenon-spherical shape of the earth and the effectsof the centrifugalforce. The "latitudeeffect"
in New Jersey is approximately1.2 regalmile, increasingnorthward.
The second theoreticalconsiderationconcerns the elevationof a stationwith respect to
sea level,since the InternationalGravity Formula predictsgravityat sea level. Ifa stationis
100 feet above
gravity
elevation
is 0.094
there
sea level_
will be less
between
mgal/ft
it is 100 feet further
than
the station
decreasing
that given
by the Formula.
and sea level
upward
from the earth's
from sea
(as would
level.
"4
center
If one considers
be the case
This
and the theoretical
is called
only the change
in a tall building),
the
value
free air effect.
of
in
this effect
On the other
hand,
for field observations
station
and sea level,
amount
determined
Bouguer,
effect.
is 0.034
no topography
sea level.
and this mass
Using
mgal/ft,
would
and the density
a density
increasing
near the station,
For detailed
is at 100 ft elevation,
in theory
by the elevation
or mass,
this effect
when one
i.e.,
increase
between
the station
with increase
there
This
effect
This
is in this case
the
by an
is called
the
of 2.67 gm/ce,
assumes
on a plain
topography,
between
attraction
and sea level
in elevation.
is considerable
(rock)
the gravitational
of the material.
that the station
work where
there is mass
terrain
that there
is
100 feet above
corrections
must
be made.
Normally,
for elevation
the free air effect
above
Free
sea
and the Bouguer,
The theoretical
as follows
effect
effect
result
are combined
-0.094'mgal/ft
(mass)
Combined
effect
level:
air effect
Bouguer
or mass,
-0.060
is a decrease
mgal/ft
in gravity
with an increase
in elevation.
Therefore
a correction
has to be made for elevation.
When these
valile
for gravity
gravity
values
resulting
mass
anomaly
effects
is related
were uniform
indicates
are taken
location.
into consideration,
The difference
anomaly."
This
more directly
the theoretical
an excess
the anomaly
of mass
(mass)
is the anomaly
to subsurface
everywhere,
we can predict
between
If both the free air and Bouguer
is the "Bouguer
anomaly
distribution
Bouguer
for any given
is the anomaly.
anomaly
the Bouguer
elevation
beneat,h
mass
would
and observed
corrections
of interest
be uniform.
are applied,
to geologists,
distribution.
the station
a theoretical
the
since
If the subsurface
In general,
and a negative
a positive
Bouguer
anomaly,
a deflclen:cy.
An isostatic
stated,
the theory
with mass
"float"
anomaly
of isostasy
irreguh:rities,
in equilibrium
correction
be expected
takes
is derived
i.e.,
that the major
mountainous
in the earth's
into account
if the area
says
by applying
crust,
the lower
is in perfect
areas
mass
isostatic
one further
theoretical
topographic
features
have
roots
of lower
much as an iceberg
does
of the root and therefore
equilibrium.
5
There
correction.
of the earth
mass,
are associated
and mountains
in water.
tend to
The isostatic
lower observed
are several
Simply
gravity
to
ways of correcting
for isostasy,
but an isostatic
A positive
anomaly
indicates
Appalachian
Mountains
a deficiency
of mass
of isostatic
anomalies
to the large
topographic
section
Jersey
indicates
an excess
have
a departure
of mass
at depth,
isostatic
features.
positive
Both isostatic
isostatic
adjustment
of gravity
SURVEYS
(Woollard,
how well adjusted
has
Triassic
anomalies,
Basin
see
indicating
The primary
crust
are shown
perfect,
The
1943b),
the earth's
anomalies
not been
condition.
a deficiency.
of the mountain.
and Bouguer
and the Newark
discussion
DETAILED
of just
isostatic
anomaly,
anomaly
or too much root for the size
is to give an indication
high is notably
from the ideal
and a negative
a 50 mgal negative
C-D. 3 For New Jersey,
For a more complete
Fall
anomaly
since
is
on cross-
the trans-New
on this line of profile
Dobrin (1960)
use
or Woollard
is negative.
(1941).
AND SUMMARIES OF RESULTS
line Studies
The work of Meier (1949)
gravity
anomalies
the coastal
in terms
plain
the so-called
in which
"Plainsboro
to be associated
of basement
fault block. ''4
rocks,
anomalies
with gabbro
parallel
or sub-parallel
Trans-New
Jersey
Johnson
tending
Both
across
(1956)
basalt
Woollard,
Gravity
and gabbro.
that there
northeast-trending
interpreting
area covered
residual
that part of
and Vine (1939)
outlined
and magnetic
highs
Bonini's
was in the Trenton
area
were minor (3-5 regal)
are considered
high gravity
with the infolded
residual
grain of Piedmont
toward
Meier's
and 3 regal lows associated
to the general
Gravity
and Ewing,
He showed
showed
was directed
variations.
Triassic
Province.
quartzite.
density
(1943a)
prong of the Piedmont
Chickies
(1949)
Woollard
with basement
associated
and Bonini
gravity
anomalies
Cambrian
which
are
rocks.
High
concentrated
the New Jersey
Coastal
his work in outlining
Plain.
He found
a section
of the gravity
that basement
topography
3) The isostatic
corrections
used in calculation
of the isostatic
anomalies
from data supplied by Dr. U. A. Uotila, Department
of Geodetic
Science,
State University,
for a value of T=30 km on the Airy-Heiskanen
System.
were
Ohio
4) This "fault block" was found not to exist by Fiske and Bonini (1956), since
the gravity anomalies
and seismic time offset reported earlier were found to be
associated
with pre-Triassic
and Triassic
rocks in a normal relationship.
6
high exmight
+40
+3O
+ 20
__
_--
u_
_:
uJ st
_ .S/
._____STATICISO
ANOMALY
- ,o
AN(IMALY
Z
,_
Z
s_,-_',_
o
F_ET
....,_:::
_..::._" ,
_
__o,,,
_D
_';ii:;;H!!!!!!!!_h:,,,,:,,,,:_,,::,,:::_:,:,
_
-
' .....
=
--
-,,,o.,,
IIIl.l.r,lll_........ii: il,:,',l,'........................
_
HHHH]H_HH_HH_
SCAL_ Iht MILES
0
FIGURE
i.
CROSS-SECTION
ANOMALIES.
FROM
GEOLOGY
5
PHILLIPSBUEG
IS
MODIFIED
vD
TO
FROM
VERTICAL EX_GGERATR3N-v _ B
$5
BARNEGAT
SECTION
ZO
BAY
C-D
25
SHOWING
OF
THE
BOUGUER
NEW
JERSEY
AND
ISOSTATIC
GEOLOGIC
MAP.
_
T _"-,=
K
--_'_°
E
explain
residual
anomalies
of the high trend
Rocky
itself
on the order
was caused
of 1 or 2 mgals on the crest
by high density
basement
of the high, but that most
or sub-basement
rocks.
Hill Diabase
Stewart
Hill diabase,
(1962)
further
outlined
confirming
the earlier
Wofford (1962)
investigated
the residual
gravity
work of Woollard
high associated
(1943a)
with the Rocky
on this body.
Round Valley
Reservoir.
ginal
This
estimate
in addition
that the diabase
and more gently
confirm
data,
the diabase
(around
to later
work by the author
dips up to 80 ° outwardly
30 °) on the southwest
cline.
Based
(1963)
material
geological
Widmer,
In general,
Valley
1960).
confirm
the ori-
on the northeast,
Magnetic
llmb,
anomalies
of the surrounding
of the Piedmont
also
is a peak
from near Wilmington,
into Manhattan
continuation
minently
Millville,
Delaware,
into Connecticut
Washington,
New Jersey,
the trans-New
feature
Bouguer
and Queens,
through
by the New Jersey
Geological
classification
Brunswick
shale
an antiSurvey,
of the Cushetunk
indicates
that the diabase
sheet.
FEATURES
trends
are parallel
to sub-parallel
to the structural
and Appalachians.
The most prominent
there
anomaly
is a flow and structurally
that the petrologic
in the form of a cone
the gravity
material
in this area
indicates
and the attitude
and probably
studies
REGIONAL
aspect,
site of the Round Valley
and his students,
from Round
limb (see
that the Cushetunk
communication)
is diabase
is intrusive
indicates
on detailed
Widmer (personal
which
Mountain,
this estimate.
Sanford
trends
of Cushetunk
value
is the
of *42 regals.
It crosses
through
Skyesville,
New York (see
D. C.
trans-New
New Jersey,
on the northeast
A lesser
group
is nearly
parallel
high is part of a series
8
of highs
Jersey
the state
just
map and cross-section).
and Massachusetts
and the trend
Jersey
in New Jersey
of Staten
Woollard
highs
near
Jersey
running
less
Cedar
on
direction,
Island
(1943a)
and southward
to the trans-New
high,
in a northeast
east
is located
of gravity
gravity
shows
a
pro-
Grove
high.
and
and
In gross
from Georgia
to
Vermont.
Although
with the Piedmont
the western
(1943)
it occurs
over
south of New Jersey,
edge of the Connecticut
has made an analysis
their relationship
of gravity
(1943a)
has
and p. 815) and concludes
of 0.5 gm/cc
maximum
source
using
by adjusting
Woollard,
and Vine (1939)
gabbroic
Jersey
Atlantic
anomalies
Triassic
discussed
values
gravity
and Massachusetts.
on
Longwell
and eastern
and size
New York and
high in detail
deep.
and gabbro
depth
Assum)ng
The
of the body.
It should
that pre-Cretaceous
adensity
of mass
source
up to 22,000
(p. 804-805
of 3.15 gm/cc
to the center
(8 kin).
velocities
suggesting
gravity
is rather
of 2.67 gm/cc
high seismic
high,
it is over the basement
Jersey
the maximum
contrast
report
associated
Basin.
for granite
the density
it is clearly
in Connecticut
the trans-New
- he calculates
of the
could
be shallower,
be noted
ft/sec
(6.71
basement
- the
that Ewing,
kin/see)
near
rock may be of
composition.
The main features
basement
in Connecticut
(26 kin) with its top near 11 miles
however,
the trans-New
Plain,
that the sc)urce of the anomaly
one might expect
to be 16 miles
Coastal
and north of New Jersey
Valley
to the Connecticut
Woollard
contrast
the New Jersey
or sub-basement
Coastal
Plain
of the Coastal
density
further
Plain
variations,
south
(Bonini
similar
1963, Gravity
anomalies
picture
are related
to results
and Woollard,
LITERATURE
Bonini, W. E., 1949, Geophysical
unpublished
M.S.E. thesis,
gravity
to pre-Cretace:)us
of investigations
1960).
CITED
investigations
in the Trenton-Consohocken
Princeton
University
in Idaho:
Idaho
Bur. of Mines
fault
and Geology,
Pamphlet
Bonini, W. E., and Woollard, G. P., 1957, Observational
accuracy of high-range
Worden gravimeters:
Am. Geophys.
U., Trans.,
v. 38, p. 147-155
1960, Subsurface
geology of North Carolina-South
Carolina
Bull. Amer. Assoc. Petrol. Geol., v. 44_ p. 298-315
Dobrin, M. B., 1960, Introduction
446 p.
on the
to Geophysical
Prospecting,
Ewing, M., Woollard, G. P., and Vine, A. C., 1939, Geophysical
and submerged
Atlantic
Coastal Plain:
Part IR, Barnegat
Geol. Soc. Amer., v. 50, p. 257-269
Fiske, R. S. and Bonini, W. E., 1956, Structure of pre-Cretaceous
Jersey,
as interpreted
from seismic refraction
measurements:
p. 1695
9
Coastal
Plain
McGraw-Hill
area,
Pa.:
132, 39 p.
geodetic
type
from seismic
data:
Book Co., Inc.,
investigations
in the emerged
Bay, New Jersey,
section:
Bull.
basement near Plainsboro,
New
Bull. Geol. SOc. Amer., v. 67,
Hersey, J. B., 1944, Gravity
Amer., v. 55, p. 417-444
investigations
of central-eastern
Johnson,
G. M., 1956, Gravity and magnetic
B.S.E. thesis,
Princeton
University
study
Pennsylvania:
of the Fort Dix area,
Bull.
Geol.
New Jersey:
unpublished
Longwell,
C. R., 1943, Geologic
interpretation
of gravity anomalies
in the southern
Hudson Valley region:
Bull. Geol. Soc. Amer., v. 54, p. 555-590
Meier, D. R., 1949, Geophysical
investigation
in the Trenton-Old
published
M.S.E. thesiS, Princeton
University
Sanders, J. E., 1963, Late Triassic
Sc., v. 261_ p. 501-524
Steenland,
N. C. and Wootlard,
of the Cortlandt
Complex,
Stewart, D. D., 1962, Gravity
published
B.S.E. thesis,
U. S. Coast
latitude
tectonic
history
Bridge
of northeastern
United
study of the Princeton-New
Princeton
University
Vreeland_ J. H., 1965, Gravity anomalies
Jersey:
unpublished
M.S.E. thesis,
Brunswick
problems
and geology of the Jenny
Princeton
University
in the construction
Wofford, G. T., 1962, Gravity study of Cushetunk
Mountain
unpublished
B.S.E. thesis,
Princeton
University.
New Jersey:
States:
area,
un-
Amer.
of dams:
New Jersey:
for each
Jump Mountain
Trans.,
Jour.
and surrounding
1943a, Geologic correlation
of areal gravitational
and magnetic
vicinity:
Bull. Geol. See. Amer., v. 54, p. 791-818
area,
studies
gravitational
and magnetic profile of North
Bull. Geol. Soc. Amer., v. 54, p. 747-790
10'
minute
area,
un-
of
New
N. Y. Acad.
Woollard, G. P., 1941, Geophysical
methods of exploration
and their application
blems in New Jersey:
Dept. of Cons. and Dev. of N. J., Bulletin 54, 89 p.
1943b, Transcontinental
to geologic
structure:
New England-
G. P., 1952, Gravity and Magnetic Investigation
of the Structure
New York: Bull. Geol. Soc. Amer., v. 63, p. 1075-1104
and Geodetic
Survey, 1942, Theoretical
gravity at sea level
by the International
Formula:
Publ. G-53, 9 p.
Widmer, K., 1960, Geological
Set. II, v. 22, p. 223-232
area,
Soc.
New Jersey:
to geologic
in New Jersey
America
Sci.,
pro-
and
and its relation