Relationships between the distribution of Amphistegina and the submerged Pleistocene reefs off western Puerto Rico


Seiglie, G.A.

Transactions of the Caribbean Geological Conference 5(5): 141

1971


Paleoecology of Amphistegina, Archaias, and Quinqueloculina (foraminifera) in Pleistocene reefs.

RELATIONSHIPS
BETWEEN
THE
DISTRIBUTION
OF
AMPHISTEGINA
AND
THE
SUBMERGED
PLEISTOCENE
REEFS
OFF
WESTERN
PUERTO
RICO*
GEORGE
A.
SEIGLIE**
UNIVERSITY
OF
PUERTO
RICO,
MAYAGUEZ
CONTENTS
Page
ABSTRACT
139
I.
INTRODUCTION
139
II.
SIMILAR
TOPOGRAPHIC
FEATURES
IN
OTHER
AREAS
_____
140
III.
TOPOGRAPHY
OF
THE
SEA
BOTTOM
BETWEEN
GUANAJIBO
AND
MASCO
BAY
141
IV.
DISTRIBUTION
OF
AMPHISTEGINA
142
V.
CONCLUSIONS
AND
SUMMARY
_____
146
REFERENCES
ABSTRACT
The
study
area
lies
off
the
central
part
of
the
western
coast
of
Puerto
Rico.
It
has
a
maximum
north-south
extent
of
12
kilom-
eters
and
is
11
kilometers
in
the
east-west
direction.
The
sample
net
consists
of
over
one
hundred
samples.
The
remnants
of
an
incipient
Pleistocene
reef
at
80
to
85
meters
of
depth
and
a
wave
cut
terrace
at
55
meters
of
depth
were
found
with
five
echo-sounder
profiles.
Three
main
foraminiferal
reef
assemblages
exist
in
the
Antillean
Caribbean
region.
Two
are
Amphistegina
faunas
(
with
no
Archaias
present):
one
in
the
Gulf
of
Mexico
and
the
other
one
off
eastern
Venezuela.
The
third,
an
Amphistegina-Archaias
fauna,
oc-
curs
in
the
warmer
waters
of
the
Antilles.
Three
shallow-water
modern
reefs
were
sampled
bordering
the
eastern
side
of
the
area
where
Amphistegina-Archaias
assem-
blage
occurs.
The
highest
percentage
of
Amphistegina
gibbosa
(up
to
61%
)
is
pres-
ent
in
these
reefs
from
8
meters
to
15
meters
of
depth.
The
percentage
decreases
down
to
approximately
80
meters
where
it
increases
to
a
maximum
of
12%
in
front
of
Los
Ne-
gros
reefs.
A
relict
foraminiferal
fauna
oc-
curs
at
this
depth.
It
consists
mainly
of
Amphistegina
gibbosa
and
Quinqueloculina
*This
project
was
supported
by
the
U.S.
Commission
of
Atomic
Energy
under
contract
AT(
40-1
)-1833.
Presented
to
the
Fifth
Carib-
bean
Geological
Conference,
Saint
Thomas,
Vir-
gin
Islands,
July
1968.
**Department
of
Geology,
University
of
Puerto
Rico,
Mayaguez,
Puerto
Rico;
and
Ma-
rine
Biology
Program,
Puerto
Rico
Nuclear
Cen-
ter.
146
lamarckiana
indicating
waters
probably
colder
than
present.
Amphistegina
gibbosa
was
found
living
off
Puerto
Rico
in
the
shallow
reefs
at
6
meters
of
depth
down
to
70
meters
of
depth.
However,
in
the
submerged
Pleisto-
cene
reefs
most
of
the
specimens
of
this
foraminifer
are
glauconitized.
Its
percentages
are
many
times
higher
in
the
glauconitized
assemblage
than
in
the
total
assemblage
of
foraminifera.
The
submerged
reefs
off
western
Puerto
Rico
correlate
in
depth
with
the
calcareous
prominences
of
the
Gulf
of
Mexico
and
the
submerged
reefs
off
the
western
coast
of
Barbados.
I.
INTRODUCTION
This
paper
is
part
of
a
project
conducted
for
the
Marine
Biology
Program
of
the
Puerto
Rico
Nuclear
Center
at
Mayagiiez.
The
purpose
of
the
project
is
the
study
of
the
distribution
of
the
species
of
foraminifera
in
the
sediments
of
the
continental
shelf
and
upper
slope
from
Guanajibo
to
Masco
Bay.
When
the
distribution
of
Amphistegina
gibbosa
d'Orbigny
was
plotted
on
a
map
it
was
evident
that
a
relation
existed
between
its
distribution
and
certain
topographic
fea-
tures
at
a
depth
of
80
to
100
meters.
This
paper
deals
with
the
significance
of
these
relationships.
More
than
100
samples
were
taken
as
shown
in
figure
1.
Samples
were
taken
with
a
tube
dredge,
a
gravity
corer,
and
a
box
corer.
Reference
to
each
type
is
made
in
the
figure
1.
139
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°
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0-200
0
300
Pli
P
5
Met
7.1000
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900
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0
ti
"
s.
0.10
5-404
D
0
S-40
2
Inv
Bolnymeinc
curve,
in
Box
corer
Tube
groyne
corer
o
°redo,
0
0
1r
5-3
-
s
n.6knc•
416
5-28
5-69
0
5-34
5.74
S-65
05-68e
5-38
5-66
5-97
S.96
.105x
0
,0
S
VS-
93
5
'
76
0
o
St
9J
5.83
5-60
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5-5
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;Ire
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5-24
5-231
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0
5.21
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5-3
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cles-3e
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5.12
5.29
0
5.33
;7
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,o,
5-48
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5-16
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5-30
5.17
s-I'
S-5
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i
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s-si
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GUEZ
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TOPOGRAPHY
OF
THE
SEA
BOTTOM
/0
Pi
P2
GRAPHIC
SCALE
I
.10r.
140
Tulane
Studies
in
Geology
Vol.
6
FIGURE
1
Thanks
are
given
to
Stephen
Walsh
and
Gregory
Telek
from
the
Puerto
Rico
Nu-
clear
Center
for
assistance
in
the
field.
The
writer
is
also
indebted
to
Dr.
Donald
Swift
from
Duke
University,
North
Carolina,
for
the
review
of
the
manuscript,
and
to
Rafael
Pabon,
Enrique
W.
Lithgow
and
Maria
E.
Rodriguez
for
the
preparations
of
glauconi-
tized
foraminifera.
H.
SIMILAR
TOPOGRAPHIC
FEATURES
IN
OTHER
AREAS
Parker
and
Curray
(1956)
and
Ludwick
and
Walton
(1957)
described
the
calcareous
prominences
at
the
middle
and
outer
shelf
of
the
Gulf
of
Mexico.
Curray
(1960)
ob-
tained
radiocarbon
dates
on
the
molluscan
shells
from
these
prominences.
He
concluded
that
an
erosional
stillstand
elapsed
between
14,000
and
16,000
years
B.P.
at
a
depth
of
approximately
88
meters,
and
that
a
re-
gression
of
the
sea
from
a
depth
of
45
to
70
meters
occurred
between
11,000
and
12,000
years
B.P.
MacIntyre
(1967)
reported
two
sub-
merged
reefs
off
the
west
coast
of
Barbados,
one
at
a
depth
of
79
meters
and
the
other
with
the
base
at
a
mean
depth
of
40
meters.
A
e
E
ms
0
ms
0
ms
Sta
63
50
ms
75
ms
Sta
80
100
ms
;50
ms
150
ms
Direction
315
°
magnetic
N
PROFILE
A4
C
O
ms
Sta
67
a
to
26
A
Direction
325
°
mognetic
N
PROFILE
8-B
0
-10
Sto
84
50
ms
75
ms
00
ms
Sto.8
50ms
b
75
ms
Ste
88
100
ms
150
ms
Direction
230
°
magnetic
N
PROFILE
E-E'
50
ms
75
ms
100ms
50
ms
75
ms
100
ms
150
ms
o65
Sta
d
76
150
0'
Sta
66
t
o.70
(aprox)
Direction:
274°
magnetic
N.
PROFILE
C
-C'
Direction:
225
°
magnetic
N
PROFILE
D-D'
No.
4
Distribution
of
Ampbistegina
Off
Western
Puerto
Rico
141
FIGURE
2
These
reefs
were
correlated
with
the
ero-
sional
levels
at
the
Gulf
of
Mexico
on
the
basis
of
depths.
Emery
(1958)
reported a
series
of
sub-
merged
terraces
in
Southern
California.
Three
of
them
lie
at
depths
of
49
meters,
81
meters
and
88
meters
respectively.
These
depths
coincide
with
the
submerged
reefs
off
western
Puerto
Rico
but
little
confidence
should
be
placed
upon
this
coincidence
be-
cause
of
the
tectonic
instability
in
Southern
California.
III.
TOPOGRAPHY
OF
THE
SEA
BOTTOM
BETWEEN
GUANA
JIBO
AND
ASIASCO
BAY
The
area
of
study
is
located
along
the
cen-
tral
part
of
the
western
coast
of
Puerto
Rico.
It
includes
Mayaguez
and
Ariasco
Bays.
The
maximum
north-south
extent
is
12
kilom-
eters,
and
11
kilometers
in
the
east-west
direction.
Sampling
range
from
a
depth
of
4
meters
to
410
meters.
The
topographic
map
of
the
sea
bottom
of
the
area
is
shown
in
figure
1
according
to
the
soundings
in
the
charts
of
the
U.S.
Navy.
The
coast
is
bordered
by
three
groups
of
shallow
reefs:
Negro
Reef
at
the
south;
Manchas
Grandes
reefs
at
the
center;
and
Manchas
Interiores
and
Manchas
Exteriores
at
the
north.
The
shallowest
ones
are
the
Manchas
Grandes
reefs
that
in
part
emerge
from
the
surface
of
the
sea
as
Rodriguez
shoals.
The
middle
and
outer
parts
of
the
Island
shelf
are
very
narrow
and
it
is
difficult
to
detect
significant
topographic
features.
How-
ever,
reliable
information
was
obtained
from
five
profiles
taken
with
the
echo
sounder
of
the
R/V
"Shimada"
of
the
Puerto
Rico
Nuclear
Center.
Their
positions
are
shown
in
figure
2
and
their
locations
in
figure
1.
The
approximate
horizontal
distance
may
be
taken
from
the
figure
1.
The
profiles
present
a
series
of
signifi-
cant
points
that
are
indicated
in
figure
2
by
the
letters
a,
b,
c,
d,
d',
and
e.
The
points
a
and
b
at
profiles
AA',
BB',
and
CC'
are
found
at
depths
of
40
and
55
meters
respectively.
They
are
poorly
de-
veloped
and
only
in
the
profile
EE',
north-
west
of
Manchas
Exteriores
a
wavecut
ter-
race
is
found
at
a
depth
of
55
meters
(point
b).
This
terrace
or
flat
reef
has
been
re-
ported
previously
by
Swift
(1967
).
The
third
significant
point,
c,
appears
in
profiles
AA',
BB',
CC',
and
DD'.
It
is
well
developed
and
the
most
important
one
for
the
purpose
of
this
paper.
The
elevation
of
point
c
in
relation
to
its
fore
and
back
base
shows
it
as
a
barrier
of
hard
bottom
at
a
depth
of
80
to
85
meters,
approximately
142
Tulane
Studies
in
Geology
Vol.
6
AMPHISTEGINA
FAUNAS
OF
THE
ANTILLEAN
CARIBBEAN
REGION
0
El
Gulf
of
Mexico
Caribbean
Sea
x
0
Gulf
of
Mexico
Amphislegina
assemblage.
X
Amphistegina
Archaias
assemblage.
0
Venezuela
Amphistegina
assemblage.
FIGURE
3
parallel
to
the
coast.
This
submerged
fring-
ing
or
barrier
reef,
has
been
sampled
several
times
with
a
tube
dredge,
but
it
has
been
impossible
to
recover
any
samples
with
the
gravity
corer
or
with
the
box
corer.
The
interpretation
of
the
remaining
in-
flection
points
d,
d',
and
e
are
beyond
the
scope
of
this
paper.
IV.
DISTRIBUTION
OF
AMPHISTEGINA
Amphistegina
in
the
Reef
Assemblages
in
the
Antillean-Caribbean
Region
The
writer
considers
that
the
Antillean-
Caribbean
region
extends
from
off
south
Brazil
up
to
the
eastern
part
of
the
Gulf
of
Mexico,
on
the
Atlantic
side
of
the
Americas.
The
four
most
abundant
and
significant
reef
foraminifera
in
this
region
are:
Am-
phistegina
gibbosa
d'Orbigny,
Archaias
angu-
latus
(Fichtell
and
Moll),
Asterigerina
carinata
d'Orbigny
and
Rotorbinella
rosea
(d'Orbigny).
They
have
been
reported
by
Bandy
(1964)
as
the
dominant
reef
assem-
blage
in
the
Batabano
Gulf,
Cuba.
The
writer
has
found
this
assemblage,
at
least
in
the
lagoon
of
Los
Rogues
Archipelago,
in
calcareous
beach
sands
of
Dominican
Re-
public
and
in
the
reefs
off
Puerto
Rico.
Hofker
(1964)
has
reported
it
from
many
calcareous
beach
sands
of
the
Lesser
Antilles.
Cushman
(1922)
reported
these
foraminifera
in
Tortugas
region
and
BEng
(1950,
1952)
in
Bahama
Banks
with
some
differences
in
the
assemblages.
The
calcareous
sands
of
Puerto
Rico
and
Dominican
Republic
ob-
served
by
the
writer
are
skeletal
reef
sands
and,
probably,
a
great
part
of
the
ones
ob-
served
by
Hofker
(1964)
are
also
skeletal
reef
sands.
Amphistegina
gibbosa
and
Archaias
angulatus
are
by
far
the
most
abundant
of
the
four
species.
This
fauna
is
referred
to
Amphistegina-Archaias
assem-
blage
in
the
map
of
figure
3.
It
is
important
to
remark
that
thing
(1950,
1952)
and
Bandy
(1964)
report
Archaias
as
a
back-reef
foraminifer
and
Amphistegina
as
a
fore-reef
one.
However,
this
separation
of
the
fauna
does
nor
occur
in
the
shallow
reefs
off
the
western
coast
of
Puerto
Rico,
where
Amphistegina
gib-
bosa,
Archaias
angulatus,
Rotorbinella
rosea
and
Asterigerina
carinata
are
all
found
liv-
ing
together,
from
6
meters
to
25
meters
No.
4
Distribution
of
Amphistegina
Off
Western
Puerto
Rico
143
of
depth
(Pirie,
Swift
and
Seiglie,
1967).
However
in
the
Sponge
Banks,
a
submerged
reef
off
the
western
shelf
of
Puerto
Rico,
Amphistegina
occurs,
living
from
30
meters
(shallowest
depth
of
the
banks)
down
to
70
meters
of
depth.
Walton
(1964)
reports
an
Amphistegina
fauna
in
the
eastern
Gulf
of
Mexico,
al-
though
living
specimens
do
not
occur
in
significant
numbers
in
the
shallow
waters,
Asterigerina
carinata
occurs
in
smaller
per-
centages.
No
Rotorbinella
rosea
or
Archaias
angulatus
have
been
reported
in
this
area
by
Walton
(1964)
nor
Parker
(1954).
This
fauna
is
referred
to
on
figure
3
as
the
Gulf
of
Mexico
Amphistegina
assemblage.
A
third
fauna
is
the
Venezuelan
Am-
phistegina
assemblage,
reported
by
Drooger
and
Kaaschieter
(1958),
and
Seiglie
(1966)
off
eastern
Venezuela.
No
Rotorbinella
rosea
is
present
and
Archaias
and
Asterigerina
are
extremely
rare
or
absent.
(See
figure
3).
The
upwelling
waters
off
eastern
Venezuela
produce
lower
temperatures
in
its
seas
per-
mitting
the
occurrence
of
temperate
zone
species
of
algae
(Diaz
Piferrer,
1967)
and
a
temperature
planktonic
foraminiferal
as-
semblage
(Mirk
1967).
This
fact
explains
the
presence
of
an
Amphistegina
fauna
simi-
lar
to
the
one
from
the
Gulf
of
Mexico.
Nora
(1958,
fig.
36),
shows
a
belt
of
Pleistocene
sediments
in
the
western
Guiana
shelf,
from
65
meters
to
95
meters,
this
belt
coincides
with
the
distribution
of
Am-
phistegina
in
that
area
(Drooger
and
Kaas-
schieter,
1958).
Two
main
reef
assemblages
occur
in
the
Antillean-Caribbean
region
according
to
the
above
mentioned
report:
a
warm
water
Amphistegina-Archaias
assemblage
and
two
less
warm
water
Amphistegina
assemblages.
These
assemblages
permit
the
subdivision
of
the
Antillean-Caribbean
foraminiferal
province
in
three
subprovinces:
Eastern
Gulf
of
Mexico
subprovince,
Antillean
sub-
province
and
Venezuelan
subprovince.
The
foraminifera
from
Bahama
Banks
and
from
off
South
Florida
are
tentatively
included
in
the
Antillean
subprovince.
It
is
important
to
remark
that
Sorites
marginalis
Lamarck
is
present
only
in
the
warmer
waters
of
the
Caribbean,
but
in
percentages
lower
than
one
per
cent.
Sorites
marginalis
and
Archaias
angulatus
are
taxo-
nomically
related
to
the
Miocene
and
prob-
ably
Pliocene
foraminifer
Marginopora
mat-
leyi
(Vaughan).
The
writer
has
observed
beds
constituted
mainly
by
Amphistegina
sp.
(no
Marginopora
is
present)
in
the
middle
and
late
Miocene
of
southern
Puerto
Rico,
alternating
with
beds
in
which
Mar-
ginopora
matleyi
is
the
dominant
species.
If
these
two
Miocene
assemblages
may
be
compared
to
the
Recent
ones
they
indicate
temperature
changes
in
that
epoch.
Recently,
Tanner
(1967)
has
stated
the
possibility
that
glacioeustatic
sea
level
changes
have
commenced
in
the
Miocene
or
Oligocene.
Nevertheless,
the
Marginopora
matleyi
as-
semblage
may
be
also
interpreted
as
a
reef
platform
or
back-reef
assemblage
and
Am-
phistegina
as
a
fore-reef
one.
Distribution
of
Amphistegina
off
Western
Puerto
Rico
The
four
species
of
reef
foraminifera
characteristic
of
Amphistegina-Archaias
as-
semblage
are
present
in
high
percentages
in
the
Recent
shallow
water
reefs
off
the
western
coast
of
Puerto
Rico
(Pirie,
Swift
and
Seiglie,
1968
and
Seiglie,
1967).
The
distribution
of
Amphistegina
gibbosa
in
Guanajibo
to
Masco
Bay
area
is
shown
in
figure
4.
The
distribution
of
the
species
is
expressed
in
percentages
in
relation
to
the
total
assemblage
of
benthonic
foraminifera.
The
higher
percentages
are
found
in
the
shallower
reefs:
40%
at
Negro
reefs,
36%
at
Manchas
Grandes
reefs
and
61%
at
Man-
chas
Exteriores
reefs.
Living
specimens
of
Amphistegina
have
been
found
in
Negro,
Manchas
Grandes
and
Manchas
Exteriores
reefs
from
8
to
20
meters
of
depth.
How-
ever,
the
number
of
living
specimens
ob-
served
at
Manchas
Exteriores
reefs
is
rather
small.
The
three
groups
of
reefs
are
sep-
arated
from
the
coast
by
slightly
deeper
bottoms
that,
at
least
in
part,
are
under
the
influence
of
the
river
muds,
so
that
the
back-reef
assemblage
is
modified.
Table
1
shows
the
relative
percentages
of
the
two
most
significant
foraminifers
of
this
assemblage
in
relation
to
the
total
foraminiferal
benthonic
assemblage.
Relatively
high
percentages
of
Amphis-
tegina
gibbosa
are
present
at
two
different
levels
in
wave-cut
terraces
at
55
meters
and
submerged
reefs
at
85
meters
of
depth
ap-
proximately.
Archaias
angulatus,
Rotorbi-
‘,s
(0
5
DISTRIBUTION
OF
50
AMPHISTEGINA
GIBBOSA
D'ORBIGNY
GRAPHIC
SCALE
„,--
o
Ix.
ANASCO
blioni
v
-----
o
ow.
RIVER
1....--in
PERCENTAGES
0
-
5%
:MANCH
S
EX
RIVES
5%-
10%
9.
Gti
i
10%
-
20%
`MANCHAS
IORE
1-1
more
than
20%
M
?CHAS,
GRADE
I
A•
MAY
GUE
Z
c
2
50
LOS
NEGROS
GUANAJIBO
RIVER
-
1
80
I
,
i4
Tulane
Studies
in
Geology
VoL
6
67°
IS'
67°10'
FIGURE
4
Percentages
in
relation
to
the
total
foraminiferal
benthonic
assemblage.
nella
rosea
and
Asterigerina
carinata
are
mostly
absent
or
exceedingly
rare.
Amphis-
tegina
is
associated
with
Quinqueloculina
lamarckiana
in
some
of
the
samples
from
the
submerged
reefs,
and
they
are
relatively
more
abundant
in
the
glauconirized
fauna.
This
association
is
found
in
shallow
waters
from
Venezuela
(BermUdez
and
Seiglie,
1963
and
Seiglie,
1966),
from
30
to
40
me-
ters
of
depth.
Its
presence
off
Puerto
Rico
may
indicate
colder
climates
when
the
sea
level
was
lower.
The
original
population
of
Amphistegina
has
been
diluted
by
the
assem-
blages
that
succeeded
after
the
submersion
of
the
reefs.
The
only
relatively
high
percentage
(7.8%)
of
Amphistegina,
was
found
at
55
meters
of
depth
in
the
wave-cut
terrace
northwest
of
Manchas
Exteriores,
repre-
sented
by
the
Profile
E-E',
figure
2.
Other
relatively
high
percentages
probably
occur
at
55
meters
in
other
places.
However,
no
appropriate
samples
have
been
obtained
probably
because
of
the
narrow
width
of
No.
4
Distribution
of
Amphistegina
Off
Western
Puerto
Rico
145
the
terrace
(points
b
in
the
profiles
of
figure
2).
The
submerged
reefs
whose
highest
points
are
approximately
at
80
meters
are
rela-
tively
the
most
easily
sampled
group.
They
coincide
with
the
points
c
in
the
profiles
of
figure
2
where
they
lie
before
the
three
shal-
low
water
modern
reefs.
They
have
signif-
icant
percentages
of
Amphistegina:
12.8%
in
front
of
Negro
reef,
5%
in
front
of
Manchas
Grandes,
and
11%
in
front
of
Manchas
Exteriores.
The
highest
percentages
of
Amphistegina
are
slightly
displaced
in
the
submerged
reefs
of
the
central
part,
up
to
100
meters
of
depth.
Station
97
from
this
depth
included
large
fragments
of
reef-rock
consisting
mainly
of
worm
tubes,
bryozoans,
attached
foraminifera
and
corals.
These
fragments
appear
identical
with
those
reported
by
Ludwick
and
Curray
(1957,
in
figure
13A)
from
the
pinnacles
of
the
deep
reef
banks
at
the
edge
of
the
continental
shelf
of
the
Gulf
of
Mexico.
Reef-rock
fragments
were
washed
to
sep-
arate
free
foraminifera.
Amphistegina
con-
stitutes
11%
of
the
foraminiferal
benthonic
assemblage.
Most
of
the
remaining
species
of
foraminifera
are
characteristic
of
this
depth,
including
Carpenteria
monticularis
Carter
and
C.
proseiformis
Goes,
that
are
the
only
observed
species
attached
to
the
fragments.
Station
Amphistegina
gibbosa
Archafas
angulatus
1.
Negro
Reefs
22A
37%
29%
23
20%
43%
24
39%
26%
59
26%
20%
62
18%
10%
2.
Manchas
Grandes
82
36%
7%
105
39%
35%
3.
Manchas
Exteriores
41A
62%
19%
87
41%
13%
100
54%
23%
101
50%
24%
102
51%
27%
TABLE
1.
Percentages
of
Amphistegina
gibbosa
and
Archaias
angulatus
in
relation
to
the
total
benthonic
foraminiferal
assemblage.
In
the
submerged
back-reefs
at
80
meters
as
well
as
in
the
wave-cut
terraces
from
80
to
60
meters
depth,
coarse
to
medium
muddy
sands
contains
low
percentages
of
Amphis-
tegina
in
relation
to
the
total
foraminiferal
benthonic
assemblage.
Similar
calcareous
sands
were
reported
by
Swift
(1967)
as
relict
Pleistocene
sands
in
Masco
Bay.
Rela-
tively
high
percentages
of
Amphistegina
oc-
curs
in
actual
beaches
and
back-reefs
sands,
but
the
foraminifer
is
generally
diluted
by
large
amounts
of
sediment.
Thus
foram-
inifera
now
living
at
60
to
80
meters
of
depth
have
rendered
the
original
population
of
Amphistegina
more
dilute
than
in
the
submerged
reefs.
Another
important
fact
in
relation
to
Amphistegina
gibbosa
is
that
its
percentage
in
the
glauconitized
assemblage
of
sub-
merged
reefs,
is
several
times
higher
than
in
the
total
population.
This
fact
requires
for
Amphistegina
tests
a
longer
in
situ
resi-
dence
and
thus
an
older
age
than
the
foraminiferal
fauna
now
living
at
that
depth.
Percentages
of
Amphistegina
in
these
reefs
and
sands
are
(see
figure
3)
from
0.5%
to
4%
of
the
total
population.
However,
the
percentages
of
glauconitized
Amphistegina
increases
up
to
more
than
35%
in
relation
to
the
total
glauconitized
foraminiferal
populations.
Table
2
shows
the
percentages
of
Am-
phistegina
to
the
total
benthonic
population
and
percentages
of
glauconitized
Amphiste-
gina
to
the
glauconitized
benthonic
popula-
tion
in
several
stations.
It
must
be
stated
also
that
the
difficulty
of
locating
and
sampling
the
80
meter
reefs
indicate
that
they
are
probably
narrow
and
thin.
No
Pleistocene
reefs
above
the
sea
level
have
been
reported
for
Puerto
Rico,
perhaps
on
account
of
its
scarcity.
However,
Station
%
in
the
Total
Population
%
in
the
Clauco-
nitized
Population
S-66
4
%
16%
S-79
2
%
35%
S-80
8.5%
16%
S-95
4.5%
33
S-96
S-97
2.5%
5
%
24
%
68%
TABLE
2.
Percentages
of
Amphistegina
gibbosa
in
relation
to
the
total
foraminiferal
benthonic
assemblage.
146
Tulane
Studies
in
Geology
Vol.
6
a
Pleistocene
reef
occurs
about
8
meters
above
the
sea
level,
south
of
Higuera
point,
western
Puerto
Rico.
Its
elevation
coincide
with
the
ones
reported
for
Barbados
(Broecker
et
al.,
1968)
from
6
to
19
meters,
corresponding
to
an
interglacial,
approxi-
mately
80,000
years
ago.
In
any
case,
the
height
above
sea
level
of
the
Puerto
Rican
reefs
indicates
a
warm
climate.
The
foram-
iniferal
fauna
contained
in
the
Puerto
Rican
reefs
consist
of
Archaias
angulatus
and
Am-
phistegina
gibbosa,
that
indicate
also
a
warm
climate.
V.
CONCLUSIONS
AND
SUMMARY
The
following
conclusions
are
based
on
the
distribution
of
Amphistegina
gibbosa
and/or
the
topographic
features
representing
submerged
reefs.
(1)
Three
main
reef
foraminiferal
faunas
are
present
in
the
Antillean-Caribbean
re-
gion:
Amphistegina-Archaias
assemblage
in
the
warmer
waters
and
two
Amphistegina
assemblages
in
the
less
warm
waters.
De-
scribed
assemblages
permit
the
subdivision
of
the
Antillean-Caribbean
foraminiferal
province
in
three
subprovinces:
the
Eastern
Gulf
of
Mexico
subprovince,
the
Antillean
subprovince
and
the
Venezuelan
sub-
province.
(2)
The
submerged
reefs
present
at
80
meters
of
depth
off
western
Puerto
Rico
cor-
respond
approximately
in
depth
and
posi-
tion
with
those
in
the
Gulf
of
Mexico
at
88
meters
of
depth
reported
by
Curray
(1960)
and
off
Barbados
at
79
meters
of
depth
reported
by
Maclntyre
(1967).
(3)
The
distribution
of
Amphistegina
gibbosa
is
associated
with
the
position
of
the
submerged
Pleistocene
reefs
off
western
Puerto
Rico
and
also
in
the
Gulf
of
Mexico
(Walton,
1964);
it
is
also
associated
with
the
position
of
the
Pleistocene
sediments
of
the
western
Guiana
shelf.
This
association
is
true
irrespective
of
whether
Amphistegina
is
Pleistocene
or
Holocene.
(4)
The
ratio
Amphistegina
to
benthonic
foraminifera
is
much
higher
if
only
glauco-
nitized
tests
are
considered.
This
indicates
that
the
Amphistegina
assemblage
of
the
submerged
reefs
is
older
than
the
living
as-
semblage.
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L.,
1964.
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Distribution
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L.,
1954.
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of
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the
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1956.
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Distribution
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Sediment
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December
30,
1968
REVIEWS
ELECTRICAL
PROPERTIES
OF
ROCKS;
U.S.
NAVAL
OCEANOGRAPHIC
GEOMAGNETIC
SURVEYS,
INFORMAL
REPORT;
REPORT
ON
AEROMAGNETIC
SURVEY
IN
JAPAN
HAMILTON
M.
JOHNSON
TULANE
UNIVERSITY
ELECTRICAL
PROPERTIES
OF
ROCKS,
by
Eleonora
Ivanova
Parkhomenko;
trans-
lated
from
Russian,
edited
and
supple-
mented
by
George
V.
Keller;
Monographs
in
Geoscience
series,
edited
by
Rhodes
W.
Fairbridge.
Published
by
Plenum
Press,
New
York,
1967,
xi
+
314
p.,
$19.50
This
book
is
the
first
devoted
specifically
to
the
electrical
properties
of
rocks.
While
until
recently
these
were
studied
mainly
in
connection
with
the
requirements
of
well
logging,
their
use
has
now
been
extended
to
mining
and
various
types
of
electrical
pros-
pecting
for
minerals.
Therefore
where
pre-
vious
use
was
primarily
in
the
shallow
crust
and
required
data
essentially
at
or
near
atmo-
spheric
pressures
and
room
temperature,
ex-
tension
of
interest
deep
into
the
earth's
crust
and
mantle
will
need
data
concerning
elec-
trical
properties
at
high
pressures
(
tens
of
kilobars)
and
high
temperatures
(
at
least
1000°C).
Laboratory
analysis
under
these
conditions
is
the
only
source
of
such
infor-
mation.
She
has
determined
that
these
elec-
trical
properties
depend
on
the
chemical
and
mineral
content
of
the
rocks,
the
genesis
and
petrographic
characteristics,
structure,
tex-
ture,
porosity,
water
content
(both
percent-
age
and
conductivity),
etc.
and
discusses
specific
electrical
properties
in
terms
of
each
of
these
factors.
The
book
is
divided
into
a
brief
review
of
petrography
and
chapters
on
dielectric
prop-
erties
of
rocks,
electrical
resistivity
of
rocks
(methods
used
to
measure
and
factors
caus-
ing
variations),
and
dielectric
loss
in
rocks.
Extensive
tables
of
dielectric
constants
of
both
minerals
(133)
and
rocks
(62)
include
all
of
the
common
ones
and
many
less
fre-
quently
encountered.
Discussion
of
value
ranges,
explanations
of
variations,
etc.
are
sufficient
and
readily
understandable;
the
writing
is
easy
to
follow
and
sentence
struc-