FLORIDA DEPARTMENT OF NATURAL RESOURCES
published by BUREAU OF GEOLOGY MAP SERIES NO. 52


MAP SERIES NO. 52


IM A ...I,%I



1A F.,,..
ii .Pea

19 '.~IT SO'
3aPn


~ is


O.n


/ I:
5eFo,,ii
cear..,. se',"ss
~se,,iie
Fii Weiin,,
-1<
.enla c~ '.0
.i


EOe'5~5 lit


y- H- s5


~-- pa, ..1 1l1 V I-r


/
saecrom


GULF OF MEX/CO


ca s, :.


s~)
tie'.


~.lW~a -
"s~e.
~ rear

~L..
'0


DEPARTMENT OF NATURAL RESOURCES
BUREAU OF GEOLOGY

This public document was promulgated at a total
cost of $843.60 or a per copy cost of $.56 for the
purpose of disseminating hydrologic data.


BOUGUER ANOMALY MAP OF NORTHWEST FLORIDA
AND ADJACENT SHELF

By
Susan Chaki and Woodson R. Oglesby
This Bouguer anomaly map of northwest Florida and
submerged portions of the continental shelf adjacent thereto
is based on data provided by the United States Department
of Defense (Air Force) Gravity Library.
The producing salt domes near the Main Pass of the
Mississippi River; the faults and Comanchean Shelf Edge to
the north; and the diapiric structures lying east thereof near
the De Soto Canyon, were copied after the Tectonic Map of
the Gulf Coast Region U. S. A. (1972) G. C. A. G. S.
Only regional features are resolved on the map, as the
spacing between stations and the margin of error, which in
the offshore is on the order of several milligals, does not
permit one to interpret structures on the small scale of salt
domes.
The Gulf Coast Geosyncline appears as a positive trough
extending eastward to 86 10' West Longitude and 29 30'
North Latitude. This Geosyncline is not evident, if mapped
on the free air anomaly, or if an inappropriate density value
is chosen for the Bouguer correction factor.
The interpretation of variations of gravity from place-to
place around the earth's surface are made by measurement of
the amount the observed gravity readings at various points
departs from theoretical gravity values, at sea level, at the
same points. Theoretical gravity values can be calculated for


MAX.


an idealized geometric figure of the earth. For most purposes,
a theoretical ellipsoid of revolution will suffice to represent
the earth and its gravitational field. Calculations based on the
foregoing principle will result in "free air" data which, when
contoured, form a free air anomaly map. The values so
contoured would give a correct representation of the gravity
amonalies present inter se, were it not for density variations
which occur between various points on the earth's surface
and a common datum (sea level) at the said points. The
Florida Platform, whether emergent or submerged, consists
of sand and porous limestones throughout the upper 2 or 3
thousand feet of section. The density of these sediments
varies from about 1.7 to 2.3, 2.00 being an approximate
mean: All densities are referred to pure water at S. T. P., the
specific gravity (density) of which is 1.00, by definition.
In discussing the Comanchean Shelf Edge, John Antoine
of Texas A&M indicated that the series of seismic profiles he
had run across the scarp successfully picked up the Shelf
Edge until his ship's position reached approximately 29" 12'
North by 87o 42' West. Thereafter, the relatively low sparker
energy available to him did not penetrate the thick blanket of
sediments which masked the scarp. Antoine agreed that a
possible interpretation was that sediments carried by the
Mississippi River through its Main Pass spread eastward to the


edge of the scarp, filled it into the crest, and spread thence
eastward over the submerged Florida Platform.
The sediments of the Gulf Coast Geosyncline are basically
of Miocene to Recent age, and are thought to attain at least
35,000 feet in thickness in the central portion of the
geosyncline off the Louisiana Coast. There is no direct
evidence of the thickness of these sediments in the portion of
this geosyncline occurring in the vicinity of the De Soto
Canyon, as no test well has been drilled thereabouts.
However, the evidence derived by gravity indicates a
considerable thickness for such sediments (thousands of feet)
as opposed to 500 feet or so on the Florida land mass to the
east.
The Santa Rosa Arch, a positive anomaly, and the
Marianna Lowlands a negative anomaly, appear as well
defined features extending southwestward from Alabama and
Georgia, respectively, into the Florida Panhandle at
longitudes 87 West and 85 o West.
The Santa Rosa Arch, unlike the (Miocene) Gulf Coast
Geosyncline, dates from the pre-Mesozoic. It probably
defines the eastern limit of the Mississippi Salt Basin in
Florida.


EXPLANATION



Location of Gravity Station


POSITIVE
ANOMALY
INCREASE


NEGATIVE
-22 ANOMALY
INCREASE


-42
FLORII


0 Salt Diapor approximate size of salt mass
SP 62

0 Salt Diapir size of salt plug unknown


Shelf Edge or Escarpment


2 Contour Interval 4 milligals

)A GEOLOGIC SURVEY MAP SERIES j I .


G 3931

"- P 52
......" / No. SE


1972


.C5


SP 70


f .fta $t ." "


2 -'toun ^
C- 7.
L' '- --^ & -.-


LO OF AREA
LOCATION OF AREA


-K


t 117


-T


ih..- I.


as


uo-


a*