Data Development

Passive Margin Development in the Atlantic and Gulf of Mexico with a

Special Emphasis on Proto-oceanic Crust. (DRAFT)

Mark E. Odegard

Grizzly Geosciences, Inc.

***** ********* *******, ***** ***-735

Sugar Land, Texas 77478

Email: abqsro@r.postjobfree.com

Abstract

Some new developments in geodynamics and plate tectonics related to the development of

continental margins have occurred in the past few years that are important in exploring for hydrocarbons.

Development of passive margins appears to proceed in five initial stages. First there is an initial fracturing

of the crust that is either propagation of a rift or development of the rift during mantle upwelling and

elevation. Second, rifting develops a zone of extended continental crust with large, more periodic half-

graben basins. Third, faster rifting develops a zone of highly extended continental crust with less well

developed and less periodic half-graben basins. The fourth stage is the formation of proto-oceanic crust.

The fifth and final stage is the development of true oceanic crust.

The development and location of basins during initial breakup of continental plates is controlled

by the location of zones of weakness that exist in the continental crust before rifting begins. The initial

direction of rifting and spreading appears to depend upon the direction of the controlling zones of

weakness. Zones of weakness may not align exactly with the preferred direction of spreading. During

rifting and for some period of time thereafter, the interaction of the various continental plates may not be

well defined. These two factors, and others, may contribute to development of a forth stage after rifting

and prior to the drift phase where the direction of spreading may be somewhat chaotic. During this phase

parts of the continental crust may be fragmented and intermingled with volcanic material produced from

the embryonic ridge system. Possibly other types of volcanism than mid-ocean ridge basalts may occur.

These factors are the basis for the formation of the proto-oceanic crust described by Dickson and

Odegard (2000) and Odegard (2002) and represent the fourth phase of margin development. This crust

undergoes further modification as it descends from its formation at or near sea level to deeper ocean

depths. Finally, in the fifth phase, true oceanic crust begins to develop.

This paper describes in greater detail the observation and characteristics of the processes

described above, particularly proto-oceanic crust. Observations and interpretation methods are shown for

various areas of the Atlantic. Finally these methods are applied to the Gulf of Mexico. Using gravity data

enhancements the early location of the Yucatan Peninsula relative to North America is derived from the

location of the boundaries between extended continental and proto-oceanic crust. This then gives insight

into the rotation of the Yucatan block and the formation of proto-oceanic crust during the opening of the

Gulf of Mexico.

Introduction

To understand how paleo-structural features may affect present day tectonic development, we

first consider the continent of Africa and its relationship to the opening of the Atlantic. The African

continent has been relatively stable over much of its existence. Thus, to see older features that may be

related to recent features, Africa would be a good place to begin.

To do this, the gravity field over the African plate is examined. Gravity records variations in the

density of the Earth. These density variations are produced by the results of geological processes that we

wish to investigate. Looking at enhancements or special visualizations of the gravity field allows us to

highlight different types of geological processes. Magnetic, topographic and bathymetric data can also be

used for similar purposes.

Extended Gravity

Gravity data over the African continent was compiled by GETECH over fifteen years ago

(Fairhead et al., 1988, 1997). Using modern topographic and bathymetric data these gravity data have

been reprocessed. During this reprocessing the free air gravity grid onshore was in-filled in areas of no

data using the EGM96 earth gravity model (Lemoine, et al., 1998). After adding corrections for the

complete Bouguer and for Isostatic compensation these data show a gravity image that extends into

areas not covered by currently available gravity measurements. Thus the use of the term Extended

Gravity is applied to these data. The extended gravity image can be used to investigate the location and

extent of tectonic features in the Earth s crust. Other enhancements are then done to these images to

highlight a variety of structural and tectonic features.

Offshore Africa, because of developments in satellite-derived gravity, the coverage is nearly

complete. In this study we use the data from Sandwell and Smith (1997) version 9.1. New processing

methods have been developed, however, that extend the coverage, accuracy and resolution of satellite

derived gravity. See Fairhead, et al. (2001) and Odegard and Fairhead (2003) for details.

African Tectonic and Linear Structural Features

When the extended gravity over the African plate is displayed (Fig. 1) many features are observed

that are associated with known plate tectonic elements. Other features, however, are associated with

tectonic/geological elements that appear to violate plate tectonics. Additional features are related to non

tectonic sources. Features that are associated with known plate tectonic elements like fracture zones can

also be observed. Some of these are indicated in the interpretation in Figure 2, but others are left so that

the reader can see uninterpreted features. In particular those associated with the Benguela volcanic line of

southern Angola are easily seen (Danforth, et al., 1997). Possible mechanisms for emplacement of these

features may be deeper tectonic processes or the extension of zones of weakness from the continent into

the oceanic plate which are described by Odegard (2003). These may be activated by processes described

in Courtillot, et al. (1997). These geodynamic processes have important consequences for the

development of basins during and after rifting.

Figure 1 Extended and satellite gravity over the African plate displayed in gray

shaded relief with a 45 degree shading azimuth. From Odegard (2003).

Figure 2 Extended gravity over the African plate with possible major linear

features oblique to plate tectonic flow. Other linear features can also be interpreted.

From Odegard (2003)

Crustal Segmentation

The segmentation of the developing and thinning crust, during and after rifting appears to be

controlled by two factors. First some zones of weakness in the continental crust appear to influence the

initial direction of opening of the rift system. During the initial rifting and perhaps for some time before

the beginning of formation of true oceanic crust (the drift phase), different local rift systems fight for

control of the final spreading direction. Even after the spreading direction is set changes in the overall

spreading direction can change, although generally at a slower pace.

Second, during and probably even after rifting has stopped, zones of weakness in continent and/or

upper mantle can segment the developing basins by propagating cracks into the lithosphere at angles

oblique to spreading. These types of features are seen offshore Africa in Figure 2. Both types of

segmentation are important to basin development. They also appear to be important to the geochemical

and heat flow development in a basin as discussed by Fryklund, et al.. (2001), Schiefelbein, et al.. (2003)

and Dickson, et al. (2005).

A Passive Margin Model

A general model for a passive continental margin has been developed and is shown in Figure 3.

This model is based on integrated gravity, magnetic, seismic, well and geological modeling on over thirty

profiles around the Atlantic continental margin (see, for example, Weger, et al., 2003). This model is a

generalization of these models and contains elements from each. The crustal layering is based upon

reflection and refraction seismic observations and the Crust2.0 model of Bassin, et al. (2000). The crustal

type zones are based primarily upon observations of basement morphology and its correlation with crustal

thickness. The layers and zones are described below.

Crustal Layers

The crustal layering shown in Figure 3 is designed to reflect the general geology of the model and

to fit the density and susceptibility of the sediments and rocks coupled with seismic horizons.

Post-Salt Sediments

These are sediments laid down after salt deposition in a basin. Usually two to three layers are

necessary to model the data. If there was no salt deposition then they are combined with the sub-salt

sediments.

Salt

Salt is shown in this diagram, but may not occur. A thick section in deeper water is shown, which

is typical of many seismic interpretations. Integrated modeling usually shows, however, that 30% to 50%

too much salt is interpreted. In the rifted and early syn-rift zones the salt can be quite thin as it is in parts

of offshore Angola where carbonate blocks slide on a section which is only tens of meters thick. This salt

is not shown in the model.

Sub-Salt Sediments

These sediments were laid down prior to salt deposition. They may be thin or absent in some

basins.

Basement

The basement morphology is important in delineating the crustal zones. Unfortunately, is many

areas the basement character is masked on seismic data by overlying salt and/or carbonates at various

levels. Fortunately the basement structure usually controls the deposition of sediments even in the

shallower sections. Because of this the gravity data usually contain a signature related to the basement

morphology. Using the proper enhancements, this signature can be isolated and used for interpretation of

crustal zones.

Areas of Volcanic Material

This can be an area either in the proto-oceanic or syn-rift zones that is composed of either

volcanic or upper mantle material or both. The affinities of either material may be oceanic or continental.

In some areas this block is composed of seaward dipping reflectors. Upper mantle material occurring in

proto-oceanic and oceanic crust is relatively common. See, for example, Egorov (2004) and Canales, et

al. (2004). The volcanic material usually does not extend down to the mantle as does the exhumed upper

mantle material.

Lower Crust

The lower crustal layer is usually ductile. Composition is indeterminate and probably varies with

crustal type. In the Crust2.0 model the lower crust is divided into two layers.

Mantle

Figure 3 shows two locations for the crust-mantle boundary. The deeper boundary (top of pink

mantle) corresponds to what would be expected from the Crust2.0 model (Bassin, et al.. 2000). The

shallower boundary (top of dark pink, base of lower crust) represents the shallowest crust-mantle

boundary typically seen in the integrated models. Over the passive margins, which have been modeled,

the crust-mantle boundary typically varies between these two extremes.

The depth to the crust-mantle boundary is generally related to the amount of attenuation of the

continental crust. The variation in thickness of this difference over a margin can sometimes be related to

differences in heat flow, but other factors, including the crustal segmentation and injected volcanics

described above, also affect heat flow.

Figure 3 Composite figure showing crustal layers and zones of crustal types, which

may occur along passive continental margins. The length of this section is typical for

offshore west Africa, but is generally shorter for other areas of the Atlantic. The

layers and zones are described in the text.

Passive Margin Crustal Zones

The passive margins of the Atlantic vary widely in style, but are usually composed of six types of

crust that occur in zones roughly parallel to the coast. These crustal types and crustal layers are shown in

Figure 3. This is somewhat similar to the crustal model described by Gibbs, et al. (2003). The crustal type

zones are:

Continental

This is a zone of pure continental crust with limited or no rifting.

Rifted

This is a zone of continental crust with small half grabens formed during the initial uplift and

rifting stage. There is limited crustal thinning.

Syn-Rift.

This is an zone of significant extension and thinning of continental crust with formation of large

half grabens. There is significant crustal thinning.

Syn-Rift II

This is a zone that is sometimes referred to as the beginning of the drift phase. It is characterized

by less well developed half-grabens. Injection of volcanic material may also occur. Continental crustal

material is severely thinned and is beginning to disappear. This phase might also be characterized as a

type of proto-oceanic crust.

Proto-Oceanic

This is a zone where true continental drift has not begun. It may be a mixture of volcanics, mantle

material and continental fragments. This zone shows spatially chaotic magnetic and sometimes

gravimetric spreading anomalies. This type of crust is discussed in greater detail in a following section.

Oceanic

This is the zone where true spreading and drift began. Magnetic spreading anomalies are spatially

coherent.

General Observations

The diagram in Figure 3 shows a pure continental to pure oceanic transect of several hundred

kilometers. This is more typical of the central west African margin. In most other margins this distance

may be significantly less. In a very few areas there is little or no transition.

Not all of these crustal types exist in all passive margins. Depending, probably, on the speed of

development and the interaction of the various tectonic blocks in the area each type may develop to a

greater or lesser extent. It is reasonably clear that the segmentation of the crust during rifting is controlled

by zones of weakness in the continental crust. Oblique zones of weakness may also have an effect on

how, and to what extent crust is thinned in a particular area. How this occurs should be investigated in the

future.

Proto-Oceanic Crust

Areas of apparent oceanic crust, which have characteristics that are not those of pure oceanic

crust, have been mapped in the North and South Atlantic Ocean basins. Neither are they extended

continental crust. This crust has been described as "Proto-oceanic Crust" (POC) by Dickson and Odegard

(2000), Odegard (2002), and others. The Syn-Rift II and proto-oceanic crustal types shown in Figure 3

have these characteristics.

To understand proto-ocean crust seismic, well, gravity, magnetic and topographic data have been,

merged in a Geological Information System (GIS). Results of this integration have shown that the POC

has a distinctive gravity and/or magnetic signature. Also, as described by Odegard and Dickson (2001),

on seismic sections POC typically shows an architecture of tilted fault blocks and on lapping fill.

Depending upon the area, POC appears to be either volcanic material, abducted mantle, separated

continental fragments, or a combination of these materials. Emplacement can occur at or near sea level, in

regions of restricted lacustrine to oceanic circulation, or open marine environments. The type of material,

timing, emplacement mechanism, and depositional environment determines how prospective these areas

are for hydrocarbon exploration. This is particularly true in deep and ultra-deep water areas. Of particular

importance is the magnitude of heat flow during and after emplacement. Odegard (2002) showed that, on

average, for the North Atlantic heat flow over proto-oceanic crust is higher than over either oceanic or

extended continental crust. The provenance and distribution of different types of proto-oceanic crust are

discussed in detail by Rosendahl, et al. (2005).

West African Proto-oceanic Crust

The first illustration of the location of the boundary of proto-oceanic crust is shown for the area

of central west Africa offshore. The isostatic gravity is shown in Figure 4 for this area. The onshore data

are the extended gravity data discussed above. The total horizontal derivative of the gravity can be used to

determine the location of the boundary between two crustal types. In some cases this boundary occurs

between areas with different textures. In others there is a linear or somewhat curved anomaly that is a

clear indication of a fault. The extended continental to proto-oceanic crustal boundary is usually of the

second type. In practice other enhancements of gravity, bathymetry and, where available, magnetic data

coupled with the geology of an area are integrated in a GIS project for interpretation.

The total horizontal derivative of isostatic gravity over central West Africa is shown in Figure 5.

The extended continental to proto-oceanic crustal boundary can be easily seen off Gabon. Off Angola this

boundary is more confused. This is probably cause by a higher degree of crustal segmentation as

discussed above. An interpretation of the approximate location the extended continental to proto-oceanic

crustal boundary is shown in Figure 6.

The interpretation terminates to the south at the Benguela Line. The Benguela Line is clearly not

a line of isolated seamounts as are seen to the northwest in Figure 5. It appears to be injected volcanic

material along a zone of weakness propagating from the continent, which has been activated by the

appearance of a mantle warm-spot as described in Courtillot, et al. (1997). Its origin was discussed by

Odegard (2003). The seamounts to the northwest in Figure 5 have the shape of donuts in the total

horizontal derivative. The island of S o Tom is seen as a very large donut. This donut shape is typical of

volcanic centers, and can be used to map them.

Figure 4 The isostatic gravity over central west Africa. Gabon is in the north and

Angola the south. The coast is shown as a green line. In this, and the following figures,

reds are highs and blues are lows.

Figure 5 The total horizontal derivative of the isostatic gravity. The proto-oceanic crust

boundary is easily seen off Gabon, but is segmented off Angola. The Benguela line is

observed at the south as somewhat linear segments of parallel highs. The donut shaped

anomalies associated with seamounts are in the northwest.

Figure 6 The interpreted total horizontal derivative showing the approximate location of

the extended continental to proto-oceanic crustal boundary.

Figure 7 The total magnetic intensity field over part of northeaster North America.

The linear feature is the New England Seamount chain and possible landward and

seaward extensions of the linear zone of weakness. An area north of the chain appears to

have little magnetic signature. To the south spreading anomalies can be clearly seen.

Northeast North America Proto-oceanic Crust

Another example of the difference between proto and pure oceanic crust, the east coast of North

America is shown in Figure 7 using the total magnetic intensity field. An area north of the linear feature

associated with the New England Seamounts shows little apparent magnetic signature, while to the south

magnetic anomalies associated with spreading can be seen. In Figure 8, which shows the dip-azimuth of

the magnetic field, the spreading anomalies can be clearly seen, while to the north these anomalies appear

to be possibly present, but with a chaotic signature.

Figure 8 The dip-azimuth total magnetic intensity field over part of northeaster North

America. The spreading anomalies can be seen to the south while the northern area of

the previous figure show a signature of spreading anomalies with a chaotic signature.

This area of chaotic signature would be characterized as an area of proto-oceanic crust. The

chaotic nature of would be attributed to the fighting which occurred during the period when the

spreading direction was being set. The signature also appears to be seen in seismic profiles.

The division between the proto and pure oceanic crust indicated by the seamount chain is

interesting. Why there is a division is not clear, but it appears to be obvious. The mechanism for the exact

method of proto-oceanic crust formation is left to future research.

Figure 9 The total horizontal derivative of isostatic gravity over part of northeaster

North America.

In this area the location of the extended continental to proto-oceanic crust transition can also

interpreted. In Figure 9 the total horizontal derivative of the isostatic gravity is shown. The location of the

extended continental to proto-oceanic crustal transition is characterized by a relatively coherent high in

this enhancement. An interpretation of the transition location is shown in Figure 10. This same location is

characterized with a coherent feature in the magnetic data in the same location. This coincidence may not

exist in all margins. The signature in the total horizontal derivative does, however, exist in most areas as

pointed out by Dickson, et al. (2003a, b). Thus we can use this signature in areas with satellite gravity

coverage but little or no magnetic coverage. This will be illustrated in the section on the Gulf of Mexico.

Figure 10 The total horizontal derivative of isostatic gravity over part of northeaster

North America showing the interpretation (black line) of the location of the boundary

between extended continental and proto-oceanic crust.

The total horizontal derivative can also be used to interpret the location of volcanic material

particularly sea mounts as discussed earlier. The volcanic centers are shown in Figure 10 by the donut

shaped anomalies or clusters of these anomalies. The island of Bermuda is show in the lower left-center

of the figure and two seamount chains are shown to the northeast. The largest of these seamount chains is

the New England hotspot trace. The origin of the New England seamount system is discussed by

Odegard (2003).

Extension to the Gulf of Mexico

The location and extent of oceanic crust in the Gulf of Mexico has been discussed by many

authors. In a recent paper by Bird, et al. (2005) summarizes well the papers, which have a variety of

hypotheses for the tectonic evolution of the area and in particular the rotation of the Yucatan Peninsula.

Bird, et al. extend the interpretation using gravity data and integrated modeling to determine the location

of the continent ocean boundary and to propose the existence of a hotspot trace. Using the techniques

described above another interpretation will be given for this area as well.

Figure 11 Free air gravity over the greater Gulf of Mexico. Data for the onshore United

States is from the PACES (2005) compilation. Data over onshore Mexico and Cuba is the

EGM96 extended gravity. Offshore data is from Sandwell and Smith (1997).

Figure 11 shows the free air anomaly of gravity over the Gulf of Mexico area. Offshore the

version 9.1 data of Sandwell and Smith (1997) were used. For the onshore United States, the new

compilation (PACES, 2005) was used. For onshore Mexico and Cuba the EGM96 extended gravity,

described above, was used, and are areas of long wavelength data. The isostatic anomaly of gravity over

this area is shown in Figure 12. This was processed using a low-pass filtered topography and bathymetry

which better fit the resolution of the data, but there are still a few artifacts. These artifacts do not affect

the interpretation.

Figure 12 Isostatic gravity over the greater Gulf of Mexico. The data were processed

with a low passed topographic and bathymetric model.

For interpreting the location of the continent-ocean boundary, or in this case the extended

continental to proto-oceanic crust transition (an acronym EC2POCT will now be used for this), the total

horizontal derivative of the isostatic gravity was calculated. This is shown in Figure 13, which is over a

smaller area covering just the Gulf of Mexico and Florida. Just to the northeast and to the north and west

of the Yucatan Peninsula an anomaly exists which could be interpreted as the EC2POCT. West of Florida

and south of Alabama and Mississippi an anomaly with a somewhat similar expression also exists.

Beneath the salt this anomaly becomes confused.

Figure 13 Total horizontal derivative of isostatic gravity over the Gulf of Mexico. Note

that this is a smaller area than Figures 11 and 12.

To further increase resolution and to view geologies which produce conflicting gravity trends, the

dip-azimuth of the total horizontal derivative was computed. This is shown in Figure 14. The dip azimuth

is the direction of the maximum gradient of gravity field, which in this case is an enhancement. It is

similar to an automatic gain control function and enhances subtle geological trends.

Figure 14 Dip-azimuth of the total horizontal derivative of isostatic gravity over the Gulf

of Mexico.

An interpretation was made over the southern EC2POCT anomaly. This is shown in Figure 15.

Under the assumption the EC2POCT for the Yucatan block would have had the same shape as the

EC2POCT for the conjugate part of the North American block the feature was rotated. The fit over the

area without salt is good, but not perfect. This interpretation is close to fitting the poles of rotation from

Marton and Buffler (1994) and Shepherd (1983). The counter clockwise rotation would be about 30 to 40

degrees.

Another interpretation is possible where the Yucatan block is translated mostly south with a

clockwise rotation of about 20 degrees. This would, however, put the western end of the North American

EC2POCT in an area with no associated significant anomaly.

Figure 15 Interpretation over the total horizontal derivative of isostatic gravity over the

Gulf of Mexico.

Putting these two interpreted EC2POCT s onto the dip-azimuth enhancement, shows a somewhat

better correlation. This is shown in Figure 16. There is a region of ambiguity where the northern gravity

signature might indicate the EC2POCT is trending almost due west rather than bulging to the north. This

ambiguity could be due to asymmetric spreading or to other factors.

In both these interpretation figures there are fainter grey lines extending the interpretation to the

south and west. This was done on the Yucatan EC2POCT, where it was extended to the large anomaly to

the south west. When this was transported to the north the extension did not go far enough to intersect a

hypothesized transform fault parallel to the east coast of northern Mexico. To do this would require a

transpressional opening of the Yucatan block against the Mexican block with subduction of the southern

end of the Yucatan EC2POCT.

Figure 16 Interpretation over the dip-azimuth of the total horizontal derivative of

isostatic gravity over the Gulf of Mexico.

No spreading anomalies are seen in the gravity data, although there are some hints of their

possible existence in Figure 14 in the southwestern area of POC.

Thus the contention here would be that proto-oceanic crust underlies a significant portion of the

Gulf of Mexico. This crust is bounded by the two EC2POCT s for the Yucatan and North American

blocks, and the transpressional fault off the east coast of Mexico.

On a final note, there are no donut shaped anomalies which would be associated with seamounts

from a hotspot trace as seen in Figure 10. There are other features that can be volcanic, which are seen in

Figure 13. The lack of this type of anomaly in the central Gulf tends to vote against, but does not

eliminate, the possibility of a hotspot trace there as proposed by Bird, et al. (2005).

Discussion

Some of the characteristics of passive margins have been discussed with a special emphasis on

proto-oceanic crust and the extended continental to proto-oceanic crust transition (EC2POCT). A method

was described, using the total horizontal derivative of the isostatic gravity coupled with other data, which

can be used to determine the location of the EC2POCT. Also discussed were the signatures of seamounts

seen in the total horizontal derivative. This technique was applied to the Gulf of Mexico.

The results indicate that a large portion of the central Gulf of Mexico is underlain by proto-

oceanic crust. No evidence exists in the image of the total horizontal derivative to indicate the presence of

hotspot traces in the central Gulf of Mexico.

Acknowledgements

This work has benefited from discussions with many people including Bill Dickson, Bruce

Rosendahl, Craig Schiefelbein, Paul Post and others. The public domain gravity data made available by

David Sandwell and Walter Smith (Sandwell and Smith, 1997) has been of untold value to many

investigators studying continental margins and basins. The TIFF images used here and in our GIS projects

were generated using software from the GMT project of Pal Wessel and Walter Smith (1991, 1998) as

modified by the author.

References

Bassin, C., G. Laske, and G. Masters, 2000, The Current Limits of Resolution for Surface Wave

Tomography in North America, EOS Trans AGU, 81, p. 897.

http://mahi.ucsd.edu/Gabi/rem.html.

Bird, D.E., K. Burke, S.A. Hall, and J.F. Casey, 2005, Gulf of Mexico tectonic history: Hotspot tracks,

crustal boundaries, and early salt distribution: AAPG Bull., v. 89, p. 311-328.

Canales, J.P., B.E. Tucholke, and J.A. Collins, 2004, Seismic reflection imaging of an oceanic

detachment fault: Atlantis megamullion (Mid-Atlantic Ridge, 30 10 N): Earth & Plan. Sci. Lett.,

222, p. 543 560.

Courtillot, V., A. Davaille, J. Besse, and J. Stock, 2003, Three distinct types of hotspots in the Earth s

mantle: Earth & Plan. Sci. Lett., 205, p. 295-308.

Danforth, A., T. Koning, and O. de Deus, 1997, Angola Petroleum Systems of the Coastal Kwanza and

Benguela Basins, Angola, presented at the Hedberg AAPG/ABGP Joint Research Symposium

"Petroleum Systems of the South Atlantic Margin" November, Rio de Janeiro, Brazil

Dickson, W.G., and M.E. Odegard, 2000, Proto-Oceanic Crust - Defining and Naming a Trend from

Congo to Benin: Poster, HGS dinner meeting, Houston, June.

Dickson, W., A.L. Danforth, and M.E. Odegard, 2003a, Gravity Signatures of Sediment Systems -

Predicting Reservoir Distribution in Angolan (and Brazilian) Basins, Geological Society of

London, Special Publication, 207: Petroleum Geology of Africa: New Themes and Developing

Technologies: p. 241-256.

Dickson, W.G., R.E. Fryklund, M.E. Odegard, and C.M. Green, 2003b, Constraints for plate

reconstruction using gravity data - Implications for source and reservoir distribution in Brazilian

and West African margin basins: Marine and Petroleum Geology, v. 20, p. 309-322.

Dickson, W.G., Schiefelbein, C.F., J.E. Zumberge, and M.E. Odegard, 2005, Basin Analysis in Brazilian

and West African Conjugates: Combining Disciplines to Deconstruct Hydrocarbon Systems, This

Volume.

Egorov, V.I.,, 2004, Bathymetry, gravity and magnetic data study between 14 and 16 N, Mid-Atlantic

Ridge. Evidence for large-scale mechanical extension, Ph.D. dissertation, Department of

Geosciences, University of Houston, Texas.

Fairhead, J.D., A.B. Watts, P. Chevalier, B. El-Haddeh, C.M. Green, G.W. Stuart, K.A. Whaler, and I.

Windle, 1988, African gravity project: Technical Report, GETECH, Department of Earth

Sciences, University of Leeds.

Fairhead J.D., G.S. Bainbridge, C.M. Green, and S.W. Reford, 1997, Large scale compilation of

magnetic, gravity, radiometric and electromagnetic data: the new exploration strategy for the 90s:

in A.G. Gubins, ed., Proceedings of Exploration 97: Fourth Decennial International Conference

on Mineral Exploration, p.805-816.

Fairhead, J.D., G.M. Green, and M.E. Odegard, 2001, Satellite-derived gravity having an impact on

marine exploration: The Leading Edge, v. 20, no. 8, p. 873-876.

Fryklund, R.E., W.G. Dickson, and M.E. Odegard, 2001, Lagoa Feia: Observations on Source Potential

and Quality: AAPG Bulletin, v. 85, no. 13, Supplement, Abstract.

Gibbs, P.B., E.R. Brush, and J.C. Fiduk, 2003, The distribution of syn-rift and transition stage source

rocks in time and space on the conjugate central/southern Brazilian and West African margins in:

Bate, R and Al Danforth, organizers, Proceedings HGS & PESGB Second International

Symposium, Africa: New plays New Perspectives, Houston, CD-ROM, unpaginated, 3 p.

(Extended Abstract).

Lemoine, F. G., S. C. Kenyon, J. K. Factor, R.G. Trimmer, N. K. Pavlis, D. S. Chinn, C. M. Cox, S. M.

Klosko, S. B. Luthcke, M. H. Torrence, Y. M. Wang, R. G. Williamson, E. C. Pavlis, R. H. Rapp,

and T. R. Olson, 1998, The Development of the Joint NASA GSFC and NIMA Geopotential

Model EGM96: NASA Goddard Space Flight Center, Greenbelt, Maryland, 20771, USA, p. 298.

Marton, G., and R.T. Buffler, 1994, Jurassic reconstruction of the Gulf of Mexico Basin, Internatnional

Geology Review, v. 36, p. 545-586.

Odegard, M.E., and W.G. Dickson, 2001, Proto-oceanic crust: type, emplacement mechanisms, and

relationships to hydrocarbon maturation: Geological Society of America Annual Meeting,

Abstract.

Odegard, M.E., 2002, Proto-Oceanic Crust: How Does it Influence Deep and Ultra-Deep Water

Exploration Offshore Eastern Canada, Greenland, Iberia and Northwest Africa?: AAPG Bulletin,

v. 86, no. 13, Supplement, Abstract.

Odegard, M.E., 2003, Geodynamic Evolution of the Atlantic Ocean: Constraints from Potential Field

Data, Extended Abstract, 8th International Congress of the Brazilian Geophysical Society, Rio de

Janeiro, Extended Abstract.

Odegard, M.E., and J.D. Fairhead, 2003, Exploration in the new century: Hart s E&P, June, p. 54-56.

PACES, 2005, Gravity data base at the Pan-American Center for Environmental Studies at the University

of Texas, El Paso, http://paces.geo.utep.edu/research/gravmag/gravmag.shtml.

Rosendahl, B.R., W.U. Mohriak, M.E. Odegard, J.P. Turner, and W.G. Dickson, 2005, West African and

Brazilian conjugate margins: Crustal types, architecture, and plate configurations; This Volume.

Sandwell, D., and W.H. Smith, 1997, Exploring the ocean basins with satellite altimeter data:

http://topex.ucsd.edu/marine_grav/explore_grav.html.

Shepherd, A.V., 1983, A study of the magnetic anomalies in the eastern Gulf of Mexico: Master s Thesis,

University of Houston, Texas, 197 p.

Schiefelbein, C.F., W.G. Dickson, M.E. Odegard, and J. Brooks, 2003, South Atlantic Margin Basin

Analysis using a G3 Approach (Geophysical, Geological and Geochemical): 8th International

Congress of the Brazilian Geophysical Society and 5th Latin American Geophysical Conference,

(Abstract).

Weger, R.J., B.R. Rosendahl, and M.E. Odegard, 2003, Integration of deep-imaging seismic

interpretations and gravity modeling on the Gabon rift margin: Tectonophysics Special Volume

"Recent advances in the study of Atlantic rifted margins", (in review).

Wessel, P., and W.H.F. Smith, 1991, Free software helps map and display data: EOS Trans. AGU, v. 72,

p. 441.

Wessel, P., and W.H.F. Smith, 1998, New, improved version of the Generic Mapping Tools released:

EOS Trans. AGU, 79, 579.

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