On: “Diapiric Salt Volume Offshore Louisiana,” by T. R. LaFehr and Alan T. Herring (GEOPHYSICS, December 1971, p. 1205–1251)

In the interest of brevity, I will summarize the points I raised and the conclusions I drew in my somewhat extended correspondence with LaFehr and Herring concerning my objections to their paper. 1) Any geologic interpretation of gravity data includes a number of assumptions. 2) Of all these assumptions, the most tenuous one is that concerning a “regional.” 3) Once assumptions have been made, the answer is only the end result of an arithmetical exercise; the conclusion has been established already. 4) In the specific case of the calculated quantity of salt in the study area in the Gulf of Mexico, many of the “facts” that had to be included in the reduction of the data are actually assumptions that, through constant repetition, are now thought of as actual knowledge. 5) The conclusion in their paper as to the quantity of salt is only one of a large family of results, though it may be in the correct magnitude.

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A fresh look at Gulf of Mexico tectonics: Testing rotations and breakup mechanisms from the perspective of seismically constrained potential-fields modeling and plate kinematics

Interpretation ◽

10.1190/int-2019-0256.1 ◽

2020 ◽

Vol 8 (4) ◽

pp. SS31-SS45

Author(s):

Daniel Minguez ◽

E. Gerald Hensel ◽

Elizabeth A. E. Johnson

Keyword(s):

Gulf Of Mexico ◽

Seismic Data ◽

Gravity Data ◽

Seafloor Spreading ◽

Plate Motion ◽

Rock Properties ◽

Satellite Gravity ◽

Spreading Model ◽

Breakup Mechanism ◽

Mantle Exhumation

Interpretation of recent, high-quality seismic data in the Gulf of Mexico (GOM) has led to competing hypotheses regarding the basin’s rift to drift transition. Some studies suggest a fault-controlled mechanism that ultimately results in mantle exhumation prior to seafloor spreading. Others suggest voluminous magmatic intrusion accommodates the terminal extension phase and results in the extrusion of volcanic seaward dipping reflectors (SDRs). Whereas it has been generally accepted that the plate motions between the rift and drift phases of the GOM are nearly perpendicular to each other, it has not been greatly discussed if the breakup mechanism plays a role in accommodating the transition in plate motion. We have developed a plate kinematic and crustal architecture hypothesis to address the transition from rift to drift in the GOM. We support the proposition of a fault-controlled breakup mechanism, in which slip on a detachment between the crust and mantle may have exhumed the mantle. However, we stress that this mechanism is not exclusive of synrift magmatism, though it does imply that SDRs observed in the GOM are not in this case indicative of a volcanic massif separating attenuated continental and normal oceanic crust. We support our hypothesis through a geometrically realistic 2D potential field model, which includes a magnetic seafloor spreading model constrained by recent published seismic data and analog rock properties. The 2D model suggests that magnetic anomalies near the continent-ocean transition may be related to removal of the lower continental crust during a phase of hyperextension prior to breakup, ending in mantle exhumation. The kinematics of breakup, derived from recent satellite gravity data and constrained by our spreading model and the global plate circuit, suggests that this phase of hyperextension accommodated the change in plate motion direction and a diachronous breakup across the GOM.

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Three‐dimensional gravity inversion using simulated annealing: Constraints on the diapiric roots of allochthonous salt structures

Geophysics ◽

10.1190/1.1487089 ◽

2001 ◽

Vol 66 (5) ◽

pp. 1438-1449 ◽

Cited By ~ 41

Author(s):

Seiichi Nagihara ◽

Stuart A. Hall

Keyword(s):

Simulated Annealing ◽

Gulf Of Mexico ◽

Gravity Data ◽

A Priori ◽

Gravity Inversion ◽

Inversion Method ◽

A Priori Information ◽

Final Density ◽

Smoothing Effects ◽

Priori Information

In the northern continental slope of the Gulf of Mexico, large oil and gas reservoirs are often found beneath sheetlike, allochthonous salt structures that are laterally extensive. Some of these salt structures retain their diapiric feeders or roots beneath them. These hidden roots are difficult to image seismically. In this study, we develop a method to locate and constrain the geometry of such roots through 3‐D inverse modeling of the gravity anomalies observed over the salt structures. This inversion method utilizes a priori information such as the upper surface topography of the salt, which can be delineated by a limited coverage of 2‐D seismic data; the sediment compaction curve in the region; and the continuity of the salt body. The inversion computation is based on the simulated annealing (SA) global optimization algorithm. The SA‐based gravity inversion has some advantages over the approach based on damped least‐squares inversion. It is computationally efficient, can solve underdetermined inverse problems, can more easily implement complex a priori information, and does not introduce smoothing effects in the final density structure model. We test this inversion method using synthetic gravity data for a type of salt geometry that is common among the allochthonous salt structures in the Gulf of Mexico and show that it is highly effective in constraining the diapiric root. We also show that carrying out multiple inversion runs helps reduce the uncertainty in the final density model.

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Gulf of Mexico GLORIA sidescan sonar geologic interpretation; ArcView data coverages

Open-File Report ◽

10.3133/ofr0019 ◽

2000 ◽

Author(s):

Valerie F. Paskevich

Keyword(s):

Gulf Of Mexico ◽

Sidescan Sonar ◽

Geologic Interpretation

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Integration of seismic and gravity data — A case study from the western Gulf of Mexico

Interpretation ◽

10.1190/int-2015-0050.1 ◽

2015 ◽

Vol 3 (4) ◽

pp. SAC99-SAC106 ◽

Cited By ~ 9

Author(s):

Irina Filina ◽

Nicholas Delebo ◽

Gopal Mohapatra ◽

Clayton Coble ◽

Gary Harris ◽

...

Keyword(s):

Gulf Of Mexico ◽

Gravity Field ◽

Gravity Model ◽

Seismic Velocity ◽

Gravity Data ◽

Public Domain ◽

Gravity Modeling ◽

Data Sets ◽

Gardner Equation ◽

Well Data

A 3D gravity model was developed in the western Gulf of Mexico in the East Breaks and Alaminos Canyon protraction areas. This model integrated 3D seismic, gravity, and well data; it was constructed in support of a proprietary seismic reprocessing project and was updated iteratively with seismic. The gravity model was built from seismic horizons of the bathymetry, salt layers, and the acoustic basement; however, the latter was only possible to map in seismic data during the latest iterations. In addition, a deep layer representing the Moho boundary was derived from gravity and constrained by public-domain refraction data. A 3D density distribution was derived from the seismic velocity volume using a modified Gardner equation. The modification comprised imposing a depth dependency on the Gardner coefficient, which is constant in the classic Gardner equation. The modified coefficient was derived from well data in the study area and public-domain velocity-density data sets. The forward-calculated gravity response of the composed density model was then compared with the observed gravity field, and the mismatch was analyzed jointly by a seismic interpreter and a gravity modeler. Adjustments were then made to the gravity model to ensure that the resultant salt model was geologically reasonable and supported by gravity, seismic, and well data sets. The output of the gravity modeling was subsequently applied to the next phase of seismic processing. Overall, this integration resulted in a more robust salt model, which has led to significant improvements in subsalt seismic imaging. The analysis of the regional trend in the observed gravity field suggested that a stretched continental crust underlay our seismic reprocessing area, with an oceanic-continental transition zone located to the southeast of our reprocessing region.

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Cenozoic gravity tectonics in the northern Gulf of Mexico induced by crustal extension. A new interpretation of multichannel seismic data

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.179.2.117 ◽

2008 ◽

Vol 179 (2) ◽

pp. 117-128 ◽

Cited By ~ 9

Author(s):

Claude Rangin ◽

Xavier Le Pichon ◽

Nicolas Flotté ◽

Laurent Husson

Keyword(s):

Gulf Of Mexico ◽

Seismic Data ◽

Gravity Data ◽

Passive Margin ◽

Lateral Motion ◽

Crustal Extension ◽

High Penetration ◽

Crustal Thinning ◽

New Interpretation ◽

Multichannel Seismic Data

Abstract The Gulf of Mexico margin in Texas is one of the most impressive examples of starved passive margin gravity collapse systems. Growth faults developed upslope and are compensated down slope by toe folding and thrusting. On the basis of new multi-channel seismic data with high penetration (down to 11 s-twtt) we present evidences for deep crustal extension and rifting that have enhanced superficial sliding. This hypothesis is supported by a significant heat flow anomaly and crustal thinning independently deduced from gravity data. This Cenozoic rifting episode is tectonically linked to left lateral motion along the Rio Bravo fault, a reactivated branch of the Texas lineament.

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Basin architecture and density structure beneath the Strait of Georgia, British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/e03-030 ◽

2003 ◽

Vol 40 (7) ◽

pp. 965-981 ◽

Cited By ~ 4

Author(s):

C Lowe ◽

S A Dehler ◽

B C Zelt

Keyword(s):

Seismic Velocity ◽

Gravity Data ◽

Velocity Model ◽

Seismic Structure ◽

Strait Of Georgia ◽

3 Dimensional ◽

The North ◽

Georgia Basin ◽

Geologic Interpretation ◽

Velocity Information

Georgia Basin is located within one of the most seismically active and populated areas on Canada's west coast. Over the last decade, geological investigations have resolved important details concerning the basin's shallow structure and composition. Yet, until recently, relatively little was known about deeper portions of the basin. In this study, new seismic velocity information is employed to develop a 3-dimensional density model of the basin. Comparison of the calculated gravity response of this model with the observed gravity field validates the velocity model at large scales. At smaller scales, several differences between model and observed gravity fields are recognized. Analysis of these differences and correlation with independent geoscience data provide new insights into the structure and composition of the basin-fill and underlying basement. Specifically, four regions with thick accumulations of unconsolidated Pleistocene and younger sediments, which were not resolved in the velocity model, are identified. Their delineation is particularly important for studies of seismic ground-motion amplification and offshore aggregate assessment. An inconsistency between the published geology and the seismic structure beneath Texada and Lasqueti Islands in the central Strait of Georgia is investigated; however, the available gravity data cannot preferentially validate either the geologic interpretation or the seismic model in this region. We interpret a northwest-trending and relatively linear gradient extending from Savory Island in the north to Boundary Bay in the south as the eastern margin of Wrangellia beneath the basin. Finally, we compare Georgia Basin with the Everett and Seattle basins in the southern Cascadia fore arc. This comparison indicates that while a single mechanism may be controlling present-day basin tectonics and deformation within the fore arc this was not the case for most of the Mesozoic and Tertiary time periods.

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Edge enhancement of potential-field data using normalized statistics

Geophysics ◽

10.1190/1.2837309 ◽

2008 ◽

Vol 73 (3) ◽

pp. H1-H4 ◽

Cited By ~ 111

Author(s):

Gordon R. J. Cooper ◽

Duncan R. Cowan

Keyword(s):

Standard Deviation ◽

Potential Field ◽

Field Data ◽

Gravity Data ◽

Edge Enhancement ◽

Potential Field Data ◽

Geologic Interpretation ◽

Derivatives Of ◽

High Pass ◽

Detection Filter

Edge enhancement in potential-field data helps geologic interpretation. There are many methods for enhancing edges, most of which are high-pass filters based on the horizontal or vertical derivatives of the field. Normalized standard deviation (NSTD), a new edge-detection filter, is based on ratios of the windowed standard deviation of derivatives of the field. NSTD is demonstrated using aeromagnetic data from Australia and gravity data from South Africa. Compared with other filters, the NSTD filter produces more detailed results.

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