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U.S. Geological Survey Open-File Report 2004-1435

Early to Middle Jurassic Salt in Baltimore Canyon Trough


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Abstract
Introduction
Geologic Setting
Data Collection
Data Processing
Geophysical Analysis
Discussion
Conclusions
Bibliography
List of Figures
List of Tables

Conclusions

Geophysical data and modeling collectively support the interpretation that a high-amplitude, low-impedance reflector near the synrift to postrift transition section in the Baltimore Canyon Trough is a salt lens. The polarity information, indicating low impedance and reflection-coefficient estimates of about -0.2, are within a range expected for a salt layer. Amplitude versus offset analysis, though limited by the narrow incidence angles (less than fourteen degrees), shows amplitude decay with increasing offset and yields a low density (2.2 g/cc). Inversion gives very low shear velocities.

One-dimensional modeling suggests a thickness in the range of 60 m in the center thinning to less than 20 m in 2 km on either side. A less pronounced low-impedance layer, with a trough-to-peak separation of 40 ms underlies the lens we have analyzed. Though this may be a second salt layer, complex interference from interlayer multiples restricts our interpretation.

A salt lens of these dimensions, 25 km wide and a maximum of 60 m thick, fits in well with the tectonic setting. The early Baltimore Canyon Trough was of limited extent, probably a maximum of 45 km wide and had restricted circulation in an arid to semi-arid paleoenvironment (Poag and Sevon, 1989). This autochthonous salt layer is relatively undisturbed, as it did not mobilize or deform significantly during the subsequent development of the Baltimore Canyon Trough.


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