ABSTRACT: Seismic Properties and Modeling of an Early Aalenian Salt(?) Layer in Baltimore Canyon Trough, Offshore New Jersey

Ann B. Swift, Myung W. Lee, C. Wylie Poag, Warren F. Agena

A continuous, high-amplitude, negative-polarity event is imaged on multichannel seismic-reflection sections over an approximately 12,000-km² area of Baltimore Canyon Trough. Geophysical characteristics are compatible with an interpretation of this reflector as a salt lens, deposited at the top of an early synrift evaporite sequence. The salt layer is about 25 km wide; its upper surface lies between 5 and 6 sec. (two-way traveltime). It is about 90-100 m thick in the central basin and thins monotonically, though asymmetrically, at the edges, unlike intrusives of otherwise similar character.

Geophysical analyses have been centered on two dip lines, U.S. Geological Survey 6 and 10, which were reprocessed using wavelet deconvolution to preserve polarity. The lens has a velocity of 4.4 km/sec and lies within strata having velocities of 5.3 to 5.7 km/sec. A trough marking the onset of the lens has an amplitude that is 10-20 db greater than adjacent events and an apparent reflection coefficient of -0.24. This value is compatible with gas-saturated sediments or an overpressured shale layer. However, observed reflection coefficients, though variable, decrease with respect to increasing offset, and linear inversion yields a low density (about 2.18 g/cm³) which contradicts the two alternative interpretations, respectively.

Integration of the true-amplitude processed line 10 and one-dimensional modeling of the salt layer further reinforce the interpretation in terms of impedance contrast and matching of interference patterns.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990