Abstract: Depth Conversion of Multichannel Seismic-Reflection Profiles over Atlantic Outer Continental Shelf and Upper Continental Slope Between Cape Hatteras and Georges Bank

John A. Grow, Robert E. Mattick, John Schlee

Six multichannel seismic-reflection profiles over the Atlantic outer continental shelf and upper continental slope have been converted to depth sections. A group of strong reflectors at depths of 2.5 to 3.0 km continue 10 to 30 km seaward of the present edge of the continental shelf in a subhorizontal attitude. As refraction velocities for these horizons exceed 5.0 km/sec, the horizons are inferred to be indurated sandstone or limestone. The age of these strata in the COST B-2 well was Early Cretaceous. The overlying Upper Cretaceous units have velocities of 2.5 to 3.5 km/sec and appear to be marine silt, shale, and chalk associated with the worldwide Late Cretaceous marine transgression. Lower Cretaceous reflectors beneath the outer shelf and upper slope are folded and block faulted on several profiles, whereas Upper Cretaceous and Tertiary units are undeformed on all profiles.

The sections indicate that the edge of the continental shelf during the Early Cretaceous was 10 to 30 km seaward of the present shelf break. Although Upper Cretaceous units continue across the outer shelf and down the continental slope on a few profiles, on most profiles the Upper Cretaceous and Tertiary units are deeply eroded. Therefore, the erosion and landward retreat of the shelf edge must have taken place primarily in the Tertiary. Although lowered sea levels during the later Tertiary glacial epochs probably account for most of the erosion, some erosion also may have taken place during marine regressions in the early Tertiary.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC