Abstract: Sedimentation on Eastern United States Continental Slope

Larry J. Doyle, Orrin H. Pilkey, C. C. Woo

Intercanyon eastern United States continental slopes are sites of active sedimentation with rates at least as high as 20 cm/10³ years. The presence of abundant shelf benthic Foraminifera, occasional broken shelf mollusk shells, and abundant mica in slope sediments all point to the continental shelf as the major Quaternary source of slope sediments.

In furnishing sediments to the slope, the adjacent shelf acts as a giant Wilfley table, retaining the coarsest and heaviest fractions while passing on the lighter, finer sediments. The Wilfley table effect results in the slope being characterized by a light heavy-mineral fraction depauperate in black opaques, zircon, and rutile relative to the shelf and leads to a continental margin which is graded on a grand scale with sand-, silt-, and clay-sized particles concentrated on the shelf, slope, and rise, respectively.

Slope sediments are high in organic content which results in reducing conditions reflected in gas pockets within the upper few meters and in the common occurrence of authigenic sulfide minerals, especially pyrite which is found as globular masses, as casts of radiolarians, and as coatings on other grains.

A major break in sediment type off Cape Hatteras is reflected by a change in mineralogy and by a dramatic increase in sand content on the south. The winnowing effect of the Florida Current is at least partly responsible for the textural changes although an increase in quartz sand at some stations south of Hatteras attests to an increase contribution from the continental shelf.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma