THE TALE OF THE LATE PLEISTOCENE SILVER ABYSSAL PLAIN TURBIDITE

In February 1977, bad weather in the area of the Hatteras Abyssal Plain forced cruise E-3-77 of the R/V Eastward southward to collect piston cores from the Silver Abyssal Plain and the margins of the Caicos Outer Ridge. The four orange-white carbonate turbidites found in the piston cores were easy to identify because their color contrasted sharply with the gray and brown muds above and below the turbidites. The uppermost carbonate layer is the thickest of the four turbidites and contains the greatest percentages of sand-sized sediment, making correlation from core to core easy. This turbidite, nicknamed the “Silver Turbidite,” is over 1.5 m thick along the southwestern limb of the Silver Abyssal Plain and thins gradually to less than 1 m toward the outer margins of the basin. Variations in the thickness of the turbidite layer suggest that the main part of the flow that deposited the Silver Turbidite was channeled between the Caicos Outer Ridge and the Bahama Escarpment until it spread fanwise across the abyssal plain floor. The turbidity current was flowing at a velocity of ~3 m/sec as it began to move across the Silver Abyssal Plain floor according to estimates based on the fall velocities of the fastest settling particles deposited from suspension. Vertical variations in grain size and the types of particles and sedimentary structures in the turbiditite suggest that the flow was surging. This study would not have been possible without Orrin Pilkey's support, advice, and willingness to permit students to dive into new areas of inquiry.