TURBIDITES OF THE NORTHEAST PACIFIC¹

Abstract

The northeast corner of the Pacific Ocean is a region of turbidity‐current activity. Cores from this area are dominated by very fine‐grained sand and medium‐grained silt that grade upward to clay. The results presented in this article are based on 217 textural analyses of turbidite layers comprising 30 piston cores. It is possible to distinguish proximal and distal facies of turbidites using characteristics of layering, grading and texture. Features of the proximal facies include wide range of layer thickness, maximum layer thickness, non‐grading, truncation of grading, textural reversals, and sand at the base of graded layers. Areas beyond main routes of submarine flows are sites of episodic addition of silt‐through clay‐sized sediment. The proportion, thickness, and mean grain size of the silt decreases with increasing distance from the main avenues of flow.

Controls on the distribution of deep‐sea sediments

“…These lithogenous sediments are likely associated with sediment re‐distribution mechanisms such as turbidity and bottom currents, which transport material such as fine sand and silt in suspension over large distances. Turbidites are known to occur in regions where subduction trenches are absent such as the Northeast Pacific [ Horn et al ., ]. Silt, which forms distinct patches in the Pacific Ocean (Figure ) may also be transported by wind as apart from clay as this grain‐size also comprises an important fraction of aeolian dust [ Gao et al ., ] and is found as quartz within deep‐sea clays [ Biscaye , ].…”

GRADED‐BED SEQUENCES EMPLACED BY TURBIDITY CURRENTS NORTH OF 20°N IN THE PACIFIC, ATLANTIC AND MEDITERRANEAN1

“…Properties of layers within a single core are related to the distance between coring site and principal avenue of transfer for a given area (Horn et al, 1971a). Bottom currents may play a major role on the continental shelf, slope and rise.…”

“…Core data from other parts of the Gulf of Alaska suggest that toward the close of the Pleistocene submarine flows lacked sufficient momentum to transport sediment across many deep areas of the gulf. Although there were many channels available as avenues for sediment transfer, the flows only reached half way to the Gulf of Alaska Abyssal Hills ( Fig.1, see also Horn et al, 1971a). The coarse layers in the cores may represent the culmination of turbidity flow in the Late Pleistocene.…”