Institution

229
Chase and Hersey, 1968). The thin transparent layer observed
in some places beneath the stratified sediments on the
south slope of the Puerto Ri co Trench (Ewi ng and others, 1968)
may also have been deposited at this time, but most of the
homogeneous sediment deposited there has probably been
masked by downslope sediment movement or has itself slumped
into the trench. Most of the transparent sediment deposited
in the trench would be masked in a similar way.
Meanwhile, downslope sediment movement and turbidity
currents from the area of the present southeastern Bahama
Banks continued to deposit flat-lying, stratified sediments
above Datum A in the region where the western Greater
Antilles Outer Ridge now lies (Figs. 3.6, 3.7, 8.2).
Although it is impossible to assess the extent of current )
deposition of lutite along the base of the Bahama Banks
during this period, the lutite which was deposited there
probably Was eroded by turbi di ty currents and redeposi ted
in the flat-lying sediments above Datum A under the present
western Gre~ter Antilles Outer Ridge. The restriction of
these post-Datum A turbidites to the western ridge sector.
suggests that they may correlate with the 3.0 km/sec layer
presently found under portions of the western Greater
Antilles Outer Ridge (see Northrop and Ransone, 1962; Savit
and others, 1964). Isolated pockets of current~deposited .
1 uti te, such as the one on the western 5i de of the seamount
in the Silver Abyssal Plain (Fig. 3.11), apparently formed
despite the turbidity-current activity. The location and . )