Institution

in age, and the ash is probably associ ated wi th the
Oligocene and Miocene volcanism in Haiti and the Dominican
Republic, respectively (Weyl, 1968). The foraminiferal
assemblage near the top of the next core to the east
(CH57-12) includes G. truncatulinoides and G. menardii
flexuosa, dating the sediment as X-zone (75,000 years) or
older. The abundant altered ashes in the lower half of the
core may be associated with late Pliocene and Pleistocene
volcanism in Hispaniola (Schuchert, 1968). Core CH57-4,
deep on the north slope of the Puerto Ri co Trench, can be
described as a breccia lutite of altered ash with layers and
inclusions of chalky nannoplankton ooze. The obvious
mixing of material at all depths (Fig. 5.2) indicates
slumping, although the regular dated sequence of lower to
upper-middle Eocene sediment argues against large-scale
disruption. The Eocene geosynclinal volcanism in the
Greater or Lesser Antilles (Weyl, 1968) may account for the
ash in this core.
119
The ages of these cores suggest that sedimentation rates
at the core locations have been extremely low (average c 1
mm/1000 yr) since Eocene time. The other cores from the
north slope of the Puerto Rico Trench are lithologically
similar to the three dated cores, in that they contain
unfoss i 1 i ferous mi xtures of altered ash and pel agi c 1 uti te;
thus all cores from the north slope are distinctly different
from outer ri dge cores, whi ch contai n only a few thi n beds
of altered ash. This suggests that the north slope of the
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