Institution

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of North America have clay-mineral assemblages resulting
dominantly from mechanical weathering; thus they are
dominated by the clay minerals chlorite and illite. Below
the 1 ati tude of Cape Hatteras, however, the sediments tend
to be enriched in kaolinite and montmorillonite, reflecting
sources in regions of tropical weathering.
If abyssal currents are transporting sediments from
the continental margin of North America into the region of
the Greater Antilles Outer Ridge, the mineralogy of the
outer ridge sediments should reflect a northern provenance.
This concept is strikingly supported by a tongue-like
extension of chlorite-enriched sediments which lies beneath
the axis of the Western Boundary Undercurrent and extends
south along the Bahama Banks into the regi on of the Greater
Antilles Outer Ridge (Figs. 4.9 and 4.10). A northern
assemblage of clay minerals on the Greater Antilles Outer
Ridge is evident when mineral compositions are determined
by ei ther the method of Bi scaye (1965) or that of Hathaway
(1972a). Hornblende, which is common in the northern
assemblage, is also observed consistently in sediments of
the are a i n flu e n c e d by the We s t ern B 0 u n d a ry Un de r cur r e n t
(i.e. the Caicos Outer Ridge - Bahama Banks Apron and the
Greater Antilles Outer Ridge). Hornblende is seldom
observed in the Puerto Ri co Trench or on the Bermuda Ri se,
where the Western Boundary Undercurrent has not deposited
sediment (Table 4.1,4.2).
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