ABSTRACT
Few studies on modern abyssal plain turbidites have attempted to
assess
the lateral extent of individual units and few have therefore been
able
to provide any information on the evolution of turbidity deposits
across
long abyssal plain distances. In the 4755 m-deep Horseshoe Abyssal
Plain,
ten distinct lithologic units (six of these Iberian
Peninsula-derived turbidites)
were delineated in nine piston cores on the basis of stratigraphic
position,
thickness (range of 20 cm to greater than 500 cm), color, sediment
type,
sedimentary structures, x-ray mineralogy, and the ubiquitous
presence of
units in all abyssal plain and supplying canyon piston cores. In
order
to make this correlation more rigorous, detailed grain size
analyses, light
and heavy mineralogy of sands, HCl treatment, and volatile solids
determinations
were performed on three of the six turbidite units, which have
volumes
of 5.7, 8.0, and 12.1 km3. These analyses further confirm
correlation over
the entire 15,000 km2 area of the Horseshoe Abyssal Plain and
certainly
provide long-distance correlations for six individual turbidites
of over
300 km for each flow. In addition, shallow subbottom reflectors
and transparent
zones seen on 3.5 kHz-P.D.R. profiles can be tied into the in situ
stratigraphy
of the piston cores.
The results of previous studies on modern abyssal plain
turbidites,
ancient turbidite deposits, and experimental lab studies are
compared with
results from the Horseshoe Abyssal Plain deposits and it is
concluded that
minor physiographic disturbances on the otherwise flat abyssal
plain floor
have resulted in marked sedimentological variation. It was found
that regular
grain size decrease and thickness decrease with increasing
distance from
the supplying canyon were not observed for individual bedding
units. The
ruling notions about lateral variations within turbidites are
questioned.
Hoyt, W.H., 1976. Long-Distance Turbidite Correlations in the
Horseshoe
Abyssal Plain. Unpublished MSc. thesis, State University of New
York at
Albany. 136pp., +x.
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