| Summary: | Holocene bulk sediment and component accumulation rates were
measured in twenty-eight piston and gravity cores taken from the
floor of the western Panama Basin and on the surrounding ridges.
Radiocarbon ages and oxygen isotope curves provided Holocene age
control in nine cores. Time datums in nineteen other cores were
inferred by correlation of calcium carbonate curves to the dated
cores. Dry bulk densities were measured in ten cores and were
estimated in the others by an empirical relationship between dry
bulk density and the percentages of sand, clay, and calcium carbonate.
Other studies of the textural, mineralogical and sand fraction composition
of near surface sediments in these cores provided analyses
which could be used to obtain accumulation rates for these components.
A general similarity between the map pattern of surface productivity
and the patterns of carbonate and opal accumulation rates
suggests a first order control of biogenic sedimentation by fertility
of surface waters. Accumulation rates of terrigenous components
are highest near the continents; the map and depth patterns suggest
dispersal by currents shallower than 2000 m or by winds. It is inferred
from textural component accumulation rate patterns that no
significant regional redistribution of sediment by winnowing occurred
during the Holocene. Deposition from deep thermohaline circulation
probably increased the accumulation rates of silt, clay, and opaline
components in the gaps between the western and eastern troughs.
Calcium carbonate accumulation rates at equal depths are generally
lower within 250 km of the edge of the continental shelf. Below
2000 m in high productivity regions > 250 km from the shelf calcium
carbonate accumulation rates decrease linearly with depth according
to a gradient of -3.3 gm CaCO₃/cm²/1000 yrs/ km. From this
gradient, two independent estimates of the lysocline in this region,
and a model of calcium carbonate accumulation, the average Holocene
rate of supply of calcite from the surface is calculated to be
5-10 gm/cm²/1000 yrs. === Graduation date: 1976
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