Sedimentary remains of fossilizable marine organisms, chiefly micropla
nktonic ones (coccolithophorids, silicoflagellates, diatoms, dinoflage
llates, radiolarians, foraminifers) have long been used for biogeograp
hic surveys, usually with the aim of unravelling paleoenvironmental se
ttings. Utilization of bottom deposits (rather than plankton samples)
has some advantages for this purpose: thanatocoenoses require smaller
sample sizes, materials are more readily available, and they eliminate
the small time-scale variability which obscures long-term trends. On
the other hand, the sedimentary imprint of planktonic distributional p
atterns is often severely distorted by fragmentation and dissolution o
f the biogenic remains, reworking of sediments, winnowing and lateral
advection of shells, especially toward lower latitudes, seasonally and
interannually variable output rates, and the integration of verticall
y heterogeneous assemblages. The biases derived from these processes r
ue reviewed, and the need for more information on selective dissolutio
n, vertical distribution patterns and planktonic reproduction and outp
ut rates is stressed. Given the assumptions used in paleoenvironmental
studies, distributional information drawn from sediment samples is le
ss prone to yielding biased information when applied to these surveys,
than to bio- or paleobiogeographic investigations; albeit the former
can also be significantly affected as a result of changes in the trait
s that govern the formation of biogenic sediments,