Abstract
Qualitative and quantitative analyses were made of the benthic and planktonic
foraminiferal associations derived from about 400 samples of the Cretan
and Sicilian Upper Miocene (Tortonian and Messinian). The quantitative data
were analyzed by means ofR- and Q-mode computer programs, which resulted
in clusterings of benthic and of planktonic foraminiferal species and the grouping
of
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the samples.
Oxygen and carbon isotope data were collected from the foraminiferal
carbonate of some 150 samples. The combination of these data with the data
from sedimentological analyses and with paleogeographic reconstructions
made it possible to arrive at fairly refined estimates of the Late Miocene
Mediterranean paleo-oceanography. The foraminiferal distribution and abundance
patterns were compared with the paleo-oceanographic interpretation
in order to trace the Late Miocene preference and tolerance patterns of the
foraminiferal species. Nutrient abundance and, to a lesser extent, salinity
were probably the main parameters controlling the Late Miocene distribution
patterns. Temperature, type of substrate, depth and pH apparently played
only a subordinate role.
The various existing models of the Messinian salinity crisis are discussed.
The roles of structural evolution, climate and oceanographic factors are considered.
Special attention is paid to the genesis of the laminated and diatomaceous
sediments. It is concluded that the laminated sediments are the result
of changes in the inflow-outflow balance of the Atlantic and Mediterranean
waters. The diatomites are ascribed to the same processes but with the additional
characteristic that they were formed in the western Mediterranean,
against shoals and landmasses, during periods of upwelling. It is suggested that
the laminated sediments were deposited during eustatic sea-levellowerings.
The ecology and paleoecology of planktonic and benthic foraminifera are
discussed extensively. It is concluded that the distribution of both groups of
foraminifera is mainly dependent on the distribution of water-masses; each
water-mass contains a characteristic faunal association. The abundance of
both groups of foraminifera is mainly linked to nutrient abundance, whereas
physical/chemical factors are of lesser importance.
A calibration of the Late Miocene distribution and abundance patterns
and those described from Recent environments suggests that the niches of
many foraminiferal species, in particular benthic taxa, changed considerably
during the last 5 to 6 m.y. This implies that the Recent distribution patterns
cannot simply be applied for the interpretation of fossil associations and for
the reconstruction of paleo-environmental conditions. A tentative model is
presented which might account for the inferred changes in habitats.
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