1,721,206 research outputs found
Paleoclimatic changes in the Serravallian record of the Mediterranean area
No full textGrzybowsky Foundation Special Publicatio
Integrated Stratigraphy (Cyclostratigraphy and Biochronology) of Middle Miocene deposits in teh Mediterranean Area and comparison with Atlantic Ocean
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Paleoclimatic changes in the Serravallian record of the Mediterranean area
No full textPlanktonic foraminiferal and oxygen isotope records of the astronomically tuned S. Nicola composite
section (Tremiti Islands, Mediterranean basin) provide new insight into the paleoclimatic evolution
during the Middle to early Late Miocene (between 12.60 and 11.10 Ma). The application of PCA
(Principal Component Analysis) to high-resolution data enabled us to examine the interactions
among the foraminiferal proxies and to identify a series of paleoclimatic events of long and short
duration that took place in the Mediterranean basin during the late Serravallian. The long term trend
in PCA-1 score plot shows that the faunal composition of the studied sedimentary record changed
significantly at 11.80 Ma. This change coincides with the significant shift from negative to positive
loading in PCA-1 and it has been correlated with the onset of the Mi5 event, which in the
Mediterranean area is testified by the first influx of neogloboquadrinids. Such a major change is preceded
by other minor events at 12.38, 12.21, and 12.00 Ma, which indicate the progressive deterioration
from warm to colder climatic conditions. The most evident step coincides with a sharp decrease
in abundance of surface species at 12.00 Ma and the relative increase of intermediate species, suggesting
a contraction of the habitat of warm faunas and increasingly eutrophic conditions. This cooling
(of sea surface water) is also supported by a gradual shift in the bulk δ18O from –2.38‰ (12.374 Ma)
to -0.28‰ (11.963 Ma). The comparison between oxygen isotope oscillations and the eccentricity
records revealed a good correspondence of the light δ18O values to eccentricity maxima. In addition,
the vanishing from the Mediterranean of the neogloboquadrinids between 11.54 Ma and 11.21 Ma
has been related to the intensification of monsoon activity with an increase in runoff. This hypothesis
is supported by more negative values in δ18O. The Mediterranean results are compared with those
from the Equatorial and North Atlantic Ocean.
keywords. paleoclimatology, planktonic foraminifera, stable isotope, late Middle Miocene, Mediterranean
Integrated Stratigraphy (Cyclostratigraphy and Biochronology) of late Middle Miocene deposits in the Mediterranean area and comparison with the North and Equatorial Atlantic Oceans: synthesis of the major results
No full textEvidence of morphological deformities in benthic foraminifera from holocene sediments of Sorrento Peninsula (South Tyrrhenian Sea)
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Mediterranean Neogene historical stratotype sections and Global Stratotype Section and Point (GSSP): state of the art
No full textChanges in calcareous nannofossil assemblages during the Mid-Pleistocene Revolution
No full textThe distribution of calcareous nannofossils are quantitatively analysed in high-resolution deepsea
core samples from North Atlantic DSDP Site 607 and Eastern Mediterranean ODP Site 967,
between marine oxygen isotope stage (MIS) 35 and 15, in order to observe the response of
calcareous nannofossils to the Mid-Pleistocene Revolution (MPR). Nannofossil abundance
patterns show major variations through MIS 25–22 and distinct higher amplitude changes from
MIS 21 upward, sometime clearly correlatable to glacial–interglacial cycles. High amplitude,
short-term, fluctuations of small placoliths and F. profunda characterize the interval through
MIS 24 to 22/21, suggesting strong instability in nutricline dynamics and surface water
productivity. Principal Component Analysis and Shannon–Weaver indices (diversity and
dominance) highlight significant shifts, mainly related to variations in the characteristics of
surfacewaters. In both sites a minimum in diversity is recorded at MIS 22/21, corresponding to a
maximum in the dominance of Reticulofenestra spp. at Site 607 and of Pseudoemiliania lacunosa
at Site 967. Above MIS 21 the increase in abundance of various taxa (C. leptoporus,
Umbilicosphaera spp., Syracosphaera spp., Rhabdosphaera spp., Oolithotus spp.) and a general
increase in diversity are related to a distinct trend toward more stable and oligotrophic surface
waters in contrast to the higher productivity and less stratified surface waters of the Early
Pleistocene.
In addition, power spectral analysis was performed on calcareous nannofossil abundances,
Shannon Index diversity values and Factor 1 of Principal Component Analysis. These show
significant peaks in the obliquity (41-kyr) and eccentricity (100-kyr) frequency bands,
indicating that the quasi-periodic oscillations in the climate proxy data are controlled by
these orbital parameters. A relationship between changes in abundance of calcareous
nannofossils and production of glacial North Atlantic Deep Water is inferred
High-resolution calcareous plankton stratigraphy in the selected time slices: “state of the art”
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