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| Titel |
Benthic faunal assemblages from the Holocene middle shelf of the South Evoikos Gulf, central Greece, and their palaeoenvironmental implications |
| VerfasserIn |
Markella Asimina Louvari, Theodora Tsourou, Hara Drinia, George Anastasakis |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250072329
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| Zusammenfassung |
| South Evoikos Gulf is an elongate, WNW – ESE trending basin, 60 km long and 15
km wide. Its floor slopes towards the south-east where the basin connects with
the Aegean Sea across a 55 m deep sill. The hydrographic network of the area is
characterized by Asopos river the small Lilas River and some other ephemeral
streams.
A sedimentary record spanning the last 13000 calyr BP was recovered at N 38°12’23.1228" E
24°8’14.2404", water depth 70 m, in this gulf. A total of 52 samples from the lower half of
the core were quantitatively analyzed for micropalaeontological (benthic foraminifera and
ostracods) study in order to reconstruct palaeoenvironmental conditions. This work
contributes to the evaluation of the modern environmental problems in South Evoikos Gulf
(hypoxia, ecosystem changes, subaquatic vegetation die-off, metal pollution) within the
context of the palaeoenvironmental record.
In the investigated core, the benthic microfaunal assemblages indicate a marine coastal
environment with a gradual transition from a circalittoral to an infralittoral restricted
environment.
The basal part of the record is characterized by Haynesina depressula Assemblage, which is
composed of Haynesina depressula, Textularia agglutinans and Bulimina aculeata.The
abundance of Haynesina depressula could be associated with normal marine conditions, but
always with periodic brackish water influence. The species composed this assemblage, which
are almost all typically infaunal, characterize sediments with a high or medium-high muddy
fraction, rich in organic matter available for the organisms that live within the sediment, and
low salinity bottom water.
Samples from the upper unit of the core indicate a nearshore, inner-shelf facies less than 50 m
deep. Common inner-shelf species in these samples include Ammonia beccarii together with
Bulimina marginata (Sgarrella & Moncharmont Zei, 1993). The highest abundance of A.
beccarii is found between 15 and 20 m water-depth in samples with intermediate percentages
of organic matter in which at least some sand fraction is present. A strict interpretation based
on the known modern distribution of A. beccarii would confine the species to upper shoreface
environments (Hayward et al. 2004). The relatively high frequency values of B. marginata
indicate a correlation with organic matter enrichment, with seasonal low oxygen content. This
hypothesis is testified also by the increase of the opportunistic species V. bradyana.
The temporal presence of V. bradyana assemblage indicates a strong influence of
Asopos River run-off, with interplay of increasing food availability and low oxygen
concentration
Three main ostracod assemblages were distinguished from the bottom to the top of the
sediment core:
At the lower part of the core ostracod assemblage consists mainly of Costa edwardsii,
Cytheridea neapolitana, Callistocythere spp., Pterygocythereis jonesii and Leptocythere spp.
At the middle part, Costa edwardsii is the dominant species with relative abundances up to
80% of the total ostracod fauna. At the upper part Costa edwardsii is the most abundant
species (20-40% of the total fauna) accompanied mainly by Loxoconcha spp., Xestoleberis
spp. and Cyprideis torosa. Ostracod abundance and diversity decrease towards the upper unit
of the studied core.
These data, and AMS radiocarbon ages determined for foraminifera and ostracods, provide
evidence of a change from oceanic influence to estuarine influence. This event is also
contemporaneous with the period which is generally characterized by increased evaporation
rate (initially at the tropic seas), retreat of glaciers and increased rainfalls (Fairbanks,
1989).
Fairbanks, R.G., 1989. A 17,000 year glacio-eustatic sea level record: influence of glacial
melting rates on the Younger Dryas event and deep ocean circulation. Nature, 342,
637-642.
Hayward, B.W., Sabaa, A.T., Grenfell, H.R., 2004. Benthic foraminifera and the Late
Quaternary (last 150 ka) palaeoceanographic and sedimentary history of the Bounty Trough,
east of New Zealand. Palaeogeography, Palaeoclimatology, Palaeoecology, 211(1-2), 59-93,
doi:10.1016/j.palaeo.2004.04.007
Sgarrella, F. & Moncharmon-Zei, M. 1993. Benthic foraminifera in the Gulf of Naples
(Italy): systematic and autoecology, Boll. Soc. Palaeont. Ital. 32, 145-264.
This research has been co-financed by the European Union (European Social Fund – ESF)
and Greek national funds through the Operational Program "Education and Lifelong
Learning" of the National Strategic Reference Framework (NSRF) - Research Funding
Program: THALIS –UOA-70/3/11669. |
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