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| Titel |
Nature and origin of fine laminated sediments from the western Nile Delta: high-resolution elemental content and lithology |
| VerfasserIn |
J. K. Lorenzen, C. Blanchet, K. Brown, T. Feseker, R. Tjallingii, W. Brückmann |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250027660
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| Zusammenfassung |
| The Nile deep-sea fan is a key location to study the temporal variations of both North African
climate and Mediterranean hydrology. Prior to the construction of a large dam on the upper
Nile River, terrigenous and marine sediments accumulated at rates of up to 150 cm/ka,
allowing the preservation of a high-resolution climatic record. Moreover, the sediment
delivery shows a strong seasonal variability, with detrital material transported during summer
and autumn floods and biogenic carbonates deposited during winter and spring productivity
blooms.
Using a 6 m-long sediment core retrieved at 700 m water depth on the upper slope of the
western Nile deep-sea fan (R/V Poseidon cruise P362/2), we aim at reconstructing the
sedimentary dynamics during the Holocene. Below 70 cm of non-laminated oxidized
sediments, millimetre-scale laminations (alternating dark-coloured and light-coloured
silty-clay layers) develop and are fully expressed between 140 cm and the bottom of the core.
A first set of 5 AMS-14C ages indicates that the laminated interval was deposited
between 9500 and 7800 cal. yr BP. This corresponds to a sedimentation rate of
~2 mm/yr and implies that the laminations could record seasonal variations. In
addition, the laminated interval corresponds to the deposition of sapropel S1 in
the Mediterranean basin. Sapropel S1 has been related to the precession-forced
maximum of the African Monsoon and oxygen depleted Mediterranean bottom
water.
Non-destructive core logging techniques (MSCL, XRF core scanning) have been applied
to resolve the seasonal changes in sediment composition at centimetre- and sub
millimetre-scale. We use the relative variations of Ca and Ti obtained by the XRF core
scanner to trace the variations of terrigenous and marine contributions. Long-term variations
indicate relatively high terrigenous contribution in the laminated part of the core, which
strongly decreases in the non-laminated top part of the core. This might be related to
channel migrations on the paleo Nile delta at about 5000 BP although this is not
confirmed by 14C dates yet. The elemental contents at 0.3 mm-resolution clearly
indicate a strong increase of terrigenous material in the dark-coloured laminae with
respect to the light-coloured laminae. As such, we relate the dark-coloured laminae to
large scale flooding of the Nile during the summer-autumn monsoon season, and
the light-coloured laminae to winter-spring bloom in the surface waters. Changes
in frequency and amplitude of Ti/Ca ratios are visible, suggesting variations in
seasonality through time. This will be further explored using time-series analysis tools. |
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