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Organic-rich layers in the Metochia section (Gavdos, Greece): evidence for a single mechanism of sapropel formation during the past 10 My

1999; Elsevier BV; Volume: 153; Issue: 1-4 Linguagem: Inglês

10.1016/s0025-3227(98)00086-3

1872-6151

Sjoerd Schenau, Assimina Antonarakou, F.J. Hilgen, Lucas Joost Lourens, Ivar A Nijenhuis, C.H. van der Weijden, W.J. Zachariasse,

Paleontology and Stratigraphy of Fossils

Three well-developed 10 Ma old sapropels from the island of Gavdos (Greece) were selected for a detailed geochemical, micropaleontological and sedimentological study. The sapropels are characterized by a high organic carbon and a low carbonate content. Productivity was higher during sapropel formation, as indicated by increased Ba contents and higher percentages of the planktonic foraminiferal species Neogloboquadrina acostaensis. Enrichment of Mo and V in the sapropels indicates less oxygenated bottom water conditions, which is supported by the flourishing of low oxygen tolerant benthic foraminifera. Variation in grainsize and the Ti/Al ratio point to an alternating dominance of fluvial (sapropels) and eolian-derived (homogeneous intervals) terrigenous clastics. Evidence for a local origin of the enhanced fluvial input comes from the gradual replacement of the sapropels by cyclic turbidite sequences which were fed by bed-load type rivers. The increased fluvial input during sapropel formation increased the sedimentation rate and caused the observed carbonate depletion. The results obtained for the Gavdos sapropels are consistent with those of previous studies of younger sapropels and related CaCO3 cycles in the Mediterranean. The consistency in most of the geochemical and micropaleontological characteristics indicates that all sapropels and related layers are the result of a single mechanism for at least the past 10 My, namely precession induced dry–wet oscillations in the Mediterranean climate. Still, the effect of this mechanism on the intensity of surface water productivity, dilution and diagenetic signals may differ from site to site, depending on location, depositional environment and intensity of the astronomical forcing.