Sapropel-like Pliocene sediments of Sicily deposited under oxygenated bottom water

Abstract

The Pliocene Punta Piccola series, deposited on the Sicily sill at 100-400 m depths, consists of alternating whitish hemipelagic marl and carbonate-poor, organic-carbon-richer, brownish dark marl. The rhythmic bedding is interpreted to result from the precession driven alternation of more or less humid periods. In the present study, we compare the mineralogical and geochemical composition (isotope ratios of oxygen and carbon; Ca, Mn, Mg, Sr, and Fe concentrations) of the carbonate fractions of the whitish marl to those of the dark layers to evaluate the environmental changes that likely produced these alternations.High Mn concentrations in the dark layers, and the occurrence of pseudo-kutnahorite (Mn-Ca mixed carbonate), bioturbation, ostracodes, and benthic foraminifera favour the hypothesis of the dark-layer deposition taking place under oxygen-bearing bottom waters. The original value of the concentration of the organic carbon in the dark layers of Punta Piccola, estimated from the ␦ 13 C measured in the carbonate fraction, was higher than the post-diagenetic one. It may have reached 7% in the dark layer 107, which was therefore a true sapropel at the time of deposition. This result indicates that anoxic conditions are not a prerequisite for sapropelic sediment formation. However, the pristine concentration of the organic carbon in the dark layers at Punta Piccola is lower than those of coeval sapropels cored in the nearby deep settings, which were deposited under an anoxic water column. This difference may result from the effect of water column anoxia on the organic carbon content.Diagenetic reactions took place in the dark layers through the oxidation of large amounts of organic matter. The dissolution of primary calcium carbonates (biogenic in origin) and the reduction of Fe and Mn oxyhydroxides led the interstitial solutions to be supersaturated towards Mn-rich calcite and/or pseudo-kutnahorite. The secondary carbonates are Mg-enriched and Sr and Fe-depleted. The negative shifts of the ␦ 18 O signal in the carbonates of the dark layers of Punta Piccola are consistent with an increased river discharge in the Mediterranean at the time of deposition. Sédiments pseudo-sapropéliques pliocènes de Sicile déposés sous des eaux de fond oxydantesMots clés. -Sapropèles, Méditerranée, Manganese, Diagenèse précoce, Anoxie.Résumé. -Les séries pliocènes de Punta Piccola, déposées sur le seuil de Sicile à 100-400 m de profondeur, sont des alternances de marnes blanchâtres hémipélagiques et de marnes brunâtres pauvres en carbonates et riches en carbone organique. Ces dépôts cycliques résulteraient de l'alternance de période plus ou moins humides, rythmées par les cycles de précession. Dans cette étude, nous comparons les compositions minéralogiques et chimiques (composition isotopique du carbone et de l'oxygène, concentrations en calcium, manganese, magnesium, strontium et fer) des fractions carbonatées des marnes blanchâtres à celles des marnes sombres pour évaluer les changements environnementaux susceptibles de conduire...

Multiproxy approach for determination of nature and origin of carbonate micro-particles so-called “micarb” in pelagic sediments

“…The Punta Piccola sedimentary cycles (Brolsma, 1978;Hilgen, 1987) are known to be strongly related to precession astronomical variations (Rossignol-Strick, 1985;Hilgen, 1991) and many paleoenvironmental, chemical and mineralogical studies have previously been performed on these orbitally-driven deposits (e.g. Foucault and Mélières, 2000;Combourieu-Nebout et al, 2004;Daux et al, 2006). Based on the clay assemblages in those sediments (Foucault and Mélières, 2000) and from geochemical arguments (oxygen stable isotopes and alkenone sea surface temperature reconstructions, Beltran et al, 2007b), those orbitally driven deposits are related to climatic alternation of weak and strong rainfall periods, which may have controlled sea surface salinity variations in the Mediterranean and to sea surface temperature variations.…”

Investigation on Applying Biodegradable Material for Removal of Various Substances (Fluorides, Nitrates and Lead) from Water

“…The main type is determined by the biological and oxide content [7]. Their chemical composition includes all the macroelements and microelements, as well as biologically active substances, such as ferments, vitamins and antibiotics, needed for plants [1,8,9]. The digging of sapropel, in addition to lake water treatment, enables the use of the collected sapropel as a biosorbent, an environment-friendly fertiliser, a feed additive, as well as in building materials and beauty industries [10][11][12].…”

Determination of Organic Compounds, Fulvic Acid, Humic Acid, and Humin in Peat and Sapropel Alkaline Extracts

“…Sapropel is a mixture of organic and inorganic materials washed into lakes from catchments and generated within the lakes. It contains all macroelements and microelements necessary for plants, as well as biologically active substances, such as vitamins, enzymes, and antibiotics [ 18 , 19 , 20 ].…”