Cyclic variations in the chemical composition of eastern Mediterranean Pliocene sediments: a key for understanding sapropel formation
Introduction
Pliocene to Holocene Mediterranean sediments contain numerous dark-colored layers, termed sapropels, which are characterized by high total organic-carbon (TOC, ≥2%), S, and Fe contents and significant enrichments in various trace elements (Calvert, 1983; Pruysers et al., 1991; Thomson et al., 1995). Different approaches have been taken to elucidate the paleoceanographic scenario that led to their formation.
The occurrence of sapropels is cyclic, and seems to correspond closely with minima in the precessional index when perihelion occurs in the Northern Hemisphere summer (Rossignol-Strick, 1983Rossignol-Strick, 1985; Prell and Kutzbach, 1987; Hilgen, 1991). Rossignol-Strick (1983)demonstrated that the temporal distribution of recent eastern Mediterranean sapropels correlates with maximum potential strength of the African monsoon, a function of orbital precession, which would have resulted in maximum discharge from the Nile River. Rohling and Hilgen (1991)postulated that increased precipitation along the northern borderlands of the eastern Mediterranean, because of increased activity of Mediterranean summer depressions, could have been an additional precession-related factor for reduced sea surface salinities during sapropel formation. δ18O-signatures of planktonic foraminifers reveal that surface water salinities must have been lower during times of sapropel formation (Williams and Thunell, 1979; Vergnaud Grazzini et al., 1986).
Carbonate cycles found in Pliocene to Holocene Mediterranean sediments have been examined by use of micropaleontological (De Visser et al., 1989; Howell et al., 1990) and magnetostratigraphical (Langereis and Hilgen, 1991; Hilgen, 1991) as well as geochemical (Van der Weijden, 1993; Van Os et al., 1994) methods. The consensus is that carbonate cycles, including intercalated sapropels, correspond closely with minima in the precessional index (e.g. Rossignol-Strick, 1983; Prell and Kutzbach, 1987; Hilgen, 1991; Lourens et al., 1992).
Few published studies deal with sources and distribution of terrigenous detrital matter in Mediterranean sediments. Investigations by Venkatarathnam and Ryan (1971)and Dominik and Stoffers (1978)are based on clay mineralogical studies of short cores. Foucault and Mélières (1995) analyzed the mineralogy of cyclic sediments from the Narbone Formation in Sicily. They found varying amounts of eolian- and fluvially-derived minerals, which, according to their interpretation, were controlled by alternation of humid and dry periods on both the northern and southern borderlands of the western Mediterranean.
In this paper high-resolution geochemical studies of Pliocene sedimentary sequences from Ocean Drilling Program (ODP) Sites 964 and 967 in the eastern Mediterranean are presented. This is one of the first attempts to investigate longer sedimentary sequences which contain several sapropels from the eastern Mediterranean by high-resolution major- and minor-element geochemistry. The basic idea behind such an approach is that any change in paleoenvironmental or climatic conditions should be reflected in major- and minor-element abundances. In particular, the question will be addressed whether cyclic chemical changes are only restricted to sapropel containing intervals, or are also seen in the non-sapropelic parts of the sedimentary sequences.
Section snippets
Sampling and methods
ODP Site 964 (Fig. 1) is located at a water depth of 3670 m in the Ionian Basin at the foot of the Calabrian Ridge on a small bathymetric high, the Pisano Plateau. Site 967 (Fig. 1) is located south of Cyprus on the lower northern slope of the Eratosthenes Seamount at a water depth of 2560 m. For our investigation we selected an interval that, according to ODP Leg 160 shipboard biostratigraphic studies (Emeis et al., 1996), belongs to nannofossil zone MNN17-16b and is 2.51 to 2.82 Ma old. This
Bulk chemistry
The sediments from both sites investigated may be regarded as marls or calcareous marls with mean CaCO3 contents (calculated from CaO) of 62% for Site 964 and 51% for Site 967 (Table 1). In order to compensate for carbonate dilution the chemical composition of the sediments is discussed here on the basis of element/Al ratios. Significant differences in the lithogenic sediment fraction of the two sites are evident: Ti/Al ratios are consistently higher at the Eratosthenes Seamount, whereas Si/Al,
Conclusions
The chemical composition of the terrigenous detrital component of Pliocene sediments from the eastern Mediterranean, ODP Sites 964 and 967, exhibits cyclic changes, which are caused by precession-induced climatic variations. Periodicity in major-element abundances reflects episodes of either enhanced eolian or fluviatile input. At ODP Site 964 (Pisano Plateau, Ionian Basin) terrigenous detrital matter chemistry reflects periods of stronger Saharan dust input alternating with fluvial input from
Acknowledgements
We thank the crew and scientific party of ODP Leg 160 for their generous support. Thanks to B. Schnetger and H. Schale for their help during sample preparation and analysis. A. Eisenhauer kindly provided the preliminary Sr-isotope measurements. We are grateful to G.J. de Lange, I.A. Nijenhuis and H.F. Passier for helpful discussions and critical comments. We further would like to acknowledge the helpful reviews by J. Thomson and G.J. de Lange. This project was financially supported by the
References (73)
- et al.
Barium and strontium concentrations in Pacific and Mediterranean sea water by direct isotope dilution mass spectrometry
Earth Planet. Sci. Lett.
(1972) Oxygen consumption, new production, vertical advection and environmental evolution in the Mediterranean Sea
Deep Sea Res.
(1989)- et al.
Interstitial water trace-metal chemistry of laminated sediments from the Gulf of California, Mexico
Mar. Chem.
(1983) - et al.
Soil-sized eolian dusts from the lower troposphere of the Eastern Mediterranean Sea
Mar. Geol.
(1977) - et al.
Sources and characteristics of the atmospheric aerosol near Damascus, Syria
Atmos. Environ.
(1990) - et al.
Discrete suspended particles of barite and the barium cycle in the open ocean
Earth Planet. Sci. Lett.
(1980) - et al.
The origin of rhythmic bedding in the Pliocene Trubi formation of Sicily, southern Italy
Palaeogeogr., Palaeoclimatol., Palaeoecol.
(1989) - et al.
Particulate barium fluxes and their relationships to biological productivity
Deep Sea Res. II
(1996) - et al.
Transport of Saharan dust across the eastern Mediterranean
Atmos. Environ.
(1982) - et al.
Geochemistry of Pacific pelagic sediments
Geochim. Cosmochim. Acta
(1958)
Astronomical calibration of Gauss to Matuyama sapropels in the Mediterranean and implication for the Geomagnetic Polarity Time Scale
Earth Planet. Sci. Lett.
Organic carbon accumulation in Bannock Basin: evaluating the role of productivity in the formation of eastern Mediterranean sapropels
Mar. Geol.
Laminated sediments from the Vrica Section (Calabria, S. Italy): evidence for Plio–Pleistocene climatic change in the Mediterranean region
Palaeogeogr., Palaeoclimatol., Palaeoecol.
Nutrient dynamics and New Production in a warm-core eddy from the Eastern Mediterranean
Deep Sea Res.
The Rosello composite: a Mediterranean and global reference section for the Early to early Late Pliocene
Earth Planet. Sci. Lett.
Late Pliocene to early Pleistocene astronomically forced sea surface productivity and temperature variations in the Mediterranean
Mar. Micropaleontol.
Late Quaternary sapropel on the Mediterranean Ridge: U-budget and evidence for low sedimentation rates
Sediment. Geol.
Elemental mass-balance of material carried by major world rivers
Mar. Chem.
Diagenetic pyritisation under eastern Mediterranean sapropels caused by downward sulphide diffusion
Geochim. Cosmochim. Acta
Geochemistry of eastern Mediterranean sediments: primary sediment composition and diagenetic alterations
Mar. Geol.
Late Quaternary climatic changes in Australia and North Africa: a preliminary interpretation
Palaeogeogr., Palaeoclimatol., Palaeoecol.
Mediterranean Quaternary sapropels, an immediate response of the African monsoon to variations of insolation
Palaeogeogr., Palaeoclimatol., Palaeoecol.
Mud redeposition and problems of assessing microfossil, isotopic and radiocarbon data in the Mediterranean
Mar. Geol.
Global maps of lake level fluctuations since 30,000 yr. B.P
Quat. Res.
Geochemical Studies of the recent sapropel and associated sediments from the Hellenic Outer Ridge, eastern Mediterranean Sea, I. Mineralogy and chemical composition
Mar. Geol.
Redistribution and geochemical behavior of redox-sensitive elements around S1, the most recent eastern Mediterranean sapropel
Geochim. Cosmochim. Acta
Geochemical signatures preserved in sediments of the Semaforo and Vrica sections (Calabria, Italy) and their relations with variations of the sedimentary regime
Palaeogeogr., Palaeoclimatol., Palaeoecol.
Possible diagenetic mobilisation of barium in sapropelic sediment from the eastern Mediterranean
Mar. Geol.
Active post-depositional oxidation of the most recent sapropel (S1) in sediments of the eastern Mediterranean Sea
Geochim. Cosmochim. Acta
Dispersal patterns of clay minerals in the sediments of the eastern Mediterranean Sea
Mar. Geol.
Faunal and oxygen isotopic evidence for surface water salinity changes during sapropel formation in the eastern Mediterranean
Sediment. Geol.
Late Quaternary history of the Nile
Nature
Stratigraphy of the western Mediterranean and southern Calabrian Ridges, eastern Mediterranean
Mar. Micropaleontol.
Geochemistry of Pleistocene sapropels and associated sediments from the Eastern Mediterranean
Oceanol. Acta
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