『Abstract
　This paper is a synthesis of the use of selected trace elements as proxies for reconstruction of paleoproductivity and paleoredox conditions. Many of the trace elements considered here show variations in oxidation state and solubility as a function of the redox status of the depositional environment. Redox-sensitive trace metals tend to be more soluble under oxidizing conditions and less soluble under reducing conditions, resulting in authigenic enrichments in oxygen-depleted sedimentary facies. This behavior makes U, V and Mo, and to a lesser extent certain other metals such as Cr and Co, useful as paleoredox proxies. Some redox-sensitive elements are delivered to the sediment mainly in association with organic matter (Ni, Cu, Zn, Cd) and they may be retained within the sediment in association with pyrite, after organic matter decay in reducing sediment. This particularity confers to Ni and Cu a good value as proxies for organic C sinking flux (frequently referred to as productivity). Elements with only one oxidation state such as Ba and P are classically used to assess paleoproductivity levels but they suffer from the fact they are solubilized under reducing conditions and may be lost from oxygen-deprived sediments. The combined used of U, V and Mo enrichments may allow suboxic environments to be distinguished from anoxic-euxinic ones. Specifically, these elements tend to be much more strongly enriched in anoxic-euxinic environments and to exhibit weaker covariation with TOC than in suboxic environments.

Keywords: Geochemistry; Trace metals; Paleoredox conditions; Paleoproductivity; Paleoenvironments; Organic matter; Molybdenum; Uranium; Vanadium; Copper; Nickel』

1. Introduction
2. The paleoenvironmental parameters concerned with trace-element geochemistry
　2.1. Productivity
　2.2. Redox conditions
3. Mode of presentation of trace elements - normalization
4. Non-hydrogenous sources of trace metals
　4.1. Detrital sources
　4.2. Hydrothermal sources
5. Manganese: a special minor element influencing the behavior of trace metals
6. Trace-metal applications to paleoenvironmental analysis
　6.1. Redox proxies with minimal detrital influences
　6.2. Redox proxies with strong detrital influence
　6.3. Productivity proxies and their relationships to redox control
7. Remobilization of authigenically enriched trace metals during diagenesis
　7.1. Postdepositional reoxygenation
8. Multi-proxy trace-element patterns
　8.1. Suboxic-anoxic vs. euxinic
　8.2. Tracers for OM abundance
　8.3. Bottom water oxygenation and/or organic matter flux?
　8.4. Interpreting paleoredox conditions from trace element-TOC covariation patterns
9. New tracks for the near future?
10. Conclusions
Acknowledgments
References

Table 1 Redox classification of the depositional environments, after Tyson and Pearson (1991)

Redox classes	Oxic	Suboxic	Anoxic	Euxinic
			No free H2S in the water column	Free H2S present in the water column
O2 concentration in bottom waters (ml O2/l H2O)	[O2]＞2	2＞[O2]＞0.2	[O2]＜0.2	[O2] ＝ 0
The values for O2 concentrations in bottom waters are valid for present-day ocean.

Fig. 2. Schematic diagram illustrating the relative enrichment of Ni, Cu, Mo, U and V versus total organic carbon (TOC). TE stands for trace elements and OM stands for organic matter. 〔Tribovillard,N., Algeo,T.J., Lyons,T. and Riboulleau,A.(2006): Trace metals as paleoredox and paleoproductivity proxies: An update. Chemical Geology, 232, 12-32.から〕 ※euxinic＝強還元性

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