(Table 1) Geochemistry of Sapropels of the Mediterranean Sea

Sapropels -organic-matter rich layers- are common in Neogene sediments of the eastern Mediterranean Sea. The formation of these layers has been attributed to climate-related increases in organic-matter production (Calvert et al., 1992, doi:10.1038/359223a0; Rossignol-Strick et al., 1982, doi:10.1038/295105a0; Rohling, 1994, doi:10.1016/0025-3227(94)90202-X) and increased organic-matter preservation due to oxygen depletion in more stagnant bottom waters (Rossignol-Strick et al., 1982, doi:10.1038/295105a0; Rohling, 1994, doi:10.1016/0025-3227(94)90202-X). Here we report that eastern Mediterranean Pliocene sapropels (Emeis et al., 1996, doi:10.2973/odp.proc.ir.160.102.1996) contain molecular fossils of a compound (isorenieratene) known to be synthesized by photosynthetic green sulphur bacteria, suggesting that sulphidic (euxinic) -and therefore anoxic- conditions prevailed in the photic zone of the water column. These sapropels also have a high trace-metal content, which is probably due to the efficient scavenging of these metals by precipitating sulphides in a euxinic water column. The abundance and sulphur-isotope composition of pyrite are consistent with iron sulphide formation in the water column. We conclude that basin-wide water-column euxinia occurred over substantial periods during Pliocene sapropel formation in the eastern Mediterranean Sea, and that the ultimate degradation of the increased organic-matter production was strongly influential in generating and sustaining the euxinic conditions.

腐泥层（sapropels）——即富有机质沉积层——广泛分布于地中海东部的新近纪（Neogene）沉积物中。这类沉积层的形成被归因于两大因素：一是与气候相关的有机质生产规模提升（Calvert等，1992，doi:10.1038/359223a0；Rossignol-Strick等，1982，doi:10.1038/295105a0；Rohling，1994，doi:10.1016/0025-3227(94)90202-X）；二是停滞性更强的底层水体发生缺氧，进而提升了有机质的保存效率（Rossignol-Strick等，1982，doi:10.1038/295105a0；Rohling，1994，doi:10.1016/0025-3227(94)90202-X）。
本研究报道，地中海东部上新世（Pliocene）腐泥层（Emeis等，1996，doi:10.2973/odp.proc.ir.160.102.1996）中检出一种化合物的分子化石——异瑞尼烯（isorenieratene），该化合物已知由光合绿色硫细菌（photosynthetic green sulphur bacteria）合成，这表明当时水柱的透光带（photic zone）内普遍存在硫化缺氧型（euxinic）环境——亦即缺氧环境。
此类腐泥层同时具有较高的微量金属含量，这大概率源于硫化缺氧型水柱中硫化物沉淀对这些金属的高效清除作用。
黄铁矿（pyrite）的丰度与硫同位素组成，与水柱中硫化铁的形成过程相吻合。
本研究最终得出结论：地中海东部上新世腐泥层形成期间，曾有相当长的时段存在全盆地尺度的水柱硫化缺氧环境；而有机质生产规模提升后的最终降解过程，对该硫化缺氧环境的形成与维持具有显著影响。