草莓状黄铁矿形成机制及其研究意义

Formation mechanism of pyrite framboid and its research significance

黄铁矿是沉积物中较为常见的矿物之一，而草莓状黄铁矿是由等粒度的亚微米级黄铁矿晶体或微晶体紧密堆积而成。基于已有的草莓状黄铁矿相关研究成果，本文综述了草莓状黄铁矿的形成机制，阐述了其对古环境恢复的意义。目前普遍认为草莓状黄铁矿的成因主要有两种，即有机成因和无机成因，前者认为有机质或细菌参与草莓状黄铁矿形成；而后者主要认为过饱和的黄铁矿浓度是微球粒草莓状黄铁矿形成的必备条件。草莓状黄铁矿粒径的大小是其古沉积环境的直接反映，被作为比较可靠的古氧化还原条件判别指标，已被广泛应用于古代及现代海洋沉积物的古环境恢复。目前，虽然草莓状黄铁矿粒径判别古环境的大小及分布范围还不统一，但普遍认为封闭的水体环境（硫化环境）草莓状黄铁矿粒径较小且变化不大，且随着含氧程度增加，草莓状黄铁矿的粒径大小增大且分布范围趋于加宽。

Pyrite is one of the common minerals in sediments and framboidal pyrites are densely packed, raspberry like, spherical aggregates of equigranular, micronsized crystals or microcrysts. Based on the previous studies of framboidal pyrites, we summarized formation mechanism of framboidal pyrites and discussed the significances of framboidal pyrites for palaeo-ocean redox conditions. At present, the genesis of framboidal pyrites is widely considered as two factors, namely abiogenic and organic genesis. The former held that organic matter or bacteria is involved in the formation of framboidal pyrite; the later insisted that supersaturated pyrite concentration is the necessary condition. Framboidal pyrite size, which is considered as an indicator of the redox condition, commonly is used to palaeo-ocean redox condition reconstruction. Although there is no consensus on exact criteria for identifing paleo- ocean redox by pyrite framboid size distribution, it is concluded commonly that framboidal pyrite size and the range of size is lesser in euxinic, and will become larger with oxyen increasing.