新西兰北岛红树林沉积物中黄铁矿微观形貌特征及其环境指示意义

Micromorphological characteristics of pyrite in mangrove sediments from North Island of New Zealand and its environmental significance

为探究红树林沉积环境自生黄铁矿形貌特征及其分布规律,利用新西兰北岛红树林沼泽区三个不同植被带采集的沉积物柱状样品,在偏光显微镜及扫描电镜下对其不同深度沉积物样品中黄铁矿数量及形貌特征进行了分类、统计。结果表明:①三个植被带沉积物样品中均存在莓球状黄铁矿、团块状黄铁矿、结核状黄铁矿及晶粒状黄铁矿,且结核状黄铁矿占比最高;②莓球状黄铁矿平均粒径7.77μm,微晶形态以八面体和五角十二面体型为主;③相比光滩区、内部林区两个植被带,红树林林缘区沉积物的莓球状黄铁矿粒径变幅较大,自形晶含量最高。初步判断本研究区沉积环境属于贫氧沉积环境,红树林林缘区水环境动荡,黄铁矿发育程度较高。相比中国海南省、厦门红树林湿地及美国西海岸Elkhorn Slough盐沼湿地沉积环境,本研究区红树林沉积环境更封闭,促进了自形晶的广泛发育。

To clarify the characteristics and spatial distribution of authigenic pyrite in mangrove sediments,three sediment cores were collected from three different vegetation zones of mangroves in North Island of New Zealand.Different types of pyrite with different depths in the sediment cores were recorded and quantified under polarized microscope and scanning electron microscopy(SEM).The results showed that:①There were four types of pyrite in the sediment samples,i.e.,framboidal,crystalline,nodular and massive pyrites.Among them,nodular pyrite was the most abundant type.②The average diameter of framboidal pyrite grain was 7.77μm,with the dominant microcrystalline shape of mainly octahedral and pentagonal dodecahedral.③Compared with pyrite in the mudflat zone and the interior mangrove zone,the framboidal pyrite in grain size deviation and the proportion of euhedral crystals were high in the fringe mangrove zone.The maturation of pyrite inferred a hypoxia environment with more turbulent water in the fringe mangrove zone.Compared with the sedimentary environment of mangrove in Hainan,Xiamen,and saltmarsh wetland in Elkhorn Slough,the mangrove sedimentary environment in this study area was more enclosed,which promoted the formation of pyrite in euhedral crystals.