论“太湖冲击坑溅射物”——来自太湖现代沉积物中铁质结核的证据  

“Impact Ejecta in Taihu Area” Revisted:Evidence from Ferruginous Concretions in Modern Sediments of Taihu Area

作　　者：黄志诚[1] 刘冠邦[1] 

机构地区：[1]内生金属矿床成矿机制研究国家重点实验室,南京大学地球科学与工程学院,南京210093

出　　处：《高校地质学报》2012年第2期379-389,共11页Geological Journal of China Universities

基　　金：内生金属矿床成矿机制研究国家重点实验室资助

摘　　要：针对太湖发现由菱铁矿组成的"铁质溅射物"和"贫铁溅射物"是太湖形成于陨石冲击的观点,本文对这些实为铁质结核样品进行了详细的矿物学、地球化学和年代学测试。数据表明,这些样品是在太湖现代沉积淤泥层中形成的菱铁矿和褐铁矿结核。结核中含有大量水生植物碎片、植物蛋白石、细菌和少量动物壳体碎片。菱铁矿高温灼烧后全部变成赤铁矿,说明太湖地区不存在菱铁矿熔融状的高温相。菱铁矿14C测年结果表明各个样品形成于年代,不是瞬间形成的。δ13C数据指示为淡水无机碳来源,并非湖区碳酸盐岩直接来源。所谓的"贫铁溅射物"实际是黄土层的成岩钙结核。这些证据表明,太湖发现的这些结核是沉积成岩期的产物,并非冲击高温溅射熔融形成的溅射物。Regarding to the opinion of the impact origin of Taihu lake based on the discovery of the iron-rich siderite ejecta and iron-poor ejecta, we restudied similar samples by way of mineralogy, geochemistry and chronology. Our data show that those samples found in Taihu Lake are in fact siderite and limonite concretions which formed in Quaternary mud layer during diagenesis. Supporting evidence come from that a large number of aquatic plant debris, opal phytolith of plants, bacteria and a few animal shell fragments were found in those concretions. After high temperature burning, siderite completely changed into hematite, indicating that the high temperature phase of siderite mineral does not exist. The siderite 14C dating shows that the various samples formed at different times. ~13C data of siderite indicates a source of inorganic carbon in fresh water, not a carbonate direct source in the Taihu area. The so-called iron-poor ejecta are actually diagenetic calcium concretions found in loess layers. Those evidences showed that the weird-shaped concretions found in the Taihu Lake are diagenetic concretion, which are not impact ejecta.

关 键 词：太湖 冲击坑溅射物 铁质结核 钙质结核14C测年 

分 类 号：P512.32[天文地球—地质学]