Siderite cannot be used as CO2 sensor for Archaean atmospheres
Siderite cannot be used as CO2 sensor for Archaean atmospheres
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DOI：
10.1016/j.gca.2017.07.027
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发表时间：
2017-10
影响因子：
5
通讯作者：
Fabian Gäb;C. Ballhaus;J. Siemens;A. Heuser;M. Lissner;T. Geisler;D. Garbe‐Schönberg
中科院分区：
文献类型：
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作者：
Fabian Gäb;C. Ballhaus;J. Siemens;A. Heuser;M. Lissner;T. Geisler;D. Garbe‐Schönberg
提出了利用中晚中生代上级型带状菱铁矿FeCO 3作为代表来约束中晚中生代大气CO2分压。这一命题的含义是，菱铁矿是一种主要的碳酸盐矿物，直接从富含Fe 2+的地中海海水中结晶出来，与大气中的CO2平衡。据我们所知，这一主张尚未被证明有效。我们测试控制CO2分压下的水-气交换实验，如果菱铁矿可以稳定作为一个主要的矿物在含Fe 2+的海水。还原海水代理富含Fe 2+和Mn 2+的平衡与还原N2-CH 4-CO2-H2气相与可变CO2。在富含Fe 2+的水组合物中稳定的固相是无定形亚铁羟基碳酸盐。结晶菱铁矿FeCO 3不是稳定相。从富锰水中沉淀的相包括结晶菱锰矿MnCO 3和可能的无定形富锰相。基于这些结果，我们建议不要使用菱铁矿带状铁地层作为CO2传感器的海洋大气。
It was proposed to utilize siderite FeCO3in mid to late Archaean Superior type banded as a proxy to constrain the CO2partial pressure of Archaean atmospheres. Implicit in this proposition is that siderite was a primary carbonate mineral that crystallized directly from Fe2+enriched Archaean seawater, in equilibrium with atmospheric CO2. To our knowledge that proposition has not been demonstrated to be valid. We test with water-gas exchange experiments under controlled CO2partial pressures if siderite can be stabilized as a primary mineral in Fe2+bearing seawater. Reduced seawater proxies enriched in Fe2+and Mn2+are equilibrated with reduced N2-CH4-CO2-H2gas phases with variable CO2. The solid phases stabilized in Fe2+enriched water compositions are amorphous ferrous iron hydroxy carbonates. Crystalline siderite FeCO3is not found to be a stable phase. The phases precipitating from Mn2+enriched water include crystalline rhodochrosite MnCO3and possibly amorphous Mn-enriched phases. Based on these results we advise against using siderite in banded iron formations as a CO2sensor for the Archaean atmosphere.