Walker J C
Department of Atmospheric and Oceanic Science, The University of Michigan, Ann Arbor 48109, USA.
Nature. 1984 May 24;309:340-2. doi: 10.1038/309340a0.
Anomalous isotopic composition has been reported for the carbon in carbonate minerals of banded iron formations. Well studied examples show and enrichment in the light isotope of carbon, 12C. This enrichment presumably reflects unusual circumstances in the deposition of these sedimentary rocks. It is suggested here that the isotopically-light carbonate results from early diagenetic oxidation by bacteria of substantial amounts of isotopically light organic carbon. The electron acceptor that permits oxidation in the absence of free oxygen is presumed to the iron(III) which may have been significantly more abundant in the initial chemical precipitate than in the post-diagenetic sedimentary rock.
条带状铁建造碳酸盐矿物中的碳已被报道存在异常的同位素组成。经过充分研究的实例显示，碳的轻同位素12C存在富集现象。这种富集大概反映了这些沉积岩沉积过程中的异常情况。本文认为，同位素较轻的碳酸盐是由细菌对大量同位素较轻的有机碳进行早期成岩氧化作用形成的。在没有游离氧的情况下允许氧化的电子受体被认为是铁（III），它在初始化学沉淀物中的含量可能比成岩后的沉积岩中要多得多。
