• journal_title：Geology
• Contributor：Joonas J. Virtasalo ; Martin J. Whitehouse ; Aarno T. Kotilainen
• Publisher：Geological Society of America
• Date：2013-01-01
• Format：text/html
• Language：en
• Identifier：10.1130/G33556.1
• journal_abbrev：Geology
• issn：0091-7613
• volume：41
• issue：1
• firstpage：39
• section：Articles

We present ⁵⁴Fe and ⁵⁶Fe data on pyrite from burrow-like and irregularly shaped pyrite concretions from Holocene postglacial lacustrine clays in the northern Baltic Sea collected using a secondary ion mass spectrometry (SIMS) microanalysis technique. The burrow-like concretions were formed in reducing, mucus-coated worm burrows in oxic surface sediments. Framboidal pyrite in the cores of the burrow-like concretions shows extensively fractionated δ⁵⁶Fe values down to −3.1‰. The framboids are cemented by poorly crystalline FeS₂ with δ⁵⁶Fe values between −2.1‰ and +1.4‰. The irregularly shaped concretions with microcrystalline textures were formed in organic-poor sediment pore spaces, and display a wide spread of δ⁵⁶Fe values up to +4.1‰. The measured δ⁵⁶Fe values reflect the preferential capture of ⁵⁴Fe to pyrite in the diagenetic sequence and the ⁵⁶Fe enrichment of remaining pore water. The diagenetic sequence of the pyrite materials is supported by previous petrographical study and ³⁴S/³²S microanalysis of the same samples. Our results demonstrate substantial early-diagenetic δ⁵⁶Fe and δ³⁴S heterogeneity within individual pyrite grains, underlining the necessity of high spatial resolution measurements in studying biological and abiological isotopic signatures.