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Biogenic magnetite in stromatolites. II. Occurrence in ancient sedimentary environments

1989; Elsevier BV; Volume: 43; Issue: 4 Linguagem: Inglês

10.1016/0301-9268(89)90062-4

1872-7433

Shin-Bin R. Chang, John F. Stolz, Joseph L. Kirschvink, Stanley M. Awramik,

Geology and Paleoclimatology Research

In this paper we report the discovery of fossil bacterial, single-domain magnetite particles in ancient stromatolites. The biogenicity of the crystals was determined by the following criteria: (1) distinctive morphology and habit, (2) composition and (3) environment of deposition. Stromatolites ranging in age from the Middle Archean to Pleistocene, composed of both carbonate and chert, were analyzed for the presence of single-domain magnetite using rock magnetic methods. The granulometry and composition of the ultra-fine-grained magnetite crystals extracted were determined by transmission electron microscopy and electron diffraction. The oldest magnetofossils were extracted from stromatolitic chert of the Gunflint Iron Formation which is approximately 2000 Ma old. The implications of these findings and the potential uses of fossil bacterial magnetite in studies of the evolution of biomineralization and prokaryotic metabolic processes, paleomagnetism, and as an indicator of ancient oxygen levels are discussed. Bacterial magnetite represents the oldest evidence of biomineralization yet discovered in the fossil record.