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[References: p. 125 (10 tit.)]

In this work, the results of interpreting the variation of the magnetic signal of iron-rich marine sedimentary rocks were presented by the example of the Cretaceous-Paleogene section of the Bakchar iron ore deposit (Western Siberia). The anomalous values of the magnetic susceptibility are determined by two factors: first, a superimposed diagenetic process accompanied by the formation of pyrrhotite, greigite, and siderite among ooidal ironstones; and second, an increase in the continental runoff, causing the accumulation of terrigenous magnetite and ilmenite in the siltstone as the climate becomes increasingly humid and the weathering intensifies. It was shown that the elevated values of the magnetic susceptibility in iron-rich deposits can be due to the formation of ferrimagnetic iron sulfides, which is indicative of methane mobilization through ancient bottom sediments.