Open AccessEffects of diagenesis on magnetic mineralogy in a Jurassic claystone‐limestone succession from the Paris Basin
Author(s) -
Moreau Marie Gabrielle,
Ader Magali
Publication year - 2000
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/1999jb900319
Subject(s) - magnetite , diagenesis , geology , remanence , dissolution , mineralogy , carbonate , natural remanent magnetization , magnetostratigraphy , grain size , magnetization , geochemistry , structural basin , geomorphology , materials science , paleontology , chemistry , magnetic field , metallurgy , physics , quantum mechanics
We performed detailed rock magnetic and geochemical analyses on a previously published Early Jurassic magnetostratigraphic section. The results improve our understanding of acquisition and preservation processes of magnetization in a series of alternating claystones and limestones. The main carrier of magnetization is magnetite. Anhysteretic remanent magnetization (ARM) varies by a factor of 40 and the ARM variations are linked to magnetite grain size. Comparison of magnetic, and geochemical data shows that when carbonate content is high (>30%) and δ 13 C ≈ 0‰, magnetite is characterized by small grain sizes, whereas when carbonate content is low (<20%), magnetite is coarse‐grained. It appears that the oxidation of organic matter by sulfate reduction controls both δ 13 C and magnetite grain size. H 2 S produced during sulfate reduction causes partial dissolution of magnetite grains, with the finest magnetite grains (those that best record the magnetic signal) being dissolved first. Despite this partial dissolution, both the direction and polarity of the original remanent magnetization are preserved.