Iron-rich chlorite coatings are efficient in preserving porosity from the development of quartz cements in deeply buried sandstones. It has been proposed that such Fe-chlorite could recrystallize from a 7(A) Fe-rich precursor clay during burial diagenesis of fluvio-deltaic sediments. An experiment was established to study the effect of sediment ingestion by macro-organism on the genesis of Fe-chlorite precursor minerals. Finely crushed granite enriched with 5% haematite was used as a synthetic sediment and Arenicola marina (lugworm)as a sediment processor. The ＜2 μm fractions of the worm casts were separated, analyzed by XRD and FTIR,and compared to the fine fraction of the initial material. The mineralogy of ingested sediments was modified with the dissolution of feldspars and haematite and the growth of kaolinite, quartz and probably a 7(A) Fe-rich clay mineral. Macro-organism can thus induce the formation of clay minerals ("bioclays") through sediment ingestion and digestion processes. Such bioclays could significantly participate in early and burial diagenetic reactions and lead to porosity-preserving Fe-chlorite in sandstones.
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