The worm gut; a natural clay mineral factory and a possible cause of diagenetic grain coats in sandstones

Abstract

Using a series of experiments, we show that the formation of clay minerals can occur biologically via the processes of sediment ingestion and excretion by worms. Specimens of lugworm, Arenicola marina, were fed a mixture of coarse grained quartz sand and unweathered, finely crushed Icelandic basalt in experimental tanks that simulated an intertidal, shallow-marine, sedimentary environment. Faecal casts as well as the starting material and samples from a control tank, collected and separated into < 2 μm fractions, were analysed using X-ray diffraction and Fourier Transform Infrared spectroscopy. The faecal samples were found to have lost plagioclase feldspar due to dissolution and to contain new clay minerals (kaolinite, illite and a 14 Å clay) not present in the original or control samples. The experiments show that macrobiotic ingestion processes induce rapid clay growth. These clays coat sand grains and may be the precursors to porosity-preserving chlorite coats found in sandstones.