Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 1 2 2004 10.5194/bg-1-113-2004 http://www.biogeosciences.net/1/113/2004/ http://www.biogeosciences.net/1/113/2004/bg-1-113-2004.html http://www.biogeosciences.net/1/113/2004/bg-1-113-2004.pdf 113 121 2004-11-25 Animal-sediment interactions: the effect of ingestion and excretion by worms on mineralogy S. J. Needham R. H. Worden D. McIlroy Dept. of Earth and Ocean Sciences, University of Liverpool, 4 Brownlow St, Liverpool L69 3GP, UK Department of Earth Sciences, Memorial University, St. John’s, Newfoundland, A1B 3X5, Cana By controlled experiments that simulate marine depositional environments, it is shown that accelerated weathering and clay mineral authigenesis occur during the combined process of ingestion, digestion and excretion of fine-grained sediment by two species of annelid worms. Previously characterized synthetic mud was created using finely ground, low-grade metamorphic slate (temperature approximately 300&deg;C) containing highly crystalline chlorite and muscovite. This was added to experiment and control tanks along with clean, wind-blown sand. Faecal casts were collected at regular intervals from the experimental tanks and, less frequently, from the control tanks. Over a period of many months the synthetic mud (slate) proved to be unchanged in the control tanks, but was significantly different in faecal casts from the experimental tanks that contained the worms <I>Arenicola marina</I> and <I>Lumbricus terrestris</I>. Chlorite was preferentially destroyed during digestion in the gut of <I>A. marina</I>. Both chlorite and muscovite underwent XRD peak broadening with a skew developing towards higher lattice spacing, characteristic of smectite formation. A neoformed Fe-Mg-rich clay mineral (possibly berthierine) and as-yet undefined clay minerals with very high <i>d</i>-spacing were detected in both <I>A. marina</I> and <I>L. terrestris</I> cast samples. We postulate that a combination of the low pH and bacteria-rich microenvironment in the guts of annelid worms may radically accelerate mineral dissolution and clay mineral precipitation processes during digestion. These results show that macrobiotic activity significantly accelerates weathering and mineral degradation as well as mineral authigenesis. The combined processes of sediment ingestion and digestion thus lead to early diagenetic growth of clay minerals in clastic sediments.