title: Early post-mortem formation of carbonate concretions around tusk-shells over week-month timescales.
abstract: Carbonate concretions occur in sedimentary rocks of widely varying geological ages throughout the world. Many of these concretions are isolated spheres, centered on fossils. The formation of such concretions has been variously explained by diffusion of inorganic carbon and organic matter in buried marine sediments. However, details of the syn-depositional chemical processes by which the isolated spherical shape developed and the associated carbon sources are little known. Here we present evidence that spherical carbonate concretions (diameters φ : 14 ~ 37 mm) around tusk-shells (Fissidentalium spp.) were formed within weeks or months following death of the organism by the seepage of fatty acid from decaying soft body tissues. Characteristic concentrations of carbonate around the mouth of a tusk-shell reveal very rapid formation during the decay of organic matter from the tusk-shell. Available observations and geochemical evidence have enabled us to construct a 'Diffusion-growth rate cross-plot' that can be used to estimate the growth rate of all kinds of isolated spherical carbonate concretions identified in marine formations. Results shown here suggest that isolated spherical concretions that are not associated with fossils might also be formed from carbon sourced in the decaying soft body tissues of non-skeletal organisms with otherwise low preservation potential.
authors.affiliation: Material Research Section, Nagoya University, University Museum, Chikusa, Nagoya, Japan.
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Yoshida
authors.affiliation: Graduate School of Environmental Studies, Nagoya University, Chikusa, Nagoya, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Ujihara
authors.affiliation: Center for Chronological Research, Nagoya University, Chikusa, Nagoya, Japan.
authors.forename: Masayo
authors.initials: M
authors.lastname: Minami
authors.affiliation: Graduate School of Environmental Studies, Nagoya University, Chikusa, Nagoya, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Asahara
authors.affiliation: Department of Education, Gifu University, Gifu, Japan.
authors.forename: Nagayoshi
authors.initials: N
authors.lastname: Katsuta
authors.affiliation: Graduate School of Environmental Studies, Nagoya University, Chikusa, Nagoya, Japan.
authors.forename: Koshi
authors.initials: K
authors.lastname: Yamamoto
authors.affiliation: Graduate School of Environmental Studies, Nagoya University, Chikusa, Nagoya, Japan.
authors.forename: Sin-iti
authors.initials: SI
authors.lastname: Sirono
authors.affiliation: Graduate School of Environmental Studies, Nagoya University, Chikusa, Nagoya, Japan.
authors.forename: Ippei
authors.initials: I
authors.lastname: Maruyama
authors.affiliation: Nagoya City Science Museum, Sakae, Nagoya, Japan.
authors.forename: Shoji
authors.initials: S
authors.lastname: Nishimoto
authors.affiliation: Quintessa UK, The Hub, Henley-on-Thames, Oxfordshire, UK.
authors.forename: Richard
authors.initials: R
authors.lastname: Metcalfe