Diagenetic changes in <i>Concholepas concholepas</i> shells (Gastropoda, Muricidae) in the hyper-arid conditions of Northern Chile – implications for palaeoenvironmental reconstructions

Abstract

Abstract. Variations in the chemical composition of fossil biogenic carbonates, and in particular of mollusc shells, have been used in a range of palaeoenvironmental reconstructions. It is of primary importance, therefore, to detect and understand the diagenetic processes that may modify the original chemical signature. This microstructural and biogeochemical study focuses on modern and fossil (Holocene and Pleistocene) shells of a littoral gastropod of Northern Chile, and on the characterization of mineral component transformations at the nanometric scale and concomitant intracrystalline organic compound modifications. The inner aragonite layer of the shell exhibits more complex deteriorations than the calcite layer. This preliminary study confirms that physical and chemical alterations of various components of mollusc shell biocrystals are complex and might manifest in different ways even within a single individual. The single criterion of determining the mineralogical composition to verify the conservation state of shell samples is insufficient.

A new form of needle-fiber calcite produced by physical weathering of shells

“…In hyper-arid conditions, diagenesis of a mollusk species with the same double mineralogy as Mytilus edulis also includes depletion of the organic matrix and exposure of the calcite needles (Guzman et al, 2009), but in this case, alteration seems to be more chemically than physically induced. In our study, the observed effects of freeze-thaw in the shell could be equated to the release of unaltered constituents into the soil, commonly seen in rocks affected by cryoturbation (see Claridge and Campbell, 2004;Van Vliet-Lanoë, 2004, 2010.…”

Microstructural details in shells of the gastropod generaCarychiellaandCarychiumof the Middle Miocene

“…; Guzmán et al . ), more carychiid shells would need to be investigated for palaeoecological reconstructions based on these structures for the Lake Rein. As the organic matrix of the periostracum provides a key source of ontogenetic and ecological information setting Carychiella eumicrum of Lake Rein apart, future research using X‐ray diffraction of shell tissue and TEM investigations of the periostracal layer would greatly augment these studies.…”

“…Although knowledge of the structure and composition of the organic components constituting the biominerals within the crystalline composites has grown considerably, that of their fossilization process is still sparse (Guzmán et al . ). Moreover, the specificity of structural organization reflects structure–function relationships, which have recently become increasingly useful in designing models for material sciences (Ehrlich et al .…”

High resolution electron backscatter diffraction (EBSD) data from calcite biominerals in recent gastropod shells

“…Here, we analyze the potential use of information provided by high resolution EBSD from biogenic calcite in two mollusk taxa, Concholepas and Haliotis, previously used in studies of complex biomineralization and paleoenvironmental studies (e.g. Dauphin et al, 2007;Guzman et al, 2007;Dauphin, 2008;Guzmán et al, 2009;Auzoux-Bordenave et al, 2010). Data from diffraction intensity and crystallographic orientation maps, and the corresponding pole figures, are discussed as well as the comparison with structural data.…”