Nacre nanostructure as a T proxy

Pupa GILBERT, University of Wisconsin - Madison, E.U. | 2 Juillet 2015

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Nacre, the iridescent inner lining of many mollusk shells, is widely studied due to its formidable fracture toughness. Nacre is iridescent because its structure alternates thin organic sheets and 0.5µm-thick aragonite crystalline tablet layers. Mechanisms of nacre biomineralization have been documented : organic sheets form first [Bevelander et al., 1969] and these underpin aragonite polymorph selection [Belcher et al., 1996 ; Falini et al., 1996 ; Meltzer et al., 2010] ; each nacre tablet starts growing from a single Nudelman site [Nudelman et al., 2006] ; tablets form a Voronoi construction [Rousseau et al., 2005], with near-epitaxial crystal growth [Schäffer et al., 1997 ; Olson et al., 2012 ; 2013] through Checa bridges [Checa et al., 2011, Olson et al. 2012] ; and c-axes gradually order away from the nacre-prismatic boundary [Gilbert et al, 2008 ; Olson et al., 2012]. What factors, biological or physical, determine nacre layer thickness (LT), however, remains unknown. Here we provide evidence that LT may depend on environmental temperature (T). We observe strong correlation of T and LT, measured with clumped isotopes [Eiler, 2007] and Polarization-dependent Imaging Contrast (PIC)-mapping [Gilbert et al., 2011], respectively, in Pinna shells from the Cretaceous, Eocene, Miocene, and modern.

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