Where Has All the Aragonite Gone? Mineralogy of Holocene Neritic Cool-Water Carbonates, Southern Australia

“…The high proportion of calcitic bryozoans with relatively low Mg contents at polar latitudes may aVect diagenesis relative to lower latitudes where bryozoans have higher Mg contents and increasingly more aragonite is present (e.g., James et al 2005). Dissolution of aragonite and its reprecipitation as calcite has been recognized as one of the main driving forces in meteoric diagenesis (James and Choquette 1983).…”

Section: Discussionmentioning

confidence: 99%

Mineralogy of Arctic bryozoan skeletons in a global context

Kukliński

Taylor

2009

Facies

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Bryozoans are major carbonate producers in some ancient and Recent benthic environments, including parts of the Arctic Ocean. Seventy-six species of bryozoans from within the Arctic Circle have been studied using XRD to determine their carbonate mineralogies and the Mg content of the calcite. The majority of species were found to be calcitic, only four having bimineralic skeletons that combined calcite and aragonite, and none being entirely aragonitic. In almost all species, the calcite was of the low-(<4 mol% MgCO 3 ) or intermediate-Mg (4-11.99 mol% MgCO 3 ) varieties. Previous regional studies of bryozoan biomineralogy have found higher proportions of bimineralic and/or aragonitic species in New Zealand and the Mediterranean, with a greater number of calcitic species employing intermediate-and high-Mg calcite. The Antarctic bryozoan fauna, however, has a similar mineralogical composition to the Arctic. The lesser solubility of low-Mg calcite compared to both Mg calcite and aragonite in cold polar waters is most likely responsible for this latitudinal pattern. However, it is unknown to what extent environmental factors drive the pattern directly through eliciting an ecophenotypic response from the bryozoans concerned or the pattern reXects genetic adaptations by particular bryozoan clades.

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“…The diffractograms were analysed by Rietveld analysis with the software package FULLPROF (Rodriguez-Caravajal, 2001) using the aragonite structure data of Jarosch and Heger (1986) and calcite structure data of Markgraf and Reeder (1985). (Fig.…”

Section: X-ray Diffraction Analysismentioning

confidence: 99%

“…In fact, aragonitic shells/skeletons are produced by hyolithids, cnidarians, algae, and the widespread and diversified molluscs. Several studies (Cherns and Wright, 2000;Wright et al, 2003;Wright and Cherns, 2004;James et al, 2005) have underscored that Phanerozoic marine faunas seem to be dominated by calcite-shelled taxa, the labile aragonitic or bimineralic groups being lost during early diagenesis (in the soft sediment, before lithification), potentially causing a serious taphonomic loss. Considering that most molluscs are aragonitic or bimineralic, this loss could be particularly detrimental both for palaeoecological and biostratigraphic studies.…”

Section: A Palaeontological Perspective Of Our Laboratory-based Hydromentioning

confidence: 99%

“…However, it has been shown that the mollusc fossil record is not so biased as expected (Harper, 1998;Cherns et al, 2008). This is due to abundant taphonomic scenarios such as early lithification/hardgrounds, storm plasters, anoxic bottoms, and high sedimentation rates that produce taphonomic windows allowing mollusc preservation (James et al 2005;Cherns et al, 2008) by controlling organic matter content and residence time in the taphonomically active zone. Even if the factors that control aragonite dissolution are multiple and their interpretation is complex, the laboratory-based hydrothermal alteration experiments performed here offer very interesting insights into the fate of the aragonitic or bimineralic hard tissues that escape early dissolution during shallow burial and have the potential to enter the fossil record.…”

Section: A Palaeontological Perspective Of Our Laboratory-based Hydromentioning

confidence: 99%

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Experimental diagenesis: insights into aragonite to calcite transformation of <i>Arctica islandica</i> shells by hydrothermal treatment

Casella¹,

Griesshaber²,

Yin³

et al. 2017

Biogeosciences

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Abstract. Biomineralised hard parts form the most important physical fossil record of past environmental conditions. However, living organisms are not in thermodynamic equilibrium with their environment and create local chemical compartments within their bodies where physiologic processes such as biomineralisation take place. In generating their mineralised hard parts, most marine invertebrates produce metastable aragonite rather than the stable polymorph of CaCO 3 , calcite. After death of the organism the physiological conditions, which were present during biomineralisation, are not sustained any further and the system moves toward inorganic equilibrium with the surrounding inorganic geological system. Thus, during diagenesis the original biogenic structure of aragonitic tissue disappears and is replaced by inorganic structural features.In order to understand the diagenetic replacement of biogenic aragonite to non-biogenic calcite, we subjected Arctica islandica mollusc shells to hydrothermal alteration experiments. Experimental conditions were between 100 and 175 • C, with the main focus on 100 and 175 • C, reaction durations between 1 and 84 days, and alteration fluids simulating meteoric and burial waters, respectively. Detailed microstructural and geochemical data were collected for samples altered at 100 • C (and at 0.1 MPa pressure) for 28 days and for samples altered at 175 • C (and at 0.9 MPa pressure) for 7 and 84 days. During hydrothermal alteration at 100 • C for 28 days most but not the entire biopolymer matrix was destroyed, while shell aragonite and its characteristic microstructure was largely preserved. In all experiments up to 174 • C, there are no signs of a replacement reaction of shell aragonite to calcite in X-ray diffraction bulk analysis. At 175 • C the replacement reaction started after a dormant time of 4 days, and the original shell microstructure was almost completely overprinted by the aragonite to calcite replacement reaction after 10 days. Newly formed calcite nucleated at locations which were in contact with the fluid, at the shell surface, in the open pore system, and along growth lines. In the experiments with fluids simulating meteoric water, calcite crystals reached sizes up to 200 µm, while in the experiments with Mg-containing fluids the calcite crystals reached sizes up to 1 mm after 7 days of alteration. Aragonite is metastable at all applied conditions. Only a small bulk thermodynamicPublished by Copernicus Publications on behalf of the European Geosciences Union. 1462 L. A. Casella et al.: Experimental diagenesis: insights into aragonite to calcite transformation driving force exists for the transition to calcite. We attribute the sluggish replacement reaction to the inhibition of calcite nucleation in the temperature window from ca. 50 to ca. 170 • C or, additionally, to the presence of magnesium. Correspondingly, in Mg 2+ -bearing solutions the newly formed calcite crystals are larger than in Mg 2+ -free solutions. Overall, the aragonite-calcite transition occurs via ...

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Where Has All the Aragonite Gone? Mineralogy of Holocene Neritic Cool-Water Carbonates, Southern Australia

Cited by 120 publications

References 57 publications

Danian cool-water coral reefs in southern Scandinavia localised over seafloor highs

Danian cool-water coral reefs in southern Scandinavia localised over seafloor highs

Mineralogy of Arctic bryozoan skeletons in a global context

Experimental diagenesis: insights into aragonite to calcite transformation of <i>Arctica islandica</i> shells by hydrothermal treatment

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Where Has All the Aragonite Gone? Mineralogy of Holocene Neritic Cool-Water Carbonates, Southern Australia

Cited by 120 publications

References 57 publications

Danian cool-water coral reefs in southern Scandinavia localised over seafloor highs

Danian cool-water coral reefs in southern Scandinavia localised over seafloor highs

Mineralogy of Arctic bryozoan skeletons in a global context

Experimental diagenesis: insights into aragonite to calcite transformation of &lt;i&gt;Arctica islandica&lt;/i&gt; shells by hydrothermal treatment

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Experimental diagenesis: insights into aragonite to calcite transformation of <i>Arctica islandica</i> shells by hydrothermal treatment