The role of skeletal micro-architecture in diagenesis and dating of Acropora palmata

Tomiak, Peter J; Andersen, Morten B.; Hendy, Erica; Potter, E-K; Johnson, Kenneth G.; Penkman, Kirsty

doi:10.1016/j.gca.2016.03.030

Cited by 22 publications

(23 citation statements)

References 88 publications

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“…Furthermore, the author reported that grain size and surface area play an important role in the process of overprinting. Diagenetically overprinted aragonitic corals were investigated by Sorauf (1980), andTomiak et al (2016). The authors observed that during early diagenesis, subsequent to decomposition of organic matrices, aragonitic units formed through fusion of pristine skeletal elements.…”

Section: Implications For Preservation In the Fossil Recordmentioning

confidence: 99%

Hydrothermal alteration of aragonitic biocarbonates: assessment of micro- and nanostructural dissolution–reprecipitation and constraints of diagenetic overprint from quantitative statistical grain-area analysis

Casella

Griesshaber

et al. 2018

Biogeosciences

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Abstract. The assessment of diagenetic overprint on microstructural and geochemical data gained from fossil archives is of fundamental importance for understanding palaeoenvironments. The correct reconstruction of past environmental dynamics is only possible when pristine skeletons are unequivocally distinguished from altered skeletal elements. Our previous studies show (i) that replacement of biogenic carbonate by inorganic calcite occurs via an interface-coupled dissolution–reprecipitation mechanism. (ii) A comprehensive understanding of alteration of the biogenic skeleton is only given when structural changes are assessed on both, the micrometre as well as on the nanometre scale.In the present contribution we investigate experimental hydrothermal alteration of six different modern biogenic carbonate materials to (i) assess their potential for withstanding diagenetic overprint and to (ii) find characteristics for the preservation of their microstructure in the fossil record. Experiments were performed at 175 °C with a 100 mM NaCl + 10 mM MgCl2 alteration solution and lasted for up to 35 days. For each type of microstructure we (i) examine the evolution of biogenic carbonate replacement by inorganic calcite, (ii) highlight different stages of inorganic carbonate formation, (iii) explore microstructural changes at different degrees of alteration, and (iv) perform a statistical evaluation of microstructural data to highlight changes in crystallite size between the pristine and the altered skeletons.We find that alteration from biogenic aragonite to inorganic calcite proceeds along pathways where the fluid enters the material. It is fastest in hard tissues with an existing primary porosity and a biopolymer fabric within the skeleton that consists of a network of fibrils. The slowest alteration kinetics occurs when biogenic nacreous aragonite is replaced by inorganic calcite, irrespective of the mode of assembly of nacre tablets. For all investigated biogenic carbonates we distinguish the following intermediate stages of alteration: (i) decomposition of biopolymers and the associated formation of secondary porosity, (ii) homoepitactic overgrowth with preservation of the original phase leading to amalgamation of neighbouring mineral units (i.e. recrystallization by grain growth eliminating grain boundaries), (iii) deletion of the original microstructure, however, at first, under retention of the original mineralogical phase, and (iv) replacement of both, the pristine microstructure and original phase with the newly formed abiogenic product.At the alteration front we find between newly formed calcite and reworked biogenic aragonite the formation of metastable Mg-rich carbonates with a calcite-type structure and compositions ranging from dolomitic to about 80 mol % magnesite. This high-Mg calcite seam shifts with the alteration front when the latter is displaced within the unaltered biogenic aragonite. For all investigated biocarbonate hard tissues we observe the destruction of the microstructure first, and, in a second step, the replacement of the original with the newly formed phase.

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Section: Implications For Preservation In the Fossil Recordmentioning

confidence: 99%

Hydrothermal alteration of aragonitic biocarbonates: assessment of micro- and nanostructural dissolution–reprecipitation and constraints of diagenetic overprint from quantitative statistical grain-area analysis

Casella

Griesshaber

et al. 2018

Biogeosciences

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“…Subsequent submarine diagenesis leads to recrystallisation of fibrous aragonite to intermediate, micritic high-Mg calcite. Tomiak et al (2016) and Regenberg et al (2007) observed formation of new mineral overgrowth during early diagenesis of coral aragonite and planktonic foraminifera calcite. The latter retained, at first, and corresponded to the carbonate phase of the original pristine skeleton.…”

Section: Implications For Preservation Of Carbonate Skeletons In the mentioning

confidence: 98%

“…Furthermore, the author reported that grain size and surface area play an important role for the process of overprint. Diagenetically overprinted aragonitic corals were investigated by Sorauf (1980) and Tomiak et al (2016). The authors observed that during early diagenesis, subsequent to decomposition of organic matrices, aragonitic units formed through fusion of pristine skeletal elements.…”

Section: Implications For Preservation Of Carbonate Skeletons In the mentioning

confidence: 99%

Assessment of hydrothermal alteration on micro- and nanostructures of biocarbonates: quantitative statistical grain-area analysis of diagenetic overprint

Casella

Griesshaber

et al. 2018

Preprint

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Abstract. The assessment of diagenetic overprint on microstructural and geochemical data gained from fossil archives is of fundamental importance for understanding palaeoenvironments. A correct reconstruction of past environmental dynamics is only possible when pristine skeletons are unequivocally distinguished from altered skeletal elements. Our previous studies (Casella et al., 2017) have shown that replacement of biogenic carbonate by inorganic calcite occurs via an interface coupled dissolution&#8211;reprecipitation mechanism. Furthermore, for a comprehensive assessment of alteration, structural changes have to be assessed on the nanoscale as well, which documents the replacement of pristine nanoparticulate calcite by diagenetic nanorhombohedral calcite (Casella et al., 2018a, b). In the present contribution we investigated six different modern biogenic carbonate microstructures for their behaviour under hydrothermal alteration in order to assess their potential to withstand diagenetic overprint and to test the integrity of their preservation in the fossil record. For each microstructure (a) the evolution of biogenic aragonite and calcite replacement by inorganic calcite was examined, (b) distinct carbonate mineral formation steps on the micrometre scale were highlighted, (c) microstructural changes at different stages of alteration were explored, and (d) statistical analysis of differences in basic mineral unit dimensions in pristine and altered skeletons was performed. The latter analysis enables an unequivocal determination of the degree of diagenetic overprint and discloses information especially about low degrees of hydrothermal alteration.

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“…These upward-thickened knobs are tall and seem to have larger corallites ( Figure 1I). Some of the corallites on the branches in scattered colonies seem visually longer and irregular (Tomiak et al, 2016; Figure 1J). However, there are currently no specific data on the morphological aspects of these knobs, and accurate measurements of corallites/calices have not been conducted.…”

Section: Coral Morphology and Knobsmentioning

confidence: 99%

“…Histological assays may reveal complex interactions of epidermal and gastrodermal tissues layers where microbioeroders and debris such as algae and sand could be present. To view morphological changes at the smallest of scales, techniques using scanning electron microscopy (SEM) can evaluate skeleton conditions including calcification, density, porosity and features such as corallite and calice morphology (Tomiak et al, 2016). Moreover, molecular and microscopic techniques as well as gross dissections can be employed to assess genotypes, endosymbiont density (zooxanthellae), and gonad development in these knobs which may reveal impacts on coral fitness (bleaching and reproduction) (Baums et al, 2014;Miller et al, 2016).…”

Section: Future Research To Resolve Current Questionsmentioning

confidence: 99%

Unusual “Knob-Like Chimney” Growth Forms on Acropora Species in the Caribbean

Rivera-Sosa

Muñiz-Castillo²,

McField

et al. 2018

Front. Mar. Sci.

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The role of skeletal micro-architecture in diagenesis and dating of Acropora palmata

Cited by 22 publications

References 88 publications

Hydrothermal alteration of aragonitic biocarbonates: assessment of micro- and nanostructural dissolution–reprecipitation and constraints of diagenetic overprint from quantitative statistical grain-area analysis

Hydrothermal alteration of aragonitic biocarbonates: assessment of micro- and nanostructural dissolution–reprecipitation and constraints of diagenetic overprint from quantitative statistical grain-area analysis

Assessment of hydrothermal alteration on micro- and nanostructures of biocarbonates: quantitative statistical grain-area analysis of diagenetic overprint

Unusual “Knob-Like Chimney” Growth Forms on Acropora Species in the Caribbean

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