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

Laura A. Casella, Sixin He, Erika Griesshaber, Lourdes Fernández-Díaz, Martina Greiner, Elizabeth M. Harper, Daniel J. Jackson, Andreas Ziegler, Vasileios Mavromatis, Martin Dietzel, Anton Eisenhauer, Sabino Veintemillas-Verdaguer, Uwe Brand, Wolfgang W. Schmahl

Publikation: Beitrag in einer FachzeitschriftArtikelForschungBegutachtung

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 interfacecoupled 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 100mMNaClC10mMMgCl2 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 amalgama-tion 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.

Originalspracheenglisch
Seiten (von - bis)7451-7484
Seitenumfang34
FachzeitschriftBiogeosciences
Jahrgang15
Ausgabenummer24
DOIs
PublikationsstatusVeröffentlicht - 21 Dez 2018

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calcite
hydrothermal alteration
carbonates
dissolution
microstructure
aragonite
carbonate
skeleton
replacement
biopolymers
porosity
fossils
magnesite
secondary porosity
grain boundary
analysis
paleoenvironment
fossil record
structural change
fossil

ASJC Scopus subject areas

  • !!Ecology, Evolution, Behavior and Systematics
  • !!Earth-Surface Processes

Dies zitieren

Hydrothermal alteration of aragonitic biocarbonates : Assessment of micro- and nanostructural dissolution-reprecipitation and constraints of diagenetic overprint from quantitative statistical grain-area analysis. / Casella, Laura A.; He, Sixin; Griesshaber, Erika; Fernández-Díaz, Lourdes; Greiner, Martina; Harper, Elizabeth M.; Jackson, Daniel J.; Ziegler, Andreas; Mavromatis, Vasileios; Dietzel, Martin; Eisenhauer, Anton; Veintemillas-Verdaguer, Sabino; Brand, Uwe; Schmahl, Wolfgang W.

in: Biogeosciences, Jahrgang 15, Nr. 24, 21.12.2018, S. 7451-7484.

Publikation: Beitrag in einer FachzeitschriftArtikelForschungBegutachtung

Casella, LA, He, S, Griesshaber, E, Fernández-Díaz, L, Greiner, M, Harper, EM, Jackson, DJ, Ziegler, A, Mavromatis, V, Dietzel, M, Eisenhauer, A, Veintemillas-Verdaguer, S, Brand, U & Schmahl, WW 2018, 'Hydrothermal alteration of aragonitic biocarbonates: Assessment of micro- and nanostructural dissolution-reprecipitation and constraints of diagenetic overprint from quantitative statistical grain-area analysis' Biogeosciences, Jg. 15, Nr. 24, S. 7451-7484. https://doi.org/10.5194/bg-15-7451-2018
Casella, Laura A. ; He, Sixin ; Griesshaber, Erika ; Fernández-Díaz, Lourdes ; Greiner, Martina ; Harper, Elizabeth M. ; Jackson, Daniel J. ; Ziegler, Andreas ; Mavromatis, Vasileios ; Dietzel, Martin ; Eisenhauer, Anton ; Veintemillas-Verdaguer, Sabino ; Brand, Uwe ; Schmahl, Wolfgang W. / Hydrothermal alteration of aragonitic biocarbonates : Assessment of micro- and nanostructural dissolution-reprecipitation and constraints of diagenetic overprint from quantitative statistical grain-area analysis. in: Biogeosciences. 2018 ; Jahrgang 15, Nr. 24. S. 7451-7484.
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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 interfacecoupled 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 100mMNaClC10mMMgCl2 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 amalgama-tion 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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T1 - Hydrothermal alteration of aragonitic biocarbonates

T2 - Assessment of micro- and nanostructural dissolution-reprecipitation and constraints of diagenetic overprint from quantitative statistical grain-area analysis

AU - Casella, Laura A.

AU - He, Sixin

AU - Griesshaber, Erika

AU - Fernández-Díaz, Lourdes

AU - Greiner, Martina

AU - Harper, Elizabeth M.

AU - Jackson, Daniel J.

AU - Ziegler, Andreas

AU - Mavromatis, Vasileios

AU - Dietzel, Martin

AU - Eisenhauer, Anton

AU - Veintemillas-Verdaguer, Sabino

AU - Brand, Uwe

AU - Schmahl, Wolfgang W.

PY - 2018/12/21

Y1 - 2018/12/21

N2 - 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 interfacecoupled 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 100mMNaClC10mMMgCl2 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 amalgama-tion 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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