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Stable Isotope Signatures of Middle Palaeozoic Ahermatypic Rugose Corals - Deciphering Secondary Alteration, Vital Fractionation Effects, and Palaeoecological Implications.

Jakubowicz M, Berkowski B, López Correa M, Jarochowska E, Joachimski M, Belka Z - PLoS ONE (2015)

Bottom Line: The results of the present study add to growing evidence for significant differences between Scleractinia and Rugosa, and agree with recent studies indicating that calcification mechanisms developed independently in these two groups of cnidarians.Consequently, particular caution is needed in using scleractinians as analogues in isotopic studies of extinct coral lineages.Answering some of the pertinent palaeoecological questions, such as that of the possibility of photosymbiosis in Palaeozoic corals, may not be possible based on stable isotope data.

View Article: PubMed Central - PubMed

Affiliation: Institute of Geoecology and Geoinformation, Adam Mickiewicz University, Poznań, Poland.

ABSTRACT
This study investigates stable isotope signatures of five species of Silurian and Devonian deep-water, ahermatypic rugose corals, providing new insights into isotopic fractionation effects exhibited by Palaeozoic rugosans, and possible role of diagenetic processes in modifying their original isotopic signals. To minimize the influence of intraskeletal cements on the observed signatures, the analysed specimens included unusual species either devoid of large intraskeletal open spaces ('button corals': Microcyclus, Palaeocyclus), or typified by particularly thick corallite walls (Calceola). The corals were collected at four localities in the Holy Cross Mountains (Poland), Mader Basin (Morocco) and on Gotland (Sweden), representing distinct diagenetic histories and different styles of diagenetic alteration. To evaluate the resistance of the corallites to diagenesis, we applied various microscopic and trace element preservation tests. Distinct differences between isotopic compositions of the least-altered and most-altered skeleton portions emphasise a critical role of material selection for geochemical studies of Palaeozoic corals. The least-altered parts of the specimens show marine or near-marine stable isotope signals and lack positive correlation between δ13C and δ18O. In terms of isotopic fractionation mechanisms, Palaeozoic rugosans must have differed considerably from modern deep-water scleractinians, typified by significant depletion in both 18O and 13C, and pronounced δ13C-δ18O co-variance. The fractionation effects exhibited by rugosans seem similar rather to the minor isotopic effects typical of modern non-scleractinian corals (octocorals and hydrocorals). The results of the present study add to growing evidence for significant differences between Scleractinia and Rugosa, and agree with recent studies indicating that calcification mechanisms developed independently in these two groups of cnidarians. Consequently, particular caution is needed in using scleractinians as analogues in isotopic studies of extinct coral lineages. Answering some of the pertinent palaeoecological questions, such as that of the possibility of photosymbiosis in Palaeozoic corals, may not be possible based on stable isotope data.

No MeSH data available.


Related in: MedlinePlus

Micro- and ultrastructure of the studied coral specimens.A-F: Microcyclus praecox, upper Eifelian, Holy Cross Mountains (Poland), UAM Tc/B/SK/20. A-B. Transmitted-light photomicrographs showing clearly distribution of septa (with 'dark lines' representing former centres of calcification; arrows) and fibrous interseptal stereome (ST). C. Close-up of a former centre of calcification (COC); note the presence of microspar to small-spar crystal mosaic (MS) cutting across the primary structural elements. D. CL view; note clear difference in the luminescence pattern between lower (dully luminescent, DL) and uppermost (red- to orange-luminescent, RL) parts of the corallite. Location of former centres of calcification is underlined by their bright luminescence (arrows). E-F. SEM photomicrographs of former centres of calcification (COC, arrows). G-L: Microcyclus roberti, lower Givetian, Madène el Mrakib (Morocco), UAM Tc/B/MM/01. G-H. Transmitted-light views showing traces of the original skeletal elements mostly preserved as ghosts within the irregular calcite crystal mosaic. Former centres of calcification (cut diagonally) with recognizable thickening deposits of fibrous stereome (ST) are indicated with arrows. I-J. CL patterns with distinct luminescence responses of a central, relatively well-preserved portion of the corallite (non-luminescent, NL), alteration rims surrounding the original skeleton, as well as diagenetic cement encrusting the corallite surface (both red-luminescent, RL; see a lower right part of G for a transmitted-light view of I). K-L. SEM photomicrographs illustrating a well-defined former centre of calcification (COC, arrows) with still recognizable original fibrous texture of interseptal stereome (ST).
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pone.0136289.g003: Micro- and ultrastructure of the studied coral specimens.A-F: Microcyclus praecox, upper Eifelian, Holy Cross Mountains (Poland), UAM Tc/B/SK/20. A-B. Transmitted-light photomicrographs showing clearly distribution of septa (with 'dark lines' representing former centres of calcification; arrows) and fibrous interseptal stereome (ST). C. Close-up of a former centre of calcification (COC); note the presence of microspar to small-spar crystal mosaic (MS) cutting across the primary structural elements. D. CL view; note clear difference in the luminescence pattern between lower (dully luminescent, DL) and uppermost (red- to orange-luminescent, RL) parts of the corallite. Location of former centres of calcification is underlined by their bright luminescence (arrows). E-F. SEM photomicrographs of former centres of calcification (COC, arrows). G-L: Microcyclus roberti, lower Givetian, Madène el Mrakib (Morocco), UAM Tc/B/MM/01. G-H. Transmitted-light views showing traces of the original skeletal elements mostly preserved as ghosts within the irregular calcite crystal mosaic. Former centres of calcification (cut diagonally) with recognizable thickening deposits of fibrous stereome (ST) are indicated with arrows. I-J. CL patterns with distinct luminescence responses of a central, relatively well-preserved portion of the corallite (non-luminescent, NL), alteration rims surrounding the original skeleton, as well as diagenetic cement encrusting the corallite surface (both red-luminescent, RL; see a lower right part of G for a transmitted-light view of I). K-L. SEM photomicrographs illustrating a well-defined former centre of calcification (COC, arrows) with still recognizable original fibrous texture of interseptal stereome (ST).

Mentions: Among the button coral specimens, M. praecox from the Holy Cross Mountains represents the one with best visible primary microstructural features when observed under transmitted-light. Former centres of calcification ('dark lines') are distinctly defined, and original stereome fibres radiating from the axial planes of septa are still easily recognizable (Fig 3A and 3B). As revealed by cross-polarized light observations, present boundaries of inclusion-rich calcite crystals usually cut across the outlines of the original skeletal features (Fig 3B and 3C), indicating that most of these structures are preserved as ghosts, rather than pristine skeletal elements themselves. SEM investigations show a generally fine (mostly in the microspar to small spar range) calcite crystal mosaic bearing little information on the original skeletal texture, though former centres of calcification are still noticeable (Fig 3E and 3F). Cathodoluminescence analyses reveal pronounced, red to orange luminescence of the upper portions of the corallites consisting of small, irregular calcite crystals, and dull to red luminescence of the lower part of the skeleton. Only the former centres of calcification stand out against the background due to their more distinct, orange luminescence (Fig 3D).


Stable Isotope Signatures of Middle Palaeozoic Ahermatypic Rugose Corals - Deciphering Secondary Alteration, Vital Fractionation Effects, and Palaeoecological Implications.

Jakubowicz M, Berkowski B, López Correa M, Jarochowska E, Joachimski M, Belka Z - PLoS ONE (2015)

Micro- and ultrastructure of the studied coral specimens.A-F: Microcyclus praecox, upper Eifelian, Holy Cross Mountains (Poland), UAM Tc/B/SK/20. A-B. Transmitted-light photomicrographs showing clearly distribution of septa (with 'dark lines' representing former centres of calcification; arrows) and fibrous interseptal stereome (ST). C. Close-up of a former centre of calcification (COC); note the presence of microspar to small-spar crystal mosaic (MS) cutting across the primary structural elements. D. CL view; note clear difference in the luminescence pattern between lower (dully luminescent, DL) and uppermost (red- to orange-luminescent, RL) parts of the corallite. Location of former centres of calcification is underlined by their bright luminescence (arrows). E-F. SEM photomicrographs of former centres of calcification (COC, arrows). G-L: Microcyclus roberti, lower Givetian, Madène el Mrakib (Morocco), UAM Tc/B/MM/01. G-H. Transmitted-light views showing traces of the original skeletal elements mostly preserved as ghosts within the irregular calcite crystal mosaic. Former centres of calcification (cut diagonally) with recognizable thickening deposits of fibrous stereome (ST) are indicated with arrows. I-J. CL patterns with distinct luminescence responses of a central, relatively well-preserved portion of the corallite (non-luminescent, NL), alteration rims surrounding the original skeleton, as well as diagenetic cement encrusting the corallite surface (both red-luminescent, RL; see a lower right part of G for a transmitted-light view of I). K-L. SEM photomicrographs illustrating a well-defined former centre of calcification (COC, arrows) with still recognizable original fibrous texture of interseptal stereome (ST).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4559396&req=5

pone.0136289.g003: Micro- and ultrastructure of the studied coral specimens.A-F: Microcyclus praecox, upper Eifelian, Holy Cross Mountains (Poland), UAM Tc/B/SK/20. A-B. Transmitted-light photomicrographs showing clearly distribution of septa (with 'dark lines' representing former centres of calcification; arrows) and fibrous interseptal stereome (ST). C. Close-up of a former centre of calcification (COC); note the presence of microspar to small-spar crystal mosaic (MS) cutting across the primary structural elements. D. CL view; note clear difference in the luminescence pattern between lower (dully luminescent, DL) and uppermost (red- to orange-luminescent, RL) parts of the corallite. Location of former centres of calcification is underlined by their bright luminescence (arrows). E-F. SEM photomicrographs of former centres of calcification (COC, arrows). G-L: Microcyclus roberti, lower Givetian, Madène el Mrakib (Morocco), UAM Tc/B/MM/01. G-H. Transmitted-light views showing traces of the original skeletal elements mostly preserved as ghosts within the irregular calcite crystal mosaic. Former centres of calcification (cut diagonally) with recognizable thickening deposits of fibrous stereome (ST) are indicated with arrows. I-J. CL patterns with distinct luminescence responses of a central, relatively well-preserved portion of the corallite (non-luminescent, NL), alteration rims surrounding the original skeleton, as well as diagenetic cement encrusting the corallite surface (both red-luminescent, RL; see a lower right part of G for a transmitted-light view of I). K-L. SEM photomicrographs illustrating a well-defined former centre of calcification (COC, arrows) with still recognizable original fibrous texture of interseptal stereome (ST).
Mentions: Among the button coral specimens, M. praecox from the Holy Cross Mountains represents the one with best visible primary microstructural features when observed under transmitted-light. Former centres of calcification ('dark lines') are distinctly defined, and original stereome fibres radiating from the axial planes of septa are still easily recognizable (Fig 3A and 3B). As revealed by cross-polarized light observations, present boundaries of inclusion-rich calcite crystals usually cut across the outlines of the original skeletal features (Fig 3B and 3C), indicating that most of these structures are preserved as ghosts, rather than pristine skeletal elements themselves. SEM investigations show a generally fine (mostly in the microspar to small spar range) calcite crystal mosaic bearing little information on the original skeletal texture, though former centres of calcification are still noticeable (Fig 3E and 3F). Cathodoluminescence analyses reveal pronounced, red to orange luminescence of the upper portions of the corallites consisting of small, irregular calcite crystals, and dull to red luminescence of the lower part of the skeleton. Only the former centres of calcification stand out against the background due to their more distinct, orange luminescence (Fig 3D).

Bottom Line: The results of the present study add to growing evidence for significant differences between Scleractinia and Rugosa, and agree with recent studies indicating that calcification mechanisms developed independently in these two groups of cnidarians.Consequently, particular caution is needed in using scleractinians as analogues in isotopic studies of extinct coral lineages.Answering some of the pertinent palaeoecological questions, such as that of the possibility of photosymbiosis in Palaeozoic corals, may not be possible based on stable isotope data.

View Article: PubMed Central - PubMed

Affiliation: Institute of Geoecology and Geoinformation, Adam Mickiewicz University, Poznań, Poland.

ABSTRACT
This study investigates stable isotope signatures of five species of Silurian and Devonian deep-water, ahermatypic rugose corals, providing new insights into isotopic fractionation effects exhibited by Palaeozoic rugosans, and possible role of diagenetic processes in modifying their original isotopic signals. To minimize the influence of intraskeletal cements on the observed signatures, the analysed specimens included unusual species either devoid of large intraskeletal open spaces ('button corals': Microcyclus, Palaeocyclus), or typified by particularly thick corallite walls (Calceola). The corals were collected at four localities in the Holy Cross Mountains (Poland), Mader Basin (Morocco) and on Gotland (Sweden), representing distinct diagenetic histories and different styles of diagenetic alteration. To evaluate the resistance of the corallites to diagenesis, we applied various microscopic and trace element preservation tests. Distinct differences between isotopic compositions of the least-altered and most-altered skeleton portions emphasise a critical role of material selection for geochemical studies of Palaeozoic corals. The least-altered parts of the specimens show marine or near-marine stable isotope signals and lack positive correlation between δ13C and δ18O. In terms of isotopic fractionation mechanisms, Palaeozoic rugosans must have differed considerably from modern deep-water scleractinians, typified by significant depletion in both 18O and 13C, and pronounced δ13C-δ18O co-variance. The fractionation effects exhibited by rugosans seem similar rather to the minor isotopic effects typical of modern non-scleractinian corals (octocorals and hydrocorals). The results of the present study add to growing evidence for significant differences between Scleractinia and Rugosa, and agree with recent studies indicating that calcification mechanisms developed independently in these two groups of cnidarians. Consequently, particular caution is needed in using scleractinians as analogues in isotopic studies of extinct coral lineages. Answering some of the pertinent palaeoecological questions, such as that of the possibility of photosymbiosis in Palaeozoic corals, may not be possible based on stable isotope data.

No MeSH data available.


Related in: MedlinePlus