Middle to Late Jurassic stable isotopes and element ratios of fossils from western India: Developing a reference temperature curve for northeastern Gondwana

Alberti, Matthias; Fürsich, Franz T.; Pandey, Dhirendra K.; Mukherjee, Debahuti; Andersen, Nils; Garbe‐Schönberg, Dieter

doi:10.1016/j.gloplacha.2022.103795

Global and Planetary Change

2022

DOI: 10.1016/j.gloplacha.2022.103795

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Middle to Late Jurassic stable isotopes and element ratios of fossils from western India: Developing a reference temperature curve for northeastern Gondwana

Matthias Alberti

Franz T. Fürsich

Dhirendra K. Pandey

et al.

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Cited by 5 publications

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Laevaptychi as reliable paleotemperature archives: high-resolution stable isotope compositions of Kimmeridgian (Jurassic) lamellar structured aspidoceratid lower mandibles from Zengővárkony (Mecsek Mountains, Hungary)

Bujtor,

Demény,

Németh

et al. 2024

Int J Earth Sci (Geol Rundsch)

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Fieldwork provided well-preserved Laevaptychus sp. ex gr. hoplisus–obliquus specimens from the lower Kimmeridgian of Zengővárkony (Mecsek Mountains, south Hungary). This study presents the stable isotope analysis of these aptychi and control samples from brachiopods (Nucleata and Pygope) derived from the Zengővárkony section bed 3. Rarely observed structures in the upper lamellar layers of the studied laevaptychi revealed 24–32 concentric lamellae that represent primary textural features and indicate excellent preservation. After careful screening for diagenetic effects, stable oxygen isotope compositions yielded seawater temperatures between 20 and 26 °C in good agreement with earlier studies on Jurassic formations, with improved precision. Our research presents for the first time that well-preserved laevaptychi may be a reliable data source for paleoclimate and paleotemperature reconstructions. Graphical abstract

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Laevaptychi as reliable paleotemperature archives: high-resolution stable isotope compositions of Kimmeridgian (Jurassic) lamellar structured aspidoceratid lower mandibles from Zengővárkony (Mecsek Mountains, Hungary)

Bujtor,

Demény,

Németh

et al. 2024

Int J Earth Sci (Geol Rundsch)

View full text Add to dashboard Cite

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Biochemically induced diagenesis of Jurassic micrite: evidence from phase analysis, carbon, oxygen, and strontium isotopes (Franconian Alb, Germany)

Blendinger

2024

Int J Earth Sci (Geol Rundsch)

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The marine Upper Jurassic rocks of the Franconian Alb consist largely of micritic carbonate of partly dolomitized reef mounds and bedded basinal limestone. All carbonates were lithified in the shallow (centimeters, meters) subsurface and have a wide range of ∂13C (≤ + 3‰ to − 10‰VPDB) but always negative ∂18O (− 1 to − 6‰VPDB). Dolomite and reef limestone show the highest ∂18O and ∂13C values. The most negative ∂13C (≥ − 10‰) occurs mainly as cement in dolomite of a basinal, partly dolomitic, biostrome interval. Basinal limestone shows intermediate ∂13C values. Because freshwater diagenesis and elevated temperatures cannot explain the observed isotope values, pH is here considered a major factor influencing the isotope signal of micritic limestone. The bulk sediment isotope signal was reset to lower values, from an original lime mud with ∂13C ≥ 3‰ and a ∂18O of ≥ + 1‰, as a result of biochemically induced diagenesis. Carbonate, probably mostly aragonite but occasionally including dolomite, was dissolved in a zone where low pH developed as a result of organic matter degradation. Dissolved carbonate was translocated by diffusion and re-precipitated as cement (ca. 50vol%) in a zone with elevated pH where all in situ lime mud ∂18O was reset. Imported cement carbonate precipitated in equilibrium with the pore fluid with negative isotope values, whereas ∂13C of the in situ lime mud remained unmodified. The negative shift of the bulk ∂13C and ∂18O is variable and depends on pH and the contribution of 12C from anaerobic sulfate reduction in the zone of cement precipitation. This produced an ubiquitous covariance of ∂18O and ∂13C. Incorporation of seawater-derived Mg2+ during recrystallization of carbonate can account for the local dolomitization. Elevated 87Sr/86Sr ratios are explained as a result of interaction of clay minerals with the stationary pore fluids. This study shows that the isotopic signal produced by biochemically induced shallow submarine subsurface carbonate diagenesis can be indistinguishable from freshwater diagenesis, that ∂18O and ∂13C of the bulk rock are always reset, and that carbonates can show, in the presence of clay minerals, elevated 87Sr/86Sr ratios even when the pore fluids were never exchanged. Graphical Abstract

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Evaluation of Degree of Alteration in Fossil Ostracods from Middle Callovian-Lower Oxfordian Beds of Southern Part of Kachchh Basin, Gujarat, India by Characterizing Surface Roughness of the Shell

Muduli,

Kumari,

Mahalakshmi

2023

Journal of the Geological Society of India

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Before proceeding with any type of analysis, the condition of preservation of microfossil shells must be determined. Preservation of the shell affects tasks, such as holotype specimen selection, distribution chart, and specimen selection for geochemical analysis. The typical way to determine the degree of alteration is to use a visual examination under the stereo microscope. The deviation of visual characteristics such as colour and smoothness of the shell surface from unaltered shells depicts the alteration status. However, our eyes are frequently misled by the roughness of the shell created by tiny crystals that form due to recrystallization during the diagenesis process and are perceived to be smooth. In turn, the shell is regarded as well-preserved. To address these limitations, we have analyzed scanning electron microscope (SEM) images of ostracod shells using ImageJ, an image processing software, to determine the roughness parameters based on the grey value of the image. In addition, we compared the values of several parameters with different types of alterations, such as recrystallization and dissolution. This study aims to characterize the surface roughness of eight selected ostracod specimens from Middle Callovian to Upper Oxfordian beds of the southern part of Mainland Kachchh. The selected eight species - Cytherella masuguluensis, Progonocythere sp. A, Progonocythere jaisalmerensis, Bythocypris rajasthanensis, Paracypris contermia, Galliaecytheridea remota, Cytherelloidea sp. A, Cytherelloidea sp. B - belong to six genera and five families.

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Middle to Late Jurassic stable isotopes and element ratios of fossils from western India: Developing a reference temperature curve for northeastern Gondwana

Cited by 5 publications

References 147 publications

Laevaptychi as reliable paleotemperature archives: high-resolution stable isotope compositions of Kimmeridgian (Jurassic) lamellar structured aspidoceratid lower mandibles from Zengővárkony (Mecsek Mountains, Hungary)

Laevaptychi as reliable paleotemperature archives: high-resolution stable isotope compositions of Kimmeridgian (Jurassic) lamellar structured aspidoceratid lower mandibles from Zengővárkony (Mecsek Mountains, Hungary)

Biochemically induced diagenesis of Jurassic micrite: evidence from phase analysis, carbon, oxygen, and strontium isotopes (Franconian Alb, Germany)

Evaluation of Degree of Alteration in Fossil Ostracods from Middle Callovian-Lower Oxfordian Beds of Southern Part of Kachchh Basin, Gujarat, India by Characterizing Surface Roughness of the Shell

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