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1. Integrated carbon, sulfur, and nitrogen isotope chemostratigraphy of the Ediacaran Lantian Formation in South China: Spatial gradient, ocean redox oscillation, and fossil distribution

   https://doi.org/10.1111/gbi.12226  

   Wang, W. ; Guan, C. ; Zhou, C. ; Peng, Y. ; Pratt, L. M. ; Chen, X. ; Chen, L. ; Chen, Z. ; Yuan, X. ; Xiao, S. ( January 2017 , Geobiology)

   The Ediacaran Doushantuo Formation in South China is a prime target for geobiological investigation because it offers opportunities to integrate chemostratigraphic and paleobiological data. Previous studies were mostly focused on successions in shallow‐water shelf facies, but data from deep‐water successions are needed to fully understand basinal redox structures. Here, we report δ¹³C_carb, δ¹³C_org, δ³⁴S_pyr, δ³⁴S_CAS, and δ¹⁵N_seddata from a drill core of the fossiliferous Lantian Formation, which is a deep‐water equivalent of the Doushantuo Formation. Our data confirm a large (>10‰) spatial gradient in δ¹³C_carbin the lower Doushantuo/Lantian formations, but this gradient is probably due to the greater sensitivity of carbonate‐poor deep‐water sediments to isotopic mixing with¹³C‐depleted carbonate cements. A pronounced negative δ¹³C_carbexcursion (EN3) in the upper Doushantuo/Lantian formations, however, is spatially consistent and may be an equivalent of the Shuram excursion. δ³⁴S_pyris more negative in deeper‐water facies than in shallow‐water facies, particularly in the lower Doushantuo/Lantian formations, and this spatial pattern is interpreted as evidence for ocean redox stratification: Pyrite precipitated in euxinic deep waters has lower δ³⁴S_pyrthan that formed within shallow‐water sediments. The Lantian Formation was probably deposited in oscillating oxic and euxinic conditions. Euxinic black shales have higherTOCandTNcontents, but lower δ³⁴S_pyrand δ¹⁵N_sedvalues. In euxinic environments, pyrite was predominantly formed in the water column and organic nitrogen was predominantly derived from nitrogen fixation orNH₄⁺assimilation because of quantitative denitrification, resulting in lower δ³⁴S_pyrand δ¹⁵N_sedvalues. Benthic macroalgae and putative animals occur exclusively in euxinic black shales. If preserved in situ, these organisms must have lived in brief oxic episodes punctuating largely euxinic intervals, only to be decimated and preserved when the local environment switched back to euxinia again. Thus, taphonomy and ecology were the primary factors controlling the stratigraphic distribution of macrofossils in the Lantian Formation.

    

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2. The Coniacian–Santonian sedimentary record in southern Tanzania (Ruvuma Basin, East Africa): Planktonic foraminiferal evolutionary, geochemical and palaeoceanographic patterns

   https://doi.org/10.1111/sed.12331  

   Petrizzo, Maria Rose ; Jiménez Berrocoso, Álvaro ; Falzoni, Francesca ; Huber, Brian T. ; Macleod, Kenneth G. ; Robinson, ed., Stuart ( December 2016 , Sedimentology)

   A 101 m thick stratigraphically complete late Coniacian–early Santonian (ca89 to 83 Ma) sedimentary sequence drilled in Tanzania (Tanzania Drilling Project Site 39) allows, for the first time, examination of the planktonic foraminiferal biostratigraphy and evolution, the depositional history, and geochemical patterns of the subtropical–tropical Indian Ocean region. The sedimentary succession corresponds to an outer shelf to upper slope setting and is dominated by calcareous clayey siltstones and mudstones. The occurrences of Tethyan marker species enable application of the tropical biozonation including identification of theDicarinella concavataandDicarinella asymetricaZones. In addition, Tanzania Drilling Project Site 39 is proposed as reference section for the Coniacian/Santonian boundary in the Indian Ocean with the boundary placed at the lowest occurrence ofGlobotruncana linneianain agreement with the Global Stratotype Section and Point (Spain). The record at Tanzania Drilling Project Site 39 provides a unique opportunity to document the planktonic foraminiferal evolution in a subtropical marginal sea environment during a key period in their evolutionary history characterized by a major radiation among the deep‐dwelling taxa. Combined documentation of lithological and geochemical changes (%CaCO₃, %C_org,δ¹³C_carbandδ¹⁸O_carb) reveals a setting influenced by continental‐derived nutrients in theDicarinella concavataZone (Lindi Formation) with a change to higher carbonate production and reduced surface water primary productivity in the overlyingDicarinella asymetricaZone (Nangurukuru Formation). Planktonic foraminiferal assemblage changes mirror the depositional and geochemical trends and indicate a progressive shift from a more eutrophic to a more oligotrophic regime through time. At the local scale, this palaeoceanographic scenario is consistent with the deepening of coastal Tanzania in response to the Late Cretaceous marine transgression registered in south‐east Tanzania. Because the tectonic evolution and sea‐level rise along the East Africa continental margin is superimposed on the Coniacian–Campanian global long‐term sea‐level high, this study hypothesizes that the epicontinental invasion of blue waters may have favoured radiation among deep‐dwelling taxa.

    

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3. Comparison of δ 13 C analyses of individual foraminifer ( Orbulina universa ) shells by secondary ion mass spectrometry and gas source mass spectrometry

   https://doi.org/10.1002/rcm.9658  

   Wycech, Jody B. ; Kelly, Daniel Clay ; Kozdon, Reinhard ; Ishida, Akizumi ; Kitajima, Kouki ; Spero, Howard J. ; Valley, John W. ( November 2023 , Rapid Communications in Mass Spectrometry)

   The use of secondary ion mass spectrometry (SIMS) to perform micrometer‐scalein situcarbon isotope (δ¹³C) analyses of shells of marine microfossils called planktic foraminifers holds promise to explore calcification and ecological processes. The potential of this technique, however, cannot be realized without comparison to traditional whole‐shell δ¹³C values measured by gas source mass spectrometry (GSMS).

   Paired SIMS and GSMS δ¹³C values measured from final chamber fragments of the same shell of the planktic foraminiferOrbulina universaare compared. The SIMS–GSMS δ¹³C differences (Δ¹³C_SIMS‐GSMS) were determined via paired analysis of hydrogen peroxide‐cleaned fragments of modern cultured specimens and of fossil specimens from deep‐sea sediments that were either untreated, sonicated, and cleaned with hydrogen peroxide or vacuum roasted. After treatment, fragments were analyzed by a CAMECA IMS 1280 SIMS instrument and either a ThermoScientific MAT‐253 or a Fisons Optima isotope ratio mass spectrometer (GSMS).

   Paired analyses of cleaned fragments of cultured specimens (n = 7) yield no SIMS–GSMS δ¹³C difference. However, paired analyses of untreated (n = 18) and cleaned (n = 12) fragments of fossil shells yield average Δ¹³C_SIMS‐GSMSvalues of 0.8‰ and 0.6‰ (±0.2‰, 2 SE), respectively, while vacuum roasting of fossil shell fragments (n = 11) removes the SIMS–GSMS δ¹³C difference.

   The noted Δ¹³C_SIMS‐GSMSvalues are most likely due to matrix effects causing sample–standard mismatch for SIMS analyses but may also be a combination of other factors such as SIMS measurement of chemically bound water. The volume of material analyzed via SIMS is ~10⁵times smaller than that analyzed by GSMS; hence, the extent to which these Δ¹³C_SIMS‐GSMSvalues represent differences in analyte or instrument factors remains unclear.

    

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4. Evidence for the development of local anoxia during the Cambrian SPICE event in eastern North America

   https://doi.org/10.1111/gbi.12334  

   LeRoy, Matthew A. ; Gill, Benjamin C. ( February 2019 , Geobiology)

   The later Cambrian Steptoean Positive Carbon Isotope Excursion (SPICE) event was an episode marked by pronounced changes to the global biogeochemical cycles of carbon and sulfur and significant extinctions on several paleocontinents including Laurentia (North America). While the exact cause(s) of these events remains debated, various lines of evidence suggest an increase in the areal extent of anoxia at the seafloor was a likely feature. Here, we explore whether changes in local oxygenation accompanied the onset of theSPICEin southern Laurentia using cores of the Nolichucky and Eau Claire Formations from Ohio and Kentucky,USA, that represent a transect into the Rome Trough/Conasauga intrashelf basin. At our study locations, the initial positive δ¹³C shift of theSPICEoccurs in conjunction with increases in the abundance and δ³⁴S of sedimentary pyrite. Further local redox conditions, tracked using iron speciation analysis, indicate anoxic conditions developed at the two proximal locations after the start of the paired isotopic excursions. However, the location near the basin center shows no indication for anoxia before or during the onset of theSPICE. While this signal may reflect the structure of local redox conditions within the basin, with the development of anoxia limited to the basin margins, we argue that authigenic iron enrichments were muted by sedimentary dilution and/or the enhanced authigenesis of iron‐bearing sheet silicates near the basin center, masking the signal for anoxia there. Regardless of the areal extent of anoxia within the basin, in either scenario the timing of the development of anoxic bottom waters was concurrent with local faunal turnover, features broadly consistent with a global expansion of anoxia playing a role in driving the isotopic trends and extinctions observed during the event.

    

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5. Carbon and nitrogen isotope fractionation of amino acids in an avian marine predator, the gentoo penguin ( Pygoscelis papua )

   https://doi.org/10.1002/ece3.1437  

   McMahon, Kelton W. ; Polito, Michael J. ; Abel, Stephanie ; McCarthy, Matthew D. ; Thorrold, Simon R. ( February 2015 , Ecology and Evolution)

   Compound‐specific stable isotope analysis (CSIA) of amino acids (AA) has rapidly become a powerful tool in studies of food web architecture, resource use, and biogeochemical cycling. However, applications to avian ecology have been limited because no controlled studies have examined the patterns inAAisotope fractionation in birds. We conducted a controlledCSIAfeeding experiment on an avian species, the gentoo penguin (Pygoscelis papua), to examine patterns in individualAAcarbon and nitrogen stable isotope fractionation between diet (D) and consumer (C) (Δ¹³C_C‐Dand Δ¹⁵N_C‐D, respectively). We found that essentialAAδ¹³C values and sourceAAδ¹⁵N values in feathers showed minimal trophic fractionation between diet and consumer, providing independent but complimentary archival proxies for primary producers and nitrogen sources respectively, at the base of food webs supporting penguins. Variations in nonessentialAAΔ¹³C_C‐Dvalues reflected differences in macromolecule sources used for biosynthesis (e.g., protein vs. lipids) and provided a metric to assess resource utilization. The avian‐specific nitrogen trophic discrimination factor (TDF_Glu‐Phe= 3.5 ± 0.4‰) that we calculated from the difference in trophic fractionation (Δ¹⁵N_C‐D) of glutamic acid and phenylalanine was significantly lower than the conventional literature value of 7.6‰. Trophic positions of five species of wild penguins calculated using a multi‐TDF_Glu‐Pheequation with the avian‐specificTDF_Glu‐Phevalue from our experiment provided estimates that were more ecologically realistic than estimates using a singleTDF_Glu‐Pheof 7.6‰ from the previous literature. Our results provide a quantitative, mechanistic framework for the use ofCSIAin nonlethal, archival feathers to study the movement and foraging ecology of avian consumers.

    

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