Carbonaceous chondrites contain organic matter, but the majority consists of complex macromolecular organic matter collected after acid demineralization. The N contents in carbonaceous chondrites are much lower than C, limiting our understanding of N-bearing functional groups. However, such N-containing compounds could be precursors for life's raw materials, making detailed chemical analysis essential. This study investigates Ncontaining organic matter such as N-heterocycles and amines, in various carbonaceous chondrites and xenolithic C-rich clasts using high-sensitivity N K-edge X-ray absorption near-edge structure (XANES) spectroscopy at SPring-8. We compared intact chondrites and insoluble organic matter (IOM) from Orgueil, Murchison, and Tagish Lake meteorites. Most chondrites exhibit three distinct N-XANES peaks: (A) pyridinic N (398.7 eV), (B) pyridinic N and/or nitriles (399.7 eV), and (C) pyrrolic N, amines, amides, and/or ammonium salts (400.8 eV). The Zag meteorite clast and ungrouped type 2 chondrites, such as Tagish Lake and Tarda, show an intense peak at 400.8 eV, indicating enrichment in non-conjugated N-compounds such as amines, amides, and/or ammonium salts. This suggests that their parent bodies contained more abundant ammonia and water. Comparing intact chondrites and IOM reveals significant differences in N-XANES features, suggesting acid-labile N-bearing moieties, like amides and ammonium salts, in addition to solvent extractable compounds such as amines and amino acids, are lost or altered during IOM extraction. This implies that extraterrestrial N compounds may be more diverse and abundant than previously recognized. These findings provide new insights into the N chemistry of meteorites and their potential contribution to the prebiotic inventory of early Earth.
This paper provides the first wide-ranging data for iodine concentrations of natural CaCO3 samples (50 in total) from various geologic and marine-biogenic sources. The geologic samples are (i) calcite and aragonite crystals grown in underground or cave environments and (ii) calcite-aragonite coexisting travertines deposited from mountain spring water. The marine-biogenic samples are shells/skeletons/spicules of bivalves, gastropods, anthozoans, hydrozoans, bryozoans and foraminifera (36 extant and 3 extinct species), each consisting of either calcite, aragonite, or both, and including two geochemical reference materials GSJ CRM JCt-1 (giant clam) and JCp-1 (scleractinian coral). The iodine concentration data show distinct differences depending on the sample source and taxonomic group, probably indicating effects of (i) environmental conditions (e.g., redox conditions) and (ii) inter-taxonomic differences in the iodine-incorporation mechanism. Some samples with lowest iodine concentrations suggest that iodine (probably iodate) is incorporated more preferentially into calcite than into aragonite, as previously demonstrated in a laboratory experiment and a crystal-structure simulation. Measurements of Ca, Mg, Sr and Na were also made for all the samples, which revealed that some calcite samples (e.g., bryozoan skeletons) were composed of magnesian calcite with Mg and Ca concentrations of similar to 12,000-42,000 ppm and similar to 370,000-340,000 ppm, respectively (i.e., the higher the Mg concentration, the lower the Ca concentration). For more accurate expression of the iodine concentration in various natural CaCO3 samples, including magnesian calcite, we propose the I/(Ca + Mg + Sr + Na) ratio instead of the I/Ca and I/(Ca + Mg) ratios; in future studies, it may be desirable to investigate, for some specific marine CaCO3 materials, whether the I/(Ca + Mg + Sr + Na) ratio can practically be a more accurate paleo-redox proxy in comparison with the I/Ca and I/(Ca + Mg) ratios. Our dataset and detailed discussion will make a significant contribution to iodine-based geochemistry and marine biology.
Volcanic eruptions that formed Ontong Java Nui (OJN) during the Aptian (similar to 120 Ma), Early Cretaceous, triggered substantial environmental perturbations, including global warming and Oceanic Anoxic Event (OAEs) 1a. However, the precise transition of OJN eruption styles and the influence of each volcanic phase on Earth's environment remains poorly understood. Here, we present Pb isotopic evidence for the OJN as the source of tuffaceous sedimentary sequence deposited on nearby Magellan Rise. Furthermore, we reviewed geochemical and lithological data around OAE1a, and updated the discussion on how the OJN emplacement influenced the earth environment. Our results point to explosive OJN eruption during the earliest phase of OAE1a based on compiled geochemical and lithological data. Stratigraphic variations in Pb isotopic compositions during this volcanic phase indicate a transition in OJN volcanism, from Kwaimbaita/Kroenke-like magma eruptions that formed the lower part of OJN to Singgalo-like magma eruptions that formed the upper part. Based on previously reported isotopic (Os and C), mineralogical, and geochemical data, this short (similar to 250 kyr) explosive volcanic phase, indicated by the Pb isotopic signal, was accompanied by extensive volatile emissions and corresponds to the onset of the previously documented early to mid-Aptian environmental perturbations (global warming, OAE1a, and the nannoconid crisis).
