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Stromatolites composed of apatite occur in post-Lomagundi-Jatuli successions (late Palaeoproterozoic) and suggest the emergence of novel types of biomineralization at that time. The microscopic and nanoscopic petrology of organic matter in stromatolitic phosphorites might provide insights into the suite of diagenetic processes that formed these types of stromatolites. Correlated geochemical micro-analyses of the organic matter could also yield molecular, elemental and isotopic compositions and thus insights into the role of specific micro-organisms among these communities. Here, we report on the occurrence of nanoscopic disseminated organic matter in the Palaeoproterozoic stromatolitic phosphorite from the Aravalli Supergroup of north-west India. Organic petrography by micro-Raman and Transmission Electron Microscopy demonstrates syngeneity of the organic matter. Total organic carbon contents of these stromatolitic phosphorite columns are between 0.05 and 3.0 wt% and have a large range of δ13Corg values with an average of -18.5‰ (1σ = 4.5‰). δ15N values of decarbonated rock powders are between -1.2 and +2.7‰. These isotopic compositions point to the important role of biological N2-fixation and CO2-fixation by the pentose phosphate pathway consistent with a population of cyanobacteria. Microscopic spheroidal grains of apatite (MSGA) occur in association with calcite microspar in microbial mats from stromatolite columns and with chert in the core of diagenetic apatite rosettes. Organic matter extracted from the stromatolitic phosphorites contains a range of molecular functional group (e.g. carboxylic acid, alcohol, and aliphatic hydrocarbons) as well as nitrile and nitro groups as determined from C- and N-XANES spectra. The presence of organic nitrogen was independently confirmed by a CN- peak detected by ToF-SIMS. Nanoscale petrography and geochemistry allow for a refinement of the formation model for the accretion and phototrophic growth of stromatolites. The original microbial biomass is inferred to have been dominated by cyanobacteria, which might be an important contributor of organic matter in shallow-marine phosphorites. [ABSTRACT FROM AUTHOR]

Introduction: Macromolecular organic matter in primitive small body materials is one of the reliable indicators to determine the chemical evolution in the early Solar System. JAXA's Hayabusa2 mission explored the carbonaceous asteroid Ryugu and collected its surface materials [1]. On December 6, 2020, the asteroid sample was returned to the Earth. Through the curatorial work at JAXA, it was reported that the Ryugu samples contain high abundances of hydrous minerals and organic matter [2, 3]. Afterward, the initial sample analysis has started from June 2021 to classify and characterize the Ryugu samples in the context of the Solar System formation. In order to uncover the significance of organic matter on C-type asteroid, the Initial Analysis Organic Macromolecule team unveiled the chemical, isotopic, and morphological compositions of macromolecular organic matter from the Ryugu samples. Samples and Methods: Chamber A aggregates (A0108) and Chamber C aggregates (C0109) collected at the first and second touchdown sites, respectively, have been analyzed. The individual intact grains from A0108 and C0109 range from 200 to 900 µm in size. Additional aggregates from Chamber A (A0106) and Chamber C (C0107) were transferred from the Soluble Organic Molecules team after their water and solvent extractions, and were treated with 6M HCl and 1M HCl/9M HF to yield insoluble organic matter (IOM) at Hiroshima University [4]. The main stream of the analytical procedures included a combination of µ-FTIR, µ-Raman spectroscopy, synchrotron-based STXMXANES, STEM-EELS-EDS, AFM-IR, NanoSIMS [4]. Additional protocols by Xe-PFIB, TXM, XRF, Solid-state 1H and 13C NMR, ToF-SIMS, Visible spectroscopy, and AFM have been included for the latter half of the initial analysis. EA-IRMS and noble gas isotope analysis of Ryugu IOM were also performed in collaboration with Soluble organic molecule (SOM) team [5] and Volatile team [6], respectively. Results and discussion: Macromolecular organic matter were abundant and has complex structures consisting of aromatic carbons, aliphatic carbons, ketones and carboxyls [7, 8]. The functional group compositions are typically seen in IOM from CI and CM chondrites. The functional group variations correlated with the morphologies of nanosized organic matter; organic nanoglobules and nanoparticles are aromatic-rich, while organic matter mixed with Mgrich phyllosilicate matrix and carbonates are IOM-like or diffuse carbon [8, 9]. The observed functional group diversity is likely influenced by aqueous evolution on the asteroid parent body without significant heating event. The dD distributions of Ryugu IOM from the Ryugu samples were within the dD range of CM, CI, and Tagish Lake chondrites [10]. The d15N of bulk C and insoluble organics from the Ryugu samples showed similar values to those from CI chondrites [10]. Extreme D and/or 15N enrichments or depletions in some carbonaceous grains could possibly have been derived from the solar nebula or protosolar molecular cloud. A very small fraction of carbonaceous particles show anomalous carbon isotopes including presolar SiC grains [11]. Ryugu organic matter likely resulted from heterogeneous aqueous processing that occurred on carbonaceous asteroids from the common primordial materials formed at an earlier stage of the solar nebula. These results proved the direct link between macromolecular organic matter in the carbonaceous asteroid and that in primitive carbonaceous chondrites. [ABSTRACT FROM AUTHOR]