Naturally occurring radioactive materials in offshore infrastructure: Understanding formation and characteristics of baryte scale during decommissioning planning.

Contaminants, including naturally occurring radioactive material (NORM) of the 238-uranium and 232-thorium decay series, have been recognized as a global research priority to inform offshore petroleum infrastructure decommissioning decisions. This study aimed to characterize pipeline scale retrieved from a decommissioned subsea well tubular pipe through high-resolution elemental mapping and isotopic analysis. This was achieved by utilizing transmission electron microscopy, Synchrotron x-ray fluorescence, photostimulated luminescence autoradiography and Isotope Ratio Mass Spectrometry. The scale was identified as baryte (BaSO4) forming a dense crystalline matrix, with heterogenous texture and elongated crystals. The changing chemical and physical microenvironment within the pipe influenced the gradual growth rate of baryte over the production life of this infrastructure. A distinct compositional banding of baryte and celestine (SrSO4) bands was observed. Radioactivity attributed by the presence of radionuclides (226Ra, 228Ra) throughout the scale was strongly correlated with baryte. From the detailed scale characterization, we can infer the baryte scale gradually formed within the internals of the tubular well pipe along the duration of production (i.e., 17 years). This new knowledge and insight into the characteristics and formation of petroleum waste products will assist with decommissioning planning to mitigate potential radiological risks to marine ecosystems.

Accelerated carbonate biomineralisation of Venetia diamond mine coarse residue deposit (CRD) material - A field trial study.

Field trials combining mined kimberlite material (Coarse Residue Deposit; CRD) and mine derived microbes show accelerated kimberlite weathering at surface conditions - a potential method for accelerated carbon sequestration via mineral bio­carbonation. A photosynthetic biofilm suspension (20L), sourced from the Venetia diamond mine (Limpopo, South Africa) pit wall, was cultured in 3 × 1000 L bioreactors using BG-11 medium. Bioreactors supplemented with Fine Residue Deposit (FRD) kimberlite material enhanced microbial growth and kimberlite weathering. This (ca. 1.44 kg) wet weight bio-amendment corresponded to ca. 1.5 × 109Acidithiobacillus spp. sized bacteria/g CRD (20 kg FRD growth supplement +60 kg FRD used for harvesting biomass +850 kg CRD used in the field trial experiment). This bio-amendment promoted carbonate precipitation and subsequent cementation under surface conditions (0-20 cm). Microbial inoculation accelerated pedogenesis of CRD materials. A soil-like substrate resulted from weathering under environmental conditions in Johannesburg from January 2020 to April 2021. Over this 15-month experiment, the biodiversity found in the inoculum shifted due to the selective pressure of the kimberlite. The natural, endogenous biosphere, when combined with the inoculum, accelerated carbonate precipitation in the upper 20 cm of the bioreactor by between +1 wt% and + 2 wt%. Conversely, carbonation of the bioreactor at depth (20-40 cm) decreased by ca. 1 wt%. All the secondary carbonate observed in the bioreactors was biogenic in nature, i.e., possessing microbial fossils. This secondary carbonate took the form of both radiating acicular crystals as well as colloform intergranular cements. This microbial inoculum and resulting geochemical changes promoted the transformation of kimberlite into a Technosol, capable of supporting the germination and growth of self-seeding, windblown grasses, which enhanced weathering in the rhizosphere. The maximum secondary carbonate production is consistent with a ca. 20 % mine site CO2e offset.

Sequential Lonsdaleite to Diamond Formation in Ureilite Meteorites via In Situ Chemical Fluid/Vapor Deposition.

Ureilite meteorites are arguably our only large suite of samples from the mantle of a dwarf planet and typically contain greater abundances of diamond than any known rock. Some also contain lonsdaleite, which may be harder than diamond. Here, we use electron microscopy to map the relative distribution of coexisting lonsdaleite, diamond, and graphite in ureilites. These maps show that lonsdaleite tends to occur as polycrystalline grains, sometimes with distinctive fold morphologies, partially replaced by diamond + graphite in rims and cross-cutting veins. These observations provide strong evidence for how the carbon phases formed in ureilites, which, despite much conjecture and seemingly conflicting observations, has not been resolved. We suggest that lonsdaleite formed by pseudomorphic replacement of primary graphite shapes, facilitated by a supercritical C-H-O-S fluid during rapid decompression and cooling. Diamond + graphite formed after lonsdaleite via ongoing reaction with C-H-O-S gas. This graphite > lonsdaleite > diamond + graphite formation process is akin to industrial chemical vapor deposition but operates at higher pressure (∼1-100 bar) and provides a pathway toward manufacture of shaped lonsdaleite for industrial application. It also provides a unique model for ureilites that can reconcile all conflicting observations relating to diamond formation.

Amber from the Triassic to Paleogene of Australia and New Zealand as exceptional preservation of poorly known terrestrial ecosystems.

The Northern Hemisphere dominates our knowledge of Mesozoic and Cenozoic fossilized tree resin (amber) with few findings from the high southern paleolatitudes of Southern Pangea and Southern Gondwana. Here we report new Pangean and Gondwana amber occurrences dating from ~230 to 40 Ma from Australia (Late Triassic and Paleogene of Tasmania; Late Cretaceous Gippsland Basin in Victoria; Paleocene and late middle Eocene of Victoria) and New Zealand (Late Cretaceous Chatham Islands). The Paleogene, richly fossiliferous deposits contain significant and diverse inclusions of arthropods, plants and fungi. These austral discoveries open six new windows to different but crucial intervals of the Mesozoic and early Cenozoic, providing the earliest occurrence(s) of some taxa in the modern fauna and flora giving new insights into the ecology and evolution of polar and subpolar terrestrial ecosystems.