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The three-dimensional distribution of melt in partially molten synthetic samples compositionally corresponding to diopside (90 wt.%)–anorthite (10 wt.%) and doped with PbO, WO3, MoO3, or Cs2O to enhance contrast was studied by X-ray computed tomography (CT) with synchrotron radiation. The heavy elements were strongly concentrated in the melt and contributed to an increase of the X-ray linear attenuation coefficient (LAC) of it. PbO was found to be compatible with silicate melt (>20 wt.% in solution) and incompatible with diopside crystals. Other oxides WO3 (∼10 wt.%), MoO3 (∼5 wt.%) and Cs2O (< 5 wt.%) are also soluble only in the melt. Such doping is useful not only for LAC control in X-ray CT measurements, but also for systematic control of the structure (wetting properties, distribution and connectivity) of partial melt. This technique gives basic information for discussion of the 3D distribution of partial melt having different wetting properties. As PbO was most effective in visualization of the diopside–anorthite partially molten system, CT images of the PbO-bearing sample were used for further 3D investigation of distribution. A distribution of dihedral angles at solid-melt-solid triple junctions ranging from 22 to 55° was observed with the 3D data. This range in angle distribution was probably caused by anisotropy of crystals and the result supports the argument that there is some limitation in a theoretical framework of stereology which estimates the 3D structure based on 2D observations. Investigators have begun to apply X-ray CT to the study of the 3D distribution of partial melts in rocks using synchrotron radiation. Our study on the effect of doping is one approach for developing a technique to investigate 3D melt distribution.
Earliest Triassic natural conodont assemblages preserved as impressions on bedding planes occur in a claystone of the Hashikadani Formation, which is part of the Mino Terrane, a Jurassic accretionary complex in Japan. In this study, the apparatus of Hindeodus parvus (Kozur and Pjatakova, 1976) is reconstructed using synchrotron radiation micro-tomography (SR–μCT). This species has six kinds of elements disposed in 15 positions forming the conodont apparatus. Carminiscaphate, angulate, and makellate forms are settled in pairs in the P1, P2, and M positions, respectively. The single alate element is correlated with the S0 position. The S array is a cluster of eight ramiforms, subdivided into two inner pairs of digyrate S1–2 and two outer pairs of bipennate S3–4 elements. The reconstruction is similar to a well-known ozarkodinid apparatus model. In addition, the μCT images show that the ‘anterior’ and ‘posterior’ processes of the S1–2 elements faced the caudal and rostral ends of the living conodont body, respectively.
The earliest fossil record of animal biomineralization occurs in the latest Ediacaran Period (c. 550 Ma). Cloudina and Sinotubulites are two important tubular taxa among these earliest skeletal fossils. The evolutionary fate of Cloudina-type fossils across the Ediacaran–Cambrian transition, however, remains poorly understood. Here we report a multi-layered tubular microfossil Feiyanella manica gen. et sp. nov. from a phosphorite interval of the lowest Cambrian Kuanchuanpu Formation, southern Shaanxi Province, South China. This newly discovered fossil is a conical tube with a ‘funnel-in-funnel’ construction, showing profound morphological similarities to Cloudina and Conotubus. On the other hand, the outer few layers, and particularly the outermost layer, of Feiyanella tubes are regularly to irregularly corrugated, a feature strikingly similar to the variably folded/wrinkled tube walls of Sinotubulites. The Feiyanella tubes additionally exhibit two orders of dichotomous branching, similar to branching structures reported occasionally in Cloudina and possibly indicative of asexual reproduction. Owing to broad similarities in tube morphology, tube wall construction and features presumably indicative of asexual reproduction, Cloudina, Conotubus, Sinotubulites and the here described Feiyanella may thus constitute a monophyletic group traversing the Ediacaran–Cambrian boundary. The tube construction and palaeoecological strategy of Feiyanella putatively indicate evolutionary continuity in morphology and palaeoecology of benthic metazoan communities across the Ediacaran–Cambrian transition.