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Cloudina? was initially documented in the Taylor Formation in Antarctica by Yochelson and Stump in 1977. In their publication, they presented views of specimens in thin-section derived from an oolitic limestone breccia. Notably, one thin section contained a presumed trilobite fragment, leading the authors to attribute the materials to the early Cambrian. The remaining fossil materials were characterized as tubes exhibiting varying quality of preservation, likely influenced by recrystallization. The thin sections revealed a fossil structure consisting of a thicker outer layer adjacent to a thinner, darker layer, followed by the inner cavity of the tube. While one specimen was reported to have two layers, it lacked other identifying features, such as the characteristic nested structure typical of Cloudina. The authors acknowledged the dissimilarity of their specimens to those reported from Namibia by Germs but noted similarities to Cloudina borrelloi from the San Juan Province, Argentina described by Yochelson and Herrera in 1974. This led the authors to tentatively identify their Antarctic specimens as Cloudina?, though subsequent reports expressed skepticism about placing the Argentinian materials within the Cloudina genus, suggesting a more plausible association with Salterella or Acuticloudina. Since the initial discovery and report by Yochelson and Stump, however, Ediacaran paleontologists have included Antarctica in the geographic distribution of Cloudina. Because these late Ediacaran tubicolus organisms, including all plausible designations of Cloudina, are currently being considered by the International Commission on Stratigraphy as an index fossil for delineating the terminal Ediacaran stage, this long-overdue reexamination of these materials now becomes both timely and important for gaining a clearer picture of the cosmopolitan nature of this genus. This presentation marks the first comprehensive reassessment of the Antarctic Cloudina? since its initial evaluation. We aim to reevaluate these materials using modern microanalysis and high-resolution photography to shed light on their taxonomy and evaluate their role in the broader context of late Ediacaran to early Cambrian tubular fossils. 

Fossils represented as Cloudina? were reported in the Antarctic Taylor Formation by Yochelson and Stump in 1977. Their assessment presented thin sections of specimens derived from an oolitic limestone breccia. Notably, one thin section contained a single presumed trilobite fragment, leading the authors to attribute the materials to the early Cambrian. The remaining fossil materials were characterized as tubes of varying preservational quality, likely overprinted by recrystallization. The structure of tubular fossils, as viewed in thin section, appeared bilayerd, showing a thicker outer layer surrounding a thinner, darker, inner layer, enveloping the innermost lumen or cavity of the tube. While one specimen was reported to have two layers, it lacked other identifying features, such as the characteristic nested structure typical of Cloudina. The authors acknowledged the dissimilarity of their specimens to those reported from Namibia by G.J.B. Germs but noted similarities to Cloudina borrelloi from the San Juan Province, Argentina described by Yochelson and Herrera in 1974. This led the authors to cautiously identify their Antarctic specimens as Cloudina?, though subsequent reports expressed skepticism about placing the Argentinian materials within the Cloudina genus, suggesting a more plausible association with Salterella or Acuticloudina. Based on this single report, Ediacaran paleontologists have often, but tenuously, expanded the geographic distribution of Cloudina to include Antarctica. As the International Commission on Stratigraphy’s Ediacaran Subcommission has defined the use of Ediacaran tubicolus organisms, including all plausible designations of Cloudina, as the leading index fossil group for placement of the terminal Ediacaran stage, this long-overdue reexamination is both timely and important for gaining a clearer picture of the cosmopolitan nature of this genus. Our initial analysis shows that these tubicolus taxa are single-walled, non-nested, and smooth-walled, gently tapering, conical tubes. Herein, we aim to aim to reevaluate the taxonomy of these fossils using modern microanalysis and high-resolution photography to shed light on their potential phylogeny and evaluate their role in the broader context of late Ediacaran to early Cambrian tubular fossils. 

Textural studies of pumice clasts have been used for decades to estimate eruption styles, particularly through bubble size distribution (BSD) analysis along with quantification of vesicle sizes, numbers, connectivity, and crystallization textures. In more recent years, studies have evolved to include finer-scale analysis by scanning electron microscopy (SEM) and large-scale digital elevation models (DEM). By integrating textural, geochemical, and SEM analysis of the vesicularity of pumice clasts, a comprehensive conduit model can be constructed, which can be further used to estimate volatile content and explosivity. In this contribution, we investigate pumice from two Quaternary deposits from the Black Rock Desert and Mineral Mountains located in west central Utah, a first-of-its kind study for these units. In hand sample, the 2.4 Ma crystal-poor Cudahy Mine pumice (SiO2 = 76.1 wt.%) appears characterized by small, uniform bubbles, whereas the <1 Ma Ranch Canyon pumice (SiO2 = 77.5%) contains ample K-feldspar phenocrysts and elongated fibrous vesicles. We employ X-ray tomographic and scanning electron microscopies to determine bubble sphericity and interconnectivity, crystal volumes, and density and vesicularity estimates. Our resulting data are used to establish a model for intra-conduit processes and eruption intensity of these two anorogenic, monogenetic rhyolite volcanoes. These imaging techniques provide a unique way to understand eruption dynamics for ancient volcanoes.