Browsing by Author "Halverson, Galen P."

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    Preservation of early Tonian macroalgal fossils from the Dolores Creek Formation, Yukon
    Maloney, Katie M.; Schiffbauer, James D.; Halverson, Galen P.; Xiao, Shuhai; Laflamme, Marc (Nature Portfolio, 2022-04-13)
    The rise of eukaryotic macroalgae in the late Mesoproterozoic to early Neoproterozoic was a critical development in Earth's history that triggered dramatic changes in biogeochemical cycles and benthic habitats, ultimately resulting in ecosystems habitable to animals. However, evidence of the diversification and expansion of macroalgae is limited by a biased fossil record. Non-mineralizing organisms are rarely preserved, occurring only in exceptional environments that favor fossilization. Investigating the taphonomy of well-preserved macroalgae will aid in identifying these target environments, allowing ecological trends to be disentangled from taphonomic overprints. Here we describe the taphonomy of macroalgal fossils from the Tonian Dolores Creek Formation (ca. 950 Ma) of northwestern Canada (Yukon Territory) that preserves cm-scale macroalgae. Analytical microscopy, including scanning electron microscopy and tomographic x-ray microscopy, was used to investigate fossil preservation, which was the result of a combination of pyritization and aluminosilicification, similar to accessory mineralization observed in Paleozoic Burgess Shale-type fossils. These new Neoproterozoic fossils help to bridge a gap in the fossil record of early algae, offer a link between the fossil and molecular record, and provide new insights into evolution during the Tonian Period, when many eukaryotic lineages are predicted to have diversified.
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    The Sedimentary Geochemistry and Paleoenvironments Project
    Farrell, Una C.; Samawi, Rifaat; Anjanappa, Savitha; Klykov, Roman; Adeboye, Oyeleye O.; Agic, Heda; Ahm, Anne-Sofie C.; Boag, Thomas H.; Bowyer, Fred; Brocks, Jochen J.; Brunoir, Tessa N.; Canfield, Donald E.; Chen, Xiaoyan; Cheng, Meng; Clarkson, Matthew O.; Cole, Devon B.; Cordie, David R.; Crockford, Peter W.; Cui, Huan; Dahl, Tais W.; Mouro, Lucas D.; Dewing, Keith; Dornbos, Stephen Q.; Drabon, Nadja; Dumoulin, Julie A.; Emmings, Joseph F.; Endriga, Cecilia R.; Fraser, Tiffani A.; Gaines, Robert R.; Gaschnig, Richard M.; Gibson, Timothy M.; Gilleaudeau, Geoffrey J.; Gill, Benjamin C.; Goldberg, Karin; Guilbaud, Romain; Halverson, Galen P.; Hammarlund, Emma U.; Hantsoo, Kalev G.; Henderson, Miles A.; Hodgskiss, Malcolm SW W.; Horner, Tristan J.; Husson, Jon M.; Johnson, Benjamin; Kabanov, Pavel; Brenhin Keller, C.; Kimmig, Julien; Kipp, Michael A.; Knoll, Andrew H.; Kreitsmann, Timmu; Kunzmann, Marcus; Kurzweil, Florian; LeRoy, Matthew A.; Li, Chao; Lipp, Alex G.; Loydell, David K.; Lu, Xinze; Macdonald, Francis A.; Magnall, Joseph M.; Mand, Kaarel; Mehra, Akshay; Melchin, Michael J.; Miller, Austin J.; Mills, N. Tanner; Mwinde, Chiza N.; O'Connell, Brennan; Och, Lawrence M.; Ossa Ossa, Frantz; Pages, Anais; Paiste, Kart; Partin, Camille A.; Peters, Shanan E.; Petrov, Peter; Playter, Tiffany L.; Plaza-Torres, Stephanie; Porter, Susannah M.; Poulton, Simon W.; Pruss, Sara B.; Richoz, Sylvain; Ritzer, Samantha R.; Rooney, Alan D.; Sahoo, Swapan K.; Schoepfer, Shane D.; Sclafani, Judith A.; Shen, Yanan; Shorttle, Oliver; Slotznick, Sarah P.; Smith, Emily F.; Spinks, Sam; Stockey, Richard G.; Strauss, Justin V.; Stueken, Eva E.; Tecklenburg, Sabrina; Thomson, Danielle; Tosca, Nicholas J.; Uhlein, Gabriel J.; Vizcaino, Maoli N.; Wang, Huajian; White, Tristan; Wilby, Philip R.; Woltz, Christina R.; Wood, Rachel A.; Xiang, Lei; Yurchenko, Inessa A.; Zhang, Tianran; Planavsky, Noah J.; Lau, Kimberly V.; Johnston, David T.; Sperling, Erik A. (Wiley, 2021-07-05)
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    Systematic paleontology of macroalgal fossils from the Tonian Mackenzie Mountains Supergroup
    Maloney, Katie M.; Maverick, Dakota P.; Schiffbauer, James D.; Halverson, Galen P.; Xiao, Shuhai; Laflamme, Marc (Cambridge University Press, 2023-03-01)
    Proterozoic eukaryotic macroalgae are difficult to interpret because morphological details required for proper phylogenetic studies are rarely preserved. This is especially true of morphologically simple organisms consisting of tubes, ribbons, or spheres that are commonly found in a wide array of bacteria, plants, and even animals. Previous reports of exceptionally preserved Tonian (ca. 950-900 Ma) fossils from the Dolores Creek Formation of Northwestern Canada feature enough morphological evidence to support a green macroalgal affinity. However, the affinities of two additional forms identified on the basis of the size distribution of available specimens remain undetermined, while the presence of three unique algal forms supports other reports of increasing algal diversity in the early Neoproterozoic. Archaeochaeta guncho new genus new species is described as a green macroalga on the basis of its well-preserved morphology consisting of an unbranching, uniseriate thallus with uniform width throughout and possessing an elliptical to globose anchoring holdfast. A larger size class of ribbon-like forms is interpreted as Vendotaenia sp. A third size class is significantly smaller than Archaeochaeta n. gen. and Vendotaenia, but in the absence of clear morphological characters, it remains difficult to assign. As Archaeochaeta n. gen. and Vendotaenia represent photoautotrophic taxa, these findings support the hypothesis of increasing morphological complexity and phyletic diversification of macroalgae during the Tonian, leading to dramatic changes within benthic marine ecosystems before the evolution of animals.
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    A template for an improved rock-based subdivision of the pre-Cryogenian timescale
    Shields, Graham A.; Strachan, Robin A.; Porter, Susannah M.; Halverson, Galen P.; Macdonald, Francis A.; Plumb, Kenneth A.; de Alvarenga, Carlos J.; Banerjee, Dhiraj M.; Bekker, Andrey; Bleeker, Wouter; Brasier, Alexander; Chakraborty, Partha P.; Collins, Alan S.; Condie, Kent; Das, Kaushik; Evans, David AD D.; Ernst, Richard; Fallick, Anthony E.; Frimmel, Hartwig; Fuck, Reinhardt; Hoffman, Paul F.; Kamber, Balz S.; Kuznetsov, Anton B.; Mitchell, Ross N.; Poire, Daniel G.; Poulton, Simon W.; Riding, Robert; Sharma, Mukund; Storey, Craig; Stueeken, Eva; Tostevin, Rosalie; Turner, Elizabeth; Xiao, Shuhai; Zhang, Shuanhong; Zhou, Ying; Zhu, Maoyan (Geological Society of America, 2021-07-07)
    The geological timescale before 720 Ma uses rounded absolute ages rather than specific events recorded in rocks to subdivide time. This has led increasingly to mismatches between subdivisions and the features for which they were named. Here we review the formal processes that led to the current timescale, outline rock-based concepts that could be used to subdivide pre-Cryogenian time and propose revisions. An appraisal of the Precambrian rock record confirms that purely chronostratigraphic subdivision would require only modest deviation from current chronometric boundaries, removal of which could be expedited by establishing event-based concepts and provisional, approximate ages for eon-, era-and period-level subdivisions. Our review leads to the following conclusions: (1) the current informal four-fold Archean subdivision should be simplified to a tripartite scheme, pending more detailed analysis, and (2) an improved rock-based Proterozoic Eon might comprise a Paleoproterozoic Era with three periods (early Paleoproterozoic or Skourian, Rhyacian, Orosirian), Mesoproterozoic Era with four periods (Statherian, Calymmian, Ectasian, Stenian) and a Neoproterozoic Era with four periods ( pre-Tonian or Kleisian, Tonian, Cryogenian and Ediacaran). These proposals stem from a wide community and could be used to guide future development of the pre-Cryogenian timescale by international bodies.