Browsing by Author "Banerjee, Dhiraj M."

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    Systematic paleontology, acritarch biostratigraphy, and delta C-13 chemostratigraphy of the early Ediacaran Krol A Formation, Lesser Himalaya, northern India
    Xiao, Shuhai; Jiang, Ganqing; Ye, Qin; Ouyang, Qing; Banerjee, Dhiraj M.; Singh, Birendra P.; Muscente, A. D.; Zhou, Chuanming; Hughes, Nigel C. (Cambridge University Press, 2022)
    Acritarch biostratigraphic and delta C-13 chemostratigraphic data from the Krol A Formation in the Solan area (Lesser Himalaya, northern India) are integrated to aid inter-basinal correlation of early-middle Ediacaran strata. We identified a prominent negative delta C-13 excursion (likely equivalent to EN2 in the lower Doushantuo Formation in the Yangtze Gorges area of South China), over a dozen species of acanthomorphs (including two new species-Cavaspina tiwariae Xiao n. sp., Dictyotidium grazhdankinii Xiao n. sp.), and numerous other microfossils from an interval in the Krol A Formation. Most microfossil taxa from the Krol A and the underlying Infra-Krol formations are also present in the Doushantuo Formation. Infra-Krol acanthomorphs support a correlation with the earliest Doushantuo biozone: the Appendisphaera grandis-Weissiella grandistella-Tianzhushania spinosa Assemblage Zone. Krol A microfossils indicate a correlation with the second or (more likely, when delta C-13 data are considered) the third biozone in the lower Doushantuo Formation (i.e., the Tanarium tuberosum-Schizofusa zangwenlongii or Tanarium conoideum-Cavaspina basiconica Assemblage Zone). The association of acanthomorphs with EN2 in the Krol Formation fills a critical gap in South China where chert nodules, and thus acanthomorphs, are rare in the EN2 interval. Like many other Ediacaran acanthomorphs assemblages, Krol A and Doushantuo acanthomorphs are distributed in low paleolatitudes, and they may represent a distinct paleobiogeographic province in east Gondwana. The Indian data affirm the stratigraphic significance of acanthomorphs and delta C-13, clarify key issues of lower Ediacaran bio- and chemostratigraphic correlation, and strengthen the basis for the study of Ediacaran eukaryote evolution and paleobiogeography. UUID: http://zoobank.org/5289fdb2-0e49-4b3b-880f-f5b21acab371.
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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.