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Soil formation and terrestrial biosignatures in the Middle Cambrian.

机译：中寒武纪的土壤形成和陆地生物特征。

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摘要

The composition and importance of terrestrial ecosystems during the Cambrian is the subject of frequent speculation due to poor preservation and a paucity of comprehensive studies. In this thesis, a geographically extensive and geologically heterogeneous Middle Cambrian weathered surface was investigated to better understand both abiotic and biotic weathering effects and site-to-site heterogeneities. The development of Alfisols and Ultisols in the study area is consistent with weathering in a subtropical climate. Western sites tended to by slightly drier as compared to eastern sites. Further heterogeneities in weathering were caused by differences in topography, with higher and better-drained sites developing drier paleosols and lower and more poorly drained sites developing wetter paleosols, and parent material, with sandy grus and paleosaprolites developing on granites and clayey paleosols and paleosaprolites developing on mafic material. As a result of these heterogeneities, no one site proved to be representative of the entire study region. Caution must be used when interpreting paleoweathering data to avoid mistaking local conditions for regional or global conditions.;A thorough geochemical analysis of the Middle Cambrian paleoweathered horizons revealed several geochemical trends that could not be explained by abiotic weathering alone. Chief among these was the peculiar depletion in phosphorus from surface horizons, especially at the Elk Point site, which was enriched in apatite content. Enrichments in organic carbon, carbon isotope composition, and apatite dissolution patterns indicate the possible presence of a deeply weathering terrestrial ecosystem. Argillan development in the zone of apatite dissolution, likely a result of calcium enrichment in soil fluids as a consequence of biological apatite dissolution and phosphorus uptake, is consistent with the behavior of modern-day mycorrhizal fungi. The presence of mycorrhizal fungi at Elk Point would extend their geologic record from 460 Ma to >503 Ma. The presence of a more deeply weathering Cambrian terrestrial ecosystem may have had important consequences for biogeochemical cycles, such as increased nutrient flow to the ocean and increased uptake of atmospheric carbon dioxide, previously not considered by other researchers due to the presumed absence of a significant terrestrial biota at this time.
机译：寒武纪期间陆地生态系统的组成和重要性由于缺乏保护和缺乏全面的研究而经常引起人们的思考。在本文中，对地理分布广泛且地质异质的中寒武纪风化表面进行了研究，以更好地了解非生物和生物风化作用以及站点到站点的异质性。研究区域中的Alfisols和Ultisols的发展与亚热带气候中的风化相一致。与东部站点相比，西部站点趋于稍微干燥。风化的进一步非均质性是由地形差异引起的，较高和较高排水的位点发育较干燥的古土壤，较低和较不排水的位点发育为较湿的古土壤，以及母体，砂砾和古近纪花岗岩在花岗岩上发育，粘土古土壤和古近纪发育在铁镁铁质材料上。由于这些异质性，没有一个站点被证明可以代表整个研究区域。在解释古风化数据时必须谨慎，以免将当地条件误认为区域或全球条件。对中寒武纪古风化层进行彻底的地球化学分析后发现，只有非生物风化不能解释几种地球化学趋势。其中最主要的是来自表层的磷的独特消耗，特别是在麋点地区，磷含量丰富。有机碳，碳同位素组成和磷灰石溶解模式的富集表明可能存在深度风化的陆地生态系统。磷灰石溶解区的Argillan发育可能是由于生物磷灰石溶解和磷吸收导致土壤液中钙富集的结果，与现代菌根真菌的行为一致。麋鹿角的菌根真菌的存在将使他们的地质记录从460 Ma扩大到> 503 Ma。寒武纪气候更深的陆地生态系统的存在可能对生物地球化学循环产生了重要的影响，例如营养物质向海洋的流动增加和大气二氧化碳的吸收增加，这是以前其他研究人员没有考虑到的，原因是假定缺少大量陆地此时的生物群系。

著录项

  • 作者

    Horodyskyj, Lev B.;

  • 作者单位

    The Pennsylvania State University.;

  • 授予单位 The Pennsylvania State University.;
  • 学科 Geology.;Geochemistry.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 139 p.
  • 总页数 139
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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