Paleosol in Galesburg Formation (Kansas City Group, Upper Pennsylvanian), Northern Midcontinent, U.S.A.: Evidence for Climate Change and Mechanisms of Marine Transgression
Paleosol in Galesburg Formation (Kansas City Group, Upper Pennsylvanian), Northern Midcontinent, U.S.A.: Evidence for Climate Change and Mechanisms of Marine Transgression
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DOI：
10.2110/jsr.69.720
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发表时间：
1999-05
影响因子：
2
通讯作者：
R. Joeckel
中科院分区：
文献类型：
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作者：
R. Joeckel
摘要中大陆上宾夕法尼亚旋回露头带北部盖尔斯堡组(堪萨斯城群，密苏里州)中广泛分布的古土壤具有明显的特征，包括重复的同形滑面和烟囱结构，这是一种古变性土壤。盖尔斯堡古土壤具有普遍的低色度灰到绿色的颜色、有机质剖面和关于S、Fe_2O_3、MnO、SiO_2和Al_2O_3的地球化学特征，这些特征表明土壤条件比当地地层序列中分布较高的高色度古土壤(特别是上劳伦斯组的高色度古变性土层)所指示的土壤条件更潮湿。在北部森林城市盆地(内布拉斯加州东南部和爱荷华州西南部)的堪萨斯城群中，以Galesburg古土壤为例，整个堪萨斯城群的低色度(即较潮湿)古土壤占优势，而宾夕法尼亚(特别是Virgilian)地层中高色度(即较干燥)古土壤的出现频率较高，这意味着密苏里晚期北美内陆的降雨量减少。通过这种密苏里-维尔吉利亚变化的降雨量不需要超过与北美洲亚热带和暖温带现代土壤相似的降雨量范围(400-1400毫米/年)。因此，与其他作者提出的北美内陆晚古生代旋回气候变化的时间尺度(105-106a)相比，气候变化具有更长的时间尺度(105-106a)。盖尔斯堡直接上方海侵海侵地层性质的区域差异进一步表明：(1)与海平面曲线重建有关的重要信息可能从MUPC的海退古土壤和随后的海退石灰岩之间的间隔中缺失，以及(2)在MUPC海侵沉积的任何特定间隔内，MUPC海侵页岩和黑色“芯”页岩的总体沉积机制可能存在显著差异。
ABSTRACT A widespread paleosol in the Galesburg Formation (Kansas City Group, Missourian) in the northern Midcontinent Upper Pennsylvanian cyclothem (MUPC) outcrop belt exhibits prominent features, including repeating sets of synformal slickensides and mukkara or "chimney" structures, which characterize it as a paleo-Vertisol. The Galesburg paleosol has pervasive low-chroma grayish to greenish coloration, an organic-matter profile, and geochemical characteristics with regard to S, Fe2O3, MnO, SiO2, and Al2O3 that indicate wetter soil conditions than those indicated by equally widespread high-chroma paleosols higher in the local stratigraphic succession (particularly a high-chroma paleo-Vertisol in the upper Lawrence Formation). The predominance of low-chroma (i.e., wetter) paleosols throughout the Kansas City Group in the northern Forest City Basin (southeastern Nebraska and southwestern Iowa), as exemplified by the Galesburg paleosol, compared to the greater frequency of high-chroma (i.e., drier) paleosols in overlying Pennsylvanian (especially Virgilian) strata, implicates decreasing rainfall in the interior of North America during the late Missourian. The variability in rainfall through this Missourian-Virgilian shift need not have exceeded the range of rainfall (400-1400 mm/a) associated with modern soil analogs in subtropical to warm-temperate North America. Thus, there is an indication of climate change on a longer-term time scale ( 105-106 a) than the intra- or inter-eustatic-cycle climate change proposed by other authors for late Paleozoic cyclothems in the North American interior. Regional differences in the nature of transgressive marine strata directly above the Galesburg further suggest: (1) that important information relevant to reconstruction of the sea-level curve is probably missing from the interval between regressive paleosols and subsequent regressive limestones in MUPCs, and (2) that there were probably appreciable differences in the overall mechanism of deposition of MUPC transgressive shales and black "core" shales within any particular interval of MUPC transgressive deposition.