The Pennsylvanian lowlands of western Pangea are best known for their diverse wetland floras of arborescent and herbaceous ferns, and arborescent horsetails and clubmosses. In apparent juxtaposition, a very different kind of flora, dominated by a xerophilous assemblage of conifers, taeniopterids and peltasperms, is occasionally glimpsed. Once believed to represent upland or extrabasinal floras from well-drained portions of the landscape, these dryland floras more recently have been interpreted as lowland assemblages growing during drier phases of glacial/interglacial cycles. Whether Pennsylvanian dryland and wetland floras were separated spatially or temporally remains an unsettled question, due in large part to taphonomic bias toward preservation of wetland plants. Previous paleobotanical and sedimentological analysis of the Markley Formation of latest Pennsylvanian (Gzhelian) age, from north central Texas, U.S.A, indicates close correlation between lithofacies and distinct dryland and wetland megaflora assemblages. Here we present a detailed analysis one of those localities, a section unusual in containing abundant palynomorphs, from the lower Markley Formation. Paleobotanical, palynological and lithological data from a section thought to represent a single interglacial/glacial phase are integrated and analyzed to create a complex picture of an evolving landscape. Megafloral data from throughout the Markley Formation show that conifer-dominated dryland floras occur exclusively in highly leached kaolinite beds, likely eroded from underlying soils, whereas a mosaic of wetland floras occupy histosols, ultisols, and fluvial overbank deposits. Palynological data largely conform to this pattern but reveal a more complex picture. An assemblage of mixed wetland and dryland palynofloral taxa is interpolated between a dryland assemblage and an overlying histosol containing wetland taxa. In this section, as well as elsewhere in the Markley Formation, kaolinite and overlying organic beds appear to have formed as a single genetic unit, with the kaolinite forming an impermeable aquiclude upon which a poorly drained wetland subsequently formed. Within a single inferred glacial/interglacial cycle, lithological data indicate significant fluctuations in water availability tracked by changes in palynofloral and megafloral taxa. Palynology reveals that elements of the dryland floras appear at low abundance even within wetland deposits. The combined data indicate a complex pattern of succession and suggest a mosaic of dryland and wetland plant communities in the Late Pennsylvanian. Our data alone cannot show whether dryland and wetland assemblages succeed one another temporally, or coexisted on the landscape. However, the combined evidence suggests relatively close spatial proximity within a fragmenting and increasingly arid environment.

中文翻译：

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宾夕法尼亚晚期植物组合之间的时空关系：来自美国西德克萨斯州马克利组的孢粉学证据

Pangea 西部的宾夕法尼亚低地以其多样的湿地植物群落而闻名，包括乔木和草本蕨类植物，以及乔木蕨类植物和棒苔藓。在明显的并列中，偶尔会瞥见一种非常不同的植物群，它们由针叶树、绦虫和 peltasperms 的旱生组合主导。这些旱地植物群曾经被认为代表来自景观排水良好部分的高地或盆地外植物群，最近被解释为在冰川/间冰期循环的干燥阶段生长的低地组合。宾夕法尼亚州的旱地和湿地植物群是否在空间或时间上是分开的仍然是一个悬而未决的问题，这在很大程度上是由于对保护湿地植物的埋藏学偏见。先前对来自美国德克萨斯州中北部的最近宾夕法尼亚 (Gzhelian) 时代的 Markley 组进行的古植物学和沉积学分析表明，岩相与不同的旱地和湿地巨型植物群组合之间存在密切的相关性。在这里，我们对这些地点之一进行了详细分析，该部分包含丰富的孢粉型，来自较低的 Markley 组。来自被认为代表单个间冰期/冰川期的部分的古植物学、孢粉学和岩性数据被整合和分析，以创建一个不断发展的景观的复杂图景。整个 Markley 组的巨型植物数据表明，以针叶树为主的旱地植物群只出现在高度浸出的高岭石层中，很可能是从下伏土壤中侵蚀出来的，而湿地植物群的马赛克占据了组织溶胶，ultisol 和河流积存。孢粉学数据在很大程度上符合这种模式，但揭示了更复杂的情况。混合湿地和旱地孢粉植物分类群的组合被插在旱地组合和上覆的含有湿地分类群的组织溶胶之间。在这一部分以及 Markley 组的其他地方，高岭石和上覆的有机层似乎是作为一个单一的成因单元形成的，高岭石形成了一个不透水的隔水层，随后在上面形成了排水不良的湿地。在一个推断的冰期/间冰期循环中，岩性数据表明可用水量的显着波动是由孢粉植物和巨型植物分类群的变化所追踪的。孢粉学表明，即使在湿地沉积物中，旱地植物群的元素也以低丰度出现。综合数据表明了复杂的演替模式，并表明宾夕法尼亚晚期的旱地和湿地植物群落的镶嵌。仅凭我们的数据无法显示旱地和湿地组合是否在时间上相互成功，或在景观上共存。然而，综合证据表明，在一个支离破碎且日益干旱的环境中，空间接近度相对较近。