Alluvial and volcanic pathways to silicified plant stems (Upper Carboniferous-Triassic) and their taphonomic and palaeoenvironmental meaning
Alluvial and volcanic pathways to silicified plant stems (Upper Carboniferous-Triassic) and their taphonomic and palaeoenvironmental meaning
复制标题
硅化植物茎（上石炭纪-三叠纪）的冲积和火山路径及其埋藏学和古环境意义
DOI：
10.1016/j.palaeo.2010.03.036
复制
发表时间：
2010
期刊：
影响因子：
--
通讯作者：
T. Grygar
中科院分区：
文献类型：
--
作者：
Petra Matysová;R. Roessler;J. Götze;J. Leichmann;G. Forbes;E. Taylor;J. Sakala;T. Grygar
岩相成像与矿物量的定性和定量仪器分析相结合，使我们能够获得硅化植物茎的物质特征，硅化植物茎在晚古生代以来的大陆盆地沉积物中相对常见。这些化石可以在其原始地层中发现，但通常已从其环境和地层背景中移除，在母岩侵蚀后重新沉积并散布在最近的陆地表面上。从 X 射线衍射分析、热阴极发光 (CL) 成像和光谱、电子显微探针分析、拉曼光谱测定和偏振光显微镜收集的分析数据可用于表征巴西、德国、捷克共和国、阿曼苏丹国、蒙古、南极洲、法国和美国盆地样品的材料特征。该集合包括在河流环境和受火山作用影响的地点发现的硅化宾夕法尼亚和二叠纪植物类群（以及一些来自三叠纪），目的是辨别在特定环境条件下形成的基本物质特征。河流岩石中宾夕法尼亚晚期和二叠纪的硅化茎包括存在结晶良好的石英（α-SiO2），有时含有微量高岭石，显示出弱的CL（主要是蓝色或深红色），解剖细节偶尔出现马赛克或斑片状保存，以及河流沉积物中湿树干的压力扭曲和随后的成岩重结晶的其他迹象。硅化初始阶段的推测二氧化硅来源是不稳定矿物的风化，主要是冲积层中的长石。在风成沉积物的木材中，检测到了莫干石与针铁矿的组合。根据我们的结果，我们认为茎在沙质或砾石河流沉积物中硅化，最常见的是长石砂和长石砂，这是相对温暖的气候和明显的降水季节性分布的指标。这种解释排除了主要由火山物质硅化的茎；它们的特点是物种多样性较高、生长地点附近硅化、矿物学杂项（通常具有非常丰富多彩的 CL 色调）以及 SiO2、蛋白石-CT 或绿柱石的亚稳态形式的存在。火山对硅化模式的影响不太受降水季节性或古气候本身的控制。
Petrographic imaging, in combination with qualitative and quantitative instrumental analyses of mineral mass, allow us to obtain material signatures of silicified plant stems that are relatively common in sediments of continental basins since the late Palaeozoic. These fossils can be found in their original strata but commonly have been removed from their environmental and stratigraphic context, redeposited, and scattered on the recent land surface after erosion of the parent rocks. Analytical data gathered from X-ray diffraction analysis, hot cathodoluminescence (CL) imaging and spectroscopy, electron microprobe analysis, Raman spectrometry, and polarised light microscopy serve to characterise material signatures of samples from basins in Brazil, Germany, the Czech Republic, Sultanate of Oman, Mongolia, Antarctica, France, and the USA. This collection includes silicified Pennsylvanian and Permian plant taxa (and a few from the Triassic) found in fluvial environments and sites influenced by volcanism with the purpose to discern fundamental material characteristics formed under particular environmental circumstances. Late Pennsylvanian and Permian silicified stems in fluvial rocks include the presence of well-crystalline quartz (α-SiO2), sometimes with a trace of kaolinite, showing weak CL (mostly blue or dark reddish), occasional mosaic or patchy preservation of anatomical details, and other signs of pressure distortion of wet trunks in fluvial deposits and subsequent diagenetic recrystallisation. The presumed silica source for the initial stage of silicification was weathering of labile minerals, mostly feldspars in the alluvium. In wood from aeolian deposits, moganite in combination with goethite was detected. Based on our results, we propose that the stems were silicified in sandy or gravelly fluvial deposits, most frequently in arkoses and arkosic sands, indicators of relatively warm climate with pronounced seasonal distribution of precipitation. Excluded from this interpretation are stems silicified primarily by volcanic material; these are distinguished by a higher species diversity, silicification close to the site of growth, miscellaneous mineralogy, usually with very colourful CL shades, and the presence of metastable forms of SiO2, opal-CT or moganite. This volcanic influence on silicification mode is less clearly controlled by seasonality of precipitation or palaeoclimate itself.