Sedimentology of a wet, pre-vegetation floodplain assemblage
Sedimentology of a wet, pre-vegetation floodplain assemblage
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DOI：
10.1111/j.1365-3091.2011.01291.x
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发表时间：
2012-04-01
期刊：
影响因子：
3.5
通讯作者：
Zaniewski, Kamil
中科院分区：
文献类型：
--
作者：
Fralick, Philip;Zaniewski, Kamil
对在重要的陆地大型植物植被之前运行的河流系统的描述集中于评估植物进化对河道样式的影响；这可能部分是由于在这些时代的河流组合中缺乏发育良好的泛滥平原演替。这项研究描述了湿润的植被前泛滥平原沉积和过程，这些沉积和过程是通过一个广泛的1.4Ga三角洲顶部河道泛滥平原组合的连续钻芯观察和推断出来的，该组合构成了加拿大安大略省Sibley组的一部分。陆上沉积以闪光、波状和透镜状层理、细粒砂岩、粉砂岩和泥岩为主，发育丰富的泥岩小碎屑。这些单元的软泥沙变形普遍存在，其中加载和注水特征最为突出。较厚的中颗粒砂岩层代表裂隙展布，其上部通常有发育不良的原生土壤。泛滥平原池塘中沉积有波浪起伏的层状沉积物，很少含有撕裂碎屑和软沉积物变形。这些沉积物与植被后泛滥平原沉积的不同之处在于：(I)在没有根状生物扰动的情况下更好地保存了分层；(Ii)泛滥平原上的波纹沙子占主导地位，可能是由于缺乏植被诱导的障碍物；(Iii)大规模产生了小型的层内碎屑；(Iv)干燥裂隙充填物由PED和局部派生的内部碎屑组成，可能在降雨事件期间在Horton陆上流动期间输送；(V)水下沉积中普遍存在的软沉积物变形特征；以及(Vi)在泛滥平原池塘中积累的层状、通常被氧化的沉积物。这些属性是缺乏大型植物植被的直接结果，并产生了与目前在类似气候环境下形成的明显不同的泛滥平原组合。
Descriptions of fluvial systems operating prior to significant terrestrial macrophyte vegetation have concentrated on assessing the impact of plant evolution on channel style; this is probably in part due to the scarcity of well-developed floodplain successions in fluvial assemblages of these ages. This study describes wet, pre-vegetation floodplain deposits and processes observed and inferred from a continuous succession of drill core through an extensive, 1.4 Ga, delta-top channelfloodplain assemblage forming a portion of the Sibley Group, Ontario, Canada. Sub-aerial deposits are dominated by flaser, wavy and lenticular bedded, fine-grained sandstones, siltstones and mudstones, with abundant small mudstone rip-up clasts. Soft-sediment deformation of these units is ubiquitous, with loading and injection features being the most prominent. Thicker medium-grained sandstone beds, representing crevasse splays, commonly have poorly developed protosols in their upper portions. Well-laminated sediments with wave ripples, and only rarely containing rip-up clasts and soft-sediment deformation, were deposited in floodplain ponds. These deposits differ from post-vegetation floodplain sediments in having: (i) better preservation of layering without rootlet bioturbation; (ii) dominance of rippled sand on the floodplain, probably due to lack of vegetation-induced baffling; (iii) large-scale generation of small, intraformational clasts; (iv) desiccation crack fills consisting of peds and locally derived intraclasts, probably delivered during Horton overland flow during rainfall events; (v) ubiquitous soft-sediment deformation features in sub-aerial deposits; and (vi) well-laminated, commonly oxidized sediment that accumulated in floodplain ponds. These attributes are the direct result of the lack of macrophyte vegetation, and produce floodplain assemblages that are distinctly different from those presently forming in similar climatic settings.