Sedimentology and depositional architecture of tufas deposited in stepped fluvial systems of changing slope: Lessons from the Quaternary Añamaza valley (Iberian Range, Spain)
Sedimentology and depositional architecture of tufas deposited in stepped fluvial systems of changing slope: Lessons from the Quaternary Añamaza valley (Iberian Range, Spain)
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沉积在不断变化的坡度的阶梯式河流系统中的凝灰岩的沉积学和沉积结构：第四纪阿纳马扎山谷（西班牙伊比利亚山脉）的经验教训
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发表时间：
2014
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影响因子：
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通讯作者：
C. Sancho
中科院分区：
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作者：
C. Arenas;M. Vázquez;G. Pardo;C. Sancho
Añamaza山谷的更新世和全新世凝灰岩（沿着山谷的阶梯状堆积，厚度达70 m）由几个被侵蚀面隔开的沉积阶段组成。八个组合的凝灰岩和相关的碳酸盐岩相，加上小的多成因碎屑相，代表了不同的河流和相关环境中发生的过程。基岩岩性和结构控制了沿着山谷的转折点的位置，并允许分离两个具有不同概念相模型的阶梯状延伸。缓坡模型包括由拦河坝梯级筑坝的大面积积水区域。在湖泊中，生物碎屑粉砂、砂和灰岩沿着植物碎屑和泥灰岩，在泥炭的地方形成沉积物。丰富的树干植丘构成了广阔的沼泽地。高边坡模型由近距离级联和拦河坝级联之间的较小筑坝区域组成，主要由苔藓植物丘和植物碎屑凝灰岩组成。一个突出的特点是广泛的陡峭的河段与植物碎屑和多源碎屑沉积物，和阶梯级联组成的叠层石和苔藓植物丘。在那里，陡峭的坡度限制了茎植物礁的保存，并有利于侵蚀。因此，每个模型的沉积物填充物的几何形状和厚度（楔形单元，由下游的梯级和拦河坝-梯级沉积物以及上游的筑坝和缓坡河道沉积物组成）不同。多层楔形体是高边坡模型的一个显著特征。这种陡峭表面上的初始断点几何形状和凝灰岩加积/加积比（例如，与流量变化有关）控制了瀑布或堰塞瀑布的生长方式，因此控制了上游沉积物的范围、厚度和垂直演变。碳酸盐相的沉积学属性和稳定同位素组成表明，更新世期间的降水/蒸发比比全新世期间更高，变化更大，与河流流量的总体减少一致。这种演变与温暖的条件相结合，在凝灰岩形成阶段占主导地位。这些结果可能有助于评估解释其他盆地的建筑模式，并强调凝灰岩作为过去水文和气候记录的重要性。
The Pleistocene and Holocene tufas of the Añamaza valley (stepped build‐ups, up to 70 m thick, along the valley) consist of several depositional stages separated by erosional surfaces. Eight associations of tufa and related carbonate facies, plus minor polygenic detrital facies, represent the processes that occurred in different fluvial and related environments. The bedrock lithology and structure controlled the location of the knickpoints along the valley and allowed separation of two stepped stretches with distinct conceptual facies models. The moderate‐slope model includes extensive standing‐water areas dammed by barrage‐cascades. In the lakes, bioclastic silts, sands and limestones along with phytoclastic and marly, at places peaty, sediments formed. Abundant stem phytoherms account for extensive palustrine areas. The high‐slope model consists of smaller dammed areas between close‐up cascades and barrage‐cascades, which were composed primarily of moss phytoherms and phytoclastic tufas. An outstanding feature is the extensive steep reach with phytoclastic and polygenic detrital sediments, and stepped cascades consisting of stromatolitic and moss phytoherms. There, the steep slope limited the preservation of stem phytoherms and favoured erosion. The geometry and thickness of the sedimentary fill (wedge‐shaped units composed of cascade and barrage‐cascade deposits downstream, and dammed and gentle‐sloped channel deposits upstream) are therefore different for each model. Multi‐storey wedges are a distinctive feature of the high‐slope model. The initial knickpoint geometry and the tufa aggradation/progradation ratio on such steep surfaces (for example, related to changes in discharge) controlled the growth style of the cascades or barrage‐cascades and, hence, the extent, thickness and vertical evolution of the upstream deposits. The sedimentological attributes and stable‐isotope composition of the carbonate facies suggest a higher and more variable precipitation/evaporation ratio during the Pleistocene than during the Holocene, consistent with an overall decrease in the river discharge. This evolution was coupled with warm conditions, which prevailed during the stages of tufa formation. These results may help to assess architectural patterns in interpreting other basins, and underscore the significance of tufas as records of past hydrology and climate.