Distal alluvial deposits in a foreland basin setting―the Lower Freshwater Molasse (Lower Miocene), Switzerland : sedimentology, architecture and palaeosols
Distal alluvial deposits in a foreland basin setting―the Lower Freshwater Molasse (Lower Miocene), Switzerland : sedimentology, architecture and palaeosols
复制标题
前陆盆地环境中的远端冲积沉积物——瑞士下淡水磨拉石（下中新世）：沉积学、建筑和古土壤
DOI：
10.1111/j.1365-3091.1992.tb02136.x
复制
发表时间：
1992
期刊：
影响因子：
3.5
通讯作者：
B. Keller
中科院分区：
文献类型：
--
作者：
N. H. Platt;B. Keller
下淡水磨拉石（Untere Susswasser Molasse）在瑞士磨拉石盆地的广阔区域内出露。粗粒冲积扇砾岩主要分布在沿着阿尔卑斯山前缘的近端盆地区域。这些砾岩向北进入一个广泛的东北向排水曲流河系统的砂岩和泥岩，该系统平行于盆地轴线。通过对基底中新统（“阿基坦期”）露头、采石场暴露和钻孔的沉积学研究，对该远端冲积层序进行了详细的相分析。远端的阿奎坦尼亚是由独特的“建筑元素”，其特征是几何形状和沉积结构。每一个都可以被分配到一个特定的沉积环境：曲流带，堤坝，决口通道和扇，漫滩细粉和古土壤，和湖泊。
曲流带砂岩沉积在以推移质组分为主的混合负荷通道中。砂岩通常由2-15 m厚、150-1500 m宽的混合和局部堆叠的带状体组成。互层波纹状、层状和斑驳状细粒堤坝砂岩和粉砂岩形成透镜状包裹体，厚达3 m，宽达30-100 m。2-4 m厚、5-10 m宽的小规模决口河道砂岩横向进入米级、中至细粒决口砂岩席。罕见的层状湖相粉砂岩仅出现在盆地的东北部。洪泛平原泥岩和泥灰岩构成了该序列的剩余部分。这些显示了各种成土特征记录周期性古土壤发展。古土壤在形态和成熟度方面表现出强烈的变化，横向横跨洪泛平原和下游沿着盆地轴线，反映了与邻近冲积河道相关的沉积速率的局部变化以及沉降和洪泛平原排水的区域变化。
各种沉积体的组织和分布的分析允许重建的河流系统，并允许开发模型的沉积结构的下淡水磨拉石在研究区。将古土壤研究整合到一个明确的结构框架中，有助于识别区域相带，并可能有助于确定地下易出砂层序的位置。
The Lower Freshwater Molasse (Untere Susswasser Molasse) crops out over a wide area of the Swiss Molasse Basin. Coarse grained alluvial fan conglomerates dominate in proximal basin areas along the Alpine front. These conglomerates pass northwards into sandstones and mudstones of an extensive northeastward draining meandering river system which ran parallel to the basin axis. Sedimentological study of outcrops, quarry exposures and boreholes in the basal Miocene (‘Aquitanian‘) has permitted detailed facies analysis of this distal alluvial sequence. The distal Aquitanian is made up of distinct ‘architectural elements’characterized by their geometries and sedimentary structures. Each may be assigned to a particular depositional setting: meander belt, levees, crevasse channels and splays, overbank fines and palaeosols, and lacustrine.
Meander belt sandstones were deposited in mixed load channels with a dominant bedload component. Sandstones commonly comprise amalgamated and locally stacked ribbon bodies 2–15 m thick and 150–1500 m wide. Interbedded rippled, laminated and mottled fine grained levee sandstones and siltstones form lenticular packages up to 3 m thick and 30–100 m across. Small scale crevasse channel sandstones 2–4 m thick and 5–10 m across pass laterally into metre scale, medium to fine grained crevasse sandstone sheets. Rare laminated lacustrine siltstones occur only in the north-east part of the basin. Floodplain mudstones and marls make up the remainder of the succession. These display a variety of pedogenic features recording cyclical palaeosol development. Palaeosols show strong variations in morphology and maturity both laterally across the floodplain and downstream along the basin axis, reflecting local variation in aggradation rate associated with proximity to alluvial channel courses as well as regional variation in subsidence and floodplain drainage.
Analysis of the organization and distribution of the various sediment bodies permits reconstruction of the fluvial system and allows development of a model for the sedimentary architecture of the Lower Freshwater Molasse in the study area. Integration of palaeosol studies into a well defined architectural framework assists recognition of areal facies belts and may aid location of sand-prone sequences in the subsurface.