Basin‐wide turbidites in a Miocene, over‐supplied deep‐sea plain: a geometrical analysis
Basin‐wide turbidites in a Miocene, over‐supplied deep‐sea plain: a geometrical analysis
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中新世供应过剩的深海平原中的盆地范围浊积岩：几何分析
DOI：
10.1111/j.1365-3091.1980.tb01177.x
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发表时间：
1980
期刊：
影响因子：
3.5
通讯作者：
Emidio Valmori
中科院分区：
文献类型：
--
作者：
F. Lucchi;Emidio Valmori
在面积为123 × 27 km的Marnoso-arenacea组（中新世，北方亚平宁山脉）盆地平原沉积物中记录了18个地层剖面，平均厚度为200 m。浊积岩占相组合的80-90%，其余为半长岩。薄层浊积岩和厚层浊积岩之间有一个大约40 cm的统计分界线;大多数突出的层（厚度> 1 m）被认为是巨浊积岩。参照主要的供给-分散系统（NW至SE），盆地平原可通过以下参数轴向细分为近端、中间和远端段：砂体含量、浊积岩中的砂/页岩比、各层和组分层的平均厚度以及厚层的频率。近40%的厚层浊积岩可追溯到整个研究区。这些盆地范围内的沉积物构成了盆地充填物的主体。几何重建表明，一些砂岩层从近端平原或邻近的扇区向下流动，而另一些则是向上流动的薄砂，表明砂体经过扇。泥岩层一般向平原的末端和边缘延伸，表明浊积岩泥除了通常绕过扇外，还受到平原积水的影响。薄层浊积岩具有低砂/页岩比或完全为泥质，代表外扇（叶和边缘沉积）砂质浊积岩的尾部或延伸至大部分或整个平原的岩片。砂岩瓣从扇体向平原推进40-50 km，在10-20 km的过渡带逐渐变薄和变浅。它们的内部几何结构显示出简单和复杂的生长模式：端员被定义为亲合和加积。个别浊积岩的原始长度，宽度和体积的估计强烈表明，流量通常被限制和偏转的盆地斜坡，无论源位置。因此，盆地沉积物的特点是厚度和体积大，泥质和细砂丰富，厚度和粒度的横向梯度极低（但在两侧附近迅速楔入）。盆地平原开发的一部分，一个细长的，供过于求的盆地与“高效”，可能三角洲喂养，分散系统。
Eighteen stratigraphic sections, 200 m thick on average, were logged in basin plain deposits of the Marnoso-arenacea Formation (Miocene, northern Apennines) over an area of 123 × 27 km. Turbidites form 80–90% of the facies association, hemipelagites the remainder. Thin and thick-bedded turbidites are separated by an approximate statistical boundary at 40 cm; most prominent beds (> 1 m thick) are qualified as megaturbidites. With reference to the main supply-dispersal system (NW to SE), the basin plain can be axially subdivided into proximal, intermediate and distal segments by means of the following parameters: bulk sand content, sand/shale ratio in turbidites, mean thickness of individual layers and component beds, and frequency of thick layers. Almost 40% of thick-bedded turbidites can be traced over the whole study area. These basin-wide deposits form the bulk of the basin fill. Geometrical reconstruction shows that some sandstone beds taper downcurrent from the proximal plain or the adjacent fan area while others thin upcurrent suggesting sand by pass of the fan. Mudstone beds in general thicken towards the end and the margins of the plain indicating that turbidite mud, besides bypassing the fan as a rule, was affected by ponding in the plain. Thin-bedded turbidites have a low sand/shale ratio or are completely muddy representing either tails of sandier turbidites of the outer fan (lobe and fringe deposits) or sheets extending to a great part of or to the whole plain. Sandstone lobes advanced from fans into the plain for 40–50 km gradually thinning and shaling out over a transitional zone of 10–20 km. Their internal geometry shows simple and complex growth patterns: end members are defined as progradational and aggradational. Estimates of original length, width and volume of individual turbidites strongly suggest that flows were usually confined and deflected by basin slopes regardless of source location. Basinal deposits are thus characterized by great thickness and volume, abundance of mud and fine sand, extremely low lateral gradients of thickness and grain size (but rapid wedging near the sides). The basin plain developed as a part of an elongated, oversupplied basin with a ‘highly efficient’, probably delta-fed, dispersal system.