Anatomy of a submarine channel-levee : An example from Upper Cretaceous slope sediments, Rosario Formation, Baja California, Mexico
Anatomy of a submarine channel-levee : An example from Upper Cretaceous slope sediments, Rosario Formation, Baja California, Mexico
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DOI：
10.1016/j.marpetgeo.2007.01.003
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发表时间：
2007-06
影响因子：
4.2
通讯作者：
I. Kane;B. Kneller;M. Dykstra;A. Kassem;W. McCaffrey
中科院分区：
文献类型：
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作者：
I. Kane;B. Kneller;M. Dykstra;A. Kassem;W. McCaffrey
迄今为止，海底河道-堤坝的相结构模型主要来自地震数据、孤立岩心数据和有限的现场研究。我们报告了对墨西哥下加利福尼亚州罗萨里奥组内上白垩统海底河道-堤坝复合体的现场观测，提供了岩相和岩相分布的高分辨率数据，以及沿垂直于河道轴的横断面的堤坝沉积厚度衰减。在堤坝内，远离河道轴线，砂岩厚度和砂岩总体比例均按幂律减小。远离河道轴的沉积结构的空间变化是可预测的，并为沉积流态提供了重要的联系。在靠近河道的位置，无结构砂体、平行叠层、翻转波纹和波纹交叉叠层（包括爬升波纹交叉叠层）是常见的；在航道远端，饥饿的涟漪十分丰富。砂岩床厚度通常会增加堤坝序列内的地层，这被解释为表明浊流强度增加和/或同时河道底板加积减少了相对堤坝起伏。然而，在最接近河道的位置，砂岩层厚度随着高度而减小；结合相和古水流分析的证据，可以推断出堤顶的位置。随着距河道轴距离的增加，最厚的河床出现在较高的高度，利用这一证据，我们提出了堤坝生长和坝顶迁移的模型。对地貌分布的定量分析表明，Cruziana 和 Skolithos 地貌相的典型痕迹叠加在“正常”背景 Nereites 地貌相上，形成了一个“生物扰动锋面”，表明该地层接近河道。通过与现代峡谷和河道的类比，克鲁齐亚纳和斯科利索斯地貌与河道的关联可能归因于氧气和营养物质的富集以及造成这些地貌的生物体可能的浊流输送。
To date, facies architecture models of submarine channel–levees have largely been derived from seismic data, isolated core data and limited field studies. We report field observations of an Upper Cretaceous submarine channel–levee complex within the Rosario Formation, Baja California, Mexico, which provide high-resolution data of lithofacies and ichnofacies distribution, and levee depositional thickness decay along transects perpendicular to the channel axis. Within the levee, both sandstone thickness and the overall proportion of sandstone decrease according to a power law away from the channel axis. Spatial variation in sedimentary structures away from the channel axis is predictable and provides an important link to the depositional flow regime. In channel-proximal locations, structureless sands, parallel lamination, overturned ripples, and ripple cross-lamination (including climbing ripple cross-lamination) are common; in channel-distal localities starved ripples are abundant. Sandstone bed thickness generally increases up stratigraphy within the levee succession, which is interpreted to indicate increasing turbidity current magnitude and/or contemporaneous channel floor aggradation reducing relative levee relief. However, in the most channel-proximal location sandstone bed thickness decreases with height; combined with evidence from both facies and palaeocurrent analysis this allows the position of the levee crest to be inferred. The thickest beds occur at higher levels with increasing distance from the channel axis, using this evidence we present a model for levee growth and migration of the crest. Quantitative analysis of ichnofacies distribution reveals that traces typical of the Cruziana and Skolithos ichnofacies are superimposed over the ‘normal’ background Nereites ichnofacies, forming a ‘bioturbation front’ which is indicative of proximity to the channel. By analogy with modern canyons and channels, the association of Cruziana and Skolithos ichnofacies with the channel may be attributed to oxygen and nutrient enrichment and possible turbidity current transport of organisms responsible for these ichnofacies.