Amazon fluid mud impact on tide- and wave-dominated Pliocene lobes of the Orinoco Delta
Amazon fluid mud impact on tide- and wave-dominated Pliocene lobes of the Orinoco Delta
复制标题
DOI：
10.1016/j.margeo.2018.08.009
复制
发表时间：
2018-12
期刊：
影响因子：
2.9
通讯作者：
Yang Peng;R. Steel;C. Olariu
中科院分区：
文献类型：
--
作者：
Yang Peng;R. Steel;C. Olariu
现代奥里诺科河三角洲是世界上最大的沿岸（沿岸的）泥浆分散系统的主要汇;它每年从亚马逊河三角洲接收约108吨。这些巨大的亚马逊泥量的古奥里诺科河三角洲继承的影响，现在调查的第一次。在上新世奥里诺科河三角洲沉积（下Morne L 'Enfer，Manzanilla和Mayaro组特立尼达）的露头中保存了丰富的流体-泥浆沉积，具有不同的风格，在潮汐为主，潮汐为主和波浪影响，风暴波浪为主的三角洲瓣。下Morne L 'Enfer组桑迪准层序（10-20 m厚）中的流体-泥浆沉积物从薄层合并形成泥底组（最大4 cm）或覆盖在下部涟漪纹层上，到上部的厚层（最大10 cm），其顶部偶尔有变形和负载结构。Manzanilla组准层序（30-40 m厚）表现出由粗到细向上（CUFU）的相序列，流体-泥浆沉积主要位于准层序的中上部，靠近单元CU和FU部分之间的过渡。大多数流体-泥层与双向、水流波纹砂岩互层，而少数泥层与侵蚀基砂岩有关，具有小规模的swaley地层和双向对称波纹。Mayaro组准层序（5-15 m厚）的特征是流体-泥浆层段交替，丘状交叉分层砂岩（HCS）向上进入混合的swaley交叉分层（SCS）砂岩。流体-泥浆层段具有平坦或不规则的顶部，偶尔被混有流体-泥浆碎屑的SCS砂岩覆盖。在潮汐和波浪主导的地层中，都有非常厚（1-1.5 m）的流体-泥浆层段，这些可能是类似于目前沿着现代亚马逊-奥里诺科河海岸迁移的泥滩的大型泥浆床型。露头分析强烈表明，流体泥银行，因为他们接近奥里诺科河三角洲前缘地区，根据三角洲前缘叶是否波或潮汐为主的不同处理。潮汐主导的三角洲瓣倾向于将泥浆困在海岸线附近和水深< 10 m的水下三角洲前缘平台上，只有少量泥浆逃逸到海上。相比之下，风暴波为主的三角洲叶有一个更动态的影响，即将到来的泥滩。在浅水中积累的泥浆往往会被侵蚀并重新沉积到风暴波底附近的深水中（15-50 m水深）。上新世亚马逊泥的体积沿着最内侧的陆架搬运并到达奥里诺科河三角洲可能受到上新世冰川-海平面高幅度波动的影响。在海平面下降和低水位期间，增加的亚马逊泥浆量将绕过深水，从而减少泥浆量漂流并融入奥里诺科河三角洲前缘。相比之下，海平面上升和高水位期将促进亚马逊泥量的增加，无论是在货架上和奥里诺科河上，类似于全新世和现代泥系统。
The modern Orinoco Delta is a major sink for the world's largest alongshore (littoral) mud dispersal system; it receives some 108tons/yr from the Amazon river delta. The influence of these huge volumes of Amazon mud on the paleo-Orinoco Delta succession is now investigated for the first time. Abundant fluid-mud deposits are preserved in outcrops from the Pliocene Orinoco Delta deposits (Lower Morne L'Enfer, Manzanilla and Mayaro formations on Trinidad) with different styles in tide-dominated, in tide-dominated and wave-influenced, and in storm wave-dominated delta lobes. Fluid-mud deposits in sandy parasequences (10–20 m thick) of the Lower Morne L'Enfer Formation change from thin layers amalgamating to form mud bedsets (up to 4 cm) or draping across ripple laminae in the lower part, to thick layers (up to 10 cm) occasionally with deformed and load structures at their top, in the upper part. The Manzanilla Formation parasequences (30–40 m thick) exhibit coarsening-to-fining-upward (CUFU) facies successions with fluid-mud deposits located mainly in the middle to upper parts of the parasequences, near the transition between the CU and FU parts of the units. Most of the fluid-mud layers are interbedded with bi-directional, current rippled-sandstones, whereas minor mud layers are associated with erosion-based sandstones with small-scale swaley strata and bi-directional symmetrical ripples. The Mayaro Formation parasequences (5–15 m thick) are characterized by alternating fluid-mud intervals and sets of hummocky cross-stratified sandstones (HCS) passing upward into amalgamated swaley cross-stratified (SCS) sandstones. The fluid-mud intervals have flat or irregular tops occasionally overlain by amalgamated SCS sandstones with fluid-mud clasts.Very thick (1–1.5 m) fluid-mud intervals occur in places in both tide- and wave-dominated strata and these are probably large muddy bedforms similar to mud banks that migrate currently along the modern Amazon-Orinoco coast. The outcrop analysis strongly suggests that the fluid-mud banks, as they approached the Orinoco delta-front area, were handled differently depending on whether the delta-front lobes were wave- or tide-dominated. Tide-dominated delta lobes tended to trap the muds near the shoreline and on the subaqueous delta-front platform in water depth < 10 m with only minor volumes escaping offshore. In contrast, storm wave-dominated delta lobes had a more dynamic impact on the approaching mudbanks. Mud accumulated in the shallow water tend to be eroded and re-deposited into deeper water near the storm wave base (15–50 m water depth).The volumes of Pliocene Amazon mud transported along the innermost shelf and arriving on the Orinoco Delta were likely influenced by high-amplitude, Pliocene glacio-eustatic sea level fluctuations. During sea-level fall and lowstand periods, increased volumes of Amazon mud would have bypassed to the deep water and thus decreased mud volumes drifted and became incorporated in the Orinoco delta front. In contrast, sea-level rise and highstand periods would have promoted increased volumes of Amazon mud both on the shelf and onto the Orinoco, similar to the Holocene and modern muddy system.