Climate, sea level and tectonic controls on sediment discharge from the Sepik River, Papua New Guinea during the Mid- to Late Pleistocene
Climate, sea level and tectonic controls on sediment discharge from the Sepik River, Papua New Guinea during the Mid- to Late Pleistocene
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DOI：
10.1016/j.margeo.2019.05.013
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发表时间：
2019-09
期刊：
影响因子：
2.9
通讯作者：
I. Aiello;S. Bova;A. Holbourn;D. Kulhanek;A. Ravelo;Y. Rosenthal
中科院分区：
文献类型：
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作者：
I. Aiello;S. Bova;A. Holbourn;D. Kulhanek;A. Ravelo;Y. Rosenthal
在流经印度尼西亚群岛山区岛屿的河流中，巴布亚新几内亚的塞皮克河是世界海洋溶质和颗粒物质的最大贡献者。在国际海洋发现计划（IODP）第363次考察期间钻探的U1484和U1485站点提供了巴布亚新几内亚北方大陆边缘主要是硅质岩斜坡沉积的连续、约555 kyr长的高分辨率记录，就在塞皮克河口附近。沉积学分析的基础上相结合的涂抹幻灯片岩相学，粒度分析，高分辨率的物理特性跟踪数据和可视化的核心描述，提供了一个前所未有的机会，调查整个变化的气候和海平面条件下，这条主要的热带河流的演变在中更新世至晚更新世。站点U1484和U1485的沉积物记录显示了一个戏剧性的岩性变化在~ 370 ka：最古老的沉积物主要是远洋泥，这表明粗颗粒的陆源排放从河流排水新几内亚高地（包括一个“原始”塞皮克河）被捕获之前到达海洋，当塞皮克河流域是一个陆表海。粗粒，质量重力（主要是混合）流的发生后~370 ka的陆表海成为一个更受限制的，浅水到非海洋盆地，可能是由于盆地填充和当地海岸范围的隆起。在过去的三个冰期-间冰期循环（约300 kyr）中，这个浅内陆盆地受到全球海平面变化的强烈影响：在海平面低水位期间，塞皮克河切入较老的沉积物，并进一步排放到浅海大陆边缘，促进质量重力流。冰消后最极端的高位期间大陆边缘的远洋泥浆沉积表明塞皮克盆地恢复到浅海条件，并且河口重新定位到进一步内陆，远离大陆架和IODP地点的位置。这也表明，在这些极端高水位期间，陆源通量的变化不仅受水文循环强度的控制，而且全球海平面变化也影响沉积物的沉积。该层序被几个大型颗粒流沉积物所打断，这些沉积物在U1484和U1485站点穿时发生，并与~280 ka和~140 ka之间的构造活动加强期有关。这些质量-重力沉积物的沉积学特征以及它们在不同地点之间缺乏相关性被解释为是由大陆边缘（包括在这些地点以北约50 km的Yalingi峡谷区域）的局部和区域故障造成的沿沿着边缘平行的、断层控制的通道的渠化流造成的，近年来在该区域也发生了大型海啸。磁化率和自然伽马辐射（代理%砂和%粘土含量，分别）的时间序列分析表明，河流流量调制的轨道频率（包括降水量尺度周期），这表明降水和河流流量不仅与岁差驱动的热带辐合带的平均位置的变化，但也高纬度气候变化。
Amongst the rivers draining the mountainous islands of the Indonesian Archipelago, the Sepik River of Papua New Guinea is the largest contributor of solute and particulate material to the world ocean. Sites U1484 and U1485, drilled during International Ocean Discovery Program (IODP) Expedition 363 provide a continuous, ~555 kyr long, high-resolution record of mainly siliciclastic slope sedimentation on the northern continental margin of PNG, just offshore the mouth of the Sepik River. Sedimentological analysis, based on a combination of smear slide petrography, particle size analysis, high-resolution physical properties track data and visual core description, offers an unprecedented opportunity to investigate the evolution of this major tropical river throughout changing climate and sea-level conditions during the mid- to late Pleistocene. The Sites U1484 and U1485 sediment records exhibit a dramatic lithologic change at ~ 370 ka: the oldest deposits are dominated by pelagic mud, suggesting that the coarser-grained terrigenous discharge from rivers draining the New Guinea Highlands (including a “proto” Sepik River) was captured before reaching the ocean, when the Sepik River basin was an epicontinental sea. The occurrence of coarser-grained, mass-gravity (mainly hybrid) flows after ~370 ka suggests that the epicontinental sea became a more restricted, shallow-water to nonmarine basin, probably due to both basin infilling and the uplift of local coastal ranges. During the last three glacial-interglacial cycles (~300 kyr), this shallow inland basin was strongly affected by global variations in sea level: during sea level lowstands, the Sepik River cut into older sediments and discharged further offshore onto the shallow continental margins, promoting mass-gravity flows. Pelagic mud deposition on the continental margin during the most extreme highstands following deglaciations suggests a return to shallow marine conditions in the Sepik Basin and repositioning of the river mouth further inland, away from the shelf and from the location of the IODP sites. This also indicates that variations in terrigenous fluxes during these extreme highstands were not solely controlled by the intensity of the hydrological cycle and that global sea level variations also influenced sediment deposition. The sequence is interrupted by several massive grain flow deposits, occurring diachronously at Sites U1484 and U1485 and related to a period of intensified tectonic activity between ~280 ka and ~140 ka. The sedimentologic characteristics of these mass-gravity deposits and their lack of correlation between sites are interpreted as resulting from channelized flows along margin-parallel, fault-controlled channels caused by local and regional failures of the continental margins including the area of the Yalingi Canyon, ~50 km north of the sites, where large tsunamigenic events have also occurred in recent years. Time series analyses of magnetic susceptibility and natural gamma radiation (proxies for %sand and %clay content, respectively) indicate that river discharge fluxes were modulated at orbital frequencies (including obliquity-scale cycles), which suggests that precipitation and river discharge were not only linked to precessionally driven shifts in the mean position of the Intertropical Convergence Zone, but also to high-latitude climate change.