Facies architecture, morphostratigraphy, and sedimentary evolution of a rapidly-infilled Holocene incised-valley estuary: The lower Manawatu valley, North Island New Zealand
Facies architecture, morphostratigraphy, and sedimentary evolution of a rapidly-infilled Holocene incised-valley estuary: The lower Manawatu valley, North Island New Zealand
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DOI：
10.1016/j.margeo.2017.06.011
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发表时间：
2017-08
期刊：
影响因子：
2.9
通讯作者：
Alastair J. H. Clement;I. Fuller;C. Sloss
中科院分区：
文献类型：
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作者：
Alastair J. H. Clement;I. Fuller;C. Sloss
从马纳瓦图河谷下游回收的水井测井和振动岩芯记录了这个淹没河流切谷河口在过去约 100 年的相结构、地貌地层和沉积演化。 30,000 年。马纳瓦图切谷河口在全新世期间迅速被填平，因此保留了全新世河口演化的完整记录。全新世填充物的底部以末次盛冰期低水位期间马纳瓦图河沉积的河流砾石为标志。砾石上覆盖着后退的海侵河流淤泥和粘土。由于海侵后期海平面上升加速，海侵河流单元仅存在于河谷下游。全新世早期，海平面上升将大量海侵海洋沉积物输送到谷口，形成了大型水下潮汐三角洲。在全新世中期，随着海平面在海平面高位期间稳定下来，这个三角洲不断吸积并随后演化形成了陆地屏障。河口中央盆地被海洋和河流沉积物迅速填充，因此缺乏演化较慢的河口所特有的泥相特征。从沙质中央盆地河口环境到上覆漫滩环境的转变极其迅速。在山谷的某些地方，过渡性河流湾头三角洲完全消失，而在大多数地方，它仅以非常薄的沉积物形式存在，表明这种快速的环境转变。河口中央盆地的填充速度非常快，仅用了 2000-2700 年。马纳瓦图河口进化历史的独特特征被解释为主要反映了古河口的快速填充，这是由海洋和河流来源向山谷提供高速率沉积物驱动的。
Water well logs and vibracores recovered from the lower Manawatu valley record the facies architecture, morphostratigraphy, and sedimentary evolution of this drowned river incised-valley estuary over the past c. 30,000 years. The Manawatu incised-valley estuary was rapidly infilled during the Holocene, and as a result preserves a complete record of Holocene estuary evolution. The base of the Holocene fill is marked by fluvial gravels deposited by the Manawatu River during the lowstand of the Last Glacial Maximum. The gravels are overlain by back-stepping transgressive fluvial silts and clays. The transgressive fluvial unit is present only in the lower reaches of the valley due to accelerated sea-level rise during the latter stages of the marine transgression. Large volumes of transgressive marine sediment were delivered to the mouth of the valley by rising sea-levels during the early Holocene, forming a large subaqueous tidal delta. This delta accreted and subsequently evolved to form a subaerial barrier in the mid-Holocene, as sea-levels stabilised during the sea-level highstand. The central basin of the estuary was rapidly infilled by marine and fluvial sediment, and consequently lacks the mud facies characteristic of less-rapidly-evolved estuaries. The transition from the sandy central basin estuarine environment to the overlying floodplain environment was extremely rapid. In some locations in the valley the transitional fluvial bay-head delta is missing completely, while in most locations it is present only as a very thin deposit, indicative of this rapid environmental transition. Infilling of the estuarine central basin was extremely rapid, taking only 2000–2700 years. The unique features of the Manawatu estuary's evolutionary history are interpreted to primarily reflect the rapid infilling of the palaeo-estuary driven by the high rates of sediment supplied to the valley from both marine and fluvial sources.