Hydrology and sediments of a temperate estuary - Mallacoota Inlet, Victoria

Mallacoota Inlet is a drowned river valley that is almost cut off from the sea by a barrier-beach complex. Additionally, a flood-tidal delta chokes the mouth of the estuary. Except for fluvial sand in the upper reaches of the estuary, sandy sediments are restricted to the seaward end where hydrodynamic activity is greatest. Muds are confined to basinal and deep-channel environments; silts occur where fresh-water discharge contributes to water circulation, and clays where circulation is restricted. In the coarse fraction of the sediments, feldspar and mica contents are highest, and quartz and carbonate are lowest, where fresh-water discharge contributes. The clay mineral assemblage in the estuarine sediments is generally similar to that of the soil and stream sediments in the source area. Geochemical results show that Fe, V, Cr, Ni, Zn, Cu, and P2O5 levels are highest in stagnant areas where organic-rich clay prevails, whereas Mn and Ti are highest in silts where fluvial discharge is dominant and water circulates relatively freely. The results of the study suggest that the restricted basinal areas of the estuary are similar to fjords in terms of physical and chemical controls on sedimentation. The coastal barrier at Mallacoota was evidently formed by landward progradation during the Holocene, and overlies apparent remnants of a similar Pleistocene barrier. Many similar restricted estuaries exist along the south coast of New South Wales.

马拉库塔河口湾是一处溺谷，几乎被障壁滩复合体与海洋隔绝。此外，涨潮流三角洲堵塞了该河口湾的口门。除河口湾上游的河流砂外，砂质沉积物仅分布于水动力作用最强的向海端。泥质沉积物局限于盆地及深水道环境；粉砂见于淡水补给参与水循环的区域，黏土则分布于水循环受限的区域。在沉积物的粗粒组分中，当存在淡水补给时，长石与云母的含量达到最高，石英及碳酸盐含量则最低。该河口湾沉积物中的黏土矿物组合，整体上与物源区的土壤及河流沉积物相似。地球化学分析结果显示，铁（Fe）、钒（V）、铬（Cr）、镍（Ni）、锌（Zn）、铜（Cu）及五氧化二磷（P₂O₅）的含量在以富有机质黏土为主的滞流区最高；而锰（Mn）与钛（Ti）的含量则在以河流径流为主、水循环相对通畅的粉砂区域最高。本研究结果表明，该河口湾的受限盆地区域在沉积作用的物理与化学控制机制上，与峡湾相似。马拉库塔沿岸的障壁显然是在全新世期间向陆进积形成的，其上覆有疑似相似的更新世障壁遗迹。澳大利亚新南威尔士州南海岸沿线分布着众多类似的受限河口湾。