Unravelling source‐to‐sink relationships of sediment in coastal regions can be particularly challenging due to a variety of transport directions and mixing within varying local environments in response to sea level fluctuations. Post‐glacial sea level rise in the Holocene has resulted in the flooding of former continental margins, locally leading to the separation of islands such as Rottnest in southwest Australia. Rottnest lies approximately 20 km offshore from the mouth of the Swan River, one of the largest permanent river systems across thousands of kilometres of west Australian coastline. In this contribution, we investigate the size, U–Pb age distribution and α‐dose values of detrital zircon grains within 13 sand samples collected from three upstream tributaries that drain the Archean Yilgarn Craton, the Swan River estuary, offshore waters surrounding Rottnest Island and modern beaches. We explore sediment derivation, storage and mixing on this passive margin. Carbonate–silicate sands of the region contain detrital zircon with Archean, Mesoproterozoic and Cambro‐Neoproterozoic age modes, reflecting regional crystalline basement. Eo‐ to Paleoarchean zircon grains, including a previously enigmatic >3500 Ma component, are traced from offshore into the estuary, and specifically the Avon River tributary. Detrital mixing models imply an overall fluvial contribution to the estuary and offshore systems of up to 50–65%. By contrast, modern beach samples are dominated by Swan Coastal Plain recycled sediment of up to 96%. The α‐dose values of the prominent 3300–3150 Ma age component suggest more efficient fluvial discharge in the Paleo‐Swan River than in more recent times. Modern estuary samples have lower average and progressively lower downstream zircon α‐dose values, consistent with prolonged chemical and physical reworking and loss of metamict grains with transport distance in the river. We conclude that fluvial drainage networks distribute a locally persistent catchment signal whilst coastal plains in tectonically quiescent settings appear characterized by sediment reprocessing and mixed provenance.

中文翻译：

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当河流与大海交汇时：长寿河口的运输和来源


由于不同的运输方向以及响应海平面波动而在不同的当地环境中混合，因此解开沿海地区沉积物的源-汇关系可能特别具有挑战性。全新世冰期后海平面上升导致前大陆边缘被洪水淹没，局部导致澳大利亚西南部的罗特尼斯等岛屿分离。罗特尼斯位于天鹅河河口约 20 公里的离岸处，天鹅河是横跨澳大利亚西部数千公里海岸线的最大永久性河流系统之一。在这篇文章中，我们调查了从太古宙伊尔加恩克拉通、天鹅河河口、罗特尼斯岛周围的近海水域和现代海滩的三条上游支流收集的 13 个沙子样本中碎屑锆石颗粒的大小、U-Pb 年龄分布和 α 剂量值。我们探索了这个被动边缘的沉积物衍生、储存和混合。该地区的碳酸盐-硅酸盐砂包含具有太古代、中元古代和寒布罗-新元古代年龄模式的碎屑锆石，反映了区域结晶基底。从Eo到古太古宙的锆石颗粒，包括以前神秘的>3500 马成分，从近海追溯到河口，特别是埃文河支流。碎屑混合模型意味着河流对河口和近海系统的总体贡献高达 50-65%。相比之下，现代海滩样本以高达 96% 的 Swan Coastal Plain 回收沉积物为主。突出的 3300-3150 马年龄成分的 α 剂量值表明，Paleo-Swan River 的河流排放比近代更有效。 现代河口样品的平均锆石α剂量值较低，下游锆石剂量值逐渐降低，这与长时间的化学和物理返工以及随着河流中运输距离而损失的晶粒一致。我们得出结论，河流排水网络分布局部持久的集水区信号，而构造静止环境中的沿海平原似乎以沉积物再加工和混合来源为特征。