Facies Evolution of Holocene Estuaries and Deltas: A Large-sample Statistical Study from Australia

Selected geomorphic features and sedimentary facies were mapped in 283 of Australia's wave- and tide-dominated estuaries and deltas to quantitatively evaluate established evolutionary facies models that depict the evolution of estuaries into deltas during stable sea level conditions. While diagnostic facies for wave- and tide-dominated estuaries and deltas approximate those specified by the models, statistical analyses of the data also reveal two additional insights regarding the evolution of estuaries to deltas. First, there is an offshore shift in the locus of sand accumulation between tide-dominated estuaries and deltas, associated with the onset of delta development. Second, the mean surface area of intertidal environments (i.e., intertidal flats, mangroves/melaleuca, saltmarsh/salt flat facies) is greater in wave-dominated deltas than in wave-dominated estuaries. Tidal penetration associated with the river establishing a more direct and permanent connection to the sea during late-stage development presents a natural impediment to continued formation of an alluvial plain and full development of the 'classic' wave-dominated delta morphology. A notional evolutionary pathway for wave-dominated estuaries is developed from the distribution of facies that predicts the rate and susceptibility of geomorphic and habitat changes. The 'classic' deltaic geomorphology may be unattainable for wave-dominated systems, except those with significant terrigenous sediment inputs. Our study is the first published example of geomorphic and sedimentary data assembled from a large number of wave- and tide-dominated estuaries and deltas across an entire continent.

研究人员对澳大利亚283个浪控（wave-dominated）与潮控（tide-dominated）河口及三角洲开展地貌特征与沉积相（sedimentary facies）制图工作，以定量评估已有的演化沉积相模式——该模式阐述了稳定海平面条件下河口向三角洲的演化过程。尽管浪控、潮控河口及三角洲的标志性沉积相与该模式所界定的特征大体一致，但对该数据集的统计分析还揭示了两项关于河口向三角洲演化的新认知：其一，在潮控河口向三角洲的演化过程中，砂体堆积的区位向海迁移，这与三角洲发育的起始阶段密切相关；其二，浪控三角洲的潮间带环境（intertidal environments，即潮滩、红树林/白千层林、盐沼/盐滩相）平均表面积大于浪控河口。在发育后期阶段，河流与海洋建立更直接且持久的连通所引发的潮汐侵入，会对冲积平原的持续形成以及‘经典’浪控三角洲地貌的完全发育形成天然阻碍。研究人员基于沉积相分布构建了浪控河口的概念性演化路径，该路径可预测地貌与生境变化的速率及易感性。对于浪控系统而言，‘经典’三角洲地貌或难以实现，除非其拥有充足的陆源沉积物输入。本研究是全球范围内首次公开报道的、对整个大陆范围内大量浪控与潮控河口及三角洲的地貌与沉积数据进行系统性整合的研究案例。