ABSTRACT

While shorelines around playa lakes have traditionally played a key role for reconstructing late Quaternary megalakes in drylands, little attention has been given to recent shorelines associated with episodic filling events of modern ephemeral playa lakes such as Kati Thanda-Lake Eyre in central Australia. We here present results from geomorphic mapping around the playa margin of Lake Eyre North and interpret these data regarding timescales and drivers of shoreline processes. The diversity and distribution of landforms point to lithology and variations in wave energies as major controls on large-scale shoreline geomorphology. Our results suggest that the presence or absence of shoreline features is an incomplete and inaccurate indicator of past lake levels. Instead, wave-built landforms in ephemeral playa lake settings need to be considered threshold-related phenomena, with differences in frequency, magnitude and rate of water level change leading to vertically differing potential for wave-driven geomorphic activity and thus topographic differences between landforms. While mainland barriers probably best represent rare peak lake levels, barrier spits or islands dominantly form at lower and intermediate levels through lower energy longshore drift, thus providing a more complete record of playa flood events. Additionally, the lowest magnitude events offer potential for frequent wetting and drying along playa margins that effectively drives salt-related production and aeolian sediment deflation. Therefore, in contrast to marine or perennial lake shorelines, the complete range of wind-driven sedimentary processes needs to be coupled with an accurate understanding of lake-specific flooding frequency and magnitude towards a comprehensive model of shoreline evolution around playa lakes.

摘要

虽然普拉亚湖周围的海岸线传统上在旱地重建晚期第四纪巨型湖泊方面发挥了关键作用，但最近与现代短暂性普拉亚湖（如澳大利亚中部的 Kati Thanda-Lake Eyre）的间歇性填充事件相关的海岸线却很少受到关注。我们在这里展示了艾尔湖北部普拉亚边缘地貌测绘的结果，并解释了这些关于海岸线过程的时间尺度和驱动因素的数据。地貌的多样性和分布表明岩性和波浪能的变化是大尺度岸线地貌的主要控制因素。我们的研究结果表明，海岸线特征的存在与否是过去湖泊水位的不完整和不准确的指标。反而，在短暂的普拉亚湖环境中，波浪形成的地貌需要考虑与阈值相关的现象，水位变化的频率、幅度和速率的差异导致波浪驱动的地貌活动的潜力在垂直方向上不同，从而导致地貌之间的地形差异。虽然大陆屏障可能最能代表罕见的峰值湖水位，但屏障喷口或岛屿主要通过较低能量的沿岸漂移在较低和中等水平形成，从而提供更完整的普拉亚洪水事件记录。此外，最低震级事件提供了沿海滩边缘频繁润湿和干燥的潜力，有效地推动了与盐有关的生产和风成沉积物的通缩。因此，与海洋或常年湖泊海岸线相比，