Gravelly beach ridges, which are formed solely by swash processes, may accurately reflect past wave conditions. The thickness (or height) of a gravelly beach ridge approximately equals the height of wave inundation, which is the sum of the surge and wave run‐up. Their ancient counterparts, if well‐preserved and identified, can be used to estimate palaeowave conditions, which can later be converted to palaeowind intensities based on wind–wave relationships. A technique is described for estimating the palaeowind speed in this paper, which is referred to as the gravelly beach‐ridge thickness technique. By comparing these estimates with instrumental wind records obtained at a modern lake, Qinghai Lake in north‐western China, the beach‐ridge thickness technique is shown to be useful for estimating the average wind speed (Vavg). When applying this method to ancient fetch‐limited basins, five parameters are necessary: (i) the thickness of the isolated gravelly beach ridge; (ii) the average depth of the water body; (iii) the palaeofetch; (iv) the angle between the palaeowind direction and the normal to the shoreline; and (v) the particle size. This technique was applied to an ancient example in the Eocene Dongying Depression, located in eastern China. The results indicate that the average wind speed of the northern wind ranged between 2·27 m sec−1 and 8·36 m sec−1 from 45·0 Ma to 42·0 Ma, and displayed a generally decreasing trend that included early strengthening followed by weakening and later strengthening during this period. The beach‐ridge thickness technique provides a new perspective on delineating palaeowind conditions and can be applied to ancient fetch‐limited basins with gravelly beach ridges worldwide. Generally, if a water body is sufficiently large (fetch exceeding 40 km), deep (average depth exceeding 10 m) and waves (or winds) are determined to approach the shoreline with high angles (angle of incidence <35°), then the calculation errors will be small to negligible.

No abstract

In the south bank of Qinghai Lake, numerous alluvial fans and coastal deposits have been formed. In terms of their developmental positions and relationships, the denudation system, depositional system, and transportation system consist of source-to-sink systems. Based on the field-investigation evidence and literature survey, it was confirmed that the developmental processes of these “source-to-sink” systems can be divided into three stages: the Early-Late Pleistocene stage, from 39 to 23 ka BP; Late Pleistocene-Early Holocene stage, from 39 to 10.7 ka BP; and modern stage. At the present time, these stages can still be identified as three levels of lake shore terraces. In the Late Pleistocene, the source-to-sink system indicates that the lake level was high, supply of clasts was sufficient, fan deltas had formed, and the lakeside plain continued to develop. At the end of the Late Pleistocene, with the sudden changes in global climate, the climate was dry and cold, and the lake level fell. At this time, the source-to-sink system showed that lake level was relatively low, supply of clasts was reduced, and transportation distance was longer; ancient sediments started to recycle in this system. Until modern times, alluvial fans in the south bank of Qinghai Lake have only rarely been developed, and the supply of clasts is primarily derived from the recirculation of paleo-shore sediments. Meanwhile, a large amount of sandy gravel beaches developed along the lake shore. By studying the multistage source-to-sink systems around modern lakes, the characteristics of the system in lake basins are enriched and provide an important analogy for researches of ancient lake basins.

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