海滩也缺乏砂-砾过渡粒级的沉积物

The grain size gap at gravel-sand transition in beach sediments

沉积物的粒度是最重要的沉积物参数之一,在河床中,表层沉积物缺乏砂–砾过渡粒级(即1~10 mm)的沉积物,被称为Grain size gap,得到广泛关注。海滩沉积物是否也是如此,是一个基本而又未知的问题。本文分析了中外228处海滩共456个表层沉积物平均粒径数据,发现海滩大概率或是平均粒径几十毫米的砾石滩,或是平均粒径几百微米的砂滩,也缺乏砂–砾过渡粒级沉积物,其粒度范围是−3.5~−1ϕ(2~11 mm),这一结果和河床的情况基本相同。造成砂–砾过渡粒级缺乏的原因应从物源、颗粒磨损和分选以及广义的物质收支分析中去寻找。

The grain size of sediments is one of the most crucial sedimentary parameters.In riverbeds,the surface sediments often lack the transitional grain sizes between sand and gravel(i.e.,1~10 mm),a phenomenon widely referred to as the"grain size gap."Whether this is also the case for beach sediments remains a fundamental yet unexplored question.Through the analysis of mean grain size data from 228 beach locations globally,we revealed that beaches also exhibit a grain size gap of sand-gravel transition,ranging from−3.5ϕto−1ϕ(2 to 11 mm).Beaches have a high probability of being either gravel beaches with mean sediment diameters of several tens of millimeter,or sand beaches with mean sediment diameters of several hundred micrometers,mirroring the findings in riverbeds.Potential reasons for this absence include particle abrasion and selective transportation.