Shell middens, sometimes in the form of mounds of great size, are a ubiquitous indicator of coastal settlement and exploitation of marine resources across the world. However, shell middens are relatively rare before the mid-Holocene because most palaeoshorelines before that time are now submerged by sea-level rise since the Last Glacial Maximum (LGM). Previously reported examples of underwater shell middens are almost unknown and of uncertain status, and it has generally been assumed that such deposits would not survive the destructive impact of sea-level rise or would be indistinguishable from natural shell deposits. Recently, two examples of underwater shell deposits have been independently discovered and verified as anthropogenic midden deposits – a Mesolithic shell midden on the island of Hjarnø in the Straits of Denmark, and a Middle to Late Archaic shell midden in the Econfina Channel of the Gulf of Mexico, Florida, USA. We report the comparative geoarchaeological analysis of these deposits, using a sedimentological approach to unravel their formation history and post-depositional transformation. Despite the differences in coastal geomorphology and geology, cultural context, molluscan taxonomy and preservation conditions between these sites, the results demonstrate similar sedimentological profiles that are distinctive of anthropogenic deposits, demonstrate their origin as subaerial deposits at the shore edge before inundation by sea-level rise, and show that these properties can be identified in sediment samples recovered from coring. These findings support arguments that such sites likely exist in greater numbers than previously assumed, that they can be identified from minimally invasive techniques without the need for extensive underwater excavation, and that they should be sought to fill critical gaps in the temporal and geographical record concerning Late Quaternary human use of coastal zones and marine resources.

贝壳中部的生物，有时以巨​​大的土丘的形式出现，是全世界沿海定居和海洋资源开发的普遍指示。但是，在全新世中期之前，壳中点相对很少见，因为自上一次冰河极盛期（LGM）以来，这段时间之前的大多数古海岸线现在都被海平面上升所淹没。先前报道的水下贝壳中点的实例几乎是未知的，并且状态不确定，并且通常认为这种沉积物将无法承受海平面上升的破坏性影响，或者与天然贝壳沉积物没有区别。最近，已经独立发现并验证了两个水下贝壳沉积物的例子，它们是人为的中层沉积物–丹麦海峡Hjarnø岛上的中石器壳中层，并在美国佛罗里达州墨西哥湾的埃菲纳河道中游至中古晚期壳。我们使用沉积学方法报告了这些矿床的比较地质考古学分析，以阐明它们的形成历史和沉积后的转化。尽管这些地点之间的海岸地貌和地质，文化背景，软体动物分类学和保存条件存在差异，但结果表明，类似的沉积特征与人为沉积物不同，它们的起源是沿岸边缘的地下沉积物，然后被海平面淹没。上升，表明在取自取芯的沉积物样品中可以识别出这些特性。这些发现支持这样的论点，即此类网站的存在可能比以前设想的要多，