US Geological Survey, Mail Stop 431, Reston, Virginia 20192, USA.
Nature. 2013 Nov 14;503(7475):252-6. doi: 10.1038/nature12714.
High-salinity groundwater more than 1,000 metres deep in the Atlantic coastal plain of the USA has been documented in several locations, most recently within the 35-million-year-old Chesapeake Bay impact crater. Suggestions for the origin of increased salinity in the crater have included evaporite dissolution, osmosis and evaporation from heating associated with the bolide impact. Here we present chemical, isotopic and physical evidence that together indicate that groundwater in the Chesapeake crater is remnant Early Cretaceous North Atlantic (ECNA) sea water. We find that the sea water is probably 100-145 million years old and that it has an average salinity of about 70 per mil, which is twice that of modern sea water and consistent with the nearly closed ECNA basin. Previous evidence for temperature and salinity levels of ancient oceans have been estimated indirectly from geochemical, isotopic and palaeontological analyses of solid materials in deep sediment cores. In contrast, our study identifies ancient sea water in situ and provides a direct estimate of its age and salinity. Moreover, we suggest that it is likely that remnants of ECNA sea water persist in deep sediments at many locations along the Atlantic margin.
美国大西洋沿海平原的深井高盐度地下水在多个地点都有记录，最近在 3500 万年前的切萨皮克湾撞击坑中也有记录。对于撞击坑中盐度增加的原因，有观点认为是蒸发盐溶解、渗透和与撞击体加热相关的蒸发所致。在这里，我们提出了化学、同位素和物理证据，共同表明切萨皮克撞击坑中的地下水是残留的早白垩世北大西洋（ECNA）海水。我们发现，海水可能有 1 亿到 1.45 亿年的历史，平均盐度约为 70‰，是现代海水的两倍，与几乎封闭的 ECNA 盆地一致。以前对古代海洋温度和盐度水平的证据是通过对深沉积岩芯中固体物质的地球化学、同位素和古生物学分析间接估计的。相比之下，我们的研究在原地确定了古代海水，并提供了其年龄和盐度的直接估计。此外，我们认为，在大西洋边缘的许多地方，ECNA 海水的残留很可能存在于深部沉积物中。
