Some studies have found that the distribution of low-salinity water within VMGRs is controlled by geological features, such as faults and low-permeability layers (for example, the Perth Basin 42) or palaeochannels (for example, East China Sea 40 or Bredasdorp Basin in South Africa 41). These examples of implied structural and stratigraphic controls on VMGRs attest to the fact that salinity distributions of VMGRs can be complex and that pervasive, wedge-shaped interpretations 28,30,32,35–37 may be oversimplified. This is borne out by recent borehole data off New Jersey 31, which revealed a complex geometry of vertically alternating freshwater–saltwater intervals that are difficult to correlate at distances of about 10 km.
At various sites around the world, pore-water profiles in low-permeability layers that start just below the sea floor and show a consistent vertical salinity decrease have been documented (Fig. 1 and Table 1). These are found on continental shelves that were exposed during the last glacial period (in the North Sea 43, Peru 44 and New Zealand 45), or where there used to be lakes when the sea level was lower (Black Sea 5 and Kau Bay, Indonesia 46). At these locations, they are probably indicators of former meteoric water circulation.
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