Neptunic dikes in Lower Jurassic sedimentary rocks of the Tethyan margins consist of internal sediment in cavities and submarine cement. The textures of the infilling sediment indicate downward and lateral movements of seawater beneath what was probably a deep-sea floor. This circulation probably was part of the hydrodynamic circulation that supplied hot, ore-bearing solutions to hydrothermal vents near a spreading-ridge system. This working hypothesis is being tested by stable-isotope studies now in progress.

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