Sentence:  A special character of these mounds [the Kess-Kess carbonate mud mounds] is the numerous <WSD>Neptunian</WSD> dikes. These are fracture systems, which have been filled with other sediments and minerals. It is suspected that these dikes represent spring conduits (seeps) during the formation of the mounds, and that the seeping fluids were of a hydrothermal nature [...]. 
Meaning of the word marked with <WSD> tags:  Formed by the action of water.