抄録
Chlorine, bromine and iodine contents were determined by neutron activation analysis on outcrop and borehole samples of the Tertiary marine and fresh-water mudstones in order to investigate the possibility of these elements as indicators for estimating the depositional paleoenvironment. The leachable halogen contents by aqueous and acidic solutions were also determined experimentally to clarify the mode of occurrence of these elements in marine mudstones. It is concluded that chlorine is not suitable as the geochemical indicator for distinguishing the marine mudstones from the fresh-water ones because the element is easily leachable from marine mudstones by the action of the meteoric or circulating waters near the earth's surface. On the other hand, bromine and iodine are considered to be promising as the indicators, since these elements are less soluble in water than chlorine. However, these elemental contents of the outcrop marine mudstones are in the same level as those of the borehole fresh-water ones. The fact implies that these elements are still questionable as the paleosalinity indicators for the depositional environment.
