Water activity (A w ) is one of the physicochemical properties that may influence microbial activity in deep subseafloor environments; however, A w for subseafloor sediments has never been examined, even at shallow depths. This study investigated A w data obtained from core samples collected during Integrated Ocean Drilling Program Expedition 337 in the deep-water coal-bearing basin off Shimokita, Japan. A w did not show any depth dependence and was relatively low in coal-bearing layers. A w at depths of 0-2466 meters below seafloor ranged from 0.95 to 0.98, which is quite high and well suited to sustaining microorganisms. A w for sedimentary rocks was less affected by lithology and porosity than it was by the NaCl concentration and degree of fluid saturation. In addition, the A w measurements performed in this study yielded results that corresponded closely with values estimated using Raoult's law and interstitial water chemistry. It therefore appears that A w for deep-marine sediments is strongly affected by pore water chemistry. The low A w anomaly in the coalbed unit is considered to be due to contamination by drilling mud and fluid into core samples.
This note presents mesoscopic and microscopic features of neptunian dykes of calcareous sediments hosted by Late Pliocene basaltic lavas of the Uegusukudake Formation of Kumejima Island, the Ryukyus. The dykes, to cm wide, consist mainly of micritic limestone rich in varied skeletal debris of a shallow marine affinity, with a subhorizontal depositional surface. Two dominant strikes of the dykes, NE and NW, are parallel and perpendicular to the modern central axis of the Okinawa Trough, respectively. The youngest foraminifera in the dykes were identified as Globorotalia inflata, of which first appearance is in Late Pliocene. Available K-Ar age data of the basaltic lava and Sr age data of the overlying Ryukyu Limestones indicate that infilling rapidly occurred during a period from. Ma to. Ma. These date are synthesized as follows. Open fractures formed due to rifting in an extensional regime, and were filled with shallow-marine calcareous sediments to form neptunian dykes under the sea. This rifting is postulated to have been related to the reactivation of rifting at the Okinawa Trough.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.