Browsing by Author "Cramm, Margaret"

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    In-situ mechanical weakness of subducting sediments beneath a plate boundary décollement in the Nankai Trough
    (2018-11-03) Hamada, Yohei; Hirose, Takehiro; Ijiri, Akira; Yamada, Yasuhiro; Sanada, Yoshinori; Saito, Saneatsu; Sakurai, Noriaki; Sugihara, Takamitsu; Yokoyama, Takahiro; Saruhashi, Tomokazu; Hoshino, Tatsuhiko; Kamiya, Nana; Bowden, Stephen; Cramm, Margaret; Henkel, Susann; Homola, Kira; Imachi, Hiroyuki; Kaneko, Masanori; Lagostina, Lorenzo; Manners, Hayley; McClelland, Harry-Luke; Metcalfe, Kyle; Okutsu, Natsumi; Pan, Donald; Raudsepp, Maija J; Sauvage, Justine; Schubotz, Florence; Spivack, Arthur; Tonai, Satoshi; Treude, Tina; Tsang, Man-Yin; Viehweger, Bernhard; Wang, David T; Whitaker, Emily; Yamamoto, Yuzuru; Yang, Kiho; Kinoshita, Masataka; Maeda, Lena; Kubo, Yusuke; Morono, Yuki; Inagaki, Fumio; Heuer, Verena B
    Abstract The study investigates the in-situ strength of sediments across a plate boundary décollement using drilling parameters recorded when a 1180-m-deep borehole was established during International Ocean Discovery Program (IODP) Expedition 370, Temperature-Limit of the Deep Biosphere off Muroto (T-Limit). Information of the in-situ strength of the shallow portion in/around a plate boundary fault zone is critical for understanding the development of accretionary prisms and of the décollement itself. Studies using seismic reflection surveys and scientific ocean drillings have recently revealed the existence of high pore pressure zones around frontal accretionary prisms, which may reduce the effective strength of the sediments. A direct measurement of in-situ strength by experiments, however, has not been executed due to the difficulty in estimating in-situ stress conditions. In this study, we derived a depth profile for the in-situ strength of a frontal accretionary prism across a décollement from drilling parameters using the recently established equivalent strength (EST) method. At site C0023, the toe of the accretionary prism area off Cape Muroto, Japan, the EST gradually increases with depth but undergoes a sudden change at ~ 800 mbsf, corresponding to the top of the subducting sediment. At this depth, directly below the décollement zone, the EST decreases from ~ 10 to 2 MPa, with a change in the baseline. This mechanically weak zone in the subducting sediments extends over 250 m (~ 800–1050 mbsf), corresponding to the zone where the fluid influx was discovered, and high-fluid pressure was suggested by previous seismic imaging observations. Although the origin of the fluids or absolute values of the strength remain unclear, our investigations support previous studies suggesting that elevated pore pressure beneath the décollement weakens the subducting sediments.
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    Thermophilic Endospore-Forming Bacteria as Models for Exploring Microbial Dispersal in Time and Space
    (2017) Cramm, Margaret; Hubert, Casey; Dunfield, Peter; Fox, Jeremy
    Thermophilic endospore-forming bacteria – “ thermospores ” – are particularly useful model organisms for exploring microbial biogeography because they remain viable for long geologic time periods owing to a dormant state that confers resistant to extreme conditions. Using high temperature incubation experiments and 16S rRNA gene amplicon sequencing, geographic and temporal thermospore dispersal in marine sediments was explored. Thermospores detected in surface sediments across the North Atlantic are likely to originate from multiple warm temperature habitats, and are viable in sediments buried ~15 000 years ago. These approaches also revealed thermospore viability following the extreme stress of prolonged -80°C exposure. Thermospore viability and dispersal on a scale of millions of years was explored in a 1.2 km long sediment core. Uneven thermospore germination posed a challenge for thermospore detection but their capacity for use as models of biological dispersal remains valid.