Micro-granulometry of sedimentary dykes, Kathmandu basin, Nepal

Soft-sediment deformation structures have been analyzed at six sites of the Kathmandu valley. Microgranulometric study (this Supplement and Fig. 3B of Mugnier et al., Tectonophysics, 2011) reveals that silty levels (60 to 80% silt) favor the development of soft-sediment deformation structures, while sandy levels (60 to 80% sand) are passively deformed. Nonetheless well sorted sand levels (more than 80% sand) generate over-fluid pressure during compaction if located beneath a silty cap, leading to fluidization and dike development. 3-D geometry of seismites indicates a very strong horizontal shearing during their development. Using a physical approach based on soil liquefaction during horizontal acceleration, we show that the fluidization zone progressively grows down-section during the shaking, but does not exactly begin at the surface. The comparison of bed-thickness and strength/depth evolution indicates three cases: i) no soft-sediment deformation occurs for thin (few centimeters) silty beds; ii) the thickness of soft-sediment deformation above sandy beds is controlled by the lithological contrast; iii) the thickness of soft-sediment deformation depends on the shaking intensity for very thick silty beds. These 3 cases are evidenced in the Kathmandu basin. We use the 30 cm-thick soft-sediment deformation level formed during the 1833 earthquake as a reference: the 1833 earthquake rupture zone extended very close to Kathmandu, inducing there MMI IX-X damages. A 90 cm-thick sediment deformation has therefore to be induced by an event greater than MMI X. From a compilation of paleo and historic seismology studies, it is found that the great (M ~ 8.1) historical earthquakes are not characteristic of the greatest earthquakes of Himalaya; hence earthquakes greater than M ~ 8.6 occurred. Kathmandu is located above one of the asperities that laterally limits the extent of mega-earthquake ruptures and two successive catastrophic events already affected Kathmandu, in 1255 located to the west of this asperity and in ~ 1100 to the east.

Hydrographical and chemical observations during an achor station in the eastern North Atlantic

Serial observations of temperature, salinity, oxygen, alkalinity and pH are presented. They were carried out during an anchor station of R.V. "Meteor" west of Cape Sao Vincente (Portugal) in the area of the maximum Mediterranean water outflow, which follows the continental slope off Portugal. Two observational results are pointed out: The Mediterranean water masses spread out into the Atlantic Ocean, consisting of two distinct layers at depth of 700 m (T=12.0 °C, S=36.15 ?) and 1250 m (T=11.3 °C, S=36.40 ?). The salinity proved to be the most significant indicator of the observed stratification. The values of dissolved oxygen content, alkalinity and pH in the very near bottom layer (1 m above the bottom at depth of 3250 m) are different from the values at depth of 15 m to 100 m above the bottom. As this phenomenon is not observed for the salinity, the changes may be interpreted in terms of chemical and biological processes at the sediment-water interface.

Fatty acids, alcohols and hydrocarbons of microbial mats from Lake 2A on Kiritimati Island

Modern microbial mats are widely recognized as useful analogs for the study of biogeochemical processes relevant to paleoenvironmental reconstruction in the Precambrian. We combined microscopic observations and investigations of biomarker composition to investigate community structure and function in the upper layers of a thick phototrophic microbial mat system from a hypersaline lake on Kiritimati (Christmas Island) in the Northern Line Islands, Republic of Kiribati. In particular, an exploratory incubation experiment with 13C-labeled bicarbonate was conducted to pinpoint biomarkers from organisms actively fixing carbon. A high relative abundance of the cyanobacterial taxa Aphanocapsa and Aphanothece was revealed by microscopic observation, and cyanobacterial fatty acids and hydrocarbons showed 13C-uptake in the labeling experiment. Microscopic observations also revealed purple sulfur bacteria (PSB) in the deeper layers. A cyclic C19:0 fatty acid and farnesol were attributed to this group that was also actively fixing carbon. Background isotopic values indicate Calvin-Benson cycle-based autotrophy for cycC19:0 and farnesol-producing PSBs. Biomarkers from sulfate-reducing bacteria (SRB) in the top layer of the mat and their 13C-uptake patterns indicated a close coupling between SRBs and cyanobacteria. Archaeol, possibly from methanogens, was detected in all layers and was especially abundant near the surface where it contained substantial amounts of 13C-label. Intact glycosidic tetraether lipids detected in the deepest layer indicated other archaea. Large amounts of ornithine and betaine bearing intact polar lipids could be an indicator of a phosphate-limited ecosystem, where organisms that are able to substitute these for phospholipids may have a competitive advantage.

Hydrocarbons, sterols and alkenones at time series station KERFIX

Hydrocarbons, sterols and alkenones were analyzed in samples collected from a 10 month sediment trap time series deployed in the Indian Ocean sector of the Southern Ocean. Fluxes and within-class distributions varied seasonally. During higher mass and organic carbon (OC) flux periods, which occurred in austral summer and fall, fresh marine inputs were predominant. Vertical fluxes were most intense in January, but limited to one week in duration. They were, however, low compared with other oceanic regions. In contrast, low mass and OC flux periods were characterized by a strong unresolved complex mixture (UCM) in the hydrocarbon fraction and a high proportion of stanols as a result of zooplanktonic grazing. Terrigenous inputs were not detectable. The alkenone compositions were consistent with previous data on suspended particles from Antarctic waters. However, UK'37 values diverged from the linear and exponential fits established by Sikes et al. (1997, doi:10.1016/S0016-7037(97)00017-3) in the low temperature range. The seasonal pattern of alkenone production implied that IPT (integrated production temperature) is likely to be strongly imprinted by austral summer and fall SST (sea surface temperature).