Home About us Contact
|
Home About us Contact | ||
|
|
||
ODP Leg (odp + leg)
Selected AbstractsDirect in situ detection of cells in deep-sea sediment cores from the Peru Margin (ODP Leg 201, Site 1229)GEOBIOLOGY, Issue 4 2004L. MAUCLAIRE ABSTRACT Microbiological investigations of deep-sea sediments recovered from the Peru Margin during the ODP Leg 201 (Hole 1229A, 1,110 mbsf) demonstrated that microoganisms were a consistent component throughout the profile. Optimization of the dilution factor and DAPI-staining procedures for direct cell counts allowed the determination of the abundance of the entire microbial community, which was about 108 cells per g dry sediment. Microbial diversity in discrete samples taken from the 110-m profile was analysed using horseradish-peroxydase-rRNA-probes. In general, the majority of the detected cells belonged to the Eubacteria kingdom with a dominance of sulphate-reducing bacteria. The composition of the suflate-reducing community varied with depth. Desulfobacteriaceae were dominant in the uppermost sulphate-reducing zone and Desulfovibrionaceae at deeper depths in the upward diffusing sulphate-rich brines. Both sulphate-reducing groups were also detected in the methanogenic zone. Similarly, Archaea were detected throughout the profile, not only in the methanogenic zone but also in the upper and lower sulphate-reducing zones. [source] Archaeal phylotypes in a metal-rich and low-activity deep subsurface sediment of the Peru Basin, ODP Leg 201, Site 1231GEOBIOLOGY, Issue 3 2004K. B. SØRENSEN ABSTRACT Site 1231 of the Ocean Drilling Project (ODP) was characterized by low concentrations of organic carbon, as well as low cell numbers and biological activity rates. A 16S rRNA survey was performed in order to analyse the microbial community composition of these central oceanic sediments. Archaeal 16S rRNA genes from subsurface sediments at Site 1231 (1.8, 9.0, and 43 mbsf) were affiliated with uncultured lineages from subsurface or hydrothermal vent habitats. Members of the Marine Group I (MGI) found in the 1.8 mbsf sediment formed distinct clusters, some dominated by phylotypes from Site 1231 and other subsurface environments. The archaeal community survey at Site 1231 indicated that several archaeal lineages were widespread in subsurface environments, marine sediments as well as hydrothermal habitats. [source] Palaeomagnetic records of the Brunhes/Matuyama polarity transition from ODP Leg 124 (Celebes and Sulu seas)GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2000Hirokuni Oda Palaeomagnetic records of the Brunhes/Matuyama geomagnetic polarity transition were obtained from deep-sea sediments of ODP Leg 124 in the Celebes and Sulu seas. Advanced piston core (APC) samples with high magnetization intensities (2,200 mA m,1,) and high sedimentation rates (8.4,10 cm kyr,1,) were recovered from this cruise. Rock-magnetic measurements revealed the carrier of the remanence to be nearly pure magnetite in the pseudo-single-domain range. Pass-through measurements at intervals of 5 mm on APC cores across the Brunhes/Matuyama polarity transition for Holes 767B, 769A and 769B were deconvolved with the magnetometer sensor response using the ABIC-minimizing method. Discrete samples were also taken from the polarity transition zones and subjected to either thermal or alternating field stepwise demagnetization. The results were generally consistent with the pass-through data after the deconvolution. Results from the three holes are in good agreement, particularly those from the two holes 100 m apart at Site 769. The transitional VGP paths from these two holes show two small loops near New Zealand before the equator is crossed. The VGPs continue to swing eastwards to the North Atlantic and then move to the northeastern margin of the Pacific Ocean. The positions of the VGP loops obtained from Site 769 are different from the VGP clusters obtained from both the known volcanic records and the sediment records at the Boso Peninsula and the North Atlantic sites with high sedimentation rates. Such a difference may imply the predominance of the non-dipole field during the transition. Relatively stable mid-high northern latitude VGPs are recognized on all three cores just after the reversal, lasting about 4000 years. The plot of relative intensity versus VGP latitude for the sediment records from the North Atlantic (DSDP Hole 609B) shows a remarkable similarity with our records. Similar patterns were also obtained for the plot of the palaeointensity versus VGP latitude for the La Palma volcanic lava records. These results may suggest the existence of a metastable state of the geodynamo, producing a zonal component just after the Brunhes/Matuyama boundary, which may have played a role in the change of the field intensity. [source] Seismic constraints on the three-dimensional geometry of low-angle intracrustal reflectors in the Southern Iberia Abyssal PlainGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2008S. M. Dean SUMMARY Several lines of evidence suggest that simple shear rifting of the continental crust, in the form of low-angle detachment faulting, occurred during the final stages of continental breakup between West Iberia and the Grand Banks. The primary evidence for such faulting is the occurrence of low-angle, high amplitude reflectors within the basement adjacent to the ocean,continent transition zone. Here we present a series of intersecting, depth migrated seismic reflection profiles that image one such reflector, the H-reflector, located on the southern edge of Galicia Bank. ,H' lies beneath several boreholes drilled during ODP Legs 149 and 173, in a region where the oceanward extent of extended continental crust steps at least 150 km westward from its location in the southern Iberia Abyssal Plain to its location off the relatively shallow Galicia Bank. In our profiles ,H' appears to define a surface that extends over a region of at least 200 km2 and that dips down ,19° to the north, towards Galicia Bank. The profiles show that a close affinity exists between ,H' and the most seaward continental crust. Based on geophysical data and ODP drilling results, we infer that the basement above ,H' is composed of continental crust deformed by extensional faults into a series of wedge-shaped blocks and thin slivers. These basement wedges have a complex 3-D geometry. ,H' rises to the basement surface on a number of the seismic profiles and appears to define locally the oceanward extent of continental fault blocks. [source] Detection of diluted marine tertiary tephra by electron spin resonance and magnetic measurementsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2003B. Ananou SUMMARY Oligocene sediments from ODP leg 115 (South Indian Ocean), Site 709 and Site 711, have been investigated using electron spin resonance (ESR) and magnetic susceptibility measurements, to detect volcanic tephra layers of supposed Ethiopian traps origin. The results obtained at room temperature, without separating the volcanic material from the bulk sediment, show that the ash-content strongly influences the lineshape and intensity of the ESR signal. As a result, the ESR alone, can be used as a powerful tool for characterizing the diluted ash-content of marine sediments. We have also found a strong similarity between the ESR spectra of the same tephra layers from the two sites. [source] | ||||||||||