Methane and sulfide fluxes in permanent anoxia: in situ studies at the Dvurechenskii mud volcano (Sorokin Trough, Black Sea)

The Dvurechenskii mud volcano (DMV), located in permanently anoxic waters at 2060 m depth (Sorokin Trough, Black Sea), was visited during the M72/2 cruise with the RV Meteor to investigate the methane and sulfide release from mud volcanoes into the Black Sea hydrosphere. We studied benthic fluxes of methane and sulfide, and the factors controlling transport, consumption and production of both compounds within the sediment. The pie shaped mud volcano showed temperature anomalies as well as solute and gas fluxes indicating high fluid flow at a small elevation north of the geographical center. The anaerobic oxidation of methane (AOM) coupled to sulfate reduction (SR) was excluded from this zone due to fluid-flow induced sulfate limitation and a fresh mud flow and consequently methane escaped into the water column with a rate of 0.46 mol/m**2/d. In the outer center of the mud volcano fluid flow and total methane flux were decreased, correlating with an increase in sulfate penetration into the sediment, and with higher SR and AOM rates. Here between 50-70% of the methane flux (0.07-0.1 mol/m**2/d) was consumed within the upper 10 cm of the sediment. Also at the edge of the mud volcano fluid flow and rates of methane and sulfate turnover were substantial. The overall amount of dissolved methane released from the mud volcano into the water column was significant with a discharge of 1.4x10**7 mol/yr. The DMV maintains also high areal rates of methane-fueled sulfide production of on average 0.05 mol/m**2/d. However, we concluded that sulfide and methane emission into the hydrosphere from deep water mud volcanoes does not significantly contribute to the sulfide and methane inventory of the Black Sea.

Susceptibility, density, iron and calcium concentrations of ODP holes 165-999B and 165-1001A

Pelagic sediments recording an extreme and short-lived global warming event, the Late Paleocene Thermal Maximum (LPTM), were recovered from Hole 999B (Colombian Basin) and Holes 1001A and 1001B (lower Nicaraguan Rise) in the Caribbean Sea during Ocean Drilling Program Leg 165. The LPTM consists of a 0.3-0.97 m calcareous claystone to claystone horizon. High-resolution downhole logging (Formation MicroScanner [FMS]), standard downhole logs (resistivity, velocity, density, natural gamma ray, and geochemical log), and non-destructive chemical and physical property (multisensor core logger [MSCL] and X-ray fluorescence [XRF] core scanner) data were used to identify composite sections from parallel holes and to record sedimentological and environmental changes associated with the LPTM. Downhole logging data indicate an abrupt and distinct difference in physical and chemical properties that extend for tens of meters above and below the LPTM. These observations indicate a rapid environmental change at the LPTM, which persists beyond the LPTM anomaly. Comparisons of gamma-ray attenuation porosity evaluator (GRAPE) densities from MSCL logging on split cores with FMS resistivity values allows core-to-log correlation with a high degree of accuracy. High-resolution magnetic susceptibility measurements of the cores are compared with elemental concentrations (e.g., Fe, Ca) analyzed by high-resolution XRF scanning. The high-resolution data obtained from several detailed core and downhole logging methods are the key to the construction of composite sections, the correlation of both adjacent holes and distant sites, and core-log integration. These continuous-depth series reveal the LPTM as a multiphase event with a nearly instantaneous onset, followed by a much different set of physical and chemical conditions of short duration, succeeded by a longer transition to a new, more permanent set of environmental circumstances. The estimated duration of these 'phases' are consistent with paleontological and isotopic studies of the LPTM

Porosity, permeability, trace elements, and carbon-oxygen isotopes at DSDP Hole 77-536

Talus deposits recovered from Site 536 show evidence of aragonite dissolution, secondary porosity development, and calcite cementation. Although freshwater diagenesis could account for the petrographic features of the altered talus deposits, it does not uniquely account for isotopic or trace-element characteristics. Also, the hydrologic setting required for freshwater alteration is not easily demonstrated for the Campeche Bank. A mixing-zone model does not account for the available trace-element data, but does require somewhat less drastic assumptions about the size of the freshwater lens. Although a seawater (bottom-water) alteration model requires no hydrologic difficulties, unusual circumstances are required to account for the geochemical characteristics of the talus deposits using this model.

Porosity, gas permeability and grain density of ODP Leg 194 sites

We report analyses of porosity and permeability of core samples from Site 1193 in the Northern Marion Platform, Sites 1196 and 1199 in the Southern Marion Platform, and Sites 1194, 1195, 1197, and 1198 from the slopes of these platforms. The samples include 415 horizontal 1-in plugs, 290 vertical 1-in plugs, and 23 whole-core pieces. Porosity and permeability analyses were possible for most, but not all, samples. Grain density measurements were also obtained for the horizontal plugs. Representative photomicrographs are provided of thin sections from 139 of the horizontal plugs and the 23 whole-core pieces.

Effective stress, porosity, p-wave velocity and mineral composition of ODP Hole 174A-1073A sediments

Porosity, permeability, and compressional (P-wave) velocity were measured as a function of stress on sediments from Ocean Drilling Program Site 1073, U.S. Mid-Atlantic continental slope. Thin sections, scanning electron microscopy, and X-ray diffraction analyses provided mineralogical characteristics of the samples. Uniaxial strain boundary conditions were imposed on the samples during consolidation tests with the maximum effective axial stress reaching 13 MPa. The maximum effective radial stress necessary to maintain uniaxial strain was 7.6 MPa. Over an effective axial stress interval of 0 to 5.2 MPa, Sample 174A-1073A-26X-2, 82-89 cm (226.65 meters below seafloor [mbsf]), exhibited the largest decrease in porosity (51% to 41%), whereas Sample 71X-1, 2-8 cm (644.70 mbsf), exhibited the smallest decrease in porosity (48% to 45%). All samples showed negligible porosity increases during unloading. The permeability (on the order of 1 x 10-17 m**2) of Sample 174A-1073A-71X-1, 2-8 cm, was twice that measured on Sample 8H-1, 23-26 cm (63.75 mbsf), even though the former was considerably deeper and older. The differences in porosity-stress behavior and permeability between shallow and deep samples is related to lithologic, mineralogic, and diagenetic differences between the sediments above and below the Pliocene-Pleistocene to Miocene unconformity. P-wave velocity for Samples 174A-1073A-41X-5, 97-103 cm (372.35 mbsf), and 71X-1, 2-8 cm, increased with decreasing porosity, but did not change significantly during unloading.