150 documents found in 312ms
# 1
Fagel, Natalie • Alleman, Laurent • Granina, L • Hatert, F • Thamo-Boszo, Edit • (et. al.)
Abstract: In order to get a complete geochemical signature, 14 P-rich concretions, chosen among the different cores, were acid digested (Table 3a and Table 3b). In a clean laboratory, 1.7 to 36 mg of concretions were digested overnight in a concentrated mixture of Suprapur acid (3 ml HCl/2 ml HNO3/1 ml HF) at 90 °C in sealed Teflon beakers. After evaporation to dryness, the residue was dissolved in 2.5 ml of 2% HNO3 Suprapur and diluted to 12 ml with Milli-Q water. During the same procedure, we have also dissolved and analysed, for comparison, a pure vivianite from Anlua, Cameroon (tubular crystals, MRAC collection).
# 2
Swann, George • Mackay, Anson • Leng, Melanie • Demory, Francois
Abstract: C/N mass ratios remain constant throughout MIS 3 and into MIS 2, with values between 6.3 and 8.9, indicating no significant terrestrial input of organic matter (Fig. 3). Low %TOC values during the interstadial increase from 0.4 to 0.7 between 57.8 and 43.7 kyr BP with a concurrent gradual increase in δ13C(organic) amid oscillations between −23.2‰ and −26.1‰ (Fig. 3). %TOC falls to 0.4 between 40.9 and 39.4 kyr BP whereas δ13C(organic) remains high at c. 24‰ with a peak value of −23.6‰ at 39.4 kyr BP. The subsequent two-stage increase in %TOC from 39 to 37.9 kyr BP and between 37.3 and 36.9 kyr BP is marked by a period of δ13C(organic) lowering to c. −26.6‰ before δ13C(organic) increases after 37.9 kyr BP to −24.8‰, values comparable to those prior to the %TOC decline at 40.9 kyr BP.
# 3
Demory, Francois • Oberhänsli, Hedi • Nowaczyk, Norbert • Gottschalk, Matthias • Wirth, Richard • (et. al.)
Abstract: No significant HIRM change is observed at the transition between oxidising and reducing conditions in the sediment (Fig. 9A). This implies that HIRM is not affected by redox conditions and further confirms that the “hard” magnetic mineral content is the best tracer of detrital input (Peck et al., 1994). On the other hand, the S-ratio seems to be related to the redox conditions in the sediment (see Section 7.2). The ARM has also to be considered with caution as it is mainly influenced by the ferrimagnetic contribution, which is itself influenced by post depositional processes. This is seen in Fig. 9 where ARM variations are partly influenced by S-ratio variations.
# 4
Swann, George • Mackay, Anson • Leng, Melanie • Demory, Francois
Abstract: All diatoms in the analysed section were extensively affected by dissolution with only c. 1% of valves in a “pristine” condition. Diatom concentrations were generally extremely low throughout MIS 3 and across the MIS 3/2 transition with samples containing a mixture of extant and extinct species (Fig. 4).
# 5
KTB, WG Geophysics
Abstract: The thermal conductivity on cores is measured in two steps (see Pribnow 1994). First, one face end of the core is sawed and polished. The half space line source is pressed against this preparated face (without further contact medium like water) by a computerized device. The position of the heat source is varied in 15 degree intervals around one semicircle. At each position, 3 repeating measurements are performed. The line source azimuth of the lowest measured thermal conductivity is the strike of the foliation plane. On the other hand, the thermal conductivity is maximal parallel to that direction. This apparent paradox can be explained by the experimental method, because the measurement plane is perpendicular to the orientation of the line source (Pribnow 1994).In a second step a calotte plane perpendicular to the strike of foliation is prepared. A second series of thermal conductivity measurements in 15 degree intervals ...
# 6
KTB, WG Geophysics
Abstract: The thermal conductivity on cores is measured in two steps (see Pribnow 1994). First, one face end of the core is sawed and polished. The half space line source is pressed against this preparated face (without further contact medium like water) by a computerized device. The position of the heat source is varied in 15 degree intervals around one semicircle. At each position, 3 repeating measurements are performed. The line source azimuth of the lowest measured thermal conductivity is the strike of the foliation plane. On the other hand, the thermal conductivity is maximal parallel to that direction. This apparent paradox can be explained by the experimental method, because the measurement plane is perpendicular to the orientation of the line source (Pribnow 1994).In a second step a calotte plane perpendicular to the strike of foliation is prepared. A second series of thermal conductivity measurements in 15 degree intervals ...
# 7
KTB, WG Geophysics
Abstract: In general, four-electrode devices are used to measure the resistivity on original (unprepared) cores and on mini cores drilled from these original cores. The in-phase and the out-of-phase signal is measured and therefore the complex resistivity is determined. All measurements are performed under surface conditions (room temperature and atmospheric pressure). Four point like electrodes are situated at the core surface along a semicircle in a plane perpendicular to the core axis. The two current electrodes are opposite to each other. The electrodes are in contact to the sample by a porous plastic material soaked with 0.1 molar NaCl solution. Voltage and current is measured by a lock-in-amplifier at 120 Hz frequency. Due to high contact resistances, only the magnitude of complex resistivity is used. By computer controlled rotating of the core and moving of the electrode arrangement along the cores z axis, resistivity as a function of azimuth and length is measured.
# 8
KTB, WG Geophysics
Abstract: In the KTB field laboratory, porosity, internal surface and permeability were determined on identical mini cores with 25.4 mm in diameter and approximately 50 mm in length. These samples were drilled either axial or radial with respect to the drill core, or parallel or perpendicular with respect to the foliation. In the KTB field laboratory, the stationary sArcy method was used with nitrogen gas as the streaming medium. The measurements were made at a constant confining pressure of 5 MPa to 6.5 MPa. The nitrogen pressure gradient was up to 2 MPa at the inflow side minus atmospheric pressure at the outflow side of the sample. Because of the low pore pressures during the measurements (max 2 MPa) the data had to be corrected for the effect of gas friction along the matrix wall, the so called Klinkenberg effect (Huenges et al. 1990). Further details, regarding equipment and evaluation are given by Pusch et al. (1986).
# 9
KTB, WG Geophysics
Abstract: In general, four-electrode devices are used to measure the resistivity on original (unprepared) cores and on mini cores drilled from these original cores. The in-phase and the out-of-phase signal is measured and therefore the complex resistivity is determined. All measurements are performed under surface conditions (room temperature and atmospheric pressure). Mini cores of 25.4 mm diameter and approximately 50 mm length are drilled from original cores. Anisotropy information is obtained by different core orientations. The complex resitivity is measured in an 4-electrode elctrolytic cell by use of a lock-in-amplifier. The applied frequency ranges from 0.5 Hz to 120 kHz. The samples are first evacuated and back-saturated with destilled water. In this case, mainly sigmas and sigmam contribute to the rock resistivity. A second cycle of evacuating and back-saturating with 0.1 molar NaCl solution leads to sigmav (Rauen 1994).
# 10
Demory, Francois • Oberhänsli, Hedi • Nowaczyk, Norbert • Gottschalk, Matthias • Wirth, Richard • (et. al.)
Abstract: Greigite levels in glacial sediments cannot be correlated between cores (Fig. 12), which suggests that greigite concentrations are driven by local processes. We suggest that faecal pellets could be a suitable microenvironment for sulphate reduction. And while greigite could potentially act as proxy for faecal pellets in glacial sediments, unfortunately, we cannot rely on this possible indicator since the greigite is very sensitive to onshore alterations after sampling (Snowball and Thompson, 1990).
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