955 resultados para Alpha spectroscopy on plated samples
Resumo:
Laboratory compressional wave (Vp) and shear wave (Vs) velocities were measured as a function of confining pressure for the gabbros from Hole 735B and compared to results from Leg 118. The upper 500 m of the hole has a Vp mean value of 6895 m/s measured at 200 MPa, and at 500 meters below seafloor (mbsf), Vp measurements show a mean value of 7036 m/s. Vs mean values in the same intervals are 3840 m/s and 3857 m/s, respectively. The mean Vp and Vs values obtained from log data in the upper 600 m are 6520 and 3518 m/s, respectively. These results show a general increase in velocity with depth and the velocity gradients estimate an upper mantle depth of 3.32 km. This value agrees with previous work based on dredged samples and inversion of rare element concentrations in basalts dredged from the conjugate site to the north of the Atlantis Bank. Laboratory measurements show Vp anisotropy ranging between 0.4% and 8.8%, with the majority of the samples having values less than 3.8%. Measurements of velocity anisotropy seem to be associated with zones of high crystal-plastic deformation with predominant preferred mineral orientations of plagioclase, amphiboles, and pyroxenes. These findings are consistent with results on gabbros from the Hess Deep area and suggest that plastic deformation may play an important role in the seismic properties of the lower oceanic crust. In contrast to ophiolite studies, many of the olivine gabbros show a small degree of anisotropy. Log derived Vs anisotropy shows an average of 5.8% for the upper 600 m of Hole 735B and tends to decrease with depth where the overburden pressure and the age of the crustal section suggests closure of cracks and infilling of fractures by alteration minerals. Overall the results indicate that the average shear wave splitting in Hole 735B might be influenced by preferred structural orientations and the average value of shear wave splitting may not be a maximum because structural dips are <90°. The maximum fast-wave orientation values could be influenced by structural features striking slightly oblique to this orientation or by near-field stress concentrations. However, flexural wave dispersion analyses have not been performed to confirm this hypothesis or to indicate to what extent the near-field stresses may be influencing shear wave propagation. Acoustic impedance contrasts calculated from laboratory and logging data were used to generate synthetic seismograms that aid in the interpretation of reflection profiles. Several prominent reflections produced by these calculations suggest that Fe-Ti oxides and shear zones may contribute to the reflective nature of the lower oceanic crust. Laboratory velocity attenuation (Q) measurements from below 500 m have a mean value of 35.1, which is consistent with previous vertical seismic profile (VSP) and laboratory measurements on the upper 500 m.
Resumo:
From 0 to 277 m at Site 530 are found Holocene to Miocene diatom ooze, nannofossil ooze, marl, clay, and debrisflow deposits; from 277 to 467 m are Miocene to Oligocene mud; from 467 to 1103 m are Eocene to late Albian Cenomanian interbedded mudstone, marlstone, chalk, clastic limestone, sandstone, and black shale in the lower portion; from 1103 to 1121 m are basalts. In the interval from 0 to 467 m, in Holocene to Oligocene pelagic oozes, marl, clay, debris flows, and mud, velocities are 1.5 to 1.8 km/s; below 200 m velocities increase irregularly with increasing depth. From 0 to 100 m, in Holocene to Pleistocene diatom and nannofossil oozes (excluding debris flows), velocities are approximately equivalent to that of the interstitial seawater, and thus acoustic reflections in the upper 100 m are primarily caused by variations in density and porosity. Below 100 or 200 m, acoustic reflections are caused by variations in both velocity and density. From 100 to 467 m, in Miocene-Oligocene nannofossil ooze, clay, marl, debris flows, and mud, acoustic anisotropy irregularly increases to 10%, with 2 to 5% being typical. From 467 to 1103 m in Paleocene to late Albian Cenomanian interbedded mudstone, marlstone, chalk, clastic limestone, and black shale in the lower portion of the hole, velocities range from 1.6 to 5.48 km/s, and acoustic anisotropies are as great as 47% (1.0 km/s) faster horizontally. Mudstone and uncemented sandstone have anisotropies which irregularly increase with increasing depth from 5 to 10% (0.2 km/s). Calcareous mudstones have the greatest anisotropies, typically 35% (0.6 km/s). Below 1103 m, basalt velocities ranged from 4.68 to 4.98 km/s. A typical value is about 4.8 km/s. In situ velocities are calculated from velocity data obtained in the laboratory. These are corrected for in situ temperature, hydrostatic pressure, and porosity rebound (expansion when the overburden pressure is released). These corrections do not include rigidity variations caused by overburden pressures. These corrections affect semiconsolidated sedimentary rocks the most (up to 0.25 km/s faster). These laboratory velocities appear to be greater than the velocities from the sonic log. Reflection coefficients derived from the laboratory data, in general, agree with the major features on the seismic profiles. These indicate more potential reflectors than indicated from the reflection coefficients derived using the Gearhart-Owen Sonic Log from 625 to 940 m, because the Sonic Log data average thin beds. Porosity-density data versus depth for mud, mudstone, and pelagic oozes agree with data for similar sediments as summarized in Hamilton (1976). At depths of about 400 m and about 850 m are zones of relatively higher porosity mudstones, which may suggest anomalously high pore pressure; however, they are more probably caused by variations in grain-size distribution and lithology. Electrical resistivity (horizontal) from 625 to 950 m ranged from about 1.0 to 4.0 ohm-m, in Maestrichtian to Santonian- Coniacian mudstone, marlstone, chalk, clastic limestone, and sandstone. An interstitial-water resistivity curve did not indicate any unexpected lithology or unusual fluid or gas in the pores of the rock. These logs were above the black shale beds. From 0 to 100 m at Sites 530 and 532, the vane shear strength on undisturbed samples of Holocene-Pleistocene diatom and nannofossil ooze uniformly increases from about 80 g/cm**2 to about 800 g/cm**2. From 100 to 300 m, vane shear strength of Pleistocene-Miocene nannofossil ooze, clay, and marl are irregular versus depth with a range of 500 to 2300 g/cm**2; and at Site 532 the vane shear strength appears to decrease irregularly and slightly with increasing depth (gassy zone). Vane shear strength values of gassy samples may not be valid, for the samples may be disturbed as gas evolves, and the sediments may not be gassy at in situ depths.
Resumo:
Geochemical analyses have been performed on sediment samples collected during Ocean Drilling Program Leg 178 from the continental rise and outer continental shelf of the Antarctic Peninsula. A suite of 21 trace elements was measured by neutron activation analysis in 39 sediment samples, and major element oxides were determined in 67 samples by electron microprobe analyses of fused glass beads. These geochemical data, combined with the X-ray diffraction and X-ray fluorescence data from shipboard analyses, provide a reasonable estimate of the mineral and chemical composition of sediments deposited along the western margin of the Antarctic Peninsula.
Resumo:
Stable isotopic values on planktonic foraminifera in a suite of cores from basins across the SE Baffin Shelf are used to extract a record of meltwater events during Termination I deglaciation. Resolution and Hatton basins lie on the SE Baffin Shelf at water depths > 500 m, seaward of major conduits for ice drainage from the eastern sector of the Laurentide Ice Sheet (LIS). Accelerator mass spectrometry 14C dates are used to constrain our chronology of events in ten cores. In Resolution Basin, three cores have 14C AMS dates on foraminifera of > 20 ka at their bases; whereas Hatton Basin cores terminate in sediments < 13 kyr. Sedimentation rates varied between 0.1 to 4.5 m/ka. Stable oxygen and carbon isotopic ratios were obtained on 146 samples of the planktonic foraminifera Neogloboquadrina pachyderma (Ehrenberg) sinistral, from seven of the ten cores. No evidence was found to indicate that test morphology or size affected delta18O. Between 7 and 13.5 ka the surface water on the shelf was on average 1 per mil lower than the open ocean signal. Significant temporal variations were found in both delta18O and delta13C. Evidence for significant low delta18O events occurred between 13 and 8 ka. The delta13C record from the planktonic foraminifera suggests a threefold division of events between 13 and 7 ka, with positive values between 10.8 and 13.0 ka, negative values between 9 and 10.8 ka, and positive values from 7 to 9 ka. The delta18O data suggest the presence of meltwater on the shelf some 3,000 years prior to the first late glacial dates on terrestrial deglaciation (at circa 10.4 ka). "Hudson Strait must be the real key to the importance of the calving process during deglaciation, because it is potentially the largest marine outlet for the Laurentide Ice Sheet and because it leads into the very center of the ice sheet.....the rates of calving through Hudson Strait during the period of initial ?18O rise unfortunately are unknown." W. F. Ruddiman (1987, p. 151)
Resumo:
Vertical permeability testing was conducted on four samples collected from Site 1109, a borehole advanced during Ocean Drilling Program Leg 180. Closed conditions were applied during each test, and the samples were measured using a constant flow approach and permeant solutions that matched the geochemistry of nearby interstitial waters. Vertical permeabilities measured at 34.5 kPa effective stress generally decreased with depth and ranged from 10**-14 m**2 at 212.53 meters below seafloor (mbsf) to 10**-18 m**2 at 698.10 mbsf. The three deepest samples differed in permeability by less than one order of magnitude. Reconsolidation testing on the shallowest sample yielded a minimum permeability of 1.56 x 10**-16 m**2 at 276 kPa effective stress. Subsequent rebound testing yielded a hysteresis-type curve, with the final permeability measuring lower than the initial permeability by nearly 1.5 orders of magnitude. Dilution experiments indicated that use of a permeant solution matching the geochemistry of the interstitial waters may be necessary for accuracy in measurements and mitigation of clay swellage and collapse during testing, but further research is mandated.
Resumo:
Magnetic measurements were made on discrete samples from the Neogene pelagic and hemipelagic sediments recovered during ODP Leg 117. Polarity zones, usually identified for uppermost 200 m, were correlated to the geomagnetic polarity time scale referring to biostratigraphic datums. Quality and resolution of the magnetostratigraphy was partly limited by the weak and relatively soft magnetic character of almost all intervals, and core disturbance by gas expansion at some Oman Margin sites. Clear polarity records of the Brunhes and Matuyama chrons (C1 to C2r) were observed at Sites 724 and 727 on the Oman continental margin. Extended reversal records of the Pliocene were found at Site 722 on the Owen Ridge and Site 728 on the Oman Margin, and correlated to the Gauss to Gilbert chrons (C2A to C3).
Resumo:
Paleomagnetic measurements were made on 913 samples from 11 holes (626B, 626C, 627B, 628A, 630A, 631A, 632A, 632B, 633A, 634A, and 635B) drilled in and around the Bahamas carbonate bank during Ocean Drilling Program Leg 101. These samples displayed a wide range of magnetic intensities (from about 1.0 A/m to 1.6 * 10**- 6 A/m) and magnetic behavior. Most samples were weakly magnetized and had low mean destructive fields; however, sediments from sections of several holes were strongly magnetic with stable magnetizations. Magnetic-polarity interpretations were made on a Campanian unit from Hole 627B, a mid-Oligocene unit from Hole 628A, and a Plio-Pleistocene section from Hole 633A. Sediments in the upper parts of Holes 627B, 632A, and 633A have high magnetic intensities that decay 2 to 3 orders of magnitude over depths of 5 to 18 mbsf. The pattern of decline of the magnetism and the change in mean destructive fields and geochemical conditions in these holes are consistent with diagenetic dissolution of the magnetic minerals in a suboxic or anoxic-sulfidic environment. Paleolatitudes were calculated from samples from 16 time units in 7 holes and compared to the apparent polar wander path of the North American plate.
Resumo:
During drilling at Sites 759, 760, and 761 of Leg 122 (Exmouth Plateau, northwest Australia), a thick section of Upper Triassic sediments was recovered. Paleomagnetic analyses were made on 398 samples from Holes 759B, 760A, 760B, and 761C. Progressive thermal demagnetization, alternating field demagnetization, or mixed treatment removed an initial unstable component and isolated a characteristic remanent magnetization which is of normal or reversed polarity. The magnetostratigraphic results allow us to propose a magnetic polarity sequence which extends from the upper Carnian to lower Rhaetian. This sequence reveals many more reversals than previously suggested from paleomagnetic studies. The magnetostratigraphic data also allow us to suggest correlations between Sites 759 and 760.
Resumo:
Chemical analyses have been carried out on 40 samples from the sediment surface and 210 samples from cores that were taken from the edge of the African continental block at the Arabian Sea (coasts of Somalia and Kenya, from Cape Guardafui to Mombasa) on the occasion of the Indian Ocean Expedition of the German research vessel "Meteor" during the years 1964/65. The carbonate content shows its maximum on the northern part of the continental shelf of Africa, where fossil reef debris furnish the detritic portion of carbonate. In the southern part of the continental shelf of Africa the portion of carbonate is low, as it is heavily diluted by the non-carbonatic detritus. It is also in the deep-sea that a lower carbonate content is encountered below the calcite compensation depth. Trace elements in the carbonates: On the shelf and in its vicinity Sr and Mg are enriched. The enrichment has been brought about by the portion of reef debris, as this latter contains aragonite (enrichment of Sr) as well as high-magnesium calcite. The greatest part of the slope contains carbonates that are poor in trace elements and mainly made up of foraminifera (and of coccoliths). Below the carbonate compensation depth another enrichment of Mg takes place in the carbonates, which is probably due to a selective dissolution of calcite in comparison to dolomite. The iron and manganese contents of the carbonates are high (iron higher in coast proximity, manganese higher in the depth), but not genuine, as they come about in the course of the extraction of the carbonates as a result of the dissolution of authigenic Mn-Fe-minerals. Non-carbonatic portion of the sediments: In coast proximity an enrichment of quartz comes about. Within the quartz-rich zone it is the elements V, Cr, Fe, Ti, and B that have been enriched in the non-carbonatic components. This enrichment must be attributed to an elevated content of heavy minerals. In the case of Ti and Fe the preliminary enrichment brought about by processes of lateritisation on the continent plays a certain role. Toward the deep-sea an enrichment of the elements Mn Ni, Cu, and Zn takes place; these enrichments must be explained by authigenic Mn-Fe-minerals. Within the Mn-rich zone a belt running parallel to the coast stands out that shows an increased Mn-enrichment. However, this increase in enrichment does not apply to the elements Ni, Cu, and Zn. It is probable that this latter increased enrichment comes about as a result of the migration of manganese to the sediment surface. (Within the sediments there prevail reductive conditions, in the presence of which Mn is capable of migration, whereas at the sediment surface its precipitation comes about under oxidizing conditions). The quantity of organic matter mainly is dependent on grain size and on the rate of sedimentation. On the shelf an impoverishment of organic matter is to be encountered, as the sediments are coarse-grained. In the depth the impoverishment must be explained on the strength of a small rate of sedimentation. Between those two ranges organic substance is enriched. P and N show an enrichment in comparison to Corg with this applying all the more the smaller the absolute quantity of Corg is. In this particular case one has to do with an enrichment coming about during the diagenetic processes of organic matter. A comparison with the sediments from the Indian and Pakistani continental border in Arabian Sea shows as follows: on the African continental border the coarse detrital material has been transported farther out to deep-sea, which has something to do with the greater inclination of the surface of sedimentation. Carbonate is found in greater abundance on the African side. Its chemical composition is influenced by reef-debris which is missing by Indian-Pakistani side. The content of organic matter is lower on the African side. Contrary to that, the enrichments of N and P compared to organic matter are of an equal order of magnitude on both sides of the Arabian Sea.
Resumo:
Bulk and clay mineral investigations were conducted on ~750 samples from four sites drilled during Ocean Drilling Program Leg 189 on the western Tasmanian margin (Site 1168), the South Tasman Rise (Sites 1170 and 1171), and the East Tasman Plateau (Site 1172). The mineralogy of the bulk sediment is very similar at all sites, and major changes coincide with the boundaries of the three main lithologic units described in the Leg 189 Initial Reports volume. The clay mineral assemblages show significant regional differences, but their major variations coincide at all sites and with major changes in regional tectonics and climate.
Effective stress, porosity, p-wave velocity and mineral composition of ODP Hole 174A-1073A sediments
Resumo:
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.
Resumo:
Constant-pressure difference and constant-flow permeability tests were conducted on core samples from Ocean Drilling Program Legs 170 and 205 from the Costa Rica subduction zone representing pelagic carbonate and hemipelagic mud lithologies. Seven whole-round core samples from Sites 1040, 1253, and 1255 were tested for vertical permeabilities. The permeabilities of the pelagic carbonate sediments range from ~4 x 10**-16 to ~1 x 10**-15 m**2. The permeabilities of the hemipelagic mud sediments vary from ~2 x 10**-18 to ~4 x 10**-18 m**2. To further characterize the sediments, grain size, total carbon, and total inorganic carbon analyses were conducted.
Resumo:
Chemical analyses of North Atlantic D.S.D.P. (Deep Sea Drilling Project) sediments indicate that basal sediments generally contain higher concentrations of Fe, Mn, Mg, Pb, and Ni, and similar or lower concentrations of Ti, Al, Cr, Cu, Zn, and Li than the material overlying them. Partition studies on selected samples indicate that the enriched metals in the basal sediments are usually held in a fashion similar to that in basal sediments from the Pacific, other D.S.D.P. sediments, and modern North Atlantic ridge and non-ridge material. Although, on average, chemical differences between basal sediments of varying ages are apparent, normalization of the data indicates that the processes leading to metal enrichment on the crest of the Mid-Atlantic Ridge appear to have been approximately constant in intensity since Cretaceous times. In addition, the bulk composition of detrital sediments also appears to have been relatively constant over the same time period. Paleocene sediments from site 118 are, however, an exception to this rule, there apparently having been an increased detrital influx during this period. The bulk geochemistry, partitioning patterns, and mineralogy of sediments from D.S.D.P. 9A indicates that post-depositional migration of such elements as Mn, Ni, Cu, Zn, and Pb may have occurred. The basement encountered at the base of site 138 is thought to be a basaltic sill, but the overlying basal sediments are geochemically similar to other metalliferous basal sediments from the North Atlantic. These results, as well as those from site 114 where true oceanic basement was encountered, but where there was an estimated 7 m.y. hiatus between basaltic extrusion and basal sediment deposition, indicate that ridge-crest sediments are not necessarily deposited during active volcanism but can be formed after the volcanism has ceased. The predominant processes for metal enrichment in these deposits and those formed in association with other submarine volcanic features is a combination of shallow hydrothermal activity, submarine weathering of basalt, and the formation of ferromanganese oxides which can scavenge metals from seawater. In addition, it seems as though the formation of submarine metalliferous sediments is not restricted to active-ridge areas.
Resumo:
The wet bulk density is one of the most important parameters of the physical and geological properties of marine sediments. The density is connected directly with sedimentation history and a few sedirnent properties. Knowledge of the fine scale density-depth structure is the base for many model calculations, for both sedimentological and palaeoclimatic research. A density measurement system was designed and built at the Alfred Wegener Institute in Bremerhaven for measuring the wet buk density of sediment cores with high resolution in a non-destructive way. The density is deterrnined by measuring the absorption of Gamma-rays in the sediment. This principle has been used since the 50's in materials research and in the geosciences. In the present case, Cs137 is used as the radioactive source and the intensity is measured by a detector system (scintillator and photomultiplier). Density values are obtainable in both longitudinal core sections and planar cross-sections (the latter are a function of the axial rotation angle). Special studies on inhomogenity can be applied with core rotation. Detection of ice rafted debris (IRD) is made possible with this option. The processes that run the density measurement system are computer controlled. Besides the absorption measurement the core diameter at every measurement point is determined with a potentiometric system. The data values taken are stored on a personal computer. Before starting routine measurements on the sediment cores, a few experiments conceming the statistical aspects of the gamma-ray signal and its accuracy were carried out. These experiments led to such things as the optimum operational parameters. A high spatial resolution in the mm-range is possible with the 4mm-thin gamma-ray measurements. Within five seconds the wet bulk density can be deterrnined with an absolute accuracy of 1%. A comparison between data measured with the new system and conventional measurements on core samples after core splitting shows an agreement within +I- 5% for most of the values. For this thesis, density determinations were carried out on ten sediment cores. A few sediment characteristics are obtainable from using just the standard measurement results without core rotation. In addition to differentes and steps in the absolute density range, variations in the "frequency" of the density-depth structure can be detected due to the close spatial measurement interval and high resolution. Examples from measurements with small (9°) and great (90°) angle increments show that abrupt and smooth transitional changes of sedirnent layers as well as ice rafted debris of several dimensions can be detected and distiflguished clearly. After the presentation of the wet bulk density results, a comparison with data from other investigations was made. Measurements of the electrical resistivity correlated very well with the density data because both parameters are closely related to the porosity of the sedirnent. Additionally, results from measurements of the magnetic susceptibility and from ultra-sonic wave velocity investigations were considered for a integrative interpretation. The correlation of these both parameters and wet bulk density data is strongly dependent on the local (environmental) conditions. Finally, the densities were compared with recordings from sediment-echographic soundings and an X-ray computer tomography analysis. The individual results of all investigations were then finally combined into an accurate picture of the core. Problems of ambiguity, which exist when just one Parameter is determined alone, can be reduced more or less according to the number of parameters and sedimentary characteristics measured. The important role of the density data among other parameters of such an integrated interpretation is evident. Evidence of this role include the high resolution of the measurement, the excellent accuracy and the key position within methods and parameters concerning marine sediments.
Resumo:
This dataset contains the results of granulometric and bulk geochemical analyses of Van Veen surface samples obtained by the Alfred Wegener Institute (AWI) in the course of the 2012 and 2013 summer field seasons. The sampling was performed along transects in depths generally <13 m, to a distance of about <5 km off Herschel Island. In 2012, 75 samples in Pauline Cove and in the vicinity of Simpson Point were obtained. Sample collection was expanded in 2013, on transects established the previous year, with additional locations in Tetris Bay and Workboat Passage. Samples consisted of approximately 100 g of the top 3-6 cm of sediment, and were frozen in the field and freeze dried at the AWI before undergoing analytical procedures. Sample locations were recorded with the onboard global positioning system (GPS) unit. Grain size distributions in our study were obtained using laser diffractometry at the AWI (Beckman Coulter LS200) on the <1 mm fraction of samples oxidized with 30% H2O2 until effervescence ceased to remove organics. Some samples were also sieved using a sieve stack with 1 phi intervals. GRADISTAT (Blott and Pye, 2001) was used to calculate graphical grain size statistics (Folk and Ward, 1957). Grain diameters were logarithmically transformed to phi values, calculated as phi=-log2d, where d is the grain diameter in millimeters (Blott and Pye, 2001; Krumbein, 1934). Freeze dried samples were ground and ground using an Elemetar Vario EL III carbon-nitrogen-sulphur analyzer at the AWI to measure total carbon (TC) and total nitrogen (TN). Tungsten oxide was added to the samples as a catalyst to the pyrolysis. Following this analysis, total organic carbon (TOC) was determined using an Elementar VarioMax. Stable carbon isotope ratios of 13C/12C of 118 samples were determined on a DELTAplusXL mass spectrometer (ThermoFisher Scientific, Bremen) at the German Research Centre for Geosciences (GFZ) in Potsdam, Germany . An additional analysis on 69 samples was carried out at the University of Hamburg with an isotope ratio mass spectrometer (Delta V, Thermo Scientific, Germany) coupled to an elemental analyzer (Flash 2000, Thermo Scientific, Germany). Prior to analysis, soil samples were treated with phosphoric acid (43%) to release inorganic carbon. Values are expressed relative to Vienna Peedee belemnite (VPDB) using external standards (USGS40, -26.4 per mil VPDB and IVA soil 33802153, -27.5 per mil VPDB).