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J. L. Bischoff

Publications and source records attributed to J. L. Bischoff.

At least 37 records · Page 2Linked to original sources
USGS1993

A flexible Au-Ir cell with quick assembly for hydrothermal experiments

The paper describes a new flexible reaction cell for high-temperature and high-pressure experiments in hydrothermal apparatus. The interior of the cell is all Au, except for two inert Ir gaskets. The design features an all Au cap that can be easily and rapidly assembled and disassembled. The capacity of the cell is approximately 240 mL, with a height of 20 cm and an o.d. of 6 cm. -Authors

American Mineralogist↗
USGS1992

Uranium-series isochron dating at El Castillo Cave (Cantabria, Spain): The "Acheulean"/"Mousterian" question

A massive flowstone layer, Level 23, near the base of the stratigraphic sequence in El Castillo Cave (Cantabria, Spain), is dated by the uranium-series isochron method to 89+11/−10 ka bp. The flowstone separates cultural layers traditionally labelled “Mousterian” (above) and “Acheulean” (below). The date reported here, in association with other recent age determinations for “Mousterian” and “Acheulean” artifact assemblages in Western Europe, calls into question the temporal significance of these archaeological designations. In addition, it further underlies the importance of the Castillo cultural sequence and allows tentative discussion of changing rates of sedimentation in the vestibule of the cave, where some 18 m of cultural and geological deposits were laid down during the course of the Upper Pleistocene.

Journal of Archaeological Science↗
USGS1992

Geochemical effects of deep-well injection of the Paradox Valley brine into Paleozoic carbonate rocks, Colorado, U.S.A.

Brine seepage into the Dolores River from ground water in Paradox Valley, Colorado constitutes a major source of salt to the Colorado River. Plants are enderway to remove this source of salt by drawing down the Paradox Valley brine (PVB) and forcibly injecting it into a deep disposal well (4.8 km). Experiments were conducted to determine the effects of deep-well injection of PVB. The results show that PVB is near saturation with anhydrite at 25°C, and that heating results in anhydrite precipitation. The amount and the rate at which anhydrite forms is temperature, pressure, and substrate dependent. Paradox Valley brine heated in the presence of Precambrian rocks from the drill core produces the same amount of anhydrite as PVB heated alone, but at a greatly accelerated rate. A 30% dilution of PVB with Dolores River water completely eliminates anhydrite precipitation when the fluid is heated with the Precambrian rocks. Interaction of PVB and Leadville Limestone is characterized by dolomitization of calcite by brine Mg which releases Ca to solution. This added Ca reacts with SO 4 to form increased amounts of anhydrite. A 20% dilution of PVB by Dolores River water has no effect on dolomitization and reduces the amount of anhydrite only slightly. A 65% dilution of PVB by Dolores River water still does not prevent dolomitization but does suppress anhydrite formation. Computer modeling of PVB by programs utilizing the Pitzer ion-interaction parameters is in general agreement with the experimental results. Ion-activity products calculated by both SOLMINEQ and PHRQPITZ are close to equilibrium with both anhydrite and dolomite whenever these phases are present experimentally, although the calculations over-estimate by a factor of 2 the degree of saturation. Some discrepancies in the calculated results between the two programs are due largely to differences in mineral solubility data.

Colorado↗
USGS1991

Gaylussite formation at Mono Lake, California

The salinity of Mono Lake has steadily increased since 1941 from 50%. to about 90%. due to diversion of tributary streams. This increase has resulted in the newly discovered precipitation of gaylussite (Na 2 Ca(CO 3 ) 2 · 5H 2 O). Chemical modeling of the lake water using Pitzer equations suggests that gaylussite has been forming year round since about 1970 when the salinity first exceeded 80%., and that it was earlier forming intermittently at lower salinities in the winter shortly after diversion began, breaking down incongruently to aragonite during summers. Lake water appears to remain at a constant 9-fold supersaturation with aragonite at all salinities, perhaps buffered by monohydrocalcite which appears to be just at saturation for all salinities. Other saline lakes also appear to be buffered by monohydrocalcite.

California↗
USGS1991

Radiometric dating of quaternary deposits and the hominid mandible of Lake Banyolas, Spain

We report results of U-series analyses of the travertine matrix surrounding the Banyolas mandible that indicate an age of 45??4 ka bp. The mandible, an archaic hominid fossil generally deemed of mid-Pleistocene age, was recovered from a travertine matrix in 1887. Similar analyses on 21 travertine samples from quarries near the discovery site yield coherent U-series dates in correct stratigraphic order, ranging from 44 ka bp to 117 ka bp. Isotopic composition of these samples and the mandible matrix show no evidence of open system behaviour. Coherent isotopic results from adjacent quarries support the validity of the date on the mandible travertine, and we conclude the mandible is much younger than previously believed. ?? 1991.

Catalonia↗
USGS1989

Accelerator 14C dates for early upper paleolithic (basal Aurignacian) at El Castillo Cave (Spain)

Three fragments of charcoal taken from different parts of the lowermost bed containing Aurignacian artifacts at El Castillo Cave yielded AMS dates of 37·7 (± 1·8) ka bp, 38·5 (± 1·8) ka bp, and 40·0 (± 2·1) ka bp (average 38·7 ± 1·9 ka bp). These dates are almost identical to new AMS dates from l'Arbreda cave in Catalunya on the same cultural horizon (average 38·5 ± 1·0 ka bp) and are significantly older than the earliest dates for Aurignacian industries in the Aquitaine and in other parts of Central and Western Europe.

Journal of Archaeological Science↗
USGS1988

A test of uranium-series dating of fossil tooth enamel: Results from Tournal Cave, France

A series of well preserved mammal bones and horse teeth was analyzed from archaeological levels of Tournal Cave (Magdalenian, Aurignacian, and Mousterain) to test the hypothesis that well-crystallized enamel behaves more as a closed system than does whole bone. The isotopic composition of bones and tooth enamels from this deposit meet criteria for confidence, and gave no reasons to suspect contamination or open-system behavior. Two samples for which 231 Pa could be analyzed showed internal concordance with the respective 230 Th ages. In spite of the favourable isotopic criteria, however, comparison of the U-series ages of the bones and the tooth enamel with stratigraphic position and 14 C control indicated the dates were not meaningful. In general, both bones and tooth enamels gave ages too young, although some were clearly too old. Neither group showed any systematic increase of age with stratigraphic depth. Tooth enamel, therefore, shows no advantage over bone for U-series dating for this site. In Tournal cave both bones and enamel are apparently open to U, which is probably cycling as a consequences of post-depositional groundwater movement.

Applied Geochemistry↗
USGS1988

Uranium-series dating of the Mousterian occupation at Abric Romani, Spain

The precise evolutionary position of the Neanderthal people continues to be a major uncertainty in human evolution. Their origin and their relationship to anatomically modern people are unclear and are clouded by poor chronology. Lithic artefacts of the Mousterian type, found throughout Europe and the Mediterranean Basin, are believed to be the tool kit of the Neanderthals, but dates within Mousterian-bearing deposits are extremely rare. We report here on 20 high-quality uranium-series dates from Mousterian beds at Abric Romani, a rock shelter near Barcelona, Spain. The dates range from 39 to 60 kyr before present ( BP ) in an orderly stratigraphic succession and provide precise chronological control on an important Mousterian archaeological site.

Nature↗
USGS1985

Phase relations and adiabats in boiling seafloor geothermal systems

Observations of large salinity variations and vent temperatures in the range of 380–400°C suggest that boiling or two-phase separation may be occurring in some seafloor geothermal systems. Consideration of flow rates and the relatively small differences in density between vapors and liquids at the supercritical pressures at depth in these systems suggests that boiling is occurring under closed-system conditions. Salinity and temperature of boiling vents can be used to estimate the pressure-temperature point in the subsurface at which liquid seawater first reached the two-phase boundary. Data are reviewed to construct phase diagrams of coexisting brines and vapors in the two-phase region at pressures corresponding to those of the seafloor geothermal systems. A method is developed for calculating the enthalpy and entropy of the coexisting mixtures, and results are used to construct adiabats from the seafloor to the P-T two-phase boundary. Results for seafloor vents discharging at 2300 m below sea level indicate that a 385°C vent is composed of a brine (7% NaCl equivalent) in equilibrium with a vapor (0.1% NaCl). Brine constitutes 45% by weight of the mixture, and the fluid first boiled at approximately 1 km below the seafloor at 415°C, 330 bar. A 400°C vent is primarily vapor (88 wt.%, 0.044% NaCl) with a small amount of brine (26% NaCl) and first boiled at 2.9 km below the seafloor at 500°C, 520 bar. These results show that adiabatic decompression in the two-phase region results in dramatic cooling of the fluid mixture when there is a large fraction of vapor.

Earth and Planetary Science Letters↗
USGS1984

Oxidation state of marine manganese nodules

Analyses of the bulk oxidation state of marine manganese nodules indicates that more than 98% of the Mn in deep ocean nodules is present as Mn(IV). The samples were collected from three quite different areas: the hemipelagic environment of the Guatemala Basin, the pelagic area of the North Pacific, and seamounts in the central Pacific. Results of the study suggest that todorokite in marine nodules is fully oxidized and has the following stoichiometry: (K, Na, Ca, Ba) .33 (Mg, Cu, Ni) .76 Mn 5 O 22 (H 2 O) 3.2 .

Geochimica et Cosmochimica Acta↗
USGS1984

Holocene age of the Yuha burial: Direct radiocarbon determinations by accelerator mass spectrometry

The view that human populations may not have arrived in the Western Hemisphere before about 12,000 radiocarbon yr BP1,2 has been challenged by claims of much greater antiquity for a small number of archaeological sites and human skeleton samples. One such site is the Homo sapiens sapiens cairn burial excavated in 1971 from the Yuha desert, Imperial County, California3-5. Radiocarbon analysis of caliche coating one of the bones of the skeleton yielded a radiocarbon age of 21,500??1,000 yr BP4, while radiocarbon and uranium series analyses of caliche coating a cairn boulder yielded ages of 22,125??400 and 19,000??3,000 yr BP, respectively5. The late Pleistocene age assignment to the Yuha burial has been challenged by comparing the cultural context of the burial with other cairn burials in the same region6, on the basis of the site's geomorphological context and from radiocarbon analyses of soil caliches. 7,8 In rebuttal, arguments in defence of the original age assignment have been presented9,10 as well as an amino acid racemization analysis on the Yuha skeleton indicating an age of 23,600??2,600 yr BP11. The tandem accelerator mass spectrometer at the University of Arizona has now been used to measure the ratio of 14C/13C in several organic and inorganic fractions of post-cranial bone from the Yuha H. sapiens sapiens skeleton. Isotope ratios from six chemical fractions all yielded radiocarbon ages for the skeleton of less than 4,000 yr BP. These results indicate that the Yuha skeleton is of Holocene age, in agreement with the cultural context of the burial, and in disagreement with the previously assigned Pleistocene age of 19,000-23,000 yr. ?? 1984 Nature Publishing Group.

Nature↗
USGS1981

The aluminosilicate fraction of North Pacific manganese nodules

Nine nodules collected from throughout the deep North Pacific were analyzed for their mineralogy and major-element composition before and after leaching with Chester-Hughes solution. Data indicate that the mineral phillipsite accounts for the major part (> 75%) of the aluminosilicate fraction of all nodules. It is suggested that formation of phillipsite takes place on growing nodule surfaces coupled with the oxidation of absorbed manganous ion. All the nodules could be described as ternary mixtures of amorphous iron fraction (Fe-Ti-P), manganese oxide fraction (Mn-Mg Cu-Ni), and phillipsite fraction (Al-Si-K-Na), these fractions accounting for 96% of the variability of the chemical composition.

Geochimica et Cosmochimica Acta↗
USGS1981

Experimental seawater-basalt interaction at 300°C, 500 bars, chemical exchange, secondary mineral formation and implications for the transport of heavy metals

Seawater and NaCl solutions were reacted with basalt (basalt glass and diabase) for several months at 300&deg;C, 500 bars and a water/rock ratio of 10. During reaction, seawater was significantly modified, increasing in Ca, H 2 S, CO 2 . SiO 2 , K. Fe, Mn. Ba, Al and H + , and decreasing in Mg and SO 4 . Basalt glass was completely replaced by smectite, wairakite, anhydrite and hematite, and diabase was partially replaced by mixed layered smectite-chlorite, anhydrite and magnetite (?). Diabase was altered more slowly than basalt glass and the corresponding changes in seawater chemistry were less pronounced. Basalt glass reacted with a 0.45 m NaCl solution resulted in the formation of smectite, albite. truscottite and wairakite. Solutions from this experiment were characterized by a relatively high pH and dominated by Ca for Na exchange reactions. At no point in this experiment were heavy metals solubilized, in contrast to the seawater experiments. This behavior illustrates the fundamental importance of seawater chemistry to heavy-metal solubility; that is, the removal of Mg from seawater generates acidity which maintains heavy metals in solution. Apparently seawater chlorinity is not capable of enhancing heavy-metal solubility by chloride complexing. Seafloor heavy-metal deposits can result from the following: Seawater-basalt interaction at moderate temperature (&sim;-300&deg;C and high effective water/rock ratios; or at relatively high temperatures (&sim;-400&deg;C) and low (e.g.< 10) water/rock ratios.

Geochimica et Cosmochimica Acta↗
USGS1981

Uranium series dating of human skeletal remains from the Del Mar and Sunnyvale sites, California

Uranium series analyses of human bone samples from the Del Mar and Sunnyvale sites indicate ages of 11,000 and 8,300 years, respectively. The dates are supported by internal concordancy between thorium-230 and protactinium-231 decay systems. These ages are significantly younger than the estimates of 48,000 and 70,000 years based on amino acid racemization, and indicate that the individuals could derive from the population waves that came across the Bering Strait during the last sea-level low.

California↗