For lack of funding, irreplaceable collections of mineral specimens may be lost. The Earth scienc... more For lack of funding, irreplaceable collections of mineral specimens may be lost. The Earth science community must rethink the role of museums as archives and outlets for information.
This paper studies the Middle Miocene ostracods from three different outcrops in the Al Khums are... more This paper studies the Middle Miocene ostracods from three different outcrops in the Al Khums area, northwestern Libya. Lithologically, these outcrops belong to the Al Khums Formation, and are considered synchronous due to the great similarity in their ostracod content. Twenty seven ostracod species, belonging to 22 genera and 13 families, were identified. Although the age of the Al Khums Formation cannot be precisely constrained based on its ostracod assemblage, the presence of the larger benthic foraminiferan subspecies Borelis melo melo allows to assign to the sequence a Middle Miocene age. The identified ostracods indicate that the depositional environment was shallow marine. This conclusion is also supported by the co-occurrence of algae, large oysters and corals. Multivariate analyses were applied to the present data to distinguish the paleobiogeographical provinces of the studied ostracod species. The results indicate that there are two distinguished bioprovinces: (1) The South Tethyan bioprovince (STP) including Algeria, Libya and Egypt, and (2) The North Tethyan bioprovince (NTP) including Spain, Italy, Malta, France, Turkey and Greece. Similarities between the ostracod assemblages of these bioprovinces suggest a good marine connection between both sides of the Mediterranean Sea during the Middle Miocene.
Experimental data of I^atil and Maury 0977), Korzhinskiy (1981), and Ruszala and Kostiner (1975) ... more Experimental data of I^atil and Maury 0977), Korzhinskiy (1981), and Ruszala and Kostiner (1975) on the hydroxyapatite-chlorapatite (HAp-ClAp) solid solution were modeled as symmetric and asymmetric solutions. Results of Latil and Maury (1977) and Korzhinskiy (1981) on the hydroxyapatite-fluorapatite (HAp-FAp) join were also modeled. The regular solution model fits the HAp-ClAp data without obvious complications, yielding binary interaction parameters (Zo) of less than 20 kJ. mol-' ' K-r. The data suggest that the HAp-ClAp solid solution may be treated as essentially ideal at or above 500 'C. Using a heat-capacity function calculated from that of FAp, the data may be reduced to give an enthalpy of formation for ClAp of-6548.027 kJ'mol-''K-' and an entropy of 457 J.mol I at298.15 K and I bar. Data on the HAp-FAp join are not conclusive, but allow the interpretation of ideal solution. Consideration of the details of F-OH interaction support this interpretation. The presence of Na as a component in the experiments of Latil and Maury (1977) is an insurmountable obstacle to modeling their results. The reversal experiments of Korzhinskiy (1981) show that FAp essentially did not re-equilibrate at 500 "C and 600 oC, in agreement with the results of earlier workers. The failure of Korzhinskiy's experiments to reach equilibrium at 700 "C is a useful indication of FAp behavior under hydrothermal conditions. For all practical purposes, ClAp-HAp and HAp-FAp solid solutions may be treated as ideal at geologic temperatures and pressures, INrnooucrroN amphibole results from the sensitivity of hydroxyl and rhe fugacities of Fand cr-bearing species are impori#:?";fl:?t1"iJry+:,h1"r"i":fl"T1xtrfft?1"ff tant variables in many petrologic and geochemical prob-;;;';;i; phases do not occur in as rilde a range of lems. Cl complexes are important instruments of mass environmenti as do apatites and are highly variable in transfer during metamorphism and during the formation composition across th; range of environments in which of porphyry-type hydrothermal ore deposits. F is capable they do occur. The apatites, however, present few of these of extensive influence on the rheology (Dingwell, 1987) problems. and phase relations (Manning, l98l; Weidner and Mar-A formula for apatite solid solutions can be written as tin, 1987) of magmas. Ca,(POo).X, where X : F, OH, Cl, or O. Substitution of Mineral indicators of the fugacities of these volatile other elements for Ca and P is relatively minor in most components have not been exploited to their full poten-natural samples. Apatites may be found in practically all tial. This is because of problems with the application of geologic environments. It is one of the few minerals near the indicators that are available. Biotites have been well-the liquidus of both silicic and basaltic rocks (Watson, calibrated for such use (
Molten calcium halide and hydroxide salts may be used as flux and reactants in determining apatit... more Molten calcium halide and hydroxide salts may be used as flux and reactants in determining apatite exchange equilibria and solid solution behavior. New experimental data and published phase equilibria are used to determine a thermodynamic model of melts and solids along the binary joins of the anhydrous apatite system Ca3(P04)2-CaC12-CaF2-Ca(OH)*. In this model, melt components are expressed as Cac,sX, where X is hydroxide or a halogen, or as Ca,.5P0 4. The derived binary interaction parameters (WC's) are sufficient to describe deviations from Raoultian behavior for the data. Standard state data are derived for molten Ca(OH)z and Ca3(POah, and for the intermediate compounds CaClF, CaClOH, and Ca2P04Cl. Melts in the CaC12-CaF2 system show ideal mixing behavior, while the calcium hydroxide-bearing molten salts form asymmetric regular solutions. The hydroxide-bearing melts show the small positive enthalpies of mixing typical for mixed-anion salts. Similar behavior is measured in simpler molten salt mixtures. The positive deviations from Raoultian behavior are not a mathematical artifact of the model. Data are less extensive for the salt-phosphate systems but cover the essential portions of the systems where salt to phosphate ratios are high. The mixtures of the molten salts and phosphates salts show large negative enthalpy interaction parameters (W,), as is expected in eutectic systems which mix a highmelting-point crystal with a low-melting-point flux. Adequate reproduction of the data requires that some entropy interaction parameters be negative, although small. This implies the presence of ordering in the melt, which is manifested in more polymerized phosphate liquids and glasses as halogenated and hydroxylated orthophosphate and pyrophosphate species. Results of the model indicate that the quaternary system is a good choice for determination of activitycomposition relations for the apatites. Comparison of common sources of standard state thermodynamic data (ROBIE et al., 1979; JANAF, CHASE et al., 1985; CODATA, GARVIN et al., 1987) shows that the data for the salts are very similar where they are not identical. At temperatures below 900°C in the ternary systems, liquid compositions will be on or near the apatite-crystalline salt cotectics, and dissolve less than 1 mol% CaJ(P04)2. This makes CaC12-CaF2 mixtures excellent candidates for determination of unambiguous apatite activity-compositional relations. Only the Ca(OHh liquidus is strongly affected by the addition of phosphate, but this effect is closely described by a regular solution model.
Central to the history of North Carolina geology and ... R. ChRis TaCkeR Geology section, Researc... more Central to the history of North Carolina geology and ... R. ChRis TaCkeR Geology section, Research and Collections North Carolina Museum of Natural sciences 11 West Jones street Raleigh, North Carolina 27601 [email protected] ... Figure 1. William e. hidden (kneeling) ...
Background: Preservation of original organic components in fossils across geological time is cont... more Background: Preservation of original organic components in fossils across geological time is controversial, but the potential such molecules have for elucidating evolutionary processes and phylogenetic relationships is invaluable. Chitin is one such molecule. Ancient chitin has been recovered from both terrestrial and marine arthropods, but prior to this study had not been recovered from fossil marine mollusks. Methodology/Principal Findings: Organics consistent with b-chitin are recovered in cuttlebones of Mississaepia mississippiensis from the Late Eocene (34.36 million years ago) marine clays of Hinds County, Mississippi, USA. These organics were determined and characterized through comparisons with extant taxa using Scanning Electron Microscopy/ Energy Dispersive Spectrometry (SEM/EDS), Field Emission Scanning Electron Microscopy (Hyperprobe), Fourier Transmission Infrared Spectroscopy (FTIR) and Immunohistochemistry (IHC). Conclusions/Significance: Our study presents the first evidence for organics consistent with chitin from an ancient marine mollusk and discusses how these organics have been degraded over time. As mechanisms for their preservation, we propose that the inorganic/organic lamination of the cuttlebone, combined with a suboxic depositional environment with available free Fe 2+ ions, inhibited microbial or enzymatic degradation.
ABSTRACT Field emission electron microprobe is capable of higher resolution and lower voltage tha... more ABSTRACT Field emission electron microprobe is capable of higher resolution and lower voltage than other microprobes, making it an ideal instrument for analysis of small accessory minerals in thin section such as apatite. In this study, the field emission electron microprobe was evaluated for analysis of fluorine and chlorine in apatite. Analysis was conducted on (001), (100) and an intermediate section of natural apatite crystals, using the JEOL JXA-8530F Hyperprobe, located at Fayetteville State University in Fayetteville, North Carolina. Conditions were beam current of 10 nanoamps, accelerating voltages from 5-20 kV, and spot sizes from 1-10 micrometers. Very short counting times were used, some as little as 2 seconds. Analytical strategies exploited the fact that excitation energies for fluorine Kα are much lower than for chlorine. Earlier studies (e.g. Stormer et al. 1993; Fialin and Chopin, 2006) documented the complex behavior of beam-driven migration, subsurface accumulation and desorption during fluorine analysis. The cumulative effect is increase and then fall of count rates with time and repeated analysis. The details of earlier studies were reproduced: (1) Apatite analysis by electron microprobe has two additional unknown variables, which are the crystallographic orientation of the unknown and of the standard. (2) The most reliable measure of fluorine cps is derived from a regression to zero time, accounting for crystal orientation; (3) Changing the analytical conditions (accelerating voltage, spot size, duration of analysis) changes only the time scale over which migration and desorption take place. New results from the JEOL Hyperprobe show that, for all crystal orientations, initial fluorine cps increase from 5 and 7 kV to 10 kV, but decrease systematically with further increases in kV, interpreted as loss of fluorine without concomitant excitation of X-rays. To date, fluorine analysis is routinely conducted at 15 and 20 kV. In contrast, chlorine initial counts increase as expected from 10 to 20 kV, but the loss of chlorine is more strongly controlled by crystal orientation. With electron beam parallel to the c-axis, chlorine counts are very low, pointing to the chlorine loss during analysis. Hence fluorine and chlorine are fractionated during analysis as a complicated function of beam energies and crystal orientation. Routine analyses of halogens in apatite are unlikely to yield a quantitative analysis, and OH calculated by the difference in a normalized analysis is less likely to be meaningful. Further, the use of 15-20 kV secondary electron or backscatter electron imaging prior to analysis should be reconsidered. Stormer et al., 1993, Am. Min., 78, 641. Fialin and Chopin, 2006, Am. Min. 91, 503.
New discoveries in North Carolina's Neoproterozoic Carolina Terrane, combined with a reexaminatio... more New discoveries in North Carolina's Neoproterozoic Carolina Terrane, combined with a reexamination of the holotype of Oldhamia recta and other material from the Yale Peabody Museum, reveal these specimens as body fossils of a rod-like organism, rather than ichnofossils. Close examination of fossils originally identified as O. recta lack: levees made by movement of a tracemaker through a sediment; internal structures indicating backfilling or fecal material; scratch marks (denoting a recumbent lifestyle); or evidence of peristaltic movement. Crossovers of rods in some instances also indicate rigidity in the fossils. Most importantly, quantitative analyses indicate Gaussian size distributions and narrow ranges of alignment for the fossils, with each respective line of evidence interpreted as body fossils aligned by currents. Because this newly discerned evidence favors a body fossil origin for these specimens, we propose that O. recta is invalid as an ichnospecies. Our research supports more quantitative approaches to augment qualitative descriptions when evaluating whether Ediacaran-age structures are trace or body fossils.
Introduction: The North Carolina Museum of Natural Sciences (NCMNS) is located in Raleigh, NC and... more Introduction: The North Carolina Museum of Natural Sciences (NCMNS) is located in Raleigh, NC and houses a wide variety of exhibits, collections and research programs related to the Natural Sciences. A group of fourteen meteorites comprise part of the Museum's holdings. All of the meteorites were found or observed to fall in NC. Several specimens are on display in the museum and all are available for research. Here we present the results of a collaboration with faculty at Fayetteville State University (FSU) to reexamine (and if necessary, reclassify) the NCMNS meteorite collection. History: The Geology Collection began with the collections of the North Carolina Geological Survey, which predates the Museum's founding in 1879. Samples have been added sporadically by purchase, trade and/or collection, principally by former Curator Harry Davis. The last effort to classify and curate these is unknown due to a twenty-three year hiatus between curators. Currently, the Collection is curated by Dr. Chris Tacker who is overseeing this re-examination of the meteorite collection as part of an effort to re-invigerate and showcase astromaterials research in North Carolina. The Collection: The collection contains fourteen specimens with several notable members. The collection contains six stony meteorites, and eight iron meteorites. The jewel of the collection is the Moore County Eucrite while the largest is the 75 kg Uwharrie iron. Five meteorites are on permanent display in the Museum: Uwharrie, Farmville, Moore County, Rich Mountain and Deep Springs meteorites. Specific problems are apparent. A meteorite listed in Museum records as "McDowell County" (found May 1921) may be the same meteorite as Wood's Mountain (found 1918); "McDowell County" is given as a synonym in the Catalogue of Meteorites. The Deep Springs meteorite is an ungrouped iron and several iron meteorites are listed only as NiFe bearing in the museums records.
The partitioning of molybdenum between magnetite (mt) and two rhyolitic melts has been determined... more The partitioning of molybdenum between magnetite (mt) and two rhyolitic melts has been determined at 800 degrees C, 1 kb of pressure, and at two oxygen fugacities. At an oxygen fugacity one-half a log unit above nickel-nickel oxide, D (super mt/melt) Mo = 0.21 + or - 0.08. A decrease in the oxygen fugacity to the graphite-methane buffer is accompanied by an increase in D (super mt/melt) Mo to 0.52 + or - 0.13. The differences in melt composition have no discernible effect.These data are interpreted by writing balanced chemical potential relationships involving independently variable phase components. The Nernst partition coefficients given above are then formulated as a function of these equilibria. Given the observed variation in D (super mt/melt) Mo with oxygen fugacity, and assuming that Fe 2 MoO 4 is the molybdenum-bearing phase component in magnetite, our data suggest that Mo(III) may be present in naturally occurring silicic magmas. Further, we suggest the establishment of critical bulk partition coefficients for ore-forming systems, defined in terms of critical values of the efficiency of removal function defined by Candela and Holland (1986). These preliminary results indicate that the crystallization of ferromagnesian or titanium-bearing phases may be important in reducing the amount of molybdenum available for orthomagmatic-hydrothermal ore formation. Oxygen fugacity may play a large role in the melt-crystal-vapor equilibria ofmolybdenum under magmatic conditions.
The distribution of molybdenum between magnetite and a high-silica rhyolite has been measured as ... more The distribution of molybdenum between magnetite and a high-silica rhyolite has been measured as a function of oxygen fugacity. All experiments were water-saturated and were performed in cold-seal pressure vessels at T = 800/sup 0/C and P = 1 kb. Reversed experiments at one-half a log unit above nickel-nickel oxide (log f/sub O/sub 2// = -13.35) yield a D crystal/melt = .16. Preliminary experiments at lower oxygen fugacities suggest higher values for D. This behavior implies that the pertinent equilibria behave according to projected chemical equations. This has important implications for the genesis of porphyry-type ore deposits. At high f/sub O/sub 2//, molybdenum will be concentrated in successive aliquots of melt as an incompatible element with respect to Fe-Ti minerals, whereas at low f/sub O/sub 2// molybdenum will behave as a more compatible element. Note that the systematics for tin would be the reverse of those for molybdenum if tin is in the divalent state in low F/sub O/s...
For lack of funding, irreplaceable collections of mineral specimens may be lost. The Earth scienc... more For lack of funding, irreplaceable collections of mineral specimens may be lost. The Earth science community must rethink the role of museums as archives and outlets for information.
This paper studies the Middle Miocene ostracods from three different outcrops in the Al Khums are... more This paper studies the Middle Miocene ostracods from three different outcrops in the Al Khums area, northwestern Libya. Lithologically, these outcrops belong to the Al Khums Formation, and are considered synchronous due to the great similarity in their ostracod content. Twenty seven ostracod species, belonging to 22 genera and 13 families, were identified. Although the age of the Al Khums Formation cannot be precisely constrained based on its ostracod assemblage, the presence of the larger benthic foraminiferan subspecies Borelis melo melo allows to assign to the sequence a Middle Miocene age. The identified ostracods indicate that the depositional environment was shallow marine. This conclusion is also supported by the co-occurrence of algae, large oysters and corals. Multivariate analyses were applied to the present data to distinguish the paleobiogeographical provinces of the studied ostracod species. The results indicate that there are two distinguished bioprovinces: (1) The South Tethyan bioprovince (STP) including Algeria, Libya and Egypt, and (2) The North Tethyan bioprovince (NTP) including Spain, Italy, Malta, France, Turkey and Greece. Similarities between the ostracod assemblages of these bioprovinces suggest a good marine connection between both sides of the Mediterranean Sea during the Middle Miocene.
Experimental data of I^atil and Maury 0977), Korzhinskiy (1981), and Ruszala and Kostiner (1975) ... more Experimental data of I^atil and Maury 0977), Korzhinskiy (1981), and Ruszala and Kostiner (1975) on the hydroxyapatite-chlorapatite (HAp-ClAp) solid solution were modeled as symmetric and asymmetric solutions. Results of Latil and Maury (1977) and Korzhinskiy (1981) on the hydroxyapatite-fluorapatite (HAp-FAp) join were also modeled. The regular solution model fits the HAp-ClAp data without obvious complications, yielding binary interaction parameters (Zo) of less than 20 kJ. mol-' ' K-r. The data suggest that the HAp-ClAp solid solution may be treated as essentially ideal at or above 500 'C. Using a heat-capacity function calculated from that of FAp, the data may be reduced to give an enthalpy of formation for ClAp of-6548.027 kJ'mol-''K-' and an entropy of 457 J.mol I at298.15 K and I bar. Data on the HAp-FAp join are not conclusive, but allow the interpretation of ideal solution. Consideration of the details of F-OH interaction support this interpretation. The presence of Na as a component in the experiments of Latil and Maury (1977) is an insurmountable obstacle to modeling their results. The reversal experiments of Korzhinskiy (1981) show that FAp essentially did not re-equilibrate at 500 "C and 600 oC, in agreement with the results of earlier workers. The failure of Korzhinskiy's experiments to reach equilibrium at 700 "C is a useful indication of FAp behavior under hydrothermal conditions. For all practical purposes, ClAp-HAp and HAp-FAp solid solutions may be treated as ideal at geologic temperatures and pressures, INrnooucrroN amphibole results from the sensitivity of hydroxyl and rhe fugacities of Fand cr-bearing species are impori#:?";fl:?t1"iJry+:,h1"r"i":fl"T1xtrfft?1"ff tant variables in many petrologic and geochemical prob-;;;';;i; phases do not occur in as rilde a range of lems. Cl complexes are important instruments of mass environmenti as do apatites and are highly variable in transfer during metamorphism and during the formation composition across th; range of environments in which of porphyry-type hydrothermal ore deposits. F is capable they do occur. The apatites, however, present few of these of extensive influence on the rheology (Dingwell, 1987) problems. and phase relations (Manning, l98l; Weidner and Mar-A formula for apatite solid solutions can be written as tin, 1987) of magmas. Ca,(POo).X, where X : F, OH, Cl, or O. Substitution of Mineral indicators of the fugacities of these volatile other elements for Ca and P is relatively minor in most components have not been exploited to their full poten-natural samples. Apatites may be found in practically all tial. This is because of problems with the application of geologic environments. It is one of the few minerals near the indicators that are available. Biotites have been well-the liquidus of both silicic and basaltic rocks (Watson, calibrated for such use (
Molten calcium halide and hydroxide salts may be used as flux and reactants in determining apatit... more Molten calcium halide and hydroxide salts may be used as flux and reactants in determining apatite exchange equilibria and solid solution behavior. New experimental data and published phase equilibria are used to determine a thermodynamic model of melts and solids along the binary joins of the anhydrous apatite system Ca3(P04)2-CaC12-CaF2-Ca(OH)*. In this model, melt components are expressed as Cac,sX, where X is hydroxide or a halogen, or as Ca,.5P0 4. The derived binary interaction parameters (WC's) are sufficient to describe deviations from Raoultian behavior for the data. Standard state data are derived for molten Ca(OH)z and Ca3(POah, and for the intermediate compounds CaClF, CaClOH, and Ca2P04Cl. Melts in the CaC12-CaF2 system show ideal mixing behavior, while the calcium hydroxide-bearing molten salts form asymmetric regular solutions. The hydroxide-bearing melts show the small positive enthalpies of mixing typical for mixed-anion salts. Similar behavior is measured in simpler molten salt mixtures. The positive deviations from Raoultian behavior are not a mathematical artifact of the model. Data are less extensive for the salt-phosphate systems but cover the essential portions of the systems where salt to phosphate ratios are high. The mixtures of the molten salts and phosphates salts show large negative enthalpy interaction parameters (W,), as is expected in eutectic systems which mix a highmelting-point crystal with a low-melting-point flux. Adequate reproduction of the data requires that some entropy interaction parameters be negative, although small. This implies the presence of ordering in the melt, which is manifested in more polymerized phosphate liquids and glasses as halogenated and hydroxylated orthophosphate and pyrophosphate species. Results of the model indicate that the quaternary system is a good choice for determination of activitycomposition relations for the apatites. Comparison of common sources of standard state thermodynamic data (ROBIE et al., 1979; JANAF, CHASE et al., 1985; CODATA, GARVIN et al., 1987) shows that the data for the salts are very similar where they are not identical. At temperatures below 900°C in the ternary systems, liquid compositions will be on or near the apatite-crystalline salt cotectics, and dissolve less than 1 mol% CaJ(P04)2. This makes CaC12-CaF2 mixtures excellent candidates for determination of unambiguous apatite activity-compositional relations. Only the Ca(OHh liquidus is strongly affected by the addition of phosphate, but this effect is closely described by a regular solution model.
Central to the history of North Carolina geology and ... R. ChRis TaCkeR Geology section, Researc... more Central to the history of North Carolina geology and ... R. ChRis TaCkeR Geology section, Research and Collections North Carolina Museum of Natural sciences 11 West Jones street Raleigh, North Carolina 27601 [email protected] ... Figure 1. William e. hidden (kneeling) ...
Background: Preservation of original organic components in fossils across geological time is cont... more Background: Preservation of original organic components in fossils across geological time is controversial, but the potential such molecules have for elucidating evolutionary processes and phylogenetic relationships is invaluable. Chitin is one such molecule. Ancient chitin has been recovered from both terrestrial and marine arthropods, but prior to this study had not been recovered from fossil marine mollusks. Methodology/Principal Findings: Organics consistent with b-chitin are recovered in cuttlebones of Mississaepia mississippiensis from the Late Eocene (34.36 million years ago) marine clays of Hinds County, Mississippi, USA. These organics were determined and characterized through comparisons with extant taxa using Scanning Electron Microscopy/ Energy Dispersive Spectrometry (SEM/EDS), Field Emission Scanning Electron Microscopy (Hyperprobe), Fourier Transmission Infrared Spectroscopy (FTIR) and Immunohistochemistry (IHC). Conclusions/Significance: Our study presents the first evidence for organics consistent with chitin from an ancient marine mollusk and discusses how these organics have been degraded over time. As mechanisms for their preservation, we propose that the inorganic/organic lamination of the cuttlebone, combined with a suboxic depositional environment with available free Fe 2+ ions, inhibited microbial or enzymatic degradation.
ABSTRACT Field emission electron microprobe is capable of higher resolution and lower voltage tha... more ABSTRACT Field emission electron microprobe is capable of higher resolution and lower voltage than other microprobes, making it an ideal instrument for analysis of small accessory minerals in thin section such as apatite. In this study, the field emission electron microprobe was evaluated for analysis of fluorine and chlorine in apatite. Analysis was conducted on (001), (100) and an intermediate section of natural apatite crystals, using the JEOL JXA-8530F Hyperprobe, located at Fayetteville State University in Fayetteville, North Carolina. Conditions were beam current of 10 nanoamps, accelerating voltages from 5-20 kV, and spot sizes from 1-10 micrometers. Very short counting times were used, some as little as 2 seconds. Analytical strategies exploited the fact that excitation energies for fluorine Kα are much lower than for chlorine. Earlier studies (e.g. Stormer et al. 1993; Fialin and Chopin, 2006) documented the complex behavior of beam-driven migration, subsurface accumulation and desorption during fluorine analysis. The cumulative effect is increase and then fall of count rates with time and repeated analysis. The details of earlier studies were reproduced: (1) Apatite analysis by electron microprobe has two additional unknown variables, which are the crystallographic orientation of the unknown and of the standard. (2) The most reliable measure of fluorine cps is derived from a regression to zero time, accounting for crystal orientation; (3) Changing the analytical conditions (accelerating voltage, spot size, duration of analysis) changes only the time scale over which migration and desorption take place. New results from the JEOL Hyperprobe show that, for all crystal orientations, initial fluorine cps increase from 5 and 7 kV to 10 kV, but decrease systematically with further increases in kV, interpreted as loss of fluorine without concomitant excitation of X-rays. To date, fluorine analysis is routinely conducted at 15 and 20 kV. In contrast, chlorine initial counts increase as expected from 10 to 20 kV, but the loss of chlorine is more strongly controlled by crystal orientation. With electron beam parallel to the c-axis, chlorine counts are very low, pointing to the chlorine loss during analysis. Hence fluorine and chlorine are fractionated during analysis as a complicated function of beam energies and crystal orientation. Routine analyses of halogens in apatite are unlikely to yield a quantitative analysis, and OH calculated by the difference in a normalized analysis is less likely to be meaningful. Further, the use of 15-20 kV secondary electron or backscatter electron imaging prior to analysis should be reconsidered. Stormer et al., 1993, Am. Min., 78, 641. Fialin and Chopin, 2006, Am. Min. 91, 503.
New discoveries in North Carolina's Neoproterozoic Carolina Terrane, combined with a reexaminatio... more New discoveries in North Carolina's Neoproterozoic Carolina Terrane, combined with a reexamination of the holotype of Oldhamia recta and other material from the Yale Peabody Museum, reveal these specimens as body fossils of a rod-like organism, rather than ichnofossils. Close examination of fossils originally identified as O. recta lack: levees made by movement of a tracemaker through a sediment; internal structures indicating backfilling or fecal material; scratch marks (denoting a recumbent lifestyle); or evidence of peristaltic movement. Crossovers of rods in some instances also indicate rigidity in the fossils. Most importantly, quantitative analyses indicate Gaussian size distributions and narrow ranges of alignment for the fossils, with each respective line of evidence interpreted as body fossils aligned by currents. Because this newly discerned evidence favors a body fossil origin for these specimens, we propose that O. recta is invalid as an ichnospecies. Our research supports more quantitative approaches to augment qualitative descriptions when evaluating whether Ediacaran-age structures are trace or body fossils.
Introduction: The North Carolina Museum of Natural Sciences (NCMNS) is located in Raleigh, NC and... more Introduction: The North Carolina Museum of Natural Sciences (NCMNS) is located in Raleigh, NC and houses a wide variety of exhibits, collections and research programs related to the Natural Sciences. A group of fourteen meteorites comprise part of the Museum's holdings. All of the meteorites were found or observed to fall in NC. Several specimens are on display in the museum and all are available for research. Here we present the results of a collaboration with faculty at Fayetteville State University (FSU) to reexamine (and if necessary, reclassify) the NCMNS meteorite collection. History: The Geology Collection began with the collections of the North Carolina Geological Survey, which predates the Museum's founding in 1879. Samples have been added sporadically by purchase, trade and/or collection, principally by former Curator Harry Davis. The last effort to classify and curate these is unknown due to a twenty-three year hiatus between curators. Currently, the Collection is curated by Dr. Chris Tacker who is overseeing this re-examination of the meteorite collection as part of an effort to re-invigerate and showcase astromaterials research in North Carolina. The Collection: The collection contains fourteen specimens with several notable members. The collection contains six stony meteorites, and eight iron meteorites. The jewel of the collection is the Moore County Eucrite while the largest is the 75 kg Uwharrie iron. Five meteorites are on permanent display in the Museum: Uwharrie, Farmville, Moore County, Rich Mountain and Deep Springs meteorites. Specific problems are apparent. A meteorite listed in Museum records as "McDowell County" (found May 1921) may be the same meteorite as Wood's Mountain (found 1918); "McDowell County" is given as a synonym in the Catalogue of Meteorites. The Deep Springs meteorite is an ungrouped iron and several iron meteorites are listed only as NiFe bearing in the museums records.
The partitioning of molybdenum between magnetite (mt) and two rhyolitic melts has been determined... more The partitioning of molybdenum between magnetite (mt) and two rhyolitic melts has been determined at 800 degrees C, 1 kb of pressure, and at two oxygen fugacities. At an oxygen fugacity one-half a log unit above nickel-nickel oxide, D (super mt/melt) Mo = 0.21 + or - 0.08. A decrease in the oxygen fugacity to the graphite-methane buffer is accompanied by an increase in D (super mt/melt) Mo to 0.52 + or - 0.13. The differences in melt composition have no discernible effect.These data are interpreted by writing balanced chemical potential relationships involving independently variable phase components. The Nernst partition coefficients given above are then formulated as a function of these equilibria. Given the observed variation in D (super mt/melt) Mo with oxygen fugacity, and assuming that Fe 2 MoO 4 is the molybdenum-bearing phase component in magnetite, our data suggest that Mo(III) may be present in naturally occurring silicic magmas. Further, we suggest the establishment of critical bulk partition coefficients for ore-forming systems, defined in terms of critical values of the efficiency of removal function defined by Candela and Holland (1986). These preliminary results indicate that the crystallization of ferromagnesian or titanium-bearing phases may be important in reducing the amount of molybdenum available for orthomagmatic-hydrothermal ore formation. Oxygen fugacity may play a large role in the melt-crystal-vapor equilibria ofmolybdenum under magmatic conditions.
The distribution of molybdenum between magnetite and a high-silica rhyolite has been measured as ... more The distribution of molybdenum between magnetite and a high-silica rhyolite has been measured as a function of oxygen fugacity. All experiments were water-saturated and were performed in cold-seal pressure vessels at T = 800/sup 0/C and P = 1 kb. Reversed experiments at one-half a log unit above nickel-nickel oxide (log f/sub O/sub 2// = -13.35) yield a D crystal/melt = .16. Preliminary experiments at lower oxygen fugacities suggest higher values for D. This behavior implies that the pertinent equilibria behave according to projected chemical equations. This has important implications for the genesis of porphyry-type ore deposits. At high f/sub O/sub 2//, molybdenum will be concentrated in successive aliquots of melt as an incompatible element with respect to Fe-Ti minerals, whereas at low f/sub O/sub 2// molybdenum will behave as a more compatible element. Note that the systematics for tin would be the reverse of those for molybdenum if tin is in the divalent state in low F/sub O/s...
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