Three tourmaline reference materials sourced from the Harvard Mineralogical and Geological Museum... more Three tourmaline reference materials sourced from the Harvard Mineralogical and Geological Museum (schorl 112566, dravite 108796 and elbaite 98144), which are already widely used for the calibration of in situ boron isotope measurements, are characterised here for their oxygen and lithium isotope compositions. Homogeneity tests by secondary ion mass spectrometry (SIMS) showed that at sub‐nanogram test portion masses, their 18O/16O and 7Li/6Li isotope ratios are constant within ± 0.27‰ and ± 2.2‰ (1s), respectively. The lithium mass fractions of the three materials vary over three orders of magnitude. SIMS homogeneity tests showed variations in 7Li/28Si between 8% and 14% (1s), which provides a measure of the heterogeneity of the Li contents in these three materials. Here, we provide recommended values for δ18O, Δ’17O and δ7Li for the three Harvard tourmaline reference materials based on results from bulk mineral analyses from multiple, independent laboratories using laser‐ and stepw...
Calcite cementation and dolomitization are key diagenetic processes in many sedimentary systems. ... more Calcite cementation and dolomitization are key diagenetic processes in many sedimentary systems. Unravelling detailed histories and timescales of cementation and replacement is, however, often compromised by the limited spatial resolution of many analytical techniques; in some cases multiple grains are co-analyzed so that diagenetic histories are blurred and reaction periods are difficult to establish. In this study we have used 10micrometer-resolution, in situ secondary ion mass spectrometry to determine the oxygen isotope composition of 197 individual, 10-50-micrometer-size crystals of dolomite and calcite from six samples in a single core of Upper Devonian middle Bakken Member siltstones and sandstones, the major tight oil formation of the Williston basin, USA. This amount of data places important constraints on the range of temperatures and times that carbonate cementation and replacement occurred. Petrographic data show that microcrystalline calcite cement is an early phase, and combined with mineralogical data suggest that much of the dolomite replaces calcite. Over spatial scales of less than a centimeter, analyses of individual calcite crystals have a range of 5% for d 18 O in the group of crystals, and for the group of individual dolomite crystals, 10%. These sub-centimeter ranges are as great as those observed in previous studies of carbonate cements sampled over many meters and remind us that previous low-resolution studies may have inadvertently analyzed mixed phases. There is no relationship between dolomite texture and isotopic composition at this spatial scale; microscale backscattered electron imagery and scanning electron microscopy cathodoluminescence zoning is seen, but cannot be resolved with a 10-micrometer spot size. Assuming, since it is an early cement, that calcite precipitated from seawater (d 18 O ¼-1.5%), it formed at ca. 15-408C, mainly at the lower temperatures. Present-day formation waters in Devonian rocks in this region have oxygen isotope compositions of 7-8% VSMOW. Using these values as a likely dolomitizing fluid, we suggest that dolomitization occurred continuously between 40 and 1408C over 150-200 million years, most likely in a fluid with a high Mg/Ca ratio resulting from gypsum formation in local evaporites. We suggest that this exceptionally low rate of dolomitization was controlled by the low rate of supply of Mg in a very sluggish flow regime; dolomitization is incomplete because of a limited supply of Mg.
Cool tropical sea surface temperatures (SSTs) are reported for warm Paleogene greenhouse climates... more Cool tropical sea surface temperatures (SSTs) are reported for warm Paleogene greenhouse climates based on the d18O of planktonic foraminiferal tests. These results are difficult to reconcile with models of greenhouse gas-forced climate. It has been suggested that this "cool tropics paradox" arises from postdepositional alteration of foraminiferal calcite, yielding erroneously high d18O values. Recrystallization of foraminiferal tests is cryptic and difficult to quantify, and the compilation of robust d18O records from moderately altered material remains challenging. Scanning electron microscopy of planktonic foraminiferal chamber-wall cross sections reveals that the basal area of muricae, pustular outgrowths on the chamber walls of species belonging to the genus Morozovella, contain no mural pores and may be less susceptible to postdepositional alteration. We analyzed the d18O in muricae bases of morozovellids from the central Pacific (Ocean Drilling Program Site 865) by ...
This is an Accepted Manuscript for the Microscopy and Microanalysis 2020 Proceedings. This versio... more This is an Accepted Manuscript for the Microscopy and Microanalysis 2020 Proceedings. This version may be subject to change during the production process.
The oxygen isotope (δ 18 O) compositions of final chamber fragments of individual shells of the p... more The oxygen isotope (δ 18 O) compositions of final chamber fragments of individual shells of the planktic foraminifer Orbulina universa were measured in situ via secondary ion mass spectrometry (SIMS) and by traditional gas-source mass spectrometry (GSMS) entailing acid digestion of sampled calcite. The paired SIMS-GSMS analyses were performed on final chamber fragments of fossil shells taken from the top of a sediment core (Holocene) as well as shells grown in laboratory culture. Multiple iterations of SIMS-GSMS analyses were conducted on final chamber fragments treated with a variety of cleaning protocols. The series of paired analyses yielded an average SIMS-GSMS δ 18 O offset (Δ 18 O SIMS-GSMS) of −0.9 ± 0.1‰ (± 2 SE). The volume of material analyzed in 10-μm SIMS spots is~10 5 times smaller than that analyzed by GSMS; hence, the extent to which these Δ 18 O SIMS-GSMS values represent real differences in analyte vs. instrumental factors remains unclear. Possible contributing factors to the SIMS-GSMS δ 18 O difference include sample-standard mismatch by SIMS, differences in standardization of SIMS and GSMS, and non-calcite contaminants in samples. Although the two datasets are consistently offset, SIMS values reproduce inter-shell δ 18 O variability delineated by shell fragment GSMS values. This strong positive covariance proved useful for bringing the two datasets into agreement (i.e. Δ 18 O SIMS-GSMS = 0), and confirms that SIMS-based foraminifer δ 18 O values record changes in calcification temperature and/or δ 18 O of seawater. Whether shells of foraminifer taxa with differing microcrystalline structures, chemical composition, and/or preservation histories register a similar Δ 18 O SIMS-GSMS value is a subject of ongoing testing.
Thank you, Jade Star and William, for your generous words and to all who nominated me for this gr... more Thank you, Jade Star and William, for your generous words and to all who nominated me for this great honor. By tradition, I believe an awardee usually takes a few minutes to say something that might be interesting about their career. I would like to share how lucky I have been, in particular, my good fortune in having good mentors, colleagues, and students. Bob Decker at Dartmouth introduced me to geology, Bob Reynolds taught mineralogy, and Dick Stoiber introduced me to research. This was during the Vietnam War. It was a turbulent period. In the spring of my senior year, 1970, the U.S. bombed Cambodia and National Guard troops killed students on the Kent State campus. To Dick's distress, I withdrew my applications to graduate school and became a carpenter. It was four years before I was ready to focus on science again. I reapplied to the University of Michigan. I was fortunate. There was a brash new faculty member, who hadn't been there four years earlier, named Eric Essene. Eric introduced me to metamorphic rocks and taught me that if I wanted to understand a rock's history, I needed to understand the constituent minerals. He instilled the rigors of thermodynamics and phase equilibrium. He also encouraged me to join MSA. Eric collaborated widely; his group blended seamlessly with that of Don Peacor and Bill Kelly and included many who remain friends and colleagues, including John Bowman, Steve Bohlen, Phil Brown, Dexter Perkins, John Geissman, and Alan Treiman. I studied granulite facies marbles from the Adirondacks for my thesis. I tried to map isograds, and that didn't work, but it started my interest in metamorphic fluids. It became clear that water and CO 2 fugacity varied locally, and some rocks were not saturated by a fluid, confounding devolatilization isograds and leading to all sorts of interesting questions that I thought might be answered with stable isotopes. As it turned out, Eric went on sabbatical my third year and suggested I take the opportunity to learn some geochemistry, but there were no isotope labs at Michigan then (that's hard to imagine now). John Bowman suggested I write Jim O'Neil at the USGS in Menlo Park. Jim generously invited me into his group. This good fortune was transformative. Jim taught me everything about stable isotopes: theory, techniques, applications, and the people. There was a steady stream of guests. Everyone in stable isotope geochemistry visited Jim and wrote something on the wall of his lab. Another piece of luck relates to a prediction that I got wrong. In the late 1990s, William Peck, Liz King, and I compared the oxygen isotope ratios of magmatic zircons from the Grenville and Superior Provinces and realized that the Archean was less variable and more nearly mantle-like than the Proterozoic. We were
This dataset for our publication (Farfan et al, 2021) combines high spatial-resolution mineralogi... more This dataset for our publication (Farfan et al, 2021) combines high spatial-resolution mineralogical and isotope data of freshwater cultured pearls with the environmental conditions of the lake in which they grew under (Kentucky Lake, TN). SIMS-based δ18O values were taken for six transects across three pearls (mirroring transects A and B for each pearl). Detailed mineralogical analyses in the form of nacre tablet thickness (sub-micron) and Raman spectroscopy data of the carbonate vibrational modes of nacre aragonite are calculated for positions along the pearls corresponding to the transects of SIMS-made pits. The corresponding Kentucky Lake environmental data is translated into pearl-nacre space along the same SIMS pits and estimated based off of raw data from the Kentucky Lake Long-Term Monitoring Program run by Murray State University, KY. Any researchers interested in the raw Kentucky Lake data must contact this program directly.
This dataset contains supplementary tables S1, S2, S3 for our publication (Farfan et al, 2021), g... more This dataset contains supplementary tables S1, S2, S3 for our publication (Farfan et al, 2021), given as Excel files.
Sampling and Analyzing Method: Acarininid shells were cast in epoxy, ground to midsection and ima... more Sampling and Analyzing Method: Acarininid shells were cast in epoxy, ground to midsection and imaged by SEM to identify suitable, well-preserved domains for analysis. In situ d18O data were acquired in the WiscSIMS Laboratory at the Department of Geoscience, UW-Madison, using a CAMECA IMS-1280 large radius multicollector SIMS. (Kita et al., 2009; Valley and Kita, 2009). Depending on the size of the target, samples were analyzed with a 10 µm or 3 µm primary beam. Four consecutive measurements of UWC-3 calcite standard (d18O = 12.40 per mille Vienna standard mean ocean water; VSMOW; Kozdon et al., 2009) were performed before and after every set of typically 10 sample analyses.
Lower ocean crust is primarily gabbroic, although 1-2% felsic igneous rocks that are referred to ... more Lower ocean crust is primarily gabbroic, although 1-2% felsic igneous rocks that are referred to collectively as plagiogranites occur locally. Recent experimental evidence suggests that plagiogranite magmas can form by hydrous partial melting of gabbro triggered by seawater-derived fluids, and thus they may indicate early, high-temperature hydrothermal fluid circulation. To explore seawater-rock interaction prior to and during the genesis of plagiogranite and other late-stage magmas, oxygen-isotope ratios preserved in igneous zircon have been measured by ion microprobe. A total of 197 zircons from 43 plagiogranite, evolved gabbro, and hydrothermally altered fault rock samples have been analyzed. Samples originate primarily from drill core acquired during Ocean Drilling Program and Integrated Ocean Drilling Program operations near the Mid-Atlantic and Southwest Indian Ridges. With the exception of rare, distinctively luminescent rims, all zircons from ocean crust record remarkably un...
Three tourmaline reference materials sourced from the Harvard Mineralogical and Geological Museum... more Three tourmaline reference materials sourced from the Harvard Mineralogical and Geological Museum (schorl 112566, dravite 108796 and elbaite 98144), which are already widely used for the calibration of in situ boron isotope measurements, are characterised here for their oxygen and lithium isotope compositions. Homogeneity tests by secondary ion mass spectrometry (SIMS) showed that at sub‐nanogram test portion masses, their 18O/16O and 7Li/6Li isotope ratios are constant within ± 0.27‰ and ± 2.2‰ (1s), respectively. The lithium mass fractions of the three materials vary over three orders of magnitude. SIMS homogeneity tests showed variations in 7Li/28Si between 8% and 14% (1s), which provides a measure of the heterogeneity of the Li contents in these three materials. Here, we provide recommended values for δ18O, Δ’17O and δ7Li for the three Harvard tourmaline reference materials based on results from bulk mineral analyses from multiple, independent laboratories using laser‐ and stepw...
Calcite cementation and dolomitization are key diagenetic processes in many sedimentary systems. ... more Calcite cementation and dolomitization are key diagenetic processes in many sedimentary systems. Unravelling detailed histories and timescales of cementation and replacement is, however, often compromised by the limited spatial resolution of many analytical techniques; in some cases multiple grains are co-analyzed so that diagenetic histories are blurred and reaction periods are difficult to establish. In this study we have used 10micrometer-resolution, in situ secondary ion mass spectrometry to determine the oxygen isotope composition of 197 individual, 10-50-micrometer-size crystals of dolomite and calcite from six samples in a single core of Upper Devonian middle Bakken Member siltstones and sandstones, the major tight oil formation of the Williston basin, USA. This amount of data places important constraints on the range of temperatures and times that carbonate cementation and replacement occurred. Petrographic data show that microcrystalline calcite cement is an early phase, and combined with mineralogical data suggest that much of the dolomite replaces calcite. Over spatial scales of less than a centimeter, analyses of individual calcite crystals have a range of 5% for d 18 O in the group of crystals, and for the group of individual dolomite crystals, 10%. These sub-centimeter ranges are as great as those observed in previous studies of carbonate cements sampled over many meters and remind us that previous low-resolution studies may have inadvertently analyzed mixed phases. There is no relationship between dolomite texture and isotopic composition at this spatial scale; microscale backscattered electron imagery and scanning electron microscopy cathodoluminescence zoning is seen, but cannot be resolved with a 10-micrometer spot size. Assuming, since it is an early cement, that calcite precipitated from seawater (d 18 O ¼-1.5%), it formed at ca. 15-408C, mainly at the lower temperatures. Present-day formation waters in Devonian rocks in this region have oxygen isotope compositions of 7-8% VSMOW. Using these values as a likely dolomitizing fluid, we suggest that dolomitization occurred continuously between 40 and 1408C over 150-200 million years, most likely in a fluid with a high Mg/Ca ratio resulting from gypsum formation in local evaporites. We suggest that this exceptionally low rate of dolomitization was controlled by the low rate of supply of Mg in a very sluggish flow regime; dolomitization is incomplete because of a limited supply of Mg.
Cool tropical sea surface temperatures (SSTs) are reported for warm Paleogene greenhouse climates... more Cool tropical sea surface temperatures (SSTs) are reported for warm Paleogene greenhouse climates based on the d18O of planktonic foraminiferal tests. These results are difficult to reconcile with models of greenhouse gas-forced climate. It has been suggested that this "cool tropics paradox" arises from postdepositional alteration of foraminiferal calcite, yielding erroneously high d18O values. Recrystallization of foraminiferal tests is cryptic and difficult to quantify, and the compilation of robust d18O records from moderately altered material remains challenging. Scanning electron microscopy of planktonic foraminiferal chamber-wall cross sections reveals that the basal area of muricae, pustular outgrowths on the chamber walls of species belonging to the genus Morozovella, contain no mural pores and may be less susceptible to postdepositional alteration. We analyzed the d18O in muricae bases of morozovellids from the central Pacific (Ocean Drilling Program Site 865) by ...
This is an Accepted Manuscript for the Microscopy and Microanalysis 2020 Proceedings. This versio... more This is an Accepted Manuscript for the Microscopy and Microanalysis 2020 Proceedings. This version may be subject to change during the production process.
The oxygen isotope (δ 18 O) compositions of final chamber fragments of individual shells of the p... more The oxygen isotope (δ 18 O) compositions of final chamber fragments of individual shells of the planktic foraminifer Orbulina universa were measured in situ via secondary ion mass spectrometry (SIMS) and by traditional gas-source mass spectrometry (GSMS) entailing acid digestion of sampled calcite. The paired SIMS-GSMS analyses were performed on final chamber fragments of fossil shells taken from the top of a sediment core (Holocene) as well as shells grown in laboratory culture. Multiple iterations of SIMS-GSMS analyses were conducted on final chamber fragments treated with a variety of cleaning protocols. The series of paired analyses yielded an average SIMS-GSMS δ 18 O offset (Δ 18 O SIMS-GSMS) of −0.9 ± 0.1‰ (± 2 SE). The volume of material analyzed in 10-μm SIMS spots is~10 5 times smaller than that analyzed by GSMS; hence, the extent to which these Δ 18 O SIMS-GSMS values represent real differences in analyte vs. instrumental factors remains unclear. Possible contributing factors to the SIMS-GSMS δ 18 O difference include sample-standard mismatch by SIMS, differences in standardization of SIMS and GSMS, and non-calcite contaminants in samples. Although the two datasets are consistently offset, SIMS values reproduce inter-shell δ 18 O variability delineated by shell fragment GSMS values. This strong positive covariance proved useful for bringing the two datasets into agreement (i.e. Δ 18 O SIMS-GSMS = 0), and confirms that SIMS-based foraminifer δ 18 O values record changes in calcification temperature and/or δ 18 O of seawater. Whether shells of foraminifer taxa with differing microcrystalline structures, chemical composition, and/or preservation histories register a similar Δ 18 O SIMS-GSMS value is a subject of ongoing testing.
Thank you, Jade Star and William, for your generous words and to all who nominated me for this gr... more Thank you, Jade Star and William, for your generous words and to all who nominated me for this great honor. By tradition, I believe an awardee usually takes a few minutes to say something that might be interesting about their career. I would like to share how lucky I have been, in particular, my good fortune in having good mentors, colleagues, and students. Bob Decker at Dartmouth introduced me to geology, Bob Reynolds taught mineralogy, and Dick Stoiber introduced me to research. This was during the Vietnam War. It was a turbulent period. In the spring of my senior year, 1970, the U.S. bombed Cambodia and National Guard troops killed students on the Kent State campus. To Dick's distress, I withdrew my applications to graduate school and became a carpenter. It was four years before I was ready to focus on science again. I reapplied to the University of Michigan. I was fortunate. There was a brash new faculty member, who hadn't been there four years earlier, named Eric Essene. Eric introduced me to metamorphic rocks and taught me that if I wanted to understand a rock's history, I needed to understand the constituent minerals. He instilled the rigors of thermodynamics and phase equilibrium. He also encouraged me to join MSA. Eric collaborated widely; his group blended seamlessly with that of Don Peacor and Bill Kelly and included many who remain friends and colleagues, including John Bowman, Steve Bohlen, Phil Brown, Dexter Perkins, John Geissman, and Alan Treiman. I studied granulite facies marbles from the Adirondacks for my thesis. I tried to map isograds, and that didn't work, but it started my interest in metamorphic fluids. It became clear that water and CO 2 fugacity varied locally, and some rocks were not saturated by a fluid, confounding devolatilization isograds and leading to all sorts of interesting questions that I thought might be answered with stable isotopes. As it turned out, Eric went on sabbatical my third year and suggested I take the opportunity to learn some geochemistry, but there were no isotope labs at Michigan then (that's hard to imagine now). John Bowman suggested I write Jim O'Neil at the USGS in Menlo Park. Jim generously invited me into his group. This good fortune was transformative. Jim taught me everything about stable isotopes: theory, techniques, applications, and the people. There was a steady stream of guests. Everyone in stable isotope geochemistry visited Jim and wrote something on the wall of his lab. Another piece of luck relates to a prediction that I got wrong. In the late 1990s, William Peck, Liz King, and I compared the oxygen isotope ratios of magmatic zircons from the Grenville and Superior Provinces and realized that the Archean was less variable and more nearly mantle-like than the Proterozoic. We were
This dataset for our publication (Farfan et al, 2021) combines high spatial-resolution mineralogi... more This dataset for our publication (Farfan et al, 2021) combines high spatial-resolution mineralogical and isotope data of freshwater cultured pearls with the environmental conditions of the lake in which they grew under (Kentucky Lake, TN). SIMS-based δ18O values were taken for six transects across three pearls (mirroring transects A and B for each pearl). Detailed mineralogical analyses in the form of nacre tablet thickness (sub-micron) and Raman spectroscopy data of the carbonate vibrational modes of nacre aragonite are calculated for positions along the pearls corresponding to the transects of SIMS-made pits. The corresponding Kentucky Lake environmental data is translated into pearl-nacre space along the same SIMS pits and estimated based off of raw data from the Kentucky Lake Long-Term Monitoring Program run by Murray State University, KY. Any researchers interested in the raw Kentucky Lake data must contact this program directly.
This dataset contains supplementary tables S1, S2, S3 for our publication (Farfan et al, 2021), g... more This dataset contains supplementary tables S1, S2, S3 for our publication (Farfan et al, 2021), given as Excel files.
Sampling and Analyzing Method: Acarininid shells were cast in epoxy, ground to midsection and ima... more Sampling and Analyzing Method: Acarininid shells were cast in epoxy, ground to midsection and imaged by SEM to identify suitable, well-preserved domains for analysis. In situ d18O data were acquired in the WiscSIMS Laboratory at the Department of Geoscience, UW-Madison, using a CAMECA IMS-1280 large radius multicollector SIMS. (Kita et al., 2009; Valley and Kita, 2009). Depending on the size of the target, samples were analyzed with a 10 µm or 3 µm primary beam. Four consecutive measurements of UWC-3 calcite standard (d18O = 12.40 per mille Vienna standard mean ocean water; VSMOW; Kozdon et al., 2009) were performed before and after every set of typically 10 sample analyses.
Lower ocean crust is primarily gabbroic, although 1-2% felsic igneous rocks that are referred to ... more Lower ocean crust is primarily gabbroic, although 1-2% felsic igneous rocks that are referred to collectively as plagiogranites occur locally. Recent experimental evidence suggests that plagiogranite magmas can form by hydrous partial melting of gabbro triggered by seawater-derived fluids, and thus they may indicate early, high-temperature hydrothermal fluid circulation. To explore seawater-rock interaction prior to and during the genesis of plagiogranite and other late-stage magmas, oxygen-isotope ratios preserved in igneous zircon have been measured by ion microprobe. A total of 197 zircons from 43 plagiogranite, evolved gabbro, and hydrothermally altered fault rock samples have been analyzed. Samples originate primarily from drill core acquired during Ocean Drilling Program and Integrated Ocean Drilling Program operations near the Mid-Atlantic and Southwest Indian Ridges. With the exception of rare, distinctively luminescent rims, all zircons from ocean crust record remarkably un...
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