Alan E. Koenig

Visualizing fossilization using laser ablation-inductively coupled plasma-mass spectrometry maps of trace elements in Late Cretaceous bones

Elemental maps generated by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) provide a previously unavailable high-resolution visualization of the complex physicochemical conditions operating within individual bones during the early stages of diagenesis and fossilization. A selection of LA-ICP-MS maps of bones collected from the Late Cretaceous of Montana (United States) and Madagascar graphically illustrate diverse paths to recrystallization, and reveal unique insights into geochemical aspects of taphonomic history. Some bones show distinct gradients in concentrations of rare earth elements and uranium, with highest concentrations at external bone margins. Others exhibit more intricate patterns of trace element uptake related to bone histology and its control on the flow paths of pore waters. Patterns of element uptake as revealed by LA-ICP-MS maps can be used to guide sampling strategies, and call into question previous studies that hinge upon localized bulk samples of fossilized bone tissue. LA-ICP-MS maps also allow for comparison of recrystallization rates among fossil bones, and afford a novel approach to identifying bones or regions of bones potentially suitable for extracting intact biogeochemical signals.

Visualizing trace element distribution in quartz using cathodoluminescence, electron microprobe, and laser ablation-inductively coupled plasma-mass spectrometry

Abstract Cathodoluminescent (CL) textures in quartz reveal successive histories of the physical and chemical fluctuations that accompany crystal growth. Such CL textures reflect trace element concentration variations that can be mapped by electron microprobe or laser ablation-inductively coupled plasmamass spectrometry (LA-ICP-MS). Trace element maps in hydrothermal quartz from four different ore deposit types (Carlin-type Au, epithermal Ag, porphyry-Cu, and MVT Pb-Zn) reveal correlations among trace elements and between trace element concentrations and CL textures. The distributions of trace elements reflect variations in the physical and chemical conditions of quartz precipitation. These maps show that Al is the most abundant trace element in hydrothermal quartz. In crystals grown at temperatures below 300 °C, Al concentrations may vary by up to two orders of magnitude between adjacent growth zones, with no evidence for diffusion. The monovalent cations Li, Na, and K, where detectable, always correlate with Al, with Li being the most abundant of the three. In most samples, Al is more abundant than the combined total of the monovalent cations; however, in the MVT sample, molar Al/Li ratios are -0.8. Antimony is present in concentrations up to -120 ppm in epithermal quartz (-200-300 °C), but is not detectable in MVT, Carlin, or porphyry-Cu quartz. Concentrations of Sb do not correlate consistently with those of other trace elements or with CL textures. Titanium is only abundant enough to be mapped in quartz from porphyry-type ore deposits that precipitate at temperatures above -400 °C. In such quartz, Ti concentration correlates positively with CL intensity, suggesting a causative relationship. In contrast, in quartz from other deposit types, there is no consistent correlation between concentrations of any trace element and CL intensity fluctuations.

Stratigraphic correlations using trace elements in apatite from Late Ordovician (Sandbian-Katian) K-bentonites of eastern North America

The early Late Ordovician sedimentary rocks of eastern North America contain a relatively large number (>100) of widespread heavily altered tephra layers (K-bentonites). These beds represent an intense period of subaerial volcanism that occurred from ca. 455 to 449 Ma. The sedimentary rocks that contain these K-bentonites display complex regional lithostratigraphic relationships ranging from clastic foreland basin facies to cratonic carbonate platform facies. Accurate correlation of these ancient ash-fall beds is essential for testing chronostratigraphic hypotheses that attempt to connect these different tectono-sedimentary provinces. Despite the relatively thorough study of a few of these K-bentonites over the past several decades, the full stratigraphic potential of these beds has yet to be realized. To test the utility of the apatite trace-element K-bentonite correlation method on a larger scale, we studied over 200 K-bentonite samples from the Mohawkian Stage of eastern North America and statistically compared our results with previous studies on the same suites of K-bentonites. Electron microprobe (EPMA) and laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) results show that apatite trace-element data provide unique bed discriminators. Each of the K-bentonite layers exhibits unique and reproducible trends in Mg, Cl, Mn, Fe, Ce, Y, and other trace-element concentrations in apatite. Statistical evaluation of results from our apatite analyses suggests correlations for 12 K-bentonite beds, providing a significant improvement in stratigraphic resolution. The stratigraphic relations indicated by these new K-bentonite fingerprints provide a rigorous means by which to evaluate some previous interpretations of biostratigraphic, chemostratigraphic, and sequence stratigraphic studies in eastern North America.

USING LASER ABLATION-INDUCTIVELY COUPLED PLASMA-MASS SPECTROMETRY (LA-ICP-MS) TO EXPLORE GEOCHEMICAL TAPHONOMY OF VERTEBRATE FOSSILS IN THE UPPER CRETACEOUS TWO MEDICINE AND JUDITH RIVER FORMATIONS OF MONTANA

Abstract Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used to determine rare earth element (REE) content of 76 fossil bones collected from the Upper Cretaceous (Campanian) Two Medicine (TMF) and Judith River (JRF) Formations of Montana. REE content is distinctive at the formation scale, with TMF samples exhibiting generally higher overall REE content and greater variability in REE enrichment than JRF samples. Moreover, JRF bones exhibit relative enrichment in heavy REE, whereas TMF bones span heavy and light enrichment fields in roughly equal proportions. TMF bones are also characterized by more negative Ce anomalies and greater U enrichment than JRF bones, which is consistent with more oxidizing diagenetic conditions in the TMF. Bonebeds in both formations show general consistency in REE content, with no indication of spatial or temporal mixing within sites. Previous studies, however, suggest that the bonebeds in question are attritional assemblages that accumulated over considerable time spans. The absence of geochemical evidence for mixing is consistent with diagenesis transpiring in settings that remained chemically and hydrologically stable during recrystallization. Lithology-related patterns in REE content were also compared, and TMF bones recovered from fluvial sandstones show relative enrichment in heavy REE when compared with bones recovered from fine-grained floodplain deposits. In contrast, JRF bones, regardless of lithologic context (sandstone versus mudstone), exhibit similar patterns of REE uptake. This result is consistent with previous reconstructions that suggest that channel-hosted microfossil bonebeds of the JRF developed via the reworking of preexisting concentrations embedded in the interfluve. Geochemical data further indicate that reworked elements were potentially delivered to channels in a recrystallized condition, which is consistent with rapid adsorption of REE postmortem.

Deep‐sea coral record of human impact on watershed quality in the Mississippi River Basin

One of the greatest drivers of historical nutrient and sediment transport into the Gulf of Mexico is the unprecedented scale and intensity of land use change in the Mississippi River Basin. These landscape changes are linked to enhanced fluxes of carbon and nitrogen pollution from the Mississippi River, and persistent eutrophication and hypoxia in the northern Gulf of Mexico. Increased terrestrial runoff is one hypothesis for recent enrichment in bulk nitrogen isotope (δ15N) values, a tracer for nutrient source, observed in a Gulf of Mexico deep-sea coral record. However, unambiguously linking anthropogenic land use change to whole scale shifts in downstream Gulf of Mexico biogeochemical cycles is difficult. Here we present a novel approach, coupling a new tracer of agro-industrialization to a multiproxy record of nutrient loading in long-lived deep-sea corals collected in the Gulf of Mexico. We found that coral bulk δ15N values are enriched over the last 150–200 years relative to the last millennia, and compound-specific amino acid δ15N data indicate a strong increase in baseline δ15N of nitrate as the primary cause. Coral rhenium (Re) values are also strongly elevated during this period, suggesting that 34% of Re is of anthropogenic origin, consistent with Re enrichment in major world rivers. However, there are no pre-anthropogenic measurements of Re to confirm this observation. For the first time, an unprecedented record of natural and anthropogenic Re variability is documented through coral Re records. Taken together, these novel proxies link upstream changes in water quality to impacts on the deep-sea coral ecosystem.

Lower cambrian metallogenesis of south China: Interplay between diverse basinal hydrothermal fluids and marine chemistry

The lowermost Cambrian metalliferous black shales of southern China represent a unique metallogenic province. The shales host a wide range of world-class synsedimentary metal deposit types. The diverse metal assemblages in these deposits are best explained by venting of multiple hydrothermal fluids including reduced H2S-rich brines, petroleum, and oxidized brines into the basin. Coinciden formation of shales that are extraordinarity rich in organic carbon and metals suggest a rapid increase in bioproductivity and anoxic/dysoxic conditions during ore formation. We propose that basinal fluids were the source of bioliming nutrients that caused eutrophication and basin-wide anoxia. The dramatic geologic and geochemical changes in this basin demonstrate the possible impacts of hydrothermal systems on the generation and sequestration of organic matter, formation of black metalliferous shales, and chemical changes of seawater.

Trace elements in Zn–Pb–Ag deposits and related stream sediments, Brooks Range Alaska, with implications for Tl as a pathfinder element

ABSTRACT The Zn–Pb–Ag metallogenic province of the western and central Brooks Range, Alaska, contains two distinct but mineralogically similar deposit types: shale-hosted massive sulphide (SHMS) and smaller vein-breccia occurrences. Recent investigations of the Red Dog and Anarraaq SHMS deposits demonstrated that these deposits are characterized by high trace-element concentrations of As, Ge, Sb and Tl. This paper examines geochemistry of additional SHMS deposits (Drenchwater and Su-Lik) to determine which trace elements are ubiquitously elevated in all SHMS deposits. Data from several vein-breccia occurrences are also presented to see if trace-element concentrations can distinguish SHMS deposits from vein-breccia occurrences. Whole-rock geochemical data indicate that Tl is the most consistently and highly concentrated characteristic trace element in SHMS deposits relative to regional unmineralized rock samples. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of pyrite and sphalerite indicate that Tl is concentrated in pyrite in SHMS. Stream sediment data from the Drenchwater and Su-Lik SHMS show that high Tl concentrations are more broadly distributed proximal to known or suspected mineralization than As, Sb, Zn and Pb anomalies. This broader distribution of Tl in whole-rock and particularly stream sediment samples increases the footprint of exposed and shallowly buried SHMS mineralization. High Tl concentrations also distinguish SHMS mineralization from the vein-breccia deposits, as the latter lack high concentrations of Tl but can otherwise have similar trace-element signatures to SHMS deposits.

Direct U-Pb dating of Cretaceous and Paleocene dinosaur bones, San Juan Basin, New Mexico: COMMENT

Based on U-Pb dating of two dinosaur bones from the San Juan Basin of New Mexico (United States), [Fassett et al. (2011)][1] claim to provide the first successful direct dating of fossil bones and to establish the presence of Paleocene dinosaurs. Fassett et al. ignore previously published work that

Reply to comments by T. Oberthür on “Trace element distribution in uraninite from Mesoarchaean Witwatersrand conglomerates (South Africa) supports placer model and magmatogenic source”

In his comments on our paper (Depine et al. 2013) on the chemistry of uraninite grains from the auriferous conglomerates of the Mesoarchaean Witwatersrand Supergroup, Oberthur (2013) highlights a number of points, some of which had not been fully discussed by us due to the limitation on space in a short “letter”. We are therefore grateful for the opportunity to expand on some of the implications of our new data in this discussion here. The abundance of major and minor elements in uraninite from the Witwatersrand has been the subject of several previous studies. We could add to this knowledge, as acknowledged by Oberthur (2013), by presenting the first data on trace element concentrations in Witwatersrand uraninite as obtained by LA-ICPMS. The main message we tried to convey in our letter has been that the mineral chemistry of the uraninite grains, now also including a range of elements hitherto not or only poorly analysed for, provides unequivocal evidence of the detrital nature of these grains. We are satisfied, though not surprised, that Oberthur, an expert with livelong experience with the studied rocks, fully concurs with this principal conclusion. For many readers, this conclusion may not be worth receiving further attention after dozens of papers have been published over the past decades on the topic of the genesis of the world’s largest gold province and the U-ores therein, in which a strong case for a modified palaeoplacer model has been made. Since the last review (Frimmel et al. 2005), the discussion on the genesis of the Witwatersrand ores has been, however, by no means closed, and views opposing to those of Oberthur and many other workers have been presented more recently. The papers by Phillips and Powell (2011), who advocate a postdepositional syn-metamorphic introduction of the gold into the host conglomerates, or by Horscroft et al. (2011), who argue for a syngenetic, microbially mediated chemical precipitation of gold, uraninite and pyrite, may serve as examples. We therefore believe that it remains timely and opportune to continue this discussion on the Witwatersrand metallogeny with new data. Oberthur (2013) dismisses any model involving syngenetic or epigenetic-hydrothermal introduction of U into the host conglomerates because of the lack of oxidising conditions under an Archaean atmosphere. We could not agree more but want to point out that this has been a circular argument for a long time. After all, the evidence for a postulated reducing atmosphere in the Archaean has come primarily from the interpretation of the ore components, specifically rounded massive pyrite and uraninite, in the Witwatersrand goldfields (Krupp et al. 1994; Frimmel 2005). Only in the last decade, largely based on the discovery of mass-independent S isotope fractionation in Archaean rocks, independent evidence in favour of an O2-deficient Archaean atmosphere could be brought forward (Farquhar et al. 2007), thus supporting the original contention of the detrital Witwatersrand mineralogy. As effectively all points raised by Oberthur (2013) are discussed in greater detail in a full paper currently under review elsewhere (Frimmel et al. 2013), in which we present Editorial handling: B. Lehmann

Spatial mapping of mineralization with manganese-enhanced magnetic resonance imaging

Paramagnetic manganese can be employed as a calcium surrogate to sensitize the magnetic resonance imaging (MRI) technique to the processing of calcium during the bone formation process. At low doses, after just 48h of exposure, osteoblasts take up sufficient quantities of manganese to cause marked reductions in the water proton T1 values compared with untreated cells. After just 24h of exposure, 25μM MnCl(2) had no significant effect on cell viability. However, for mineralization studies 100μM MnCl(2) was used to avoid issues of manganese depletion in calvarial organ cultures and a post-treatment delay of 48h was implemented to ensure that manganese ions taken up by osteoblasts is deposited as mineral. All specimens were identified by their days in vitro (DIV). Using inductively coupled plasma optical emission spectroscopy (ICP-OES), we confirmed that Mn-treated calvariae continued to deposit mineral in culture and that the mineral composition was similar to that of age-matched controls. Notably there was a significant decrease in the manganese content of DIV18 compared with DIV11 specimens, possibly relating to less manganese sequestration as a result of mineral maturation. More importantly, quantitative T1 maps of Mn-treated calvariae showed localized reductions in T1 values over the calvarial surface, indicative of local variations in the surface manganese content. This result was verified with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We also found that ΔR1 values, calculated by subtracting the relaxation rate of Mn-treated specimens from the relaxation rate of age-matched controls, were proportional to the surface manganese content and thus mineralizing activity. From this analysis, we established that mineralization of DIV4 and DIV11 specimens occurred in all tissue zones, but was reduced for DIV18 specimens because of mineral maturation with less manganese sequestration. In DIV25 specimens, active mineralization was observed for the expanding superficial surface and ΔR1 values were increased due to the mineralization of small, previously unmineralized areas. Our findings support the use of manganese-enhanced MRI (MEMRI) to study well-orchestrated mineralizing events that occur during embryonic development. In conclusion, MEMRI is more sensitive to the study of mineralization than traditional imaging approaches.