Loess origin, transport, and deposition over the past 10,000 years, Wrangell-St. Elias National Park, Alaska

Contemporary glaciogenic dust has not received much attention, because most research has been on glaciogenic dust of the last glacial period or non-glaciogenic dust of the present interglacial period. Nevertheless, dust from modern glaciogenic sources may be important for Fe inputs to primary producers in the ocean. Adjacent to the subarctic Pacific Ocean, we studied a loess section near Chitina, Alaska along the Copper River in Wrangell-St. Elias National Park, where dust has been accumulating over the past ~10,000 years. Mass accumulation rates for the fine-grained (\u3c20 \u3eµm) fraction of this loess section are among the highest reported for the Holocene of high-latitude regions of the Northern Hemisphere. Based on mineralogy and geochemistry, loess at Chitina is derived from glacial sources in the Wrangell Mountains, the Chugach Mountains, and probably the Alaska Range. Concentrations of Fe in the silt-plus-clay fraction of the loess at Chitina are much higher than in all other loess bodies in North America and higher than most loess bodies on other continents. The very fine-grained (\u3c2 \u3eµm) portion of this sediment, capable of long-range transport, is dominated by Fe-rich chlorite, which can yield Fe readily to primary producers in the ocean. Examination of satellite imagery shows that dust from the Copper River is transported by wind on a regular basis to the North Pacific Ocean. This Alaskan example shows that high-latitude glaciogenic dust needs to be considered as a significant Fe source to primary producers in the open ocean

Strontium Isotopic Composition of Paleozoic Carbonate Rocks in the Nevada Test Site Vicinity, Clark, Lincoln, and Nye Counties, Nevada and Inyo County, California.

Ground water moving through permeable Paleozoic carbonate rocks represents the most likely pathway for migration of radioactive contaminants from nuclear weapons testing at the Nevada Test Site, Nye County, Nevada. The strontium isotopic composition (87Sr/86Sr) of ground water offers a useful means of testing hydrochemical models of regional flow involving advection and reaction. However, reaction models require knowledge of 87Sr/86Sr data for carbonate rock in the Nevada Test Site vicinity, which is scarce. To fill this data gap, samples of core or cuttings were selected from 22 boreholes at depth intervals from which water samples had been obtained previously around the Nevada Test Site at Yucca Flat, Frenchman Flat, Rainier Mesa, and Mercury Valley. Dilute acid leachates of these samples were analyzed for a suite of major- and trace-element concentrations (MgO, CaO, SiO2, Al2O3, MnO, Rb, Sr, Th, and U) as well as for 87Sr/86Sr. Also presented are unpublished analyses of 114 Paleozoic carbonate samples from outcrops, road cuts, or underground sites in the Funeral Mountains, Bare Mountain, Striped Hills, Specter Range, Spring Mountains, and ranges east of the Nevada Test Site measured in the early 1990's. These data originally were collected to evaluate the potential for economic mineral deposition at the potential high-level radioactive waste repository site at Yucca Mountain and adjacent areas (Peterman and others, 1994). Samples were analyzed for a suite of trace elements (Rb, Sr, Zr, Ba, La, and Ce) in bulk-rock powders, and 87Sr/86Sr in partial digestions of carbonate rock using dilute acid or total digestions of silicate-rich rocks. Pre-Tertiary core samples from two boreholes in the central or western part of the Nevada Test Site also were analyzed. Data are presented in tables and summarized in graphs; however, no attempt is made to interpret results with respect to ground-water flow paths in this report. Present-day 87Sr/86Sr values are compared to values for Paleozoic seawater present at the time of deposition. Many of the samples have 87Sr/86Sr compositions that remain relatively unmodified from expected seawater values. However, rocks underlying the northern Nevada Test Site as well as rocks exposed at Bare Mountain commonly have elevated 87Sr/86Sr values derived from post-depositional addition of radiogenic Sr most likely from fluids circulating through rubidium-rich Paleozoic strata or Precambrian basement rocks

A strontium and neodymium isotopic study of Apollo 17 high-Ti mare basalts: Resolution of ages, evolution of magmas, and origins of source heterogeneities

A combined Sr and Nd isotopic study of 15 Apollo 17 high-Ti mare basalts was undertaken to investigate geochronological and compositional differences between previously identified magma types (A, B1, B2, and C). Whole-rock and mineral separates for one of the least-evolved Type B1 basalts, 70139, yield Sm-Nd and Rb-Sr isochron ages of 3.71 +/- 0.12 Ga and 3.65 +/- 0.13 Ga, respectively. A more-evolved, Type A basalt, 71539, exhibits a slightly older Sm-Nd isochron age of 3.75 +/- 0.07 Ga and a Rb-Sr isochron age of 3.67 +/-0.10 Ga. Although these two ages are non-resolvable by themselves, compilation of all available geochronological data allows resolution of Type A and B1/B2 ages at high levels of confidence (>99%). The most reliably dated samples, classified according to their geochemical type, yield weighted average ages of 3.75 +/- 0.02 Ga for Type A (N = 4) and 3.69 +/- 0.02 Ga for Type B1/B2 (N = 3) basalts. Insufficient geochronological data are available to place the rare, Type C basalts within this stratigraphy. We propose that age differences correlate with geochemical magma type, and that early magmatism was dominated by eruption of Type A basalts while later activity was dominated by effusion of Type B1 and B2 basalts.Whole-rock isotopic data yield distinct differences in initial Sr and Nd isotopic compositions between Types A, B1, B2, and C basalts. Types A, B1, and C exhibit restricted intra-group compositional variations and lie along well-defined whole-rock isochrons. These data are consistent with petrogenetic models involving closed-system fractionation of observed microphenocrysts from chemically and isotopically distinct parental magmas. In contrast, a wide range of Type B2 initial isotopic compositions indicates mixing of several distinct components during magma evolution.The Sm-Nd whole-rock isochron age for Type A, Bl, and C basalts of 3.79 +/- 0.15 Ga is within error of Apollo 17 eruptive activity. However, the very well-defined Sr whole-rock isochron age of 4.02 +/- 0.05 Ga is 270 to 330 Ma older than eruptive ages. Isotopic and petrological arguments indicate that extensive Rb/Sr fractionation did not occur at the time of melt generation. Therefore, the 4.0 Ga Sr whole-rock isochron age records a significant event at which time geochemical heterogeneities were established within the originally homogeneous basalt source regions. Types A and C sources were enriched in Rb/Sr, with little or no concurrent modification of 87Sr/86Sr, Sm/Nd, or 143Nd/144Nd. Infiltration of similar-aged KREEP magmas into mantle cumulate sources cannot explain both Sr and Nd isotopic data. Instead, we suggest a metasomatic origin in which Rb, transported as a chloride complex in halogen-rich fluids, was preferentially mobilized relative to Sr and the REEs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29272/1/0000331.pd

SUMOylation by Pias1 Regulates the Activity of the Hedgehog Dependent Gli Transcription Factors

Hedgehog (Hh) signaling, a vital signaling pathway for the development and homeostasis of vertebrate tissues, is mediated by members of the Gli family of zinc finger transcription factors. Hh signaling increases the transcriptional activity of Gli proteins, at least in part, by inhibiting their proteolytic processing. Conversely, phosphorylation by cAMP-dependent protein kinase (PKA) inhibits Gli transcriptional activity by promoting their ubiquitination and proteolysis. Whether other post-translational modifications contribute to the regulation of Gli protein activity has been unclear.Here we provide evidence that all three Gli proteins are targets of small ubiquitin-related modifier (SUMO)-1 conjugation. Expression of SUMO-1 or the SUMO E3 ligase, Pias1, increased Gli transcriptional activity in cultured cells. Moreover, PKA activity reduced Gli protein SUMOylation. Strikingly, in the embryonic neural tube, the forced expression of Pias1 increased Gli activity and induced the ectopic expression of the Gli dependent gene Nkx2.2. Conversely, a point mutant of Pias1, that lacks ligase activity, blocked the endogenous expression of Nkx2.2.Together, these findings provide evidence that Pias1-dependent SUMOylation influences Gli protein activity and thereby identifies SUMOylation as a post-translational mechanism that regulates the hedgehog signaling pathway

Water-table fluctuations in the Amargosa Desert, Nye County, Nevada

Pleistocene ground-water discharge deposits approximately 20 km southwest of Yucca Mountain were previously thought to represent pluvial water-table rises of 80 to 120 m. Data from new boreholes at two of the three discharge sites indicate that the modern water-table is at depths of only 17 to 30 m and that this shallow water is part of the regional ground-water flow system rather than being perched. Calcite in equilibrium with this modern ground water would have isotopic compositions similar to those in Pleistocene calcite associated with the discharge deposits. Carbon and uranium isotopes in both ground water and discharge deposits imply that past discharge consisted of a mixture of both shallow and deep ground water. These data limit Pleistocene water-table fluctuations at the specified Amargosa Desert discharge sites to between 17 and 30 m and eliminate the need to invoke large water-table rises

Multivariate Analysis of Hydrochemical Data for Jewel Cave, Wind Cave, and Surrounding Areas

Abstract Jewel Cave National Monument and Wind Cave National Park in South Dakota contain two of the six longest caves worldwide. These caves contain subterranean lakes that are important points of intersection between the water table of the Madison aquifer and the caves. During 2015 to 2017, several subterranean lakes were discovered in Jewel Cave, which previously was thought to be above the regional water table. The objectives of this study were to better understand the hydrology of the recently discovered subterranean lakes in Jewel Cave and to evaluate their relation or possible connection to similar lakes in Wind Cave. Both objectives align with National Park Service resource management purposes. Multivariate analysis, consisting of principal component analysis (PCA), cluster analysis, and end member mixing, was applied to hydrochemical data for 70 sites within and surrounding Jewel Cave and Wind Cave. Hydrochemical data consisted of the contents of major ions (Ca, Mg, Na, HCO3, Cl, Si, SO4), arsenic (As), strontium (Sr), uranium (U), stable isotopes of oxygen and hydrogen (δ18O, δ2H), radiogenic isotope ratios of strontium and uranium (87Sr/86Sr and 234U/238U), pH, and electrical conductivity (EC) in water samples. Five hydrogeologic domains were classified on the basis of PCA and cluster analysis for the area encompassing Jewel Cave and Wind Cave in the southern Black Hills. The Artesian 1 and Artesian 2 domains represent primarily artesian springs and surrounding groundwater, the East and West domains represent areas where Madison and Minnelusa aquifer rocks are at or near the land surface, and the Precambrian domain represents the Precambrian aquifer. Multivariate analysis indicates that the Jewel Cave area is part of the West domain and that Wind Cave is part of the East domain. End member mixing was applied to estimate that groundwater in the Jewel Cave area primarily was derived from the West domain and secondarily from the Precambrian domain. Jewel Cave and Wind Cave contain lakes that are well connected to regional groundwater flow in the Madison aquifer

Non-depleted sub-continental mantle beneath the Superior Province of the Canadian Shield: Nd-Sr isotopic and trace element evidence from Midcontinent Rift basalts

Midcontinent Rift flood basalts represent a sample of the relatively shallow, sub-continental upper mantle beneath the Canadian Shield at 1.1 Ga. A thick sequence of olivine tholeiite lavas, including minor intermediate to rhyolitic lavas, from the Portage Lake Volcanics (PLV) in northern Michigan have initial Nd and Sr isotopic compositions which cluster near Bulk Earth values. The effects of assimilation of old LREE-enriched continental crust into mantle-derived fractionating liquids are isotopically discernible in evolved lavas as well as in olivine tholeiites from the lowest portion of the volcanic pile. However, the effects of crustal contamination decrease with stratigraphie height and are absent in more primitive lavas in the upper half of the section. Therefore, the youngest olivine tholeiites preserve the isotopic characteristics of their sub-continental mantle source area which, at 1095 Ma, had ε{lunate}Nd(T) and ε{lunate}Sr(T) values of about +0.8 and +2, respectively. Incompatible trace element compositions from the PLV olivine tholeiite suite support the interpretation of a mantle source slightly enriched in LIL elements relative to chondritic compositions as opposed to a suite of hybrid magmas resulting from mixtures between depleted mantle and enriched crustal end-members. The source for PLV tholeiites is substantially less depleted than previously reported mantle values from the Superior Province. An origin for the PLV source is compatible with either of several mantle evolution models. The PLV source may have been associated with upwelling of a LIL element-enriched, asthenospheric plume which emplaced non-depleted material from deeper sources into the shallow subcontinental mantle beneath the Midcontinent Rift during continental break-up. Alternatively, the PLV source may have originated by enrichment of refractory sub-continental lithospheric mantle which was previously depleted in incompatible trace elements during Archean-aged melt extraction and continental crust formation. Concurrent generation of carbonatite magmas in other areas beneath the Superior Province indicates the widespread presence of sub-continental mantle with substantially higher ε{lunate}Nd(T) and lower ε{lunate}Sr(T) than the PLV source. Combined tholeiite and carbonatite data indicates the presence of large, chemically distinct regions in the upper mantle beneath the Superior Province at 1.1 Ga. © 1989

Evidence for an unsaturated-zone origin of secondary minerals in Yucca Mountain, Nevada

The unsaturated zone (UZ) in Miocene-age welded tuffs at Yucca Mountain, Nevada, is under consideration as a potential site for the construction of a high-level radioactive waste repository. Secondary calcite and silica minerals deposited on fractures and in cavities in the UZ tuffs are texturally, isotopically, and geochemically consistent with UZ deposition from meteoric water infiltrating at the surface and percolating through the UZ along fractures. Nonetheless, two-phase fluid inclusions with small and consistent vapor to liquid (V:L) ratios that yield consistent temperatures within samples and which range from about 35 to about 80 C between samples have led some to attribute these deposits to formation from upwelling hydrothermal waters. Geochronologic studies have shown that calcite and silica minerals began forming at least 10 Ma and continued to form into the Holocene. If their deposition were really from upwelling water flooding the UZ, it would draw into question the suitability of the site as a waste repository