Michael Spilde

Geomicrobiology of Cave Ferromanganese Deposits: A Field and Laboratory Investigation

Abstract Unusual ferromanganese deposits are found in several caves in New Mexico. The deposits are enriched in iron and manganese by as much as three orders of magnitude over the bedrock, differing significantly in mineralogy and chemistry from bedrock-derived insoluble residue. The deposits contain metabolically active microbial communities. Enrichment cultures inoculated from the ferromanganese deposits produced manganese oxides that were initially amorphous but developed into crystalline minerals over an 8-month period and beyond; no such progression occurred in killed controls. Phylogenetic analyses of sequences from clone libraries constructed from culture DNA identified two genera known to oxidize manganese, but most clones represent previously unknown manganese oxidizers. We suggest that this community is breaking down the bedrock and accumulating iron and manganese oxides in an oligotrophic environment.

Evidence for Microbial Involvement in Pool Finger Precipitation, Hidden Cave, New Mexico

Although speleothems are usually considered inorganic precipitates, recent work has demonstrated hitherto unsuspected biogenic influence in some twilight areas. We have expanded this notion to the dark zone, examining pool fingers from Hidden Cave, New Mexico, to test for possible bacterial involvement. The pool fingers in Hidden Cave are pendant speleothems that formed subaqueously in paleo-pools. They are 1 to 4 cm in diameter and 5 to 50 cm long. A knobby, irregular external shape is underlaid by a layered interior on two scales, a 0.5 to 1.0 cm alternation between dense and porous layers and a mm-scale alternation between dark micritic calcite and clear dogtooth spar. The micrite is similar to microbialites identified in modern and ancient carbonates. Fossil bacteria were found in all layers. These include (1) calcified filaments 1 w m in diameter and 5–50 w m long and (2) micro-rods 0.1 w m by 1–2 w m. Most filaments are curved rods with a smooth surface but rare examples display a diamond crosshatch surface. The micro-rods occur as isolated crystals to dense meshes. We interpret the micro-rods as calcified bacilliform bacteria and the filaments as calcified filamentous bacteria. Carbon isotopic data are slightly more negative (by - 0.5 to - 1.0% in micritic layers than in dogtooth spar layers, suggesting a greater microbial influence in the micritic layers. Based on these similarities to known microbialites (e.g., petrographic fabrics, the presence of fossil bacteria, and the suggestive carbon isotopic data), we conclude that microbial activity was an intimate part of pool finger formation in Hidden Cave. The significance of such involvement goes beyond speleological contexts to wider questions of identification of biosignatures in rocks on earth and beyond.

Diogenites as asteroidal cumulates: Insights from orthopyroxene major and minor element chemistry

Abstract Diogenites appear to be cumulates formed from one or more igneous reservoirs in the interior of asteroid 4 Vesta. Magmatism in this parent body gave rise to a series of related lithologies designated howardites, eucrites, and diogenites or “HED.” Eucrites are pigeonite/plagioclase basalts, and diogenites are orthopyroxenites. Howardites are brecciated mixtures of eucrites and diogenites. The major objective of this paper is to characterize the major and minor element chemistry of orthopyroxene in diogenites and to interpret these data in terms of a petrogenetic model. This study, which involves interpretation of ~ 1,200 high-quality electron microprobe analyses, demonstrates that the systematics of Ca, Fe, and Mg in orthopyroxene were largely reset by reaction with melt and by subsolidus exchange. However, the systematics of the minor elements Al, Cr, and Ti still effectively record their igneous history. Aluminum and Ti are highly correlated with the incompatible trace elements (e.g. Yb, Y) and thus are useful fractionation indicators. As many as twenty of the twenty-three diogenites studied may have formed from one igneous system based on Al, Cr, and Ti systematics in orthopyroxene. The Al content of the orthopyroxene in the twenty diogenites forms the basis for a fractionation sequence with Peckelsheim the least fractionated and LEW 88008 the most fractionated. Roda and Manegaon, and possibly ALHA77256, fall off the main compositional trends and may belong to different melt systems. The coupled substitutions that incorporate Al, Cr, and Ti into the orthopyroxene crystal structure are VICr3+-IVAl3+, VIAl3+-VIAl3+, and VITi4+-2IVAl3+. The dominant substitutional couple in the early stages of crystallization is VICr3+-IVAl3+ while VIAl3+-IVAl3+ is dominant in the late stages. These findings demonstrate the importance of understanding the coupled substitutions for minor elements when assessing the appropriate mineral/melt partition coefficients (D values) or when discussing whether an element is compatible or incompatible. For example, in diogenitic orthopyroxene, Al has three different compatibilities (D values) with VICr3+-IVAl3+ more compatible than VIAl3+-IVAl3+ which is more compatible than VITi4+-2IVAl3+. Based on the assumption that D Al increases during crystallization from 0.05 to 0.1 corresponding to the crystallization interval represented by Peckelsheim to LEW 88008, 60% crystallization is required. The melt parental to LEW 88008 is estimated to contain ~12 wt% Al2O3, very near plagioclase saturation.

Sulfur isotopic systematics in alteration assemblages in martian meteorite Allan Hills 84001

Abstract ALH84001 is a coarse-grained, clastic orthopyroxenite meteorite related to the SNC meteorite group ( s hergottites, n akhlites, C hassigny). Superimposed upon the orthopyroxene-dominant igneous mineral assemblage is a hydrothermal signature. This hydrothermal overprint consists of carbonate assemblages occurring in spheroidal aggregates and fine-grained carbonate-sulfide vug-filling. The sulfide in this assemblage has been identified as pyrite, an unusual sulfide in meteorites. Previously, Burgess et al. (1989) reported a bulk δ 34 S for a SNC group meteorite (Shergotty) of −0.5 ± 1.5‰. Here, we report the first martian δ 34 S values from individual sulfide grains. Using newly developed ion microprobe techniques, we were able to determine δ 34 S of the pyrite in ALH84001 with a 1 a precision of better than ±0.5‰. The δ 34 S values for the pyrite range from +4.8 to +7.8‰. Within the stated uncertainties, the pyrite from ALH84001 exhibits a real variability in δ 34 S in this alteration assemblage. In addition, these sulfides are demonstrably enriched in 34 S relative to Canon Diablo troilite and sulfides from most other meteorites. This signature implies that the planetary body represented by ALH84001 experienced processes capable of fractionating sulphur isotopes and that hydrothermal conditions changed during pyrite precipitation (T, pH, fluid composition, etc.). The fractionated signature of the sulphur in the pyrite is most likely attributed to either conditions of pyrite precipitation (low temperature, reduced (low f o 2 ) and moderately alkaline (pH > 8) environment) or enrichment of fluids in 34 S by surface processes (weathering or impact processes) prior to precipitation. These new data are not consistent with the pyrite recording either biogenic activity or atmospheric fractionation of sulphur through nonthermal escape mechanisms or oxidation processes. This study also demonstrates the usefulness of ion microprobe measurements of sulphur isotopes in constraining conditions on other planetary bodies.

Trace-element partitioning between immiscible lunar melts: An example from naturally occurring lunar melt inclusions

Abstract Evidence for liquid immiscibility on the Moon has been documented in melt inclusions in minerals that crystallized from mare basalts, within mesostasis in mare basalts and in at least one sample of a lunar plutonic rock. This study focuses on trace-element partitioning between immiscible melt pairs occurring as inclusions in plagioclase. These inclusions are blade-like in shape and range in length from 2 to 150 μm. They consist of two coexisting glasses separated by a sharp meniscus. The colorless, low-index glass (felsite) is spherical and immersed in a dark-brown, high-index glass (high-Fe basalt). The Fe-rich basaltic component of the inclusion is quartz + hypersthene normative with low Mg/(Mg + Fe) and variable SiO2 content (between 34 and 45 wt%). The felsic component has a SiO2 content between 72 and 82 wt% and variable K2O (4.4 to 8.5 wt%) In most cases, the partitioning behavior of the trace elements agrees with behavior either predicted or measured in experimental and natural systems. The high charge density elements preferentially partition into the basaltic component. High P2O5 and a wider solvus increase the Dbasalt/felsite for these elements. In contrast to many experimental studies and in agreement with studies of natural silicate liquid immiscibility, the Dbasalt/felsite for Ba indicates a preference for the felsic component. This difference in Ba behavior between experimental and natural samples has been attributed to differences in melt polymerization and compensation for charge unbalance within the polymerized melt structure. The apparent differences in Dbasalt/felsite for Sr and divalent Eu between the Apollo 11 high-Ti basalts and Apollo 12 low-Ti basalts may be a result of either subtle differences in bulk composition or the extent of plagioclase plating on inclusion walls. Based on our partitioning data from melt inclusions and the chemical characteristics of lunar felsites, the latter cannot be a product of simple fractional crystallization. Silicate liquid immiscibility can account for fractionation of Ba/ La, K/U, and Ba/U in the lunar felsites and the limited variation in Zr/La. However, it cannot account for the REE pattern of the lunar felsites or the fractionation of U/La. These characteristics must be attributed to whitlockite crystallization prior to the onset of liquid immiscibility.

A biosignature suite from cave pool precipitates, Cottonwood Cave, New Mexico.

Calcite cave pool precipitates often display a variety of potential biosignatures from the macroscopic to the submicroscopic. A fossil cave pool in Cottonwood Cave, New Mexico, exhibits older stalactites and stalagmites that are completely coated in brown, laminated calcitic crust that extends down as pool fingers and u-loops. The pool fingers and u-loops are mainly micrite to clotted micrite, some recrystallized to microspar, with some isopachous spar layers. Micrite, particularly clotted micrite, is usually interpreted by carbonate workers as microbial in origin. Scanning electron microscopy examination of etched pool fingers, u-loops, and the brown crust revealed abundant calcified microbial filaments and biofilm. Energy dispersive X-ray analysis showed that these features have excess carbon, above that found in pure calcite. Independent carbon analysis indicated that these same samples contain up to 0.2% organic carbon. Since pool fingers hang down but form underwater, we hypothesize they are biogenic with hanging microbial filaments or biofilm acting as nuclei for calcite precipitation. Because of the abundance of micrite and fossil filaments, we further hypothesize that these pendant features formed during a period of plentiful nutrients and active hydrological activity when the pool was literally dripping with microbial slime. Although each of these lines of evidence could be interpreted in other ways, their combined weight strongly suggests the cave pool precipitates in Cottonwood Cave are biogenic. These investigations can be used to help inform extraterrestrial life-detection studies.

The Lodran primitive achondrite: petrogenetic insights from electron and ion microprobe analysis of olivine and orthopyroxene

The Lodran primitive achondrite is thought to represent some of the earliest events in the differentiation of chondritic asteroids. Most researchers who studied Lodran believe that it is a restite from which a melt, enriched in the incompatible trace and minor elements, was extracted. This process is reflected by a lack of feldspar in the Lodran mineral assemblage. Presumably, after or during melting, a reduction event took place resulting in an increase in Mg/Fe near the rims of both olivine and orthopyroxene. The reduction process is far more advanced in olivine than in pyroxene because of the more rapid FeMg diffusion rates in olivine. Narrow reaction rims (<10 μm) around orthopyroxene grains show a depletion in Ca, Al, Cr, Ti, REEs, and Y and an increase in Mg (reverse zoning). These systematics are largely the result of melting and to a lesser extent of reduction. Significant reaction of olivine has taken place by reduction and/or sulfidatuon and to a lesser extent by melting. This is reflected by a decrease in Fe, Co, and Ni and an increase in Mg towards the rims of olivine. The reactions by which reduction and/or sulfidation of olivine took place are not confirmed. However, the following represent two possible reactions:

Terrestrial analogs of martian sulfates: Major and minor element systematics of alunite–jarosite from Goldfield, Nevada

Abstract Alunite and jarosite from Goldfield, Nevada, show spectacular relationships between early alunite and later jarosite. In some cases, jarosite overgrows alunite with the same crystallographic orientation and sharp contacts. Electron microprobe analyses of these phases show that they fall in the alunitejarosite quadrilateral defined by alunite, KAl3(SO4)2(OH)6; natroalunite, NaAl3(SO4)2(OH)6; jarosite, KFe3 3+(SO4)2(OH)6; and natrojarosite, NaFe33+(SO4)2(OH)6. A large compositional gap occurs between alunite-natroalunite and jarosite-natrojarosite. This gap has no crystal chemical basis because Al and Fe3+ can readily substitute for each other in octahedral site coordination. We believe the “on-off switch” behavior between early alunite and later jarosite is caused by an oxidant entering the system, oxidizing Fe2+ in solution to Fe3+, raising the Eh and possibly oxidizing H2S to lower the pH, and thus stabilizing jarosite relative to alunite. The activity of Fe (as Fe2+) increased in the solution because of prolonged alunite crystallization but could not readily enter the crystal structure until it was oxidized to Fe3+. The jarosite overgrowths show striking oscillatory zoning of Na- and K-rich bands. This reflects up to an order of magnitude change in the fluid K/Na ratio. These textures are interpreted to represent rapid growth and kinetic control of delivery of free Na and K to the crystal-fluid interface. This could be due to some combination of Na and K diffusion rates in the solution and complex ion breakdown involving Na and K.

Activities and Ultrastructural Effects of Antifungal Combinations against Simulated Candida Endocardial Vegetations

ABSTRACT In vitro pharmacodynamic model (PDM) simulation of serum antifungal concentrations may predict the value of combination antifungal regimens against Candida sp. endocarditis. We investigated the effects of combinations of flucytosine (5FC), micafungin (Mica), and voriconazole (Vor) against Candida-infected human platelet-fibrin clots, used as simulated endocardial vegetations (SEVs). Single clinical bloodstream isolates of Candida albicans, Candida glabrata, Candida parapsilosis, and Candida tropicalis were used. All four isolates were susceptible to 5FC, while C. glabrata was resistant to Vor and C. tropicalis had a paradoxical resistance phenotype to Mica. The SEVs were prepared with an initial inoculum of 1 × 106 CFU/g of SEV and added to a PDM, which utilized yeast nitrogen broth-2% glucose and incubation at 35°C and simulated antifungal pharmacokinetic profiles. Fungal densities in the SEVs were determined in quadruplicate over 72 h. Scanning electron microscopy (SEM) was used to evaluate treatment and control SEVs. Vor was the least active single agent against all Candida spp. except for C. parapsilosis, where it was comparable to Mica. In contrast, 5FC was the most active against all Candida spp. except for C. tropicalis, where it was comparable to Mica. The combination of 5FC plus Vor was superior to either agent alone against C. parapsilosis. The combination of Vor plus Mica was inferior to the use of Mica alone against C. tropicalis. The triple combination of 5FC plus Vor plus Mica was no better than single or dual agents against any of the Candida spp. The ultrastructural features of infected SEVs were unique for each Candida sp., with C. parapsilosis in particular manifesting friable biofilm clusters. In general, 5FC and Mica were superior in their rates and extents of fungal burden reduction compared to Vor against Candida-infected SEVs. Evaluation of 5FC and Mica in animal models of Candida endocarditis is warranted.

SIMS studies of planetary cumulates; orthopyroxene from the Stillwater Complex, Montana

Abstract Igneous cumulate rocks provide an important record of planetary magmatism, but there are pitfalls in their interpretation. The rocks are composed of cumulus minerals plus assemblages that crystallized from trapped melt. Cumulus minerals may react with the trapped melt and other cumulus phases during subsolidus reactions, thus losing a direct record of their igneous history. One of the best approaches for estimating the melt compositions parental to the cumulates is to analyze the cores of cumulus phases for elements with slow diffusion rates (e.g., REE) because these most reliably retain a record of the mineral-melt partitioning. Many of the cumulus orthopyroxene grains from the Stillwater Complex analyzed in this study have augite lamellae in their interiors but lamellae-free rims. Secondary ion mass spectrometer (SIMS) analysis shows that these orthopyroxene rims have lower Sr, Y, Zr, and Ce concentrations relative to the cores. These systematics were apparently caused by migration of augite exsolution lamellae, which preferentially incorporate these trace elements, out of the rims of the orthopyroxene grains. SIMS analyses for REE in orthopyroxene cores show lower LREE concentrations, (Ce/ Yb)n and (Dy/Yb)n than the isotope dilution data on mineral separates (Lambert and Simmons, 1987). We believe that these differences result from one or more contaminating phases (e.g., augite and plagioclase) in the orthopyroxene mineral separates. The SIMS data yield calculated parental melts similar to sills found below the Stillwater Complex, which have previously been suggested as possible parental melts (Helz, 1985). A major focus of this study was to determine whether the onset of plagioclase crystallization at the bronzitite zone-norite zone contact was the result of fractionation until plagioclase saturation of the magmas parental to the bronzitites, or if mixing of a second magma with higher Al activity was the cause of plagioclase crystallization. The data presented in this paper, coupled with existing data, support the magma-mixing model.