Laboratory simulations of prebiotic molecule stability in the jarosite mineral group; end member evaluation of detection and decomposition behavior related to Mars sample return     

J. Michelle Kotler  C. Doc Richardson  Jill R. Scott 《Planetary and Space Science》2009,57(12):1381-1388

Recently, the prebiotic amino acid glycine has been found associated with natural jarosite samples from locations around the world. Since the discovery of jarosite on Mars, extensive research focuses on linking this mineral group with possible detection of biosignatures in the geologic record on Earth and Mars. Multiple analytical methods, including extraction and mass spectrometry techniques, have identified glycine and other biomolecules in jarosite samples. The jarosite end members jarosite (sensu stricto-potassium jarosite), natrojarosite (sodium jarosite), and ammoniojarosite (ammonium jarosite) have different thermodynamic stabilities, decompose at different rates, and have potentially different susceptibilities to substitution. The relationship between the thermodynamic stability of the jarosite end members and the effect that glycine has on the thermal decomposition behavior of each end member was investigated using thermal gravimetric analysis. Introducing glycine into the synthesis procedure (75 ppm) of the potassium, sodium, and ammonium jarosite end member has elucidated the effects that glycine has on the thermal stability of the mineral group. Potassium jarosite appears to be the least susceptible to the effects of glycine, with the sodium and ammonium end members showing marked changes in thermal decomposition behavior and decomposition rates. These results suggest that the sodium and ammonium jarosites are more suitable targets for identifying signs of prebiotic or biotic activity on Mars and Earth than the potassium jarosites. These results have implications for current in situ investigations of the martian surface and future sample return missions.  相似文献   

Modern Sphagnumδ13C signatures follow a surface moisture gradient in two boreal peat bogs,James Bay lowlands,Québec     

Julie Loisel  Michelle Garneau  Jean‐François Hélie 《第四纪科学杂志》2009,24(3):209-214

Carbon isotopic composition of Sphagnum macrofossils can potentially be used as a palaeohydrological tool for peat‐based climatic studies since a relationship between Sphagnum δ¹³C values and peatland surface moisture has been presented in previous studies. In order to verify this hypothesis, modern Sphagnum δ¹³C values were measured along a moisture (microtopographic) gradient in two boreal peat bogs. Isotopic measurements were performed on bulk material of S. fuscum, S. magellanicum, S. capillifolium and S. pulchrum. Isotopic variations found within and between Sphagnum species along the microtopographic gradient were compared using analysis of variance. A significant positive correlation (P < 0.0001) was found between Sphagnum δ¹³C values and their position along the surface moisture gradient. Results show that ¹³C‐depleted values are related to low water table depths (WTD), while ¹³C‐enriched values correspond to a water table that is close to the peat surface. Although the mechanisms underlying carbon fractionation processes in mosses are not well understood, we demonstrate that water resistance to CO₂ diffusion is an important fractionation process that is observed in bulk Sphagnum δ¹³C measurements, since drier and wetter samples exhibit consistent and very different isotopic signatures. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Advance,deglacial and sea‐level chronology for Foxe Peninsula,Baffin Island,Nunavut          下载免费PDF全文

Daniel J. Utting  John C. Gosse  Samuel E. Kelley  Kayla J. Vickers  Brent C. Ward  Michelle S. Trommelen 《Boreas: An International Journal of Quaternary Research》2016,45(3):439-454

The impact of the Laurentide Ice Sheet (LIS) deglaciation on Northern Hemisphere early Holocene climate can be evaluated only once a detailed chronology of ice history and sea‐level change is established. Foxe Peninsula is ideally situated on the northern boundary of Hudson Strait, and preserves a chronostratigraphy that provides important glaciological insights regarding changes in ice‐sheet position and relative sea level before and after the 8.2 ka cooling event. We utilized a combination of radiocarbon ages, adjusted with a new locally derived ΔR, and terrestrial in‐situ cosmogenic nuclide (TCN) exposure ages to develop a chronology for early‐Holocene events in the northern Hudson Strait. A marine limit at 192 m a.s.l., dated at 8.1–7.9 cal. ka BP, provides the timing of deglaciation following the 8.2 ka event, confirming that ice persisted at least north of Hudson Bay until then. A moraine complex and esker morphosequence, the Foxe Moraine, relates to glaciomarine outwash deltas and beaches at 160 m a.s.l., and is tightly dated at 7.6 cal. ka BP with a combination of shell dates and exposure ages on boulders. The final rapid collapse of Foxe Peninsula ice occurred by 7.1–6.9 cal. ka BP (radiocarbon dates and TCN depth profile age on an outwash delta), which supports the hypothesis that LIS melting contributed to the contemporaneous global sea‐level rise known as the Catastrophic Rise Event 3 (CRE‐3).  相似文献   

Young-of-the-year oyster,Crassostrea virginica,reproduction in coastal Georgia     

Francis X. O’Beirn  Peter B. Heffernan  Randal L. Walker  Michelle L. Jansen 《Estuaries and Coasts》1996,19(3):651-658

Young-of-the-year (YOY) oysters (Crassostrea virginica) in the Gulf of Mexico mature sexually and spawn in their first year. This study determined whether YOY oysters in the southeastern United States also mature and spawn in their first year. In 1991 and 1993, 300 YOY oysters were marked in May and 20–30 were sampled in subsequent months along with 20 adult controls. Two sites were chosen in 1991 (House Creek and Skidaway River) and one in 1993 (Skidaway River). At House Creek, YOY oysters were mature and spawned in September. YOY oysters at Skidaway spawned in October. Adult oysters did not appear to spawn in 1991. In 1993, the adult oysters spawned in August and September whereas, the YOY oysters spawned heavily in October. Oyster recruitment in coastal Georgia extends through October. The potential contribution of YOY oysters to this late season set is substantial, given that the YOY oysters are relatively large (≈4 cm) and are found in greater numbers than the adults. Oysters are capable of having two, if not more, generations within one year, prior to exposure of disease-causing organisms. Also, this particular reproductive strategy would increase the oysters suitability as a test subject in population genetic studies.  相似文献   

Statistical analysis of the microlithotype sequences in the Bulli Seam, Australia, and relevance to permeability for coal gas     

Michelle Smyth  Michael J. Buckley 《International Journal of Coal Geology》1993,22(3-4)

Sequential microlithotype analyses through the Permian Bulli Coal, Sydney Basin, Australia, enable determination of the abundance, locations and thicknesses of various microlithotypes in the seam. Statistical analyses allow prediction of these parameters. Microlithotype analyses may be used as a means of predicting seam permeability in relation to coal gas drainage, if used in conjunction with reported correlation between coal type and seam reservoir properties.A combination of sequential microlithotype analyses and statistical modelling provide data on the number, location and thicknesses of individual bands of vitrite, vitrinertite, inertite and mineral-rich coal. A Markov chain describes both the order and thickness of the bands in the seam. Local ordering of microlithotypes is similar, irrespective of vertical orientation, which suggests that analyses and predictions may be possible using representative, randomly oriented samples. Statistical modelling can be used to characterise the seam using a small number of parameters. These include the elements of the transition probability matrix of the Markov chain, from which many seam properties such as maximum band thickness, thickness distribution of bands and spacing of thick bands can be predicted.The permeability of vitrite-rich coal in the seam is 30 mD and it is 2.3 mD for inertite-rich coal. In general, for the Bulli seam, vitrite-rich plies are expected to provide better flow paths for coal gas than inertite-rich plies, because of the abundance of cleat systems in vitrite. Using this information, it thus may be possible to predict gas and water flow paths in a seam from microlithotype analyses, thereby leading to the development of a rapid method for assessing the comparative permeabilities of coal plies.  相似文献   

Serpentinite protrusions in the oceanic crust     

Enrico Bonatti 《Earth and Planetary Science Letters》1976,32(2):107-113

Serpentinite may be a significant component of the oceanic crust, not as a continuous layer, but as vertical tectonic protrusions and sills emplaced from the upper mantle into fault zones parallel to the axis of spreading ridges. The diapiric emplacement of serpentinite bodies occurs within 100–200 km of ridge axis, with a rate of ascent on the order of 1 mm/year. Serpentinite protrusions may cause small-scale linear magnetic anomalies parallel to ridge axis. Serpentinites are distributed in the oceanic crust according to an orthogonal pattern, with large serpentinite protrusions aligned along major fracture zones, and smaller serpentinite bodies emplaced in bands parallel to ridge axis.  相似文献   

Neogene crustal emersion and subsidence at the Romanche fracture zone,equatorial Atlantic     

E. Bonatti  M. Sarnthein  A. Boersma  M. Gorini  J. Honnorez 《Earth and Planetary Science Letters》1977,35(3):369-383

Partly phosphatized, oolitic-biogenic limestones were recovered 950–1300 m below sea level from two sites near the crest of a transverse ridge running parallel and adjacent to the Romanche fracture valley (equatorial Atlantic). Some of the biogenic contituents of the limestones (the benthonic foraminiferal genusAmphistegina; corals of the genusStylophora sp., scaphopods, etc.); their paleofacies assemblage (including echinoderms, gastropods, calcareous algae, etc.); and the presence of a well-developed oolitic facies, indicate that the limestones formed in very shallow water close to sea level. In addition, several features of the limestones (including the presence of stromatolite-like laminae, and dissolution features typical of subaerial diagenesis) suggest that the summit of the transverse ridge might have undergone episodes of emersion. The limestones were formed on a shallow carbonate bank at around the Miocene-Pliocene boundary, i.e., 5 ± 1 Myr ago, as determined by the age of fossil planktonic foraminifera and corals. The transverse ridge must have subsided since that time at an average rate of 0.2 mm/yr. It is unlikely that the vertical motions of the Romanche transverse crustal block were caused solely by accreting plate margin- or mantle plume-related volcanic and/or tectonic processes. It is suggested instead that such motions are related to vertical tectonism typical of large oceanic fracture zones.  相似文献   

Geochemical effects on metals following permanganate oxidation of DNAPLs   总被引：2，自引：0，他引：2  

Crimi ML  Siegrist RL 《Ground water》2003,41(4):458-469

The application of in situ chemical oxidation for dense, nonaqueous phase liquid (DNAPL) remediation requires delivery of substantial levels of oxidant chemicals into the subsurface to degrade target DNAPLs and to satisfy natural oxidant demand. This practice can raise questions regarding changes in subsurface conditions, yet information regarding potential effects, especially at the field scale, has been lacking. This paper describes an evaluation of the effects on metals associated with in situ chemical oxidation using potassium permanganate at Launch Complex 34 (LC34), Cape Canaveral Air Station, Florida. At LC34, high concentrations of permanganate (1 to 2 wt%) were injected into the subsurface as part of a demonstration of DNAPL remediation technologies. In a companion experimental effort at the Colorado School of Mines, field samples were characterized and laboratory batch and mini-column studies were completed to assess effects of permanganate oxidation on metals in the subsurface one year after completion of the field demonstration. Results indicated there was potential for long-term immobilization of a portion of introduced manganese and no treatment-induced loss in subsurface permeability due to deposition of manganese oxides particles, which are a product of the oxidation reactions. Permanganate treatment did cause elevated manganese, chromium, and nickel concentrations in site ground water within the treated region. Some of these metals effects can be attenuated during downgradient flow through uncontaminated and untreated aquifer sediments.  相似文献   

Flexural uplift of a lithospheric slab near the Vema transform (Central Atlantic): Timing and mechanisms     

Enrico Bonatti  Daniele Brunelli  W. Roger Buck  Anna Cipriani  Paola Fabretti  Valentina Ferrante  Luca Gasperini  Marco Ligi   《Earth and Planetary Science Letters》2005,240(3-4):642-655

The Vema Transverse Ridge (VTR) is a prominent, long and narrow topographic anomaly that runs for over 300 km along a sea floor spreading flow line south of the Vema transform at 11° N in the Atlantic. It rises abruptly about 140 km from the axis of the Mid-Atlantic Ridge (MAR) in 10 Myr old crust and runs continuously up to 25 Myr old crust. It reaches over 3 km above the predicted lithospheric thermal contraction level. It is absent in crust younger than 10 Myr; thus, the uplift of the VTR must have ended roughly 10 Ma. The VTR is interpreted as the exposed edge of a flexured and uplifted slab of oceanic lithosphere that was generated at an 80 km long MAR segment. Based on satellite gravimetry imagery this MAR segment was born roughly 50 Ma and increased its length at an average rate of 1.6 mm/yr. Multibeam data show that the MAR-parallel sea floor fabric south of the VTR shifts its orientation by 5° to 10° clockwise in 11–12 Myr old crust, indicating a change at that time of the orientation of the MAR axis and of the position of the Euler rotation pole. This change caused extension normal to the transform, followed between 12 and 10 Ma by flexure of the edge of the lithospheric slab, uplift of the VTR at a rate of 2 to 4 mm/yr, and exposure of a lithospheric section (Vema Lithospheric Section or VLS) at the northern edge of the slab, parallel to the Vema transform. Ages of pelagic carbonates encrusting ultramafic rocks sampled at the base of the VLS at different distances from the MAR axis suggest that the entire VTR rose vertically as a single block within the active transform offset. A 50 km long portion of the crest of the VTR rose above sea level, subsided, was truncated at sea level and covered by a carbonate platform. Subaerial and submarine erosion has gradually removed material from the top of the VTR and has modified its slopes. Spreading half rate of the crust south of the transform decreased from 17.2 mm/yr between 26 and 19 Ma to 16.9 mm/yr between 19 and 10 Ma, to 13.6 mm/yr from 10 Ma to present. The slowing down of spreading occurred close in time to the change in ridge/transform geometry, suggesting that the two events are related. A numerical model relates lithospheric flexure to extension normal to the transform, suggesting that the extent of the uplift depends on the thickness of the brittle layer, consistent with the observed greater uplift of the older lithosphere along the VTR.  相似文献   

Quantifying PCE and TCE in DNAPL Source Zones: Effects of Sampling Methods Used for Intact Cores at Varied Contaminant Levels and Media Temperatures   总被引：1，自引：0，他引：1  

Robert L. Siegrist  Kathryn S. Lowe  Michelle L. Crimi  Michael A. Urynowicz 《Ground Water Monitoring & Remediation》2006,26(2):114-124

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