Palynostratigraphy of the Zorritas Formation,Antofagasta region,Chile: Insights on the Devonian/Carboniferous boundary in western Gondwana     

Claudia V. Rubinstein  Elodie Petus  Hans Niemeyer 《地学前缘(英文版)》2017,8(3):493-506

The Middle Member of the Zorritas Formation in the Antofagasta region of northern Chile, yielded terrestrial and marine palynomorph assemblages which span the Devonian/Carboniferous boundary. The assemblages show a clear predominance of terrestrial palynomorphs with 70 miospore species, 18 marine phytoplankton species, two non-marine algae and one chitinozoan species, all coming from 15 productive levels. Palynomorphs are poorly preserved and most of them are reworked. Three palynological associations are recognized based on miospores. These are assigned to the Tournaisian–Visean, Tournaisian and probable latest Famennian. Age assignments are discussed in the frame of the spore zonal schemes established for Euramerica and western Gondwana. The stratigraphical distribution of spores allows the identification of the probable position of the Devonian/Carboniferous boundary within the Zorritas Formation. This system boundary is proposed for the first time in Palaeozoic sedimentary rocks of northern Chile. The presence of Gondwanan typical miospore species indicates affinities with this palaeocontinent even though the Tournaisian and Tournaisian–Visean miospore associations support the cosmopolitanism already suggested for the early Carboniferous flora. The significant number of reworked palynomorphs together with the sedimentological analysis of the studied sections, suggest that these deposits were severely impacted by the climatic change and major sea level fluctuations. Similar conditions were recorded in coeval western Gondwana basins.  相似文献   

The effect of ground ice on the Martian seasonal CO₂ cycle     

Robert M. Haberle  Francois Forget  James Schaeffer  Nora J. Kelly 《Planetary and Space Science》2008,56(2):251-255

The mostly carbon dioxide (CO₂) atmosphere of Mars condenses and sublimes in the polar regions, giving rise to the familiar waxing and waning of its polar caps. The signature of this seasonal CO₂ cycle has been detected in surface pressure measurements from the Viking and Pathfinder landers. The amount of CO₂ that condenses during fall and winter is controlled by the net polar energy loss, which is dominated by emitted infrared radiation from the cap itself. However, models of the CO₂ cycle match the surface pressure data only if the emitted radiation is artificially suppressed suggesting that they are missing a heat source. Here we show that the missing heat source is the conducted energy coming from soil that contains water ice very close to the surface. The presence of ice significantly increases the thermal conductivity of the ground such that more of the solar energy absorbed at the surface during summer is conducted downward into the ground where it is stored and released back to the surface during fall and winter thereby retarding the CO₂ condensation rate. The reduction in the condensation rate is very sensitive to the depth of the soil/ice interface, which our models suggest is about 8 cm in the Northern Hemisphere and 11 cm in the Southern Hemisphere. This is consistent with the detection of significant amounts of polar ground ice by the Mars Odyssey Gamma Ray Spectrometer and provides an independent means for assessing how close to the surface the ice must be. Our results also provide an accurate determination of the global annual mean size of the atmosphere and cap CO₂ reservoirs, which are, respectively, 6.1 and 0.9 hPa. They also indicate that general circulation models will need to account for the effect of ground ice in their simulations of the seasonal CO₂ cycle.  相似文献   

Field-ionization mass spectrometry: application to geochemical analysis     

J.D. Payzant  I. Rubinstein  A.M. Hogg  O.P. Strausz 《Geochimica et cosmochimica acta》1979,43(8):1187-1193

The thiourea adduct, thiourea non-adduct and aromatic fractions from a series of Alberta oil sand bitumens have been subjected to field ionization mass spectrometric analyses. Field ionization mass spectra feature little fragmentation and the molecular weight distributions of compounds in the fractions are readily obtained. Using this method, the various acyclic and cyclic saturated hydrocarbons and the hydrocarbon and thiophenic aromatic materials may be distinguished by compound type and number of carbon atoms. The effect of biodegradation on crude oils is illustrated in the results from the series of oil sand bitumens and their asphaltene pyrolysis products. Field ionization mass spectrometry is potentially an important new analytical tool in organic geochemistry.  相似文献   

Removal of tributyltin (TBT) by live and dead microalgal cells   总被引：3，自引：0，他引：3  

Tam NF  Chong AM  Wong YS 《Marine pollution bulletin》2002,45(1-12):362-371

The removal of tributyltin (TBT) from artificial wastewater by dead and live cells of four microalgal species, Chlorella miniata, C. sorokiniana, Scenedesmus dimorphus and S. platydiscus was investigated. Dead cells were generally more efficient in removing TBT during three days exposure. More than 90% and 85% TBT were removed by dead cells of Scenedesmus and Chlorella, respectively. Although the removal percentages of live microalgae were smaller, TBT was continuously absorbed and degraded, and TBT removal percentages similar to respective dead cells were achieved at the end of 14 days treatment. Degradation products, DBT and MBT, were recorded mainly inside the cells, and intracellular MBT concentrations were significantly higher than DBT. In terms of TBT removal, Scenedesmus cells were more effective than Chlorella, probably due to larger cell sizes and biomass. However, TBT specific uptake and degradation by Chlorella was higher than in Scenedesmus. The highest specific TBT uptake values, as well as the highest degradation, were recorded in C. miniata, a Hong Kong isolate.  相似文献   

UPROOTED LIVES: GENDER, VIOLENCE AND DISPLACEMENT IN COLOMBIA     

Donny Meertens  Nora Segura-Escobar 《Singapore journal of tropical geography》1997,17(2):165-178

During the last decade, more than 600,000 people have been forced to leave rural areas and migrate to regional urban centres in Colombia as a result of political violence in which guerrilla and paramilitary groups and the armed forces are the principal actors. The number of displaced people is still increasing. Nearly 60 per cent of them are women, and at least 25 per cent of the displaced households are headed by women, most of whom are widows. Focusing on three regions of the country - the northern Caribbean Coast, the central Middle Magdalena region and the Eastern Plains - the effects of forced displacement on women and men are analysed in terms of intra-household relationships, survival strategies and gender identities. The paper evaluates the gains and losses for women and men in the process of displacement. It argues that displacement has the strongest impact on women during the stage of “destruction”, while men, confronted with unemployment and loss of identity, are most affected during the stage of “reconstruction”.  相似文献   

Microbially induced sedimentary structures in Archean sandstones: A new window into early life   总被引：3，自引：1，他引：3  

Nora Noffke   《Gondwana Research》2007,11(3):336-342

Until now, the most valuable information on the early life on the Archean Earth derived from bacterial fossils and stromatolites preserved in precipitated lithologies such as chert or carbonates. Also, shales contain complex biomarker molecules, and specific isotopes constitute an important evidence for biogeneicity.In contrast, because of their low potential of fossil preservation, sandstones have been less investigated. But recent studies revealed a variety of ‘microbially induced sedimentary structures — MISS’ that differ greatly from any other fossils or sedimentary structures. ‘Wrinkle structures’, ‘multidirected ripple marks’, ‘biolaminites’, and other macrostructures indicate the former presence of photoautotrophic microbial mats in shallow-marine to tidal paleoenvironments. The MISS form by the mechanical interaction of microbial mats with physical sediment dynamics that is the erosion and deposition by water agitation. The structures occur not only in Archean tidal flats, but in equivalent settings throughout Earth history until today.MISS are not identified alone by their macroscopic morphologies. In thin-sections, the structures display the carpet-like fabrics of intertwined filaments of the ancient mat-constructing microorganisms. Geochemical analyses of the filaments proof their composition of iron minerals associated with organic carbon.In conclusion, microbial mats colonize sandy tidal settings at least for 3.2 Ga years. Therefore, Archean sandstones constitute an important archive for the exploration of early life.  相似文献   

Geochemistry of the thiourea adduct fraction from an Alberta petroleum     

I. Rubinstein  O.P. Strausz 《Geochimica et cosmochimica acta》1979,43(8):1387-1392

The thiourea adducted saturated hydrocarbon fraction (TUA) from a mature Alberta crude oil has been studied in detail. The predominating classes of compounds were found to be the acyclic isoprenoids, alkylcyclohexanes and alkylmethylcyclohexanes. Simulation experiments indicated that the alkylcyclohexanes and the alkylmethylcyclohexanes may have been formed by the advanced diagenesis of biologically occurring fatty acids.  相似文献   

Quantifying stream-loss recovery in a spring using dual-tracer injections in the Snake Creek drainage,Great Basin National Park,Nevada, USA     

Humphrey  C. Eric  Gardner  Philip M.  Spangler  Lawrence E.  Nelson  Nora C.  Toran  Laura  Solomon  D. Kip 《Hydrogeology Journal》2023,31(4):1051-1066

Simultaneous short-pulse injections of two tracers (sodium bromide [Br^–] and fluorescein dye) were made in a losing reach of Snake Creek in Great Basin National Park, Nevada, USA, to evaluate the quantity of stream loss through permeable carbonates that resurfaces at a spring approximately 10 km down drainage. A revised hydrogeologic cross section for a possible flow path of the infiltrated Snake Creek water is presented, and the results may inform water management in the region. First arrival and peak concentration of the two tracers occurred at 9.5 and 12.7 days after injection, respectively. Fracture transport simulations indicate that Br^– preferentially diffuses into immobile regions of the aquifer, and this diffusive flux is likely responsible for the major differences in the breakthrough curves. When considering the diffusive tracer flux, total apparent Br^– and fluorescein dye recoveries were 16.9–22.1% and 21.7–24.3%, respectively. These findings imply that consideration of diffusive flux and long-term monitoring in fracture-dominated flow may support accurate quantification of tracer recovery. In addition, the apparent power law slopes of the breakthrough tails for both tracers were steeper at early times than have been attributed to heterogeneous advection or channeling in meter-scale tests, but the late-time Br^– power law slope becomes less steep than has been attributed to diffusive exchange. These deviations may reflect fracture transport patterns that occur at larger scales.

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(Mis)trusting the process: how post-disaster home buyout processes can degrade public trust     

Schwaller  Nora Louise  Campbell  Leah  Nguyen  Mai Thi  Smith  Gavin 《Natural Hazards》2022,111(3):2681-2702

Natural Hazards - Federally funded housing buyout programs are the dominant method of government-supported retreat in the USA. Done correctly, buyouts can reduce pre-disaster vulnerability and...  相似文献   

Climatically induced lake level changes during the last two millennia as reflected in sediments of Laguna Potrok Aike,southern Patagonia (Santa Cruz,Argentina)   总被引：1，自引：0，他引：1  

Torsten?HaberzettlEmail author  Michael?Fey  Andreas?Lücke  Nora?Maidana  Christoph?Mayr  Christian?Ohlendorf  Frank?Sch?bitz  Gerhard?H.?Schleser  Michael?Wille  Bernd?Zolitschka 《Journal of Paleolimnology》2005,33(3):283-302

The volcanogenic lake Laguna Potrok Aike, Santa Cruz, Argentina, reveals an unprecedented continuous high resolution climatic record for the steppe regions of southern Patagonia. With the applied multi-proxy approach rapid climatic changes before the turn of the first millennium were detected followed by medieval droughts which are intersected by moist and/or cold periods of varying durations and intensities. The total inorganic carbon content was identified as a sensitive lake level indicator. This proxy suggests that during the late Middle Ages (ca. AD 1230–1410) the lake level was rather low representing a signal of the Medieval Climate Anomaly in southeastern Patagonia. At the beginning of the Little Ice Age the lake level rose considerably staying on a high level during the whole period. Subsequently, the lake level lowered again in the course of the 20th century.  相似文献