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Lewis R. DARTNELL Manish R. PATEL Michael C. STORRIE‐LOMBARDI John M. WARD Jan‐Peter MULLER 《Meteoritics & planetary science》2012,47(5):806-819
Abstract– Even in the absence of any biosphere on Mars, organic molecules, including polycyclic aromatic hydrocarbons (PAHs), are expected on its surface due to delivery by comets and meteorites of extraterrestrial organics synthesized by astrochemistry, or perhaps in situ synthesis in ancient prebiotic chemistry. Any organic compounds exposed to the unfiltered solar ultraviolet spectrum or oxidizing surface conditions would have been readily destroyed, but discoverable caches of Martian organics may remain shielded in the subsurface or within surface rocks. We have studied the stability of three representative polycyclic aromatic hydrocarbons (PAHs) in a Mars chamber, emulating the ultraviolet spectrum of unfiltered sunlight under temperature and pressure conditions of the Martian surface. Fluorescence spectroscopy is used as a sensitive indicator of remaining PAH concentration for laboratory quantification of molecular degradation rates once exposed on the Martian surface. Fluorescence‐based instrumentation has also been proposed as an effective surveying method for prebiotic organics on the Martian surface. We find the representative PAHs, anthracene, pyrene, and perylene, to have persistence half‐lives once exposed on the Martian surface of between 25 and 60 h of noontime summer UV irradiation, as measured by fluorescence at their peak excitation wavelength. This equates to between 4 and 9.6 sols when the diurnal cycle of UV light intensity on the Martian surface is taken into account, giving a substantial window of opportunity for detection of organic fluorescence before photodegradation. This study thus supports the use of fluorescence‐based instrumentation for surveying recently exposed material (such as from cores or drill tailings) for native Martian organic molecules in rover missions. 相似文献
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The metastable, high-temperature portion of the microcline-lowalbite solvus has been experimentally determined at atmosphericpressure by the fused-salt alkali ion exchange technique (Bachinski),and by the homogenization—unmixing technique (Müller).Analytical smoothing of each set of pairs of coexisting compositionsyields critical temperatures and compositions of 885 °Cand 27 mol per cent KAISi3O8, and 887 °C and 24 mol percent KAISi3O8, respectively. The differences between the solviare real and the lack of coincidence of the two is attributable,to varying extents, to differences in the structural state,composition, twinning, and heat treatment of the starting materials.Previous workers' estimates of the position of the one-feldspar-two-feldsparfield boundary are in general accord with the experimental solvi. 相似文献
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A strong correlation in the geometry and mineralogy of two cement generations of a Quaternary with a Precambrian calcarenite enables us to reconstruct the diagenetic history of the Precambrian limestone. Both calcarenites contain two cement generations (A and B) of which A consists of dolomite, B of calcite. The following diagenetic stages can be recognized: after deposition of the allochems in a shallow marine environment, cementation in the intertidal zone with magnesian calcite (cement A) led to the formation of beachrock (Stage 1). By lowering of the sea level, the beach rock was shifted into the supratidal zone, but still remained under the predominant influence of the sea water (breakers, spray). During longer periods of aridity, the magnesian calcite of cement A and of the allochems was transformed into dolomite by brines derived from sea water with very high Mg/Ca ratio (> 15), whereas aragonite and calcite remained unaffected. After further lowering of the sea, an increasing influence of meteoric water caused the wet transformation of aragonitic allochems to sparry calcite and to the precipitation of sparry calcitic cement B. 相似文献
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SUMMARY
Along the eastern coast of the Gez Gölö, a salt lake formerly belonging to the larger "Paleo-Tuz Gölö" in central Anatolia, about 6.5 m of lake sediments of probably Pleistocene age were studied.
The sediment series consists of fine-grained unconsolidated dolomite muds representing the basin sedimentation of the old lake.
Nine lithified beds (oomicrites, intramicrites, intraoomicrites, intrabiomi-crites and dololutites with smaller amounts of allochems) are intercalated. These beds were deposited in very shallow water in the littoral zone of the paleo-lake. There is direct evidence that the beds were occasionally exposed to the air after deposition. This led to desiccation (with mud cracks, breaking up of intraclasts) and subaerial cementation due to the influx of fresh water (rain water, springs).
These now lithified carbonate sedimentary rocks were submerged and subsequently covered with mud. During this sub-aquatic phase the rock beds as well as the unconsolidated muds were dolomitized by an extremely high Mg/Caratio of the lake water which in the present Tuz Gölü amounts to about 150! It cannot be excluded, however, that dolomitization already took place or was initiated during the subaerial phase ("supratidal dolomite"). 相似文献
Along the eastern coast of the Gez Gölö, a salt lake formerly belonging to the larger "Paleo-Tuz Gölö" in central Anatolia, about 6.5 m of lake sediments of probably Pleistocene age were studied.
The sediment series consists of fine-grained unconsolidated dolomite muds representing the basin sedimentation of the old lake.
Nine lithified beds (oomicrites, intramicrites, intraoomicrites, intrabiomi-crites and dololutites with smaller amounts of allochems) are intercalated. These beds were deposited in very shallow water in the littoral zone of the paleo-lake. There is direct evidence that the beds were occasionally exposed to the air after deposition. This led to desiccation (with mud cracks, breaking up of intraclasts) and subaerial cementation due to the influx of fresh water (rain water, springs).
These now lithified carbonate sedimentary rocks were submerged and subsequently covered with mud. During this sub-aquatic phase the rock beds as well as the unconsolidated muds were dolomitized by an extremely high Mg/Caratio of the lake water which in the present Tuz Gölü amounts to about 150! It cannot be excluded, however, that dolomitization already took place or was initiated during the subaerial phase ("supratidal dolomite"). 相似文献
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Phacotus and Coccomonas, two carbonate-secreting, non-marine, planktonic chlorophyte genera, are important sediment contributors mainly in hard water lakes. The calcite loricae of these flagellate algae exhibit characteristic features easily recognizable under the microscope, making Phacotus and Coccomonas important facies fossils for the recognition of ancient non-marine environments. The fossil record of Phacotus can be traced back to the Miocene and it is probable that further research could extend this record into pre-Tertiary periods. 相似文献
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Kerguelen Hotspot Magma Output since 130 Ma 总被引：10，自引：8，他引：10
COFFIN MILLARD F.; PRINGLE M. S.; DUNCAN R. A.; GLADCZENKO T. P.; STOREY M.; MULLER R. D.; GAHAGAN L. A. 《Journal of Petrology》2002,43(7):1121-1137
The Kerguelen hotspot (Indian Ocean) has produced basalt for 相似文献
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Evidence from a Late Pleistocene eolianite in Fuerteventura, Canary Islands, demonstrates that red algal clasts replaced by low-magnesian calcite in the subaerial environment show a partial re-constitution of their original high-magnesian calcite mineralogy when they are exposed subsequently to sea water. This process only affects the cell walls of the red algae, which, owing to their specific microarchitecture (extremely small crystal size, very large specific surface area), offer the most favourable conditions for dissolution-reprecipitation or diffusion processes. High-magnesian caicite precipitated as a second generation cement on fresh water calcitic cement is an equivalent of the high-magnesian calcite cement which at many locations on the island leads to the formation of beachrock in Holocene intertidal sediments. 相似文献
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40Ar/39Ar Geochronology of the Rajmahal Basalts, India, and their Relationship to the Kerguelen Plateau 总被引：3，自引：0，他引：3
KENT RAY W.; PRINGLE MALCOLM S.; MULLER R. DIETMAR; SAUNDERS ANDREW D.; GHOSE NARESH C. 《Journal of Petrology》2002,43(7):1141-1153
During the mid-Cretaceous, extensive magmatism occurred in theIndian Ocean to form volcanic portions of the southern and centralKerguelen Plateau, Elan Bank and Broken Ridge. Basalt was eruptedalso along the rifted margin of eastern India (Rajmahal). Weinvestigated the ages of these Indian basalts using 40Ar/39Arincremental-heating experiments on whole rocks. Our resultsare consistent with the hypothesis that the lava pile of 相似文献