Springs in karstic carbonate rocks frequently carry a sediment load as well as a dissolved load. Analysis of morphology and
mineralogy of suspended sediment from three contrasting karst springs reveals a suite of clastic particles that reflect both
source areas and processes that take place within the aquifer. Nolte Spring in Lancaster County, Pennsylvania, USA, discharges
sediment of apparently precipitated calcite, indicating that at some point in the aquifer or vadose zone, water exceeds saturation
with respect to calcite. Sediment morphologies and chemical conditions in the aquifer point to two different scenarios for
this precipitation. The other two springs, Arch Spring in Blair County, Pennsylvania and Bushkill Spring in Northampton County,
Pennsylvania, show no evidence of calcite precipitation. Arch Spring discharges mainly layer silicates, while Bushkill Spring
discharges mainly silica.
Resumen Los manantiales en rocas carbonatadas karstficadas tienen frecuentemente una carga de sedimentos y de sólidos disueltos. Los
análisis de la morfología y mineralogía de los sedimentos suspendidos de tres manantiales kársticos contrastados revela un
conjunto de partículas clásticas que reflejan ambas áreas fuente y los procesos que tienen lugar dentro del acuífero. Nolte
Spring en el Condado de Lancaster, Pennsylvania, USA, descarga sedimento de calcita aparentemente precipitada indicando que
en cierto punto del acuífero o en la zona vadosa, el agua supera la saturación con respecto a la calcita. La morfología de
los sedimentos y las condiciones químicas en el acuífero apuntan a dos escenarios diferentes para esta precipitación. Los
otras dos manantiales, Arch Spring en el Condado de Blair, Pennsylvania y Bushkill Spring en el Condado de Norhtampton, Pennsylvania,
no muestran evidencia de precitación de calcita. Arch Spring descarga principalmente filosilicatos mientras que Bushkill Spring
descarga fundamentalmente Sílice.
Résumé Les sources situées en contexte carbonaté karstique charrient fréquemment, outre les matières dissoutes, une charge solide.
La morphologie et la minéralogie des sédiments en suspension issus de trois sources karstiques de caractéristiques distinctes
ont été analysées : une série de particules clastiques, reflétant à la fois les secteurs des sources et les processus internes
de l’aquifère, en ressort. Les sédiments issus de Nolte Spring (Comté de Lancaster, Pennsylvanie, Etats-Unis) sont constitués
de calcite apparemment précipitée: ceci indique que l’eau atteint la sursaturation vis-à-vis de la calcite à un certain point
de l’aquifère ou de la zone non-saturée. La morphologie des sédiments et les conditions chimiques au sein de l’aquifère mènent
à deux scénarii différents pour expliquer cette précipitation. Les deux autres sources, Arch Spring (Comté de Blair, Pennsylvanie)
et Bushkill Spring (Comté de Northampton, Pennsylvanie), ne présentent aucun indice de précipitation de calcite. Arch Spring
exporte essentiellement des phyllosilicates, alors que la silice est majoritaire à Bushkill Spring.
The behavior of sulfide minerals during the physical and chemical changes accompanying seafloor alteration was studied in three basalt flows from the bottom of D.S.D.P. Hole 418A, Leg 53. The rocks are mildly altered, and contain primary, authigenic, and vein sulfide minerals. Sulfide habit, mineralogy, and trace element content are inter-related and are correlated with the extent and type of silicate and oxide alteration. Incipient alteration at > 90°–100°C was accompanied by low temperature reequilibration of pyrrhotite, and locally, by the oxidation of pyrrhotite to pyrite plus magnetite. The dominant stage of alteration, at ≤90°C, is characterized by dissolution and local redistribution of pyrite and chalcopyrite, whose precipitation appears to be controlled by the water/rock ratio and the extent to which the water has been modified by reaction with the basalt. Chalcopyrite was concentrated relative to pyrite by slight changes in fluid composition caused by reaction with other minerals. Concurrent precipitation of smectite causes a net increase in rock volume, tending to restrict seawater access. Calculations of rock cooling rate through time suggest that the most prolonged hydrothermal circulation occurs at low temperatures, giving rise to pervasive low temperature alteration assemblages. 相似文献
Sugarloaf Mountain is a 200-m high volcanic landform in central Arizona, USA, within the transition from the southern Basin and Range to the Colorado Plateau. It is composed of Miocene alkalic basalt (47.2–49.1?wt.% SiO2; 6.7–7.7?wt.% MgO) and overlying andesite and dacite lavas (61.4–63.9?wt.% SiO2; 3.5–4.7?wt.% MgO). Sugarloaf Mountain therefore offers an opportunity to evaluate the origin of andesite magmas with respect to coexisting basalt. Important for evaluating Sugarloaf basalt and andesite (plus dacite) is that the andesites contain basaltic minerals olivine (cores Fo76-86) and clinopyroxene (~Fs9-18Wo35-44) coexisting with Na-plagioclase (An48-28Or1.4–7), quartz, amphibole, and minor orthopyroxene, biotite, and sanidine. Noteworthy is that andesite mineral textures include reaction and spongy zones and embayments in and on Na-plagioclase and quartz phenocrysts, where some reacted Na-plagioclases have higher-An mantles, plus some similarly reacted and embayed olivine, clinopyroxene, and amphibole phenocrysts.Fractional crystallization of Sugarloaf basaltic magmas cannot alone yield the andesites because their ~61 to 64?wt.% SiO2 is attended by incompatible REE and HFSE abundances lower than in the basalts (e.g., Ce 77–105 in andesites vs 114–166?ppm in basalts; Zr 149–173 vs 183–237; Nb 21–25 vs 34–42). On the other hand, andesite mineral assemblages, textures, and compositions are consistent with basaltic magmas having mixed with rhyolitic magmas, provided the rhyolite(s) had relatively low REE and HFSE abundances. Linear binary mixing calculations yield good first approximation results for producing andesitic compositions from Sugarloaf basalt compositions and a central Arizona low-REE, low-HFSE rhyolite. For example, mixing proportions 52:48 of Sugarloaf basalt and low incompatible-element rhyolite yields a hybrid composition that matches Sugarloaf andesite well ? although we do not claim to have exact endmembers, but rather, viable proxies. Additionally, the observed mineral textures are all consistent with hot basalt magma mixing into rhyolite magma. Compositional differences among the phenocrysts of Na-plagioclase, clinopyroxene, and amphibole in the andesites suggest several mixing events, and amphibole thermobarometry calculates depths corresponding to 8–16?km and 850° to 980?°C. The amphibole P-T observed for a rather tight compositional range of andesite compositions is consistent with the gathering of several different basalt-rhyolite hybrids into a homogenizing ‘collection' zone prior to eruptions. We interpret Sugarloaf Mountain to represent basalt-rhyolite mixings on a relatively small scale as part of the large scale Miocene (~20 to 15 Ma) magmatism of central Arizona. A particular qualification for this example of hybridization, however, is that the rhyolite endmember have relatively low REE and HFSE abundances. 相似文献
Branched glycerol dialkyl glycerol tetraether lipids (GDGTs) are membrane lipids of soil bacteria that occur ubiquitously in soil, but their occurrence as intact polar lipids (IPLs) has not been well studied. Here, we report the identification and distribution of IPL-branched GDGTs throughout a depth profile of a Swedish peat bog. In addition to two reported glycosidic IPL branched GDGTs, we identified IPL branched GDGTs with a hexose-glycuronic acid, phospho-hexose, or hexose-phosphoglycerol head group, based on mass spectrometry. A selected reaction monitoring (SRM) assay was developed to monitor changes in head group distribution with depth. The abundance of the IPL branched GDGTs increased below the water table, suggesting that they were primarily produced in this part of the peat. This was supported by the concentrations of core lipid and IPL-derived branched GDGTs, which also substantially increased below the water table. However, individual IPL trends differed, which may be due to changes in the microbial community composition with depth or to different degradation rates for the different IPL branched GDGTs. The SRM method was also applied to two different soil types, which showed that similar IPL branched GDGTs as those in peat were present, albeit with different distributions. 相似文献
The severe rainstorm of January 3, 4 and 5, 1982, in the San Francisco Bay area, California, produced numerous landslides, many of which transformed into damaging debris flows. The process of transformation was studied in detail at one site where only part of a landslide mobilized into several episodes of debris flow. The focus of our investigation was to learn whether the landslide debris dilated or contracted during the transformation from slide to flow.
The landslide debris consisted of sandy colluvium that was separable into three soil horizons that occupied the axis of a small topographic swale. Failure involved the entire thickness of colluvium; however, over parts of the landslide, the soil A-horizon failed separately from the remainder of the colluvium.
Undisturbed samples were taken for density measurements from outside the landslide, from the failure zone and overlying material from the part of the landslide that did not mobilize into debris flows, and from the debris-flow deposits. The soil A-horizon was contractive and mobilized to flows in a process analogous to liquefaction of loose, granular soils during earthquakes. The soil B- and C-horizons were dilative and underwent 2 to 5% volumetric expansion during landslide movement that permitted mobilization of debris-flow episodes.
Several criteria can be used in the field to differentiate between contractive and dilative behavior including lag time between landsliding and mobilization of flow, episodic mobilization of flows, and partial or complete transformation of the landslide. 相似文献
Anaerobic ammonium oxidation (anammox) has been recognized as a major process resulting in loss of fixed inorganic nitrogen in the marine environment. Ladderane lipids, membrane lipids unique to anammox bacteria, have been used as markers for the detection of anammox in marine settings. However, the fate of ladderane lipids after sediment burial and maturation is unknown. In this study, anammox bacterial cell material was artificially matured by hydrous pyrolysis at constant temperatures ranging from 120 to 365 °C for 72 h to study the stability of ladderane lipids during progressive dia- and catagenesis. HPLC-MS/MS analysis revealed that structural alterations of ladderane lipids already occurred at 120 °C. At temperatures >140 °C, ladderane lipids were absent and only more thermally stable products could be detected, i.e., ladderane derivatives in which some of the cyclobutane rings were opened. These diagenetic products of ladderane lipids were still detectable up to temperatures of 260 °C using GC-MS. Thus, ladderane lipids are unlikely to occur in ancient sediments and sedimentary rocks, but specific diagenetic products of ladderane lipids will likely be present in sediments and sedimentary rocks of relatively low maturity (i.e., C31 hopane 22S/(22S + 22R) ratio <0.2 or ββ/(αβ + βα + ββ) ratio of >0.5). 相似文献