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31.
The terraces at the confluence of Kali Gandaki and Miristi Khola (West Nepal) consist of coarse-grained deposits which are considered to be Late Pleistocene to Holocene in age. The stacking pattern of lithofacies is characterised by an alternation of fluvial and debris flow deposits. These periodic changes in sedimentation processes are attributed to climatic variations.Deposits of extended, highly mobile, braided rivers most probably developed under glacial conditions and reflect high sediment supply and high water discharge rates. Deposits of small, only moderately braided river systems evolved during a warmer climate with comparatively low sediment supply and water discharge rates. The mobilisation and redeposition of morainic material by enormous debris flows predominately occurred at the beginning of a warm period and was triggered by earthquakes, glacier lake outburst floods or strong monsoonal rain. 相似文献
32.
Christian Brandes Carolin Schmidt David Colin Tanner Jutta Winsemann 《International Journal of Earth Sciences》2013,102(8):2239-2254
Analysing the paleostress field in sedimentary basins is important for understanding tectonic processes and the planning of drilling campaigns. The Subhercynian Basin of northern Germany is a perfect natural laboratory to study the paleostress field in a developing foreland basin. The simple layer-cake geometry of the basin-fill is dominated by several piercing and non-piercing salt structures. We derived the paleostress field from the orientation of fracture sets, faults, slickensides and stylolites. On a regional scale, the basin-fill is characterized by a horizontal compressional paleostress vector that is mainly NNE-SSW-oriented, which reflects the Late Cretaceous inversion phase in Central Europe. We show that the local paleostress field is distinctly perturbated due to the salt structures. Along the edge of the salt pillows, the maximum horizontal paleostress vector is deflected by up to 90° from the regional trend. In the case of the Elm salt pillow, it forms a radial pattern. Restoration of balanced cross-sections demonstrates at least 9 % of the shortening of the north-western part of the Subhercynian Basin was achieved by folding. The salt structures in the north-western Subhercynian Basin are the result of varying stress conditions. Initial extension in the Triassic caused first salt movements that prevailed during the Jurassic and Early Cretaceous. Most important is the Late Cretaceous contractional phase that shortened the diapirs and led to the formation of the salt pillows between diapirs due to detachment folding. We derive four main controlling factors for such salt-dominated contractional basins: (1) the wedge-shape basin-fill is the product of the dynamic load at the southern margin of the basin, (2) a basal salt layer fed the diapirs and acted as a detachment horizon during the later shortening, (3) detachment folding was the dominating deformation mechanism during contraction, and (4) the pre-existing diapirs controlled the position of the detachment folds. 相似文献
33.
Salt rim synclines contain important hydrocarbon and coal resources in central Europe. The Schöningen salt rim syncline is filled with >300 m of Early to Middle Eocene unconsolidated clastics with interbedded lignitic coal seams that are mined at the surface. In this study, 357 lithologic logs are integrated with measured outcrop sections and paleo‐botanical data to interpret the depositional environments and sequence stratigraphic framework of the rim syncline fill. As salt withdrew, it generated an elongate mini‐basin that mimicked an incised valley. The sustained accommodation and slow broadening of the syncline affected the stratigraphic architecture and contributed to the preservation of coal units. The clastic units in the syncline filled in seven depositional stages: (1) tidally influenced fluvial estuarine channels; (2) mixed tide‐ and wave‐ dominated estuaries; (3) prograding wave dominate deltas; (4) transgressive shoreline deposits; (5) braided fluvial channels; (6) estuaries; and (7) prograding tide‐dominated channels. The succession defines four 3rd order sequences and several higher order sequences that are possibly related to Milankovitch cycles. The higher order sequences are dominantly characterized by stacked transgressive cycles of thick, lowstand coals overlain by estuarine sands. The nearly continuous warm and wet Eocene climate was conducive to continuous peat production with a climatic overprint recorded in the mire type: ombrotrophic mires developed in wetter times and rheotrophic mires developed in relatively drier conditions pointing to the presence of orbitally controlled seasonality. Both mire types were impacted by the interplay of subsidence and base‐level. The continuous dropping of the mires below base‐level via subsidence protected the mires against erosion and may account for the absence of coals outside of the rim synclines in the region. 相似文献
34.
Anaerobic oxidation of methane and sulfate reduction along the Chilean continental margin 总被引：3，自引：0，他引：3
Tina Treude Jutta Niggemann Paul Wintersteller Antje Boetius Bo Barker Jørgensen 《Geochimica et cosmochimica acta》2005,69(11):2767-2779
Anaerobic oxidation of methane (AOM) and sulfate reduction (SR) were investigated in sediments of the Chilean upwelling region at three stations between 800 and 3000 m water depth. Major goals of this study were to quantify and evaluate rates of AOM and SR in a coastal marine upwelling system with high organic input, to analyze the impact of AOM on the methane budget, and to determine the contribution of AOM to SR within the sulfate-methane transition zone (SMT). Furthermore, we investigated the formation of authigenic carbonates correlated with AOM. We determined the vertical distribution of AOM and SR activity, methane, sulfate, sulfide, pH, total chlorins, and a variety of other geochemical parameters. Depth-integrated rates of AOM within the SMT were between 7 and 1124 mmol m−2 a−1, effectively removing methane below the sediment-water interface. Single measurements revealed AOM peaks of 2 to 51 nmol cm−3 d−1, with highest rates at the shallowest station (800 m). The methane turnover was higher than in other diffusive systems of similar ocean depth. This higher turnover was most likely due to elevated organic matter input in this upwelling region offering significant amounts of substrates for methanogenesis. SR within the SMT was mostly fuelled by methane. AOM led to the formation of isotopically light DIC (δ13C: −24.6‰ VPDB) and of distinct layers of authigenic carbonates (δ13C: −14.6‰ VPDB). 相似文献
35.
S. Grassmann B. Cramer G. Delisle J. Messner J. Winsemann 《International Journal of Earth Sciences》2005,94(5-6):979-989
The geological history of Germany’s largest and most productive petroleum accumulation, the Mittelplate oil field in Schleswig-Holstein
(Northern Germany), is reconstructed by simulating the structural and thermal evolution along a 2D cross-section. The Mittelplate
field is located at the western flank of the Büsum salt dome at the transition from the Schleswig-Holstein mainland to the
German North Sea Sector. Organic geochemical data confirm the Lower Jurassic Posidonia Shale to be the predominant oil source
rock in the Schleswig-Holstein area. The studied section is characterized by salt walls and salt domes built up by Permian
evaporites. Reconstruction of the structural and thermal evolution of the Mittelplate field by means of basin modelling reveals
the dominating influence of salt dynamics on the entire petroleum system: The development of secondary rim-synclines during
salt rise provided accommodation space for the deposition of the Posidonia Shale as well as the deltaic Middle Jurassic reservoir
sandstones. The rise of the nearby Oldenswort salt wall controlled the timing of maturation and petroleum generation during
Cenozoic times. Hydrocarbon migration from the Posidonia Shale into the reservoirs occurred up-dip from the deeper subsiding
rim-syncline into the structural trap with the Middle Jurassic reservoir sandstones pinching out at the flank of the Büsum
salt dome. Along the modelled 2D section the field’s recent temperature field and its complex reservoir architecture are reconstructed. 相似文献
36.
A stainless steel soil corer which was filled with homogenized soil was used to measure the flux (J) of NO between soil and atmosphere and the vertical profile of the NO mixing ratios (m) in the soil atmosphere, both as function of the NO mixing ratio (mm
a
) in the atmosphere of the headspace. The NO emission flux decreased linearly with increasing NO mixing ratio and turned into a deposition flux after passage of the compensation point (m
c) at about 400 ppbv NO. Almost the same compensation point was obtained when the turnover of NO was measured in flask-incubated soil samples as function of the NO mixing ratio. The flux (J) of NO at the soil-atmosphere interface was calculated from the production rate (P) of NO and the NO uptake rate constant (k) that were measured in these flask-incubated soil samples using the diffusion model of Galbally and Johansson (1989). The calculated fluxes agreed within <15% with those actually measured. The vertical profiles of NO were fitted to an exponential function and analyzed by Fick's first law of diffusion. The shape of the profiles indicated a net production of NO in the upper 10 cm soil layer when the atmospheric NO mixing ratio was below the compensation point and in a net consumption of NO when the atmospheric NO mixing ratio was above the compensation point. In soil layers below 10 cm depth, the turnover of NO resulted in compensation of production and consumption rates. Measurement of the actual diffusion coefficient using SF6 showed that gas transport in the soil core was not only due to molecular diffusion but in addition due to a bidirectional gas flow. The experimentally determined diffusion coefficient was smaller than that computed from soil porosities, but resulted together with the additional transport term in NO fluxes that were close (< ±15%) to those measured. This is the first comprehensive study of NO concentration profiles and turnover rates in soil providing a theoretical basis for modelling NO fluxes at the soil-atmosphere interface. 相似文献
37.
The sedimentary succession of a Late Jurassic (Oxfordian to basal Kimmeridgian) carbonate ramp is described and interpreted.
The study area is located in the central part of the Lower Saxony Basin in NW Germany, which forms part of the Central European
Basin. Eight well-exposed and undeformed sections of the study area (Süntel area, Wesergebirge and eastern part of the Wiehengebirge)
provide detailed information about lithofacies and lateral thickness variations. Biostratigraphically, the age of these sediments
is poorly constrained. Twenty microfacies types are recognized that can be grouped into seven facies associations: (a) strongly
bioturbated marlstones deposited near storm wave base (SWB), (b) foraminifera-rich wackestones, (c) wackestones and floatstones
with biostromes and (d) bioclastic limestones deposited between SWB and fair-weather wave base (FWWB), (e) oolitic and iron-oolitic
limestones and (f) siliciclastic sediments deposited above FWWB, and (g) lagoonal deposits. These facies associations characterize
a storm dominated shallow mixed carbonate-siliciclastic ramp. Based on facies changes, quartz content, and gamma ray logs,
the Korallenoolith Formation can be subdivided into a lower carbonate-dominated and an upper siliciclastic-dominated part,
build up by different scales of small- to large-scale deepening- and shallowing-upward cycles. A preliminary correlation of
measured outcrops of this formation is presented. 相似文献
38.
Ferric iron reduction was studied in a pilot-scale enclosure experiment for passive biological remediation of an acidic mine pit lake in Lusatia, Germany. The metabolic properties of prokaryotes involved in Fe(III) reduction may be important for the outcome of biological remediation, as chemolithotrophic Fe(III) reduction can counteract the desired pH increase, but heterotrophic Fe(III) reduction will provide the necessary Fe(II) for precipitation of sulfide minerals following sulfate reduction. Therefore, vertical profiles of sediment parameters related to iron and sulfur cycling were determined in conjunction with viable counts of different ferric iron-reducing micro-organisms using selective media. Findings were compared to an untreated reference site. The addition of organic matter stimulated ferric iron reduction and sulfate reduction in the enclosure and led to elevated pH and accumulations of ferrous iron and reduced sulfur compounds. Numbers of neutrophilic heterotrophic Fe(III) reducers increased during treatment, those of acidophilic heterotrophic Fe(III) reducers remained similar, and those of acidophilic chemolithotrophic Fe(III) reducers decreased. Zones of ferric iron-reducing activity corresponded well with microbial depth profiles; however, viable counts of neutrophilic or acid-tolerant Fe(III) reducers must have been underestimated based on the corresponding observed activity levels. Ferric iron reduction by chemolithotrophic acidophiles seemed to be of minor importance, so a lowering of pH values due to Fe(III) reducing activity is unlikely. 相似文献
39.
Kerstin Huber Kaarina Weckström Ruth Drescher-Schneider Johann Knoll Jutta Schmidt Roland Schmidt 《Journal of Paleolimnology》2010,43(1):131-147
A sediment core section from Längsee, a small meromictic lake in the southern Alpine lowland (Carinthia, Austria) close to the Würmian ice margin, was investigated by means of diatoms and pollen. The main aims of the study were to reconstruct water temperature as a signal of climate change during the last glacial termination, compare the aquatic and terrestrial response to the changing climate, and place our findings into a climatic frame on the northern hemispheric scale. A calibration data set (ALPS06) of 116 lakes was constructed using data from newly studied lakes and from two previously published data sets and we established a transfer function for predicting summer epilimnetic water temperatures (SEWT). A locally weighted weighted average regression and calibration model (R jack 2 = 0.89; RSMEP = 1.82°C) was applied to the fossil diatom assemblages in order to reconstruct SEWT. Three major sections were distinguished in the time window of approximately 19–13 cal ka BP, which fitted well with the oxygen isotope curve and the isotope-event stratigraphy from the Greenland ice-core GRIP. The first section was a warming period (SEWT range from 11.6 to 18.0°C; average 15.8°C = ca. 6°C below present) called the Längsee oscillation, which probably correlates with the warmer sub-section (GS-2b) of the Greenland Stadial 2. The subsequent section represents a climate cooling, called the Längsee cold period (SEWT range between 10.6 and 15.9°C; average 12.9°C), which probably corresponds with the sub-section GS-2a of the Greenland Stadial 2, the Heinrich 1 cold event of the North Atlantic, and partially the Gschnitz Stadial in the Alps. The Längsee cold period shows a tri-partition: Two colder phases are separated by a warmer inter-phase. The passive ordination of the core sample scores along maximum water depth indicated that the Längsee cold period was drier than the Längsee oscillation. Strong short-term fluctuations during the Längsee oscillation and the Längsee cold period indicate climate instability. The third section represented climate warming during the Längsee late glacial interstadial (=Greenland Interstadial 1, GI-1) with an average SEWT of 17.5°C. From the minor climatic fluctuations during this interstadial, mainly indicated by pollen, the fluctuation most likely related to the Gerzensee oscillation showed a SEWT decline. During the early immigration and expansion period of shrubs and trees, aquatic and terrestrial records showed distinct discrepancies that might have arose because of time lags in response and differences in sensitivity. 相似文献
40.
Alexander N. Krot Tasha L. Dunn Michail I. Petaev Chi Ma Kazuhide Nagashima Jutta Zipfel 《Meteoritics & planetary science》2024,59(4):809-835
We report on the primary and secondary mineralogies of three coarse-grained igneous calcium-aluminum-rich inclusions (CAIs) (Compact Type A [CTA], Type B [B], and forsterite-bearing type B [FoB]) from the Northwest Africa (NWA) 5343 (CK3.7) and NWA 4964 (CK3.8) carbonaceous chondrites, compare them with the mineralogy of igneous CAIs from the Allende (CV3.6) chondrite, and discuss the nature of the alteration processes that affected the CK and CV CAIs. The primary mineralogy and mineral chemistry of the CK3 CAIs studied are similar to those from Allende; however, primary melilite and anorthite are nearly completely absent. Although the secondary minerals identified in CK CAIs (Al-diopside, andradite, Cl-apatite, clintonite, forsterite, ferroan olivine, Fe,Ni-sulfides, grossular, ilmenite, magnetite, plagioclase, spinel, titanite, and wadalite) occur also in the Allende CAIs, there are several important differences: (i) In addition to melilite and anorthite, which are nearly completely replaced by secondary minerals, the alteration of CK CAIs also affected high-Ti pyroxenes (fassaite and grossmanite) characterized by high Ti3+/Ti4+ ratio and spinel. These pyroxenes are corroded and crosscut by veins of Fe- and Ti-bearing grossular, Fe-bearing Al,Ti-diopside, titanite, and ilmenite. Spinel is corroded by Fe-bearing Al-diopside and grossular. (ii) The secondary mineral assemblages of grossular + monticellite and grossular + wollastonite, commonly observed in the Allende CAIs, are absent; the Fe-bearing grossular + Fe-bearing Al-diopside ± Fe,Mg-spinel, Fe-bearing grossular + Fe,Mg-olivine ± Fe,Mg-spinel, and Ca,Na-plagioclase + Fe-bearing Al-diopside + Fe-bearing grossular assemblages are present instead. These mineral assemblages are often crosscut by veins of Fe-bearing Al-diopside, Fe,Mg-olivine, Fe,Mg-spinel, and Ca,Na-plagioclase. The coarse-grained secondary grossular and Al-diopside often show multilayered chemical zoning with distinct compositional boundaries between the layers; the abundances of Fe and Ti typically increase toward the grain edges. (iv) Sodium-rich secondary minerals, nepheline and sodalite, commonly observed in the peripheral portions of the Allende CAIs, are absent; Ca,Na-plagioclase is present instead. We conclude that coarse-grained igneous CAIs from CK3.7–3.8 s and Allende experienced an open-system multistage metasomatic alteration in the presence of an aqueous solution–infiltration metasomatism. This process resulted in localized mobilization of all major rock-forming elements: Si, Ca, Al, Ti, Mg, Fe, Mn, Na, K, and Cl. The metasomatic alteration of CK CAIs is more advanced and occurred under higher temperature and higher oxygen fugacity than that of the Allende CAIs. 相似文献