Experimental insights into laser diffraction particle sizing of fine‐grained sediments for use in palaeoceanography     

LUKAS JONKERS  MAARTEN A. PRINS  GEERT‐JAN A. BRUMMER  MARTIN KONERT  BRYAN C. LOUGHEED 《Sedimentology》2009,56(7):2192-2206

Grain‐size measurements of fine‐grained sediments based on laser diffraction may contain spurious information due to the over‐estimation of the size and proportion of platy particles. Consequently, some regard the use of laser diffraction particle sizing in palaeoceanography inappropriate. Here, it is shown experimentally that such concerns are not warranted. Laser diffraction particle sizing is known to be fast, precise and allows for detailed particle sizing over a broad size range; it is therefore potentially a very powerful technique if the complications associated with it can be overcome. As most sediments are mixtures of different components transported by different mechanisms, inferences of past environmental parameters require decomposition of the grain‐size record in question. Useful decomposition can only be performed if changes in the contribution of the components are registered predictably by the measuring device. This study reports on mixing experiments which show that the Fritsch A22 laser diffraction particle sizer does indeed register small changes in the contribution of the mixing components in a predictable way. Mixing proportions estimated from the measurements do, however, differ from the initial mixing proportions, but these can be converted with only small errors. Application of the conversion equations to a North Atlantic grain‐size record that showed consistent slowdown of deep‐ocean circulation in response to millennial scale ice‐rafting events during the last glacial does not quantitatively affect the original inferences. Laser diffraction particle sizing of fine‐grained sediments therefore yields reproducible and useful data for palaeoceanographic reconstructions.  相似文献   

The Palaeozoic history of the Western Desert of Egypt   总被引：1，自引：0，他引：1  

MARTIN L. Keeley 《Basin Research》1989,2(1):35-48

Abstract A formal stratigraphical scheme is proposed for the Palaeozoic succession encountered in the subsurface of the Western Desert of Egypt, and is compared to other published schemes in North Africa. Two groups and seven formations span the interval from the Mid Cambrian to the Early Permian. The resolution between these superficially similar clastic-dominated units is enhanced by the use of the palyno-stratigraphical zonation devised by Gueinn & Rasul. It is apparent from an analysis of this rock sequence that two depositional regimes can be recognized. In the first of these, the Ghazalat Basin lay over the central Western Desert, and was bounded by high axes to the west and south-east. An inversion event of Early Tournaisian age preceded a new depositional regime, centred along the Libyan border: the Tehenu Basin. A poorly understood sequence of strike-slip movements on the Trans-African Lineament is shown to be the most likely cause of this complex basin history. One consequence of this hypothesis is, however, to throw into question the validity of correlations made with the Gulf of Suez Palaeozoic succession, across the Trans-African Lineament.  相似文献   

Isotopic composition and origin of polar precipitation in present and glacial climate simulations   总被引：1，自引：0，他引：1  

MARTIN WERNER  MARTIN HEIMANN  GEORG HOFFMANN 《Tellus. Series B, Chemical and physical meteorology》2001,53(1):53-71

The Hamburg atmospheric general circulation model (AGCM) ECHAM‐4 is used to identify the main source regions of precipitation falling on Greenland and Antarctica. Both water isotopes H₂¹⁸O and HDO are explicitly built into the water cycle of the AGCM, and in addition the capability to trace water from different source regions was added to the model. Present and LGM climate simulations show that water from the most important source regions has an isotopic signature similar to the mean isotope values of the total precipitation amount. But water from other source regions (with very different isotopic signatures) contributes an additional, non‐negligible part of the total precipitation amount on both Greenland and Antarctica. Analyses of the temperature‐isotope‐relations for both polar regions reveal a solely bias of the glacial isotope signal on Greenland, which is caused by a strong change in the seasonal deposition of precipitation originating from nearby polar seas and the northern Atlantic. Although the performed simulations under LGM boundary conditions show a decrease of the δ ¹⁸O values in precipitation in agreement with ice core measurements, the AGCM fails to reproduce the observed simultaneous decrease of the deuterium excess signal.  相似文献   

GENTILE IMPRESSIONS OF SALT LAKE CITY,UTAH, 1849–1870*     

MARTIN MITCHELL 《Geographical review》1997,87(3):334-352

ABSTRACT. The landscape of Salt Lake City, Utah, drew considerable comment between 1849 and 1870 from non-Mormon travelers. These experiences, chiefly of overland emigrants, foreign travelers, and military personnel, include first impressions, feelings on entry, and later reactions. The setting, material landscape, Mormon citizenry, and travelers' attitudes toward early Salt Lake City Mormon customs and institutions are discussed.  相似文献   

TWO METHODS FOR CONTINUOUS MONITORING OF HARMONIC DISTORTION IN VIBROSEIS SIGNALS1     

J. E. MARTIN  R. E. WHITE 《Geophysical Prospecting》1989,37(7):851-872

The quality of Vibroseis survey data can be improved by continuously monitoring the vibrator's baseplate and reaction mass accelerations. Equipment failures can be detected as they occur, rather than relying on similarity trials at the beginning and end of the day's production. Equipment faults can then be corrected as they happen and thus would not have a detrimental effect on the quality of the survey data. Source efficiency can be optimized by monitoring the amount of harmonic distortion generated by the vibrator at different drive levels on the different surfaces which may be encountered during a survey. Phase problems introduced by poor coupling of the baseplate to the ground can also be identified and addressed in the field. Rapid analysis of vibrator signals is required if continuous monitoring is to be useful. Frequency-time (f-t) analyses of vibrator signals are often used in processing centres, but are slow and require a large storage capacity which makes the technique unsuitable for a field analysis system. The two methods proposed to analyse vibrator signals entail the use of hodograms and time-varying notch filters. Hodograms provide a qualitative analysis of harmonic distortion and vibrator performance. A fast, time-varying notch filter gives quantitative and qualitative information about the harmonic distortion present in the signal and can be used to identify problems with vibrator behaviour. Both the hodogram and fast, time-varying notch filter methods can analyse the vibrator's reaction mass and baseplate accelerations as it progresses through its sweep and can present automatically interpreted results to the operator before moving to the next vibrator point.  相似文献   

Travertines in the northern Hula Valley, Israel   总被引：1，自引：0，他引：1  

ARIEL HEIMANN  EYTAN SASS 《Sedimentology》1989,36(1):95-108

This study describes the field and petrographic relationships of a widespread deposit of Pleistocene travertines in the northern Hula Valley, northern Israel. The travertines interfinger with conglomerate deposits and basaltic lava flows. Field relationships and radiometric dating indicate that the travertines accumulated intermittently over the past million years, and their formation virtually stopped 25 000 years ago. The travertines are characteristically highly porous. Some of the pores, as well as some spar-filled voids, preserve the shapes of stalks and leaves. The abundance of plant material suggests that photosynthesis, rather than bacterial or abiogenic processes, was the main mechanism which induced carbonate precipitation. The reasons for travertine accumulation in the past and for the cessation of its formation today are ascribed to differences in the palaeogeographic setting. In the past, water flow is viewed as having been mostly sluggish, and a widespread and shallow sheet of water was formed. The lush vegetation, combined with the relatively long residence time of the water in the area, led to increased efficiency of the calcium carbonate precipitation. Today, by contrast, water flows rapidly in gorges, precipitating only a small fraction of its load of dissolved calcium carbonate. The conjectured change in hydrological conditions is ascribed to rejuvenation of faulting activity in the Late Quaternary.  相似文献   

Palaeovalleys and protozoan assemblages in a Late Carboniferous cyclothem, Sydney Basin, Nova Scotia     

MARTIN R. GIBLING  WINTON G. WIGHTMAN 《Sedimentology》1994,41(4):699-719

The early Stephanian Bonar Cyclothem of the Sydney Basin, Nova Scotia, contains an erosional surface cut through coastal plain strata with economic coals and distributary channel bodies. The erosion surface is interpreted as a palaeovalley 20 m deep and at least 7 km wide that marks a sequence boundary formed during relative fall in sea level. The palaeovalley is filled with stacked alluvial channel bodies which become more isolated as the valley fill passes upward into red, alluvial plain deposits, probably laid down in an anastomosed river system. In an adjacent, interfluve area, calcretes and red, vertic palaeosols cap coastal strata. Assemblage analysis of agglutinated foraminifera and thecamoebians indicates that the palaeovalley was filled with freshwater sediments before an initial marine transgression flooded the alluvial surface and adjacent interfluve. Valley incision probably reflects glacioeustatic sea level fall. However, the alluvial nature of the valley deposits suggests that valley filling reflects an abundant sediment supply during lowstand and/or transgressive stages and was not a direct consequence of sea level rise. During the subsequent transgression phase, aggradation was rapid as sediment supply apparently kept pace with rising sea level. Features of both channel and extra-channel facies suggest that seasonality intensified during the transition from coastal plain to palaeovalley and alluvial plain deposition.  相似文献   

Mineralogy and petrology of a piemontite-bearing schist, western Otago, New Zealand   总被引：1，自引：0，他引：1  

YOSUKE KAWACHI  RODNEY H. GRAPES  DOUGLAS S. COOMBS  MARTIN DOWSE 《Journal of Metamorphic Geology》1983,1(4):353-372

Abstract. Pink piemontite-spessartine-bearing and grey-green spessartine-bearing manganiferous quartzose schists derived from siliceous pelagites, and green quartzofeldspathic schists, are described from the greenschist facies of the Haast Schist terrane, near Arrow Junction, western Otago. Electron microprobe data are reported for sphene, spessartine-rich garnet, manganoan epidote, piemontite, tourmaline, phengitic muscovite, chlorite, albite, haematite, rutile, manganoan calcite and chalcopyrite. Metamorphism occurred at about 6.4kbar, 400°C. X_co2 was above the quartz-rutile-calcite-sphene buffer (X_co2± 0.02) throughout the recorded metamorphic history of the piemontite schists. It dropped from above to below this critical buffering value in a spessartine-rich schist and it was close to or below the buffering value in the quartzofeldspathic schists. Production of piemontite required high f_O2, believed to be inherited from MnO_x in the parent pelagite. Substantial loss of O₂ (e.g. minimum of 0.19% by weight in one rock) during diagenesis and/or metamorphism is inferred. In the grey-green schists this inhibited piemontite formation. Slight loss of O₂ and Ca²⁺ accompanied minor late-stage replacement of piemontite by second generation spessartine. Observed zoning and mineral replacements indicate rise of temperature, drop in pressure, or invasion by solutions of lower f_O2 and X_CO2 equilibrated with surrounding schists. The detailed chemistry of the minerals studied correlates with available Mn and with bulk-rock (Fe³⁺ x 100)/(Fe²⁺+ Fe³⁺). The oxidation ratio ranges from 24 in average green quartzofeldspathic schist, through 78 in average grey-green manganiferous quartzose schist, to almost 100 in some piemontite-bearing schists. As Fe²⁺ gives way to Fe³⁺, Mg/Fe ratios tend to rise in chlorite, phengite, tourmaline, spessartine, and calcite, Mn increases and Ti decreases in haematite, Mn increases in spessartine and calcite, and Fe increases in rutile. Available divalent cations are depleted relative to Al; chlorite is more aluminous, and phengite more paragonitic than in typical Haast schists.  相似文献   

Dolomite formation in the dynamic deep biosphere: results from the Peru Margin   总被引：1，自引：0，他引：1  

PATRICK MEISTER†  JUDITH A. MCKENZIE†  CRISOGONO VASCONCELOS†  STEFANO BERNASCONI†  MARTIN FRANK‡  MARCUS GUTJAHR§  DANIEL P. SCHRAG¶ 《Sedimentology》2007,54(5):1007-1032

Early diagenetic dolomite beds were sampled during the Ocean Drilling Programme (ODP) Leg 201 at four reoccupied ODP Leg 112 sites on the Peru continental margin (Sites 1227/684, 1228/680, 1229/681 and 1230/685) and analysed for petrography, mineralogy, δ¹³C, δ¹⁸O and ⁸⁷Sr/⁸⁶Sr values. The results are compared with the chemistry, and δ¹³C and ⁸⁷Sr/⁸⁶Sr values of the associated porewater. Petrographic relationships indicate that dolomite forms as a primary precipitate in porous diatom ooze and siliciclastic sediment and is not replacing the small amounts of precursor carbonate. Dolomite precipitation often pre‐dates the formation of framboidal pyrite. Most dolomite layers show ⁸⁷Sr/⁸⁶Sr‐ratios similar to the composition of Quaternary seawater and do not indicate a contribution from the hypersaline brine, which is present at a greater burial depth. Also, the δ¹³C values of the dolomite are not in equilibrium with the δ¹³C values of the dissolved inorganic carbon in the associated modern porewater. Both petrography and ⁸⁷Sr/⁸⁶Sr ratios suggest a shallow depth of dolomite formation in the uppermost sediment (<30 m below the seafloor). A significant depletion in the dissolved Mg and Ca in the porewater constrains the present site of dolomite precipitation, which co‐occurs with a sharp increase in alkalinity and microbial cell concentration at the sulphate–methane interface. It has been hypothesized that microbial ‘hot‐spots’, such as the sulphate–methane interface, may act as focused sites of dolomite precipitation. Varying δ¹³C values from −15‰ to +15‰ for the dolomite are consistent with precipitation at a dynamic sulphate–methane interface, where δ¹³C of the dissolved inorganic carbon would likewise be variable. A dynamic deep biosphere with upward and downward migration of the sulphate–methane interface can be simulated using a simple numerical diffusion model for sulphate concentration in a sedimentary sequence with variable input of organic matter. Thus, the study of dolomite layers in ancient organic carbon‐rich sedimentary sequences can provide a useful window into the palaeo‐dynamics of the deep biosphere.  相似文献   

On the influence of the Alps on a cold front   总被引：1，自引：0，他引：1  

KLAUS P. HOINKA  MARTIN HAGEN  HANS VOLKERT  DIETRICH HEIMANN 《地球，A辑:动力气象学与海洋学》1990,42(1):140-164

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