Typological analysis of demographic changes in the Tuscan communes     

Bottai M  Costa M  Formentini U 《Rivista geografica italiana》1978,85(4):321-347

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Lithologic transition and bed thickness periodicities in turbidite successions of the Antola Formation, Northern Apennines, Italy     

I. PETER MARTINI  MARIO SAGRI  JOHN H. DOVETON 《Sedimentology》1978,25(5):605-623

The Antola Formation of Upper Cretaceous age crops out extensively in the Northern Apennines and consists of graded units of calcareous sandstones, sandstones, marlstones, and shales. It can be subdivided into the Cerreto, Antola Marlstone, Bruggi, and S. Donato Members on the basis of bed thicknesses and percentage of shales. Although the whole formation is interpreted as a deep-sea basin plain deposit, the members constitute lateral facies subdivisions which range from proximal, thick-bedded turbidities that show a prevalence of thinning upward cycles in bed thicknesses to distal turbidites that show predominantly thickening upward cycles and have a high percentage of shale. Repetitive patterns in the lithological sequence of the turbidite association are generally distinctive and are satisfactorily described as first order Markov chains. Only the Antola Marlstone Member has an additional second order Markov property. Imaginary eigenvalues of the transition probability matrices of all but the Bruggi Member demonstrate a strong cyclic character in the lithologic ordering within the formation. The behaviour of the Antola Marlstone and of the Bruggi may reflect the influence of a secondary ophiolitic intra-basinal source of clastics that contributed sandy turbidites and olistostromes. Systematic long-term variations in the sequence of bed thickness development in some sections of the Antola Formation are often subtle and equivocal, and pose special problems in interpretation. Fourier analysis was applied to the task of partitioning fundamental wavelengths from “background noise” introduced by essentially random depositional processes. In all members there is (1) strong short-term wavelength of two to three beds indicative of alternating thin and thick beds and judged to be typical of turbidite sequences; (2) an intermediate wavelength ranging from about five beds (proximal facies), eight beds (distal) to nine beds (very distal), which have both thinning and thickening upward trends, interpreted respectively as valley fill due to shifting talwegs of low density turbidity currents, and to progradational, flat turbidite lobes; (3) a poorly defined long-term wave-length of from thirty to greater than sixty beds that may be related to an unspecified trend in the evolution of the sedimentary basin. Phase angles associated with the coniputed power spectra give indications as to the asymmetry (thickening or thinning upward) or symmetry of the representative units.  相似文献   

Bedforms produced by fine, cohesionless, granular and flakey sediments under subcritical water flows     

PETER A. MANTZ 《Sedimentology》1978,25(1):83-103

Experiments have been conducted in a 10 m long laboratory flume to investigate the bedforms which develop from fine, cohesionless sediment beds. Two grades of near uniformly sized silica grains (of median nominal diameters 15 and 66 μm) and six grades of micaceous flakes (ranging in median nominal diameter from 15.5 to 76 μm) were used. A steady subcritical water discharge, which was increased in steps after several hours, was applied to a flat bed of each grade. The developing bedform sequence for fine granular beds was identified as many small-sized primary ripples, isolated primary, transverse primary, secondary ripples and then possibly dunes; this development was almost the same as that observed for coarser grains. The sequence for fine flake beds differed from grains. Only the single bedform type of parting lineations was observed; with increased discharge, the lineations began to oscillate and eventually enter into fluid suspension. The low discharge parallel lineations were thought to be generated by ‘streaks’ or lanes of transversely alternate high and low velocity fluid which have been reported to exist in the viscous sub-layer of a turbulent-smooth boundary, whilst the higher discharge wandering lineations were attributed to low velocity streak ‘bursts’.  相似文献   

A cine-camera technique for process measurement on a ridge and runnel beach     

PETER WRIGHT 《Sedimentology》1976,23(5):705-712

Previous attempts to quantify beach processes with techniques involving direct measurement have met with varying degrees of success. Problems encountered can be attributed to three main areas of difficulty: (1) the rapidity of change in both process operation and the subsequent production and development of bed forms; (2) the inclement nature of the weather conditions during which the most rapid beach changes take place; (3) interference with the flows being measured, by the equipment. A photographic method is described here, which to a great extent overcomes these problems, and can be operated cheaply by a solitary field investigator.  相似文献   

Recent sand volcanoes in the sand of a dike under construction     

PETER NEUMANN-MAHLKAU 《Sedimentology》1976,23(3):421-425

Sand volcanoes are small volcano-like features. They range in diameter from a few centimetres to several metres. Five volcanoes with a maximum diameter of 2 m were observed during the construction of a dike on the coast of Northwestern Germany. The cones reached heights of about 15 cm with craters in the middle. The rise of the volcanoes is explained by de-watering of sediment.  相似文献   

Miscibility of Tremolite and Hornblende in Progressive Skagit Metamorphic Suite, North Cascades, Washington     

MISCH  PETER; RICE  JACK M. 《Journal of Petrology》1975,16(1):1-21

Tremolite-hornblende relationships are reported for high gradeand relatively low grade zones within the Barrovian type SkagitSuite, using rocks that range widely enough in composition toqualify as potential hosts of any calcic amphibole from practicallyA1-free to A1-rich types. Out of over 100 samples analysed bymicroprobe, 22 representative analyses are listed, with end-membercalculations. In the sillimanite grade core of the Skagit Suite, calcic amphibolesfrom various, commonly metasomatized metamorphic ultramaficsand genetically related hornblendites, from amphibolites, schistsand gneisses, and from some metamorphosed impure dolomites showcontinuous solid solution between tremolite and highly aluminoushornblendes ranging from almost Fe-free to moderately Fe-richtypes. A1_total/A1^IV is nearly constant and approximates 1?44.The second group of calcic amphiboles studied is from the lower-mediumrange of the epidote amphibolite facies (comprehensively defined),that is, from near and above the oligoclase isograd. Host rocksare variously metasomatized meta-peridotites, and amphibolitesand schists. There is a large compositional gap between analysesof tremolites and of moderately to highly aluminous hornblendes.A1_total/A1^IV approximates 1?73 both in the tremolite and hornblendefields, as against 1?44 at high grade. Fe-poor hornblendes,such as are stable at high grade, were not found at the lowergrade. At both grades, Al shows good overall correlation withNa+K, with A occupancy, and with Ti (with more Ti at high grade). The compositional gap between tremolite and hornblende analysesfrom the lower grade rocks does not necessarily define a solvusbecause no tremolite-hornblende pairs were found. Rather, theanalyses provide outer limits on the possible width of a solvusat this grade (T). However, certain data suggest that a truemiscibility gap not only exists but probably is not a greatdeal narrower than the gap between the actual analyses. Besides,the proposed restriction on A1/Fe ratios at this grade wouldreduce the probability of finding tremolite-hornblende pairs.  相似文献   

Assessment of the mycoflora of commercial poultry feeds sold in the humid tropical environment of Imo State, Nigeria     

I. C. Okoli DVM  M. Sc.  Ph.D.  C. U. Nweke B.S. Agric. Tech.  C. G. Okoli B.Sc  M. Sc.  Ph.D.  M. N. Opara DVM  M.Sc 《International Journal of Environmental Science and Technology》2006,3(1):9-14

This study was carried out to identify the common moulds growing in selected commercial poultry feed sold in Owerri, Imo State, Nigeria. Forty-eight bulk samples derived froml92 bags of feeds were collected from broiler starter (BS), broiler finishers (BF), grower mash (GM) and layer mash (LM) across 4 different brands of ommercial poultry feeds, which included Livestock (LF), Top (TF) Guinea (GF) and Vital (VF) feeds. The feed samples were collected during the rainy season months of June, July and August. The common moulds isolated from these feeds were Aspergillus sp., Peicillium sp.,Mucor sp., Yeast sp., Rhizopus sp., Epicoecum sp., Gymnoaseus sp., Cladosporium sp., Mortierella sp. as well as Bacteria. Generally, more organisms were isolated in June than the other months with Mortierella sp. being the only one not isolated in that month. Vital feed with 8 different isolates had the highest diversity of fungal species while the others had between 4 and 5 species. Prevalence rates across the feed types, generally ranged from 18.76% in layer mash to 30.03% in broiler finisher. The four Aspergillus sp. isolated came from GM and BF. This study highlights the need for constant monitoring of moulds in commercial feedstuff produced in the humid tropical environments such as Imo state, Nigeria. There is also the need to routinely include fungal growth nhibitors in commercial feeds since moulds are capable of reducing the nutritional values of feedstuff as well as elaborating pathogenic toxins.  相似文献   

Up-temperature flow of surface-derived fluids in the mid-crust: the role of pre-orogenic burial of hydrated fault rocks   总被引：1，自引：0，他引：1  

C. CLARK  M.  HAND  K.  FAURE  A. SCHMIDT MUMM 《Journal of Metamorphic Geology》2006,24(5):367-387

The Walter‐Outalpa shear zone in the southern Curnamona Province of NE South Australia is an example of a shear zone that has undergone intensely focused fluid flow and alteration at mid‐crustal depths. Results from this study have demonstrated that the intense deformation and ductile shear zone reactivation, at amphibolite facies conditions of 534 ± 20 °C and 500 ± 82 MPa, that overprint the Proterozoic Willyama Supergroup occurred during the Delamerian Orogeny (c. 500 Ma) (EPMA monazite ages of 501 ± 16 and 491 ± 19 Ma). This is in contrast to the general belief that the majority of basement deformation and alteration in the southern Curnamona Province occurred during the waning stages of the Olarian Orogeny (c. 1610–1580 Ma). These shear zones contain hydrous mineral assemblages that cut wall rocks that have experienced amphibolite facies metamorphism during the Olarian Orogeny. The shear zone rock volumes have much lower δ¹⁸O values (as low as 1‰) than their unsheared counterparts (7–9‰), and calculated fluid δ¹⁸O values (5–8‰) consistent with a surface‐derived fluid source. Hydrous minerals show a decrease in δD_(H2O) from ?14 to ?22‰, for minerals outside the shear zones, to ?28 to ?40‰, for minerals within the shear zones consistent with a contribution from a meteoric source. It is unclear how near‐surface fluids initially under hydrostatic pressure penetrate into the middle crust where fluid pressures approach lithostatic, and where fluid flow is expected to be dominantly upward because of pressure gradients. We propose a mechanism whereby faulting during basin formation associated with the Adelaidean Rift Complex (c. 700 Ma) created broad hydrous zones containing mineral assemblages in equilibrium with surface waters. These panels of fault rock were subsequently buried to depths where the onset of metamorphism begins to dehydrate the fault rock volumes evolving a low δ¹⁸O fluid that is channelled through shear zones related to Delamerian Orogenic activity.  相似文献   

Alpine reworking of Ordovician protoliths in the Western Carpathians: Geochronological and geochemical data on the Muráñ Gneiss Complex, Slovakia     

A.S. Gaab  M. Jank  U. Poller  W. Todt 《Lithos》2006,87(3-4):261-275

Magmatic protoliths of Ordovician age have been identified in the metamorphic rocks of the Muráñ Gneiss Complex, Veporic Unit (Central Western Carpathians). Vapor digestion single zircon U–Pb dating yields an intrusion age of 464 ± 35 Ma (upper intercept) for the granite protolith. A lower intercept age of 88 ± 40 Ma records amphibolite-facies metamorphic overprint in the Cretaceous, during the Alpine orogeny. Geochemical and isotopic data suggest crustal origin of the orthogneiss. Nd_initial are between − 2.6 and − 5.0 and T_DM^Nd between 1.3 and 1.5 Ga (two-step approach). ⁸⁷Sr / ⁸⁶Sr_initial ratios vary between 0.7247 and 0.7120, and a steep REE pattern further constrains the crustal affinity of these rocks. Associated amphibolite bodies have Nd_initial values of 6.5, ⁸⁷Sr / ⁸⁶Sr_initial ratio of 0.7017, and a flat REE pattern. They are interpreted as MORB derived metabasites. Whole-rock Pb isotope analyses define a linear array in a ²⁰⁶Pb / ²⁰⁴Pb vs. ²⁰⁷Pb / ²⁰⁴Pb diagram with an age of ca. 134 Ma, consistent with intense Alpine metamorphism and deformation.

These basement rocks of the Central Western Carpathians are interpreted as Ordovician magmatic rocks intruded at an active margin of Gondwana. They represent the eastern prolongation of Cambro–Ordovician units of the European Variscides, which were part of the peri-Gondwana superterrane and accreted to Laurussia during the Variscan orogeny. Variscan metamorphic overprint is not recorded by the isotopic data of the Muráñ Gneiss Complex. Alpine metamorphism is the most dominant overprint.  相似文献   

The Usage of Ground Penetrating Radar (GPR) in Designing Blast Pattern     

G. U. Aldas  S. Kadioglu  E. Ulugergerli 《Rock Mechanics and Rock Engineering》2006,39(3):281-290

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