Fan Head Research Articles

Diagenetische und epigenetische U-, Ba- und Buntmetall-Mineralisation im obertriadischen ?Burgsandstein?, S�ddeutschland

Sandstone-hosted U deposits of the Upper Triassic “Burgsandstein” have attracted considerable attention during the last decades. Paleogeographically, these arenaceousargillaceous rocks represent a fan-playa environment, with a great variability as to fluvial drainage patterns such as braided and meandering streams. Furthermore, duricrusts are very widespread throughout the entire “Sandsteinkeuper” (Upper Middle Keuper). Three types of ore deposition are encountered: Phosphatization took place proximal to the fan head, whereas silcretes (petrified wood) and caliches occur towards the centre of the basin. U black ore with minor Cu-, Pb-, Fe-, and Co sulfides precipitated from ground waters when entering less permeable lithologies under reducing conditions. At a later stage, faults terminating within the Upper Triassic series were mineralized with BaSO4.

Late Pleistocene Fan-Deltas Along the Dead Sea Rift

ABSTRACT Late Pleistocene lacustrine fan-deltas which developed in an arid, disequilibrated submergent environment along the western fault scarp of the Dead Sea Rift are characterized by: 1) alluvial fan deposits of crudely stratified conglomerate beds and horizontal and cross-bedded sandstones. The conglomerates and sandstones are cone-shaped and comprise the entire sequence in the fan head area; 2) fan-front thick and thin interlayers of ripple cross-laminated sandstones and mudstones which constitute a sedimentary belt a few kilometers wide in front of the fan; and 3) fan-influenced detrital laminated chalks. Both the interlayered and the laminated units appear as widespread sheet bodies whose basal contacts are gradational and upper contacts, sharp and disconformable. The rapid rise of lak level resulted in the buildup of upward-fining sequences. At the end of the Pleistocene, the lake level dropped; it began to rise again during the Holocene and, contemporaneously, new fan deltas began building up.

Resedimented conglomerates of Huronian (lower Aphebian) age, from the north shore of Lake Huron, Ontario, Canada

Conglomeratic rocks are present near the top of a dominantly arenaceous sequence, previously ascribed entirely to the Huronian Mississagi Formation, in a belt extending for about 60 km east of Blind River, on the north shore of Lake Huron. These conglomeratic rocks and the massive and planar laminated sandstones which overlie them are herein named the Lauzon member, after the thickest exposed development of the sequence at Lauzon Lake in Striker Township. The presence of dropstones in the sequence at Lauzon Lake suggests that the member is best considered as part of the Bruce Formation. Conglomeratic rocks within the Lauzon member include granule-supported boulder, cobble, and pebble conglomerate; sand-supported cobble and pebble conglomerate; intact framework graded and non-graded pebble and cobble conglomerates; stratified conglomerates and conglomeratic sandstones; and disrupt framework conglomerates. These conglomeratic rocks lack abundant mud-grade matrix material and, hence, are readily distinguished from (glaciogenic?) mixtites of the Ramsay Lake, Bruce, and Gowganda Formations. Conglomerates of the Lauzon member were probably deposited from sediment gravity flows within a series of subaqueous fans or fan head valleys which may have been initiated by contemporaneous movements along a precursor to the Murray Fault system at the onset of the Bruce glaciation.

Stratification in Willow Creek Alluvial Fan, Eureka Valley, Inyo County, California: ABSTRACT

Stratification in the entrenched main channel in the upper 5 mi (of 12) of Willow Creek fan was analyzed by means of continuous-strip photos and sections spaced 2,000 ft apart. Average and maximum bed thicknesses decrease, respectively, from 1.7 and 6.0 ft near the fan head to 1.0 and 3.9 ft downfan. Individual beds extend from 10 to > 500 (700?) ft, although few beds extend > 200 ft. Gravel forms pack (framework), pack-float (transitional), and float (puddingstone) fabrics. Most cobbles and boulders are subspherical and subround, and thus usually do not form distinctly oriented fabrics. Stream deposits exhibit distinct channel geometry, pack fabric, and little silt and clay. Mudflow fabrics vary from pack to float. Some are uniform; others grade laterally from float to pack within 25 ft. Mudflows show high length:thickness ratios; the majority of mudflows lack graded bedding. The ratio of mudflows to stream deposits exceeds 70% and increases downfan. Float beds generally contain 15% silt and clay, whereas pack beds usually contain > 60% gravel and variable amounts of silt and clay. All deposits are poorly to extremely poorly sorted, and range from strongly coarsely skewed to symmetrical. Silt forms most of the matrix of mudflows, whereas clay ranges from only 1% to 7%. In the silt-clay fraction, feldspars exceed quartz, and clay minerals are minor in amount, the result of semiarid climate (17 in. rainfall/year), dominance of granitic rocks with large feldspar phenocrysts in the drainage basin (> 60%), and predominantly mudflow transport. End_of_Article - Last_Page 356------------

Sedimentation of an Alluvial Fan in Southern Nevada

An alluvial fan sequence in the southern Arrow Canyon Range, Nev., consists of an earlier mudflow and a younger stream deposit. Particles of both phases have an exponential decline in size away from the source area. The mudflow has a steeper curve of particle-size decline and a lower correlation coefficient than the stream deposit. The stream deposit is largely the result of reworking of the older mudflow, but has a consistently lower particle size caused by weathering and splitting of the particles. A general increase in the rod- and disc-shaped pebbles downstream is due to transportation in traction and suspension, respectively. Fan head entrenchment is the result of a change from mudflow to stream conditions and the development of a new fan profile.

Fans—Their Types, Characteristics, and Application

A fan is defined by the British Standards Institution as “a machine which propels air continuously, the total fan head never exceeding 1 lb. per sq. in.” When the pressure is above this limit the field of blowers is entered. The paper deals descriptively with modern fans and their applications under the following three main types: ( a) propeller fans, ( b) centrifugal fans, ( c) axial flow fans. The differences in their characteristics and construction appear to justify the classification of ( a) and ( c) as different types. After recapitulation of the fundamental formulae used in assessing the output, power requirements, and efficiencies of centrifugal fans, the author discusses various test results on actual installations, with some of which he was personally concerned. Axial-flow fans are considered both from manufacturing and from aerodynamical viewpoints, and test results are given, together with curves showing the power absorbed and the efficiency achieved. In the latter part of the paper the author deals with various applications of fans: to the ventilation of buildings, ships, and mines; as a method of supplying draught to boiler installations by mechanical means; and in the operation of dust extraction plant. The control of fan speed and output by hydraulic couplings is compared with methods of adjusting the inlet vanes, in order to achieve the same result.

The Definition of the Quantity-Head Characteristic of Fans

Abstract The purpose of a fan characteristic is to delineate useful information regarding the performance of a fan in its installation. Specifically, the quantity-head characteristic shows the quantity of air delivered against a certain resistance in the intended installation. The authors discuss the set up of four basic arrangements of fan types and installations, and describe three currently used fan-head definitions. The definitions of fan head are evaluated, the fan head being defined as the discharge static head minus the inlet total head. A primary arrangement of each type of fan is described and a single primary quantity-head characteristic for each type of fan is defined. If a fan is installed in any arrangement other than its primary one, the primary characteristic cannot be assumed to apply, but a separate test must be conducted to determine its characteristic in its intended arrangement. Results of complete tests of a fan installed in its four possible arrangements are given to illustrate the principles which are set forth.