The folding has been due to layer parallel slip that took place along the least cohesive bedding planes involving little or no distortion of mass making the layers. This tutorial is divided into three parts; they are: 1. This particular mechanism of folding is responsible for a typical character of the concentric folds in which: (i) Anticlines become sharper with depth; Those folds in which the degree of folding is observed to be similar for indefinite depths are grouped as similar folds. In such folds, the axial regions are thicker than the limb regions indicating a plastic type of movement of the material of rocks from the limb regions to the axial regions during the process of folding. Parts of a Fold 3. These folds are produced by tangential pressures which lift up the beds slowly and vertically at the crests. Syncline: are the most modern materials which are located in the core or center fold 1. Folds generally occur at great depths in the earth’s crust where the rock layers are exposed to high temperatures and pressures. A syncline consists of beds bent downwards with limbs dipping towards each other. These folds are the reverse of anticlines in all details and may be described as those folds in which: (i) The strata are downarched, that is, these become CONVEX DOWNWARDS; (ii) The geologically younger rocks occupy a position in the core of the fold and the older rocks form the outer flanks, provided the normal order of superposition is not disturbed. Dome Fold or Quaquaversal Fold or Pericline: Dome fold consists of a set of rock beds lifted centrally giving the feature of a dome. The axial plane in this case divides the fold into two equal halves. A fold system consisting of a number of symmetrical anticlines and synclines, with their axes horizontal and parallel is called a non-plunging fold system. Folds are classified into two main types namely anticlines or up-folds and synclines or down-folds. Two major types of folds recognized on the basis of thickness of the layers as a measure with depth are the concentric (or parallel folds) and the similar folds: The strata in concentric or parallel folds have reacted to the effecting tangential compression in such a way that the thickness of the involved layers remained uniform and constant even after folding. Terms of Service 7. Hence, anticlines and synclines are favourite terms with the geologists and students of geology. These folds in which the thickness of the rocks is not affected during the process are termed as Open folds, and the other type with thickened crests or troughs and thinner limbs as Closed folds. After the domes are eroded, the younger rocks appear surrounding the older rocks. Plagiarism Prevention 4. Disclaimer 8. Stratified rocks were formed from sediments deposited in flat horizontal sheets, but in some places the strata have been warped. It may be described as a special type of fold with exceptionally flattened top and steeply inclined limbs almost forming three sides of a rectangle. FOLDS I. FOLDS - type of deformation superimposed on some type of layering A. These are group of folds in which all the axial planes are essentially parallel, meaning that all the component limbs are dipping at equal amounts. The hinge zones are, therefore, not very sharp. Classification, Delineation and Measurement of Nonparallel Folds By JOHN B. MERTIE, Jr. Disclaimer 9. The area of the rock bed sunk may be circular or oval shaped. Slumps in soft sediments and flow folds in lavas are examples of primary folds. Any fold in which fold axis is NOT HORIZONTAL, i.e. Consequently, the classification results of seven protein classes were improved. Content Filtrations 6. Folds that maintain uniform layer thickness are classed as concentric folds. In this case the limbs of anticlines dip towards each other and the limbs of synclines dip away from each other. Similar folds tend to display thinning of the limbs and thickening of the hinge zone. This material is then compressed and uplifted in the second stage of orogeny, (the mountain building activity) to gradually take the shape of mountain systems. Folds vary widely in size; some may be hundreds of kilometers across, whereas others measure just a few centimeters or less. Account Disable 11. 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