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Academic Articles<br />
I-STRUCTURE GEOLOGY<br />
Folds are probably the structure that comes to mind when we say the words<br />
(geological structure), so why is the fold such a distinctive term related to<br />
geological structures ...<br />
well folds are waves in stratified rocks, these rocks were once horizontal strata<br />
but they have been buckled...<br />
Folds are usually formed by compressional stress. like any architectural<br />
structure a fold has its terminology which describe it fold terminology :<br />
1- limbs : The generally planar region of a<br />
fold which lies between two adjacent hinge<br />
lines and is confined between the zones of<br />
maximum curvature.<br />
2- inflection point : the point where the<br />
sense of curvature is converted .<br />
3- hinge: place of maximum curvature on<br />
the fold .<br />
4- axes : it is the intersection of the axial<br />
plane with a bed in the fold<br />
5- axial plane : imaginary planar surface<br />
defined by the connection of the hinges and<br />
symmetrically divides the fold .<br />
6- wave length : distance between two<br />
peaks or two troughs<br />
7-median surface : an imaginary surface<br />
connecting adjacent infliction points<br />
8- amplitude : it is the distance form the<br />
median plane to the hinge<br />
Folds are classified according to the attitude of<br />
their fold axes which can be called a hinge line if<br />
the fold isn't cylindrical . the axes can be vertical<br />
or inclined and in some cases horizontal like the<br />
recumbent fold.<br />
Most famous types of folds<br />
1- anticline<br />
2- syncline<br />
3- dome<br />
4- basin<br />
1- Anticline is the fold where every limb<br />
dips away from the peak<br />
anticlines form one of the most<br />
important hydrocarbon trap formations<br />
about 80 % of the world's petroleum<br />
was found in anticlines.<br />
antiforms are folds that take the shape<br />
of an anticline but it's younging<br />
direction is inverted an anticline should<br />
have the oldest rock in the center .<br />
anticlinorium is a large scale anticline<br />
with smaller folds inside it<br />
2- Syncline is the fold<br />
where the limbs dip<br />
toward the trough<br />
a synclinorium is a large<br />
syncline which has minor<br />
folds in it<br />
Dome and basin aren't like the typical folds<br />
because they have more of a circular plane than<br />
a linear one .<br />
3- The dome is<br />
convex upward<br />
and the strata dip<br />
outward towards<br />
the center<br />
4- Basin is concave<br />
upward and the<br />
strata dip inward<br />
towards the center
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