What Killed The Dinosaurus ?

It is one of the Greatest puzzles in Paleontology.

For more than 150 millions years, dinosaurs dominated the earth. They were so successful that other animal groups -- mammals included -- had little chance of playing anything more than secondary roles.

Then, 65 million years ago, the dinosaurs vanished from the world forever.

Did they meet a quick and catastrophic end or did they fade away gradually ?

details : http://www.pbs.org/wgbh/evolution/extinction/dinosaurs/

Evolution oF Thrusting

The overall evolution, therefore, is for thrusting to begin at deeper levels and to progress upward and outward (i.e., away from the root zone) from a major sedimentary basin. Ductility contrast in the stratigraphic section encourages a stair-step evolution of thrusts, which we know as ramping. A relatively flat portion of a thrust plane, particularly where it remains parallel to bedding within a single lithology, is referred to as decollement. If this flattening of the thrust plane occurs at the boundary between the sedimentary section and basement, it is called basal decollement.
The progressive stacking of thrust faults may develop in piggyback fashion, where younger thrusts form in the footwall or, alternatively, in overstep fashion, where thrusts become younger toward the root zone. Piggybacking seems prevalent on a regional scale and is by far the more significant progression. At the same time, both piggyback and overstep thrusting occur on a more local level, often as a result of imbrication.
Imbricates occur most often in two structural positions of high stress concentration-near the toe of a major thrust and above ramps in a thrust plane. They dip steeply as they approach the surface, and stack slice after slice of the same stratigraphic section along faults, which sole out into a major thrust plane. Continued movement along this plane after the imbricates have formed will rotate them, so they can become vertical and overturned.
As discussed by Dahlstrom (1970), imbrication actually offers a basic model for foreland thrusting-as the scale of a cross section is increased to become more regional, major thrusts themselves become imbricates of the largest faults (i.e., those with the greatest displacement). These, in turn, can be thought of as subsidiary faults to a basal detachment or decollement plane that marks the structural boundary between basement, usually crystalline metamorphic or plutonic rocks, and sedimentary cover.

Stress - Fault Mechanism

Principal Axes of Stress
Material behavior science, through its detailed analysis of stress conditions, has derived an important conclusion that has proven very useful in structural geology: for any point in a homogeneous stress field, there exist three mutually orthogonal planes along which all shear stresses vanish and only the components of normal stress exist. These three planes are known as the principal planes of stress, and the axes of their intersection are thus the principal axes of stress. These axes are used to describe what are referred to as the three principal stresses. This ideal triaxial system makes everything simpler, since it allows us to speak in terms of only normal stresses, i.e., compression, or "squeezing," and extension, or "pulling apart" ( Figure 3 ).
In geology, principal stress is usually spoken of in terms of compression, which is taken as positive, and tension as negative. (For materials and engineering science, the opposite is true-i.e., tension is positive, compression is negative.) The three principal axes, or stress directions, are correspondingly written as s1 (maximum principal stress), s2 (intermediate principal stress), and s3 (least, or minimum, principal stress). For our purposes, it is useful to understand four special states of stress:
1. uniaxial stress, where two principal stresses are zero and the other is nonzero
2. biaxial stress, where two principal stresses are nonzero and the other is zero
3. triaxial stress, where all three principal stresses are nonzero
4. pure shear stress, where s1 equals s3 and is nonzero, while s2 is zero. This is actually a special case of biaxial stress.Within the earth's crust, the most common stress situation is triaxial, with s1 > s2> s3> 0.

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