Dip of a plane in an imaginary vertical plane that is not perpendicular to the strike.

apparent dip </= to true dip

• disconformity
• angular unconformity
• nonconformity
• buttress unconformity

beds of the rock sequence above and below the unconformity are parallel to one another, but there is a measurable age difference between the age sequences.

• Disconformity surfaces represents a period of undeposition and/or erosion

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unconformities at which strata were deposited on a basement of older crystalline rocks. The crystalline rocks may be either plutonic or metamorphic 

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strata below the unconformity have a different attitude than strata above the unconformity. beds below are truncated at the unconformity while the beds above the unconformity roughly parallel the unconformity surface. therefore if the unconformity is tilted, the overlying strata are tilted by the same amount.

• Occurrence means that the sub-unconformity strata were deformed (tilted/folded) then were truncated by erosion prior to deposition of the rocks above the unconformity (Active Tectonism)

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(onlap unconformity) occurs where beds of the younger sequence were deposited in a region of significant predepostional topography. 

• formed when sea level rises, burying islands with sediment. However along the margins of the island, the layers appear to be truncated by the unconformity. rocks below may/not be parallel to the unconformity
• different from angular in that the younger layers are truncated by the unconformity at the surface.

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1. Descriptive Geometric Analysis (geometric features in rock described by shape and the use of a 3-dementional space to describe the structures orientation)
2. Kinematic Analysis (determination of the movement paths rocks took during transformation from the undeformed to the deformed state)
3. Mechanical Analysis (study of processes on the atomic scale that allows structures to develop)

Force per unit area acting on a plane

• σ=F/area

1. Law of Original Horizontality - layers of strata are originally deposited horizontally
2. Law of Superposition - strata follow one another in chronological, but not necessarily continuous order
3. Stratigraphic continuity - strata occur in laterally continuous and parallel layers in a region

1. rotation (pivoting of a body around a fixed axis)
2. translation (change in position of a body)
3. strain (distortion or change in shape of the body)

• Brittle - loss of cohesion across a mesoscopic discrete surface. Common in Uppercrust
• Ductile - formed by opposite of Brittle, occurs in deeper part of crust

• deformation - collective displacement of points in a body, the complete transformation from the initial to the final geometry of a body
• strain - changes of points in a body relative to one another, distortion of the body

Deformation is not a vector entity, but a second order tensor (similar to stress)

Non-coaxial Strain

a change in length divided by the original length, dimension less quantity

• expressed as elongation (e)

e=(l-lo)/lo

l=final length

lo=original length

measure change in angle (angular shear) between two lines that were originally perpendicular

• angular shear=ψ
• shear strain=γ=tanψ

for use in calculations associated with the Mohr circle for strain

• quadratic elongation=λ=(l/lo)^2=(1+e)^2

root of quadratic elongation, a convenient strain parameter that directly relates to the dimensions of the strain ellipsoid 

• s=λ^(1/2)=l/lo=1+e

plots the ratio of the maximum stretch over the intermediate stretch on the vertical axis and the ratio of the intermediate stretch over the minimum stretch of the horizontal axis

• k=(a-1)(b-1)=slope of line as it passes through origin
• a=x/y=(1+e1)/(1+e2)
• b=y/z=(1+e2)/(1+e3)

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Ramsay diagram uses the natural logarithm of the values a and b and is a modification of the flinn diagram

• ramsay has more advantages in that, small strains that plot near the origin and large strains that plot away from the origin are more evenly distributed. Also allows a graphical evaluation of the incremental strain history because it plots a path along straight lines