Geology 209 Final Chapters 8 & 9

Chapter 8&9

Fossils

________ represent the vestiges of ancient life forms.

Body fossils

Most frequent, has part or whole of organism preserved, includes hard parts, palaeontology

Trace fossils

Represents organism’s activities, original organism left traces of moving and feeding, sedimentary petrology

Chemical fossils

Represents chemical combinations of certain substances produced by an organism or existing in its body and the minerals in the surrounding environments, geo chemistry

Recrystallization

The conversion of original minerals of the test into different minerals, common transformation is aragonite to calcite

Moldic preservation

The original test or shell dissolves after being embedded into the rock, creates an empty space that preserves external and internal features

Moldic preservation replacement

Particular case of moldic preservation, new space from dissolution is filled with new material

Pyritization

Most frequent case of replacement

Permineralization

Results from the filling of pore spaces by opal, or chalcedony, trees are prone to this

Carbonization

Occurs when fossils are buried into Earth’s crust, organic material is expelled except for carbon, frequent in plants

Congealment

Occurs at high latitudes, thick layer of frozen soil and rock and the uppermost part of the Earth’s crust, fossilized soft tissue

Amber

Fossilization happens in natural resin, allows three dimensional fossilization when resin was liquid, fossilized soft tissue

Tar pits

Occurs in in zones with oil seeps, organisms stuck in viscous fluids

Metasomatosis

Complete replacement of the chemical and mineralogical composition of a fossil

Structural geology

Represents the study of rock deformation in response to applied force

Principle of original layer horizontality

Deformed and tilted layers are the result of crustal movements

Force

The push or pull that result in a change in the motion of a physical body of given mass

Stress

The amount of force per unit area

Change in place (displacement)

A rock volume is moved from one place to another

Change in position (rotation)

Occurs when a rock spins around a center or an axis

Change in shape (strain)

Represents the internal deformation of a rock response to force or stress

Confining stress

Equal in all three directions of the space for a certain point in the Earth’s crust, occurs in rock burial

Differential stress

The amount of stress is higher in certain directions, occurs in crustal movements

Compression

Stress pushes on a rock

Tension

Stress stretches a rock

Shear

Stress is applied in two opposite directions

Fluid pressure

Is given by the fluids in rock pores and occurs mostly in the case of sedimentary rocks, pressure is opposite to general stress and reduced effects of total stress

Brittle deformation

Upper portion of crust, rocks are weak due to low pressure, fractures are dominant structures

Ductile deformation

Occurs with depth increase, rocks are strong due to high pressure, folds are dominant structure

Folds

Structures that result from lateral compression of the Earth’s crust

Branches

The two convergent or divergent sides of the fold, aka limbs

Fold crest

Highest part of fold

Trough

Lowest part of fold

Fold axis

A line defined by the points of maximum curvature

Axial plane

Defined by the axes that subdivide the fold into two equal parts

Anticline

Branches converge upwards

Syncline

Branches converge downwards

Monocline

One branch going downwards

Upright

Axial plane is vertical, the two limbs dip in opposite directions

Inclined

Axial plane is inclined, the two limbs dip in opposite directions

Overturned

Axial plane is inclined, the two limbs dip in the same directions

Recumbent

Axial plane is horizontal, the two limbs dip in opposite directions

Joints

Fractures in which the two resulting blocks present no movement with respect to each other

Faults

Fractures in which two resulting blocks present a significant displacement

Footwall

Situated below the fault plane

Hanging wall

Situated above the fault plane

Normal faults

The hanging wall presents a downward displacement when compared to the footwall

Reverse fault

The hanging wall presents an upward displacement when compared to the footwall

Thrust faults

Reverse faults which dip at a low angle

Strike-slip faults

The displacement is horizontal, along the strike

Dip-slip faults

There is only vertical displacement, along the dip

Oblique-slip faults

Most common, both horizontal and vertical displacement