Very brief guide for exam 3. Be sure to review notes, text book and compose your own notes and outlines. Review and learn terms/word and how they apply. The following is alist of topics – it may or may not be complete and is not all –inclusive.Good luckGeologic TimeStratigraphic principles and relative time-order in which events occurOriginal horizontality; superposition, cross cutting, inclusions, faunal(or biotic) succession, uniformitarianism – know all of these.- Law of Original Horizontality: layers of sedimentary rock are always deposited in a nearly horizontal plane- Law of Superposition: in any sequence of sedimentary rocks, the oldest beds are at the bottom and the youngest are at the top- Cross-Cutting Relationships: a pattern that is disrupted is older than whatever caused the disruption- Faunal Succession: Fossil organisms succeed each other in time in an orderly and recognizable manner- Uniformitarianism: the processes that shaped the Earth throughout its history were the same processes as those operating today- Inclusionso Fragments of the preexisting rockGeologic time. Eras and periodsEras: Paleozoic, Mesozoic, Cenozoic – periods in each Eras (be able to associated the proper time period in each Era)Know the age of earth the beginning and end time for each Era- EARTH is 4.6Billion yrs.- Precambrian: 4600 M yrs. - Paleozoic: 570 M yrs.- Mesozoic: 248 M yrs.`- Cenozoic: 65 M yrs.What is an unconformity? How does one form and why?• A “gap” in Geologic record• Unconformities– Angular unconformity• Horizontal beds overlie a flat erosional surface formed from titled or folded beds– Disconformity• Sedimentary rock overlie parallel sedimentary beds (need an erosional surface or absolute dates to identify)– Non-Conformity• Sedimentary rocks overlie igneous or metamorphic rocksAbsolute time of each EraHow calculatedAbsolute time of earth, geologic eras-half of parent and half of daughter is one half life, Structure and Deformation:Strike and dipDip direction• Measure the direction of rocks with respect to North– STRIKE• Measure the inclination of rocks– DIP– Geographic direction (DIP DIRECTION)– Divergence from the horizontal plane (DIP ANGLE)• STRIKE – the intersection of the horizontal plane (ground surface) with an inclined plane (the inclined rocks)• Strike is measured and recorded in degrees from North• DIP – maximum angle of inclination from the horizontal (Dip direction is ALWAYS 90˚ from the Strike)Type of structures 1. Vertical Uplift– Uniform vertical stress uplifts rocks, evenly2. Tilting– Non-uniform vertical stress uplifts rocks, and raises one section higher3. Folding– Compressional stress plastically deforms rocks DUCTILE Behavior4. Faulting– Tension, Compression or Shear stress!– Rocks break therefore: BRITTLE behaviorFactors influencing brittle and ductile behavior- Stress caused by Plate tectonic movement; magma bodies; crustal readjustment- Stress may be vertical, compressive, tensional, shearing- The response of the rocks to the stressBRITTLE v. DUCTILE behavior- Ductile rocks Bend (Folds)o Plastic v. Elastic- Brittle rocks Fracture (Faults)Ductile structures:PlasticAnticline, syncline (compressive stress, only)Folds: core, axis, axial plane, limbs, anticline, syncline, Overturned, recumbent, asymmetric, symmetricPlunging; non plungingThe stress orientation necessary to produce folds• Antiforms – Limbs dip away from axis IF the oldest Rock unit is in the core it is called an ANTICLINE• Synforms – Limbs dip towards axis IF the youngest rock is in the core it is called a SYNCLINE- Symmetric axial plane is vertical, limbs dip in opposite directions at the same angle of dip- Asymmetric axial plane at an angle, limbs dip in opposite directions at different angles of dip- Overturned axial plane at an angle, limbs dip in the same direction but at different angles of dip- Recumbent axial plane and limbs areBrittle structures• An unfilled FRACTURE in a rock is called a JOINT– (A fracture infilled with minerals is called a VEIN)• A Fracture in which some movement or DISPLACEMENT has occurred is called a FAULT• The movement occurs along a FAULT PLANE• Faults can originate from all three types of stress:– Compressive; Tension; ShearFaults: Dip slip faults; fault plane, trace, hanging wall; foot wall; normal fault, reverse fault, thrust fault, tension; compression the type of fault produced by each type of stress field.• If Fault blocks move Up or Down the Fault Plane it is a Dip-Slip Fault– Normal Faults– Reverse Faults– Thrust Faults• If Fault blocks move in the direction of the Strike, it is a Strike-Slip Fault-Horizontal movement occur along strike of fault plane• If there is a combination of Dip-slip and Strike-slip it is an Oblique-slip fault• Normal fault Hanging wall moves down relative to Footwall• Reverse fault Hanging wall moves UP relative to Footwall; results from compression• Thrust fault A Type of reverse fault Low dip angle along fault planeStrike-slip faults; left lateral; right lateral; shearOblique slipRelationship of structures to stress fields or orientations; tectonic boundaries; other geologic featuresIsostasy ppt18 slide27-30 • ISOSTASY – Less dense crust “floats” on denser mantle• Mountains have deep “roots” of lower density crust• Erosion or removal of exposed mountains causes crust to rise upward• The Modern exposure of the Appalachians may be a result of Isostatic Rebound!Cumberalnd Plateau, Valley and Ridge; Blue Ridge; Piedmont – rock types and structures. Know these. Ppt19 slide 47- Cumberland Plateau-sedimentary- Valley & Ridge –sedimentary - Blue Ridge-metamorphic - Piedmont- high metamorphic rockPlate boundaryConvergent boundaries and mountain buildingOrogeny – what is it. What evidence exists for resolving orogenies• Orogeny – mountain building event.• Convergence!• Volcanism• Collision• Note: Local Mountains can be built from other causes!I. Subductiona. Oceanic-continental crustb. Oceanic-oceanic crustII. Collisionc. Continental-continental crustSubduction• Subduction – two types of mountain building• volcanic island arc– Oceanic plate subducted under another oceanic plate• continental volcanic arc– Oceanic plate subduction under continental plateVolcanic arcs; island arcs – where/why?- When two oceanic plates converge, one is subducted beneath the other, causing