Physical Geology Review TXESS Revolution - Summer Institute A, 2010 Physical Geology Review the expanse of material is vast! Jon Olson

Internal Structure of the Earth granitic/basaltic crust = 0-40 km; mantle = 40-2900 km; outer core (liquid) = 2900-5200 km; inner core = 5200-6400 km from: www.usgs.gov

Guidelines for Structural Analysis reference frame law of original horizontality (rocks deposited on nominally horizontal surfaces) law of superposition (deposition of new layers are on top of old layers) stratigraphic continuity (deposits tend to be continuous laterally, or discontinuous strata that lie in the same plane are equivalent in time) nature of contacts stratigraphic (bedding or unconformities) intrusive (igneous or sedimentary) tectonic (fractures/faults)

Basic Principles principle of superposition younger rocks are deposited on top of older rocks

Basic Principles law of original horizontality all sediments originally laid down in horizontal layers Grand Canyon, Arizona

Basic Principles law of original horizontality non-horizontal bedding implies some sort of deformation The Alps of Sisteron, France

Interpreting Field Data strike and dip measurements topography following geologic structure geologic cross-sections

“Undeformed”, horizontal rock Cedar Point, UT

Horizontal Bedding in Sedimentary Rocks younger original horizontality older original horizontality lateral continuity superposition

Strike and Dip

Looking in strike direction, dip is angle from horizontal arrow pointing down dip

Interpreting Field Data strike and dip = attitude of planes (beds, fractures, ...) strike is intersection of plane with horizontal dip is angle between plane and horizontal

Vertical Beds Miocene Monterey Fm Vertical Beds Miocene Monterey Fm., California coast Laminated bedding with selective dolomitization (yellow beds) 1 meter

Orientation of Planes (strike) Horizontal is reference frame 3d block diagram Strike is intersection between plane and horizontal North is reference direction

Orientation of Planes (dip) vertical cross-section view strike dip angle Dip is inclination of plane from horizontal, measured in vertical plane perpendicular to strike

Folds and Faults - folds are evidence of ductile rock deformation - faults represent brittle rock deformation

Monocline on the San Juan River, Utah

Lateral Continuity (or lack thereof!)

Faults Fault vertical cross-section view dip angle Hanging Wall Footwall

Faults 3d block diagram Fault Hanging Wall Footwall

Dip-Slip (Normal) Footwall Hanging Wall

horizontal stretching = extension Dip-Slip (Normal) Footwall Hanging Wall horizontal stretching = extension vertical thinning

Dip-Slip (Reverse) Footwall Hanging Wall

horizontal shortening = contraction, Dip-Slip (Reverse) Hanging Wall Footwall horizontal shortening = contraction, vertical thickening

Strike-Slip strike-slip faults are typically vertical, Footwall Hanging Wall strike-slip faults are typically vertical, but they can be dipping like this one

Strike-Slip (right-lateral) Footwall Hanging Wall as you step across the fault, the block you are stepping onto moves to the right

Strike-Slip (left-lateral) Hanging Wall Footwall as you step across the fault, the block you are stepping onto moves to the left

Oblique-Slip Footwall Hanging Wall

Oblique-Slip Footwall Hanging Wall both strike-slip and dip-slip

Normal Fault with Basin Shaped Fold in Hanging Wall shear sense = normal Foot Wall Fault Plane Hanging Wall Bedding Slip vector

Fault drag & shale smear

Strike-slip fault and Drag folding

Slickensides = shear

Reverse Fault in Core

Geologic Cross-section Map view A B A B Cross-section view

Fracture Types shear failure – faults relative displacement is parallel to fracture face = shearing mode tensile failure – joints, veins, dikes a fracture with relative displacement perpendicular to fracture face = opening mode

Joint are “just” cracks…. (looking at dip slopes) orientation changes from bed to bed

Joints (looking at bed scarps)

A Joint filled with minerals = vein Bristol Channel, UK Ouachita Mtns., Arkansas

A “Joint” filled with magma = dike Mt. Moran, Grand Tetons, WY

Famous Fractures in the Movies The Middle East? hardly! from Transformers

Volcanic Neck and Igneous Dike: Shiprock dike How about New Mexico? propagating dike volcanic source curving path to line up with earth stresses Volcanic Neck and Igneous Dike: Shiprock dike volcanicsource

Igneous Rock Features from Press and Siever, Understanding Earth

Other Geomorphic Features

Glacial Moraine & U-shaped Valley

Glacial Moraine

Immature River – Steep, V-shaped Canyons Yellowstone River Immature River – Steep, V-shaped Canyons

Mature, meandering river (Yellowstone River)

High energy rivers – heavy sediment load channel cut & fill, graded bedding braided stream

Alluvial fan

Unconformities represent non-deposition or erosion often indicate tectonic events or global sea level change, laterally very continuous types disconformity (parallel sed layers above and below, missing some time) nonconformity (sed rocks on top of igneous/metamorphic basement) angular unconformity (rocks above and below have different orientation)

Angular Unconformity

Disconformity

Cambrian Flathead ss on top of Precambrian granite Nonconformity Cambrian Flathead ss on top of Precambrian granite