Geology 101 section 1

Study Guide Supplement for Final Exam

The final exam will cover all the material on the study guide for Exam 1, on the study guide for Exam 2, and the material in this guide. It will be a comprehensive final.

Reading:

Textbook: CH 12, CH 13, CH 14 (p. 366-378), CH 16 (p. 421-441)

Class notes, handouts, especially on river systems.

Outline of Topics:

• Weathering and Erosion

  • physical weathering: ice, water, wind, roots

    • effects of joints, fractures, bedding planes

    • spheroidal weathering

    • wind cuts into rock 1 m above ground

  • chemical weathering: oxidation, hydration, hydrolysis

    • chemical stability of minerals on earth's surface

    • carbonic acid from rainwater and CO₂

    • depends on climate, tropical vs. arid: effects on monuments

  • differential weathering: in Grand Canyon, cliffs are hard and slopes are soft

  • limestones and karst

    • dissolution of calcite, depends on composition and fabric

    • can leave large caverns, lots of water flow

    • stalactite and stalagmite precipitation in caverns

    • cavern collapse to sinkholes: karst terrain

    • dependence on climate: cliffs in arid Grand Canyon vs. karst in tropical China

  • Soils: depend on bedrock type, past & present climate, vegetation

    • loose-rock regolith; soil horizons: leached zone (eluviated), accumulation zone

    • zones develop over 1000 to 1 million years

    • tropical laterite soils: red, heavily leached, only oxides left - bauxite Al ore

    • temperate pedalfer soils: big leached zone, not much accumulation zone

    • arid pedocal soils: carbonate cements together accumulation zone, hardpans, calcrete or caliche. 1-2 meters down and 1-2 m thick, hard to drill or rip.

• River Systems

  • dynamic sediment collection (headwaters), transport, and dispersal (deltas and alluvial fans) systems

  • transport by rolling bedload (gravel), saltation (sand), suspension (silt, clay)

  • energy and competency - maximum particle size, flow velocity

    • where a river slows it drops its larger-sized sediment load

  • amount of flow - amount of transported sediment

  • river deposition = aggradation

  • hydraulic gradient: grade = rise(or fall)/run; most rivers < 1 ft per 1000 ft (0.1%)

  • graded stream profiles: large gradient at source, small gradient at base level

    • flow and velocity, competency are proportional to gradient

    • larger sizes carried at steep top of profile

    • profile changes with damming, headward erosion, delta progradation

  • morphology

    • braided streams at high gradient, dynamic anastomosing channels, gravel bars

    • meandering rivers at low gradient, flood plains, natural sand levees, overbank silt and clay deposits, dynamic meandering by cut banks and point bars, cut-off meanders, oxbow lakes

  • effects of uplift: rate of uplift versus rate of downcutting by river

    • low uplift vs. downcutting: incised meanders - Colorado Plateau

    • medium uplift vs. downcutting: fluvial terraces, V-shaped valleys, common

    • high uplift vs. downcutting: wineglass canyons - Death Valley, Sierran Front

  • effects of more flow during floods

  • deposition of cross-bedded sand; progradation in direction of flow

  • imbricated gravel deposits, leaning in flow direction

  • fluvial terraces as indicators of uplift events (earthquakes)

  • slumping of steep channels to form V-shaped valleys

  • alluvial fans - end of small river in arid regions

    • poorly-sorted clastic sediment - mudflows of cobbles, gravel, sand, slit, clay

    • a radial graded stream profile in every direction from the canyon mouth

    • fan center at mouth is highest point

    • braided stream channels on fan surface

    • flatter bajadas between fans

    • wind blowing fine sediment from fan surface forms desert pavement

    • during last ice age MgO deposits formed desert varnish

  • deltas - end of river in large lake or sea

    • big deltas only in passive-margin plate-tectonic environments

    • meandering distributary channels with sandy natural levees

    • swamps with overbank fines between channels

    • topset (channel sand), foreset (prograding fine sand), and bottomset (silts and clays) beds - deltaic sequence and importance to oil exploration

    • delta progradation (seaward) by successive deposition

      • early hint of geologic time from Nile delta progradation

    • terminal channel lobes - source of sediments for marine realm

• Marine Realm

  • continental shelf, slope, rise, and abyssal plain physical environments

  • deep-sea fans: submarine canyons, turbidity currents, turbidites (w/ graded bedding)

  • longshore currents - predominant wave/wind direction, transport sand

  • effects of construction: groins and wharfs interrupt longshore transport, scalloping

• Glaciation (climate change not covered)

  • alpine: valley glaciers, cirques, U-shaped valleys, hanging valleys

  • continental: ice caps and sheets

  • deposition: till (poorly sorted), moraines, outwash (braided streams), lakes, eskers

• Resources (only water and petroleum covered)

  • porosity vs. permeability: properties of clays vs. sands, special props. of fractures, limestones

  • aquifers and reservoirs; aquicludes and seals/barriers

  • water table and hydraulic head (gradient = rise/run)

  • drawdown of water table around pumping well

  • saturated and unsaturated zones

  • sedimentary basins make aquifers and oil/gas reservoirs - global distribution

  • gravity exploration for basin, reservoir thickness

  • traps to oil migration (upward) - structural control

  • seismic exploration for trap structures and stratigraphy