Geology 102

Oceanic Crust

Crust beneath oceans, 5-8 km thick, mafic composition, average density 3 g/cm3, rocks approx 180 million yrs old or less.

Continental Crust

Crust beneath continents, 20-70 km thick, felsic composition, less dense 2.7 g/cm3, rocks older (up to 4 billion yrs old).

Lithosphere

Crust plus uppermost mantle, rigid and brittle behavior.

Asthenosphere

Below lithosphere, partially molten rock, plastic behavior.

Wegener's Evidence

Continents fit, geological and paleontological similarities, paleoclimatic evidence, Glossopterisflora.

Uniformitarianism

Belief in consistent geological processes over time.

Seafloor Spreading

Process where oceanic plates move apart at mid-ocean ridges.

Subduction

Oceanic crust forced beneath continental crust at convergent boundaries.

Transform Boundary

Plates slide past each other, no crust produced or consumed.

Mantle Convection

Heat-driven movement in the mantle, drives plate tectonics.

Seismic Tomography

Mapping mantle temperature anomalies using seismic waves.

Triple Junction

Boundary between three tectonic plates.

Orogenesis

Process of mountain building.

Terrane

Distinctive region of Earth's crust behaving as a coherent block.

Endogenic Processes

Geological processes originating inside Earth's crust.

Exogenic Processes

Geomorphic processes originating at or near the earth’s surface, including mass wasting, weathering, erosion, and deposition by various processes.

Weathering

Exogenic processes altering the physical and chemical state of rock material at or near the earth’s surface, involving physical and chemical processes leading to rock decomposition.

Erosion

The pick up and transport of material by agents like water, wind, ice, gravity, and waves.

Physical Weathering

Mechanical breakage of rock by stress, thermal expansion, frost wedging, dominant in cold and dry environments.

Chemical Weathering

Dissolution and clay production, dominant in hot and wet environments with faster rates than physical weathering.

Soil

Loose sediment with organic matter, air, and water at the earth's surface, essential for plant growth.

Mass Wasting

Downslope movement of material due to gravity, involving landslides, varying in speed and size.

Shear Strength

The resistance of materials to sliding along internal planes, influenced by normal force, internal friction, cohesion, and pore water pressure.

Falls

Free fall or forward rotation of rock or sediment from steep slopes, producing talus slopes.

Slides

Downslope movement of intact material along planes of weakness, with features like scarps and slump blocks.

Flows

Fluid-like movement of sediment or rock, including mudflows, debris flows, and lahars.

Creep

Slow movement due to expansion and contraction of soil, producing terracettes and common in valleys.

Discharge

Volume of water flowing past a point per unit time (m3/sec)

Q = A * V

Equation for Discharge where Q is Discharge (m3/sec), A is cross-sectional area of the channel (m2), and V is stream velocity (m/sec)

Erosion

Involves hydraulic action, abrasion, and corrosion in stream processes

Transportation

Involves Bedload, Suspended load, and Dissolved load in stream processes

Deposition

Occurs when a stream is incapable of transporting all the material it carries

Stream Capacity

Maximum amount of material a stream can carry, determined by stream discharge

Stream Competency

Maximum size of particles a stream can carry, determined by stream velocity

Base Level

Lowest point to which a stream erodes, with Absolute base level being sea level

Glaciers

Thick mass of ice originating from snow compaction and recrystallization

Milankovitch Cycles

Changes in orbital dynamics linked to glacial oscillations

Uniformitarianism

Geological processes are uniform through time, implying a very old Earth

Steno’s Principles

Superposition, Original Horizontality, Lateral Continuity, Cross-Cutting Relationships in stratigraphic age relationships

Faulting

The fault must be younger than the original layering of the beds.

Unconformities

Temporal gaps at the contact separating two successive rock units due to erosion or a period of no deposition.

Angular Unconformity

Underlying strata tilting, erosional surfaces, paleosols, gravel lag deposit.

Disconformity

Underlying and overlying strata parallel, irregular erosional surfaces, paleosols, gravel lag deposit.

Nonconformity

Sedimentary strata overlying older igneous/metamorphic rocks exposed to erosion before being covered.

Stratigraphy

Study of stratified rocks, including geometric relations, compositions, origins, and age relations.

Correlation

Demonstrating correspondence between geographically separated parts of a stratigraphic unit.

Lithostratigraphy

Produces a "layer-cake" pattern in rock units with boundaries assumed to represent time.

Facies

Set of characteristics of a rock body presenting a particular environment, with lateral shifts recorded in vertical strata.

Biostratigraphy

Defined by fossil content, including stratigraphic range and biozones based on taxa ranges in the record.

Relative Age - Fossils

Fossils provide a means of establishing the relative ages of rocks based on Smith's principle of fossil succession.

Absolute Age - Radiometric Dating

Dating based on the decay of a radioactive parent isotope to a stable daughter isotope at a fixed rate.