(See also Pat's basic geology study guide
destructive process at or near the Earth’s surface where rocks are broken down either mechanically or chemically without erosion; the end products are particles (clasts) and solutions
is the mechanical breakdown or disintegration of rocks in place that results in clasts or fragments:
The main mechanisms for physical weathering are…
freezing of water
salt crystal formation
is the chemical breakdown of rocks that results in solutions
The main mechanisms for chemical weathering are…
form when particles (clasts) and/or solutions that result from weathering are eroded, transported, deposited, and lithified.
lithification is result of cementation and compaction
main cements: oxides (commonly reddish), calcite (commonly effervesces), or silica
are places where sediment can accumulate; main types: terrestrial, marine, nearshore marine
other types: lacustrine (lakes);
higher energy (big clasts) vs. low energy (fine particles settling out of suspension)
terrestrial includes alluvial fans, rivers, dunes caves, peat bogs, (harder to preserve terrestrial ones owing to erosion)
marine and nearshore marine include reefs, abyssal ocean, continental slope and fan, beach, delta, turbidity currents, and nearshore
Made of particles or clasts (detritus); includes such rocks as conglomerate (w/ rounded gravel and larger clasts), breccia (w/ angular larger clasts), sandstone, siltstone, shale, mudstone
know sediment name based on clast size: e.g. boulder > 256 mm; cobble 256–64 mm; pebble 64–2 mm; sand 2–1/16 mm; silt 1/16–1/256 mm; clay <1/256 mm; gravel—general term for an assortment of larger particles regardless of size.
Precipitated from solutions; include limestones (many types—see lab handout) gypsum, chert (deep sea silica), halite, diatomite
Includes coal and oil shale
rounded vs. angular
well-sorted vs. poorly sorted
boulder >1/256 mm
cross bed (How do these form? What can they tell us?)
ripple marks (assymentrical or current; symmetrical or oscillation)
unconformities, angular unconformity
form via recrystallization in the solid state owing to heat and/or pressure
Regional—form over huge areas where mountain building (convergent boundaries) causes thickening crust and/or faults that carry rocks down to depth and then back up.
Contact—form adjacent to hot intrusion, e.g. plutons (batholiths and stocks), dikes, sills, and laccoliths. Examples include hornfels
What are the geothermal gradient and pressure gradient?
parent rock or protolith
foliated (platy or rod_shaped crystals) vs. non-foliated (calcite or quartz of other equant-shaped mineral)
metamorphic grade, index minerals, metamorphic facies (ex: blueschist facies, the zeolite facies)
foliated metamorphick rocks, examples: slate, phyllite, schist, gneiss, migmatite
non-foliated metamorphic rocks: marble, greenstone, hornfels, quartzite
relative dating—simply ways to determine if rocks are older or younger than others; uses principles of stratigraphy (see below)
absolute dating—ways of using the radiometric clocks of unstable isotopes to date rocks or organic material: e.g. Uranium-lead dating; radiocarbon dating, half life, etc.
original horizontality – tilted beds have been deformed by folding and/or faulting
superposition – what’s on top is younger
cross-cutting relationships – what cuts through is younger
inclusion – what’s picked up or included is older than what it’s in