GEOS102- SEDIMENTARY/METAMORPHIC ROCKS

detrital/clastic

sedimentary rock made up of solid particles. eg sandstone, mudstone

chemical/non detrital

sedimentary rock made up of dissolved chemicals. eg limestone, gypsum, chert

silt stone

grain too fine to see but gritty against teeth

mudstone

grain too fine to see but smooth against teeth

disc form

grain form where the long and intermediate lengths are equal but not the short (round but flat)

spheroid form

grain form where all sides are equal (round)

blade form

grain form where all sides are different (long and flat)

roller form

grain form where the intermediate and short sides are equal (round but long)

roller rock

this form is generally found down a river

disc

this form is generally found on a beach

ripples

sedimentary structure where you can see symmetry and current direction

cross bed

sedimentary structure where you can tell younging and current direction

graded bedding

sedimentary structure where you can see younging direction

convolute bedding

sedimentary structure which you can't tell current direction or younging

load cast

sedimentary structure where you can tell younging direction (but its backwards!)

flute casts

sedimentary structure where you can tell younging and current flow (but its backwards!)

law of superposition

in a sequence of sedimentary rocks, the oldest is at the bottom and the youngest is at the top

law or original horizontality

Most sediments are laid down in strata (beds) that are horizontal, or nearly so, and which are often parallel

Law of lateral continuity

Layers of sediment initially extend laterally in all directions

principle of cross-cutting relationships

a geological feature the cuts across another geological feature, is younger than the feature it cuts through

principle of faunal succession

fossil organisms appear, exist for a period of time, then go extinct in an evolutionary ordered succession

principle of inclusions

a rock fragment or included rock found in another rock must be older than the rock enclosing it

walther's law

rock strata conformably overlying another must have been deposited in an adjacent depositional environment

non conformity

seperates non-sedimentary rocks from younger sedimentary rocks

discomformity

seperates two sequences of sedimentary rocks where the lower sequence has been eroded but not tilted prior to deposition of a younger sequence

angular unconformity

seperates two sequences of sedimentary rocks the lower sequence tilted and eroded prior to younger sequence

paraconformity

seperates two sequences of sedimentary rocks of different ages with no erosion apparent an the unconformity is parallel to bedding

protolith

original rock in a metamorphic rock

regional metamorphism

metamorphism which involves pressure, temperature and deformation

contact metamorphism

metamorphism which is dominated by temperature (formed from lava intrusion)

foliation

alignment of platy minerals

schistosity

foliation in a high grade metamorphic rock, when mica is visible

slate texture

lowest metamorphic grade: fine grained, splits into sheet-like pieces, parallel upper and lower surfaces

phylite texture

lower metamorphic grade: might be greenish, no longer parallel surfaces, fine grained

schist texture

higher metamorphic grade: coarse grained, light and dark grains visible, micas create strong foliation. might be garnet

gneiss texture

highest metamorphic grade: light and dark minerals in distinct layers

hornfels

rock which is formed by being the closest to the igneous intrusion

geothermal gradient

rate of increase in temperature with increasing depth

low geothermal gradient

low temperature, high pressure facies. zeolite, then blueschist

normal geothermal gradient

regional metamorphism, high temperature, high pressure. zeolite, greenschist, amphibolite, granulite

high geothermal gradient

contact metamorphism, high temperature, low pressure