paper 2 Flashcards
Diagenesis definition
the chemical and physical processes that turn sediments into sedimentary rocks
Diagenesis processes
1) cementation - infill of pore spaces by mineral cement
2) compaction - sediments squeezed by overlying sediment which decreases porosity and permeability
3) recrystallisation - crystals change in size and shape
4) dissolution - minerals dissolve where grains press into each other.
siliclastic rocks
silica based rocks such as mudstone and sandstone
methods to improve a dame site
Grouting - drilling hole and pumping in liquid cement to reduce porosity and improve stability of faults.
construct barrier underneath dam - prevent leakage underneath keeping it more stable
how does temperature affect silica content of magma and why
silica content increases as temperature decreases due to fractional crystallisation which crystalises some contents of the magma which causes the silica to be more strong in the remaining mixture.
How does silica affect magma
increased viscosity, - therefore divergent plate boundaries are mafic which produce shield volcanoes and convergent plate boundaries are silicic which create strata volcanoes.
what is the focus
point inside the earth where the earthquake occurs
what are ripple marks
sedimentary structures which indicate agitation by water
what are carbon films
thin coatings of carbon
mechanism of preservation resulting in carbon films
1) soft organism contains organic carbon
2) burial
3) subject to load pressure
4) causes increased temp and pressure
5) increased carbon % leaving carbon coating
epifaunal/infaunal definitions
epifaunal - lived attached to the surface
infaunal - live in the sediment eg in burrows
process of trilobites growing
1) cephalon breaks along facial structure
2) soft body exits the exoskelaton
3) it is vulnerable until new exoskelaton hardens
sedimentary basin
low lying area in the earths crust where sediments accumulate
how can the geometry of a sedimentary basin be determined
1) seismic surveys
2) correlation of sediments
isochemical
having a constant chemical composition
names of igneous intrusions by depth
hypabyssal - shallow intrusion
plutonic - deep intrusion
bowens reaction series elements
1) olivine
2) pyroxene
3) hornblend
4) biotite
fractional crystalisation
when certain elements crystalise faster resulting in a different sollution
gravity settling
metallic minerals have higher densities which causes them to sink to the bottom of the magma chamber
filter pressing
when a liquid-crystal magma mixture is subject to pressure, the liquid will be forced out
BIF formation
1) iron in seawater originates from MOR volcanism
2) oxygen produced in the iron from photosynthesis
3) oxidation causes iron minerals to come out of solution
Wilson cycle definition
process that explains the opening and closing of ocean basins due to the formation of supercontinents
Wilson cycle process
1) rifting and break up of continents
2) opening of oceans by seafloor spreading
3 closure of oceans by subduction
4) mountain building by convergent continent-continent collision
facies association
a group of sediments which represent one depositional environment
erosion
the wearing of sediment during transport
mature sediment
grains in the sediment are well sorted and well rounded
types of cement
calcite, quartz, hematite, limestone
dessecation cracks
cracks throughout soil due to lack of moisture
cross bedding
forms during deposition on inclined surfaces and indicates the depositional environment had a constant flow
p wave shadow zone
103-142 degrees - caused by liquid outer core refracting the waves
relative dating methods
1) superposition - sediments deposited ontop of eachother with the lowest one being the oldest
2) cross cutting relationships - unconformity must be younger than the rock it cuts through
3) original hoizontallity - beds were deposited horizontally
4) included fragments - rocks containing fragments of older rocks
methods of geotechnical site investigation
1) surface mapping (of folds and faults)
2) subsurface mapping (use of boreholes)
3) satellite photos
convergent evolution
independent evolution of similar features with different unrelated species
saurischian dinosaurs
Saurischian: reptile dinosaurs (forwards facing pubis) could be either:
* Therapod – Bipedal with sharp curved teeth, flesh eater.
* Sauropod – large size, long neck/tail, for legged stance, and herbivores.
ornithischian dinosaurs
Ornithischian: Bird dinosaurs (backward facing pubis)
* Bipedal
* Plant eaters
* Thumb spike for defence
* Legs much larger than arms
