Unconformities As + A2 Flashcards

Question

Delta top

Answer 1

Above water mostly dis channels + swap + flood plains swap = anaerobic = form peat = diagentic processes = form coal Trees grow here = form seat earth (sand and clay rich soil delta switching- channles oft change course lateral changes in coarse to sea Sep dep here called TOP SETS C grained + gravel to Channel sandstone (often crossbedded)

Answer 2

River meets sea C grained dep first to silt last (finer lower down and marine fossils may be found) front of delta eventually migrates into sea - leads to vert succession (fining down) Sed dep here called FORE SETS C sand oft crossbedded crescent shaped mouth bars form here E lost as enters sea = very clean sand as current removes fine sed

Answer 3

Dep at low E in deeper H2O Dep here called BOTTOM SET clay and silt thinly bedded lacks sed structures lithify = form Shale May contain marine fossils

Answer 4

Dep at low E in deeper H2O Dep here called BOTTOM SET clay and silt thinly bedded lacks sed structures lithify = form Shale May contain marine fossils

Answer 5

form as Delta progrades into sea D top overlays earlier D front Shale-silt-sandstone-seat earth-coal (upward) coal and roots give away

Answer 6

Cresent shaped mouth bars silt and sand where dis channel enters sea

Answer 7

Sorted by size often sub mature C nearer source med downstream e.g. sand fine at mouth e.g. clay some rivers end in shallow marine=quick dep

Answer 8

Min mature eroded by attrition and abrasion calcite sometimes present usually in sol to dry and arid texturally mature (W rounded and sorted) Highest E

Answer 9

Poor sorted tillite has large range angular Glacial till = dep name May be transported by melt water = fluvial glacial dep= like river

Answer 10

sep dep in littoral zone (H to L tide) High E also dep on cont shelf see sorting with distance

Answer 11

Polymicritic = C grained sed rock containing clasts of many diff rock types Oligomictic = " few diff rock types Monomicritic = " single rock type

Answer 12

Beach and Shallow sea

Answer 13

all the characteristics of a sedimentary rock that are produced by its environment of deposition and allow it to be distinguished from rock deposited in laterally adjacent environment

Answer 14

vertical succession of facies reflects lateral changes in the environment e.g. transgression when dep enviro migrates laterally sed of dep can lay on top of each other

Answer 15

any thing associated with rocks that is non living all physical + chemical characteristics

Answer 16

includes all the palaeological characteristics of a rock

Answer 17

a specific sequence of rocks associated with a type of environmental change e.g. transgression limestone-shale-sandstone-pebbles

Answer 18

relies on recognizing rock types or sequence/succession of rock types marker horizons useful as rare and easily identifiable e.g. iridium usually large scale or whole earth

Answer 19

short distance-use relative thickness/pattern of thickness varve deposits used for correlation- alt light dark layers sed in glacial lake, vary in thickness based for summer dep due to amount of meltwater produced downhole logging- create borehole-send equipment down-take tests to find properties- match up layers

Answer 20

diachronus beds- same lithology but dep at diff times look the same transgression and regressions - sandstone dep at 2 places but diff times but look same lithologically

Answer 21

use assemblages of fossils to find rocks of same age fossil or trace fossils contained in rocks, assume same age zone fossils= most useful

Answer 22

evolved rapidly + short stratographic range abundant easily preserved- hard easily identifiable found in lots of different rock types wide geo distribution best- ammonites, trilobites and graptolites

Answer 23

fossils may only be found in 1 enviroment so only in 1 or 2 rock types some fossils have large range - along time without much change so give large age range some fossils = delicate so only preseved in low e enviro not all sed rocks contain fossils take sig amount of time to spread around world - so diff time period first and last apperance hard to pinpoint weather and redep in 2nd rock dervied fossil cause confusion

Answer 24

all unconformities represent a break in time or a period when no sediment was deposited. result of changes in enviro or changes in earths movements and erosion usually represented are a squiggly line

Answer 25

Angular non-conformity disconforminty

Answer 26

old beds are dipped young beds are horizontal caused by erosion most likely to come up

Answer 27

old beds are horizontal and so are young beds erosion causes it hard to spot

Answer 28

young sedimentary rock is horizontal on top of older igneous rock e.g. eroded batholith exposed at surface

Answer 29

limited by church ideas idea that rocks and structures were formed by violent large scale short scale events e.g. earthquakes explained mass extinctions in fossil record

Answer 30

hutton observed erosion to sedimentation to sedimentary rock 'great geological cycle'= formation and destruction of rocks observed that some processes are very slow - life evolves by gradual changes so rocks also take a long time to form no reason it should be different now than in the past

Answer 31

theory that changes in earths crust during geological history have resulted from the actions of continuous uniform processes

Answer 32

ripple marks crossbedding graded bedding desiccation cracks salt pseudomorphs imbricate structure

Answer 33

symm-formed by oscillating current most common at beach - tides (bidirectional flow) saltation assym-formed by current in 1 direction common in rivers + shallow sea + desert (wind) rivers, beach, shallow sea

Answer 34

sand moved by wind + river + marine current (high e) deposited - form dunes + sand bars unidirectional flow gentle slope on windward side - steep on lee side as avalanched (max 37 degrees) dunes migrate only slip face is preserved - produces crossbedding set deserts - larger m or rivers- smaller cm

Answer 35

largest heaviest grains at bottom, finer on top progressively finer abrupt change at bedding plane forms when e levels drop + sediment settles out of suspension found in sandstones + conglomerates forms in rivers- lakes, turbidite

Answer 36

only in clay rich sediment loss of H2O due to evap - mud contracts forms polygonal shaped blocks separated by cracks each crack has V shaped cross section - wide top narrow base as more evap at top cracks are only preserved is they are infilled with sediment playa lakes/ arrid enviro

Answer 37

cubic halite crystals grow at surface of bed due to evap of salty water as sed dries out in heat crystals partly embedded in sed once dry the lake refills with H2O - crystals dissolve and the moulds are infilled with sediment - takes on cube shape of halite crystal less soluble salts come out of sultion first round edges of lake playa lake. arrid

Answer 38

pebbles roll along stream bed + pile up against each other flat disk + blade like pebbles stack up against each other long axis is roughly parallel orientation provides max resistance to movement pebbles inclined in an upstream direction tops point down stream in density flow they point in flow direction river

Answer 39

way up - slope should be concave if they are convex they are upside down current direction - only asymmetrical, gentle slope inclines in direction current symm = equal flow in both direction depositional environment- most are rivers or water - symmetrical always intertidal if small scale asymmetrical- large scale - desert small scale - river

Answer 40

way up - right way up convex wrong way convex current direction -remains steep side of asymmetrical ripple mark so we can tell direction in same way deposition environment - river or wind large scale (m) - desert small scale (cm) - river

Answer 41

way up - fining up is correct, fining down wrong way up doesn't indicated current direction deposition environment-associated with mass sed drop of continental shelf e.g. turbidite

Answer 42

way up - correct wide at top narrow at the bottom don't show current direction environment of deposition - playa lake, arid wet- dry

Answer 43

Way up - no current direction - yes, dip of pebbles is opposite to current direction environment of deposition- river (fluvial) sometimes seen post tsunami

Answer 44

way up - no current direction - no deposition environment - arid evaporation (playa lake)