zone fossils Flashcards
best 3 fossils to use as zone fossils
amomoids
graptolites
micrfossils
why are graptolites good zone fossils
can establish zones in the ordovician as small as 4Ma
what period are grapolites associated with
Ordovician
when did graptolites go extinct
devonian
what about composition makes graptolites a good zone fossil
scleroprotien shell = well preserved
what is bad about graptolites as zone fossils
too delicate to be preserved in some environments
what is good about ammonoids as zone fossils
widely distributed (NECKTONIC)
rapid evolution
numerous
what is good about ammoniod composition as a zone fossil
calcereous exoskeleton
bad thing about ammonid zone fossils
destroyed in high energy seas
good points about microfossil zone fossils
numerous
preserved in small chippings
can correlate boreholes
benefits of radiolaria (microfossils) as zone fossils
SILICA skeleton - can be preserved below carbon compensation depth
problems with microfossils as zone fossils
small = difficult to work with
