BIOSTRATIGRAPHY: Age Dating

1
BIOSTRATIGRAPHYAge Dating Correlation

• GEOL 3213

2

• GEOLOGIC TIME SCALE
• Know the
• periods
• eras
• eons
• Ma
• 1.6
• 65
• 251
• 410
• 544
• 2500
• 4000
• 4650

201
251
4650
3
FORAMINIFERA

• Simplified evolutionary chart based on wall
  structure
• 5 major wall types
• Pseudochitinous
• Arenaceous
• Microgranular
• Porcelaneous
• Hyaline
• Higher taxa have long ranges
• Higher taxa 1st approximations of ages

4
Acmes of Diversity

• Late Devonian to Carboniferous
• Ordovician (especially Medial Ordovician)

Conodonts
5
Number of Genera Per Epoch

• 2 major acmes
• 4 extinctions
• End Ordovician
• End Devonian
• End Permian
• End Triassic

6
Biostratigraphic Zonation

• Some conodont zones represent only about 1 Ma,
  while others may be 2-3 Ma long.
• This is good for the Paleozoic Era.

7
Conodont Index Fossil Genera

• Many conodont genera have short time ranges!

8
Ranges of Fossils

• Indicate time
• Experience
• Evolution

9
INDEX FOSSILS

• Used for dating
• rocks
• geologic events
• Biozones
• different kinds
• range zones are very common
• named for 1 or 2 fossils in zone
• Excellent index fossil
• 1) narrow time range
• 2) wide geographic distribution
• 3) abundant
• 4) easily recognized
• 5) microscopic for petroleum geologists who use
  well cuttings

concurrent- range zone
time
assemblage zone
10
Why Microfossils for Correlation?

1. Short geologic range.
2. Widespread distribution. Many microscopic
   organisms are part of the floating plankton in
   the oceans. These species are readily distributed
   over large areas by ocean currents. Facies
   independence (not restricted to one particular
   rock type present in many rock types). For
   example, plankton falls into any sediment that is
   forming on the sea floor.
3. Distinctive easily recognized forms by
   non-specialists.
4. Abundance Because microfossils are so tiny,
   hundreds to thousands of specimens may be present
   in small sediment samples. Preservable
   (fossilizable) hard part fossils should be
   abundant enough to be collected in sufficient
   quantity for thorough study. (Petroleum
   geologists like them because many can survive the
   rigors of the drill bit.)

11
Kinds of Biozones

• Taxon range zone
• Defined by 1st last appearance of a single
  taxon
• Named after the taxon
• Teilzone
• Observed range zone in a local section
• Acme zone (peak zone)
• Great abundance of a species
• Restricted to only a short part of its total
  duration
• Concurrent-range zone ( 2 taxon)
• Overlapping range is the biozone
• Named usually after both taxa, e. g., 2 species
• Interval zones
• Successive 1st or last occurrences of partially
  overlapping ranges.
• Lineage zone (phylozones)
• Successive first appearances of evolving species
  in a lineage
• Assemblage zone
• Makes use of almost every species in the
  assemblage
• Hard to work with because involves many taxa
• May be the best kind of biozone because data rich

12
End of File
13

• Tree rings