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BIOSTRATIGRAPHY: Age Dating & Correlation. GEOL 3213. GEOLOGIC TIME SCALE Know the: periods eras eons Ma: 1.6 65 251 410 544 2500 4000 4650. 201. 251. 4650. FORAMINIFERA. Simplified evolutionary chart based on wall structure 5 major wall types: Pseudochitinous Arenaceous
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BIOSTRATIGRAPHY:Age Dating & Correlation GEOL 3213
GEOLOGIC TIME SCALE • Know the: • periods • eras • eons • Ma: • 1.6 • 65 • 251 • 410 • 544 • 2500 • 4000 • 4650 201 251 4650
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
Acmes of Diversity • Late Devonian to Carboniferous • Ordovician (especially Medial Ordovician)
Number of Genera Per Epoch • 2 major acmes • 4 extinctions: • End Ordovician • End Devonian • End Permian • End Triassic
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.
Conodont Index Fossil Genera • Many conodont genera have short time ranges!
Ranges of Fossils • Indicate time • Experience • Evolution
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 geologistswho use “well cuttings” concurrent- range zone time assemblage zone
Why Microfossils for Correlation? • Short geologic range. • 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. ] • Distinctive & easily recognized forms by non-specialists. • 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.)]
Kinds of Biozones • Taxon range zone • Named after the taxon • Acme zone • Great abundance of a species • Restricted to only a short part of its total duration • Concurrent-range zone • Overlapping range is the biozone • Named usually after both taxa, e. g., 2 species • 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
