Changes

==Planktonic vs. benthic “tops”==

==Planktonic vs. benthic “tops”==

Planktonic (floating) and nektonic (swimming) organisms are generally less affected by local environmental factors such as water depth, physical obstacles, or changes in substrate than are benthic species (bottom dwellers). This characteristic makes the fossils of planktonic forms—particularly calcareous nannofossils, planktonic foraminifera, dinoflagellates, and graptolites—and nektonic organisms such as conodonts excellent regional and even worldwide time markers in marine strata. Summaries of zonations based on the ranges of planktonic microorganisms include Blow<ref name=ch17r17>Blow, W., H., 1979, The Cainozoic Globigerinida: Leiden, E., J. Brill, 1413 p.</ref> Kennett and Srinivasan<ref name=ch17r51>Kennett, J., P., Srinivasan, M., S., 1983, Neogene Planktonic Foraminifera: APhylogenetic Atlas: Stroudsburg, Pennsylvania, Hutchinson Ross, 265 p.</ref> Bolli et al.<ref name=ch17r18>Bolli, H., M., Saunders, J., B., Perch-Nielsen, K., 1985, Plankton Stratigraphy: Cambridge, Cambridge University Press, 1032 p.</ref> Berggren and Miller<ref name=ch17r11>Berggren, W., A., Miller, K., G., 1988, Paleogene tropical planktonic foraminiferal biostratigraphy and magnetobiochronology: Micro[[paleontology]], vol. 34, no. 4. p. 362–380., 10., 2307/1485604</ref> and Berggren et al..<ref name=ch17r15>Berggren, W., A., Kent, D., V., Swisher, C., Aubry, M.-P., 1995, A revised Cenozoic geochronology and chronostratigraphy, in Berggren, W., A., Kent, D., V., Aubry, M.-P., Hardenbol, J., eds., Geochronology, Time Scales, and Global Stratigraphic Correlation: Society for Sedimentary Geology (SEPM) Special Publication 54, p. 127–208.</ref>

Planktonic (floating) and nektonic (swimming) organisms are generally less affected by local environmental factors such as water depth, physical obstacles, or changes in substrate than are benthic species (bottom dwellers). This characteristic makes the fossils of planktonic forms—particularly calcareous nannofossils, planktonic foraminifera, dinoflagellates, and graptolites—and nektonic organisms such as conodonts excellent regional and even worldwide time markers in marine strata. Summaries of zonations based on the ranges of planktonic microorganisms include Blow<ref name=ch17r17>Blow, W., H., 1979, The Cainozoic Globigerinida: Leiden, E., J. Brill, 1413 p.</ref> Kennett and Srinivasan<ref name=ch17r51>Kennett, J., P., Srinivasan, M., S., 1983, Neogene Planktonic Foraminifera: APhylogenetic Atlas: Stroudsburg, Pennsylvania, Hutchinson Ross, 265 p.</ref> Bolli et al.<ref name=ch17r18>Bolli, H., M., Saunders, J., B., Perch-Nielsen, K., 1985, Plankton Stratigraphy: Cambridge, Cambridge University Press, 1032 p.</ref> Berggren and Miller<ref name=ch17r11>Berggren, W., A., Miller, K., G., 1988, Paleogene tropical planktonic foraminiferal biostratigraphy and magnetobiochronology: Micro[[paleontology]], vol. 34, no. 4. p. 362–380., 10., 2307/1485604</ref> and Berggren et al..<ref name=ch17r15>Berggren, W., A., Kent, D., V., Swisher, C., Aubry, M.-P., 1995, A revised Cenozoic geochronology and chronostratigraphy, in Berggren, W., A., Kent, D., V., Aubry, M.-P., Hardenbol, J., eds., Geochronology, Time Scales, and Global Stratigraphic Correlation: Society for Sedimentary Geology (SEPM) Special Publication 54, p. 127–208.</ref>

Benthic taxa are most useful for detailed local correlations and paleoenvironments. Many are too environmentally sensitive, however, to be good regional markers. Distribution of benthic forms is frequently restricted by basin configuration or other barriers to migration.

Benthic taxa are most useful for detailed local correlations and paleoenvironments. Many are too environmentally sensitive, however, to be good regional markers. Distribution of benthic forms is frequently restricted by basin configuration or other barriers to migration.

Changes in the abundance or species composition of fossil assemblages within a biostratigraphic zone are useful in refining correlations.

Changes in the abundance or species composition of fossil assemblages within a biostratigraphic zone are useful in refining correlations.

The illustration below shows how variations in the relative proportion of individual species within assemblages can be used to characterize correlatable fossil “populations.”

[[:file:applied-paleontology_fig17-15.png|Figure 2]] shows how variations in the relative proportion of individual species within assemblages can be used to characterize correlatable fossil “populations.”

[[file:applied-paleontology_fig17-15.png|thumb|{{figure number|17-15}}See text for explanation.]]

[[file:applied-paleontology_fig17-16.png|left|thumb|{{figure number|3}}See text for explanation.]]

==Ratios of in situ vs. reworked species==

==Ratios of in situ vs. reworked species==

Ratios or percentages of in situ vs. reworked calcareous nannofossil or palynomorph species may differentiate among distinct sediment packages.

Ratios or percentages of in situ vs. reworked calcareous nannofossil or palynomorph species may differentiate among distinct sediment packages.

The figure below shows how a comparison of the presence and abundance of different components of the assemblage (e.g., in situ vs. reworked faunas and floras) may enhance local correlations and help us identify sediment source. Generally, where in situ fossils are relatively abundant, reworked fossils are less common.

[[:file:applied-paleontology_fig17-16.png|Figure 3]] shows how a comparison of the presence and abundance of different components of the assemblage (e.g., in situ vs. reworked faunas and floras) may enhance local correlations and help us identify sediment source. Generally, where in situ fossils are relatively abundant, reworked fossils are less common.

 

==High-resolution biostratigraphy==

==High-resolution biostratigraphy==