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Dr. J Bret Bennington Department of Geology. Marine Microfossils. What are marine microfossils?. Fossilized remains of small organisms or tiny hardparts of larger organisms. Plankton Benthic fauna Many different groups representing animals, protists, and a variety of algae.

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Marine Microfossils

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Marine microfossils l.jpg

Dr. J Bret Bennington

Department of Geology

Marine Microfossils

What are marine microfossils l.jpg

What are marine microfossils?

  • Fossilized remains of small organisms or tiny hardparts of larger organisms.

  • Plankton

  • Benthic fauna

  • Many different groups representing animals, protists, and a variety of algae.

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Protistan Microfossils

  • Mineralized test (shell) formed by amoeba-like protozoans.

  • Foraminifera - calcareous (calcium carbonate) or agglutinated (test composed of cemented grains of sand or other sediment).

  • Radiolaria - test composed of silica.

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Foraminifera - sarcodina (amoeba)

Protistan Microfossils

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Foraminifera - sarcodina (amoeba)

  • Benthic forams

  • live in sediments

  • relatively large

  • Planktic forams

  • live floating in the water column

  • relatively small

Protistan Microfossils

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Foraminifera - sarcodina (amoeba)

Benthic forams

Protistan Microfossils


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Planktic forams


Protistan Microfossils

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Radiolarians - Spumellarians

Protistan Microfossils


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Radiolarians - Nacellarians

Protistan Microfossils


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Animal Microfossils

  • Mineralized shells and teeth produced by metazoans (multicellular animals).

  • Ostracods - calcareous (calcium carbonate) shell produced by tiny crustaceans.

  • Conodonts - calcium phosphate “teeth” produced by an extinct group of vermiform (worm-like) vertebrates.

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Ostracods - Arthropoda

Animal Microfossils


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Conodonts - Vertebrata

Animal Microfossils

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Conodonts - Vertebrata

conodont apparatus

Animal Microfossils

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Conodonts - Vertebrata

Animal Microfossils

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microwear facets

Conodonts - Vertebrata

Animal Microfossils

calcium phosphate

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Algal Microfossils

  • Mineralized tests and plates produced by a variety of unicellular algae.

  • Coccolithophorids - tiny algae that produce calcareous plates - main component of chalk.

  • Diatoms - algal cells that produce paired tests (called frustules) composed of silica.

  • Dinoflagellates - marine algae that produce organic cysts preserved in sedimentary rock. Also the cause of most harmful algal blooms (HABs).

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Coccolithophorids - Haptophyta


Algal Microfossils

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Chalk Cliffs, England

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Diatoms - Chrysophyta


Pennate - benthic, parasitic

Centric - planktic

Algal Microfossils

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Diatoms - Chrysophyta


Algal Microfossils

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Diatoms - Chrysophyta


Algal Microfossils

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Dinoflagellates - Pyrrhophyta




Algal Microfossils

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Dinoflagellates - Pyrrhophyta

Living cell


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Why are marine microfossils useful?

  • Biostratigraphy - dating rock layers using fossils.

  • Environmental reconstruction - identifying different marine environments in the past.

  • Paleothermometry - determining ocean water temperature in the past.

  • Paleoclimatology - reconstructing climate change through Earth’s history.

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From Sugarman, et. al, 1995

Biostratigraphic zones - intervals of time defined by the presence of particular fossil species.

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From Sugarman, et. al, 1995

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From Sugarman, et. al, 1995

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Deep Sea Drilling Project ship - Glomar Challenger

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Recovering sediment cores from the deep ocean.

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  • Fossil foram species can be used to date age of seafloor and sediment layers.

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Stable Isotopes




CO2 + H2O = HCO3-1 + H+

2 HCO3-1 + Ca++ = CaCO3 + H2CO3

  • O18 is preferentially removed from seawater during calcite formation.

  • This effect is sensitive to temperature.

  • Ratio of O18 / O16 in shell is temperature dependent.

  • Can be measured using a mass spectrometer.

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Mass Spectrometer

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Increasing 18O in calcite relative to water

Change in isotopic ratio in carbonate shell with change in water temperature.

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Modern sea-surface temperature

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less ice

negative excursion

more ice

positive excursion

d18O due to ice buildup

Glaciations cause more d18O to accumulate in seawater.

This happens because 16O evaporates preferentially and becomes trapped on land as glacial ice.


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Average d18O curve

from 5 deep sea cores

(foram calcite).

After Imbrie et al. (1984)

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Onset of Cenozoic cooling trend - development of cold deep ocean circulation.

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Navesink Formation, central New Jersey

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Benthic foraminifera

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Benthic foraminifera

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Planktic foraminifera

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Ostracod valve

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Burrowing echinoid spine

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Fish denticle

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