Marine Microfossils

Dr. J Bret BenningtonDepartment of Geology

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.

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.

Protistan Microfossils

Foraminifera - sarcodina (amoeba)

Protistan Microfossils

Foraminifera - sarcodina (amoeba)

Benthic forams• live in sediments• relatively large

Planktic forams• live floating in the water column

• relatively small

Protistan Microfossils

Foraminifera - sarcodina (amoeba)

Benthic forams

Calcite

Protistan Microfossils

Foraminifera

Planktic forams

Calcite

Protistan Microfossils

Radiolarians - Spumellarians

Silica

Protistan Microfossils

Radiolarians - Nacellarians

Silica

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.

Animal Microfossils

Ostracods - Arthropoda

calcite

Animal Microfossils

Conodonts - Vertebrata

Animal Microfossils

Conodonts - Vertebrata

conodont apparatus

Animal Microfossils

Conodonts - Vertebrata

Animal Microfossils

Conodonts - Vertebrata

microwear facets

calcium phosphate

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).

Algal Microfossils

Coccolithophorids - Haptophyta calcite

Chalk Cliffs, England

Algal Microfossils

Diatoms - Chrysophyta silica

Pennate - benthic, parasitic Centric - planktic

Algal Microfossils

Diatoms - Chrysophyta silica

frustules

Algal Microfossils

Diatoms - Chrysophyta silica

Algal Microfossils

Dinoflagellates - Pyrrhophyta Sporopollenin

living fossil

Dinoflagellates - Pyrrhophyta

Living cell Cyst

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.

From Sugarman, et. al, 1995

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

From Sugarman, et. al, 1995

Coccoliths

From Sugarman, et. al, 1995

Foraminifera

Deep Sea Drilling Project ship - Glomar Challenger

Recovering sediment cores from the deep ocean.

Foraminifera

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

O16 O18

Stable IsotopesOxygen

99.76% .2%

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.

Mass Spectrometer

Incr

easi

ng 18

O in

cal

cite

rel

ativ

e to

wat

er

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

Modern sea-surface temperature

more ice

positive excursion

less ice

negative excursion

18O due to ice buildup

Glaciations cause more 18O to accumulate in seawater.

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

H216O

cooling

warming

Average 18O curvefrom 5 deep sea cores(foram calcite).After Imbrie et al. (1984)

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

Navesink Formation, central New Jersey

70XBenthic foraminifera

Benthic foraminifera

70X

Planktic foraminifera 70X

Ostracod

70X

Ostracod valve

70X

Burrowing echinoid spine

70X

Fish denticle

70X