marine microfossils dr. j bret bennington department of geology
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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