Marine Microfossils
Dr. J Bret Bennington
Department 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 amoebalike protozoans.
• Foraminifera - calcareous (calcium
carbonate) or agglutinated (test composed
of cemented grains of sand or other
sediment).
• Radiolaria - test composed of silica.
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
Protistan Microfossils
Calcite
Foraminifera
Planktic forams
Calcite
Protistan Microfossils
Radiolarians - Spumellarians
Protistan Microfossils
Silica
Radiolarians - Nacellarians
Protistan Microfossils
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.
Ostracods - Arthropoda
Animal Microfossils
calcite
Conodonts - Vertebrata
Animal Microfossils
Conodonts - Vertebrata
conodont apparatus
Animal Microfossils
Conodonts - Vertebrata
Animal Microfossils
Conodonts - Vertebrata
microwear facets
Animal Microfossils
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).
Coccolithophorids - Haptophyta
Algal Microfossils
calcite
Chalk Cliffs, England
Diatoms - Chrysophyta
Pennate - benthic, parasitic
Algal Microfossils
silica
Centric - planktic
Diatoms - Chrysophyta
silica
frustules
Algal Microfossils
Diatoms - Chrysophyta
Algal Microfossils
silica
Dinoflagellates - Pyrrhophyta
living
Algal Microfossils
Sporopollenin
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.
Stable Isotopes
Oxygen
O16
O18
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
Increasing 18O in calcite relative to water
Change in isotopic ratio in carbonate shell with change in water
temperature.
Modern sea-surface temperature
d18O due to
ice buildup
less ice
Glaciations
cause more
d18O to
accumulate in
seawater.
This happens
because 16O
evaporates
preferentially
and becomes
trapped on
land as glacial
ice.
negative excursion
H216O
more ice
positive excursion
Average d18O curve
from 5 deep sea cores
(foram calcite).
warming
After Imbrie et al. (1984)
cooling
Onset of Cenozoic cooling trend development of cold deep ocean circulation.
Navesink Formation, central New Jersey
70X
Benthic foraminifera
70X
Benthic foraminifera
Planktic foraminifera
70X
70X
Ostracod
70X
Ostracod valve
70X
Burrowing echinoid spine
70X
Fish denticle