Ch 3 Microfossils and Biostratigraphy
Instructor Guide
INSTRUCTOR GUIDE
Chapter 3 Microfossils and Biostratigraphy
SUMMARY
Microfossils are important, and in places the dominant constituents of deep sea sediments
(see Chapter 2). The shells/hard parts of calcareous microfossils can be geochemically
analyzed, for example by stable isotopes of oxygen and carbon, which are powerful proxies
(indirect evidence) in paleoceanography and climate change studies (see Chapter 6).
Microfossil evolution has provided a rich archive for establishing relative time in marine
sedimentary sequences. In this chapter you will gain experience using microfossil distributions
in deep-sea cores to apply a biostratigraphic zonation and interpret relative age, correlate
from one region of the world ocean to another, and calculate rates of sediment
accumulation. In Part 3.1, you will learn about the major types of marine microfossils and
their habitats; you will consider their role in primary productivity in the world oceans,
their geologic record and diversity through time, as well as the relationship between
microfossil diversity and sea level changes through time. In Part 3.2, you will explore
microfossil distribution in a deep-sea core and consider microfossils as age indicators. In Part
3.3, you will apply microfossil first and last occurrences (datum levels) in a deep-sea core to
establish biostratigraphic zones. In Part 3.4, you will use these same microfossil datum levels
to determine sediment accumulation rates. In Part 3.5, you will explore the reliability of
microfossil datum levels in multiple locations.
Goal: to gain experience with the use of
microfossil evolution in establishing relative
time.
Objectives: After completing this exercise
your students should be able to:
1. Infer paleoecological and
paleobiological information using
microfossil distribution data.
2. Make observations about microfossil
abundance data and make hypotheses to
explain their observations.
3. Apply a biostratigraphic zonation to
microfossil abundance data and use it to
interpret relative ages.
4. Use microfossil data to calculate rates
of sediment accumulation.
5. Use microfossil data to test the
reliability of microfossil datum levels in
multiple locations, and correlate
sedimentary sequences at different
locations.
FIGURE 3.1. Four species of planktic foraminifers from the tropical western Atlantic: upper left:
Globigerinoides ruber, upper right: Globigerinoides sacculifer, lower left: Globorotalia menardii, lower
right: Neogloboquadrina dutertrei. Scale bar=100 µm (100 µm=0.1 mm). Photo courtesy of Mark Leckie.
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Ch 3 Microfossils and Biostratigraphy
Instructor Guide
I. How Can I Use All or Parts of this Exercise in my Class?
(based on Project 2061 instructional materials design.)
Part 3.1
Part 3.2
Part 3.3
Part 3.4
Part 3.5
Title (of each part)
What are
Microfossils?
Application of First
& Last Occurrences
30-45
minutes
Yes, but doing
Part 3.1 in
lecture works
well
Sediment
Accumulation
Rates
<30 minutes
Datum
Reliability
How much class time will I
need? (per part)
Can this be done
independently (i.e., as
homework)?
Microfossils in
Deep Sea
Sediment
<30 minutes
Yes, as
homework, lab
or discussion
section
~30 minutes, plus
discussion time
Yes, as homework,
lab or discussion
section
What content will students be introduced to in this exercise?
Phyto- & zooplankton
distributions, abundances &
X
X
X
diversity
Geologic timescale and/or
X
X
Geomagnetic polarity timescale
Sea level change
X
Trophic levels & productivity
X
Age determination using fossils,
index fossils, biozones, datums,
X
X
first/last occurrences
Extinction
X
X
Sed accum rates, age-depth
plots
Calibration & correlation of
X
different types of data
Unconformities, hiatus
Reliability and uncertainty
What types of transportable skills will students practice in this exercise?
Make observations (describe
X
X
X
what you see)
Plot data, determine lines of best
fit, interpret graphs, diagrams,
X
X
photos, tables
Pose hypotheses or predictions
X
X
X
Perform calculations & develop
quantitative skills
Decision-making, problem
X
X
X
solving & pattern recognition
What general prerequisite
Basic biology
Basic biology
Basic biology and
knowledge & skills are
and Earth
and Earth
Earth science
required?
science
science
What Anchor Exercises (or
Parts of Exercises) should be
done prior to this to guide
student interpretation &
reasoning?
Ch. 2:
Seafloor
Sediments
Part 3.1
Parts 3.1-3.2
Yes, as
homework,
lab or
discussion
section
X
<30
minutes
Yes, as
homework,
lab or
discussion
section
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Basic math
and Earth
science
Parts 3.1-3.3
Basic
geography
and Earth
science
Parts 3.13.4
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Ch 3 Microfossils and Biostratigraphy
What other resources or
materials do I need? (e.g.,
internet access to show on-line
video; access to maps, colored
pencils)
What student misconception
does this exercise address?
What forms of data are used
in this? (e.g., graphs, tables,
photos, maps)
What geographic locations
are these datasets from?
How can I use this exercise
to identify my students’ prior
knowledge
(i.e.,
student
misconceptions,
commonly
held beliefs)?
How
can
I
encourage
students to reflect on what
they have learned in this
exercise?
[Formative
Assessment]
How can I assess student
learning after they complete
all or part of the exercise?
[Summative Assessment]
Where can I go to for more
information on the science in
this exercise?
Instructor Guide
None
Access to world
map or ocean
floor map
None
None
Access to
world map
or ocean
floor map
Kingdoms of
life; how
productivity
works
Photos,
graphs
Evolution of life
(first and last
occurrences of
organisms)
Photos, map,
tables
How relative age is
assigned to (deepsea) sediments
How agedepth plots
are
constructed
Tables,
graph
Dispersal of
species;
science is
testable
Map,
tables
N/A
Western
equatorial
Pacific, NW
Pacific –
Shatsky Rise
NW Pacific –
Shatsky Rise, North
Pacific Ocean
NW Pacific –
Shatsky
Rise, eastern
equatorial
Pacific
NW Pacific –
Shatsky
Rise,
Caribbean
Sea
Diagram, chart,
tables
Prior knowledge and misconceptions can be identified by examining student
answers of open ended questions and/or though class discussion. Student
ideas on evolution, correlation, reliability will certainly be drawn out in this
exercise.
Exercise Parts can be concluded by asking: On note card (with or without name) to
turn in, answer: What did you find most interesting/helpful in the exercise we did
above? Does what we did model scientific practice? If so, how and if not, why not?
See suggestions in Summative Assessment section below.
See the Supplemental Materials and Reference sections below.
II. Annotated Student Worksheets (i.e., the ANSWER KEY)
This section includes the annotated copy of the student worksheets with answers for each Part
of this Chapter. This instructor guide contain the same sections as in the student book
chapter, but also includes additional information such as: useful tips, discussion points,
notes on places where students might get stuck, what specific points students
should come away with from an exercise so as to be prepared for further work, as
well as ideas and/or material for mini-lectures.
Part 3.1. What are Microfossils? Why are they Important in
Climate Change Science?
WHAT ARE MICROFOSSILS?
While there are many types of tiny animals and microorganisms living in the sunlit surface
waters of the ocean, at depth in the water column and on the seafloor, most of these
organisms do not possess the hard parts necessary for them to be preserved on the
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Ch 3 Microfossils and Biostratigraphy
Instructor Guide
sedimentary record as fossils. However, recalling from Chapter 2, there are some groups of
organisms that have mineralized shells or other hard parts consisting of carbonate
(CaCO3) or silica (SiO2), and others that possess a tough organic wall. The vast majority of
the “microfossils” preserved in deep-sea sediments are single-celled protists belonging to
the Kingdom Protoctista (i.e., not plants, not animals). Many of these protists reside in the
upper water column and passively drift with other types of plankton at the whim of ocean
currents (planktic habitat), mostly within or near the photic zone (the upper part of the
water column where there is enough sunlight available to drive photosynthesis). Some of
these shelled protists are able to photosynthesize and they are called phytoplankton,
whereas those that do not are called zooplankton. Examples of phytoplankton include the
calcareous coccolithophorids (calcareous nannofossils) and siliceous diatoms; examples
of zooplankton include the calcareous planktic foraminifers (“planktic forams”; Figure 3.1)
and the siliceous radiolarians (Figure 3.2).
In addition to planktic microfossils, there are a number of important microfossil groups that
live on the seafloor (benthic habitat), including the benthic foraminifera and ostracods.
Benthic “forams” live at all depths and all latitudes, from coastal salt marshes and estuaries
to the deepest parts of the ocean, and from tropical coral reefs to frigid polar waters.
Ostracods are tiny crustaceans (i.e., true animals) with two calcareous valves (shells) that
superficially resemble microscopic clams.
Earth scientists study modern living organisms and the microfossils left behind.
Micropaleontologists specialize in the study of microfossils, those fossils that are small
enough to require the use of a microscope to identify the features of specimens and recognize
species.
Figure 3.2. Calcareous
microfossils (calcareous
nannofossils and planktic forams)
and siliceous microfossils
(diatoms and radiolarians). All are
single-celled protists with
mineralized hard parts. The
calcareous nannofossils (x400;
polarized light) and diatoms (x100;
plain light) are photosynthetic
primary producers (i.e., autotrophs). The planktic foraminifera (x50; reflected light) and radiolarians (x100;
plain light) are consumers (i.e., heterotrophs). Planktic foram photomicrograph courtesy of Dave Walker; all
other photomicrographs from the IODP School of Rock 2005.
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Ch 3 Microfossils and Biostratigraphy
Instructor Guide
1 In Chapter 2, Seafloor Sediments, you learned that there are a variety of marine
microfossils found in deep-sea sediments. Why are microfossils found in deep-sea sediments?
Explain.
Some marine organisms such as some groups of plankton have mineralized hard parts (shells
or tests), composed of CaCO3 or SiO2. When these organisms are eaten or die, they “rain
down” to the seafloor as individual shells, or aggregates or in fecal pellets of larger organisms
and are preserved into the sedimentary record. They are buried by more microfossils or other
types of sediment over time.
Trophic Levels and Productivity
2 What types of organisms make up the base of the food chain (i.e., food webs, food
pyramids) on land?
Plants
3 Why are these organisms at the base of the food chain?
They create their own food through photosynthesis and are therefore consumed by other
organisms that cannot make their own food; i.e., plants are autotrophs and primary
producers.
4 What types of organisms make up the base of the food chain in the ocean?
In the surface ocean, phytoplankton are the base of the food chain (and photosynthetic
bacteria called cyanobacteria)
5 How might these organisms be similar, and how might they differ from those on land?
They are similar in that they are both autotrophs and can produce their own nutrition from
inorganic material through photosynthesis.
They differ in that phytoplankton can only produce food within the photic zone, or upper
~100-150 m of the water column. Also, phytoplankton are very tiny compared to land plants.
6 It is very cold and pitch black on the seafloor below 1000 m water depth. Speculate about
the types of organisms that make up the base of the food chain in the deep ocean.
Chemosynthetic bacteria and archea, e.g., associated with hydrothermal vents at spreading
centers and methane seeps along continental margins
MARINE MICROFOSSILS AND PRODUCTI VITY
The siliceous diatoms and calcareous coccolithophorids (and other calcareous
nannofossils) are similar to plants, in that they contain chlorophyll and, like plants, they are
autotrophs (“self-feeding”; Figure 3.2). These autotrophs synthesize organic molecules
(e.g., carbohydrates, proteins, and fats) from inorganic molecules (CO2, water, and
nutrients) using solar radiation. In other words, they make organic carbon from inorganic
carbon. Such organisms are considered to be primary producers because they manufacture
the organic materials that other types of organism require as food; thus, primary producers
form the basis of many marine food chains/food pyramids. The process of organic carbon
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Ch 3 Microfossils and Biostratigraphy
Instructor Guide
production in the sunlit surface waters is called photosynthesis. Free oxygen (O2) is
produced by the reduction of CO2 and water during photosynthesis. The generalized reaction
below describes the process of photosynthesis:
6CO2 + 6H2O + inorganic + solar energy → C6H12O6 + 6O2
nutrients
carbon
dioxide
water
nitrates, phosphates,
trace elements & vitamins
glucose
free oxygen
(simple sugar)
The siliceous radiolarians and calcareous planktic foraminifers (Figures 3.1 & 3.2) are
similar to animals in that they are consumers, and like animals, they are heterotrophs
(“other feeding”; Figure 3.2) and depend on other organisms, either autotrophs or other
heterotrophs, for their food. The dinoflagellates are a diverse group of organic-walled
protists that include both autotrophs and heterotrophs. The process of organic carbon
consumption is called respiration. Carbon dioxide (CO2) is released as a product during
respiration. The generalized reaction for respiration is the reverse of that for photosynthesis:
C6H12O6 + 6O2 → 6CO2 + 6H2O + solid waste + chemical energy
& nutrients
‘food’
oxygen
(carbohydrates,
proteins, fats)
carbon water
dioxide
to be broken-down
further by bacteria
for metabolic
processes
Note: The oxidation, degradation, and decomposition of organic matter by bacteria in the water
column and on the seafloor releases CO2 and nutrients back to the marine environment where these
raw materials are again available for use by autotrophs in the production of new organic carbon.
Read the box on Marine Microfossils and Productivity and then answer Questions 7–12.
7 How do calcareous nannofossils differ from foraminifera? Make a list.
Calcareous Nannofossils
Contain chlorophyll
Autotrophs (make their own food)
Primary producers
Photosynthesis
Foraminifera
Heterotrophs (require food)
Consumers
8 What is the difference between an autotroph and a heterotroph?
Autotrophs are self-reliant and can produce their own food (e.g., carbohydrates, proteins, and
fats) while heterotrophs must rely on getting their food from autotrophs or from other
heterotrophs.
9 Are trees autotrophs or heterotrophs? Explain.
Trees are autotrophs. They use photosynthesis to sustain themselves, converting inorganic
carbon (CO2) into organic carbon (organic matter: carbohydrates, proteins, and fats).
10 Are humans autotrophs or heterotrophs? Explain.
Humans are heterotrophs. They are consumers and must rely on eating autotrophic things
(vegetables and fruits) or other heterotrophic things such as other animals.
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11 Why is photosynthesis a fundamentally important Earth systems process?
It is the mechanism by which phytoplankton, cyanobacteria, algae, plants, and trees thrive.
Without it, we wouldn’t have oxygen on Earth, which is such a vital by-product of
photosynthesis. It makes up the base of the food chain that many animals rely on. It also
has a fundamental impact on climate. Photosynthesis draws down CO2 from the atmosphere;
vegetation and soils on land, and phytoplankton and deep-sea sediments in the ocean are
important sinks for CO2.
12 The global carbon cycle describes the exchange of different types of carbon compounds
(e.g., CO2, organic carbon, CaCO3) between the various carbon reservoirs (e.g., atmosphere,
biosphere, ocean, solid Earth) in the Earth system (see Chapter 5). Speculate how changes in
photosynthesis might have an impact on the carbon cycle and therefore the global climate.
Vegetation and phytoplankton draw down CO2 from the atmosphere through photosynthesis,
which could lead to global cooling if the rate of photosynthesis or organic carbon burial
increased. If photosynthesis were to decrease, then CO2 would increase in the atmosphere
resulting in global warming.
Marine Microfossils of the Mesozoic and Cenozoic Eras
The major mineralized microfossil groups have geologic records that extend back more than
100 millions years (Figures 3.3 & 3.4); in fact, the radiolarians are found in marine rocks
dating back to 540 million years ago! Microfossils are very useful in scientific ocean drilling
and in the oil and gas industry because their tiny size and great abundance in marine
sediments allows geoscientists to reconstruct ancient environmental conditions, establish
the relative age of the sedimentary layers (i.e., fossils found in lower or deeper strata are
older than fossils found in higher or shallower strata; fossil occurrences can be used to
identify the relative order of past events), and correlate the sedimentary layers with other
localities around the world.
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FIGURE 3.3. Generalized abundance and taxonomic diversity (numbers of species, genera, or
families; this form of “diversity” is also known as taxonomic richness) of major mineralized marine
plankton groups through time. From Gradstein, 1987.
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FIGURE 3.4. Comparison of phytoplankton diversity (numbers of species and genera, or richness, among
the calcareous nannofossils, dinoflagellates, and diatoms) and global sea level. Note: when global sea level
was much higher than today, for example during the greenhouse climates of the Cretaceous and early
Tertiary periods, vast areas of the continents were flooded by shallow seas, called epicontinental seas or
epeiric seas. From Katz et al., 2005.
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13 Consider diversity (i.e., numbers of species and numbers of genera) through the
Mesozoic and Cenozoic Eras (Figures 3.3 & 3.4). In very general terms, describe the pattern
of evolution (i.e., times of increasing or decreasing diversity) of each of the following groups
of microfossils:
(a) Calcareous nannofossils
- Major radiation throughout Jurassic and Cretaceous; radiation in the early Paleogene
and minor radiation in the Neogene
- Gradually increased from the Triassic to the end of the Cretaceous
- Abruptly declined at the K/Pg boundary
- Abrupt increase at the PETM followed by a gradual decline through remainder of the
Cenozoic
(b) Diatoms
- Minor radiations in the mid-Cretaceous and Late Cretaceous; major radiations in the
Eocene and Neogene
- Gradual increase from the Early Cretaceous followed by a slight decline at the
Albian-Cenomanian boundary
- Abrupt increase at the Campanian followed by a rapid decrease at the K/Pg
boundary
- Increase at the end of the Eocene and again during the Neogene
(c) Dinoflagellates
- Major radiation in Late Jurassic through mid-Cretaceous, Late Cretaceous, and early
Paleogene
- Gradual increase from the Triassic to mid-Albian
- Abrupt decline at the Coniacian followed by a rapid increase to the midMaastrichtian
- Abrupt decrease at the K/Pg boundary followed by an abrupt increase to the PETM
where it declines gradually after
(d) Planktic Foraminifers
- 3 or 4 major radiations: mid-Cretaceous, Late Cretaceous, Paleogene, and Neogene
- Rapid increase from the Coniacian to the K/Pg boundary
- Abrupt decrease at the K/Pg boundary followed by an increase to the end of the
Eocene
- A gradual increase from the Oligocene to the present
(e) Radiolarians
- High diversity from the middle Jurassic to the K/Pg boundary
- Abrupt decline in diversity at the K/Pg boundary
14 Are there any similarities in the diversity patterns between any of the groups? If so,
describe.
- All show a major decrease in diversity at the K/Pg boundary, especially the calcareous
plankton: calcareous nannofossils and planktic forams
- All show an increase in diversity (except radiolarians) at the PETM
- All show a general gradual increase in diversity leading up to the Cretaceous
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15 Do phytoplankton and zooplankton groups track each other? Explain.
Yes, in general. Zooplankton abundances rely on phytoplankton as a food source.
16 Based on Figure 3.4, are there any similarities between the pattern of plankton
Diversity and global sea level change? If so, describe.
Yes – in general, plankton diversity parallels changes is sea level, particularly during the
Mesozoic and Paleogene. However, during the Neogene, planktic foram and especially diatom
diversity increases while global sea level is falling.
17 Hypothesize about why similarities between plankton diversity and global sea level might
exist.
During times of high sea level and widespread shallow seas, phytoplankton are abundant and
many diversify during the Mesozoic and early Paleogene; perhaps this is driven in part by
more niche spaces available for diversification. Also global warmth and increased weathering
rates may have provided increased nutrient availability in some marine environments.
Part 3.2. Microfossils in Deep-Sea Sediments
Consider this scenario: We have a core of deep-sea sediment from a known location that
has been described and sampled. What else do you want to know about this core?
A next logical step is to make an age determination in order to provide a temporal context
for the core. Without an age, it is very difficult to tell a story, geologic or otherwise (e.g.,
“Once upon a time . . . ”, or “Long, long ago in a galaxy far, far away . . . ”).
Geoscientists depend on reliable age assignments in order to (1) calibrate paleomagnetic
records and other types of geologic data against the geologic time scale, (2) calculate
rates of sediment accumulation, and (3) correlate core intervals representing a specific
time from one location to another around the world oceans.
1 List your ideas on how geoscientists determine the “age” of a sequence of sedimentary
layers.
This question could be addressed by students in a variety of ways: 1) think-pair-share, 2)
small group, or classroom discussion, the latter featuring the instructor making a list on the
board, overhead, or computer (projected on to a screen) based on student input. Another
very effective variation is to have think-pair-share followed by a general classroom
discussion. The result will be a list created from student input. As the list comes
together in your classroom discussion, there may be opportunities for teachable moments.
Some possible responses:
• Fossils (or microfossils) – you might ask how fossils can be used to determine the age
of sediments.
14
•
C dating – this is one of the most common replies and misconceptions in age dating.
Many introductory students are very unfamiliar with the principles of radiometric age
dating and the variety of radiometric dating techniques, but they’ve all ‘heard’ of 14C
dating. You might ask what type of materials can actually be dated. 14C dating is
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Ch 3 Microfossils and Biostratigraphy
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restricted to relatively young (<60,000 years) carbon-containing materials, including
calcium carbonate.
• Magnetism (or paleomagnetism) – this will be explored and described in the next
exercise module, but you might ask how magnetism-paleomagnetism can be used to
determine the age of sediments. I suggest not going into much detail if you plan to also
do the exercise module on paleomagnetism.
The above discussion will reveal the nature of your students’ existing knowledge about age
determination.
The “boxes” in these modules are brief snips of information that are useful background and
provide additional context for the module.
SMEAR SLIDES AND CALCAREOUS NANNOFOSSILS
A smear slide is made to investigate the composition and texture of sediments (recall how
you used smear slide data in Chapter 2 to determine sediment lithologies). To prepare a
smear slide, a small amount of sediment from the core, collected with a toothpick, is mixed
with a couple of drops of water to make a slurry (Figure 3.5). This slurry is smeared in a very
thin layer across the glass slide, which is then dried on a hot plate. Adhesive and a cover slip
are added. The adhesive is cured under a black light (UV radiation) for about 5 minutes. Now
the slide is ready to be examined using a transmitted light microscope.
FIGURE 3.5. Making a smear slide. Note the sample label affixed to the glass slide describing exactly where this
toothpick smear slide came from. Photo courtesy of Tina King.
Micropaleontolgists specializing in calcareous nannofossils use a high-powered
transmitted light microscope to study these very tiny microfossils (Figure 3.6). They
typically work with magnifications of 1000–1400x and use different types of light to
accentuate the subtle features of the calcite hard parts, including plane-polarized light,
plane-polarized light with a phase contrast filter, and cross-polarized light.
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Figure 3.6. A geoscientist using a transmitted light microscope. Photo by Mark Leckie.
2 Two photomicrographs of smear slides containing calcareous nannofossils are shown
below, one using plane-polarized light (Figure 3.7) and the other using cross-polarized light
(Figure 3.8). Can you see some particles that look like they could be of biological origin?
Circle some of these microfossils.
Your students will probably see the star-shaped particles in the top photomicrograph (Figure
3.7) from a smear slide (plane-polarized light). These organisms are a type of calcareous
nannofossil called “discoasters”. The plate of calcareous nannofossil species (Figure 3.9) has
several examples of species of the genus Discoaster.
The bottom photomicrograph (Figure 3.8) from a smear slide (cross-polarized light) looks like
a starry night (like Vincent Van Gogh’s “starry night” painting, or Don McLean’s song about
Vincent Van Gogh called “Starry Starry Night”). The “stars” are one or more species of
calcareous nannofossils, some of which are illustrated on the plate of individual species
photomicrographs (Figure 3.9). Hopefully your students notice the distinctive cross-shaped
“extinction pattern” on each of the starry particles. This is due to the interference of the
cross-polarized light passing through the calcite crystal of each individual nannofossil
specimen. Figure 3.9 has several nice examples of the extinction pattern expressed by
different species.
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(previous page) FIGURE 3.7. Smear slide of sample 807A-8H-5, 51 cm from Ontong Java Plateau in the
western equatorial Pacific using plane-polarized light; 400x magnification. Photo courtesy of the IODP School of
Rock, 2005.
FIGURE 3.8. Smear slide of sample 807A-8H-2, 70 cm from Ontong Java Plateau in the western equatorial Pacific
using crossed-polarized light; 400 = magnification. Photo courtesy of the IODP School of Rock, 2005.
3 Do your best to identify one or two of the tiny microfossils in the two smear slides (Figures
3.7 & 3.8) using the collection of calcareous nannofossil species shown in Figure 3.9. Put a
box around the microfossil you are identifying (Figure 3.7 and/or Figure 3.8) and write the
name of the species next to the box.
Your students could have some fun with this.
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FIGURE 3.9. Selected species of calcareous nannofossils identified and illustrated by Paul Bown. These are
biostratigraphically useful zonal marker species. All photomicrographs x1000. Dark field=cross-polarized
light; clear field=plane-polarized light with phase contrast filter. Bold numbers refer to specimen numbers on the
original published plates. From Bown, 2005.
Table 3.1 shows the distribution of calcareous nannofossils in Hole 1208A from the
central high of Shatsky Rise in the northwest Pacific (Figure 3.10). Site 1208 was cored
during Ocean Drilling Program (ODP) Leg 198.
4 Remember from Chapter 1 that sediments deeper in a cored interval accumulated before
the sediments above; in other words, the sequence is oldest at the bottom and youngest at
the top. Likewise, the species deeper/lower in the sedimentary sequence are older than the
species that occur higher in the sequence. Make a list of observations about the
distribution of species within the core as shown in Table 3.1. Also, make a list of questions
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that you may have about the distribution of species in this table. What additional
information would you like to know about the species and their distribution in the Site 1208
drill site?
Observations students may make:
• Species don’t occur in all samples.
• There are many species in these samples.
• Some species occur more-or-less persistently from one sample to the next and then
disappear
• Some species are abundant or common in the samples, while other species are few or
rare.
• Some species occur in the lower part of the sequence but not in the upper part, while
other species only occur in the upper part of the sequence.
• The species in the sediment samples changes up-section (i.e., the species at this site
change over time)
• Species of the genus Discoaster disappear above 100 mbsf.
It’s important to remind students that as they ‘read’ the table of microfossil data and make
observations, the samples listed in the table come from sediments that accumulated layer by
layer, with the oldest sediments and their contained microfossils at the bottom of this list of
samples, and the youngest samples at the top. They might think of this sequence of sediment
samples as a tape-recorder of geologic history; like pages in a book.
FIGURE 3.10. Location of ODP Site 1208 on Shatsky Rise
in the northwest Pacific. Shaded bathymetric contours;
mbsl = meters below sea level. From Bown, 2005.
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One option is to enlarge Table 3.1 on 11”x17” paper as an alternative to using the
distribution table provided in the book. A high resolution version of Table 3.1 (along with all
figures and tables in the book) is included on the website. TABLE 3.1. Rows of samples, the depth of
those samples in the hole (mbsf=meters below seafloor), and columns of species (both Genus and species are
italicized, e.g., Emiliania huxleyi).*
*The letters correspond to the relative abundance of individual species in each sample based on a visual
estimate (blank= not present; A=abundant; C=common; F=few; R=rare; •=very rare). The column labelled
“Preservation” refers to the degree of breakage of nannofossils, calcite dissolution, or calcite overgrowths on the
nannofossils in each sample (G=good; M=moderate; P=poor). The column labelled “Abundance” describes the
relative proportion of calcareous nannofossils in each sample compared with other constituents such as other types
of microfossils or mineral components such as clay (A=abundant). These data were produced by Paul Bown, a
shipboard scientist during ODP Leg 198 (Bown, 2005; http://www-odp.tamu.edu/publications/198_SR/104/104.htm).
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Questions that students may have:
• Why do some species come and go (i.e., why don’t they occur consistently from one
sample to the next)?
• Why do some species show variability in abundance from one sample to the next?
• Why do some species suddenly disappear up-section?
• Why do other species suddenly appear in the section?
These are possible ‘teachable moments’ about ecology, paleoecology, and evolution.
There are a number of different directions you could go from here. The exercises that follow
will focus more on the application of these observations rather than the ecology of the
organisms or processes of evolution.
Additional Information:
The classroom discussion about this distribution table will generate a buzz. Is this site typical
of the distribution of calcareous nannofossils in deep-sea sediments?
5 Fossil occurrences can be used to identify the relative order of past events. Geoscientists
“read” the sedimentary record from bottom to top (i.e., from older to younger). How might
the species data in Table 3.1 be useful for determining how old the sediment layers are in
this drill site? Explain.
Microfossils may indicate age because:
• Species have known geologic ranges (i.e., species evolve and become extinct;
species not living today existed for a finite time on Earth before becoming extinct).
• Species ranges are known from a similar pattern of first occurrences (evolution)
and last occurrences (extinction) at multiple locations.
• Species first and last occurrences are referred to as “datums”.
• Species first and last occurrences, and their individual ranges are predictable and
testable.
Students are not likely to grasp the concept of first and last occurrences, or a species
stratigraphic range right away. The concepts listed above provide the teachable moment.
Part 3.3. Application of Microfossil First and Last Occurrences
The presence of microfossils in many types of deep-sea sediments provides a basis for
determination of age. The recurrent (and testable) pattern of fossil first occurrences
(FOs) and last occurrences (LOs) recognized by paleontologists studying sedimentary
sequences reveals the relative sequence of evolutionary origination and extinction of
species through time. In other words, in a distribution table showing the occurrences of
species in a deep-sea core, like Table 3.1, the lowest occurrence of a species represents
the first time (i.e., first occurrence, FO) this particular taxon was found in this area of the
northwest Pacific. This can be considered the evolutionary first appearance, or time of
origination of this new species. By contrast, the highest occurrence of a species
represents the last time (i.e., last occurrence, LO) this particular taxon was found in this
area. This can be considered the evolutionary last appearance, or time of extinction of this
species. Because of these evolutionary events, microfossil species found in marine
sediments are unique to a particular interval of geologic time and this property makes
them very useful for age determination (Figure 3.11).
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1 How can geoscientists test whether a pattern or sequence of fossil first and last occurrences
is consistent and repeatable?
We hope that the students would suggest that another deep-sea site should be investigated
to see if the same sequence of first and last occurrences is present at more than one site. By
the way, this is precisely the exercise developed in Part 5 (‘How reliable are microfossil
datums?’).
BIOSTRATIGRAPHY
Biostratigraphy is the study of sedimentary layers based on fossil content. Paleontologists
organize sedimentary layers into biozones based on the first and last occurrences of
selected species; such zonal marker species (index fossils) are more suitable than other
species for biostratigraphy, because they have short stratigraphic ranges, are geographically
widespread, easily recognized, and well preserved. These levels of origination and extinction
of marker species are called biostratigraphic datum levels. The ages of the
biostratigraphic datum levels can be determined by multiple methods including paleomagnetic
stratigraphy and radiometric age dating (this will be explored in Chapter 4, Paleomagnetism
and Magnetostratigraphy).
Zonal marker species are used to differentiate intervals of geologic time in a
sedimentary section cored from the deep sea, thus essentially determining the age of
successive layers of sediment. In the case illustrated in Figure 3.11, the distribution of
eight microfossil species (A to I) is shown in a 120-meter cored interval. Four of these species
(A, C, E, and G) have been established previously as zonal marker species because their
first and/or last occurrences have been shown to be reliable biostratigraphic datum levels.
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FIGURE 3.11. Two-part diagram illustrating how biostratigraphy is applied to a deep-sea sedimentary section or
other fossiliferous sedimentary rocks. The upper panel shows a hypothetical deep-sea sedimentary section
containing microfossils. Letters A to I indicate species of microfossils that occur in the cored interval. Vertical
bars illustrate in which parts of the cored interval each species is found; this is also referred to as a species’
stratigraphic range. The down arrows imply that the species also occurs in older sediments (i.e., this cored
interval does not represent the total stratigraphic range of the species). The biozones on the right (Zones 23–28)
show discrete intervals of the core based on microfossil first or last occurrences. The lower panel shows a
hypothetical biostratigraphic zonal scheme based on a specific sequence of zonal marker species B/FOs and
T/Los. The zonal scheme shown in the lower panel can be applied to the cored sedimentary section because some
of the zonal marker species are present in the cored sedimentary section. Diagram courtesy of Mark Leckie.
Figure 3.12 shows biozones for two types of marine microfossils: calcareous nannofossils
(CN zones) and planktic foraminifers (N zones) which have been correlated to the
geomagnetic polarity time scale. Zonal marker species first and last occurrences (B=base or
first occurrence; T=top or last occurrence) are shown on the right side of the figure and are
used to recognize the base and top of the microfossil biozones similar to the example shown
above. Notice that these biostratigraphic datum levels have ages assigned to them in
Figure 3.12. For example, the base (B, or first occurrence) of Emiliania huxleyi is 0.26 Ma
(Ma=mega-annums, or millions of years ago), and the top (T, or last occurrence) of
Discoaster hamatus is 9.63 Ma. We will investigate how the ages of these biostratigraphic
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datum levels are determined in Chapter 4, Paleomagnetism and Magnetostratigraphy.
FIGURE 3.12.
Biozones for planktic
forams (N zones) and
calcareous
nannofossils (CN
zones), along with the
corresponding
geomagnetic polarity
time scale, geologic
epochs, and ages. The
boxed part of the
timescale is the
interval represented
by the calcareous
nannofossil data in
Table 3.2. Shipboard
Scientific Party, 2002,
Explanatory notes.
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Table 3.2 shows is the distribution of calcareous nannofossil species in Hole 1208A on
Shatsky Rise in the Northwest Pacific. This table is nearly identical with Table 3.1 and depicts
the stratigraphic occurrence of species found in samples analyzed from Hole 1208A. The first
column corresponds to a sample identifier (core-section, interval) and the second column
is the depth in Hole 1208A (meters below seafloor, mbsf) for each of the samples. What is
different about this version of the distribution table (compared to that shown in Table 3.1) is
the addition of several columns: Geochronology, Nannofossil Zone, and Nannofossil
Datum. These are to be filled in as part of this exercise.
One option is to enlarge Table 3.2 on 11”x17” paper as an alternative to using the
distribution table provided in the book. A high resolution version of Table 3.2 (along with all
figures and tables in the book) is included on the website.
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TABLE 3.2. Distribution of calcareous nannofossil species in Hole 1208A on Shatsky Rise in the Northwest
Pacific.*
* Modified from: Bown, 2005; http://wwwodp.tamu.edu/publications/198_SR/104/104.htm
Note that if a zonal marker species does not occur in the data table for Hole 1208A, you will need to lump two
zones or subzones together (e.g., CN10a-b). B = base (or first occurrence, FO), T = top (or last occurrence, LO)
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In this exercise you will interpret and apply the calcareous nannofossil zonal scheme
(CN zones) presented in Figure 3.12 to the actual nannofossil distribution data from
Hole 1208A (Table 3.2).
Step 1: Find the species of calcareous nannofossils that correspond with the CN zone
boundaries shown in Figure 3.12; these are the zonal marker species (i.e., species names
that line up with zone boundaries). Each zonal marker species will either be a base (B) or a
top (T).
Step 2: Find each of these zonal marker species on the Hole 1208A distribution table on the
following page. Be sure to note whether you need the base (first occurrence) or top (last
occurrence) of the species range. Please note: some zonal species may not be present in the
Hole 1208A data.
For example: The two youngest biozones are interpreted on Table 3.2: See previous page.
• The base, or first occurrence of Emiliania huxleyi (distribution highlighted in gray) is used
to define the boundary between Zone CN14b and CN15. E. huxleyi first occurs in sample
2H-CC, so this sample is the lowest sample in Zone CN15. Draw a horizontal line across the
distribution table between sample 2H-CC and the underlying sample 3H-5, 107 cm. This line
represents the boundary between Zone CN14b and CN15. The age of this level in Hole 1208A
is 0.26 Ma.
• The top, or last occurrence of Pseudoemiliania lacunosa (distribution highlighted in
gray) is used to define the boundary between Zone CN14a and CN14b. P. lacunosa last
occurs in sample 4H-5, 60, so this sample is the highest sample in Zone CN14a. Draw a
horizontal line across the distribution table between sample 4H-5, 60 and the overlying
sample 3H-CC. This line represents the boundary between Zone CN14a and CN14b. The age
of this level in Hole 1208A is 0.46 Ma.
2 Interpret biozones for the remainder of the Hole 1208A distribution table (Table 3.2) by
locating the CN zonal marker species and drawing horizontal lines on Table 3.2
corresponding with the zone boundaries. Fill in the columns of Table 3.2 for
Geochronology, Nannofossil Zone, and Nannofossil Datum as shown for the two
examples described above. Geochronology is a geologic time unit and refers to the
Epoch/Age of the sediment (e.g., Pleistocene, late Pliocene, early Pliocene, late Miocene,
middle Miocene).
Next page: Interpreted distribution table is shown on next page. Species highlighted in gray
are the index (marker) species for the zones. Horizontal lines show the biozone boundaries.
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3 In this investigation you learned how to apply a biostratigraphic zonal scheme to a cored
sedimentary sequence from the seafloor of the North Pacific Ocean. This process essentially
enabled you to convert depth to age for that sedimentary sequence. What does knowing
“age” now allow you to explore about the history of environmental and climate change?
For example: 1) to determine relative age of a fossiliferous sedimentary sequence (because
some species have known or predictable first and last occurrences relative to other species),
2) to correlate from one location to another so that you can relate the sediments and their
history of deposition from one place to another (need to do this to reconstruct geologic
history), and 3) to calculate rates of sedimentation/sediment accumulation (Part 3 of this
exercise), and other geologic processes provided you can determine the absolute age of the
species first and last occurrences (this latter piece is described in detail in Chapter 4Paleomagnetism/Magnetostratigraphy exercise module; see discussion of Geomagnetic
Polarity Time Scale).
Part 3.4. Using Microfossil Datum Levels to Calculate
Sedimentation Rates
Table 3.3 [next page] presents a summary of select calcareous nannofossil species datum
levels observed at Site 1208 (ODP Leg 198) on the central high of Shatsky Rise in the
Northwest Pacific (from Bown, 2005). FO = first occurrence, LO = last occurrence. This
list represents a subset of all the species shown on the distribution table (Tables 3.1 and 3.2)
analyzed in Part 3.2 and Part 3.3 (i.e., most of these are the zonal marker species). These
taxa have well established datum level ages and are therefore useful for establishing the age
of the sedimentary sequence (age model) at Site 1208. Note: The age-depth data in Table
3.3 are derived from the biostratigraphic zonation that was done in Part 3.3.
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TABLE 3.3. Calcareous nannofossil datum levels, ages, and depths from Hole 1208A (from Bown, 2005).
Depth
(mbsf)
Age
(Ma)
FO Emiliania huxleyi
14.24
0.26
Shipboard Scientific Party, 2002
LO P. lacunosa
30.30
0.46
Shipboard Scientific Party, 2002
FO G. omega
43.11
0.95
Shipboard Scientific Party, 2002
FO G. caribbeanica
87.90
1.73
Shipboard Scientific Party, 2002
LO D. brouweri
100.16
1.95
Shipboard Scientific Party, 2002
LO D. pentaradiatus
116.40
2.52
Shipboard Scientific Party, 2002
LO D. surculis
119.08
2.63
Shipboard Scientific Party, 2002
LO D. tamalis
128.70
2.78
Shipboard Scientific Party, 2002
LO Large Reticulofenestra
163.90
3.82
Shipboard Scientific Party, 2002
FO D. tamalis
166.66
4.20
Young, 1998
LO Sphenolithus
166.66
3.65
Shipboard Scientific Party, 2002
LO Amaurolithus
168.88
4.56
Shipboard Scientific Party, 2002
FO D. asymmetricus
168.88
4.20
Young, 1998
FO C. cristatus
187.90
5.07
Shipboard Scientific Party, 2002
LO D. quinqueramus
207.00
5.54
Shipboard Scientific Party, 2002
FO Amaurolithus
235.52
7.39
Shipboard Scientific Party, 2002
FO D. quinqueramus
250.80
8.20
Shipboard Scientific Party, 2002
FO D. berggrenii
250.80
8.20
Shipboard Scientific Party, 2002
LO D. hamatus
265.94
9.63
Shipboard Scientific Party, 2002
FO C. calyculus
270.10
10.10
Young, 1998
FO D. hamatus
274.20
10.48
Shipboard Scientific Party, 2002
FO C. coalitus
279.70
10.79
Shipboard Scientific Party, 2002
LO C. miopelagicus
285.06
10.90
Young, 1998
LO C. premacintyrei
295.41
12.30
Young, 1998
LO C. floridanus
295.41
13.19
Shipboard Scientific Party, 2002
Datum
Age Data Source
Note: LO large Reticulofenestra = LO Reticulofenestra pseudoumbilicus; LO Amaurolithus = LO Amaurolithus
primus.
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1 Using the graph paper provided and the age and depth data in Table 3.3, construct an
age–depth plot similar to the example below (Figure 3.13) from ODP Site 846 in the eastern
equatorial Pacific (note that the data points represent calcareous nannofossil datum levels).
Place Age (Ma) on the x-axis across the top of the plot, and Depth (mbsf) on the y-axis
with zero depth at the top with increasing depth down the left-hand side of the page. Be sure
to plan out your graph based on the range of the x and y values: when labeling your
axes, ensure that the values between each tick mark are equal and that your graph can
accommodate all the data (i.e., approximately 14 million years of record and approximately
300 m of drilled section).
The rate of sediment accumulation can be
calculated by dividing depth by age. For example, in
the age–depth plot in Figure 3.13, the interval from
300 mcd (meters composite depth) to the surface
accumulated at a rate of approximately 43 m/myr
(meters per million years): 300 m/7 myr = 42.9
m/myr.
2 Note the change in slope at approximately 300 mcd
in Figure 3.13. What was the sedimentation rate for the
interval from 300 mcd to 425 mcd? Show your work.
425 m – 300 m = 125 m
16 Ma – 7 Ma = 9 my
125 m/9 my = 13.9 m/my
FIGURE 3.13. Example of an age–depth plot from ODP 846 in the eastern equatorial Pacific. A series of “best fit lines” illustrate changes in
sediment accumulation rate. From Shipboard Scientific Party, 1992.
Interpretation: sediment accumulation rates increased from 13.9 m/my to 42.9 m/my ~7
million years ago (7 Ma). This begs the question ‘why?’, and could lead to other
investigations by your students. For example, going to the Initial Reports Volume of ODP Leg
138 (http://www-odp.tamu.edu/publications/138_IR/138ir.htm) and reading the original
descriptions of Site 846 by the shipboard scientists (See Chapter for Site 846), particularly
noting if any changes in lithology or sediment geochemistry were noted at ~300 mcd.
3 If the slope on an age–depth plot is zero (i.e., horizontal), what would this tell you about
the rate of sediment accumulation? What would be the implication for the sedimentation
history if a segment of the age-depth plot is horizontal?
This would imply that no sediment is represented, but there is a significant period of time
represented where no sedimentary record exists. A horizontal line on an age-depth plot
constructed in the manner described above means there must be an unconformity and
hiatus (missing record) in the section. This begs the question: How could sediments be
missing from this deep-sea section? There are several possibilities: 1) erosion (bottom
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currents or slump/mass wasting of sediments on a slope), 2) non-deposition (sediment
supply cut-off for a time), or 3) dissolution of material raining down through the water
column (specifically microfossils composed of calcium carbonate including calcareous
nannofossils and planktic forams).
4 Draw a best-fit line or multiple best-fit lines through the Site 1208 data that you
plotted.
(a) How can your graph help you determine the rate at which sediment accumulated at
Site 1208?
It will be clear that a single best-fit line through the data does not adequately capture
the trend. Instead, multiple best-fit line will work better. Students are likely to choose
different segments. These are interpretations, and people can differ in how the data are
interpreted. The important point is for students to see that a change in depth also
means a change in age, and this is how scientists can determine the rate of sediment
accumulation: Y meters of sediment accumulated in X amount of time.
(b) Why does the slope of the best-fit lines change?
A series of best-fit line segments best describes the sediment accumulation rate
history at Site 1208. The slope of each line segment reflects sedimentation rate in
meters per million years (m/myr). The slopes of the line segments increase toward
the present, implying that sedimentation rates have steadily increased over the past 13
million years.
5 (a) Calculate the sedimentation rate of each of your best-fit line segments (i.e., where
you interpret a change in slope). Use units of meters per million years (m/myr). Show
your work. Label each line segment with its sedimentation rate.
Asterisks on Table
3.3 (right)
show the inflection
points for ‘best-fit’
line segments; the
values between
the asterisks
represent the
sedimentation
rate in m/myr.
See next page.
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(b) Was the sedimentation rate constant at Site 1208 over the past 13 million years? If
not, describe how the rate of sedimentation changed over time.
The sedimentation rate was not constant over the past 13 myr. Based on the best-fit line
segments, it is clear that sedimentation rate at Site 1208 has increased toward the present
day.
(c) Propose some hypotheses to explain these changes in sedimentation rate at this site
through time. What data would you need to test these hypotheses?
Students may generate a variety of best-fit line segments. Regardless of which datums they
use as inflection points in their own solution/interpretation, they should see increasing slopes
toward the top of the section reflecting a steady increase in sediment accumulation rates
toward the present. In the solution provided, 4 line segments are identified, including a
possible unconformity/hiatus at the base of the study interval.
Possible hypotheses to explain why sedimentation rates have increased since the late
middle Miocene:
1. Increased terrigenous input through time (i.e., more erosion on land and increased
input of mud to the ocean).
2. Increased productivity by plankton (could also be related to hypothesis 1; increased
erosion on land can lead to increased availability of nutrients needed by
phytoplankton).
These ideas could be tested by reading the original descriptions of Site 1208 by the shipboard
scientists (http://www-odp.tamu.edu/publications/198_IR/198ir.htm; See Chapter
for Site 1208 under Volume Contents; http://wwwodp.tamu.edu/publications/198_IR/chap_04/chap_04.htm), particularly checking text
and figures for any changes in sediment composition, sediment geochemistry, or physical
properties (color reflectance, magnetic susceptibility) that may have taken place in this part
of the section. From the Site 1208 chapter you can learn that there is a change in color and
an increase in magnetic susceptibility in the sediments, reflecting an increase in terrigenous
sediments since the Miocene. However, an increase in diatoms suggests that productivity also
increased during this time.
Part 3.5. How Reliable are Microfossil Datum Levels?
As we observed in Part 3.3, the presence of microfossils in many types of deep-sea sediments
provides a basis for age determination. The recurrent (and testable) pattern of fossil first
occurrences (FOs) and last occurrences (LOs) recognized by paleontologists studying
sedimentary sequences reveals the relative sequence of evolutionary origination and
extinction of species through time. Because of these evolutionary events, microfossil
species found in marine sediments are unique to a particular interval of geologic time making
them very useful for age determination.
By comparing the microfossil distribution at one site with other deep-sea sites from the
same latitudinal belt (i.e., tropical-subtropical, temperate, or subpolar-polar) geoscientists
can test whether the pattern or sequence of fossil first and last occurrences is consistent
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and repeatable. In this exercise, we will compare the nannofossil distribution found in
temperate Site 1208 (ODP Leg 198) on Shatsky Rise in the Northwest Pacific (latitude,
longitude: 36°7.6’N, 158°12.1’E) with the nannofossil distribution found in tropical-subtropical
Site 999 (ODP Leg 165) in the Caribbean Sea (12°44.6’N, 78°44.4’W).
Table 3.3 (in Part 3.4) presents a summary of select calcareous nannofossil species datum
levels observed at temperate Site 1208 (ODP Leg 198) on Shatsky Rise in the Northwest
Pacific (from Bown, 2005). Note: FO = first occurrence, LO = last occurrence. This list
represents a subset of all the species shown on the distribution table analyzed in Part 3.2 and
Part 3.3; these taxa are the most useful for constructing an age model for the sediments
cored at Site 1208.
Table 3.4 presents a summary of select calcareous nannofossil species datum levels observed
at tropical-subtropical Site 999 (ODP Leg 165; Figure 3.14) in the Caribbean Sea (from
Kameo and Bralower, 2000). Note: B= base, T = top (similar to FO = first occurrence and
LO= last occurrence).
FIGURE 3.14. Sites drilled during ODP Leg 165 and location of ODP Site 999 in the Caribbean Sea. From Kameo and Bralower, 2000.
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TABLE 3.4. Calcareous nannofossil datum levels, ages, and depths from Hole 999A; B=base (or first occurrence,
FO), T=top (or last occurrence, LO) (from Kameo and Bralower, 2000).
Datum and Bioevent
Zone
(base)
Age
(Ma)
Core, Section, Interval (cm)
Upper
Depth
(mbsf)
Lower
B Emiliania huxleyi
CN15
0.25
165-999A2H-1, 100
165-999A2H 1, 122
8.71
T Pseudoemiliania lacunosa
CN14b
0.41
2H-7, 30
2H-CC
17.00
0.85
4H-4, 22
4H-4, 72
31.57
0.95
4H-6, 100
4H-7, 30
35.50
B Reticulofenestra asanoi
1.16
5H-1, 72
5H-1, 100
36.96
T Gephyrocapsa spp. (large)
1.21
5H-4, 22
5H-4, 72
41.07
T Helicosphaera sellii
1.27
5H-7, 30
5H-CC
45.50
B Gephyrocapsa spp. (large)
1.45
6H-4, 100
6H-4, 122
51.21
B Gephyrocapsa oceanica
1.65
7H-1, 22
7H-1, 72
55.57
T Calcidiscus macintyrei
1.65
7H-1, 22
7H-1, 72
55.57
T Reticulofenestra asanoi
B Gephyrocapsa parallela
CN14a
B Gephyrocapsa caribbeanica
CN13b
1.73
7H-1, 100
7H-1, 122
56.21
T Discoaster brouweri
CN13a
1.97
7H-CC
8H-1, 100
65.10
T Discoaster pentaradiatus
CN12d
2.38
9H-3, 72
9H-3, 122
78.07
T Discoaster surculus
CN12c
2.54
10H-1,122
10H-2, 22
85.07
T Discoaster tamalis
CN12b
2.74
10H-5,122
10H-6, 21
91.07
T Reticulofenestra ampla
2.78
10H-5,122
10H-6, 21
91.07
T Reticulofenestra minutula (circ. fonn)
3.36
12H-4, 72
12H-5, 22
108.32
T Sphenolithus spp.
3.65
13H-1,122
13H-2, 22
113.57
T Reticulofenestra pseudoumbilicus
CN12a
3.80
13H-6,100
13H-7, 30
121.00
T Amaurolithus primus
CN11a
4.37
16H-5,100
16H-6, 22
147.96
B Ceratolithus rugosus
CN10c
5.04
16H-CC
17H-1, 100
150.60
T Ceratolithus acutus
CN10c
5.04
17H-5,100
17H-6, 22
157.46
B Ceratolithus acutus
CN10b
5.34
18H-1,100
18H-2, 22
160.96
5.34
18H-2,100
18H-3, 22
162.46
5.56
18H-6,100
18H-7, 30
168.50
5.88
19H-1,100
19H-2, 22
170.46
T Triquetrorhabdulus rugosus
T Discoaster quinqueramus
T Amaurolithus amplificus
CN10a
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Ch 3 Microfossils and Biostratigraphy
Datum and Bioevent
Instructor Guide
Zone
(base)
Age
(Ma)
Core, Section, Interval (cm)
Depth
(mbsf)
Upper
Lower
6.50
19H-7, 22
19H-CC
178.46
7.24
22X-2, 22
22X-2, 100
199.71
T paracme Reticulofenestra pseudoumbilicus
6.80
23X-6, 22
23X-7, 22
209.07
T Minylitha convallis
6.70
25X-2, 23
25X-3, 21
223.90
8.35
26X-2, 22
26X-2, 100
231.61
8.85
27X-2, 24
27X-3, 24
241.59
8.43
27X-5, 22
27X-5, 100
245.71
9.43
28X-6, 22
28X-7, 22
257.17
9.36
29X-1, 22
29X-1, 100
259.01
9.36
29X-6, 22
29X-7, 22
266.87
B Amaurolithus amplificus
B Amaurolithus spp.
B Discoaster berggrenii
CN9b
CN9a
B paracme Reticulofenestra pseudoumbilicus
B Discoaster loeblichii
CN8b
B Minylitha convallis
T Discoaster hamatus
CN8a
T Catinaster calyculus
B Discoaster hamatus
CN7a
10.39
29X-CC
30X-1, 22
268.11
B Catinaster calyculus
CN7b
10.70
30X-2, 21
30X-3, 21
270.46
10.39
30X-3,100
30X-4, 21
272.36
10.71
30X-5, 21
30X-5, 100
274.61
T Discoaster kugleri
11.50
31X-CC
32X-1, 22
287.31
B common Discoaster kugleri
11.74
33X-6,100
33X-7, 30
305.60
T Coronocyclus nitescens
12.12
35X-2, 24
35X-3, 23
318.49
T Cyclicargolithus floridanus
13.19
35X-7, 20
35X-CC
325.40
T Coccolithus miopelagicus
B Catinaster coalitus
CN6
In this exercise, we will compare the sequence of calcareous nannofossil datum levels
at Site 1208 in the Northwest Pacific with the sequence of select calcareous nannofossil
datum levels observed at Site 999 in the Caribbean Sea. There are a few minor differences in
the ages of the datum levels between the two sites reflecting continued improvement in the
calibration of these datum levels since the two individual data sets were published, 2005 and
2000, respectively. Remember: first occurrence (FO) = base (B), and last occurrence
(LO) = top (T).
1 Place a check (√) next to the species datum levels common to both lists (Tables 3.3
and 3.4); place a (X) next to the species datum levels not used, or not recognized in the
other site. Do the species datum levels occur in the same order at both localities? Explain.
See attached tables. Note, an arrow was used instead of the (x). Most of the datums occur in
the same order. For the datums in common to both sites, the exceptions are:
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Ch 3 Microfossils and Biostratigraphy
•
•
Instructor Guide
The first occurrences/base (FO or B) of Catinaster calyculus and Discoaster hamatus
are reversed at the two sites; however, the datums are close to each other in each of
the sites.
The FO/B of Catinaster calyculus and last occurrence/top (LO or T) of Coccolithus
miopelagicus are reversed at the two sites; however, the datums are close to each
other in each of the sites.
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Ch 3 Microfossils and Biostratigraphy
Instructor Guide
Important take-away message: many datums are in common at both sites, which
allows correlation between the two regions. However, students may ask: why weren’t all
the same datums used at both sites? Great question! The two ODP sites were studied by
different specialists. These data come straight from the literature; no modifications have been
made (sorry for any typos!). Different workers have different approaches, including the use of
secondary datums (i.e., those datums not used to define established zones) or favorite
species known to be reliable age indicators. You’ll notice that the specialists who studied Site
999 utilized many secondary marker species that were either not recognized at Site 1208, or
not utilized for the biostratigraphy by the specialists who analyzed the calcareous nannofossils
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Ch 3 Microfossils and Biostratigraphy
Instructor Guide
at Site 1208. Alternatively, the Caribbean is different from the North Pacific;
paleobiogeographic differences between the two regions may also explain some of the
differences between the two sites. Teachable moment here about nannofossil paleoecology
and paleoenvironment; tropics (Site 999 = 12°N latitude) compared with northern
subtropics (Site 1208 = 36°N latitude).
2 Provide a hypothesis or two to explain the similarities and differences of the
nannofossil assemblages at the two sites based on the information provided in the
tables. How might you test your hypotheses?
Similarities are likely due to the rapid and widespread dispersal of calcareous nannofossils.
Differences could be ascribed to environmental/ecologic differences between the two sites,
which are from two different ocean basins (North Pacific and Caribbean) and different zonal
belt (Site 1208 = 36°N latitude, Site 999 = 12°N latitude). These paleobiogeographic
differences may have affected certain species more than others. These results could be
further tested by examining the distribution of calcareous nannofossil species in other deepsea sites. You might ask your students if they would expect to see similar results at all deepsea sites, or only those sites from tropical-subtropical latitudes.
Comparison of Sediment Accumulation Rate Histories
3 On the graph paper provided plot age vs. depth, putting age (in millions of years, Ma)
across the top (x-axis) and depth in the hole (meters below sea floor, mbsf) down the left
side (y-axis). Plot the microfossil datum levels that are in common to both sites. Note: if
you’ve already plotted the Site 1208 datum levels in Part 3.4, you could add the Site 999
datum levels to the same plot. Use solid circles (•) for the Site 1208 datum levels and open
circles (+) for the Site 999 datum levels.
See next 3 pages for plot keys.
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Ch 3 Microfossils and Biostratigraphy
Instructor Guide
Page 38 of 44
Ch 3 Microfossils and Biostratigraphy
Instructor Guide
Side by side comparison of Sites 1208 and 999
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Ch 3 Microfossils and Biostratigraphy
Instructor Guide
(a) Calculate sedimentation rates for all best-fit line segments for both sites. Show your work.
See plots on previous pages for sedimentation rate answers.
(b) Characterize the patterns of sedimentation at both sites. How are the sedimentation
histories similar, and how are they different?
Site 999 has much more uniform sedimentation over the past 13 myr compared with Site
1208. However, it is nteresting that both these sites show an increase in sedimentation rates
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Ch 3 Microfossils and Biostratigraphy
Instructor Guide
toward the present.
(c) Provide possible explanations for the similarities and/or differences.
As with Site 1208, there are multiple ways to interpret the changes in sedimentation rate.
Site 1208 is influenced by runoff and climatic conditions in Asia (westerly winds), and by
changes in productivity in the northwest Pacific. Site 999 is influenced by runoff from Central
America and the emergent Andes Mountains of northern South America, as well as seasonal
changes in the position of the Intertropical Convergence Zone (ITCZ). Onset of Northern
Hemisphere glaciation at ~2.6 Ma may have contributed to increased meridional temperature
gradients that affected everything from precipitation patterns and runoff to biological
productivity.
III. Summative Assessment
There are several ways the instructor can assess student learning after completion of this
exercise. For example, students should be able to answer the following questions after
completing this exercise (note this is just a small sampling of the types of questions that
could be asked):
1. You are examining the microfossils from two different sediment cores from the sea floor
(see sketch below). In Core A the last occurrence of Discoaster brouweri occurs at 20 meters
below sea floor. In Core B the last occurrence of Discoaster brouweri occurs at 30 meters
A
B
below sea floor. Based on this
information what
can you conclude?
20 m, L.O. of
D. brouweri
30 m, L.O. of
D. brouweri
a. The layer that includes the last occurrence of D. brouweri in Core A is older.
b. The layer that includes the last occurrence of D. brouweri in Core A is younger.
c. The layer that includes the last occurrence of D. brouweri in Core A must be
the same age as the layer that includes the last occurrence of D. brouweri in
Core B.
2. Continuing the scenario in #1, what would you do next to determine the age of this layer in
core A?
a. Radiometrically-date that specific microfossil sample in your core
b. Use this index fossil to determine the biozone, and therefore the fossil-based
age.
c. Count the layers of sediment and they will always give you the age
d. Go to a museum and find this species in an exhibit display
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Ch 3 Microfossils and Biostratigraphy
Instructor Guide
3. The pattern of fossil first occurrences (FOs) and last occurrences (LOs) in the sedimentary
sequences reveals
a. evolutionary origination and extinction of species through time
b. magnetic reversals through time
c. plate tectonics through time
d. inclination through time
4. Which of the following are criteria for being an index fossil (i.e., marker species)?
a. A species that had a long temporal range (i.e., species existed a really long time)
b. A species that had a wide geographic range
c. A species that is easy to identify
d. All of the above
e. B and C only
Examine the age-depth plot below (Shipboard Scientific Party, 1992; same as Figure 3.13)
to answer questions 5 & 6.
5. What is the sedimentation rate (in m/myr) for the
interval from 0 to 300 meters below sea floor?
a. 0.023 m/myr
b. 7 m/myr
c. 43 m/Myr
d. 300 m/Myr
6. Does this interval (0-300 mbsf) have a higher or
lower sedimentation rate than the sediments below
300 mbsf?
a. higher
b. lower
c. these are the same
Short Answer:
1. Why is it important to determine the age of a sequence sediments (or rock or ice, etc)?
2. List way age can be determined in a geologic sequence. Do you only go with one way to
determine age or multiple ways if you can? Why?
3. What are the steps in using fossils to determine age of a sedimentary sequence?
4. What uncertainties are there in determining age using fossils? How can these uncertainties
in age determination be reduced?
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Ch 3 Microfossils and Biostratigraphy
Instructor Guide
5. If we compared two sedimentary sequences from two different locations and found that
they contain the same biozone boundary (e.g., top of CN 14a), are the layers from these two
different sequences the same age? Explain. Are they necessarily the depth? Explain.
6. What are biozones? How are the biozones in a new location (e.g., like the case study we
did from the NW Pacific) determined?
7. What are First Occurrences (FO) and last Occurrences (LO)? Be able to find FO and LO for
given species in table to define biozones. [Remember FO is also Base and LO is also Top.]
8. How might you explain an older species being above a younger species in your sedimentary
sequence? [note: this is not the norm, older should be deeper (below) younger, so what could
mix this up?]
IV. Supplemental Materials
•
•
•
To download a poster of microfossils made by teachers for teachers go to:
http://joidesresolution.org/node/265
For a short video taken on the JOIDES Resolution showing how core samples are taken
and
processed
for
foraminifera
biostratigraphy
go
to:
http://www.nisd.net/jay/joides/index.htm then selected “Processing core samples &
observing
micro
fossils
with
Dr.
Leckie
(video)”
or
go
to:
http://www.schooltube.com/video/a4ca5da84f1145a7d1e6/
The Microfossil Image Recovery and Circulation for Learning and Education
("MIRACLE") website has a wealth of images and descriptions of the main microfossil
groups: http://www.ucl.ac.uk/GeolSci/micropal/welcome.html. It includes descriptions
of the history, classification, applications, biology, lifestyle, preparation techniques, and
observation techniques of foraminifera, calcareous nannofossils, diatoms, radiolarians,
conodonts, ostrocods, and dinoflagellates. It also contains many links to academic and
professional organization sites that focus on micropaleontology.
V. References
Bown, P.R., 2005, Cenozoic calcareous nannofossil biostratigraphy, ODP Leg 198 Site 1208
(Shatsky Rise, Northwest Pacific Ocean). Proceedings of the Ocean Drilling Program,
Scientific Results, Bralower, T.J., et al. (eds), vol. 198, College Station, TX, Ocean Drilling
Program, pp. 1–44. http://www-odp.tamu.edu/publications/198_SR/104/104.htm
Gradstein, F., 1987, Report of the Second Conference on Scientific Ocean Drilling (Cosod II),
European Science Foundation, Strasbourg, France, p. 109.
Kameo, K. and Bralower, T.J., 2000, Neogene calcareous nannofossil biostratigraphy of Sites
998, 999, and 1000, Caribbean Sea. In Proceedings of the Ocean Drilling Program, Scientific
Results, vol. 165, Leckie, R.M., et al. (eds), College Station, TX, Ocean Drilling Program, pp.
3–17. http://www-odp.tamu.edu/publications/165_SR/chap_01/chap_01.htm
Katz, M.E., et al., 2005, Biological overprint of the geological carbon cycle. Marine Geology,
217, 323–38.
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Ch 3 Microfossils and Biostratigraphy
Instructor Guide
Shipboard Scientific Party, 1992, Site 846. In Initial Reports of the Ocean Drilling Program,
vol. 138, Mayer, L., et al., College Station, TX, Ocean Drilling Program, pp. 256–333;
doi:10.2973/odp.proc.ir.138.111.1992.http://wwwodp.tamu.edu/publications/138_IR/VOLUME/CHAPTERS/ir138_11.pdf
Shipboard Scientific Party, 2002, Explanatory notes. In Proceedings ODP, Initial Reports of
the Ocean Drilling Program, vol. 198, Bralower, T.J., et al., College Station, TX, Ocean
Drilling
Program,
pp.
1–63.
doi:10.2973/odp.proc.ir.198.102.2002.
http://wwwodp.tamu.edu/publications/198_IR/198TOC.HTM
Young, J.R., 1998, Neogene. In Calcareous Nannofossil Biostratigraphy, Bown, P.R. (ed.),
Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 225–65.
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