INSTRUCTOR GUIDE Chapter 12 Interpreting Antarctic Sediment Cores

41 Pages·2012·1.35 MB·English

Ch 12 Interpreting Antarctic Sediment Cores Instructor Guide

INSTRUCTOR GUIDE
Chapter 12
Interpreting Antarctic Sediment Cores: A Record
of Dynamic Neogene Climate

SUMMARY
This set of investigations focuses on the use of sedimentary facies (lithologies interpreted to
record particular depositional environments) to interpret paleoenvironmental and paleocli-
matic changes in Neogene sediment cores from the Antarctic margin. Particular attention
will be given to characteristics of settings close to the ice (ice-proximal) and far from the ice
(ice-distal) in high-latitude settings. In Part 12.1, you will build your knowledge of polar sediment
lithologies and the corresponding facies through conceptual diagrams, geological reasoning, and use
of core images and core logs (a graphical summary of the sediments). In Part 12.2, the core log for
the entire 1285 m ANDRILL 1-B core is presented. You will characterize each of the key
lithostratigraphic subdivisions and use your knowledge of depositional facies to write a brief history
of the Neogene climatic and environmental conditions in the Ross Sea region. In Part 12.3, you will
use your core log reading skills and facies knowledge to evaluate patterns in the Pliocene sediments
from ANDRILL 1-B. You will correlate quantitatively patterns in your dataset with cycles in insolation,
influenced by changes in the Earth’s orbit during the Pliocene.

FIGURE 12.1. ANDRILL Scientists discussing a part of the ANDRILL-1B core in the Core Lab, McMurdo Station Season
2006/7. Courtesy of the ANDRILL Program.

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Ch 12 Interpreting Antarctic Sediment Cores Instructor Guide
Goal: to assess the nature of Antarctic climate change during the Neogene.

Objectives: After completing this exercise your students should be able to:
1. Recognize and differentiate among the different primary sedimentary facies
proximal to and distal from ice in high-latitude settings and connect each facies to a
particular depositional environment.
2. Apply their understanding of facies and the lithologic log of the ANDRILL 1-B core
to write a brief history of Neogene climate and environmental conditions in the
Ross Sea region of Antarctica.
3. Qualitatively and quantitatively describe the patterns of deposition in the Pliocene,
and correlate these to orbitally-driven cycles of insolation change.

I.How Can I Use All or Parts of this Exercise in my Class?
(based on Project 2061 instructional materials design)

Part 12.1 Part 12.2 Part 12.3
Title (of each part) What Sediment ANDRILL 1B – The Pliocene Sedimen-
Facies are common Big Picture tary Patterns in the
on the Antarctic ANDRILL 1-B Core
Margin?
How much class time 40 to 60 mins + 30 to 120 mins 40 to 80 mins
will I need? (per part) (depends on (depends on (depends on student
amount of discus- amount of discus- level, amount of
sion, extra material sion and extra ma- discussion and stu-
used, student ex- terial used, or dent comfort with
perience, or ‘mini-lectures’ math and rate cal-
‘mini-lectures’ given, and student culations)
given) experience)

Can this be done in- Yes. Would need Yes. Would need Yes. Would need
dependently (i.e., as follow-up discus- follow-up discussion follow-up discussion
homework)? sion in class in class in class. Might need
preparatory review
of rate calculations.
What content will students be introduced to in this exercise?
Science as human endeavor
Judgement, x x x
decision-making,
problem-solving
Science as an evolving process / Nature of Science
New Research builds on x x x
previous research
Unexpected discoveries x x x
Exploratory research vs. x
focused questions
Research enabled by x x
technology (technology
change through time)

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Ch 12 Interpreting Antarctic Sediment Cores Instructor Guide
Earth History Archives (nature of the sedimentary record)
How do you know about x x x
earth history? Types of
archives outcrops vs.
cores
Where do you go to learn x x x
about earth history?
Land vs. sea vs. ice
Geographic awareness x x x
Awareness of deep time x x
Marine sediments (dis- x x x
tribution & controls on
distribution)
Stratigraphic Principles
Relative dating x x x
Subdivisions of geologic x
time
Unconformities, hia- x x x
tuses, missing records
Climate Change
Glacial-interglacial cy- x x x
cles
Climate change can be x x
gradual
Greenhouse - Icehouse x
Climate change can be x
abrupt
Regional to global scales x x
of change
Ocean-atmosphere-bios
phere-cryosphere sys- x x x
tem interac-
tions/feedbacks
High latitude climate x x x
change sensitivity
What types of transportable skills will students practice in this exercise?
Make observations (de- x x x
scribe what you see)
Recognize trends x x x
(abrupt vs. gradual vs.
patterns)
Plot data – map, graph, x
pictoral form
Form Questions x
Interpret graphs, dia- x x x
grams, photos, tables
Make hypotheses or x x x
predictions
Test a hypothesis x x x
Critical reading & analy- x
sis
Synthesize/integrate & x x x
draw broad conclusions

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Ch 12 Interpreting Antarctic Sediment Cores Instructor Guide
Math Integration
Perform calculations x x
(rates, averages, unit
conversions) & develop
quantitative skills
Communication
Written communication x x
Making persuasive, well x x x
supported arguments
Uncertainty in Science
Identifying assumptions x x x
& ambiguity
Levels & types of un- x x
certainty (quantitative
vs. qualitative)
Significance/evaluation x x x
of uncertainties &
ambiguity
What general prereq- None required, but 1.Ability to summa- 1. Ability to follow
uisite knowledge & prior exposure to rize / write in clear instructions
skills are required? the following topics written english 2. Basic knowledge
would be helpful: 2. Ability to read of what a sed core is
1. Antarctic Geog- stratigraphic col- 3. Ability to read
raphy umns stratigraphic col-
2. Nature of the 3. Basic under- umns
Cryosphere standing of the 4. Basic math skills
3. Nature of sedi- concept of different (rate calculations)
ment cores depositional envi- 5. Knowledge of
4. General strati- ronments long-term orbital
graphic principles 4. Ability to make variations of eccen-
5.General geologic simple estimates tricity, obliquity, and
time scale and determine ap- precession (see Cli-
proximate percent- mate Rhythms mod-
ages ule)

What Anchor Exer- 1.Intro to Cores Part 1 of this exer- 1. Parts 1 and 2 of
cises (or Parts of Ex- exercises cise this exercise;
ercises) should be 2.Cenozoic Over- 2.Intro to Cores 2.Intro to Cores ex-
done prior to this to view exercises exercises ercises 3.Cenozoic
guide student inter- 3.Seafloor Sedi- 3.Cenozoic Over- Overview exercises
pretation & reason- ments exercises view exercises 4.Seafloor Sedi-
ing? 4. Past Antarctic 4.Seafloor Sedi- ments exercises
Climates exercises ments exercises 5. Past Antarctic
5. Past Antarctic Climates exercises
Climates exercises 6. Climate Rhythms
exercises
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Ch 12 Interpreting Antarctic Sediment Cores Instructor Guide
What other resources 1.World map or 1.World map or 1.World map or
or materials do I globe; Map of Ant- globe; Map of Ant- globe; Map of Ant-
need? (e.g., internet arctica or the Arctic arctica or the Arctic arctica or the Arctic
access to show 2.Internet connec- 2.Internet connec- 2. Document camera
on-line video; access tion and data pro- tion and data pro- or over head pro-
to maps, colored jector for viewing jector for viewing jector for discussion
pencils) videos, and access videos, and access of figures
to supplementary to supplementary 3. Calculators
materials materials 4. Maps / figures
3.Document cam- 3.Document camera from ‘Past Antarctic
era or over head or over head pro- Climates’ exercises
projector for dis- jector for discussion for use in discussions
cussion of figures of figures 5. Earth-Sun-Moon
4. You may want to 4. Calculators model if students
print out/laminate 5. Highlighters help need assistance with
images in Figure 3 students select seasons and obliq-
for use in class abundant facies in uity, eccentricity and
Table 2 (Question 5) precession.
6. Hand-lens or 6. Symbols used for
magnifying glass to sediment portrayal in
help read fine print sediment core logs
in Figure 1 – or print
out of enlarged ver-
sions

What student mis- 1.All sediment is 1.There really isn’t 1.Thre is no real
conception does this the same much one can do reason for changes in
exercise address? 2. Nothing can live with a a sediment seafloor sediment
in ‘cold’ water core from the sea- 2. All cores of a fixed
(diatoms) floor length represent an
3.Diatoms are 2. Only igneous equal amount of time
plants (they are rocks provide pa- (i.e. rate of sedi-
not plants) leomagnetic data mentation does not
4. The depositional 3. The information matter)
environment at one is too complex to 3. Repeated patterns
fixed locality can- make any interpre- in sedimentation are
not change over tations just chance
time (they DO 4. Microscopes are
change over time) used only for biol-
5. There is no order ogy
or reason for the
sedimentary se-
quences that we
see.
6. It is all in Ant-
arctica, so it won’t
tell us anything
useful about cli-
mate change be-
cause it has always
been cold there

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Ch 12 Interpreting Antarctic Sediment Cores Instructor Guide
What forms of data 3-D sketch, cross Videos, core logs, Core logs, thick-
are used in this? (e.g., section, written tables nesses, age data
graphs, tables, pho- descriptions, core
tos, maps) images, core logs
What geographic lo- Antarctica Antarctica (Ross Antarctica (Ross Sea
cations are these Sea region) region)
datasets from?
How can I use this Instructor ‘grading’ Instructor ‘grading’ Instructor ‘grading’
exercise to identify of exercises checks of exercises checks of exercises checks
my students’ prior on student under- on student under- on student under-
knowledge (i.e., stu- standing of: standing of: standing of:
dent misconceptions, Sedimentary envi- Data that can be Reading core logs;
commonly held be- ronments, order of ‘collected’ from a complete guided rate
liefs)? depositional events sediment core; es- calculations; make
(& Walthers Law); timate percentages; connections (orbital
sedimentological develop simple cycles)
terminology and reasoned interpre-
reasoning; ability tations
to predict and de-
velop hypotheses –
and test them; how
to apply knowledge
of depositional en-
vironments in core
interpretation

How can I encourage 1.Ask students: what they found interesting/useful?
students to reflect on 2.Ask students: what was new?
what they have 3.Ask students: what questions it makes them want to ask?
learned in this exer-
cise? [Formative As-
sessment]
How can I assess See suggestions in Summative Assessment section at end of
student learning after Instructor Guide
they complete all or
part of the exercise?
[Summative Assess-
ment]
Where can I go to for See the supplemental materials and reference sections at end of
more information on Instructor Guide
the science in this
exercise?
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Ch 12 Interpreting Antarctic Sediment Cores Instructor Guide
What is the Context This could be used as a final review & capstone activity in an
for use of these exer- introductory geoscience course, or as an introductory review in an
cises? upper-level geoscience course that incorporates sedimentology or
climate change.
Part 1 could be used to introduce students to sedimentary facies
and Walthers Law; Part 1 could be a stand-alone exercise.
Part 2 could be used as a stand-alone exercise for students al-
ready familiar with glaciomarine depositional settings, but it does
require the understanding that is built in Part 1.
Part 3 is designed to follow Part 2, but it could (if adapted) be a
stand-alone exercise IF students are adequately prepared.
ALL of these exercises benefit enormously from construction of
knowledge in the Past Antarctic Climates Ch 11 exercise, although
they do not depend on it.

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
Chapter 12. This instructor guide contains 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 12.1. What Sediment Facies are Common on the Antarctic Mar-
gin?

Figures 12.2 & 12.3 illustrate the variety of depositional environments and sediment types
possible at the margin of a glacially influenced land mass, such as in the Ross Sea region, Antarctica.
Figure 12.2 shows outlet glaciers from the East Antarctic Ice Sheet (EAIS, upper left) cutting through
the rocks of the Trans Antarctic Mountains to the Ross Sea (lower right). Note that Nothofagus trees
would have only been present during a period of temperate or warmer conditions. In Figure 12.3 the
glacier (stippled) is flowing from right to left, into Antarctic Ocean waters. The different sediment
lithologies are labeled (e.g., diamict).
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Ch 12 Interpreting Antarctic Sediment Cores Instructor Guide
A
A
B
A
C
B
A
B D
C
B
C
D

FIGURE 12.2. General paleoenvironmental setting for sedimentation along the flanks of the Trans Antarctic
Mountains in late Oligocene time. From Hambrey et al., 2002. Nothofagus refers to southern beeches (Genus Nothofagus,
Family Nothofagaceae) which are native to temperate oceanic to tropical regions in the southern hemisphere.

FIGURE 12.3. Cross section showing a conceptual model for growth and decay of a tidewater glacier in Lambert
Graben Fjord, Lambert Glacier Region, Antarctica. From Hambrey and McKelvey, 2000. The vertical scale is in meters and
the horizontal scale is in kilometers. Letters A–D are explained in Question 1.

1 Match locations A–D in the conceptual model (Figure 12.3) to locations within the paleonvi-
ronmental setting (Figure 12.2). Do this by writing letters A–D on Figure 12.2. In the following
table, explain why you placed each letter where you did.

If this exercise is done in class you could start by asking the students to compare and contrast the
two figures. You may need to provide guidance in reading the captions, and emphasize the im-
portance of reading figure captions and legends, and review the difference between a cross-section
and a 3-D visualization, as well as conceptual models. Students may need reminding that the white
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Ch 12 Interpreting Antarctic Sediment Cores Instructor Guide
represents rocks sticking up above the pale blue ice, and that the sea is gray. For information on the
role of the grounding line go to http://nsidc.org/sotc/iceshelves.html or Conway (1999) or Anderson
(2007). The Lambert Glacier region is not the closest comparison to the Ross Sea Region, but these
figures are the best diagrams available in the published literature. Some of the selections simply
involve matching words for environmental settings – others involve 3-D thinking. For more detailed
discussion of Glacial Marine depositional settings refer to the texts of Martini et al. (2001), Menzies
(2002), Benn and Evans (1998), and Bennett and Glasser (1996).

Location Your Reasoning
A. On the surface Location (see Figure 12.2): Beneath the ice; below (down-ice of) the crevasses that mark the transition from the
of, and beneath, East Antarctice Ice Sheet (EAIS) the valleys occupied by the outlet glaciers. The location needs to be ‘up-ice’ from
grounded outlet the grounding line (which can be treated as the position of the ‘coastal plain’ beneath the ice).
glacier Reasoning: If the ice melts, any sediment on the ice surface would be deposited where the ice was. The location is
far enough back from the front of the ice to be ‘above’ the maximum reach of seawater under the ice. Arguments for
how far ‘up-ice’ the location could be are complex – relatively little is known about how much sediment is carried and
deposited by the EAIS.
B. Region where Location (see Figure 12.2): Either where it says ‘braided river’ OR beneath the ice close to (above or below) the
a braided river, or grounding line, which in this case can be approximated as the position of the coastal plain beneath the outlet gla-
subglacial melt- cier.
water, enters Reasoning: Sub-glacial and pro-glacial streams may carry large volumes of sediment. These streams may tran-
ocean waters sition to braided streams away from the ice front. An important alternative is the environment beneath the ice both
above and below the grounding line; sub-glacial water can transport and organize glacially deposited sediment –
and sediment that is melting out of the overlying ice.

C. Marine region Location: (see Figure 12.2): Anywhere beneath icebergs
characterized by Reasoning: This location is beneath current icebergs. Note that Figure 12.2 is a ‘snapshot’ for a fixed moment in
icebergs time; icebergs will move away front the ice front until they melt; under appropriate conditions they may also move
parallel to the coast – this means that there will be a ‘zone’ in front of the ice in the ocean where icebergs may be
present; this zone will essentially run approximately parallel to a coastline that is marked by outlet glaciers and ice
shelves.
D. Marine region Location: (see Figure 12.2): Anywhere in the bottom right of Figure 12.2 – to the right of the dashed line marked
below wave base ‘below wave base’
and seaward of Reasoning: This location is seaward of the line that marks ‘wave base’, and is also seaward of any of the icebergs.
melting icebergs This zone will broadly parallel a coastline marked by outlet glaciers and offshore icebergs.

The following section introduces several important lithologies that are diagnostic of ice-distal to
ice-proximal depositional settings in polar regions. Note that these lithologies are more specific than
the general marine lithologies (e.g., siliceous ooze, glaciomarine) of the global ocean that were
introduced in Chapter 2.
Answer Questions 2–5, based on:
• The information on sediment type in the boxes below
• Figures 12.2 & 12.3
• The short videos ‘5:Telling Time’ (2007) and ‘6:Cenozoic Global Climate’ (2007)
from http://www.andrill.org/iceberg/videos/2007/index.html
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Ch 12 Interpreting Antarctic Sediment Cores Instructor Guide

The following four questions focus on only four of sediment types deposited near and at glaciated
continental margins. These are the ‘end-member’ sediment types used here for building the sedi-
ment core interpretations. For images of these settings go to: http://nsidc.org/gallery/ .

SEDIMENT TYPE: DIATOMITE
Diatoms are an important group of single-celled free-floating photosynthetic protists (i.e., phyto-
plankton) that precipitate an opaline silica shell. They are particularly important in areas of open
water around Antarctica. Some species of diatoms thrive in the ocean waters under ice shelves.
Sediment made up of diatoms is called diatom ooze or siliceous ooze if it is unlithified, and di-
atomite if it is lithified. These sediments are typically a pale yellowish brown or greenish grayish
yellow in color and may be bedded or laminated; sometimes they are bioturbated.

2 If you are interpreting the history of depositional conditions on the continental margin of Antarc-
tica, what important piece of environmental information about a location would you gain from
the presence of diatom-rich sediments at that site?

For images and information on diatoms and diatomite to supplement this information go
to: http://www.indiana.edu/~diatom/diatom.html
and http://www.ucmp.berkeley.edu/chromista/bacillariophyta.html

The presence of diatom-rich sediments indicates open-water conditions, with the water being clear
enough (free of suspended sediment) for diatoms to photosynthesize, and subsequently settle to the
seafloor. Conversely, this indicates that the immediate vicinity was not covered by ice, or beneath a
sediment plume.

SEDIMENT TYPE: SEDIMENT CONTAINING ICEBERG-RAFTED DEBRIS
When a glacier terminates in the ocean, icebergs can break off (or ‘calve’) from the front of that
glacier or ice shelf, and drift out to sea. The icebergs carry sediment particles that were eroded by
and embedded in the glacier as it moved across the land. The particles range from clay- to
gravel-sized. As the iceberg melts, the sediment particles are released and settle on the seafloor.
The most noticeable particles deposited by this process are the larger gravel-sized particles, which
are called iceberg-rafted debris (IRD); these particles are particularly noticeable as isolated large
grains within finer grained sediment (terrigenous sands, silts, and muds). The finer grained sediment
containing the IRD may also contain a low concentration of diatoms, particularly at locations further
from the end of the glacier as open-marine conditions become more dominant.
3. If you are interpreting the history of depositional conditions on the continental margin of Ant-
arctica, what important piece of environmental information about a location would you gain
from the presence of a mud that contains a few percent of diatoms, as well as isolated gravel-sized
(or larger) grains?

The presence of diatoms indicates that the region is in the vicinity of open water, which allows
diatoms to photosynthesize. They subsequently die naturally and fall to the seafloor. The presence of
mud indicates fall-out of suspended sediment that could be derived from a sediment plume or as-
sociated with turbidity currents carrying material winnowed from diamictites at the submarine exits
of subglacial streams. The presence of isolated gravel grains tells us that icebergs carrying sediment
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