Transcript Seafloor Sediments

Seafloor Sediments Investigation (Ch 2 p. 27)
Goal: To explores marine sediments using cores,
photos, and smear slide data.
Objectives: After this exercise, you (your students)
should be able to:
• Describe the physical characteristics of sediment cores.
• Identify major sediment components and their origin.
• Make smear slides, and use composition and texture
data from smear slide samples to determine the
lithologic names of the marine sediments.
• Make a map showing the distribution of the primary
sediment lithologies of the Pacific and North Atlantic
Oceans.
• Explain the distribution of marine sediments on their
map.
• Predict what the sediment lithologies are at other
locations on the sea floor (e.g., in the Indian Ocean).
Pedagogy
• Student Inquiry
• Real Data
• Constructivist approach
do-talk-do-talk-do….
To Do: form teams
Part 2.1. Predict (individually and then in your
team):
1. What kinds of materials might you expect to find on
the seafloor?
2. Is there any geographic pattern to the distribution of
these materials?
You will investigate these questions using empirical data and
teamwork. And then hypothesize why the sediments are
distributed the way they are.
Goal for you to learn both WHAT we know about seafloor
sediments and HOW we know it.
p. 27
p. 28-33
Initial Inquiry into Seafloor Sediments:
Core Observation
Part 2.2 Q1: Find your team’s assigned cores in:
• Core Photos (p.60-79; or access high resolution photos at:
http://iodp.tamu.edu/database/coreimages.html)
• Table 2.1 (p. 28-29)
• On the base map (p. 32-33).
Make a list of observations and questions.
[Follow with whole group discussion.]
Assigning Unique Identification Codes to Scientific Samples
Scientific ocean drilling site locations, from:
http://iodp.tamu.edu/scienceops/maps.html
Example of sample nomenclature and core photo.
The standard labeling for ocean drilling samples.
From ODP Leg [i.e., Expedition] 199 Initial Reports Volume, Explanatory Notes:
http://www-odp.tamu.edu/publications/199_IR/chap_02/chap_02.htm)
TO DO in your group:
Q2 (p.30): Design a way to
organize and record your visual
observations that could be used
by all of the students in the class
for all of the cores. [Follow with
whole group discussion.]
Q3 (p. 31): Using the agreed
upon approach, describe your
core. [Follow with group
presentations of cores.]
Q4 (p. 34): Explain why a
systematic, complete, and
consistent method of recording
observations is important.
Sediment Composition (think back to your predictions)
p. 35-51
• Composition (minerals & microfossils) and texture are the primary
data used to “name” the sediment:
TO DO:
Part 2.3 Q1 (p. 37): Match smear
slide data for your core’s samples
listed Table 2.2 (p. 42-51) to mineral
and fossil images in Fig 2.3.
Extension Lab: Make a sample request from IODP (http://iodp.tamu.edu/curation/samples.html)
and make your own smear slides. Try to identify the components, using the following
resources:
• Images in Fig 2.3, p. 35-36.
• http://www.noc.soton.ac.uk/gg/BOSCORF/curatorial/grain_id.html
• Rothwell, Minerals and Mineraloids in the Marine Sediments.
Sediment Classification….Name that Sediment!
TO DO: Q2, (p. 37) For your assigned core(s), determine the
dominant sediment types in the samples.
HOW?
– Use the smear slide data (Table 2.2, p. 42-51).
– Look at the core photos p. 60-79, or access high res digital
core photos at
http://iodp.tamu.edu/database/coreimages.html)
– Use the Decision Tree p. 38-41.
– Record your sediment names in Table 2.2 AND (Part 2.4,
Q1, p. 52) plot on your map AND on “class” map using
colors on p. 52.
Do example together
Important information about using the Decision Tree (p.38-41):
The decision tree aims to capture the most distinctive (i.e., end-member, dominant)
sediment types:
• Calcareous ooze: biogenic sediments composed of calcareous nannofossils and/or
foraminifers.
• Siliceous ooze: biogenic sediments composed of diatoms, radiolarians, sponge
spicules, and/or silicoflagellates.
• Red clays: very fine terrigenous sediment that often contains siliceous microfossils,
fish teeth, Mn-Fe micronodules, and/or volcanic glass.
• Terrigenous sediment: siliclastics; sediment from the weathering of continents or
volcanic islands.
• Glaciomarine sediment: sediment containing terrigenous sand, pebbles, or cobbles
transported to the sea by icebergs.
Note, while the above 5 sediment types are the most distinctive sediment types, mixed
sediment types are common. In addition, the sediment type can also change within a
core. For example the sediment could alternate between two or more sediment types or
gradually change from one to another.
In any of the sediment types, but especially in biogenic oozes and deep sea red clays,
layers of volcanic ash may be distinguishable.
TO DO: Q2 & Q3 (p. 52-54). Analyze class map. Develop
hypotheses for what controls the distribution of each of the
primary sediment types in the modern ocean.
How does this distribution compare to your initial predictions?
Distribution of Marine Sediments– there is a rhyme and reason!
YOU derived this sediment type map from core data!
Q4 (p.54): How does your map compare to this one?
Distribution of the primary sediment types on the seafloor (from Davies and Gorsline, 1976; Rothwell, 1989)
Idea for extension: Interpret the rest of map (draw boundaries between
different primary sediment types)
Follow-Up Exercise with Lecture
on Marine Sediments
Terrigenous Sediment
• derived from the weathering
& erosion of rocks on land:
sand & mud
• accumulates along
continental margins
• masks other sediment types
because of high
sedimentation rates
Glaciomarine Sediment
• Terrigenous – but a special
type that indicate glacial
conditions on land.
• Can accumulate far from
land via iceberg rafting.
• Best recognized by
dropstones in cores.
Biogenic Rich Sediment = Ooze
What are the requirements
for biogenic ooze to
accumulate ?
1. Productivity in the surface waters
2. Preservation (i.e., not dissolved) as
settle through the water column
3. High relative abundance (i.e.,
avoid dilution by other sediment
types)
Key points for Lecture on Marine
Sediments
Calcareous Ooze
• composed of carbonate
shells of plankton (CaCO3)
• accumulates on
bathymetric highs (above
CCD) & beyond the
continental margins
Siliceous Ooze
• composed of the siliceous
shells of plankton (SiO2)
• accumulates under areas of
high productivity
Follow-Up Exercise with Lecture
on Marine Sediments
Deep Sea Red Clay
• wind-blown dust & current
transported clays
• accumulates on the abyssal
plains (deep broad sea
floor)
• mixed with minerals that
precipitate on the sea floor
and some siliceous
microfossils
• very slow sedimentation
rates
Exploring Further:
Q5b (p. 55): Is calcareous ooze in the N Atlantic found at the same depth, shallower
depths, or deeper depths than in the N. Pacific? Why?
Q6 (p. 55): The map you constructed represents the modern distribution of sediment
types in the Pacific Ocean. Do you think this map would also represent sediment type
distribution in the geologic past and in the geologic future? What factors might vary (in
the past and in the future) that could change the distribution of sediment types?
Exploring The Instructor Guide
See handout for
most of the
instructor guide;
For full guide go
to DROPBOX.
Exploring Scientific Data Collected from Marine Expeditions
To Do: See Scientific Ocean Drilling Initial Results Volume(s) (online:
http://www.iodp.org/scientific-publications/ or get a hard copy). Explore
Initial Results Vol overall.
Idea for extension: Write (type, single spaced) a 1-page summary of the
types of scientific data collected from cores, how it is reported and
organized, and your comments and questions on it.
Ideas for Extension: Refine Your Core Description
and Sediment Classification
• Refine based on Explanatory Notes section of an Initial Results
(IR) volume:
-methodologies and symbols used in descriptions
http://publications.iodp.org/proceedings/320_321/102/102_f8.htm
http://publications.iodp.org/proceedings/320_321/102/102_3.htm
- lithostratigraphy: naming the sediments (and then defining
lithostratigraphic units)
-http://publications.iodp.org/proceedings/320_321/102/102_f9.htm
• Find the core description online (IR volumes) for your core.
Compare your core description to the published description.
Write a reflection on: the strengths and weakness of your
description, how you would modify your approach in the future.