Download GEOS412, Ocean Sciences Homework 2: Marine Sediments Due

Name:
GEOS412, Ocean Sciences
Homework 2: Marine Sediments
Due February 1 in class
Introduction: In this lab you will examine a suite of sediment samples from various
parts of the world ocean. The objective here is to familiarize you with the common types
of sediments found in the deep sea that blanket much of the ocean floor (a few shallow
water samples are also included). You will have a chance to see the types of biogenic
particles (fossils) that make up much of this sediment, and to think about the possible
controls on sediment distribution patterns on the sea floor.
Please be sure to bring your textbook (Pinet) to lab for this exercise.
General instructions. Please BE CAREFUL with all samples. The samples you are using
were obtained with some difficulty from the Integrated Ocean Drilling Project (formerly
Deep Sea Drilling Project) and other core repositories and are not easily replaced. Please
follow your TA’s instructions and do not waste these valuable samples.
PART I. Reading. As background material for this lab, please be sure to read Chapter 4
of Pinet. Also take a look at the brief summary article on the web on deep sea scientific
drilling at http://geology.about.com/cs/escibasics/a/aa101203a.htm
This article has links to sites describing the various scientific drill ships and drilling
programs that collectively have revolutionized our understanding of plate tectonics, the
seafloor and the sediments that blanket the seabed.
PART II Sample Location and site characterization. This part of the exercise consists
of filling in the table below. It should be done before you come to lab. This way we don’t
have to have internet access at the same time you are doing microscope work. First you
will need to do some detective work to determine where the various samples (numbered
by microscope station below) came from, and for the older samples, do some units
conversions. The table you will produce will help you answer the questions posed below.
In some cases the information is partially provided for you and in others you will have to
do some searching to get it.
Samples 1-5. For the DSDP samples, first refer to the map below to locate the
approximate location of the sample (this will let you determine the ocean basin or sea
where the sample came from). Once you know the approximate location you will be able
to get more information on the drill site where these samples were collected at
http://www.ngdc.noaa.gov/mgg/geology/dsdp/area/areas.htm
Click on the appropriate ocean basin or sea from which the sample was obtained and
then find the sample’s latitude and longitude based on the hole and leg numbers (see table
below) By convention negative latitudes are south of the equator and negative longitudes
are west of Greenwich, England. Note that location information in this file is provided
using decimal degrees. You can then click on the hole number to obtain additional
information about the drill site, which will be useful for some questions later on. Now use
the NOAA interactive bathymetric map of the world to determine the depositional setting
(e.g., ridge, absyssal plain, etc.) for each DSDP sample. This map (which you’ve used
before) is at
http://ibis.grdl.noaa.gov/cgi-bin/bathy/bathD.pl
You will need to zoom in on the approximate area for each sample and then pan to move
the upper corner onto the “exact” latitude/longitude. This takes some practice as the pan
mechanism isn’t very good (at least with my browser)-try to get the upper right corner
within a few tenths of a degree long/lat of the core sample site, and then record the
environmental setting (topography, flat, rugged, elevated etc) using the color scale on the
right side of the map. To get the precise water depth for each site click on the hole
number. This will take you to a page called “Core Data from the Deep Sea Drilling
Project” with the leg and hole number as subtitles. Look in the table for the row labeled
“Site Summary Information” and click on “original”. This will give you summary data on
the core site. The 8th column from the left is the water depth in meters. For example, for
site 310, leg 32, the depth is 3516m. Record the depths for all six DSDP sites in your
table.
Sample 6. Padre Island. See Figure 2. Padre Island is the barrier island directly east of
Corpus Cristi, Texas. This beach sand can be assumed to have been collected at 0m water
depth. Locate Padre Island on Figure 2 (zoom in) and put the approximate longitude and
latitude information in the table.
Sample 7. Backreef sample- Nonouti, Kiribati (locate the ocean basin using the
geographic coordinates given)
Figure 1: Map of DSDP Drill Sites
Figure 2. Bathymetric Map of the SE US continental margin.
Table 1. Sample Station Data
Microscope Identifier
Ocean
Longitude
Sample #
Basin/Sea
1
2
3
4
5
6
7
DSDP Leg
17, Hole
166
DSDP Leg
19, Hole
183
DSDP Leg
23, Hole
229
DSDP Leg
91, Hole
595
DSDP Leg
90, Hole
591
Padre
Island
Kiribati
Atoll
173E
Latitude
Approx.
Water
Depth
Environmental
Setting (e.g.
beach, abyssal
plain, oceanic
rise etc)
1.42ΕN
10m
Backreef
Lagoon
PART III. To be done in lab. The samples listed in the table above are laid out at
microscope stations. Please do not mix them up or bring them to a different station.
Refer to your textbook figures 4-14 (p. 121) and 4-16 (p. 124) for help in answering
questions. Your TA will provide you with the “field of view” diameter for each
microscope setup, which you will need to estimate several of the questions below and to
make your scale bars.
Sample 1
1A. Look at the sample. Carefully draw some of the objects you see, making sure to
include a scale bar.
1B. Identify these fossils by comparison with Pinet Fig 4-14.
1C. Are these fossils from single-celled or multicelled organisms?
1D. Are they zooplankton or phytoplankton?
1E. Are all of the fossils from the same species or do you see multiple species?
1F. What is the skeletal composition of these types of fossils? Is this consistent with the
map of deep sea deposits shown on Pinet Fig. 4-16 (p. 120)?
1G. According to the DSDP logs for the sediment core from which this sample was
obtained, the bottom of the core (310m below the sea floor) contains fossils that can be
dated at about 125 million years in age. Calculate an average sedimentation rate for this
site over this entire period in cm/1,000 years. Show your work.
1H. How does this average rate compare with the modern rates of sedimentation for this
area and sediment type shown in Pinet figure 4-16b?
1I. Can you come up with an explanation as to why the two rates may be different?
1J. The sample you have here is 125.6m below the sea floor. Assuming a relatively
constant sedimentation history over the entire history of the core, and assuming that the
top of the core is modern sediments (i.e. 0 million years) what would you estimate the
age of the sample you are looking at to be? Show your work.
1K. (After lab ends). Now go back to the Site 166 core data at
http://www.ngdc.noaa.gov/mgg/geology/dsdp/data/17/166/index.htm and click on the
row “age profile” “original”. This will give you a data table that shows the geologic time
periods for various intervals of the core. The time period is given by the letter
abbreviations and the depth interval (in meters below sea floor) corresponding to that
interval is given in the 3rd and 4th columns. What is the age range of the 125.6m sample?
Use the geological time scale handout your TA gives you to determine the age of the
UOLIG (=Upper Oligocene).
How does this correspond with your earlier age estimate for the sample?
1L. What does this imply about sedimentation rates in the deep sea?
Sample 2.
2A. Based on your identification of the primary fossil components of this sample, is this
sediment a siliceous or a calcareous ooze?
2B. Now look at the map on p. 362 in Pinet of primary productivity in the oceans along
with the map of sediment distribution in Figure 4-16 (p. 124). We will learn a lot more
about primary productivity later in the semester, but basically primary production is the
rate at which living organisms (mostly single celled algae) are growing (hence being
“produced”) in a given area. In this graph it is expressed as grams of carbon “fixed” (as
living tissue) per square meter of ocean (all the way down through the water column) per
year. Is there any relation between productivity at the locations of samples 1 and 2 and
sediment type? Why?
Sample 3.
3A. Draw and identify the dominant fossil types in this biogenic ooze. Include your scale
bar. Are these fossils made of mostly silica or carbonate?
3B. Why are you finding these types of fossils in sample 3 but not in sample 1 or 2?
(Hint-Tuesday’s lecture should help you out here)
3C. Look at and record the color of the sediment in this sample. Light reddish or
brownish colors in sediments typically indicate the presence of oxidized iron (the fully
oxidized iron mineral hematite is a red-rust color) and/or limonite (a yellowish brown
iron hydroxide). Blackish, dark gray or dark green colors often indicate the presence of
reduced iron (iron sulfides like pyrite) or reducing agents such as organic matter. Dark
colors are also common in conditions of rapid burial (i.e. high sedimentation rates) where
organic matter does not have the opportunity to become oxidized at the sea floor as it
settles. Do you think this sediment was deposited under oxidizing or reducing conditions?
What does this tell you about the seafloor in this area?
(Because the sample has been sitting around for a while at the earth’s surface (and thus
has been partly oxidized) the best way to get a handle on this is to look at the sediment
that has been trapped inside of the conical fossils)
3D. Now go back to the site information table for this location at
http://www.ngdc.noaa.gov/mgg/geology/dsdp/area/areas.htm and find the age profile for
this sample site. This particular core sample was collected from 19m below the sea floor.
Using the age profile table and your time scale (beginning of the Holocene =10,000 years
ago), estimate the age of this sample and the sedimentation rate for this site. Show your
work.
3E. Compare this rate with what you calculated for Site 1. Given the site location
differences (look at your map) how would you explain the difference?
Sample 4. Give the Munsell color and average particle size of this sample (for the color,
look at the specimen on the microscope slide rather than in the jar). Is this sample a
biogenic ooze? If not, what is the origin of these particles?
Sample 5.
5A. In this sample the fossils making up the ooze have been largely degraded into
fragments. Some individuals may still be visible, at least as general shapes. Try to
identify these but don’t bother drawing them (hint: you’ve seen them in at least one
previous samples). What processes might explain the fact that the skeletons have mostly
been broken down into fragments (hint: consider the water depth)?
5B. Consider all of the biogenic oozes and nonbiogenic deep sea sediments you have
examined so far. Look at the water depths that they were obtained from. Can you come
up with an explanation for the general patterns of accumulation you have observed (hint:
it may be helpful to review Chapter 4 of Pinet before answering this)?
Sample 6. Is this a terrigenous or biogenous sand? Based on the geographic origin of this
sample, explain briefly where you think these particles originally came from?
Sample 7. Examine this sample from the “back-reef” environment of the Kiribati Atoll.
This is the lagoon formed between the reef surrounding the island and the island itself. Is
this material carbonate or terrigenous? How does it differ from other sandy samples you
have examined thus far? Do you think the skeletal debris is derived from planktonic or
benthic organisms? What does the grain size of this sample indicate about the
environment of deposition?