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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?