Marine Sedimentation and Sea Floor Materials

Introduction to Marine Ecology & Oceanography

Marine Sedimentation - Chapter 4

Workshop Questions: Sediment Descriptions from Sea Floor Cores

  • Data Reference: Use Table 5-2 from provided materials for sediment descriptions.

  • Graphing Instructions:

    • Part 1(a): Plot percentage calcium carbonate from Table 5-2 versus depth for cores 1-16 on the provided graph.

    • Graphing Notes:

      • Use dots for each sample.

      • Do not connect dots within the same ocean.

      • Omit samples lacking CaCO3 values.

Sharp Reduction in Calcium Carbonate

  • Part 1(b): Explain the sharp reduction in calcium carbonate below a depth of about 4000 meters in Ocean A.

    • Hypothesis: Possible causes include changes in pressure, temperature, or biological/chemical activity at depth. The carbonate compensation depth (CCD) may play a role here.

Depth Variations in Ocean A vs. Ocean B

  • Part 1(c): Explore the difference in the depth at which sharp reductions in calcium carbonate occur in Ocean A compared to Ocean B.

    • Considerations: Variations in ocean water properties, such as temperature and salinity, as well as biological activity could contribute to these differences.

Depth Profile of Cores

Graphing Profiles

  • Part 2: Plot a depth profile for each line of cores in Ocean A and Ocean B.

    • Materials: Use colored pencils to indicate dominant sediment types for each core:

    • Red: Clays

    • Blue: Oozes

    • Yellow: Sand, silt, or terrigenous clays

    • Black: Volcanic rock or basalt

Sediment Changes and Locations

  • Part 3: Discuss why sediment types change as the continent is approached.

  • Part 4: Investigate why there are no red clays in the Ocean B profile.

  • Part 5: Examination of why pelagic sediments like oozes and red clays are absent in cores 8-9 despite their oceanic nature.

Explanation of Sediment Layers

Core 5 Analysis

  • Part 6: Investigate the presence of calcareous ooze beneath red clay in Core 5.

    • Hint: Consider horizontal movement of the ocean floor caused by sea-floor spreading and the age-related sinking of the sea floor.

Sands in Cores Analysis

  • Part 7: Analyze the presence of sands in Core 14 of Ocean B at 3000 meters versus the absence in Core 3 of Ocean A.

    • Suggested Reasons: Differences in sediment transport processes, local geological features, or proximity to land could explain variations.

Accumulation Rates of Sediments

Time Needed for Sediment Accumulation

  • Part 8:

    • (a) Calculate the time required to deposit 2.5 cm of red clay, knowing it accumulates at an average rate of about 1 mm per 1000 years.

    • Calculation:

      • 2.5 cm = 25 mm

      • Time = 25imes100025 imes 1000 = 25,000 years

    • (b) Determine how much time is represented by a 10-meter long core containing 5 meters of ooze and 5 meters of red clay.

    • Assumption: Rate of ooze accumulation is ten times that of red clay.

    • Therefore, time for ooze: 5 m of ooze at 1mm/100years1 mm/100 years = 5,000extyears5,000 ext{ years}

    • Time for red clay: 5 m at 1mm/1000years1 mm/1000 years = 5,000extyears5,000 ext{ years}

    • Total Time for Core: 10,000 years.

Additional Questions - Homework

Short Answer Questions

  1. Deep-sea deposits are typically categorized into three types: bulk emplacement, pelagic sediment, or __ (complete missing term).

  2. A slurry is a mixture of water and (complete missing term).

  3. A debris flow may contain rock, gravel, water, sand, or __ (complete missing term).

  4. Pelagic sediments are subdivided into an inorganic component, mostly red clay, and an organic component termed _ (complete missing term).

  5. Calcareous oozes contain the remains of zooplankton, such as foraminifera or pteropods, and of phytoplankton, such as (complete missing term).

  6. Siliceous oozes contain mainly the remains of diatoms and __ (complete missing term).

  7. Under sufficient pressure, sand transforms into sandstone, and mud transforms into shale or __ (complete missing term).

Long Answer Question

  1. Question: Explain specifically how dust storms in the Sahara Desert of North Africa are affecting environments in North and South America.

    • Expected Discussion Points: Potential implications on air quality, climate influences, nutrient cycling, and ecological impacts in both continents.