Geology 106 Laboratory

Studies in the geologic history of deep ocean basins

For this exercise you will work with sections of core obtained for the Ocean Drilling Program (ODP) by the drillship JOIDES Resolution, as part of fundamental scientific exploration and investigation on the geology of the Earth's ocean basins. Cores contain stratigraphic records of ocean sedimentation on the ocean floor and samples of oceanic crust.  The cores to be examined show two characteristic suites, which include both shallow and deep marine deposits.One is a suite of deposits associated with the sinking of a continental shelf, such as occurs along the margins of newly formed continental blocks after continental breakup. During subsequent continental drift, the newly formed continental margins and oceanic crust gradually cool, subsiding and becoming covered with ocean waters.  Rates of sedimentation on the continental shelf determine shelf water depths.  These deposits and rocks are a characteristic suite of the rifting phase of the Wilson cycle. The other is a suite of deposits associated with the drowning of a carbonate platform, such as found in the mid Pacific Ocean basin.  Newly formed volcanic islands and plateaus are soon colonized with carbonate-producing organisms. As volcanism ceases, the volcanic mass and ocean crust slowly subside, while carbonate-producing organisms generate reefs with large quantities of sediment, typically as an atoll reef complex. The outward growth of reefs produces a characteristic suite of carbonate platform sediments.

The following core sections are available for study (click on a link to view the cores):

• Group 1: 760B-22-2, 842B-4-1, 865A-89R-3, 865A-90R-3, 879A-17R-1, 1023A-5-6; and
• Group 2 807B-3H, 812B-13R, 814A-29X, 816A-11H, 865A-28-1, 865A-90-6.

Print the following pages to use for the lab excercise

• Core group sheet (blank);
• Group table (blank) (print this twice, once for each group);
• Depositional environments figure; and
• Sedimentary rocks and sedimentary rock classifications

Procedures

1. Examine the core sections for each group and briefly describe the color, the grain size (general terms), identify fossils (if any seen), describe the bedding type and any sedimentary structures present, and identify the lithology.  (Look only; do not handle.  This is research material.)

2. Interpret the depositional environments of each core section, by reference to one of the named environments shown on the diagrams of depositional environments. In addition to those named in the diagram, you should expect to see fine-grained sediments (oozes) of the deep marine pelagic environment.

3. Apply the concept of Walther's Law to arrange the Group 1 core sections into a vertical succession expected for a subsiding continental margin that subsides to great depths. This should show the progression of depositional environments that would be found on a rifting margin of a continent (remember the Wilson cycle). Write a short geologic history of change in depositional environments, lithology, and any additional details that you can determine from these core sections.

4. Apply the concept of Walther's Law to arrange the Group 2 core sections into a vertical succession. This should show the progression of depositional environments that would be found on a subsiding atoll island complex. Write a short geologic history of change in depositional environments, lithology, and any additional details that you can determine from these core sections.

Modified on Friday, 26-Sep-2008 12:37:14 CDT.