2001-2002 OTRC PROJECT: SEAFLOOR CHARACTERIZATION – CENTRAL AND EASTERN GULF OF MEXICO
OBJECTIVE:
To determine the spatial distribution of geotechnical and geophysical properties of the surficial marine sediments of the Northwestern Slope Region, Gulf of Mexico.
APPROACH:
A total of 190 piston cores (120 which are on hand and 70 that were recovered during December 2001) have been or will be analyzed at 4-cm intervals for the following geotechnical properties: bulk density, water content, porosity, void ratio, liquid and plastic limits, compressional wave velocity, and acoustic impedance.
Shear strength will be determined at 20-cm intervals. Select cores will be split, described in detail, and photographed.
The majority of the core sites have been or will be surveyed with a "CHIRP" high-resolution geophysical subbottom-profiler. The correlation of geotechnical properties to high-resolution seismic records of the areas where sediment cores were taken will aid in: (1) the description of basic sediment morphologic features, (2) indicating depositional histories, (3) identifying lithostratigraphic and geotechnical stratigraphic units 1 to 3 meters below the seafloor, and (4) mapping sediment horizons and stratigraphic units from region to region. The goal is to concretely illustrate where problematic sediments exist, suggest how they may have formed, and what hazards they might pose to seafloor structures.
DEPLOYMENT OF RESULTS:
This research will result in a Master of Science thesis for Mr. William Cain, a graduate student in the Department of Oceanography. The results will also be distributed in a report and a compiled data CD. We hope to put the data in a GIS format.
ANTICIPATED PROJECT DURATION: One year, extending through January 2003.
PROJECT PLAN FOR YEAR 1 (2001-2002):
Scope of Work:
One hundred and twenty cores have been examined to date. The remaining 70 cores will be analyzed in 2002 as stated above.
Anticipated Results: See approach section above.
Sponsorship: OTRC Industry Sponsors
PRINCIPAL INVESTIGATOR (S) & OTHERS INVOLVED IN PROJECT:
PI(s): William R. Bryant, Professor
Department of Oceanography, TAMUOthers: William Cain, Graduate Student
Department of Oceanography, TAMU
Date: December 2003
Project Name: Seafloor Characterization – Central and Eastern Gulf of Mexico
TEES Project Number: 32518-1510F Industry Funded
Principal Investigators: Dr. William R. Bryant
Estimated Completion Date: May 2004
Project Description:
Determine the spatial distribution of geotechnical and geophysical properties of the surficial marine sediments of the Northwestern Slope Region of the Gulf of Mexico.
Progress:
A total of 190 piston cores, have been or analyzed at 4 cm intervals for the following geotechnical properties;
Liquid and plastic limits have been determined on special cores. Shear strength has been determined at 20 cm intervals. Select cores have been split, described in detail and photographed. Will Cain the graduate student supported by this project has completed his M.S. and graduated last summer. He is now a Ph.D. graduate student in the Department of Oceanography. The data resulting from this project is in the process of being intergraded with the data generated by Mr. Mat Meyer on a previous contract, “Geotechnical properties of sediments from the western continental slope of the Gulf of Mexico”. The core data (1 GB) from the two studies is at present being organized into a GIS system by Chris Jenkins of db SEABED, at the Institute of Arctic & Alpine Research (INSTAAR) University of Colorado at Boulder. The data integration should be finished by early 2004. The GIS data will be placed on CD s and distributed to those interested.
- Bulk Density
- Water Content
- Porosity
- Void Ratio
- Liquid and Plastic Limits
- Compressional Wave Velocity
- Acoustic Impedance
Reports & Publications:
Will Cain, Classification of Sediments from the North-Central and Eastern Deep-Water Gulf of Mexico, 2002, M.S. Thesis, Department of Oceanography, Texas A&M University, College Station, Texas
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Date: June, 2003
Project Name: Geotechnical Properties Of Sediment From The North-Central And Eastern Deepwater Gulf of Mexico
Project Number: 32518-1510F Industry Funded
Principal Investigator: William R Bryant
Estimated Completion: September 2003
Project Progress:
The current progress of the study of geotechnical/physical properties of surficial sediments in the north-central and eastern Gulf of Mexico is on track and the project is due to be completed in September of 2003. Efforts on the project to this point have been to test the cores, ranging in length from 0.5 to 10 meters, for the parameters discussed below and to cultivate an understanding of surficial sediments. Following is a summary of recent analyses and findings.
A comparison has been made using several methods for categorizing regions of sediment based on wet-bulk density. This comparison analyzed sediment density using density profiles, forty centimeter, down-core averages, and by cluster analysis using the statistical package for the social sciences program and found that surface sediment densities in the North-central and eastern Gulf of Mexico fall into three basic categories. Those below 1.45 g/cc, between 1.45 and 1.65 g/cc, and those above 1.65 g/cc. These categories were mapped to find where these regions of sediment occur and some interesting results were produced. Low (<1.45g/cc) density sediments are concentrated in the intraslope basins region overlying the salt canopy along the continental slope, medium (1.45-1.65g/cc) density sediments exist in the highly eroded region along the Sigsbee Escarpment, and high (>1.65g/cc) density sediments are found out in the depocenters of the Mississippi River. Figure 1 is a representation of the sediment wet-bulk densities, 0 to 40cm down from the ocean floor as described above. Then 36 ideal cores in these regions were selected and analyzed for sediment type, sediment structure, shear strength, and photographed for the OTRC report. Included is the sediment description of one ideal core, (figure 2) used to illustrate regional characteristics. Basic analysis has been made to understand more clearly the characteristics, unique to each region based on these ideal cores. An analysis of the overall physical property relationships has been made and plots calculated to show how these cores reflect the general trend of the wet-bulk density vs. p-wave velocity of surface sediments in the Gulf of Mexico. (See figure 3)
Figure 1: Nearest neighbor representation of the density categorization in 40 cm intervals. Blue represents averaged grain densities below 1.45 g/cc. Yellow represents averaged grain densities between 1.45 and 1/65 g/cc. Red represents averaged grain densities above 1.65 g/cc.
Figure 2: Physical characteristics, description and properties of core CGP058
Figure 3: The relationship between density and velocity for all 10,000 data points
At the completion of this project, all data from this project will be integrated with the data generated in the previous project, “Geotechnical properties of sediments from the western continental slope of the Gulf of Mexico”, and will be organized for easy access via an electronic (web-browser) format. A compact disk containing the data will be submitted to OTRC for distribution.
Date: November, 2002
Project Name: Geotechnical Properties Of Sediment From The North-Central And EasternDeep-Water Gulf of Mexico
Principal Investigator: William R Bryant
Estimated Completion: September 2003
Progress:
The current progress of the geotechnical/physical properties of surficial sediments in the north-central and eastern Gulf of Mexico is on track and is due to be finished in September 2003. Efforts of the project to this point have been to test cores, ranging in length from 0.5 to 10 meters, for the parameters discussed below and to cultivate an understanding of surficial sediments. Below is a summery of what has been completed since August 2001 and what is proposed for the remainder of the project.All cores (CGP001 - CGP215; BHP001 – BHP071; CON001 – CON007; DGoMBE 1-50) 283 in total have been analyzed by a GEOTEK multi-scanning core logger (MSCL). The MSCL records bulk grain-density, p-wave velocity, impedance, void ratio, water content, and porosity at 2cm intervals along the length of each core. All core records have been processed and corrected for anomalous data points. A map of all core locations is illustrated in Figure 1.
Statistical analyses using SPSS (Statistical Package for the Social Sciences) have been used to correlate the average sediment properties, mentioned above, at 40cm intervals for every core. Among with the analyses preformed, cluster analyses have been calculated in an effort to combine all the average property data in hopes of isolating changes in basic sedimentary regimes, not only laterally, but also vertically across the central and eastern parts of the deep-water northern Gulf of Mexico. Sediment surface maps have been created using this statistical data, including contour maps of the averages for each 40cm interval for each sediment property.
A general database in Microsoft Access has been created for storage, retrieval, and analysis of all the data collected for all cores, at each 2cm interval. Any data point or multiple criteria can be retrieved from a simple mouse click menu within Access. This was completed in hopes of more accurately identifying peaks found in density or velocity plots from the MSCL. With such a large base of data Access helps manage the bulk of the data, facilitates navigation through the numbers, and allows for complex manipulation of the data.Thirty-six select cores have been split, visually described in detail, photographed, tested for shear strength via vane shear at 20cm intervals, and will be tested for liquid and plastic limits. Additional cores may undergo this more complete form of analysis if time permits. All data resulting from this project will be organized and easily accessible in electronic (web-browser) form and a CD containing the data will be submitted to OTRC for distribution.
Figure 1: Core locations
OTRC PROJECT STATUS REPORT
Project Name: Seafloor Characterization – Central and Eastern Gulf of Mexico
Project Number: 32518-1510F (industry sponsored)
Principal Investigators: William R. Bryant
Estimated Completion Date: May 2003
Project Description:
The objective of this project is to determine the spatial distribution of geotechnical and geophysical properties of the surficial marine sediments of the Northwestern Slope Region, Gulf of Mexico through analysis of 190 piston cores (120 which are on hand and 70 that were recovered during December 2001). The correlation of geotechnical properties to high-resolution seismic records of the areas where sediment cores were taken will aid in: (1) the description of basic sediment morphologic features, (2) indicating depositional histories, (3) identifying lithostratigraphic and geotechnical stratigraphic units 1 to 3 meters below the seafloor, and (4) mapping sediment horizons and stratigraphic units from region to region. The goal is to concretely illustrate where problematic sediments exist, suggest how they may have formed, and what hazards they might pose to seafloor structures.
Progress:
To date the following has been completed:
1) All cores (CGP001 - CGP215; BHP001 – BHP071; CON001 – CON007) have been analyzed via multi-scanning core logger (MSCL). The MSCL records bulk grain density, p-wave velocity, impedance, void ratio, water content, and porosity at 2cm intervals along the length of each core.
2) All core records have been processed and corrected for poor data points.
3) Statistical analyses using SPSS (Statistical Package for the Social Sciences) have been used to correlate the average sediment properties, mentioned above, for the top 40cm of each core. This will help in the designation of surficial, sedimentary boundaries in the central and eastern Gulf of Mexico.
4) Several sediment surface maps have been created using this preliminary data including contour maps of the top 40cm averages, for each sediment property.
5) A general database has been created for storage, retrieval, and analysis of all the data collected for individual cores, at each 2cm interval.By the end of September, ideal cores will be identified for each proposed sediment regime. These cores will then be split, visually described in detail, photographed, x-rayed (if necessary), vane sheered at 20cm intervals, and tested for liquid and plastic limits. (At this point 16 of 40 ideal cores have been completed via this method. If time permits more cores may be added.) This work is on schedule to be completed as a Master’s thesis in May of 2003.
Reports & Publications: N/A
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