Goldberg, D.; Meltser, A.; Myers, G.; Masterson, W. (2003): Comparison of multi-sensor spectral gamma ray tool (MGT) and conventional spectral gamma ray logs, ODP Site 1179. Texas A&M University, Ocean Drilling Program, College Station, TX, United States, In: Sager, William W., Kanazawa, Toshihiko, Escutia, Carlota, Araki, Eiichiro, Arney, James E., Carlson, Richard L., Downey, Warna S., Einaudi, Florence, Haggas, Sarah L., Hayasaka, Yasutaka, Hirata, Kenji, Horner-Johnson, Benjamin C., Mandernack, Kevin W., McCarthy, Francine M. G., Moberly, Ralph, Mochizuki, Masashi, Pedersen, Rikke Ohlenschlaeger, Salimullah, Ali R. M., Shinohara, Masanao, Werner, Carl-Dietrich, Proceedings of the Ocean Drilling Program; scientific results; Northwest Pacific Seismic Observatory and hammer drill tests; covering Leg 191 of the cruises of the drilling vessel JOIDES Resolution; Yokohama, Japan, to Apra Harbor, Guam; Sites 1179-1182; 16 July-8 September 2000, 191, georefid:2005-072229

The Multi-Sensor Spectral Gamma Ray Tool (MGT) developed for the Ocean Drilling Program (ODP) utilizes common-depth stacked data from an array of small detectors to improve the vertical resolution of natural gamma ray logs. The first field results using the MGT were obtained at ODP Site 1179 in the northwest Pacific, which penetrated clay and ash-bearing marine ooze. Data were processed postcruise to correct for borehole size effects and logging speed variations, and the tool was recalibrated at a commercial testing facility. The standard Schlumberger gamma ray tool (HNGS) was also run over the same depth interval at this site. Comparisons of the MGT and HNGS logs agree closely in total measured gamma ray counts (gAPI), although the vertical resolution of the MGT was observed to be significantly greater than the HNGS. Estimates of elemental concentrations from both tools agree well for K but differ for U and Th. Based on this comparison, the HNGS underestimates U concentration by approximately 1-2 ppm and the MGT underestimates Th concentration by 70%-80%. Enlarged borehole size (>42 cm) and the low gamma ray levels in these sediments, as well as the intrinsic differences in detector geometry and gamma ray processing methods, may explain the observed differences in U and Th estimates. The MGT log provides the enhanced vertical resolution critical to resolve the geochemical signature of thin beds and high-frequency periodicity in complex stratigraphic sequences.
West: 159.5700 East: 159.5800 North: 41.0500 South: 41.0400
Expedition: 191
Site: 191-1179
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