Lithostratigraphy determined from downhole logs in the AND-2A borehole, southern Victoria Land Basin, McMurdo Sound, Antarctica
During the 2007–2008 austral spring season, the ANDRILL (Antarctic Drilling project) Southern McMurdo Sound Project recovered an 1138-m-long core, representing the last 20 m.y. of glacial history. An extensive downhole logging program was successfully carried out. Due to drill hole conditions, logs...
| Published in: | Geosphere |
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| Main Authors: | , , , |
| Format: | Article in Journal/Newspaper |
| Language: | unknown |
| Published: |
2013
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| Subjects: | |
| Online Access: | https://epic.awi.de/id/eprint/33140/ https://doi.org/10.1130/ges00774.1 https://hdl.handle.net/10013/epic.41640 |
| Summary: | During the 2007–2008 austral spring season, the ANDRILL (Antarctic Drilling project) Southern McMurdo Sound Project recovered an 1138-m-long core, representing the last 20 m.y. of glacial history. An extensive downhole logging program was successfully carried out. Due to drill hole conditions, logs were collected in several passes from the total depth at 1138.54 m below seafl oor (mbsf) to 230 mbsf. After data correction, several statistical methods, such as factor analysis, cluster analysis, box-and-whisker diagrams, and cross-plots, were applied. The aim of these analyses was to use detailed interpretation of the downhole logs to obtain a description of the lithologies and their specifi c physical properties that is independent of the core descriptions. The sediments were grouped into the three main facies, diamictite, mudstone and/or siltstone, and sandstone, and the physical properties of each were determined. Notable fi ndings include the high natural radioactivity values in sandstone and the high and low magnetic susceptibility values in mudstone and/or siltstone and in sandstone. A modifi ed lithology cluster column was produced on the basis of the downhole logs and statistical analyses. It was possible to use the uranium content in the downhole logs to determine hiatuses and thus more accurately place the estimated hiatuses. Using analyses from current literature (geochemistry, clasts, and clay minerals) in combination with the downhole logs (cluster analysis), the depths 225 mbsf, 650 mbsf, 775 mbsf, and 900 mbsf were identifi ed as boundaries of change in sediment composition, provenance, and/or environmental conditions. The main use of log interpretation is the exact defi nition of lithological boundaries and the modifi cation of the paleoenvironmental interpretation. |
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