|
DATA REPORT: Geology of Reef-Front Carbonate Sediment Deposits around Oahu, Hawaii
|
||||||||||
|
Vibracore analysis methodsHome > data > vibracores > methods The surface of longitudinally-split vibracores was carefully cleaned using a small trowel and brush in order to best expose textural and compositional features. Cores were labeled and photographed under polarized white light using a 35 mm camera (slide film). Core lithology was described in detail to delineate sedimentary structures, texture and composition. Grain size of the sand fraction was determined utilizing a grain size comparison strip under binocular examination. Larger clasts were measured with a millimeter scale. Color was recorded using the GSA Rock Color chart. A lithologic sketch was constructed at a scale of 1 inch = 1 meter and column width scaled to grain size. Standard lithologic symbols were used to illustrate lithologic unit contacts, sedimentary structures (both physical and biogenic), texture and composition. Summary lithologic descriptions were written by combining megascopic and binocular core lithology examination and thin section petrographic analyses. Small samples (approximately 100 grams) of unconsolidated core material were obtained at several levels within each core. All distinct lithologic units were sampled. Cores displaying apparently uniform lithology from top to bottom were sampled at least in the uppermost and lowermost portions. Samples were washed in fresh water and decanted to remove the suspended mud (i.e., silt and clay) fraction, which was retained by filtering. Both fractions were air dried and weighed to determine the sand+gravel to mud ratio. The sand fraction was systematically split down to a 10-20 gram portion for thin section preparation. Samples were vacuum-impregnated in a blue-dyed epoxy resin and thin sectioned. Modal analyses were preformed on all thin sections (n = 151) utilizing a standard, polarizing petrographic microscope equipped with a mechanical stage and a tally counter. At least 200 framework fraction grains were identified and tallied for each thin section. Textural features such as grain size, sorting and roundness also were determined in thin section. |
|||||||||
|
Top of page
|
||||||||||
|
http://geopubs.wr.usgs.gov/open-file/of03-441/data/vibracore/methods.html For more information, please contact: Monty Hampton
Pages created and maintained by Laura Zink Torresan USGS Privacy Statement | Disclaimer | Feedback | Accessibility |
||||||||||
