Abstract
Optically stimulated luminescence (OSL) dating provides an absolute age control for marine deep-sea sediment. Optical history of target minerals such as quartz and feldspar in the sediment is critical for the OSL dating that includes not only natural processes but also artificial exposure process to the daylight during sediment coring and sampling. An onboard complete optical covered procedure for marine sediment coring from deep-sea bottom for the OSL sample was developed in order to avoid any optical exposure during the sediment sampling. The methods includes: (1) a black-colored inner tube is set up in the outer core barrel of sediment corer before sediment coring, (2) the black inner corer is carefully drawing out from outer core barrel after returning of the corer on deck, (3) both ends of section (top and bottom parts of the section) are covered by opaque caps just after sectioning of the core, (4) splitting of the whole-rounded core is carried out during the night on deck. The section is moved in the dark room and split into half-semicircle pillar-shaped core by using wire in the room, (5) split sections are pack into large opaque plastic bag and store in refrigerator (3 degree Celsius) before sampling, (6) aliquot sample for the OSL is taken from each section in the dark room and stored in small opaque plastic bag before analysis, (7) any sample preparation for the OSL is performed in the dark laboratory. By following the methods, only top and bottom parts of the section and outer rim of the sediment core may be affected by light exposure during the core processing, but the central part of the aliquot slice of the section is completely safe by exposure to daylight and available for the OSL measurement. The sediment coring in the complete dark side following the method results in fine OSL dating. The proposed procedure of this study will be a methodological standardization of optical covered sediment coring of deep-sea sediment.
