GATHODOLUMINESCENCE INVESTIGATIONS AND TRACE-EI . EMENTANALYSIS OF OUARTZ BY MICRO . PIXE : tMPLtCAilONS FOR DTAFENETTC AND PROVENANCE STUDIES lN SANDSTONE
Hot-cathodoluminescence (CL) microscopy and high-resolution trace-element analyses by Particle lnduced X-ray Emission (micro-PIXE) using the proton microprobe have been applied to samples of quartz arenite in order to obtain information about their diagenetic environment and the provenance of quartz detritus. The occurrence of an intensely zoned orange-brown cemenl generation within quartz overgrowths in quartzitic lenses from the Fontainebleau Sand (Oligocene, Paris Basin) coincides with increased Fe concentrations of up to 192 ppm. ln contrast, the Fe content of a nonluminescing generation within the same overgrowths is significantly lower. This finding suggests that the CL is either activated by the Fe itself or caused by defects induced by the incorporation of Fe into the structure. Detrital grains of quaflz from sandstone samples of different ages and locations (Wiehengebirgsquarzit, Upper Jurassic, northwestem Germany; Fontainebleau Sand, Oligocene, Paris Basin) yield a good correlation between CL color and Fe and Ti concentrations, with Fe (up to 455 ppm) being more abundant in red-browniuminescing grains and Ti (up to 298 ppm) confined to grains with blue-violet luminescence. Ti is universally present in quartz from plutonic and extrusive igneous rocks, but rarely observed in quartz from metamorphic rocks. This supports the general contention that the blue-violefluminescing quartz was formed under higher temperatures than the quartz with brown luminescence, an observation important for studies of sandstone provenance. Conceming the mechanisms of CL activation, these results do not unequivocally prove that the observed colors are activated by the elements sought. Despite the advantages of the microanalytical technique, the observed trace-element contents may still reflect submicroscopic inclusions rather than element incolporation into the structure.
Complex quartz overgrowths as revealed by microprobe cathodoluminescence
Conventional luminescence petrography of sandstones has only distinguished texturally homogeneous overgrowths of quartz from detrital grains. Microprobe cathodoluminescence, however, reveals extraordinary heterogeneity in overgrowths from a wide variety of locations, geologic ages, sedimentary facies, petrographic textures, and burial histories. The complexity of overgrowths is expressed by distinct luminescent and non-luminescent zones, and flamboyant and irregular textures. Interpretation of features previously undetected by conventional luminescence petrography may result in a better understanding of conditions under which quartz cement forms. Preliminary results for Morrow, Kekiktuk, Ivishak, Cardium, Tuscaloosa, and Middle Jurassic sandstones (offshore Norway) indicate that pressure solution between detrital grains is not a major source of silica cement even in very fine-grained sandstones. In contrast, pressure solution at overgrowth-overgrowth boundaries can produce significant amounts of silica. However, the source of initial silica for the overgrowths that are subsequently pressolved is uncertain in these rocks. Abundant fracturing of quartz grains occurs relatively early in the burial history and can be concurrent with overgrowth development. In most instances the fracturing is not accompanied by significant translation. Oxygen isotope data for quartz overgrowths isolated from their detrital cores suggest that precipitation of cement took place over a relatively narrow temperature range that corresponds tomore » depths shallower than the present-day depth. In view of the multiple zoning of the overgrowths, the temperatures most likely represent an average of a complex history of multi-event quartz cementation that occurred over a considerable temperature span, but principally at temperatures less than 75/degree/C.« less
Archaeological Survey of Dangoyama Kofun by 3DGPR
We presented a three-dimensional ground penetrating radar (3DGPR) system for the archeological investigation in a harsh site, where we have to deal with many trees and/or great topographic variations. This system consists of a commercial GPR system with a laser positioning system. With this system, we can move the GPR antenna freely, on which a positioning detector can record accurate position for each GPR data trace. We applied our 3DGPR system at Dangoyama Kofun, a burial mound, in Fukushima prefecture, Japan. A lot of trees and bushes covered the survey area and cannot be cut. We acquired six datasets in two days in this area. We successfully imaged the boundary between the original surface of the burial mound and the covering soil clearly at about 0.3 m depth around the mound. Furthermore, we found some strong reflections appeared at 0.8 m depth in the top area of the mound, which can be from the artificial parts of the burial mound. The results would greatly aid the following archaeological excavation. In addition, we compared the non-interpolated depth slice with interpolated depth slice at same position and demonstrated that the interpolation process on threedimensional GPR data may introduce some artifacts which might mislead our interpretation.