Paper No. 0
Presentation Time: 2:50 PM
PROVENANCE INTERPRETATION OF TERTIARY SANDSTONES FROM THE CHEJU BASIN (NE EAST CHINA SEA): A COMPARISON OF CONVENTIONAL PETROGRAPHIC AND SCANNING CATHODOLUMINESCENCE TECHNIQUES
Cheju Basin is a Tertiary intracratonic basin, filled with largely nonmarine sediments located SW of the Korea Peninsula, beneath the NE East China Sea. Commercial petroleum companies drilled 10 deep wells in this basin between the late 1970s and the 1990s. We have examined 70 samples from four representative wells from the basin by conventional petrographic techniques and an additional 9 samples by scanning cathodoluminescence (SEM-CL) imaging using a cathodoluminescence detector attached to a scanning electron microscope. Sandstone detrital modes determined from petrographic analysis indicate that Cheju Basin sediments were derived from a predominantly recycled-orogen tectonic setting. Source rocks were primarily metasedimentary/sedimentary, although subordinate plutonic rocks were likely present. Minor to major quantities of volcaniclastic sediments were also contributed intermittently to the basin. SEM-CL imaging of quartz from 9 of the same samples examined petrographically yielded somewhat different results. SEM-CL results show that metamorphic quartz predominates over other types of quartz. Volcanic quartz is quite scare, even in samples that contain significant amounts of volcaniclastic detritus. This discrepancy reflects the generally low content of quartz in basic to intermediate volcanic rocks. Plutonic quartz is readily identifiable in SEM-CL images, in contrast to the difficulty in identifying plutonic components by petrographic analysis. These results indicate that the most reliable interpretation of provenance comes when both conventional petrographic techniques and specialized quartz-provenance techniques (in this case SEM-CL) are used together. Our data suggests that the Cheju Basin areas may have been connected by land to a sediment source on the Korea Peninsula during Oligocene to Miocene time. Alternatively, a land source may have existed to the northwest along a narrow massif or suture belt now inundated by the East China Sea. Regional subsidence in Pliocene time initiated the onset of marine conditions in the Cheju Basin; however, the same land source may have continued to furnish sediments to the basin.