IEG 환경지질연구정보센터

10월

26일(수)․층서퇴적학│석유지질학

2011 추계지질과학연합학술발표회 초록집 23

Provenance interpretation of Lower Cretaceous Sindong Group sandstones using SEM-cathodoluminescence

and optical microscopy

Joohhyeon Yi

․Yong Il Lee

School of Earth and Environmental Sciences, Seoul National University, [email protected]

The Sindong Group (Early Cretaceous) is the lower sequence deposited in the Gyeongsang Basin, SE Korea. It comprises three stratigraphic units, the Nakdong, Hasandong and Jinju formations with decreasing age, and they were deposited, respectively, in the alluvial, fluvial and lacustrine settings. Based on the paleocurrent analysis, the Sindong group sediments were interpreted to have been originated from uplifted basement rocks such as Precambrian granitic gneisses and Jurrassic granites located to the northwest and west of the Gyeongsang Basin. In this study, to determine the provenance, detrital quartz grains of the Sindong sandstones were discriminated into plutonic, volcanic and metamorphic quartz using scanning electron microscopy-cathodoluminescence with optical microscopy (SEM-CL/OM).

18 samples were collected from three different parts of the Gyeongsang Basin (northern, middle, and southern parts) and a minimum of 200 quartz grains per sample were analyzed.

The SEM-CL analysis reveals that 67~94% of the quartz grains in all samples were derived from metamorphic rocks, 5~30% from plutonic rocks, and 0~6% from volcanic rocks. The proportions of quartz grains of the Sindong group sandstones suggest derivation from either a single geologically heterogeneous source terrane or multiple source areas. Major source lithologies are metamorphic rocks and granitic rocks but notable amounts of quartz were also derived volcanic rocks.

In the northern part, source lithology distribution of the drainage area seems to have not been changed with time because of no significant change of proportions of quartz type with decreasing age.

In the central and southern parts, the proportion of plutonic and volcanic quartz increased with decreasing stratigraphic age. This means that distribution of plutonic source rocks increased in the corresponding source regions and the volcanic activity became active in the source area during deposition of the Sindong Group. The granitic and metamorphic rocks of the Precambrian Yeongnam massif were the major contributors of detrital quartz grains to the Sindong Group.

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