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The Cretaceous Gyeongsang Basin, SE Korea, developed on a continental are massif, is filled with 6-9 km thick, nonmarine (alluvial, fluvial, and lacustrine) deposits and subduction-related volcanogenic rocks. The Kusandong Tuff is a thin (2-4 m thick) but laterally extensive (ca. 200 km long) ignimbrite sheet, rhyodacitic in composition and rich in crystals (40-60 vol.%). The tuff has been used as an important key bed for stratigraphic classification and correlation of the basin fill. Overall sedimentary and compositional characteristics of the tuff suggest, however, that the northern and southern parts of the tuff represent different ignimbrite units. The northern part of the tuff (NKT), lying above an erosional contact, consists of a massive division and an overlying stratified division, whereas the southern part (SKT), lying conformably above the substrate, has a basal layered division beneath a massive division. The NKT has distinctively higher crystal (51-61 vol.%) and lithic (7.0-7.8 vol.%) contents compared with the SKT, which contains 35-48 vol.% crystals and 0.2-2.5 vol.% lithic fragments. Major and trace element compositions are also different, suggesting that the NKT and the SKT originated from compositionally different magmas. These results suggest that the use of the Kusandong Tuff as an event stratigraphic unit needs to be reconsidered and the formations adjacent to the Kusandong Tuff need to be redefined, especially in the Milyang subbasin.[PUBLICATION ABSTRACT]
The Cretaceous Gyeongsang Basin, SE Korea, developed on a continental are massif, is filled with 6-9 km thick, nonmarine (alluvial, fluvial, and lacustrine) deposits and subduction-related volcanogenic rocks. The Kusandong Tuff is a thin (2-4 m thick) but laterally extensive (ca. 200 km long) ignimbrite sheet, rhyodacitic in composition and rich in crystals (40-60 vol.%). The tuff has been used as an important key bed for stratigraphic classification and correlation of the basin fill. Overall sedimentary and compositional characteristics of the tuff suggest, however, that the northern and southern parts of the tuff represent different ignimbrite units. The northern part of the tuff (NKT), lying above an erosional contact, consists of a massive division and an overlying stratified division, whereas the southern part (SKT), lying conformably above the substrate, has a basal layered division beneath a massive division. The NKT has distinctively higher crystal (51-61 vol.%) and lithic (7.0-7.8 vol.%) contents compared with the SKT, which contains 35-48 vol.% crystals and 0.2-2.5 vol.% lithic fragments. Major and trace element compositions are also different, suggesting that the NKT and the SKT originated from compositionally different magmas. These results suggest that the use of the Kusandong Tuff as an event stratigraphic unit needs to be reconsidered and the formations adjacent to the Kusandong Tuff need to be redefined, especially in the Milyang subbasin.[PUBLICATION ABSTRACT]
Springer 2003