Geochemical logging of shallow-sea tidal bar sediment cores using a XRF core scanner: an application of XRF core-scanning to lithostratigraphic analysis

Abstract

In order to evaluate the relationship between lithostratigraphy and geochemistry of core sediments using a XRF core scanner, two drilled-cores collected on a large tidal bar, outer Asan Bay of Korea were examined. Stable isotopes of organic carbon and nitrogen and organic carbon and CaCO_3 measured by a CHN analyzer were additionally used for correlation of the investigated cores, complemented by ^(14)C ages of foraminifera. The Asan bay tidal bar deposits can be divided into four major facies assemblages: a) fluvial deposits, b) transgressive gravel lag deposits, c) estuarine tidal flat deposits and d) tidal bar deposits in ascending order. The Holocene stratigraphy reveals an overall trend of upward-coarsening textural composition indicative of transgressive deposition coupled with local sea-level rise, tidal-flat muds being overlain by sand-dominated tidal bar successions. These lithostratigraphic units correlate well with the chemical logging data. Terrigenous elements such as Al, Si, K, Ti and Fe show distinctly the greatest value at the interval of fluvial deposits, and medium value in tidal mud beds. However, these elements are poorer in uppermost tidal bar succession. The opposite pattern is shown in biogenic elements such as Ca, Mn, Br and Sr. Organic matter contents and stable isotopes of organic carbon and nitrogen reveal that terrigenous organic matters were dominated in tidal mud deposits, by contrast, at the upper sand bar interval, organic matters were derived from marine environment. The XRF core scanning data seem to be thus applicable, thereby chemical logging data being paleoenvironmental proxy.