The Chemical Composition and Surface Texture of Transparent Heavy Minerals from Core LQ24 in the Changjiang Delta

Abstract

The assessment of textural and compositional modifications of detrital sediments is required to reconstruct past source to sink dynamics. The Changjiang Delta is an ideal location to study the sedimentary environment from the Pliocene to Quaternary transition. In the present study, we aim to decipher the response of heavy minerals to mechanical wear and chemical weathering since the Pliocene. With the application of a scanning electron microscope and an electron probe, the geochemistry and surface texture of different heavy minerals (amphibole, epidote, and tourmaline groups) with grain-size fractions of 32–63 µm and 63–125 µm were studied. The result shows that the surface texture of unstable minerals (amphibole, epidote) changed under strong chemical weathering in the Pliocene sediments. By contrast, unstable minerals of the Pleistocene sediments are relatively fresh and similar to those of the modern Changjiang sediment. The stable mineral tourmaline does not exhibit morphology changes in different chemical weathering conditions. No effect of grain size on geochemical composition is noticed. The single minerals of very fine sand and coarse silt show similar geochemical and morphological features. The integration of mineralogy, geochemical data, and grain size parameters yield a more precise understanding of the physical and chemical response of heavy minerals to different weathering conditions. The outcome of the study is also helpful in deciphering sediment provenance changes and environmental changes in the Changjiang basin.