Magneticdating com
24-Jul-2020 13:19
The identification and quantification of heavy minerals is one of the most sensitive approaches to classify the various provenance terrains and depositional environment conditions [8,9].However, heavy mineral assemblages are affected by hydraulic sorting during transportation, chemical weathering during deposition, and dissolution during diagenesis [10,11,12,13].In contrast, high proportions of unstable mineral (amphibole 40%) in the Pleistocene strata indicate relatively weak chemical weathering or minor diagenetic effects [3,27].The high heavy mineral concentration (HMC) values in some of the Pleistocene samples define a placer trend, probably due to hydraulic sorting [13,20].
In this study, unstable (amphibole, epidote) and stable (tourmaline) heavy mineral in grain size fractions of 32–63 µm and 63–125 µm were analyzed by using a scanning electron microscope (SEM) and an electron probe (EP).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.With the application of clay minerals, geochemistry, and heavy mineral analyses, researchers have documented different sedimentary environments during the Pliocene to Pleistocene transition [26,27].
Heavy mineral analysis evinces the presence of high contents of zircon and extremely low contents of amphibole (5%) in Pliocene sediments of the Changjiang Delta, which is related to strong chemical weathering or diagenesis during this time (Figure 1).The Quaternary strata comprised several sedimentary sequences, which were composed of sand at the bottom and clayey silt at the top, suggesting a fluvial environment (Figure 2).
