The compositional relation of selected clay sediments to late Pleistocene-Holocene depositional environments from Italy and China

Abstract

Mineralogical and textural variations in Upper Pleistocene and Holocene clay sediments from three cores taken in different depositional environments: the Venetian lagoonal littoral zone, the South Yellow Sea and the Yangtze River Delta, are reported. The compositional variations of clay layers from the three sites are attributed to major global climatic changes. Although the compositional difference of clay sediments of the three sites reflects the petrology of their different areas of provenance, the relative abundance and textural variations show a correlation with climatic-driven changes in their depositional environment. In the Venice lagoon the carbonate content decreases from cold to warm periods whereas in the Yangtze River delta and in the South Yellow Sea carbonates are absent or not significant, and the most noticeable changes are given by the total clay mineral content variations (chlorite, smectite, mixed-layer clay minerals and muscovite) and feldspar. There is a general increase in abundance of clay minerals and a decrease in feldspar content during warm periods. The cores from all three study sites have overconsolidated continentally-derived clay layers at the Pleistocenel/Holocene (ca. 10,000 BP) boundary. The overconsolidated nature of these hard clay layers is due to long subaerial exposure under a cold and dry climatic regime before the Holocene (Flandrian) transgression.