The organic deposits derived from the mangrove swamps form reliable stratigraphic markers within the Late Quaternary sequence of Kerala–Konkan Basin. Three generations of such deposits have been identified. The older one is dated to around 43,000–40,000 14C yr B.P., with a few dates beyond the range of radiocarbon. The younger ones date from the Middle Holocene to latest Pleistocene (10,760–4540 14C yr B.P.) and the Late Holocene (<4000 14C yr B.P.). Pollen analyses confirm that the deposits are mostly derived from the mangrove vegetation. Peat accumulation during the period 40,000–28,000 14C yr B.P. can be correlated with the excess rainfall, 40–100% greater than modern values, of the Asian summer monsoon. The low occurrence of mangrove between 22,000 and 18,000 14C yr B.P. can be attributed to the prevailing aridity and/or reduced precipitation associated worldwide with Last Glacial Maximum, because exposure surfaces and ferruginous layers are commonly found in intervals representing this period. The high rainfall of 11,000–4000 14C yr B.P. is found to be the most significant as the mangrove reached an optimum growth around 11,000 14C yr B.P. but with periods of punctuated weaker monsoons. From the present and previous studies, it has been observed that after about 5000 or 4000 14C yr B.P., the monsoons became gradually reduced leading to drying up of many of the marginal marine mangrove ecosystems. A case study of Hadi profile provided an insight to the relevance of magnetic susceptibility (χ) to record the ecological shift in Late Holocene.

Changes in soil chemistry in response to varying climatic regimes can alter the equilibria of soil systems and result in different clay minerals. Variations in phyllosilicate clay composition can reflect temporal and spatial climatic changes, such as summer/winter monsoon cycles. The objective of this research was to investigate the mineralogy of the clay fractions as a proxy for determining variations in the East Asian monsoon climate, based on a section at Chaoyang in China spanning the last 0.423 Ma BP. The clay mineralogy record in the Chaoyang section was compared with other proxies as recorded in this section and with other palaeoclimatic indicators, including oxygen isotopes from oceanic sediments and loess–palaeosol sections on the Chinese Loess Plateau (CLP). The results from clay mineralogy and related climatic studies show that the summer monsoon has a trend of four increased stages and four decreased stages; whereas the winter monsoon displays the opposite trend. During the last 0.423 Ma BP, the strongest winter monsoon occurred around 0.243–0.311 Ma BP. During this period, which included an intense winter monsoon, the soil in the section had the least illite, one of the smallest kaolinite and illite/Chlorite (I/C) indices and an overall decreasing clay content. The period 0.225–0.243 Ma BP had the strongest summer monsoon over the last 0.423 Ma BP. This period had the greatest amount of illite, the highest I/C index, greater overall clay content and the strongest magnetic susceptibility signal. Additionally, this section contained the smallest mean grain size. The multi-monsoon climate cycles of alternating cold-dry and warm-moist conditions as recorded in the Chaoyang section corresponded well with multiple glaciation cycles based on deep sea sediments. This indicates that the Chaoyang section provides a record of palaeoclimate changes in northeast China that can be linked to mineralogical suites to assist in reconstructing the palaeoclimate over the Late Middle Pleistocene, and complements the global palaeoclimate records in the CLP.