长江三角洲晚新生代沉积物有机碳、总氮和碳酸盐组成及古环境意义

长江三角洲地区埋深达320m的PD钻孔揭示了上新世以来河湖相、滨海相和三角洲相的沉积环境特征。钻孔沉积物中有机碳、总氮和碳酸盐组成变化较大,但具有一定的规律性。上新世东部地区气候较暖湿,古湖泊发育,化学风化强烈,有机质保存率较低;早更新世气候波动较大,相对温湿气候下高等植被发育;中、晚更新世长江流域气候逐渐变冷干,晚第四纪气候变化较显著,流域植被类型发生明显变化;全新世气候转暖,有机质保存率高。有机碳、总氮和碳酸盐组成揭示的古气候变化与孢粉、沉积地层等资料相当吻合,与相邻内陆地区的第四纪古环境研究认识也具有明显的可比性。本研究也揭示,运用有机碳、总氮和碳酸盐组成重建我国东部地区第四纪古环境和季风演化史具有相当的难度,必须充分考虑沉积地层不连续性、粒度、有机质来源、埋藏成岩环境以及陆海相互作用等多因素的复杂影响,同时需要结合有机碳同位素等分析来深化古环境研究。

Compositions of organic elements and carbonate in the late Cenozoic sediments of the Changjiang Delta: Implication for paleoenvironmental changes

Strata of Core PD in the Changjiang Delta with a core length of 320 m are primarily composed of lacustrine, fluvial, littoral and deltaic sedimentary facies. Compositions of organic elements (total organic carbon and total nitrogen; TOC and TN) and CaCO3 show large but somewhat regular variations in the core. East China was relatively warm and wet in the late Neogene and paleo-lakes well developed. However, organic matters decomposed to a great extent and yielded poor reservation in the sediment because of sulfate reducing action. In the early Pleistocene, the paleoclimate changed considerably and the higher plants developed in the Changjiang drainage basin. In the middle and late Pleistocene the Changjiang basin gradually became colder and dryer with large paleoclimate variability and great changes of the plant types. With the onset of Holocene, the paleoclimate turned warm and wet and organic matters were well preserved in the sediments. Late Cenozoic paleoclimatic changes in the Changjiang valley reconstructed by compositions of organic elements and CaCO3 can be well correlated with the pollen spore observations, and be also teleconnected with inland researches. However, Quaternary paleo-environmental reconstruction by using organic elemental and carbonate compositions should be prudent due to complicated influences of strata continuity, grain size composition, sources of organic matter, and post-depositional changes. More work including organic carbon isotope and/or biomarker analyses are urgently needed to improve our understanding of paleoenvironmental changes in East China and the Changjiang drainage basins.