钙结岩记录的古环境变化研究进展

Review of Palaeoenvironmental Studies Recorded by Calcretes

较系统地评述了利用钙结岩进行古环境研究的现状,指出了研究中应注意的问题和在国内古环境研究中的应用前景.土壤钙结岩中有机质的δ13C被广泛地应用于重建过去的生态环境;土壤碳酸盐包含的C、O稳定同位素组成能够指示土壤形成的气候,同时也是研究植被演替、古气候变化、水文条件变化的重要手段.国内有关钙结岩的研究主要局限在土壤钙结岩及土壤碳酸盐,且集中在相对干旱的北方地区,而来自南方的报道很少.应加强对南方地区钙结岩的研究,特别是对地下水钙结岩的研究.在研究中,应注意区分原生与次生碳酸盐、定量古环境重建、年代测定和钙结岩形成机理等问题.尽管利用钙结岩稳定同位素的组成来解释古环境存在不确定性,但是由于影响稳定同位素比率组成的因素已经被熟知且它们的影响相对微弱,基于详细岩石学观察的微量取样及相应的同位素测定、测年技术可以避开这种不利影响,因而有较好的应用前景.

The works of palaeoenvironmental studies by using calcretes are reviewed systematically; and the existing problems and prospective for palaeoenvironmental studies in China are pointed out. δ^13C of organic matter in pedogenic calcrete is widely used in the reconstruction of the past ecological environment. δ^13C ＆ δ^18O of pedogenic calcrete are climate proxies during the time of their formation, and can be indicative of changes in palaeoclimate, vegetation succession and hydrological conditions. Related studies in China centre on pedogenic calcrete and soil carbonate rock, and concentrate in the relatively arid north, and the few reports from the South. We believe that more attention should be paid to calcretes in the South, especially for the groundwater calcrete. In future work, we should pay attention to the distinction between primary and secondary carbonate, quantitative palaeoenvironmental reconstruction, dating and formation mechanism of calcrete and so on. Although uncertainty exists in the use of stable isotope composition of calcretes to explain the palaeoenvironment situation, they have better application prospects because the factors which impact on the ratio of their stable isotope composition have been well known and they are relatively weak and can be relieved based on detailed observation and the micro-petrological sampling and corresponding isotope determination, dating technology.