摘要
微体古生物分析已经证明是沿海平原和陆架海侵研究的最重要手段之一。由于我国第四纪海侵研究大量工作是在海陆过渡相地层中进行,而对于过渡相化石群古生态和埋葬学方面复杂性认识不足,往往会导致微体化石的错用。河口微体化石的溯流搬运,海岸带低pH环境下钙质壳体的溶解作用,氯化钠型盐湖中有孔虫的产出以及河床摆动造成与海侵、海退相似的化石序列,都可能引起微体化石在海侵研究中错误解释和应用。本文通过澳大利亚和中国的实例进行论证,并提出今后研究工作的建议。
Micropaleontological analysis has been proved to be one of the most useful techniques in marine transgression studies for coastal plains. Microfossils, mainly foraminifers and ostracodes, provide sensitive criteria in recognizing sedimentary facies and reconstrucring palececological conditions, such as water salinity. An example is the Holocene at the West Lake, Hangzhou, East China. Despite of the monotonous lithology of muddy sediments, the succession of microfossils has revealed a salinity cycle caused by marine transgression. However, micropaleontological data can not be interpreted correctly, unless the taphonomical aspects and sedimentological background are taken into consideration. This is particularly true for the coastal zone where microfauna sensitively responds to sea-level changes, but is exposed to intensive taphonomical processes. Tidal current, storm or eolian process may transport marine microfossils such as foraminifers onto supratidal zone or certain nonmarine environments. Small-sized foraminiferal tests, for example, are transported over a hundred of kilometer upstream in the Yangtze River estuary. Microfossils reworked from the preceding transgression or even older deposits are another misleading factor in transgression studies. On the other hand, calcareous microfossils may be dissolved in coastal zone with low pH which is widespread in Tropics and Subtropics, where marine transgression deposits may be barren of microfossils and, hence, mistaken for non-marine. This is illustrated with examples from Australia and China. The occurrence and abundance of microfossils are to a great extent controlled by coastal and estuarine processes. The meander migration of river channel can give rise to an alternation of fossil-bearing and barren layers sometimes misinterpreted as transgression records. The microfossils abundance in deposits is controlled mainly by deposition rate and fossil preservation, and should not be used for paleobathymetric reconstruction.
出处
《第四纪研究》
CAS
CSCD
1992年第4期321-331,共11页
Quaternary Sciences
基金
国家自然科学基金
