西沙石岛风成碳酸盐沉积的早期成岩作用
摘要: 西沙石岛风成碳酸盐沉积形成于晚更新世，正处于早期成岩阶段。通过薄片、扫描电镜、稳定碳、氧同位素、常量元素和微量元素分析，对石岛风成碳酸盐岩的早期大气淡水成岩作用进行了研究。发现石岛风成碳酸盐沉积的早期成岩固结主要在大气淡水作用下完成，其中蒸发成岩作用在初始固结中可能起着主要作用；在大气淡水作用影响下，部分碎屑颗粒发生溶蚀和新生变形，新生的微亮晶低镁方解石（5~15 μm）镶边胶结在颗粒及孔隙周围，并成为主要的胶结物；而作为大气渗流带和潜流带典型产物的亮晶胶结物则很少占据主导地位。海水成岩作用主要表现为对早期成岩作用的改造，会造成锶、镁含量的增高，但影响范围仅止于浅表层，而且对δ13C和δ18O值的影响微弱。生物化学作用可能参与了古土壤中灰质壳与根管石的形成，但在风成碳酸盐沉积的整体成岩上不具意义。大气淡水成岩作用会造成石岛风成碳酸盐岩δ13C和δ18O值的降低，并使碎屑发生新生变形而导致锶、镁的淋溶。成壤风化作用会导致Al、Fe、Mn、Y、Cr元素在古土壤中明显富集，其中Al、Fe、Mn的富集与成壤风化作用有关，而Y、Cr元素则可能源于长期暴露引起的风尘或火山灰的相对富集。
Early Diagenesis of Late Pleistocene Aeolian Carbonate Sediment on Shidao Island, Xisha Islands
Abstract: The surface sediments on Shi Island of Xisha Islands are aeolian sediments, which have been formed during late Pleistocene, and they are undergoing early diagenesis. Through the detailed observation of outcrops, sections and SEM, combing with the analysis of stable isotope of carbon and oxygen, major elements and trace elements, we found the aeolian seddiments had been consolidated mainly in meteoric diagenetic environment, and the evaporation diagenesis might play an important role during the early consolidation of the aeolian sediments. Under the influence of meteoric diagenesis, part of clasts have been leached and experienced neomorphism. And the newly producted microspar low magnesium calcite (410 m) cements usually pectinally inlayed on the surface of grains or pores in form of graininess, and became main cements. However, the content of calcsparite cements, which usually taken as the marker products of vadose and phreatic diagenesis, were generally less than the microspar cements in the most of rocks. The sea water mainly influenced and altered the former meteoric diagenesis, could raise the content of Sr and Mg, while only the surface of aeolianite had been affected. And the sea water diagenesis had a little influence about the δ13C and δ18O of the aeolian carbonatite. However, the formation of calcrete and rhizoliths, which were mainly developed in the paleosols, might have been affected by biochemical process. But the biochemical process had little sense for the whole diagenesis of the aeolian sediments. The meteoric diagenesis could decline the δ13C and δ18O of the aeolian sediments, and leach the Sr2+ and Mg2+ by the neomorphism. For the pedogenesis, the palaeosols are relative abundant in Al (aluminium), Fe (ferrum), Mn (manganese), Y (yttrium) and Cr (chromium) than the aeolian calcarenite. Nevertheless, the concentration of Y (yttrium) and Cr (chromium) showed little relationship with pedogenesis, and we induced that they might come from travel fatigue or volcanic ash during the relatively long term exposure.
西沙石岛风成碳酸盐沉积的早期成岩作用[J]. 沉积学报, 2013, 31(2): 220-236.
| 引用本文: |
西沙石岛风成碳酸盐沉积的早期成岩作用[J]. 沉积学报, 2013, 31(2): 220-236.
|
Early Diagenesis of Late Pleistocene Aeolian Carbonate Sediment on Shidao Island, Xisha Islands[J]. Acta Sedimentologica Sinica, 2013, 31(2): 220-236.
| Citation: |
Early Diagenesis of Late Pleistocene Aeolian Carbonate Sediment on Shidao Island, Xisha Islands[J]. Acta Sedimentologica Sinica, 2013, 31(2): 220-236.
|
点击查看大图
下载:
