中国东部石炭纪以来双气囊花粉富集规律与古气候演变

中国东部双气囊花粉首次出现于早石炭世末期，迄今已有近3亿年的历史。晚石炭世以来，包括松科、罗汉松科、古老松柏粉类、具缝双囊粉类、原始无肋双囊粉类及具肋双囊粉类在内的双气囊花粉，在地质发展历史上不仅仅展现为随时间的新老交替过程，而且呈现出明显周期性富集现象。3亿年来，双气囊花粉至少存在三个层次的周期性盛衰过程。一级周期时限约45-50Ma，双气囊花粉往往在其早期阶段富集出现，晚期阶段明显衰退。中国东部重要的双气囊花粉富集期包括：晚石炭世晚期一早二叠世早期、晚二叠世末期一早三叠世早期、晚三叠世末期一早侏罗世早中期、晚侏罗世晚期一早白垩世早期、早白垩世末期一晚白垩世早期、晚白垩世末期古近纪早期、新近纪中期至更新世。双气囊花粉盛衰过程的二级周期时限约15-17Ma，该级周期叠加在一级周期之上，并使其复杂化。一般情况下，在任意一个一级周期之内，前两个二级周期之早、中期阶段，双气囊花粉可达到较高的富集程度，而第三个二级周期内，双气囊花粉往往不甚发育，这是由一级周期本身的性质所决定的。双气囊花粉类盛衰过程还存在着超级周期性，这种超级周期由两个一级周期组成，时限约为100Ma。地史上，此级别周期有4期，其地质时限如下：石炭纪一中二叠世末期、晚二叠世早期一晚侏罗世初期、晚侏罗世早期晚白垩世晚期(马斯特里赫特早期)、晚白垩世末期至今。在同一超级周期之内，两个一级周期转折处双气囊花粉仍占据较突出地位，为弱转折所在。不同超级周期之间，一级周期转折处双气囊花粉含量急剧衰减，且喜热耐干孢粉类型富集出现，特化类型分布普遍，为强转折所在。双气囊花粉类盛衰过程还明显地与古气候演化、全球构造变动、海平面升降、缺氧沉积发育、以及盆地演化过程之间存在着明显的相关性。这些规律表明，全球自然背景演化过程有着统一的机制，而双气囊花粉类盛衰历史为发现这些自然背景演化过程基本规律，以及探索其演化机制提供了重要线索。

ENRICHMENT PATTERNS OF DISACCITES AND PALAEOCLIMATE CHANGE IN EASTERN CHINA SINCE CARBONIFEROUS

Disaccate pollen first occured at the end of the Early Carboniferous and have lasted for nearly 330 million years on the earth. They cyclically increased and declined in abundance from the Carboniferous to the Quaternary at three levels, i.e. supercycles, first-level cycles and second-level cycles. Each supercycle as expressed in the rise and fall processes of disaccites, was composed of two first-level cycles and lasted about 100 Ma. There were 4 supercycles in the geological history, namely, the end of the Early Carboniferous-late Middle Permian, the early Late Permian-late middle Late Jurassic, the early Late Jurassic-late Late Cretaceous (early Maestrichtian), and the late Late Cretaceous-Quaternary. If two first-level cycles were within one supercycle with a Weak Turning Point, the disaccites would be important. If two first-level cycles were not in one supercycle and there was a Strong Turning Point, disaccites would decrease sharply, and the morphologically abnormal types would widely occur, thermophilic and dry-tolerant spores and pollen would be enriched. The first-level cycles lasted about 45-50Ma. Disaccites enriched in the prophase and declined distinctly in the anaphase of the first level cycles. In geological history, the important disaccites enrichments at the first level cycles were in the Late Carboniferous-Early Permian, late Late Permian-early Early Triassic, late Late Triassic-early middle Jurassic, late Late Jurassic-early Early Cretaceous, late Early Cretaceous-early Late Cretaceous, late Late Cretaceous-Early Paleogene and Middle Neogene-Pleistocene. The second level cycles lasted about 15-17Ma, which was superposed on the first level and made them complicated. In general, disaccites highly enriched in the first 2 second-level cycles, and declined during the third ones. Obviously, the rise and fall processes of disaccites are related to the climate, global tectonic movement and sea level changes, anaerobic or aerobic sedimentary environment and basin-forming process. The cyclical changes seem to imply a common mechanism in global natural environment evolution. The cyclical alternations of disaccites provide important clues for seeking the basic law of such kind of evolution.