云南早寒武世澄江化石库中两种埋藏相的化石定量分析

通过昆明海口马房村同一个采坑的化石连续采集和统计,对澄江化石库中两种埋藏相(以事件层泥岩和背景层泥岩所代表)内化石保存和组合特征进行定量研究,结果表明:(1)事件层内化石量并不随单一事件层厚度变化而变化。物种在剖面上不同层位的事件层内分布不均匀,表现为单层富集现象;而背景层内的化石含量与背景层的沉积厚度有关,背景层的沉积厚度越厚,化石数量就越多。(2)事件层与背景层内化石组合和结构存在很大差异。事件层内化石组合与背景层内化石组合相比具有更多的物种组成和更复杂的古群落结构;而背景层内化石组合面貌单调,在剖面上保持稳定。(3)事件层内化石生物体腐烂发生在埋藏之后,绝大多数化石生物是被活埋后保存下来的;而背景层内化石主要表现为外壳和弱矿化有机质生物表皮在海床表面长时间停滞而堆积形成,明显受到时间均衡作用(time-average)的影响。(4)事件层内化石在埋藏前无搬运作用,或发生近原栖息地的快速搬运,埋藏后无生物扰动。背景层内大量壳体相连的双瓣壳节肢动物化石和完整海绵体化石的存在则表明,背景层代表一个低氧、低能并具有有限生物扰动的沉积环境。

QUANTITATIVE COMPARISON OF THE FOSSIL ASSEMBLAGES BETWEEN THE EVENT AND BACKGROUND MUDSTONES FROM THE EARLY CAMBRIAN CHENGJIANG LAGERST(A)TTE, YUNNAN

Qualitative and quantitative variations in preservation (completeness, degree of decay) and fossil composition between event and background layers demonstrate that: (1) for event deposits, fossils are unevenly distributed in different layers, and the number of fossils shows no relation to the thickness of each layer, and the fossil compositions suggest conspecific and polytaxic concentration in some layers. But for background layers, the number of fossils related to the thickness of the layer. Usually the thicker background layer is the more fossil individuals it contains. (2) Comparison of fossil compositions between event layers and background layers indicate dramatic differences. Event layers show more complexity than background layers in composition of fossils and the structure of paleocommunity. Fossil assemblages of event layers may reflect variation of palaeocommunity from different horizons. (3) Decay processes of most organisms in event layers took place after they were buried, or the organisms were buried when even they were still alive. But the organisms of background layers had suffered long decay processes before they were finally buried. As well the fossil assemblages were significantly affected by time-averaging. (4) The fossil assemblages of event layers were autochthonous or parautochthonous, and show no bioturbation after the burial. The presence of abundant articulated shells and sponge fossils in the background layer indicates that they deposited in a stagnant and anoxic bottom water environment with rare scavengers and limited bioturbation.