(Table 1) Distribution of planktonic foraminifera in the Paleocene/Cretaceous section of DSDP Hole 93-605

Analysis of planktonic foraminifers from Section 605-66-1 established the Cretaceous/Tertiary (K/T) boundary between 68 and 73 cm. Comparison with the detailed zonation established at El Kef, Tunisia, indicates that some of the section may be missing, probably because of drilling disturbance. The preservation of the planktonic foraminifers is generally good, particularly in the basal Paleocene section. However, extensive dissolution and the many broken specimens render quantitative estimates unreliable. There were no microtektite-like spherules to suggest a layer rich in extraterrestrial components, as have been found in most complete pelagic K/T boundary sections. The better preservation of Paleocene foraminiferal test in this core and in many other DSDP cores from other basins is probably due to a change in oceanic carbonate chemistry exactly at the K/T boundary. This may have been caused by a temporary and almost complete disappearance of carbonate-fixing organisms at the boundary.对605-66-1岩芯中的浮游有孔虫（planktonic foraminifers）开展分析后，确定白垩纪/第三纪（K/T）界线位于68至73 cm深度区间。将该剖面与突尼斯埃尔凯夫（El Kef, Tunisia）建立的详细生物地层分带方案进行对比后发现，本剖面存在部分地层缺失，其成因大概率为钻井扰动。该剖面内浮游有孔虫的保存状况整体良好，尤以古新统底部剖面为最佳。不过，由于广泛的溶蚀作用以及大量破碎的标本，定量估算结果失去可靠性。本次分析未发现类似微陨球粒（microtektite-like spherules）的地外组分富集层，而此类特征在多数完整的远洋K/T界线剖面中均有产出。本岩芯以及其他盆地内诸多深海钻探计划（Deep Sea Drilling Project, DSDP）岩芯中，古新世有孔虫壳体（foraminiferal test）的保存效果更佳，这或许与K/T界线处海洋碳酸盐化学的突变密切相关。该化学变化可能由界线处固碳酸盐生物的暂时性近乎完全消亡所引发。