(Table 2) Taxonomic composition of diatoms in dredged samples from the island-side slope of the Kuril-Kamchatka Trench

Studies of diatoms from dredge samples collected on the island slope of the Kuril-Kamchatka Trench have allowed to recognize well-preserved marine diatom assemblages corresponding to assemblages of the followed Oligocene zones: Rhizosolenia oligocaenica (subzone ''a'', 33.6-31 Ma), Cavitatus rectus (29.6-28.2 Ma), and Rocella gelida (28.2-24.0 Ma) as identified in the North Pacific zonal scale. Description of these assemblages and their complete taxonomic composition are presented. Diversity of species together with abundance and degree of preservation of diatoms and accompanying siliceous microorganisms suggests their autochtonous origin and favorable conditions of their development. Assemblages of the Early Oligocene zones Rhizosolenia oligocaenica and Cavitatus rectus recognized in sediments of the outer zone of the Lesser Kuril Ridge (submarine slope of the Shikotan Island) and on the Vityaz' submarine ridge were most probably formed under conditions of a vast shelf, while assemblage of the Late Oligocene zone Rocella gelida encountered only in the region of the Lesser Kuril Ridge formed under more deep-water conditions, presumably, over an island slope. Deepening of the basin in the region of the outer zone of the Lesser Kuril Ridge in Late Oligocene probably reflects one of stages of evolution of the Kuril-Kamchatka Trench.针对取自千岛-堪察加海沟（Kuril-Kamchatka Trench）岛坡的海底拖网采样硅藻开展研究，得以识别出保存完好的海洋硅藻组合，这些组合对应北太平洋分带标尺下划定的如下渐新世（Oligocene）组合带：*Rhizosolenia oligocaenica*（亚带a，33.6~31 Ma）、*Cavitatus rectus*（29.6~28.2 Ma）与*Rocella gelida*（28.2~24.0 Ma）。本文详述了这些硅藻组合及其完整的分类学组成。硅藻及伴生硅质微生物的物种多样性、丰度与保存程度，表明其为原地成因且形成于适宜的生长环境中。在小千岛海岭（Lesser Kuril Ridge）外缘带（色丹岛（Shikotan Island）海底坡）的沉积物以及维特亚兹海脊（Vityaz' submarine ridge）上发现的早渐新世（Early Oligocene）组合带*Rhizosolenia oligocaenica*与*Cavitatus rectus*的硅藻组合，大概率形成于广阔陆架环境；而仅在小千岛海岭区域发现的晚渐新世（Late Oligocene）*Rocella gelida*组合带，则形成于更深的水体环境，推测发育于岛坡之上。晚渐新世时期小千岛海岭外缘带区域的盆地沉降，可能反映了千岛-堪察加海沟演化的一个阶段。