Lithostatigraphy of the CESAR cores

Sixteen piston cores and twelve gravity cores were successfully recovered from northern and southern crests of the eastern Alpha Ridge andfrom the Alpha Ridge graben. All but one core contain late Cenozoic muds with variable amounts of sand- to pebble-sized clastic material that probably reflects transport by ice during the past 4-5 Ma. Sixteen Cenozoic-Holocene lithostratigraphic units have been delimited on the basis of sediment texture, structure, colour, detrital carbonate and authigenicferromanganese content. The composition of the upper 13 units in the CESAR cores is similar to the Fletcher's Ice Island cores; hence most units can be broadly correlated over most of the Central Arctic Ocean. Three new lithostratigraphic units (A1-A3) occur at the base of CESAR cores from the northern Alpha Ridge crest. Paleomagnetic and palynological data indicate a Late Miocene-Early Pliocene age for unit A3, which confirms previous reports of a slow sedimentation rate during the Cenozoic. CESAR core 6 was obtained from an erosional surface on top of a fault block at the north edge of the Alpha Ridge graben. This core contains ca. 2m of laminated diatom ooze of Campanian-Maastrichtian age and two ?Paleogene volcanic ash units below a brown mud unit which probably corresponds to units A2 and A3. The biosiliceous ooze contains no foraminifera or silicoflagellates and only few dinoflagellates. There is little difference in biogenic or clastic sediment content between light and dark laminae and the rhythmites do not appear to be annual varves produced in an upwelling environment. The microstructure and fluctuating mineral composition of the laminae most closely resemble those of lami- nated chert beds in the Triassic forearc basins of Japan.

研究团队从东阿尔法海岭（Alpha Ridge）的南北峰顶以及阿尔法海岭地堑（Alpha Ridge graben）中成功获取了16根活塞岩心（piston cores）与12根重力岩心（gravity cores）。除1根岩心外，其余所有岩心均含有晚新生代（late Cenozoic）泥质沉积物，其中砂级至砾级碎屑物质的含量存在差异，这大概率反映了过去4~5 Ma间冰运搬运作用的影响。研究人员依据沉积物结构（sediment texture）、沉积构造（sediment structure）、颜色、陆源碳酸盐（detrital carbonate）及自生铁锰矿物（authigenic ferromanganese）含量，共划分出16个新生代-全新世（Cenozoic-Holocene）岩石地层单元（lithostratigraphic units）。CESAR岩心中上部13个地层单元的组成与弗莱彻冰岛岩心（Fletcher's Ice Island cores）相近，因此多数地层单元可在北冰洋中部（Central Arctic Ocean）大部分区域进行广泛对比。来自阿尔法海岭北峰顶的CESAR岩心底部，发育3个全新的岩石地层单元（A1~A3）。古地磁与孢粉学数据显示，A3单元的形成时代为晚中新世-早上新世（Late Miocene-Early Pliocene），这证实了此前关于新生代期间沉积速率缓慢的研究结论。CESAR-6岩心采自阿尔法海岭地堑北缘一处断块（fault block）顶部的侵蚀面（erosional surface）。该岩心含有约2m厚的坎潘期-马斯特里赫特期（Campanian-Maastrichtian）纹层状硅藻软泥（laminated diatom ooze），在褐色泥质单元之下还发育2层疑似古近纪（Paleogene）火山灰层，该褐色泥质单元大概率对应A2与A3单元。该生物硅质软泥中未发现有孔虫（foraminifera）与硅鞭藻（silicoflagellates），仅含有少量甲藻（dinoflagellates）。明暗纹层（light and dark laminae）之间的生物成因沉积物与碎屑沉积物含量差异极小，且该韵律层（rhythmites）并非形成于上升流环境（upwelling environment）中的年纹层（annual varves）。该纹层的微观结构（microstructure）与矿物组成波动特征，与日本三叠纪弧前盆地（Triassic forearc basins of Japan）中的纹层状燧石层（laminated chert beds）极为相似。