(Table 2) Details of laminated intervals of ODP Leg 158 holes@en

Scanning electron microscope (SEM)-based analyses of the laminated diatom oozes encountered during Leg 138 reveal three major laminae types. The first lamina type is composed of multiple layers of ~20-?m-thick diatom mats, which form laminae dominated by assemblages of the pennate diatom, Thalassiothrix longissima. More than one variety/subspecies of T. longissima occurs within these laminae (referred to as the T. longissima Group). The second lamina type is composed of a mixed-assemblage of several species of diatoms (centric and pennate varieties), calcareous nannofossils, and subordinate quantities of radiolarians, silicoflagellates and foraminifers. The third lamina type is dominated by an assemblage of nannofossils and minor amounts of those fossil components mentioned above. This last form of lamination is compositionally similar to the background sediment type, foraminifernannofossil ooze (F-NO). Two lamina associations occur within the laminated intervals; the first comprises alternations of T. longissima Group and mixed-assemblage laminae (average thickness is ~6 mm) and the second is composed of T. longissima and nannofossil-rich laminae (average thickness is ~3.5 mm). The arrangement of laminae probably originates from the deposition of multiple layers of 20-?m-thick mats from one mat-flux episode. The much thinner nannofossil-rich laminae are interpreted to represent periods of more ônormalö deposition between mat-flux episodes. The occurrence of several varieties/subspecies of T. longissima within individual mat layers is consistent with observations of Rhizosolenia diatom mats in the modern world ocean.对138航次（Leg 138）中获取的层状硅藻软泥开展的扫描电子显微镜（SEM）分析表明，该套沉积存在三类主要纹层。第一类纹层由多层厚度约20微米的硅藻垫构成，该类纹层以羽纹硅藻（pennate diatom）长形海毛藻（Thalassiothrix longissima）的组合为主体，且此类纹层中存在不止一个长形海毛藻的变种/亚种（后文统称为长形海毛藻群（T. longissima Group））。第二类纹层由多种硅藻（涵盖中心硅藻（centric diatom）与羽纹硅藻）、钙质超微化石（calcareous nannofossils），以及少量放射虫（radiolarians）、硅鞭藻（silicoflagellates）和有孔虫（foraminifers）的混合组合构成。第三类纹层以超微化石组合为主体，仅含有少量前文提及的化石组分。该类纹层的组成与背景沉积类型——有孔虫-钙质超微化石软泥（foraminifer-nannofossil ooze, F-NO）高度相似。在层状沉积段内存在两类纹层组合：第一类为长形海毛藻群纹层与混合组合纹层的互层（平均厚度约6毫米），第二类则由长形海毛藻纹层与富超微化石纹层构成（平均厚度约3.5毫米）。纹层的排布大概率源于单次硅藻垫通量事件中多层约20微米厚硅藻垫的沉积作用。厚度更薄的富超微化石纹层被认为代表了硅藻垫通量事件之间的“常规”沉积时期。单个硅藻垫层中存在多种长形海毛藻变种/亚种的现象，与现代海洋中根管藻（Rhizosolenia）硅藻垫的观测结果一致。