Absolute abundances of benthic and planktonic foraminifers in samples of ODP Hole 149-901A (Table 1)

Dark gray laminated silty claystones (Unit II) drilled at Site 901 contain Tithonian benthic foraminifer assemblages that indicate a neritic depositional environment and probably dysaerobic bottom-water conditions. Three benthic foraminifer zones are distinguished within Unit II. The upper part of the unit is dominated by Spirillina polygyrata, contains Globospirillina spp. (Samples 149-901A-3R-1, 10-12 cm, to 149-901A-3R-1, 75-77 cm) and is interpreted as late Tithonian. Samples 149-901A-3R-1, 87-89 cm, to 149-901A-6R-1, 74-76 cm, contain Epistomina uhligi and Lingulina franconica and are probably early Tithonian. The early Tithonian Neobulimina atlantica Zone is characterized by the occurrence of the zonal marker and Epistomina uhligi and reaches from Sample 149-901A-6R-1, 128-130 cm, to the base of the drilled-sequence. The sediments and benthic foraminiferal assemblage characteristics of the Tithonian-aged sequence in Hole 901A are unknown elsewhere in the Atlantic and may represent deposition in a marginal shelf basin with increased terrigenous and organic flux.

于901站位钻取的深灰色纹层状粉砂质泥岩（dark gray laminated silty claystones）第II岩性单元中，产出指示浅海沉积环境（neritic depositional environment）、大概率对应低氧底层水环境（dysaerobic bottom-water conditions）的提通期（Tithonian）底栖有孔虫组合（benthic foraminifer assemblages）。该岩性单元内可识别出3个底栖有孔虫带（benthic foraminifer zones）。该单元上部以多旋卷螺形虫（Spirillina polygyrata）为优势类群，产出Glospirillina属（Globospirillina spp.）标本，对应样品层位为149-901A-3R-1的10~12 cm至75~77 cm区间，该层位被解释为提通期晚期沉积。样品层位介于149-901A-3R-1的87~89 cm至149-901A-6R-1的74~76 cm区间的岩心中，产出乌利希表孔虫（Epistomina uhligi）与法兰克福舌形虫（Lingulina franconica），其沉积时代大概率为提通期早期。提通期早期的大西洋新Bulimina带（Neobulimina atlantica Zone）以分带标志种（zonal marker）及乌利希表孔虫的出现为典型特征，分布层位自样品149-901A-6R-1的128~130 cm区间延伸至本次钻取序列的底部。目前大西洋其他区域尚未见关于901A钻孔（Hole 901A）中该类提通期沉积序列及其底栖有孔虫组合特征的报道，该序列可能形成于陆源物质与有机质输入通量升高的陆缘陆架盆地（marginal shelf basin）环境中。