Knoll A H, Kaufman A J, Semikhatov M A, Grotzinger J P, Adams W
Botanical Museum, Harvard University, Cambridge, Massachusetts 02138, USA.
Geology. 1995 Dec;23(12):1139-43. doi: 10.1130/0091-7613(1995)023<1139:sutstu>2.3.co;2.
Sedimentary rocks in the western Anabar region, northwestern Siberia, preserve an exceptional record of evolution and biogeochemical events near the Proterozoic-Cambrian boundary. Carbon isotopic data on petrographically and geochemically screened samples collected at 1 to 2 m intervals support correlation of the lower Anabar succession (Staraya Reckha and lower Manykai Formations) with sub-Tommotian carbonates of the Ust'-Yu-doma Formation in southeastern Siberia. In contrast, the upper Manykai and most of the overlying Medvezhya Formation appear to preserve a sedimentary and paleontological record of an evolutionary important time interval represented in southeastern Siberia only by the sub-Tommotian unconformity. Correlation of the Anabar section with other northern Siberian successions that contain well-dated volcanic rocks permits the estimate that the sub-Tommotian unconformity in southeastern Siberia spans approximately 3 to 6 m.y. Diverse small shelly fossils (but not archaeocyathans) previously thought to mark the base of the Tommotian Stage evolved sequentially throughout this earlier interval.
西伯利亚西北部阿纳巴尔地区西部的沉积岩，保存了元古宙 - 寒武纪边界附近演化和生物地球化学事件的非凡记录。以1至2米的间隔采集的经过岩相学和地球化学筛选的样本的碳同位素数据，支持了阿纳巴尔下部层序（旧列哈组和下部曼凯组）与西伯利亚东南部乌斯季 - 尤多马组的托莫特阶以下碳酸盐岩的对比。相比之下，上部曼凯组及大部分上覆的梅德韦日组似乎保存了一个在演化上很重要的时间间隔的沉积和古生物学记录，而在西伯利亚东南部，这个时间间隔仅由托莫特阶以下不整合面代表。将阿纳巴尔剖面与其他含有年代测定良好的火山岩的西伯利亚北部层序进行对比，可以估计西伯利亚东南部的托莫特阶以下不整合面跨越了大约300万至600万年。此前被认为标志着托莫特阶底部的各种小壳化石（但不包括古杯类）在这个更早的时间间隔内依次演化。
