Kaufman A J, Knoll A H
Botanical Museum, Harvard University, Cambridge, MA 02138, USA.
Precambrian Res. 1995;73:27-49. doi: 10.1016/0301-9268(94)00070-8.
The recent proliferation of stratigraphic studies of delta 13C variation in carbonates and organic C in later Neoproterozoic and basal Cambrian successions (approximately 850-530 Ma) indicates a strong oscillating trend in the C-isotopic composition of surface seawater. Alone, this trend does not adequately characterize discrete intervals in Neoproterozoic time. However, integrated with the vectorial signals provided by fossils and Sr-isotopic variations, C isotope chemostratigraphy facilitates the interbasinal correlation of later Neoproterozoic successions. Results of these studies are evaluated in terms of four stratigraphic intervals: (1) the Precambrian/Cambrian boundary, (2) the post-Varanger terminal Proterozoic, (3) the late Cryogenian, and (4) the early Cryogenian. Where biostratigraphic or radiometric data constrain the age of Neoproterozoic sedimentary sequences, secular variations in C and Sr isotopes can provide a level of stratigraphic resolution exceeding that provided by fossils alone. Isotopic data place strong constraints on the chemical evolution of seawater, linking it to major tectonic and paleoclimatic events. They also provide a biogeochemical framework for the understanding of the initial radiation of macroscopic metazoans, which is associated stratigraphically, and perhaps causally, with a global increase in the burial of organic C and a concomitant rise of atmospheric O2.
最近，对新元古代晚期和寒武纪早期（约8.5亿至5.3亿年前）碳酸盐岩和有机碳中δ13C变化的地层学研究激增，这表明表层海水的碳同位素组成呈现出强烈的振荡趋势。仅凭这一趋势，不足以充分表征新元古代的离散时间间隔。然而，结合化石和锶同位素变化提供的矢量信号，碳同位素化学地层学有助于新元古代晚期地层的盆地间对比。这些研究结果根据四个地层间隔进行评估：（1）前寒武纪/寒武纪边界，（2）瓦兰吉尔期之后的新元古代末期，（3）晚成冰纪，以及（4）早成冰纪。在生物地层学或放射性测量数据能够确定新元古代沉积层序年龄的地方，碳和锶同位素的长期变化能够提供比仅依靠化石更高的地层分辨率。同位素数据对海水的化学演化施加了严格限制，将其与主要的构造和古气候事件联系起来。它们还为理解宏观后生动物的初始辐射提供了一个生物地球化学框架，这种辐射在地层上与之相关，甚至可能在因果关系上与全球有机碳埋藏量的增加以及随之而来的大气氧气含量的上升有关。
