ABSTRACT

The boundaries of the Sandbian Stage are defined by graptolites. Because of their rare occurrence in the Estonian part of the Baltoscandian palaeobasin, other fossils, including conodonts, are used for biostratigraphy as good alternatives. Since the definition of Sandbian Stage/Age in 2002, information about conodonts from this time interval in Baltsocandia has improved considerably. In this paper, existing data on Sandbian conodont faunas from the Estonian part of the Baltoscandian palaeobasin, including the most recent information from the Velise V-97 core section (western part of mainland Estonia), is evaluated. Dating of these strata in the region is addressed and partly updated. Comparison of conodont successions from other regions of Baltoscandia with those from the Estonian sections is used to check consistency of known conodont zones. The rich conodont succession from the Velise V-97 drill core is considered a representative one for the Sandbian-age carbonate ramp environment in Baltoscandia. Most of the principal conodont zones within the Sandbian Stage were recognised whilst the lower and upper boundary intervals of the stage are poorly resolved. Despite the rich conodont faunas available, the boundaries of the Sandbian Stage are currently not clearly definable in the conodont succession. However, further detailed studies on the morphology and evolution of the earliest Amorphognathus (A. inaequalis and A. tvaerensis in particular), based on rich and well preserved material from different parts of Baltoscandia, might provide useful criteria for location of the Sandbian and Katian boundaries in non-graptolitiferous carbonate sections.

摘要

沙边阶的界线以笔石为界。由于它们在巴尔托斯堪尼亚古盆地的爱沙尼亚部分很少见，因此包括牙形石在内的其他化石被用作生物地层学的良好替代品。自 2002 年定义 Sandbian Stage/Age 以来，Baltsocandia 这一时期的牙形石信息有了很大改善。本文评估了波罗托斯堪尼亚古盆地爱沙尼亚部分的沙边牙形石动物群的现有数据，包括 Velise V-97 核心部分（爱沙尼亚大陆西部）的最新信息。该地区这些地层的年代已得到解决和部分更新。将来自 Baltoscandia 其他地区的牙形石演替与爱沙尼亚剖面的牙形石演替进行比较，以检查已知牙形石区域的一致性。Velise V-97 钻芯中丰富的牙形石演替被认为是巴尔托斯坎迪亚地区 Sandbian 时代碳酸盐斜坡环境的代表。Sandbian 阶段内的大部分主要牙形石区域都被识别出来，而阶段的上下边界间隔则很难分辨。尽管有丰富的牙形石动物群，但沙边阶段的边界目前在牙形石演替中尚不清楚。然而，对最早的形态和进化的进一步详细研究 Sandbian 阶段内的大部分主要牙形石区域都被识别出来，而阶段的上下边界间隔则很难分辨。尽管有丰富的牙形石动物群，但沙边阶段的边界目前在牙形石演替中尚不清楚。然而，对最早的形态和进化的进一步详细研究 Sandbian 阶段内的大部分主要牙形石区域都被识别出来，而阶段的上下边界间隔则很难分辨。尽管有丰富的牙形石动物群，但沙边阶段的边界目前在牙形石演替中尚不清楚。然而，对最早的形态和进化的进一步详细研究Amorphognathus（特别是A. inaequalis和A. tvaerensis）基于来自 Baltoscandia 不同地区的丰富且保存完好的材料，可能为非笔石碳酸盐剖面中的 Sandbian 和 Katian 边界的位置提供有用的标准。