ABSTRACT

Nineteen ichnotaxa, together with algal and invertebrate remains, and various pseudo-traces and sedimentary structures are described from the Torneträsk Formation exposed near Lake Torneträsk, Lapland, Sweden, representing a marked increase in the diversity of biotic traces recorded from this unit. The “lower siltstone” interval of the Torneträsk Formation contains mostly simple pascichnia, fodinichnia and domichnia burrows and trails of low-energy shoreface to intertidal settings. The assemblage has very few forms characteristic of high-energy, soft-sediment, foreshore or upper shoreface environments (representative of the Skolithos ichnofacies).

Uranium-lead (U-Pb) LA-ICPMS analysis of zircon from a thin claystone layer within the “lower siltstone” interval yielded a maximum depositional age of 584 ± 13 Ma, mid-Ediacaran. Most of the zircon is represented by rounded detrital grains that yield dates between 3.3 and 1.0 Ga. Although the age of the basal sandstone-dominated interval of the Torneträsk Formation remains elusive owing to the absence of fossils, the ichnofossil suite from the overlying “lower siltstone” interval lacks deep arthropod trackways, such as Rusophycus and Cruziana, and is suggestive of a very early (Terreneuvian, possibly Fortunian) Cambrian age. The ichnofauna is otherwise similar to early Cambrian trace fossil assemblages from other parts of Baltica, regions further south in modern Europe, and from Greenland.

摘要

在瑞典拉普兰 Torneträsk 湖附近暴露的 Torneträsk 组中描述了 19 种鱼类目，连同藻类和无脊椎动物遗骸，以及各种假痕迹和沉积结构，表明从该单元记录的生物痕迹多样性显着增加。Torneträsk 组的“下部粉砂岩”层段主要包含简单的 pascichnia、fodinichnia 和 domichnia 洞穴以及低能量海岸到潮间带环境的小径。该组合很少具有高能、软沉积物、前滨或上岸面环境（代表Skolithos地层相）的特征。

铀铅 (U-Pb) LA-ICPMS 分析来自“下粉砂岩”层段内薄粘土层的锆石，得出的最大沉积年龄为 584 ± 13 Ma，埃迪卡拉纪中期。大多数锆石以圆形碎屑颗粒为代表，产生的日期在 3.3 到 1.0 Ga 之间。尽管由于缺乏化石，Torneträsk 组以基底砂岩为主的层段的年龄仍然难以捉摸，但来自上覆“下层”的地层化石套件粉砂岩”间隔缺乏深的节肢动物轨迹，如Rusophycus和Cruziana，并且暗示了一个非常早的（Terreneuvian，可能是 Fortunian）寒武纪时代。在其他方面，该鱼群与来自波罗的海其他地区、现代欧洲更南部地区和格陵兰岛的早期寒武纪遗迹化石组合相似。