A Timanian foreland basin setting for the late Neoproterozoic–Early Palaeozoic cover sequences (Dividal Group) of northeastern Baltica

LA-ICP-MS U–Pb and Hf-isotope data on detrital zircons from the Ediacaran and Cambrian Dividal Group demonstrate that the autochthonous cover sequence above the Fennoscandian Shield in northernmost Scandinavia is not derived from an easterly Archaean and Palaeoproterozoic source within Baltica as commonly thought. Detrital zircon age populations on four samples from the Dividal Group are dominated by Mesoproterozoic zircons with relatively few Palaeoproterozoic and Archaean zircons. Two samples, from Altevann and Reisadalen have, in addition, a significant population of Ediacaran zircons (<em>c.</em> 570–560 Ma), indicating a Timanian source area for most of the lower Cambrian Dividal Group sediments. The ¹⁷⁶Hf/¹⁷⁷Hf isotope data show the Ediacaran zircons to be derived from two separate plutonic complexes within the Timanides. It is argued that the Dividal Group sediments were deposited in a foreland basin south and SW of the Timanide Orogen. Similarities with clastic zircon age populations from Cambrian deposits in Akkajaure, Ladoga/White Sea and St Petersburg areas indicate that this foreland basin possibly extended southward for at least 1000 km. A foreland basin setting for the Ediacaran and Cambrian deposits in Central and Southern Scandinavia can thus account for the enigmatic Neoproterozoic detrital zircons in these deposits.

针对埃迪卡拉纪（Ediacaran）与寒武纪（Cambrian）迪维达尔群（Dividal Group）的碎屑锆石（detrital zircons）开展的激光剥蚀电感耦合等离子体质谱法（LA-ICP-MS）铀-铅（U-Pb）与铪同位素（Hf isotope）分析数据表明：斯堪的纳维亚最北部的芬诺斯坎迪亚地盾（Fennoscandian Shield）之上的原地盖层序列，并非如学界普遍认知的那样，源自波罗的古陆（Baltica）内部东侧的太古代（Archaean）与古元古代（Palaeoproterozoic）物源区。迪维达尔群的4件样品的碎屑锆石年龄分布以中元古代（Mesoproterozoic）锆石为主，古元古代与太古代锆石占比相对较低；其中采自阿尔特万（Altevann）与赖萨达伦（Reisadalen）的2件样品此外还存在显著的埃迪卡拉纪锆石群体（约570~560 Ma），表明下寒武统迪维达尔群的多数沉积物的物源区为蒂马尼造山带（Timanides）。¹⁷⁶Hf/¹⁷⁷Hf同位素数据显示，上述埃迪卡拉纪锆石源自蒂马尼造山带（Timanide Orogen）内两个独立的深成岩体组合，研究认为迪维达尔群沉积物沉积于该造山带南侧与西南侧的前陆盆地（foreland basin）中。与阿卡约雷（Akkajaure）、拉多加/白海（Ladoga/White Sea）及圣彼得堡（St Petersburg）地区寒武纪沉积岩中的碎屑锆石年龄分布特征的相似性表明，该前陆盆地可能向南延伸至少1000 km，因此斯堪的纳维亚中南部埃迪卡拉纪与寒武纪沉积的前陆盆地背景，可合理解释这些沉积中存在的谜一般的新元古代（Neoproterozoic）碎屑锆石。