ABSTRACT

Ludfordian strata exposed in the Burgen outlier in eastern Gotland, Sweden record a time of initial faunal recovery after a global environmental perturbation manifested in the Ludfordian Carbon Isotope Excursion (LCIE). Vertebrate microfossils in the collection of the late Lennart Jeppsson, hosted at the Swedish Museum of Natural History, hold the key to reconstruct the dynamics of faunal immigration and diversification during the decline of the LCIE, but the stratigraphic relationships of the strata have been debated. Historically, they had been placed in the Burgsvik Formation, which included the Burgsvik Sandstone and the Burgsvik Oolite members. We revise the fauna in the Jeppsson collection and characterize key outcrops of Burgen and Kapellet. The former Burgsvik Oolite Member is here revised as the Burgen Oolite Formation. In the Burgen outlier, back-shoal facies of this formation are represented and their position in the Ozarkodina snajdri Biozone is supported. The shallow-marine position compared to the coeval strata in southern Gotland is reflected in the higher δ¹³C_carb values, reaching +9.2‰. The back-shoal succession includes high-diversity metazoan reefs, which indicate a complete recovery of the carbonate producers as the LCIE declined. The impoverishment of conodonts associated with the LCIE in southern Gotland might be a product of facies preferences, as the diverse environments in the outlier yielded all 21 species known from the formation. Fish diversity also returned to normal levels as the LCIE declined, with a minimum of nine species. In line with previous reports, thelodont scales appear to dominate samples from the Burgen outlier.

摘要

在 Ludfordian 碳同位素偏移 (LCIE) 中出现的全球环境扰动之后，瑞典哥特兰东部布尔根异常值中暴露的 Ludfordian 地层记录了动物群最初恢复的时间。瑞典自然历史博物馆收藏的已故 Lennart Jeppsson 收藏的脊椎动物微化石是重建 LCIE 衰落期间动物群迁徙和多样化动态的关键，但地层的地层关系一直存在争议。历史上，它们被放置在 Burgsvik 地层，其中包括 Burgsvik 砂岩和 Burgsvik 鲕粒岩成员。我们修改了 Jeppsson 收藏中的动物群，并对 Burgen 和 Kapellet 的主要露头进行了表征。前 Burgsvik Oolite 成员在此被修订为 Burgen Oolite 组。支持Ozarkodina snajdri Biozone。与哥特兰岛南部同期地层相比，浅海位置反映在较高的 δ ¹³ C_{碳水化合物}值上，达到 +9.2‰。后滩序列包括高度多样性的后生生物礁，这表明随着 LCIE 的下降，碳酸盐生产商已完全恢复。与哥特兰岛南部 LCIE 相关的牙形石的贫化可能是相偏好的产物，因为异常值的多样化环境产生了地层中已知的所有 21 种物种。随着 LCIE 的下降，鱼类多样性也恢复到正常水平，至少有 9 个物种。与之前的报告一致，thelodont 尺度似乎在 Burgen 异常值的样本中占主导地位。