Melanosclerites from the Late Ordovician to earliest Silurian of Estonia and their palaeogeographical implications

Abstract

This study presents a new analysis of the Late Ordovician to earliest Silurian melanosclerites from the Kaugatuma core on Saaremaa Island, Estonia. By observing a large number of fossil melanosclerites, this study carefully reviews previous records and makes taxonomic emendations. Twelve species (including one in open nomenclature) that can be assigned to nine genera are identified, including the most typical elements, which were first reported by Alfred Eisenack eight decades ago. Based on a revised dataset of melanosclerite occurrences from 21 localities around the world, the Palaeozoic palaeogeographical occurrences of these organisms with uncertain affinity are then plotted on an up-to-date map to determine their palaeogeographical potential. Although the spatial distribution of melanosclerites shows patchy occurrences resulting from sparse research efforts, a tendency to occur in low-latitude, warm-water regions can be detected. All the reported occurrences are confined within the tropics and subtropics, with most of them restricted to 30° north and south of the equator during the Early Palaeozoic. This distribution pattern is compared with that of Palaeozoic hydroids, showing an overlap in palaeogeographical distribution, with both occurring in Baltica, Laurentia, Siberia, South China, and the northeastern part of Gondwana, but absent from high-latitude regions. If future work can confirm their postulated close biological affinity, the palaeogeography of the two types of fossils can be combined to complement each other.

Keywords:

• biological affinity
• Estonia
• Lower Palaeozoic
• melanosclerites
• palaeogeography
• taxonomic revision

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Funding

This work was funded by the National Natural Science Foundation of China (grant numbers 41772001 and 41872151). This work is also supported by the State Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of Geology and Palaeontology, CAS) (No. 213120), the Natural Science Foundation of Hunan Province (No. 2021JJ30816), and the Administrative Committee of Zhangjiajie UNESCO Global Geopark (No. 202001). Thanks are also given to Thomas Servais and one anonymous referee for constructive comments that greatly improved the paper. This is a contribution to the IGCP 653 and 735 Projects.

Notes on contributors

Minghao Du

MINGHAO DU is a doctoral student in Central South University, China. He is interested in Early Palaeozoic palynology. He is also adept at using quantitative methods to reconstruct biodiversity dynamics and palaeoenvironments, especially in the Early Palaeozoic.

Jaak Nõlvak

JAAK NÕLVAK is a specialist at Tallinn University of Technology, Estonia. He has long devoted himself to the Ordovician and Silurian chitinozoan biostratigraphy in the Baltica Region. His research has effectively promoted the delineation and global comparison of Baltica chitinozoan biostratigraphy.

Jingqiang Tan

JINGQIANG TAN is a professor of petroleum geology and geochemistry at Central South University. He received his PhD in petroleum geology from the Technical University of Berlin (TU-Berlin, Germany) and the German Research Center for Geosciences (GFZ-Potsdam, Germany) in 2014. He spent two years as a postdoctoral fellow in the Center for Petroleum Geochemistry at the University of Houston in the United States. His research primarily focuses on the geology and geochemistry of unconventional resources and the stimulation of unconventional reservoirs. In recent years, his research interests have also included integrated biostratigraphy and chemostratigraphy in gas-bearing shale.

Shijia Gao

SHIJIA GAO is a graduate student of Central South University. For her undergraduate degree, she mainly studied oil- and gas-related geology, including geochemistry, palaeontology, geohistory, stratigraphy, geophysics, etc. Now she is working on the middle graptolitic shales of Hunan Province, South China.

Wenhui Wang

WENHUI WANG is an associate professor at Central South University, China since the end of 2016. Her two primary research interests are: (1) Palaeozoic planktonic palaeontology and stratigraphy – she is working on several localities yielding graptolitic biostratigraphy from South China near the Cambrian/Ordovician and Ordovician/Silurian boundaries; and (2) the analysis of palynomorphs from the Lower Palaeozoic shales and their relationship with shale gas. She is Co-leader of the IGCP 735 Program.