Paleotemperature record of the Middle Devonian Ka\u010d\xe1k Episode

Monica Pondrelli,Thomas J Suttner,Michal Kubajko,Erika Kido,Luca Simonetto,Michael M Joachimski,Stanislava Vodrážková,Carlo Corradini,Maria G Corriga

doi:10.1038/s41598-021-96013-3

Abstract

The Middle Devonian Epoch, ~ 393–383 million years ago, is known for a peak in diversity and highest latitudinal distribution of coral and stromatoporoid reefs. About 388 million years ago, during the late Eifelian and earliest Givetian, climax conditions were interrupted by the polyphased Kačák Episode, a short-lived period of marine dys-/anoxia associated with climate warming that lasted less than 500 kyr. Reconstruction of the seawater temperature contributes to a better understanding of the climate conditions marine biota were exposed to during the event interval. To date, conodont apatite-based paleotemperatures across the Eifelian–Givetian boundary interval have been published from Belarus, France, Germany and North America (10–36° S paleolatitude). Here we provide new δ18Oapatite data from the Carnic Alps (Austria, Italy) and the Prague Synform (Czech Republic). For better approximation of the paleotemperature record across the Kačák Episode, a latitude-dependent correction for Middle Devonian seawater δ18O is applied. Because δ18Oapatite data from shallow marine sections are influenced by regional salinity variations, calculated mean sea surface temperatures (SST) are restricted to more open marine settings (22–34° S paleolatitude). Water temperatures reach ~ 34 °C in the Prague Synform and ~ 33 °C in the Carnic Alps and suggest that SSTs of the southern hemisphere low latitudes were ~ 6 °C higher than previously assumed for this time interval.

Highlights

The Middle Devonian Kačák Episode[1] is known as a minor global extinction event associated with a eustatic sea level rise[2]
In the Carnic Alps, the δ18Oapatite record of the Zuc di Malaseit Basso (ZMB) section includes 11 measurements covering an interval between the lower part of the kockelianus Biozone and the entry of the timorensis Biozone. δ18Oapatite values are between 18.2 to 19.1‰ (VSMOW)
The condensed pelagic sequence of the Wolayer “Glacier” section yielded abundant conodonts, which were extracted from cm-thick limestone levels separated along slightly uneven stylolite layers. δ18Oapatite values measured across the Eifelian–Givetian boundary vary between 17.7 and 18.0‰ (Fig. 3; Supplementary Fig. 1)

Summary

Introduction

The Middle Devonian Kačák Episode[1] is known as a minor global extinction event associated with a eustatic sea level rise[2]. Biodiversity analysis has shown that mainly a mmonoids5,14–16, conodonts[10,11,17,18] and trilobites[19,20] suffered from a certain taxonomic loss It appears that extinction was not the main response of faunal communities to environmental changes but rather habitat tracking and speciation events. New insights about the late Eifelian global warming period known as the Kačák Episode were generated by analysis of latitudinally dependent paleotemperature patterns reconstructed from conodont apatite. We discuss late Eifelian to earliest Givetian paleotemperature estimates based on new δ18Oapatite data from a shallow to deeper water transect within the Carnic Alps (Austria, Italy) and an offshore section from the Prague Synform (Czech Republic). Because paleotemperature estimates from shallow marine localities appear to be biased by varying salinities, the temperature record across the Kačák Episode is limited to more open marine deposits of the Carnic Alps

Methods

Results

Discussion

Conclusion