Tracing the Eocene–Oligocene transition: a case study from North Bohemia

Abstract

Geology and palaeontology of the Roudníky area, situated between the Most Basin and the České středohoří Mountains in North Bohemia, the Czech Republic, is treated in detail. The volcano-sedimentary structure underlying the basin with the included fossiliferous layers is newly interpreted as a maar-diatreme. The radiometric age of the basalts was determined to 35.4 ± 0.9 Ma and 37.1 ± 0.9 Ma -late Eocene, Priabonian. The fish fauna consists of amiids characteristic of other adjacent late Eocene sites while the co-occurring macroflora includes many elements that are typical of the Oligocene. Closest relations are to the fauna and flora of the Větruše Hill at Ústí nad Labem. Based on palaeoclimatic estimates the major turnover from subtropical to warm-temperate climatic regimes in North Bohemia appears to have initiated in the late Eocene by an increase of seasonality and the resulting vegetation change from the evergreen to mixed mesophytic forest types well before the maximum temperature drop of mean annual temperature at ca 33.5 Ma.•

Estimation of late Eocene (Bartonian–Priabonian) terrestrial palaeoclimate: Contributions from megafloral assemblages from central Germany

“…However, it has repeatedly been stated that the examined floras indeed indicate differences in the annual distribution of precipitation, but summer drought or "aridity" has never been confirmed by any quantitative study (Table 2). Recently, Kvaček et al (2014) indicated again similar results with 541 mm (3WET) and 86 mm (3DRY) for the late Eocene flora of Knau that is also a site in the Weißelster Basin and the Zeitz FA (Mai and Walther, 2000). Furthermore, it must be questioned whether notophyllous broad-leaved forests could be established in a period when main growing seasons coincide with drought or "aridity".…”

“…Both areas, the coastal and riparian habitats of the Weißelster Basin as well as the Bohemian "hinterland" including volcanic environments, feature a similar floristic composition, determined by using the integrated plant record vegetation analysis (IPR-vegetation analysis) which indicates the occurrence of broad leaved evergreen forests for both regions (Kvaček et al, 2014).The Bohemian flora of Roudníky (35.4 ± 0.9 Ma) is an exception as it mirrors the gradual change towards mixed mesophytic forests (MMF) by immigration of deciduous, temperate taxa and stepwise extinction of subtropical and tropical plants, and thus the proceeding global cooling trend towards the EOT. The flora of Roudníky shows MAT ranges of 13.6-18.0°C with CA and 10.0 ± 1.3°C determined by CLAMP (Kvaček et al, 2014). No flora corresponding to Roudníky is currently known from the latest Eocene of the Weißelster Basin.…”

“…In contrast, central European vegetation in the Atlantic Boreal phytoprovince (sensu Mai, 1995) underwent only minor (e.g. Kvaček et al, 2014) or almost no detectable changes throughout the late middle and late Eocene, indicating that there was presumably no significant climate change. This fact has been expressed for instance by the establishment of the Floral Assemblages ("Florenkomplex" sensu Mai, 1995) Zeitz (herein after referred to as Zeitz FA) for central Germany Walther, 1985, 2000) or Hordle-Zeitz for the Atlantic Boreal phytoprovince (Mai, 1995) indicating no fundamental changes in megaflora composition between c. 38.5 and 35.0 Ma b. p. in the respective region.…”

“…Repeatedly it has been demonstrated that no mountain glaciers were present except for smaller ice sheets developing during the late Eocene in Arctic regions (Eldrett et al, 2004) and on Antarctica (Kennett, 1977;Zachos et al, 2001;DeConto and Pollard, 2003;Coxall et al, 2005). Moreover, remarkable climatic changes and temperature excursions have been recognized from the Eocene such as the Paleocene-Eocene Thermal Maximum (PETM; McInerney andWing, 2011, Röhl et al, 2007) and the Eocene-Oligocene turnover (EOT; Kvaček et al, 2014;Lear et al, 2008, Zachos et al, 2001. The latter is often equated with Stehlin's "Grande Coupure" in the fossil record of European vertebrates (e.g.…”

“…This fact has been expressed for instance by the establishment of the Floral Assemblages ("Florenkomplex" sensu Mai, 1995) Zeitz (herein after referred to as Zeitz FA) for central Germany Walther, 1985, 2000) or Hordle-Zeitz for the Atlantic Boreal phytoprovince (Mai, 1995) indicating no fundamental changes in megaflora composition between c. 38.5 and 35.0 Ma b. p. in the respective region. This supposed stasis of predominantly evergreen notophyllous broad-leaved forest vegetation (Kvaček et al, 2014) ends near the EOT when modern Arcto-Tertiary elements massively immigrate into central European floras (Kvaček and Walther, 2001;Kvaček et al, 2014).…”