Late Frasnian–Famennian climates based on palynomorph analyses and the question of the Late Devonian glaciations

Abstract

Palynomorph distribution in Euramerica and western Gondwana, from the Latest Givetian to the Latest Famennian, may be explained, to some extent, by climatic changes. Detailed miospore stratigraphy dates accurately the successive steps of these changes. Interpretation is built on three postulates which are discussed: Euramerica at slightly lower latitudes than generally accepted by most paleomagnetic reconstructions; a conodont time-scale accepted as the most used available subdivision of time; and Late Devonian sea-level fluctuations mainly governed by glacio-eustasy. The Frasnian-Famennian timescale is also evaluated.The comparison, based on conodont correlations, between Givetian and most of the Frasnian miospore assemblages from, respectively, northern and southern Euramerica demonstrates a high taxonomic diversity in the equatorial belt and much Ž . difference between supposed equatorial and sub tropical vegetations. On the contrary, a similar vegetation pattern and therefore probably compatible climatic conditions were present from tropical to subpolar areas. A rather hot climate culminated during the Latest Frasnian when equatorial miospore assemblages reached their maximum width. The miospore diversity shows also a rather clear global Late Frasnian minimum which is also recorded during the Early and Middle Famennian but only in low latitude regions while, in high latitude, very cold climates without perennial snow may explain the scarcity of miospores and so, of vegetation.The Early and Middle Famennian conspicuous latitudinal gradient of the vegetation seems to attenuate towards the Late and Latest Famennian but this might be above all the result of the development, of cosmopolitan coastal lowland vegetations Ž . downstream swamps depending more on the moisture and equable local microclimates than on the probably adverse climates of distant hinterland areas. During that time, periods of cold climate without perennial snow cover and with rare vegetation may have alternated with less cold but wetter climates, thus giving rise to the development of mountain glaciers in high latitudes and explaining the jerking character of the global major marine regression. In high latitude regions, the development of an ice cap reaching sea level is only recorded by the end of the Latest Famennian, immediately below the Ž . DCB but, even if glacial evidences are not known at near the FFB, a short 0.1 Ma? glaciation seems the best reasonable explanation of the major eustatic fall following the Kellwasser Event. The sudden growth and decay of a hypothetical ) Corresponding author. Tel.: q32-4-366-5498; fax: q32-4-366-5338.Ž . E-mail address: maurice.streel@ulg.ac.be M. Streel . Earliest Famennian ice sheet can be explained by the reduction and, later, increase in greenhouse capacity of the atmosphere. These changes in the atmospheric CO might have provoked changes in the mode of ocean-atmosphere operation. It may 2 also be partly controlled by a volcanic paroxysm andror bolide impacts. The Hony microtektites represe...

The Late Devonian (Frasnian/Famenian) mass extinction: a proposed test of the glaciation hypothesis

“…The gla ciers in Gond wana reached their max i mum ex pan sion phase in the lat est Famennian, dated to the LE-LN spore zonal in ter val on land (Streel et al, 2000a;Caputo et al, 2008), and cor re lated to the Mid dle-Late praesulcata cono dont zonal in ter val in the sea (Isaacson et al, 2008). At the same strati graphic ho ri zon ice-rafted gla cial debris, in some cases metre-sized dropstones (Brezinski et al, 2010: fig.…”

“…Ex tinc tions as so ci ated with the max i mum ex pansion phase of the Famennian gla ci ation took place in two pulses: the first pulse oc curred in the ma rine realm at about 360 Ma in the Late Famennian, is dated to the Mid dle praesulcata Cono dont Zone at the Hangenberg Black Shale ho ri zon (Kai ser et al, 2006). The sec ond pulse of ex tinc tion oc curred in the terres trial realm and took place at about 359 Ma in the lat est Famennian, is dated to the Late praeculcata Cono dont Zone, and co in cides with the max i mum ex pan sion of the ice sheets on land in Gond wana (Streel et al, 2000a).…”

The Devonian/Carboniferous boundary in the Holy Cross Mountains (Poland)

“…This phe nom e non was linked with a large-scale gla cial ep i sode in the south ern hemi sphere, causing rel a tively rapid sea level fall (Streel et al, 2000;Sandberg et al, 2002;Caputo et al, 2008;Isaacson et al, 2008;Kalvoda et al, 2013;Kumpan et al, 2013).…”

Magnetic susceptibility evolution and sedimentary environments on carbonate platform sediments and atolls, comparison of the Frasnian from Belgium and Alberta, Canada

“…The Middle Frasnian (early Late Devonian) was a time of a globally warm (greenhouse) climate (for a recent review, see Streel et al, 2000;Joachimski et al, 2004;Hladil et al, 2005) and of high sea level (Vail et al, 1977;Johnson et al, 1985; and for a recent review, see Hladil, 2002). During the Devonian, the Earth's surface temperature reaches a peak during the Givetian and according to Streel et al (2000) those hot climates lasted until the Latest Frasnian.…”

“…During the Devonian, the Earth's surface temperature reaches a peak during the Givetian and according to Streel et al (2000) those hot climates lasted until the Latest Frasnian. During the Frasnian, this hot period was interrupted by two short-term cooling events in the Late rhenana zone and at the base of the Frasnian-Famennian transition (Joachimski et al, 2004) (which is younger than studied interval, see here-under).…”