No 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...

No abstract

No abstract

No abstract