Neogene woods from western Peruvian Amazon and palaeoenvironmental interpretation

Abstract

Vegetation dynamics in the Western Amazonian Basin are studied using knowledge of palaeobotany. Fossil wood specimens from eroded sediments on the banks of the Amazon in the Iquitos region of Peru come from layers dated as Middle Miocene to Pliocene. Samples include branch fragments or entire tree trunks either as compressed lignites or silicified stems. The wood can be assigned to modern genera of various families still present in the South American flora. Samples from the Middle Miocene Pebas Formation show affinities with taxa now occurring in rain forests: Anacardium (Anacardiaceae), Calophyllum (Clusiaceae), Buchenavia and Terminalia (Combretaceae), Andira/Hymenolobium (Fabaceae), Hurniriastrum (Humiriaceae), Cariniana and Eschweilera (Lecythidaceae), Guarea (Meliaceae) and Mimosaceae, which indicates that part of the Recent Amazon Basin flora pre-dates contact with North America. Growth rings are absent or indistinct in the fossils, a characteristic feature of low-elevation rain forests. The fossil assemblage evokes "Hylaea Amazonia" and especially the "terra firme" forests of the modern Amazon delta and surroundings. Fossil wood samples from the Pliocene Amazonas Formation resemble Cedrela (Meliaceae) and are semi ring-porous. The Cedrela wood occurence shows a vegetation change between mid-Miocene and now in the western Amazon Basin.