Neogene Tree Trunk Fossils from the Meshgin Shahr Area, Northwest Iran

Abstract

In 2016, an extensive fossil forest was discovered near Meshgin Shahr, northwest Iran. Silicified tree trunks occur in Miocene fluvial sediments and at multiple stratigraphic levels within a 27-m thick sequence of Pleistocene volcaniclastics. The Miocene trunks likely represent stream transport. Pleistocene examples originated during repeated eruptive events when volcaniclastic sediments buried a standing forest. The site, informally named Meshgin Shahr Fossil Forest, was registered in 2017 as a national natural monument by the Iranian Cultural, Handicraft and Tourism Organization. To date, 16 fossilized trunks have been found, all but one of them representing gymnosperms. The ancient coniferous forest was very different from modern forests in Iran and adjacent Azerbaijan, a result of climatic changes that were principally caused by the demise of the Paratethys Sea and by rain shadow effects caused by the uplift of the Alborz and Zagros mountain ranges. X-ray diffraction patterns reveal that woods from the fossil forest contain three types of silica: opal-CT, pure quartz, and a mixture of opal-CT and quartz. In addition, optical photomicrographs show the abundant presence of amorphous opal-A. Mineralogic variations occur among different fossil trees and within a single trunk. These silica polymorphs resulted from a combination of processes: silica minerals precipitated in multiple episodes under differing geochemical conditions and the diagenetic transformation of an opaline parent material.

Extensive vertebrate tracksite from the Upper Red Formation (middle–late Miocene), west Zanjan, northwestern Iran

“…Megagyrolithes asdescensis is a large spiral burrow attributed to crustaceans (Gaillard, 1980). Myers et al (2019), in an aquaria-based study, reported sedimentary structures resembling planar lamina and ripple cross lamina with grain sizes ranging from fine sand to gravel made by a sand-sifting goby, and they noted that these structures may have a long history in the geological record reflecting feeding styles and bio-resuspension behaviors of macrofauna from different time periods (Myers et al, 2019). Numerous gutter-like furrows, up to 60 cm wide and up to 9 m long, have been reported from the shallow Middle Jurassic sea floor from Liesberg, Switzerland, and interpreted as feeding traces made by large marine vertebrates, most likely plesiosaurs and ichthyosaurs searching for food in the lime mud (Geister, 1998).…”

Life in the woods: Taphonomic evolution of a diverse saproxylic community within fossil woods from Upper Cretaceous submarine mass flow deposits (Mzamba Formation, southeast Africa)

“…The processes involved in outer shelf siliceous permineralization are poorly documented but require a generous source of free silica. This might derive from the breakdown of volcanic glass from ash beds intercalated within a sedimentary succession (Maguire et al, 2016), the dissolution of feldspars (Mustoe et al, 2020), or from more exotic sources, such as silica-charged marine seep fluids, and/or dissolution of associated sponge-or radiolarian-rich deposits (Kuechler et al, 2012). In the case of the wood-rich Hauterivian-Barremian Birdrong Sandstone of Western Australia, the source of permineralizing silica may have been from the overlying (Aptian) Windalia Radiolarite.…”

Mineralogical and paleobotanical investigations of Oligo-Miocene petrified wood from the southwest of Thrace Basin (NW Turkey)

“…Especially opal-A is not well recognized in XRD patterns but it appears as an amorphous mineral inoptical and SEM microscopy of some samples of Malkara-Keşan region petrified wood. On the other hand, opal-A formed in petrified wood cells that contain a small quartz-filled fracture produces a pattern that appears to indicate quartz composition (Mustoe et al, 2020).…”

“…This is not common in fossil wood, but some petrified wood specimens from arid regions include gypsum. The presence of this mineral in silicified wood from the Malkara-Keşan region probably represents a time when ground water contained dissolved sulfate, causing Ca toprecipitate as CaSO 4 rather than as CaCO 3 or Ca 5 (PO 4 ) 3 (Mustoe et al, 2020). If gypsum is present, the Ca:S ratio should be 1:1 (Mustoe, 2021).…”