希腊莱斯沃斯岛中新世木化石研究进展

Progress in the study of Miocene petrified woods from Lesvos,Greece

希腊莱斯沃斯岛是世界上最为著名的木化石产地之一,出露有由中新世火山活动而形成的大规模矿化森林,保存有大量的植物以及部分动物化石。其中大多数木化石横卧或直立原地埋藏,并保留比较完整的根系,是目前保存最完整的新生代矿化森林生态系统。本文对莱斯沃斯岛已报道的木化石进行详细梳理分析,共计8科15属32种,包括裸子植物6科11属22种,被子植物2科4属10种,并着重介绍了发现自莱斯沃斯的代表性木化石特有类群系统古生物学属性。通过木化石反映的植物类群,初步恢复莱斯沃斯岛中新世属于北半球亚热带气候,总体比较温暖潮湿,有着明显的季节性变化特征。最后对莱斯沃斯岛木化石的埋藏环境进行了简要讨论,并对今后的研究进行了展望。

Utilizing fossil plants to reconstruct palaeoclimate and palaeoenvironment not only enriches the understanding of climate evolution in geological history,but also provides clues for exploring climate changes in both the past and the future.The study of fossil woods provides evidence for the reconstruction of forest composition and climate fluctuations in the geological past(Falcon-Lang and Cantrill,2001;Falcon-Lang,2005;Jiang et al.,2016;Wang et al.,2017;Xie et al.,2018).The Cenozoic represents an era with frequent volcanic activities,and it is also a time when plants rapidly developed and gradually attained its dominance of the landscape as in a modern flora.In areas with volcanic eruptions,local forests were probably buried and became petrified.The petrified forests in Lesvos Island of Greece were formed during the Miocene volcanic activities.The Lesvos Island Global Geopark covers the whole island and represents one of the first European and Global Geoparks.It is especially famous for its well-preserved fossil woods in the world.The Lesvos petrified forests contain some animal fossils and a great number of plant fossils with extremely abundant petrified woods.Most of these woods are stems and roots that are often preserved upright and in situ.The fossil woods are mainly concentrated in the west of the island that includes four parks,i.e.,Mpali Alonia,Sigri,Plaka and Nisiopi islands.In order to better study and protect the fossil wood forests,a national nature reserve was established in 1985 by the Greece Government,and the Natural History Museum of Petrified Forests was established in Lesvos in 1994(Zouros,2004,2010 a).A detailed study of the Lesvos petrified forests can provide evidence for better reconstructing of palaeovegetation evolution,palaeoclimatic and palaeoenvironmental changes,as well as geological and tectonic movements in the Mediterranean region.Since 2017,we have conducted geological surveys of the petrified forests of Lesvos Island.In these surveys,we aimed to reveal the taxonomic diversity of fossil woods and to further reconstruct the palaeovegetation and palaeoclimatic changes during the Miocene.In this study,we mainly focus on the progress of classification and diversity of the Miocene Lesvos fossil woods,and briefly discuss their significance on fossil taphonomy,palaeoclimate and palaeoenvironment.The geological setting and lithostratigraphic system of the Lesvos area have been divided into four parts(Kelepertsis and Esson,1987;Zeng,2018):(1)The autochthonous series occurs in the southeast area of Lesvos with the basement in the east of Lesvos;(2)The volcano-sedimentary series is in tectonic contact with the autochthonous series(tectonic cover,Late Paleozoic to Triassic sediments in the southeast of Lesvos);(3)The tectonic cover of ophiolites is overthrust on the Triassic rocks;and(4)The meta-alpine formations are distributed in the west of Lesvos Island,and are subdivided into the Neogene and the Quaternary.The Neogene includes pyroclastic materials,various types of lava,and sedimentary deposits of marine or lacustrine origin.The lithostratigraphic framework based on previous studies(Pe-Piper,1980;Koufos et al.,2003;Pe-Piper et al.,2014,2019 a,2019 b)roughly divides the Miocene,in ascending order,into the following formations:The oldest Cenozoic rocks,the Gavathas Formation,is consisted of lacustrine marls,shales,sandstones and lignites(New fossil plant sites have been found in this set of strata recently);The Eressos Formation is represented by widespread andesite-dacite domes;The Sigri Formation overlies the Gavathas and Eressos formations and underlies the Skoutaros Formation;The Skoutaros Formation consists of basalt and andesite flows;The Polychnitos Formation is divided into seven ignimbrites zones;and the Skalohorion Formation is represented by younger andesite and dacite lavas with hornblende and biotite.The study of fossils in Greece dates back to the 5 th century B.C.,when the natural philosopher Xenophanes first observed and recorded some fossil leaves of laurel(Mayor and Bodson,2000;Velitzelos et al.,2014).In the 3 rd century B.C.,Theophrastus(372–287 B.C.),who came from Eressos of Lesvos,made the first palaeobotanical study on the fossil flora of Lesbos and of Greece,and described different types of fossilization.The earliest study on the fossil wood of Lesvos dates back to 1835–1849.Unger(1852)first reported and described the Cenozoic fossil woods from Lesvos(Velitzelos et al.,2014,2019).Since then,several wood fossils of Lesvos Island have been identified by Flinche,and some taxa identified by Unger have been revised(Fliche,1898).During 1990–2010,Süss and Velitzelos conducted systematic and taxonomic studies on the fossil woods of Lesvos Island and described 16 gymnosperm wood species(Süss and Velitzelos,1993,1994 a,1994 b,1997,1998,1999,2000,2001,2009,2010;Süss,1997,2003).Since 1995,Zouros and his team have conducted a series of investigations and conservations on the fossil woods(Velitzelos and Zouros,1997,1998;Zouros et al.,2004,2007;Zouros,2004,2010 a,2010 b).In recent years,Velitzelos et al.(2014,2019)described some fossil woods of Lesvos Island and reported nine species of Arecaceae.It is noted that certain fossil wood taxa have been described from Lesvos Island by some authors(Mantzouka et al.)However,these publications were not officially approved by the Museum of Natural History of the Petrified Forest of Lesvos,thus these published data were not included in our data set at the time being.About 32 species of fossil woods referable to 15 genera of eight families have been recognized from Lesvos.These plants are assigned to gymnosperms(22 species of 11 genera in six families)and angiosperms(10 species of four genera in two families).In addition,some fossil leaves and reproductive organs(five gymnosperms and 29 angiosperms)were also discovered in Lesvos.It is noteworthy that most of the fossil woods reported before 2010 were assigned to gymnosperms,while those published after 2010 were mainly assigned to angiosperms.Most of the fossil woods from Lesvos are mainly represented by conifers(mostly Protopinaceae and Cupressaceae)and angiosperms(predominantly Arecaceae).Some fossil woods have not yet been systematically identified,and other woods are preliminarily assigned to Quercus(Fagaceae),Salix(Salicaceae)and Rhamnus(Rhamnaceae).The systematic features of the representative fossil wood taxa discovered in Lesvos are briefly introduced.Lesbosoxylon(six species)and Taxodioxylon(four species)are the dominant genera.Taxaceae,Podocarpaceae and Ginkgoaceae are also reported.In addition,some species of Cedroxylon,Tetraclinoxylon,Thujoxylon and Glyptostroboxylon are recognized.Two genera of conifer wood,Chimairoidoxylon Süss et Velitzelos emend.Süss and Lesbosoxylon Süss et Velitzelos,have been documented.For angiosperm fossil wood,about nine species of Arecaceae are reported from Lesvos.At some localities of Lesvos,at least three distinct pyroclastic deposit periods can be identified.Anatomical structures of the fossil woods suggest that the climate of Lesvos during the Miocene was warm temperate to subtropical,and was generally warm and humid with distinct seasonality.The main elevation of the forest was 500–1000 meters,and there were broad-leaved trees and palms in the low elevation area.Additionally,the burial condition and environment of wood fossils in Lesvos are briefly discussed with further prospects of future investigations.It is clear that systematic palaeontological studies on the fossil woods from Lesvos Island is still in the process of data accumulation.Therefore,detailed systematic and taxonomic study of many newly discovered wood fossils is very much necessary.