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TitleAge, stratigraphy, sedimentology and tectonic setting of the Sigri Pyroclastic Formation and its fossil forests, Early Miocene, Lesbos, Greece
AuthorPe-Piper, G; Piper, D J WORCID logo; Zouros, N; Anastasakis, G
SourceBasin Research 2019 p. 1-20,
Alt SeriesNatural Resources Canada, Contribution Series 20190127
Mediapaper; on-line; digital
File formatpdf (Adobe® Reader®)
AreaSigri; Lesbos Island; Greece
Lat/Long WENS 25.8333 26.1667 39.2500 39.1667
Subjectsregional geology; stratigraphy; tectonics; paleontology; sedimentology; geochronology; mineralogy; geochemistry; Neogene; Miocene; volcanology; bedrock geology; lithology; igneous rocks; volcanic rocks; pyroclastics; tuffs; ignimbrites; clays; andesites; dacites; volcanic ash; volcaniclastics; sedimentary rocks; conglomerates; sandstones; structural features; faults, strike-slip; domes; paleosols; fossils; fossil plants; petrified wood; tectonic setting; crustal evolution; crustal structure; basin evolution; burial history; hydrothermal systems; veins; dykes; laccoliths; intrusions; volcanism; lava flows; flow velocities; alteration; hydrothermal alteration; silicification; argillization; colour; diagenesis; radiometric dating; argon argon dating; sedimentary structures; channels; fluvial deposits; paleodrainage; depositional history; facies; lithofacies; clasts; paleogeography; Sigri Pyroclastic Formation; Sigri Petrified Forest; Eressos Formation; Gavathas Formation; Mesotopos-Tavari Caldera; Phanerozoic; Cenozoic; Tertiary
Illustrationsgeoscientific sketch maps; cross-sections; stratigraphic columns; photographs; lithologic sections; photomicrographs; tables; rose diagrams; plots; bar graphs; geochronological charts
ProgramGSC Atlantic Division
Released2019 04 13
AbstractThe Petrified Forest of Lesbos comprises silicified tree fossils at multiple stratigraphic levels within the Lower Miocene Sigri Pyroclastic Formation. Our objective was to understand the interplay of tectonic setting, structural evolution, volcanological setting and basin evolution in the preservation of this remarkable natural monument. Sections were logged for lithology, sedimentary structures and hydrothermal alteration. Orientations of fallen fossil trees were measured. Samples were taken for mineralogical and geochemical analysis. 40Ar/39Ar dating was carried out on mineral separates from four samples. Widespread andesite?dacite domes, the Eressos Formation, intrude and overlie metamorphic basement and are overlain by the Sigri Pyroclastic Formation, which comprises several hundreds of metres of pyroclastic flow tuffs (unwelded ignimbrites) interbedded with fluvial conglomerate and volcaniclastic sandstone. The Sigri Pyroclastic Formation ranges in age from 21.5 to 22 Ma, where it overlies the lacustrine Gavathas Formation, to younger than 18.4 Ma. Tuffs and fluvial conglomerates in the Sigri Pyroclastic Formation coarsen eastwards, and petrified trees and soil horizons occur throughout the Formation. The recurrence of pyroclastic flows was approximately one every 20 ka, so destructive flows were relatively infrequent, allowing the development of climax vegetation between most eruptions. Conglomerate?filled channels show that rivers flowed westwards. Tree fall directions indicate NW to N movement of pyroclastic flows, implying a source near the younger Mesotopos-Tavari caldera to the south. The basin, which formed in a NNE?trending dextral strike?slip regime, provided some topographic steering. Following the Sigri Pyroclastic Formation at ca. 18 Ma, there was a rapid increase in the pace of volcanic activity, with the eruption of thick lava sequences and welded ignimbrites, and intrusion of dykes and laccoliths in SW Lesbos. Rapid burial by permeable tuffs, silica from alteration of volcanic ash, and later hydrothermal circulation all contributed to the preservation of the petrified trees.
Summary(Plain Language Summary, not published)
A comprehensive new interpretation of the geological setting of the famous Petrified Forest of Lesbos, Greece and its relationship to the volcanological evolution of the area.

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