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Showing results for tags 'tree trunks'.
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During our explorations in search of fossils, we obviously favor sedimentary rocks; I invite you to follow me with my wife in search of fossils… in volcanic rocks! (only observation without sampling) In the center of the volcanic massif of Cantal (central France), we explored a not very accessible valley where outcrop deposits of breccias of dense pyroclastic flows, in search of fossil woods of Villafranchian age (upper Pleistocene). According to an old reference (conference , 1969) one can find: “sometimes tree trunks inclined in all directions and sometimes branches. They are black, it is charcoal, produced by combustion in the absence of oxygen. After their reduction in carbon, certain woods underwent a strong fumarolic activity with silicification in opal cristobalite, generally respecting the vegetal structures.” By anatomical study in microscopy, 5 genera have been identified: Cedroxylon, Piceoxylon, Cornoxylon, Fagoxylon, Ulmoxylon. They suggest a temperate or mountain type climate. The conservation of carbonized organic matter indicates that the rock emplacement temperature must have been relatively lower than at the volcanic magma exit point estimated at 900°C according to mineralogy. The pyroclastic flow therefore destroyed a forest by descending the slope of the volcano while cooling. Let us now see in some photos what we discovered with wonder: 2 fossiliferous sites, the first with only one vertical trunk in an overhanging cliff, the second with multiple trunks preserved or hollowed out and branches on the bank of the river (without signs of silicification on these 2 sites found about 300 meters apart). There must therefore still be other nearby sites, but the difficult access to the site probably keeps them out of sight.
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