|[Note Guidelines] Photographer's Note|
|Varvite is the name used by the geologists to designate a special kind of sedimentary rock formed by the repetitive succession of plates or layers, each one of them deposited during the period of one year.|
Each plate or layer of varvite is, actually, a pair formed of an inferior portion, thicker (from centimeters to decimeters), of sandstone or siltstone, with a lighter color, followed by a thinner portion (milimeters) of siltstone or mudstone, with a darker color (dark gray).
The name derives from the word varve, of Swedish origin, generally used to designate sedimentary seasonal deposits, that is, controled by the variation of the seasons of the year. The most common type of varve is represented by plates, or layers, of sediments deposited in lakes formed in front of the glaciers, through the water dams produced by the ice melting, during the phase of moving back of the glaciers.
The rhythmites from the Brazilian Permian have shown a characteristic ichnofauna related to glacial environments. These rhythmites, considered as varvites, occur in two sedimentary basins located in Central (Sanfranciscana Basin) and Southern (Paraná Basin) Brazil. The classical exposure is the varvite of Itararé Group (Paraná Basin, Permian) nearby the city of Itu (central-eastern of São Paulo State).
Sedimentological, palynological and paleomagnetic evidenceindicate probable seasonal (annual) control on the deposition ofthe lithologic pairs of the varvite, as in Pleistocene varve clays.About 300 pairs are present in the Itu quarry.
Typical sedimentary structures of the varvite arebeautifully exposed in the quarry, as well as abundant ichnofossilsassigned to aquatic, benthonic invertebrates. Though relativelyrare, dropstones of varied composition and size (up to 2 metersin diameter) and mounds of glaciogenic debris liberated fromicebergs are found dispersed in the rock.
Probable depositional environment of the varvite was aproglacial water body or lake partially or temporarily in contactwith the glacier margin. The light, sandstone/siltstone beds/laminae were deposited by dense flows /turbidity currents duringsummer, followed by the settling of muds from suspension duringwinter, when the lake was frozen over.
The Itu quarry, the best exposure of glacial rhythmiteknown in the Paraná Basin, represents a classic geologicalmonument related to late Paleozoic glaciation. The monument iswell preserved within the Parque do Varvito (Varvite Park).
This is one of some images that I obtained during the expedition whom we made during one day entire for a geologic route where we could better study and understand the processes of rocky formation of the terrestrial crust.
To know more:
ge-fleur, Nephrotome2, tcr, roges has marked this note useful
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nice portrait !
Good thinking and really artistic !
Jolie mille feuilles ou bien de vieux livres empilés...
- [2009-07-08 10:38]
Voici une information et une photo intéressante!
Merci pour ce partage
- [2009-07-08 11:34]
What interesting capture and a great note, very good for all of us!Congratulation!
Must be hard to find a way to photograph this. The POV you've chosen is brilliant and results in very artistic lines / composition.
Your note is very helpful and interesting.
- [2009-07-08 17:13]
Isso parece massa folheada feita com rochas.
Interessante e nítida imagem com bom enquadramento e
- [2009-07-09 7:21]
Ola Paulo !
Muito interessante imagem sugerida por você!
Beautiful cores, excelente contraste.
Eu sabia que algo do mesmo.
Tenha um bom dia,
- [2009-07-10 3:16]
very interesting Rocks, good shot!
Great capture showing all the different layers in your rock fromation. I find rocks so interesting, there are so many different colours, textures and sizes. Good notes and well shown.