estruturas pós- deposicionais€¦ · 1 estruturas pós-deposicionais importÂncia das estruturas...
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Estruturas Estruturas Estruturas pppóóósss---
deposicionaisdeposicionaisdeposicionais
IMPORTÂNCIA DAS ESTRUTURAS PÓS-DEPOSICIONAIS
Após a deposição, o sedimento está sujeito a outra série de processos modificadores das suas características primárias. Estes processos incluem um conjunto de estruturas que também são conhecidas pela designação genérica de estruturas reotrópicas (reologia é a ciência que estuda a deformação e o escoamento da matéria).
1.Estruturas formadas por comportamento quasi-líquido;
2.Estruturas formadas por comportamento hidroplástico;
3.Estruturas formadas por comportamento quasi-sólido;
4.Estruturas de ação biogênica.
http://www.huxley.ic.ac.uk/research/basins/lonergan/images/bigdyke.gif
A maior intrusão clástica conhecida em
afloramento! Este dique (e também sill) clástico
intrude pelitos miocênicos (rochas brancas na
foto), podendo chegar a 10 m de largura.
www.answersingenesis.org/ Home/Area/feedback/n...
www.ulg.ac.be/geolsed/ processus/processus.htm
course1.winona.edu/.../ sole_marks/newpage3.htm
This photo shows the relationship between load structures and flame
structures. The weight of the overlying beige sandy layer created the load
structures and caused concurrent injection of the darker mud into the sand, creating flame structures.
Estruturas de escorregamento (slump structures)
Estas estruturas formam-se tipicamente em leitos intercalados de pelito e pelitoarenoso que tenham sido rapidamente depositados. A deformação ocorre quase
imediatamente à deposição pelo movimento de sedimentos consolidados a
semi-consolidados, principalmente por causa da gravidade. Acamamentos que
apresentam soft-sediment defomation podem ser normalmente distinguidos de
acamamentos deformados tectonicamente pela presença de lâminas não
deformadas acima e abaixo do horizonte deformado.
http://course1.winona.edu/csumma/images/sedstrux/convolute.jpg
Estruturas almofadadas (Ball and Pillow)São massas arredondadas de areia
que “caem” para dentro
de pelitos ainda
inconsolidados devido ao
peso da camada de areia
sobrejacente da qual as massas de areia se
desprenderam. Estruturas de impacto (Impact Structures)
As camadas sedimentares
subjacentes são
deformadas pelo impacto de “pedras” desprendidas
de geleiras se derretendo
ou de erupções
vulcânicas. As camadas
subseqüentes acomodam-
se sobre o obstáculo
formando um lençol.
http://tesla.jcu.edu.au/Schools/Earth/EA1001/Sedimentary/Sedimentary%20Structures.html
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www.ulg.ac.be/geolsed/ processus/processus.htm
www.geologyrocks.co.uk/ tut.php?id=3
Estruturas de sobrecarga (load casts) ...Load Casts
Load casts, unlike flute casts, are deformational structures, rather than erosional structures. They occur commonlyalong the bases of sandstone beds that overlie mudstone or shale beds. While they may sometimes resemble flutecasts, load casts can be differentiated from flute casts by their greater irregularity of shape and the lack of anyindication of paleoflow direction. Load casts range in size, and may be associated with other deformationalstructures like flame structures and/or ball-and-pillow structures. Load casts form in settings where water-saturatedmuddy sediments are buried rapidly by coarser (sandy) sediments, creating a situation where dewatering of the mudcannot take place. The weight of the overlying sand causes it to sink unevenly into the muddy substrate, creating
these features. (course1.winona.edu/.../ sole_marks/newpage3.htm)
©Earth and Ocean Sciences
www.eos.ubc.ca/courses/ eosc221/sed/sili/load.html
course1.winona.edu/.../ sole_marks/newpage3.htm
These are relatively large load casts, seen in cross-sectional view. The
weightof the overlying sand was sufficient to cause the darker muddy layer to
rupture, such that deformation became more intense, making it difficult to distinguish boundaries between beds.
II. Acamamento convolucionado
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Convolute Lamination. Plage
Victor, Quebec. Undeformed
laminae below are overlain by
deformed laminae in upper part
of bed.
http://course1.winona.edu/csumma/images/s
edstrux/convolute2.jpg
http://course1.winona.edu/csumma/image
s/sedstrux/softsed2.jpg
Kingston Peak Formation,
southeastern California. Note
the deformed beds near the
center of the photo, overlain by
undeformed beds in the upper
part of the photo (under the
scale).
Images (c) 2003 Andrew Alden, licensed to About.com, Inc.
Images (c) 2003 Andrew Alden, licensed to About.com, Inc.
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ESTRUTURAS BIOGÊNICAS
Tuff horizon within offshore-lacustrine black shales, duplication caused by over-
thrusting during post-depositional sliding of not completely consolidated package.
www.geologie.uni-wuerzburg.de/.../ tuffgel1.gif
Clastic dyke formed of pale sandstone within dark shale. The dyke originates from a sandstone layer, and the originally soft
sand has been forced downwards into (presumably) a deep crack in the mud. Eventually, the sand came in contact with a
sand layer below (centre of photo) and could penetrate no further. When the sand and mud were compacted during deeper
burial, the mud was squashed much more than the sand, which had to accommodate the shrinking mud thickness by
becoming contorted. Hammer for scale. Horton Bluff (Carboniferous)
http://meguma.earthsciences.dal.ca/classes/2203/cm01/2203-cm01-sl25.htm
http://meguma.earthsciences.dal.ca/classes/2203/cm01/images/2203-cm01-sl27.jpg
Convolute lamination with flame structure, formed in ripple-drift cross-laminated sandstone. The water-rich
sediment was "soupy" and the laminae were deformed as water escaped from between the grains. A mud layer
below was squeezed up into some of the sand, generating flame structures. Modern sea shells for scale (outcrop
along coastal cliff). Sydney (Carboniferous)