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)