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Solution-collapse breccias on Svalbard

 
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Bjarne Rafaelsen
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PostPosted: 15 Aug 2005 12:35    Post subject: Solution-collapse breccias on Svalbard Reply with quote

The paper "Solution-collapse breccias of the Minkinfjellet and Wordiekammen Formations, Central Spitsbergen, Svalbard: a large gypsum palaeokarst system" by Eliassen, A. and Talbot, M.R. describes large volumes of carbonate breccia in the late syn-rift and early post-rift deposits of the Billefjorden Trough, Central Spitsbergen.

Read more in: Sedimentology, 2005, vol, 52, p. 775–794.
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Marcos F. Bueno de Moraes
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Joined: 13 Oct 2005
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Location: Petrobras-Petróleo Brasileiro S.A.

PostPosted: 21 Oct 2005 17:26    Post subject: Carbonate/Evaporite solution-collapse model Reply with quote

Dear Bjarne,

I have read this paper ("Solution-collapse breccias of the Minkinfjellet...", Eliassen & Talbot) and in my opinion, it is very interesting. The mechanism of brecciation (solution-collapse origin) is well explained and supported by petrographic and geochemical analysis. Also is very interesting the photographs of a large V-structure (fig.5e, a true "seismic scale"), collapsed features (fig.6c) and related breccias facies (fig. 5a, b).
Bjarne, could you answer three questions mine (or indicate who can answer)?
1) According the fig.'s 5a and 5b (breccia facies), the first one seems a very good permeability/porosity conditions and, by the other hand, the second one seemingly shows tight conditions or completely cemented by evaporite (?). These conclusions are right, and there is a predominance of one of this breccia facies in a collapsed zones?
2) There is a structural control for the distribution of these collapsed features?
3) The hydrothermal origin is completely ruled out?
Many thanks once more. :D
Best regards,
Marcos Bueno (exploration geophysicist).
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Bjarne Rafaelsen
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PostPosted: 24 Oct 2005 08:03    Post subject: Reply to Mr. Bueno Reply with quote

Dear Mr. Bueno

I appreciate your interest in the "Billefjorden breccias" and I hope this answers your questions.

1) Generally the vast majority of exposed breccias do not contain pore-filling cement as shown in fig 5b (which is calcite not anhydrite) thus the exposed breccias seem to have an open pore network. However these types of collapse breccias are commonly plugged by detrital matrix and are not always the best reservoir rocks. One cannot rule out that the seemingly good reservoir properties of the exposed breccias in Billefjorden may contain a lot more matrix in the subsurface (weathering of unconsolidated matrix can be a factor here).

2)The breccia system is best developed in close vicinity to the important Billefjorden Fault Zone and the thickest breccia units seem to be directly associated with faults. It is thus my opinion that the karst system is to a large degree controlled by tectonism. The faults probably acted as important vertical aquifers for the dissolving waters.

3)There are no good evidence for a hydrothermal origin for this karst system. Fluid inclusion data from the breccia cements are dominantly monophase containing fresh water. We were not able to find inclusions with increased salinity. In my opinion this is a strong indication that this is a meteoric karst system.

Best regards
Arild Eliassen

------------------
Posted on behalf of Arild Eliassen
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Marcos F. Bueno de Moraes
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PostPosted: 24 Oct 2005 13:43    Post subject: Reply to Mr. Eliassen Reply with quote

Dear Mr. Eliassen,
First of all, many thanks for your attention answering my questions and congratulations for your very interesting paper.
I am interested in this topic because when we consider the involved processes (salt dissolution, carbonate brecciation, collapsed features, fracturing, dolomitization), we can think in a very special type of exploratory prospect for oil accumulation. I am sending some references about this theme. One of them emphasizes the drilling in collapse features reaching lost circulation and suggesting a high permeability breccia zone (from Broomhall & Allan,1987). By the other hand, another examples show a brecciated zone completely cemented (by calcite or reprecipitated evaporites), and the most interesting zones (in exploratory way) are very fractured surrounding host rocks.
Please Mr. Eliassen, in examples from Svalbard are there significant dolomitization events? If yes, what dolomitization types are present (marine, hypersaline reflux, HTD)? Are they early or late processes? Are the adjacent host rocks very fractured or no? and are the fracture systems opened or closed?.

The references about solution-collapse breccias are (if you wish, I have others):
Broomhall,R.W. & Allan,J.R., 1987: "Regional Caprock-destroying dolomite on the middle Jurassic to early Cretaceous Arabian Shelf". Society of Petroleum Engineers, SPE Formation Evaluation, December 1987, pp. 435-441.
Pomoni-Papaioannou,F. & Karakitsios,V., 2002: "Facies analysis of the Trypali carbonate unit (Upper Triassic) in central-western Crete (Greece): an evaporite formation transformed into solution-collapse breccias". Sedimentology, 49, pp.1113-1132.
Harrison,M.J.; Marshak,S.; McBride,J.H., 2004: "The Lackawanna synclinorium, Pennsylvania: A salt-collapse structure, partially modified by thin-skinned folding". Geological Society of America Bulletin, Nov./Dec.2004, V.116, No. 11/12, pp. 1499-1514.

Thank you again, Mr. Eliassen. Thank you Mr. Bjarne. :D
Marcos Bueno.
Exploration Geophysicist.
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Bjarne Rafaelsen
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PostPosted: 25 Oct 2005 08:47    Post subject: Relpy to Marcus Bueno Reply with quote

Dear Mr. Bueno,

Dolomitization of the host rocks is very common. The upper part of the Minkinfjellet Formation is dominated by dolomites. It is my interpretation that the majority of the dolomites are of early origin and formed by seepage-reflux processes. The breccia clasts itself commonly show evidence of dedolomitization which is likely to have been caused by the flushing of Calcium sourced from anhydrite/gypsum dissolution (which infers an early phase of dolomitization).

Fracturing of the surrounding host rocks is indeed present. However, I never focused my work on these fractures, so I cannot give you detailed information on the intensity or the nature of the fracture system.

You may be interested in these papers concerning the sedimentology and diagenesis of the host rocks:

Eliassen, A. & Talbot, M. R.: Sedimentary facies and depositional history of the mid-Carboniferous Minkinfjellet Formation, Central Spitsbergen,
Svalbard. Norwegian Journal of Geology,Vol. 83, pp. 299-318.

Eliassen, A. & Talbot, M. R.: Diagenesis of the mid-Carboniferous Minkinfjellet Formation, central Spitsbergen Svalbard. Norwegian Journal of Geology,
Vol. 83, pp. 319-331.

The papers can be downloaded free of charge (PDFs) here:
http://www.geologi.no/cgi-bin/geologi/imaker?id=4332&visdybde=2&aktiv=4332

Regards
Arild

----------------------
Posted on behalf of Arild Eliassen
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