fault vs joint

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fault vs joint

Postby GroundquestMSA » Mar 13, 2014 3:01 pm

I'm working on writing a cave description and am interested in the control of its orientation. For 2800', the main passage is almost perfectly straight, and where it isn't clogged with clay or breakdown, "ceiling heights" range from 50' - 90'. The passage is relatively narrow, 10' - 25' wide and smaller toward the ceiling (which is never really seen, just a continually shrinking crack). So far, none of the minor passages diverge from the trend of the main cave, but parrallel it. The passage leans to the left a bit, on the way in, I wanted to call it 11-O'clock Cave but it already had a name. My questions: Is jointing commonly responsible for passage so large, and so straight over such distances? Palmers Cave Geology says that faulting is not usually a major factor in cave orientation, but how do I rule out the possibility?

Probably these are commonplace circumstances, but I've been in tiny caves for too long, and I don't know nothin'.

Thanks!
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Re: fault vs joint

Postby rlboyce » Mar 13, 2014 5:14 pm

How distinguishable is the geology inside the passage? Is the bedding pronounced? You will probably find this to be a "no duh" suggestion, but if you can match geologic features on each side of the passage, you should be able to calculate if there has been displacement after taking some measurements.
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Re: fault vs joint

Postby Martin Sluka » Mar 14, 2014 4:49 am

The carstification allways follows the weekest parts of bedrock. It could be physical and chemical properties of bedrock, geological structures, ...
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Re: fault vs joint

Postby NSS8921 » Mar 14, 2014 8:00 am

Also look for slickinsides. If present, there is a fault.
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Re: fault vs joint

Postby Chads93GT » Mar 14, 2014 11:46 pm

How about doing it the easy way. Find and download the counties geological map from the USGS. It will have faults prominently pronounced on the geology map. If there are no faults in the area on the map....................safe bet its just a big ole crack that got big.
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Re: fault vs joint

Postby NSS8921 » Mar 17, 2014 6:43 am

Chads93GT wrote:How about doing it the easy way. Find and download the counties geological map from the USGS. It will have faults prominently pronounced on the geology map. If there are no faults in the area on the map....................safe bet its just a big ole crack that got big.


Chad, some states, like Virginia, are riddled with faults, so only major faults show on the geological maps. Check out Gilley Cave (VA) to see lots of faults.

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Re: fault vs joint

Postby gindling » Mar 17, 2014 10:11 am

I would say without any indications of faulting like slickenslides or offset features in the rock that you are dealing with jointing. If there is a thin bed of breccia between two layers of rock that shows you that there was movement like an overthrust and the breccia is the mashed up bits crushed between the two moving layers later cemented by calcium in the groundwater. There are some caves out west that are mainly formed by the dissolution of this breccia. There are many caves where jointing causes very long, narrow and tall, straight passages. At least that is my experience.
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Re: fault vs joint

Postby GroundquestMSA » Mar 17, 2014 5:30 pm

gindling wrote:There are many caves where jointing causes very long, narrow and tall, straight passages.


Good deal, that's what I needed to know.
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Re: fault vs joint

Postby arizonaowl » Sep 15, 2014 5:09 pm

If there has been movement, however slight, it should be considered a fault. You may be talking about a "microfault." Al Copley 20845
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