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Thread: Calibrating Earth's history

  1. #1 Calibrating Earth's history 
    Forum Isotope Bunbury's Avatar
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    I came across this site http://www.earth-time.org/about.html while looking for references on the KT boundary, which is supposed to be exposed on a small mountain near where I live. I've been looking a couple of times but haven't found it convincingly, so I was trying to find some decriptions on line to help narrow down the places to look.

    Anyway, so I found the Earthtime site and this http://www.ceps.unh.edu/pdf/dalton.pdf Nature article about the KT boundary a bit to the east of here at Bijou Creek (not where I was looking). Earthtime is a project to calibrate the geological timescale of the earth more precisely than has been achieved up to now.

    If I ever find the KT boundary on the mountain I'll post some pictures. It is actually a good place to look because a basalt cap that flowed over the area about 63 million years ago has preserved the underlying layers, while surrounding material has been eroded away. So the strata are exposed in the sides of the mountain (it's actually a mesa). It keeps me out of trouble on the weekends.

    Edit: This is a pic of what I thought might be it - the red layer above is porphyry basalt; the black layer is a soft shale like material that could conceivably be be ash at the KT boundary; the bottom layer is clearly different from the top layer, but also seemed to be hard and is probably another basalt layer. Any geologists out there?

    [/img]


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    There are a couple of KT divisions near us. One is within the Scollard Formation east of Calgary (where we collect dino and other remains). The 'boundary' between the Cretaceous and Tertiary is not so much geologic as biologic....you probably won't 'see' a physical difference. The iridium evidence is within the same members of the same formations. 'If' an event takes place on the globe and it has little physical impact at a macro level (such as a comet) then the geologic processes on Earth are not impacted. Rivers still flow...winds blow...etc. little if anything 'geologic' is altered. Most of any change is a minutia of the short term weather and 'thin skin' of biology'. Think of the Earth as a Jeep driving down a muddy road and accumulating mud on the grill and the comet or asteroid as a mosquito that hits the grill...the Jeep keeps going and most f the evidence of the bug is eroded away or covered by more mud. More mud accumulates. The evidence of the bug is minute and may be present only as a trace of DNA within the mud (such as the iridium in a geologic formation). You can't see the iridium. There is nothing that 'jumps out' as different.

    When we hike in the Scollard formation there is no visual difference above or below the KT line. Geologic sediments (bentonite cly) didn't 'stop'. Geologic forces continued more or indifferent to the metamorphical mosquito hitting. We'll find dino bits below the iridium boundary such as hadrosaurs, ceratopsians, etc. and other vertebrates such as croc, turtles, fish, champsosaurs, etc.). Above the line we find all the same vertebrate remains exept for the dinos. There are many sceptics among paleontlogists of the bolide impact extinction theory. Here in Alberta we have a continuous detailed record of dinos from aout 82 through to the KT boundary and there is more of a leaning towards less dramatic causes of dino extinction.


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    Forum Isotope Bunbury's Avatar
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    Good points.

    If the geologic process is sedimentation then yes, there’s no reason for there to be a visual difference in the rocks above and below the KT line. The basalt capping of South Table Mountain was an intermittent igneous process, though, and the KT line might have been deposited in between basalt outflows separated by thousands of years. On the other hand it should have been eroded away over thousands of years, before it was protected. The photo shows an interesting black line, but it’s probably not the KT line.

    There are other areas on the mountain, below the cap, where the rock is sedimentary and the strata are well exposed. Unfortunately access is blocked behind barriers put there for revegetation, which I respected.
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    WYSIWYG Moderator marnixR's Avatar
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    Peter Ward in his book "On Methusaleh's trail" describes the site near Zumaya in spanish Basque land as follows :

    But in Boundary Bay, as you cross the promontory that separates this inlet from Stairway Bay, you are immediately struck by a dramatic change: the purple marls, so uniform in color and thickness, are overlain by a spectacular assemblage of more thickly bedded strata of bright pinkand white. The effect is stunning. Wit the first view of the strata in Boundary Bay you know that something dramatic happened here. So profound a change in both the colour and the thickness of the rocks could not have occurred unless the enviroonmental conditions that controlled sedimentation were themselves drastically altered.

    i happened to pass there last summer, but must have missed seeing the right exposures, because i didn't see anything matching the above description
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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    Quote Originally Posted by Bunbury
    Good points.

    If the geologic process is sedimentation then yes, there’s no reason for there to be a visual difference in the rocks above and below the KT line. The basalt capping of South Table Mountain was an intermittent igneous process, though, and the KT line might have been deposited in between basalt outflows separated by thousands of years. On the other hand it should have been eroded away over thousands of years, before it was protected. The photo shows an interesting black line, but it’s probably not the KT line.

    There are other areas on the mountain, below the cap, where the rock is sedimentary and the strata are well exposed. Unfortunately access is blocked behind barriers put there for revegetation, which I respected.
    The sedimentary layers are unlikely to have any visible KT layer. You will find ash layers, coal layers, etc. in the exposures. In the Scollard formation (and Hell Creek in Montana) we don't find the extinction line by looking at it but by measuring 'x' centimeters above the other visible ash and coal layers. Every so many hundreds of thousands of years or 'whatever' there can be huge volcanic eruptions that impact all of western North America...these dwarf the geologic evidence of asteroids or comets hitting the Earth.

    You live in a great part of the continent to explore around looking for fossils and so on. We've often just roamed the backroads of parts of Colorado and where it borders with Utah or Wyoming and explored for paleo remains. The actual 'Rockies' in Colorado aren't great...they are mostly igneous rock in Colorado (sedimentary up here) but other areas are super. I've had a lot of success finding Eocene vertebrates on the area north of Craig and into Wyoming. There are paleo keeners in the state and probably societies you can join and participate in field trips. Once out a few times and 'getting the eye' then you're ready head out and do your own exploring. As the saying goes, a bad day of fishing (or fossil hunting) is still better than a good day doing anything else.
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    This is odd; I recall seeing photos of the KT boundary. I also find mention on the web such as this:

    scientists believe the sooty K-T boundary material is a world-wide fallout from a giant asteroid impact, and that it was this catastrophic event that caused the demise of the dinosaurs"
    And this site :

    http://esp.cr.usgs.gov/info/kt/stop2a.html

    has this photo:



    Figure 9. Photograph of the Starkville North K-T boundary site showing the sedimentary units. The arrow at the top of the exposure shows the position of the K-T boundary sequence.
    Jellyologist, you clearly know what you are talking about. Can you help clarify what these internet sites may be talking about?

    Perhaps if climate and vegetation were sufficiently affected by an impact (or other) , then there might be a geological shift in sedimentation?
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    Forum Isotope Bunbury's Avatar
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    Yes, I've seen similar photos, especially at Raton pass in southern CO and northern New Mexico, but the South Table Mountain location is
    Historically very important, this is the first site in North America where the K-T boundary was identified. In 1943, geologist Roland Brown documented the occurrence of dinosaur bones at the base of the ridge, and earliest Tertiary plants and mammals at the top of the ridge. Brown surmised that the K-T boundary lies within a 15-or-so-metre interval between the dinosaur-bearing rocks and the mammal-bearing rocks.

    In the 1990s, study of fossil pollen (palynology) refined the position of the K-T boundary to within an interval of 20 to 25 cm.
    http://nature.ca/discover/field/eber...0/denvr1_e.cfm

    This does not say the KT boundary shows up as a black line; just that its existence can be deduced from various proxies. Perhaps I read more into it than was there.
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    WYSIWYG Moderator marnixR's Avatar
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    i'd say that if there is a clay layer at the boundary (which i think is the case in many localities) then you would expect to wear away preferentially and thus show up as a marker line in the rock face

    obviously depends on how thick the layer is
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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  10. #9  
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    Jellyologist wrote:
    The 'boundary' between the Cretaceous and Tertiary is not so much geologic as biologic....you probably won't 'see' a physical difference.
    You are correct. A paper by Kaufmann et al says:
    Here, the
    Cretaceous-Tertiary boundary interval within the Denver Formation is exposed in an erosional escarpment
    and associated badlands (Fig. 2). Brown (1943) first noted the approximate position of the K-T boundary ip
    this area within a sequence that showed no obvious stratigraphic breaks.
    Fig. 2 shows four photographs which I can't reproduce here, but I've seen the exact spot from below, without attempting to climb up. There's no obvious difference above and below, and no obvious line of clay. My geologist and archeologist brother in law will be here in December and, weather permiting, we'll get up there and take our own pictures. (Quite boring pictures I expect.)

    The photo I posted in the opening post is quite definitely not the KT boundaty.
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