K-T Boundry

[Abaddon]

I'm just curious, how far down is the K-T Boundry?

[Missourian]

Welcome to the forum.

The K-T is at the surface in many places. Otherwise, it can be as much as thousands of feet below the surface (under younger strata), or completely eroded away (where older rocks are exposed).

[Missourian]

In many cases, though, there may be a hiatus between the Cretaceous and Paleogene, with the K-T transition missing from the strata.

[Ludwigia]

I'm just curious, how far down is the K-T Boundry?

Depends on where you're standing...

http://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_boundary

[painshill]

There are lots of places worldwide where you can see it, with various degrees of accessibility, vertical exposure and closeness to the surface. Probably the closest to the surface you can see it as a clear boundary in America is at Trinidad Lake State Park in the Raton Basin of Colorado (marked with a white line in this pic):

[pic from Nationalparks, modified by Geologyguy – Creative Commons license]

Here’s a few specimens from my collection. This one from the Badlands near Drumheller in Alberta, Canada:

This one from Tom Gato in Hawaii:

And this one from Agost in Spain:

The K-T boundary has been renamed now as the K-Pg (Cretaceous–Paleogene) boundary, but retaining the German origin of Cretaceous spelled with a ‘K’.

Edited July 3, 2013 by painshill

[Missourian]

The K-T boundary has been renamed now as the K-Pg (Cretaceous–Paleogene) boundary, but retaining the German origin of Cretaceous spelled with a ‘K’.

I think 'K-T' should be retained along with 'K-Pg' because it is well-ingrained in the popular culture as well as the scientific literature. It's a nod to history.

More importantly, 'K-T' makes me think of:

while 'K-Pg' makes me think of:

When it comes to knock-out extinction events, I have to go with Mr. T.

[Paleoworld-101]

As others have said, it various according to where you are on earth.

The K-Pg boundary is, surprisingly, not anywhere to be seen here in Australia. It is present in New Zealand however.

[rejd]

As others have said, it various according to where you are on earth.

The K-Pg boundary is, surprisingly, not anywhere to be seen here in Australia. It is present in New Zealand however.

So would that mean the it is still below you or has it all been eroded away?

[bdevey]

I think 'K-T' should be retained along with 'K-Pg' because it is well-ingrained in the popular culture as well as the scientific literature. It's a nod to history.

More importantly, 'K-T' makes me think of:

MrT.jpg

while 'K-Pg' makes me think of:

2107671-porky.jpg

When it comes to knock-out extinction events, I have to go with Mr. T.

I agree

[Paleoworld-101]

So would that mean the it is still below you or has it all been eroded away?

I think for the most part it's been eroded away, as the majority of Australia is far older than the Cretaceous period.

[Ludwigia]

I think for the most part it's been eroded away, as the majority of Australia is far older than the Cretaceous period.

I don't know much about the geology of Australia, but wasn't it the case that Australia never got under water during the cretaceous period and therefore nothing much was deposited anyway, but rather even the older layers were being eroded away at that time?

[Paleoworld-101]

I don't know much about the geology of Australia, but wasn't it the case that Australia never got under water during the cretaceous period and therefore nothing much was deposited anyway, but rather even the older layers were being eroded away at that time?

During the Cretaceous a large inland sea called the Eromanga covered much of Eastern Australia at a time long before the end of the Cretaceous, about 110 million years ago. It is these deposits that make up the vast majority of Cretaceous rock in Australia. The younger late Cretaceous sediment is gone, possibly due to the fact that by that stage the inland sea had vanished, and as you said, there wasn't much deposition. But what little sediment there was being deposited has surely been eroded away since.

Edited July 4, 2013 by Paleoworld-101

[Ludwigia]

During the Cretaceous a large inland sea called the Eromanga covered much of Eastern Australia at a time long before the end of the Cretaceous, about 110 million years ago. It is these deposits that make up the vast majority of Cretaceous rock in Australia. The younger late Cretaceous sediment is gone, possibly due to the fact that by that stage the inland sea had vanished, and as you said, there wasn't much deposition. But what little sediment there was being deposited has surely been eroded away since.

Thanks for filling me in on the details. You learn something new every day as long as you ask silly questions

[painshill]

Actually, there is one place in Australia where you can see the boundary.

From the Australian Heritage Database:

"The contact between stratigraphic layers representing the actual K/T boundary is vividly exposed in Giralia Range, but nowhere else in Australia: a thin bed of the Boongerooda Greensand overlies two metres of soft fossiliferous limestone. The greensand was almost certainly formed in a cold ocean, but the immediately-underlying limestone must have formed in much warmer waters. This contact demonstrates that in a virtual geological instant, the marine fauna changed on a scale not seen since the Permo-Triassic extinction 180 million years earlier, at the close of the Palaeozoic era 250 million years ago (McNamara 1997; Craig 2002)."

[Paleoworld-101]

Actually, there is one place in Australia where you can see the boundary.

From the Australian Heritage Database:

"The contact between stratigraphic layers representing the actual K/T boundary is vividly exposed in Giralia Range, but nowhere else in Australia: a thin bed of the Boongerooda Greensand overlies two metres of soft fossiliferous limestone. The greensand was almost certainly formed in a cold ocean, but the immediately-underlying limestone must have formed in much warmer waters. This contact demonstrates that in a virtual geological instant, the marine fauna changed on a scale not seen since the Permo-Triassic extinction 180 million years earlier, at the close of the Palaeozoic era 250 million years ago (McNamara 1997; Craig 2002)."

That is news to me, thanks!

Surprising though considering the fact that I have read quite a few times that the boundary is not visible in Australia, as well as watched documentaries that stated this. I also can't find any other reference that says so apart from the one you found. Hmmm....

[painshill]

That is news to me, thanks!

Surprising though considering the fact that I have read quite a few times that the boundary is not visible in Australia, as well as watched documentaries that stated this. I also can't find any other reference that says so apart from the one you found. Hmmm....

There are plenty of references for the Miria Formation – it’s an important and well-documented fossil site. This summary from “Australia's Fossil Heritage: A Catalogue of Important Australian Fossil Sites” (The Australian Heritage Council):

The Miria Formation is a thin (0.6–2.1 metres) mid-shelf, latest Maastrichtian (Late Cretaceous) foraminiferal calcarenite and calcisiltite with its main exposure in the Giralia Range. The Miria represents the only Late Maastrichtian surface unit in Australia and contains a rich and diverse macrofossil assemblage.

The end of the Maastrichian marks one of the most severe global extinction events known to science (the end-Cretaceous mass extinction event). Virtually all organisms were affected and many became extinct, including…… larger planktic foraminifera. Some or all of the upper part of the Miria can be referred to the very last planktic foraminifera (Abathomphalus mayaorensis zone) of the Maastrichtian. The significance of the site is thus closely tied to the age of the formation at the very end of the Mesozoic. Monographs on several of the major invertebrate groups have been published, including ammonites, bivalves, scaphopods and gastropods……

….. Their presence [referring to ammonites] in the Miria Formation helps to date it to the Maastrichtian, 71-65 million years ago. Palaeontologists have described more than 60 other species of marine mollusc in addition to nearly 30 species of ammonite. The site also includes Australia’s most diverse Late Cretaceous shark tooth assemblage and the most diverse assemblage of corals from the Mesozoic era of Australia. These coral species only occur elsewhere in Cretaceous rocks in Antarctica and southern India, which during the Mesozoic era were connected to Australia as part of Gondwana.

The Miria Formation crops out over a strike distance of some 80-100 kilometres in the Giralia anticline (see Henderson and McNamara 1985: fig. 1). It rests with a disconformity on the late Campanian to early Maastrichtian Korojon Calcarenite and is succeeded disconformably by the mid-Palaeocene (upper Selandian – lower Thanetian) Boongerooda Greensand. In many places weathering has reduced the formation to a residual surface, littered with phosphatic steinkerns of molluscan macrofossils, mainly ammonites and a nautiloid. Partial and complete sections are present in the northern part of the anticline…..

…..The Miria Marl is one of very few Maastrichtian surface rocks in the country (the other few are all also in Western Australia) and the only one with a rich and diverse macrofossil assemblage. Ammonites….. are the most common macrofossil in the Miria, and are far more abundant here than anywhere else in the world in rocks of Maastrichtian age.

Here’s the general stratigraphy from “Structural Interpretation and Hydrocarbon Potential of the Giralia Area, Carnarvon Basin” (Crostella & Iasky):

[Apologies for the thread hijack Abaddon]

Edited July 4, 2013 by painshill

[Paleoworld-101]

There are plenty of references for the Miria Formation – it’s an important and well-documented fossil site. This summary from “Australia's Fossil Heritage: A Catalogue of Important Australian Fossil Sites” (The Australian Heritage Council):

The Miria Formation is a thin (0.6–2.1 metres) mid-shelf, latest Maastrichtian (Late Cretaceous) foraminiferal calcarenite and calcisiltite with its main exposure in the Giralia Range. The Miria represents the only Late Maastrichtian surface unit in Australia and contains a rich and diverse macrofossil assemblage.

The end of the Maastrichian marks one of the most severe global extinction events known to science (the end-Cretaceous mass extinction event). Virtually all organisms were affected and many became extinct, including…… larger planktic foraminifera. Some or all of the upper part of the Miria can be referred to the very last planktic foraminifera (Abathomphalus mayaorensis zone) of the Maastrichtian. The significance of the site is thus closely tied to the age of the formation at the very end of the Mesozoic. Monographs on several of the major invertebrate groups have been published, including ammonites, bivalves, scaphopods and gastropods……

….. Their presence [referring to ammonites] in the Miria Formation helps to date it to the Maastrichtian, 71-65 million years ago. Palaeontologists have described more than 60 other species of marine mollusc in addition to nearly 30 species of ammonite. The site also includes Australia’s most diverse Late Cretaceous shark tooth assemblage and the most diverse assemblage of corals from the Mesozoic era of Australia. These coral species only occur elsewhere in Cretaceous rocks in Antarctica and southern India, which during the Mesozoic era were connected to Australia as part of Gondwana.

The Miria Formation crops out over a strike distance of some 80-100 kilometres in the Giralia anticline (see Henderson and McNamara 1985: fig. 1). It rests with a disconformity on the late Campanian to early Maastrichtian Korojon Calcarenite and is succeeded disconformably by the mid-Palaeocene (upper Selandian – lower Thanetian) Boongerooda Greensand. In many places weathering has reduced the formation to a residual surface, littered with phosphatic steinkerns of molluscan macrofossils, mainly ammonites and a nautiloid. Partial and complete sections are present in the northern part of the anticline…..

…..The Miria Marl is one of very few Maastrichtian surface rocks in the country (the other few are all also in Western Australia) and the only one with a rich and diverse macrofossil assemblage. Ammonites….. are the most common macrofossil in the Miria, and are far more abundant here than anywhere else in the world in rocks of Maastrichtian age.

Here’s the general stratigraphy from “Structural Interpretation and Hydrocarbon Potential of the Giralia Area, Carnarvon Basin” (Crostella & Iasky):

Giralia.jpg

[Apologies for the thread hijack Abaddon]

Wow, thanks!

[63rover]

Perhaps I am missing something. The two posts documenting evidence of the KT or K Pg boundary evidence in Australia talk about pre and post KT formations but what of the boundary layer itself? It is clearly evident in other parts of the world and indeed is quite thick, as I hope I am not being with this question, but it seems to not be discussed in these posts. Is it nonexistent, very thin or just not discussed? Could weather patterns of the KT era have been similar to those of today and blown most, if not all, ash and debris around Australia?

Just wondering. Saw one of "those" documentaries tonight and started looking for info. Ended up here.

Regards, Clive

[Al Dente]

Perhaps I am missing something. The two posts documenting evidence of the KT or K Pg boundary evidence in Australia talk about pre and post KT formations but what of the boundary layer itself? It is clearly evident in other parts of the world and indeed is quite thick, as I hope I am not being with this question, but it seems to not be discussed in these posts. Is it nonexistent, very thin or just not discussed?

The boundary clay layer that marks the beginning of the Danian (Early Paleocene) and contains evidence of the impact (the iridium anomaly) would not be in the section that painshill posted in post #16.

[painshill]

The boundary clay layer that marks the beginning of the Danian (Early Paleocene) and contains evidence of the impact (the iridium anomaly) would not be in the section that painshill posted in post #16.

Just to clarify… the original question was: “how far down is the KT Boundary?” which then led to a discussion of whether or not it’s exposed and visible in Australia. It is, at the location in the Giralia Range that I referenced.

But a “boundary” is not the same thing as a “layer”. A boundary is a clear division between two layers. Wiki uses the words “geological signature, usually a thin band” and that’s exactly what it is… a signature which manifests itself as division between pre- and post- impact strata. The signature may be represented by a layer within which one or more of the following may be present: an iridium anomaly about 30 times higher than the Earth’s typical background crustal levels; sedimentary ash; carbonized vegetation and soot; fullerene bucky balls; glassy microtektites; or tsunami deposits.

The amounts of any of those materials (and whether they are present at all) varies enormously according to the distance from the impact and other factors. Even if they aren’t present, the global effect of the impact was such that the boundary can sometimes be readily determined through the climatic and other indirect effects on post-impact sediments such they are visually distinguishable from the strata below. And that’s the case in the Giralia range.

[63rover]

That clarifies things nicely thank you.

[Bev]

Fascinating read! So, I did a search for the KT boundary/layer in Minnesota, but really came up with nothing. We do have Cretaceous in the western part.

What kind of search do I need to do to find out if that layer is visible in Minnesota, IA or WI? Might just have to make a drive.

[Auspex]

Any MinnesOta Paleocene on the geo map?

[piranha]

On 8/3/2014 at 9:56 AM, Bev said:

...We do have Cretaceous in the western part.

 

 

Bev,

 

Minnesota has Cretaceous strata scattered across the entire state.

 

 

Here is a nifty bulletin that covers this topic in great detail:

 

Sloan, R.E. (1964)

The Cretaceous system in Minnesota.

Minnesota Geological Survey, Report of Investigations, 5:1-64

 

OPEN ACCESS PDF

 

 

 

[Bev]

I was just looking up Paleocene and found we have a lot of cretaceous. THANK YOU Piranha! Will check out the PDF!