Unconformities are the geologic features which convinced Hutton and Lyell that the earth was old. An unconformity is a period of erosion found between two rock layers. The evidence of erosion can be severe or mild, but the interval does represent a significant period of time between the deposition of the older (lower) rocks and younger(upper rocks).

Siccar Point is a famous outcrop on the Scottish coast south of Edinburgh. Here is a picture of it.

http://comp.uark.edu/~sboss/siccar.jpg

The lower (now vertical) rocks are Ordovician shales. There is no way that these shales could have been deposited vertically. They had to be deposited horizontally. After they had solidified, they were deformed by crustal collision. The collision was the Silurian collision of Avelonia (part of Britain) with North America. the deformed (now vertical) shales were eroded. At the unconformity (the intersection of the vertical and horizontal rocks in the picture) there are pebbles of eroded Ordovician shale. Then at some later point, the land sank beneath the waves again and the Devonian Old Red Sandstone was deposited on top of the eroded Ordovician surface. These rocks were initially horizontal when they were deposited but gentle tilting of the land has now tilted them slightly. This sequence of actions takes time. (And for another day, I will note, this sequence of deformation shows why runaway subduction can't explain the pattern of continental collisions.)

Now, this is not the only type of erosional unconformity of its kind. Raymond Moore, in Historical Geology, 1933 McGraw-Hill, p. 160 shows a similar type of unconformity between the Ordovician and Silurian of western Pennsylvania. Here is the picture

http://home.entouch.net/dmd/Unconfor...nnsylvania.JPG

The Ordovician strata to the left of the picture was initially horizontal when it was deposited. It was then deformed to the vertical (like the lower rocks at Siccar point), and eroded. But these Ordovician rocks were also heated to the point where they are partically metamorphosed. At this time, the line marked 'unconformity' was slightly tilted and there are pebbles of the metamorphosed Ordovician rocks at the surface of the unconformity.

At this point, the Medina sandstone was deposited, once again, it was deposited horizontally. After the Medina sandstone lithified, it too was deformed, making it stand vertically but by coincidence bringing the lower Ordovician rocks almost to horizontality again.

The evidences of time in this unconformity are the erosional pebbles at the unconformity surfce, as well as the fact that the Ordovician rocks were heated and the Medina sandstone wasn't. This proves that the Medina sandstone couldn't be there during the heating event. It takes a long time for the rocks to cool down after heating. David Tyler will probably claim that water convection can reduce the time (and he is correct), it still takes time for larger unfractured rocks to cool down because conduction of heat is so slow.

Now some of the unconformities can be quite large as my favorite unconformity taken from a seismic line along the Alabama-Mississippi border.

http://home.entouch.net/dmd/appalach1tw.jpg

For a full explanation of this unconformity see:

http://home.entouch.net/dmd/appalach1.htm

Do any YECs have explanations for this data? Do you think you should ask your leaders why they don't show this kind of geologic data in the YEC literature?

Today @ 09:00 PM post located here
grmorton:

Unconformities are the geologic features which convinced Hutton and Lyell that the earth was old. An unconformity is a period of erosion found between two rock layers. The evidence of erosion can be severe or mild, but the interval does represent a significant period of time between the deposition of the older (lower) rocks and younger(upper rocks).

As usual, great illustrations, Glen. And well described.

Sometimes, I also point out to my friends who think that unconformities do not exist that there is another implicit unconformity in pictures such as these: the one we live on.

 












[ALIGN=CENTER][GLOW=ORANGE]GOD[/GLOW]

JUST     WORKS     IN     MYSTERIOUS    WAYS [/ALIGN]




















[align=right]please do not ask any more embarrasing questions. thank you.
[/align]

Yesterday @ 09:00 PM post located here
Response to grmorton:

Unconformities are the geologic features which convinced Hutton and Lyell that the earth was old. An unconformity is a period of erosion found between two rock layers. The evidence of erosion can be severe or mild, but the interval does represent a significant period of time between the deposition of the older (lower) rocks and younger(upper rocks).

Siccar Point is a famous outcrop on the Scottish coast south of Edinburgh. Here is a picture of it.

Indeed it is, and it is true that unconformities have been viewed as compelling evidence for deep time. Unfortunately, Hutton must have presupposed deep time, because it does not emerge from the field data.

The following is from the conclusion of my web article at: http://www.biblicalcreation.org.uk/s...es/bcs100.html

The generally accepted interpretation of the Siccar Point rocks is as follows. Closure of the Iapetus Ocean during the Silurian produced the folding and elevation of the Silurian greywackes. This is known as the Caledonian Orogeny. Subaerial erosion processes produced the relict topography in a desert environment. The localised fragmentation of the greywackes and the deposition of calcite represent the formation of a fossil soil, where water carrying calcite found its way to the surface and evaporated leaving calcite behind. The area began to subside slowly and flash flooding brought down Old Red sands and conglomerates to cover the erosion surface.

The question being asked is: how much of this scenario is required by the field evidences, and how much is deduced from presuppositions? What evidence is there for flash flooding? Or is it just assumed that because material is red and conglomeratic, it must be associated with flash flooding? (Sheet conglomerates are different from fan conglomerates, and it is the latter which should be associated with flash flooding. Other mechanisms of a more catastrophic nature may be better associated with sheet conglomerates). How extensive is the surficial fragmentation and calcite deposition? Does the "fossil soil" hypothesis stand up to investigation? What is to be made of the lack of differential weathering? an observation that is not addressed in the consensus view outlined above.

It is worth noting that modern studies of these unconformities have not been published. There is consequently a lack of data and greater scope for differing interpretations. A full discussion of these matters lies outside the scope of this note. However, sufficient has been said to show that Hutton's interpretation does not necessarily follow from the field evidences but it appears to have been imposed on them. The empirical data are consistent with, and favour, geological catastrophism.

These sites are traditionally linked to Hutton's "rock cycle", often abbreviated to "The rock cycle". Students of geology are introduced early to the concept of uniformitarianism: present day slow rates of geologic activity are the basis for interpreting the rock record. Few appear to familiarise themselves with the controversies that surrounded this concept from its inception. Georges Cuvier (1825) was one of the leading geologists of his day who was convinced that uniformitarian processes are totally inadequate to explain past geologic activity:

"We now propose to examine those changes which still take place on our globe, investigating the causes which continue to operate on its surface This portion of the history of the earth is so much the more important, as it has been long considered possible to explain the more ancient revolutions of its surface by means of these still existing causes. But we shall presently see that unfortunately this is not the case in physical history: the thread of operations is here broken, the march of nature is changed, and none of the agents that she now employs were sufficient for the production of her ancient works." (page 12).

It is argued in this paper that these key historical sites do not substantiate the uniformitarian approach. Tyler (1990) proposed an alternative rock cycle based on the tectonic control of geological processes. This rock cycle is amenable to catastrophist interpretations of orogenies, erosion, deposition and metamorphism. It is suggested to be a more appropriate interpretative framework for understanding Hutton's unconformities. John Playfair's (1805) concluding comments are a fitting conclusion for this paper: "We returned, having collected, in one day, more ample materials for future speculation, than have sometimes resulted from years of diligent and laborious research".

Cuvier, G. 1825. Essay on the theory of the earth. 3rdedition. Blackwood, Edinburgh.
Playfair, J. 1805. Biographical account of the late Dr James Hutton. Trans. Roy. Soc. Edinburgh. 5, 39-99.
D.J. Tyler, 1990. A tectonically-controlled rock cycle, In: Walsh, R.E. and Brooks, C.L. (Eds): Proceedings of the Second International Conference on Creationism, Creation Science Fellowship, Inc., Pittsburgh, PA, Volume II, 293-301.

-------------

I am still of this opinion. Those who see deep time in the Siccar Point Unconformity bring it there by their theories.

The evidences of time in this unconformity are the erosional pebbles at the unconformity surfce, as well as the fact that the Ordovician rocks were heated and the Medina sandstone wasn't. This proves that the Medina sandstone couldn't be there during the heating event. It takes a long time for the rocks to cool down after heating. David Tyler will probably claim that water convection can reduce the time (and he is correct), it still takes time for larger unfractured rocks to cool down because conduction of heat is so slow.

The erosional pebbles certainly show evidence of time, but how much depends on your mechanism of lithification. Different degrees of metamorphism are also evidences of time, although cooling rates are much shorter than you generally hear from our uniformitarian leaders. Yes, Glenn, I do think convective cooling to be very important. None of these evidences argue for deep time.

Now some of the unconformities can be quite large as my favorite unconformity taken from a seismic line along the Alabama-Mississippi border.

Do any YECs have explanations for this data? Do you think you should ask your leaders why they don't show this kind of geologic data in the YEC literature?

Large unconformities are evidences of large scale erosive episodes. Unconformities that are laterally extensive, cut across a variety of sediment types, and leave essentially no relict topography are actually evidence for non-uniformitarian processes operating in the Earth's past. They are not well accounted for by conventional geological ideas. Why is it that the problems of explaining these unconformity characteristics are rarely even echnowledged to exist, let alone explained, by uniformitarian leaders?

I have not noticed creationist geologists avoiding this kind of data. It seems to me that Glenn is creating a straw man to make a point. Can you please be specific?

Today @ 03:54 PM post located here
dtyler:

A full discussion of these matters lies outside the scope of this note. However, sufficient has been said to show that Hutton's interpretation does not necessarily follow from the field evidences

No, insufficient has been said indeed. You have only dealt with the rocks above the unconformity without discussing the rocks beneath it. Further, you have criticized Hutton's interpretations on a basis of age (no modern studies), whilst offering no alternative interpretation of your own for Siccar, but a bunch of generalized references of similar antiquity (and presumably thus in your view irrelevancy) to Hutton. More importantly, you have not even shown how an alternative interpretation might even be possible, even though you cannot currently offer one.

I will give you a hand.

a) The rocks beneath the unconformity are bedded so each represents an event. How much time is recorded by the deposits and the bedding planes?

b) they are lithified/metamorphosed at low grade. This takes burial to a couple of kilometres. How quickly could they have been buried that far?

c) they are folded. This is plastic deformation which requires time at depth. How long were the rocks buried for?

d) they were uplifted. How quickly could they have been uplifted?

e) they were weathered down. How quickly could they have been weathered down?

As for the rocks above the unconformity;

a) They contain rounded pebbles from the underlying older rocks. How quickly can a pebble be rounded?

b) they contain microscopic particles of silt, sand and clay derived from the older rocks. How quickly could solid rock be broken down, not just to pebbles, but to grains of sand?

c) they are bedded. Each bed represents an event. How much time does each event represent, and how much time do the bedding planes represent?

e) they are lithified. This requires deep burial and time. How deep were they buried, how long did it take to bury them, and how long were they buried for?

They are uplifted and being weathered again. How long did it take to uplift them?

Never mind a bit of calcrete!

What evidence is there for flash flooding? Or is it just assumed that because material is red and conglomeratic, it must be associated with flash flooding? (Sheet conglomerates are different from fan conglomerates, and it is the latter which should be associated with flash flooding. Other mechanisms of a more catastrophic nature may be better associated with sheet conglomerates)

A good question. Fan conglomerates develop in areas of high topographic gradient. They fan out towards areas of lower gradient, where they pass into sheets of conglomerate and interbedded sand, and then into sands and silts. In Glen's picture we seem to be looking at some very thinly bedded sands and ?possibly very thin, fine, gravelly conglomerates.

Do you think that is a fan? Remember, there are no modern descriptions of this outcrop, and Hutton, you say, tends to presuppose his descriptions- I wouldn't trust him if I were you. I can see a lot of planar bedding and cross-bedding in that picture. What does that tell you about the hydraulic regieme? Care to hazard a guess as to what the sedimentary system above the unconformity is, how it got there, and how long it took to get there?

Oh, and while we're on the problem of a lack of modern research at Siccar, one thing it does have going for it is that it is visited by hundreds of geologists every year. Like all of them, I've been there, and- like all of them- felt no need to tear my hair out at the way in which that charlatan Hutton misread the empirical data. Authoritative statements like:

Hutton's interpretation does not necessarily follow from the field evidences but it appears to have been imposed on them

Can only have come from someone who has also been to the outcrop. In that light, especially as you clearly have the inside track on thousands of geologists, might I ask why you've not published on the problem?

K

PS. So far my impression of your geological background is that a) you are using references often from near two centuries ago, interspersed with beginner's textbooks from 40 years ago, use quaint terms like 'greywacke' and 'old red', and do not understand more modern ones ('platform', for instance). It is therefore not suprising you believe that:

Students of geology are introduced early to the concept of uniformitarianism: present day slow rates of geologic activity are the basis for interpreting the rock record

As that is also a 19th-century view. I would be deeply interested to learn where- or when- you studied?

[quote]Today @ 06:20 PM post located here
Kulindrichnus:

"Students of geology are introduced early to the concept of uniformitarianism: present day slow rates of geologic activity are the basis for interpreting the rock record"

As that is also a 19th-century view. I would be deeply interested to learn where- or when- you studied?

I was wondering the same thing. My experience as a student was not as David describes it. I was never told that all geological processes were slow and continuous. Perhaps he does come from an earlier generation of geological training. Or perhaps this is just his wishful explanation of why his particular viewpoint is not prevalent (i.e. there must be some kind of outside influences betraying his scenario). I find it interesting that this statement comes from someone who accuses Glenn of setting up a strawman argument.

I am also curious as to what, if presuppositions are as strong as David suggests, was the pre-Huttonian presupposition and why did it suddenly fail when people actually started looking at rocks?

Today @ 07:41 PM post located here
Response to aniso:

"Students of geology are introduced early to the concept of uniformitarianism: present day slow rates of geologic activity are the basis for interpreting the rock record"

My experience as a student was not as David describes it. I was never told that all geological processes were slow and continuous. Perhaps he does come from an earlier generation of geological training. Or perhaps this is just his wishful explanation of why his particular viewpoint is not prevalent (i.e. there must be some kind of outside influences betraying his scenario). I find it interesting that this statement comes from someone who accuses Glenn of setting up a strawman argument.

All the guide literature that I have that addresses the Siccar Point locality takes this stance. Can you introduce me to some that do not?

Glenn's post made no reference to any of these new ideas on geological timescales. I was responding to him.

I am also curious as to what, if presuppositions are as strong as David suggests, was the pre-Huttonian presupposition and why did it suddenly fail when people actually started looking at rocks?

You can find my thoughts on that on the BCS site - "The discovery of geological time.
http://www.biblicalcreation.org.uk/s...es/bcs080.html

Can I make some general points based on the feedback received. First, the web article is written with the intention of making people think. I want people to reconsider the traditions that have been handed down over the years and that are having an adverse effect on the health of geological science. I was not setting out an alternative model and make no apologies for not doing this. It is not because I do not have thoughts on the matter - but because the objective of the article was to make people receptive to change in the light of the evidence presented, and to realise that not to change is bad science.

Second. There is an urgent need for serious work to be done, rethinking the data from Siccar Point and the surrounding area. Circumstances do not allow me to do it, but I will welcome any opportunity to support someone who is prepared to give their energies to it.

I find on numerous occasions in these discussions that the initial reaction to what I am saying is highly negative - implying that I do not know what I am talking about. However, this is often followed by a comment to say that what's all the fuss about! Geologists are quite familiar with this material anyway! This is not the best way to engage in debate. It is very confusing for people who have little background in geology. Can I put in a plea for us to focus on the geological issues? This will mean less looking for holes in the arguments of the opposition. It will mean more willingness to listen to those who take a different view from ourselves.

I would also like to remind everyone that this is TheologyWeb. I am willing to participate in discussions because science needs a theological foundation and there are many scientific issues that impinge on Christianity (and vice versa). I am not wanting to participate in a free-for-all on every aspect of geological science. This is not because it does not interest me, but because the discussion will not lead anywhere without some shared presuppositions (see the thread on Presuppositions in Science 2).

On this topic, you may be interested in the comments of Paul Garner and myself on a recent TV series called "The Big Question".
http://www.biblicalcreation.org.uk/b...n/default.html
Stephen Hawking on the origin of the Universe; Harry Kroto on the origin of life; Richard Dawkins on life in an evolving world; Susan Greenfield on being human and Ian Stewart on how it will all end. The series certainly showed that "science" is not "objective" but built on foundations brought by researchers.

"Large unconformities are evidences of large scale erosive episodes. Unconformities that are laterally extensive, cut across a variety of sediment types, and leave essentially no relict topography are actually evidence for non-uniformitarian processes operating in the Earth's past. They are not well accounted for by conventional geological ideas. Why is it that the problems of explaining these unconformity characteristics are rarely even echnowledged to exist, let alone explained, by uniformitarian leaders?"

What, there are no modern flat areas eroded across inclined strata and/or crystalline rocks? This is silly. Geologists will readily enough point to Florida and Australia's Null Arbor Plains as examples of the undersides of future regional paraconformities, or Nebraska and Kansas as the undersides of future mild but broad disconformities, or Chesapeake Bay or any large estuary as the underside of a future disconformity of slightly greater relief (more like the unconformity on top of the Redwall Limestone in Arizona). Likewise, much of Australia or the inselberg reion of southern Africa or (admittedly less well known) the Tampoketsa and the Horombe and Analabe plateaus in Madagascar are all easily seen as the bottom halves of future fairly flat to very flat angular unconformities and nonconformities. The largest ones are not at all "non-uniformitarian", even in David's restricted sense, and do not appear to indicate large-scale erosion. Instead they are presumed to represent very LONG-scale erosion, typically very very very slow, representing planation down to base level during periods (or in places) of exceptional stability (again, see Australia). Many of these show very mature weathering profiles relative to their climatic setting, testifying to their lengthy development, and the some of the profiles have been studied specifically for comparison with ancient unconformities.

For whatever it's worth, Donna Balin redescribed the Siccar Point unconformity for a field guide for the 1990 International Sedimentological Conference in Nottingham, England, where she spells out the evidence for her interpretation in reasonable detail. She also wrote up the calcretes in the Old Red Sandstone in Balin, D.F., 2000, Calcrete morphology and karst development in the Upper Old Red Sandstone at Milton Ness, Scotland, in, Williams, Brian P. J., ed., Geological Society Special Publications, v. 180.

Today @ 08:54 AM post located here
dtyler:

Large unconformities are evidences of large scale erosive episodes. Unconformities that are laterally extensive, cut across a variety of sediment types, and leave essentially no relict topography are actually evidence for non-uniformitarian processes operating in the Earth's past. They are not well accounted for by conventional geological ideas. Why is it that the problems of explaining these unconformity characteristics are rarely even echnowledged to exist, let alone explained, by uniformitarian leaders?

Just about the largest unconformities on the planet are cratonic shields. Are you suggesting mainstream geologists are ignoring those? If not, which ones are you speaking of?

Also, sequence stratigraphy is basically the study of unconformities at all scales, primarily with respect to changes in relative sea level. It's mainly used by oil companies to find oil. I find it hard to imagine they are ignoring anything - not when it makes them money.

I'm curious. Where are you getting these notions that geologists are ignoring certain portions of the geologic record? I can't figure out if you are simply not reading the available literature, are too far removed from mainstream geology to see what we're doing, or simply ignoring it. I work in a very small field of geology, but even I know most of what you are accusing us of ignoring is complete hogwash.

Perhaps that is why the professional geologists replying to your posts here are on the defensive. You portray us as incompetent, brainwashed idiots.

dtyler:

Tyler (1990) proposed an alternative rock cycle based on the tectonic control of geological processes. This rock cycle is amenable to catastrophist interpretations of orogenies, erosion, deposition and metamorphism. It is suggested to be a more appropriate interpretative framework for understanding Hutton's unconformities.

David, I took a look at your 1990 article. I am amazed at what you don't know about geology. You write:

"In recent years, the role of tectonic processes in the formation of sediments has been recognised and given more prominence. To take one example: few students of English geology will be unaware of the Alston and Askrigg blocks in the Pennines. Tectonic movements of these blocks are invoked to explain observed patterns of sedimentation. In some instances, evidences for synsedimentary faulting are present, showing even more clearly that tectonic activity and sedimentary processes are linked." David Tyler, "A Tectonically-controlled rock Cycle," in Walsh et al editors, Proceedings of the Second International Conference on Creationism, (Pittsburgh: Creation Science Fellowship, Inc., 1990), p. 294

David, I have worked off and on for 30 years in the Gulf of Mexico Basin, and I can tell you that synsedimentary faulting has been invoked for much longer than that 30 years. The entire Gulf of Mexico basin (from the Oklahoma-Texas Border down to Mexico is full of growth faults, which are faults moving when the sediment was being deposited. The additional sediment added weight to the fault block, and acted as a feedback loop increasing the throw on the fault. Why you think this is a new idea (synsedimentary faulting) is way beyond me.

The erosional pebbles certainly show evidence of time, but how much depends on your mechanism of lithification. Different degrees of metamorphism are also evidences of time, although cooling rates are much shorter than you generally hear from our uniformitarian leaders. Yes, Glenn, I do think convective cooling to be very important. None of these evidences argue for deep time.

Fine, but it won't help you. Woodmorappe and Snelling analyzed the issue and realized that it would take around 3000 years for convective cooling to cool a batholith. Given that they obviously used parameters designed to favor the YEC cause, it still creates problems for YECs. They write:

“The effects of changing permeability K, on cooling time, is striking. An infinitely long batholith that is 11 km wide, 16.5 km thick, and is buried 20 km below the surface of the ground, when at zero rock permeability (that is, conductive cooling only) needs a few million years to cool. But with the intensity of convective cooling that is allowed by a permeability K of 10 millidarcies (easily exceeded—see below), the time to cool this batholith falls to a mere 3000 years.” Andrew A. Snelling, and John Woodmorappe, “The Cooling of thick Igneous Bodies on a Young Earth,” Proceedings of the Fourth International Conference on Creationism, (Pittsburgh: Creation Science Fellowship, Inc., 1998), p. 532

Given that there are many different layers of metamorphism and many different episodes in some localities, to have 3000 years to cool the rocks each time still means that the earth is considerably older than 6000 years.

Large unconformities are evidences of large scale erosive episodes. Unconformities that are laterally extensive, cut across a variety of sediment types, and leave essentially no relict topography are actually evidence for non-uniformitarian processes operating in the Earth's past.

I have posted unconformities from seismic which show relict topography. Perchance you weren't paying attention. In the initial post of this thread there is a hill and valley shown at the unconformity. The hill is about 400 feet. That is hardly something to be sneezed at. And below is a map of the topography on the unconformity at Hibernia field.

http://home.entouch.net/dmd/kimmunconfTW.jpg

They are not well accounted for by conventional geological ideas. Why is it that the problems of explaining these unconformity characteristics are rarely even echnowledged to exist, let alone explained, by uniformitarian leaders?

There is no problem except with your knowledge of unconformities. I just posted a pic with a relict topography. What is your problem with that?

I have not noticed creationist geologists avoiding this kind of data. It seems to me that Glenn is creating a straw man to make a point. Can you please be specific?

It is hard to be specific when I have never ever seen a seismic section in a YEC article. Can you point me to one example?

Yesterday @ 10:45 PM post located here
dtyler:

All the guide literature that I have that addresses the Siccar Point locality takes this stance. Can you introduce me to some that do not?

Glenn's post made no reference to any of these new ideas on geological timescales. I was responding to him.

Guide literature? Sorry, but are these your usual source of information? But your statement indicates that geologists are brainwashed into uniformitarianism. I was simply stating that such was not my case.

Neither was it the case that I was taught all geological processes are uniform and slow.

Can I make some general points based on the feedback received. First, the web article is written with the intention of making people think.

Okay, we've thought about it and found your arguments unconvincing. What's next?

I want people to reconsider the traditions that have been handed down over the years and that are having an adverse effect on the health of geological science.

You mean like the YEC interpretation of Genesis?

Your statement reminds me of the tactic popular in some of our political debates that the opponent is actually deranged and shouldn't be taken seriously. Rather a simplistic way of handling a disagreement.

I was going to respond to the rest of your post, but perhaps later. In the meantime, please reread it yourself and imagine an evolutionist writing the same things and see what you think. You expect us to be soooo open-minded that we give time to a concept that is outdated and disproven, and yet I dare say that you have closed your own mind to mainstream interpretation.

Yesterday @ 11:43 PM post located here
Response to SedRocks:

What, there are no modern flat areas eroded across inclined strata and/or crystalline rocks? This is silly. Geologists will readily enough point to Florida and Australia's Null Arbor Plains as examples of the undersides of future regional paraconformities, or Nebraska and Kansas as the undersides of future mild but broad disconformities, or Chesapeake Bay or any large estuary as the underside of a future disconformity of slightly greater relief (more like the unconformity on top of the Redwall Limestone in Arizona). Likewise, much of Australia or the inselberg reion of southern Africa or (admittedly less well known) the Tampoketsa and the Horombe and Analabe plateaus in Madagascar are all easily seen as the bottom halves of future fairly flat to very flat angular unconformities and nonconformities. The largest ones are not at all "non-uniformitarian", even in David's restricted sense, and do not appear to indicate large-scale erosion. Instead they are presumed to represent very LONG-scale erosion, typically very very very slow, representing planation down to base level during periods (or in places) of exceptional stability (again, see Australia). Many of these show very mature weathering profiles relative to their climatic setting, testifying to their lengthy development, and the some of the profiles have been studied specifically for comparison with ancient unconformities.

No doubt it would be silly if my comments were applicable to this level of detail. The observational data that is relevant to Siccar Point is that there is essentially *no* differential weathering when comparing the harder and the softer rocks. Today's weathering brings out the differences easily. The photo's accompanying my essay show that. The observation I would make is that this lack of differential erosion, in general, is not regarded as an interesting observation by most geologists visiting the site.

Standing back, there is a relict topography at Siccar point. Another of my photos on the web shows that - and many more images could be used to make the same point. Many unconformities do have a relict topography. This is to be expected. But what do we make of planar unconformities?

We are not referring here to a bedding plane that gets covered - but an eroded surface that is covered. It is my view that *any* modern weathered surface will show a topography - differential weathering is ubiquitous. Yet, there are numerous examples of erosional unconformities that are planar. Perhaps the best known is the Cambrian Unconformity in the Grand Canyon. There are numerous cases here in the UK. I am suggesting that this phenomenon has not received the attention it deserves by field geologists. This led to my comment, paraphrasing Glenn, as follows:

"Large unconformities are evidences of large scale erosive episodes. Unconformities that are laterally extensive, cut across a variety of sediment types, and leave essentially no relict topography are actually evidence for non-uniformitarian processes operating in the Earth's past. They are not well accounted for by conventional geological ideas. Why is it that the problems of explaining these unconformity characteristics are rarely even echnowledged to exist, let alone explained, by uniformitarian leaders?"

You have objected to this comment - but I want to press the point again. There is a real issue here for geologists to understand, and my own view is that it cannot be explained by reference to modern-day processes of erosion.

Much thinking about geomorphology has been moulded by Davis. He used the word peneplanation to describe mature eroted topographies. So when people see a flat eroded horizon, they switch into Davisian mode and refer to "peneplanation". The problem with Davis's ideas is that they were not systematically tested against field data. they are being abandoned with time - although many concepts and attitudes linger on.

You refer me to Australia in your feedback comments. Here are some comments on peneplanation by an Australian geologist (1998):
"The dogged persistence of the Davisian model of universal down-wasting as well as the similarly inadequate Penckian model of scarp back-wasting are prime geologic examples of the importance of sociological factors in governing theory acceptance and rejection. Davis’ model owes a lot to Darwin and together with Marxism, the formulation and rise of these should perhaps be viewed in terms of Modernist demands for the ‘Big Universal Theory’. If Davisian cyclicity has limited value in the tectonically vigorous volcanic landscapes described by Gerardo Bocco, it is also a complete turkey when applied to stable cratonic and passive margin settings such as those found in Australia (and other Gondwana fragments); here the extensive preservation of Mesozoic and Palaeogene etch and/or exhumed surfaces high in the landscape poses a major challenge to peneplanation."
http://main.amu.edu.pl/~sgp/gw/wmd/wmd.html

Basically, maturity and long times will not get you to flat bedding planes. They will bring you to a mature differentially weathered topography. If you want the flat, extensive unconformities that we see in the rock record, we need to look for different mechanisms - and this is where catastrophism comes in like a breath of fresh air.

Today @ 10:58 AM post located here
dtyler:


Basically, maturity and long times will not get you to flat bedding planes. They will bring you to a mature differentially weathered topography. If you want the flat, extensive unconformities that we see in the rock record, we need to look for different mechanisms - and this is where catastrophism comes in like a breath of fresh air.

So your saying the cratons are the result of catastrophic erosion? All because you think extensive planation over long periods of time would result in differential weathering?

Differential weathering is more an artifact of the variability of the rocks in an area and their respective characteristics/properties (esp. hardness), isn't it? Crystalline rocks will not weather as easily as limestone, for example.

Again, the oldest portions of the continents are the cratons and they are, for the most part, flat because they are composed of metamorphic rocks with the same basic hardness (due to homogenization). Additionally, once rocks get to about sea level, it gets really hard to weather them, so anything sticking up will get hit the hardest. In the long, long run, the result will be planation.

I still don't see where mainstream geologists are ignoring unconformities.

"Large unconformities are evidences of large scale erosive episodes. Unconformities that are laterally extensive, cut across a variety of sediment types, and leave essentially no relict topography are actually evidence for non-uniformitarian processes operating in the Earth's past. They are not well accounted for by conventional geological ideas. Why is it that the problems of explaining these unconformity characteristics are rarely even echnowledged to exist, let alone explained, by uniformitarian leaders?"

I just noticed this so added to my original post via edit.

Couldn't planation across various lithologies (implying differing hardnesses) be the result of weathering at low elevations? Such as at sea level?

Dave Tyler said " The observational data that is relevant to Siccar Point is that there is essentially *no* differential weathering when comparing the harder and the softer rocks. ...... The observation I would make is that this lack of differential erosion, in general, is not regarded as an interesting observation by most geologists visiting the site. ... [However?] Standing back, there is a relict topography at Siccar point."

I think this depends on what you mean by 'essentially none'. If you want a discussion of very local details, I took pictures at Siccar Point of a trough or channel a couple of meters wide filled with cobbles and pebbles that apparently included some reworked clasts of the Silurian bedrock (and how did that get lithified in a short geological history, by the way?). This was cut into a wider than usual band of less resistant rock. (I assumed that the pebbles meant that the paleosurface was sloping rather than horizontal, even if fairly smooth.) I also took a picture of a slightly thicker than usual resistant Silurian sandstone, which protruded 20 cm or so above the surrounding surface. So there is differential erosion. Nonetheless the unconformity is indeed overall quite flat, but most of the Silurian beds there occur as thin alternations that would not be expected to develop differential relief.

I also think that Dave is overestimating the flatness of flat unconformities. Except in three-dimensional seismic reconstructions like the lovely image posted by Glenn, it is very rare to see unconformities as anything other than a fairly linear, two-dimensional, strip a few tens or 100's of meters long, and many landscapes would show phenomenal flatness if viewed in that fashion. Also note that many landscapes can show impressive flatness in some directions but not in others: I'd cite the modern plateau top along the Grand Canyon's rim as a prime example of something that is misleadingly flat and extensive, while having much the same dimensions and relief as the portion of the Cambrian Unconformity cropping out below it). Note that the Siccar Point outcrop, phenomenal though it is, is really quite tiny, and note that if you sampled Glenn's wonderful complex paleosurface at typical outcrop scales, what you would mostly see is flatness. A few meters below me as I type is a regional unconformity between Mississippian and Pennsylvanian strata. When you reconstruct it regionally, you discover a system of big incised valleys, with relief on the order of 110-170 m. However, none of the outcrops show anything other than an extremely flat contact.

As related evidence, I note that paraconformities essentially never survive detailed region-wide examination without people finding enough paleolandscape to merit calling them disconformities.

I disagree that geologists are not intersted in unconformities and are not studying them. As Rach12 noted, sequence stratigraphy is basically the stratigraphy of regressions and transgressions over unconformities, and the geomorphology of the pretty flat landscapes that they represent. My experience on field trips is that unconformities fascinate geologists and provoke all kinds of discussions.

I also disagree that "Large unconformities are evidences of large scale erosive episodes." There's no shortage of mechanisms to produce flat landscapes, even if you set aside regional exposure of continental shelves, carbonate platforms, delta tops, and other depositional plains, and re-exposure of an even older flat surface. Climate can be important, as can water tables. In a dry climate, everything may blow away down to a resistant stratum or down to the water table. In a semiarid climate, a regionally developed calcrete may later become a resistant surface. Dry montane settings can develop pediments, which are very flat (smooth), albeit non-horizontal. In a periglacial climate, solifluction can cause extensive planation. In a frigid climate, glaciation can bulldoze a landscape very flat. In the tropics, deep chemical weathering followed by erosive stripping can create a fairly flat etch plane. Coastal karst planes can dissolve everything down to the water table. Transgressions can easily bevel a landscape down to just below sea level ('the saw of the sea'). Even though Davis' ideas on peneplanes (or peneplains) have fallen out of favor (as you said), this was because (1) Davis' ideas had lots of hypothesizing and ad hocing relative to actual data, (2) when data finally arrived, Davis' old, mature, and young surfaces often did not have great, intermediate, and recent ages, and (3) peneplains often turned out to be less flat than everyone supposed that Davis claimed they should be. Nonetheless, there is nothing wrong with the concepts that, given time and stable conditions, streams tend to cut a landscape down to base level. I don't see that we need to infer non-actualistic processes or events to explain unconformities, and I don't see the unconformities that I'm familiar with as the result of large erosive events so much as long erosive episodes.

I don't exactly disagree with your quote re Australia. However, I think the author is exaggerating significantly, for rhetorical effect, with respect to the persistence of Davisian concepts of peneplanation and evolutionary cycles of landscapes, the inadequacy of scarp-backwasting, and the relevance of marxism and modernism here,. Note also that I talked very advisedly about planation rather than peneplanation, precisely because of problems with Davisian theories. Nonetheless, that author is totally right, if no longer very newsworthy, that "extensive preservation of Mesozoic and Palaeogene etch and/or exhumed surfaces high in the landscape poses a major challenge to peneplanation." All that aside, however, it is irrelevant to my point that much of Australia, including the old high etch-surfaces and exhumed surfaces AND THE SURFACES LEADING UP TO THEM are remarkably flat, and indeed in many areas phenomenally flat, and are not very elevated, so that even a modest transgression could create an angular unconformity of broad extent, little regional relief, and, in many areas, almost no local relief, over numerous significant lithological changes. (My understanding is that it is also evident that the Australian landscape developed over a long time rather than due to a sudden large-scale event- see books and papers by Ollier, for example.)

One of the closest things I have seen to a peneplain-like surface is the now dissected and tilted surface preserved as the coplanar and absolutely smooth tops of a series of high plateaus (the tampoketsa), developed over a variety of bedrock types in the NW corner of the Malagasy craton. The surface includes some thoroughly weathered regolith, and the remnants are astoundingly flat. If such a surface had became buried by a transgression before it's present degree of erosion, it would have become exactly the sort of totally planar angular unconformity and nonconformity that Dave says cannot be explained by modern geology.

Yesterday @ 05:58 PM post located here
dtyler:

...

Standing back, there is a relict topography at Siccar point. Another of my photos on the web shows that - and many more images could be used to make the same point. Many unconformities do have a relict topography. This is to be expected. But what do we make of planar unconformities?

We are not referring here to a bedding plane that gets covered - but an eroded surface that is covered. It is my view that *any* modern weathered surface will show a topography - differential weathering is ubiquitous. Yet, there are numerous examples of erosional unconformities that are planar. Perhaps the best known is the Cambrian Unconformity in the Grand Canyon. There are numerous cases here in the UK. I am suggesting that this phenomenon has not received the attention it deserves by field geologists.

Tell us, David, is there anything unusual about these 'planar unconformities'? Could it be that they represent a well-known process that simply isn't happening right now, but the evidence is actually right in front of us?

No, David, you are way wrong on geologists interest in unconformities and particularly the basal Cambrian unconformity. I can remember visiting this point in time on several field trips and even some of my professors' exact words about it from decades ago. Once again, you lead me to repeat a question asked of you earlier: where and when did you get your geological training? It is clearly different from that of the rest of us. Perhaps if you could explain this, it might clarify why we view the world so differently.

[quote]Yesterday @ 12:31 AM post located here
response to rach12 (post #9):

Just about the largest unconformities on the planet are cratonic shields. Are you suggesting mainstream geologists are ignoring those? If not, which ones are you speaking of?

Cratonic shields are certainly deeply eroded, but my understanding of them is that they have a relict topography. Certainly this is the case in NW Scotland, where the unconformity between the Torridonian Sandstone and the Lewisian gneiss is very uneven. But compare this with the Torridonian/Cambrian Eriboll Formation. This unconformity is a remarkable linear feature, with no relict topography in the Torridonian. The large unconformities that I am referring to are like this.

Also, sequence stratigraphy is basically the study of unconformities at all scales, primarily with respect to changes in relative sea level. It's mainly used by oil companies to find oil. I find it hard to imagine they are ignoring anything - not when it makes them money.

Indeed – but the same argument could be used *before* sequence stratigraphy. Oil geologists were paid to be observant. Yet the sequence stratigraphers have shown there’s much more to be seen in the rock record than was previously appreciated. I could also mention Derek Ager – he’s been able to see things that others have missed because his expectations were different.

I'm curious. Where are you getting these notions that geologists are ignoring certain portions of the geologic record? I can't figure out if you are simply not reading the available literature, are too far removed from mainstream geology to see what we're doing, or simply ignoring it. I work in a very small field of geology, but even I know most of what you are accusing us of ignoring is complete hogwash.
Perhaps that is why the professional geologists replying to your posts here are on the defensive. You portray us as incompetent, brainwashed idiots.

The basic point I would make is that we all come to the field data with a conceptual framework that filters what we see. Surely you have come across people who describe how they suddenly realised that they were missing important data in the rocks? It was not so long ago that I heard someone describing his experiences of mapping granite outcrops. It seemed at first as though the outcrop was monotonous: granite, granite, granite. But, inspired by more recent thinking about dyke injection (rather than emplacement as diapirs) the monotony vanished. Different textures could be seen, and internal boundaries that could be mapped. The outcrop started to look different. For this researcher, the difference was triggered by a different mental model of how granites were emplaced.

This is not to say that the researcher before was an “incompetent, brainwashed idiot”! he was a competent field geologist. But his mental models did affect him so that he did not perceive (or appeared to ignore) significant data in the rocks.

If the professional geologists replying to my posts are “on the defensive”, I have not noticed this. They appear to me to be on the offensive. I suspect that if I were not advocating a historic creation and global flood, my geological remarks would not be regarded as particularly controversial. None of my ideas are particularly original - there is nearly always a link with published literature somewhere.