Geologic Column

That's a great post.

Indeed, I don't think that igneous intrusives and metamorphic rock have ever much been covered at . BUT, I think such areas of geology are rather remote to the real theme of this topic. They are seemingly doomed to be lost in "yet another geological column topic".Perhaps roxrkool could propose a new "Igneous and Metamorphic Rocks" topic, before such discussion goes to far in this topic. If so, please link back to a good spot in this topic.The non-admin mode is too feeble to himself pull off starting the topic.Adminnemooseus

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double postThis message has been edited by roxrkool, 03-31-2005 03:29 PM

I don't know if I agree, Moose. I don't think met/ig rocks are remote to this theme. Unless of course this topic was intended to be strictly a discussion on sedimentary rocks in geologic columns. If so, that should probably be made more clear in the thread title.The modus operandi of the YECs when discussing geology is to divorce all geologic features from their surroundings and then extrapolate a plausible means of Noachic formation for that one feature. Hell, most times it doesn't even have to be that plaussible.Geos know that a limestone, if you follow it out far enough, will many times interfinger or grade into shale, or sandstone, or various other marine, near-shore, or shore facies rocks. And these relationships tell us what was happening at the time - be it marine transgression or or regression.YECs will only consider the limestone - and only the limestone that does not abut against a cross-bedded sandstone with lizard tracks on it. They don't discuss what happens to that limestone laterally because that would entail explaining why that limestone becomes sandy and contains tetrapod dinosaur tracks and pterosaur fossils.If you think most of the geologic column is composed solely of sedimentary rocks with metamorphic/igneous rocks only occurring at the base of the column (e.g., Grand Granyon), then of course it's quite easy for them to say the met/ig rocks are preflood and the sedimentary rocks are syn- and post-flood. Well, as we've found out, it's pretty difficult to refute this interpretation - especially if the YEC knows (or thinks they know) even the tiniest bit about geology. They know the buzzwords, but not much more and they're willing to ignore any mention that disputes their perfectly plausible explanation.How do you convince a YEC (layperson) that geologists can tell if a sandstone or limestone was eroded after lithification? Geologists can use their handlens and look closely at an erosional surface and see how the individual quartz or calcite grains on that surface are flattened - like teeth after years of chewing gritty food, they are worn down. If the sand was unconsolidated at the time of erosion, the grains would simply move about, but sand or calcite is trapped by cement and can't move; it is therefore subjected to abrasion. I can explain it a hundred times, but if I don't have a photo to show people, they can continue denying the fact..
However, what happens if you ask a YEC to explain/interpret large igneous provinces? Portions of the globe where igneous rocks cover thousands of square kilometers?The massive Siberian Traps cover an area of 2.6 million km2 and temporally/stratigraphically coincide with the largest mass extinction in the history of the planet - the Permian extinction. These basaltic flows are stratigraphically located in rocks that, according to YECs, should have been erupted during the Noachic flood. And yet, no pillow basalts are present to suggest deposition in water. No chemical analyses of contemporaneous marine deposits indicate a massive influx of volcanic gases into the ocean. Textures of igneous-water interaction should be abundant, but they are not.YECs can get away with assuming all sediment was deposited by flood water, but they can't when it comes to metamorphic and igneous rocks. Those are much more difficult to explain in the context of a Noahic flood. And that's why I think it's vitally important to mention metamorphic and igneous rocks in any discussion concerning geologic columns.This message has been edited by roxrkool, 03-31-2005 03:34 PM

I think that "Geologic Column" topics have rightly been intended to be focused on the themes of sedimentation and stratigraphy. I find no problem with including volcanism (eg. Siberian Traps and other) in this.Certainly, all of the Earth's geology ties together. Igneous and metamorphic rocks can be part of the discussion.But I think that the more specific other aspects of the Earth's composition and structure are deserving of having their own more specific topics. This would include such things as stress/strain analysis of folding and faulting, and such things as igneous and metamorphic petrology.Why a pegamite is very coarse grained, and why an obsidian is glass does not belong in a sedimentation and stratigraphy topic. Why you get the various grades of contact and regional metamophism do not belong in a sedimentation and stratigraphy topic. They are wothy of their own topics.Adminnemooseus

roxrkool,Questions from a geology newbie. Is it possible for magma to intrude into sediments that are not lithified? Would lithified and unlithified sediments yield the same metamorphic features when exposed to magma?

Yes. I refer you to Message 8 for some rocks and associated textures of 1) basaltic material mixing with subaerial unconsolidated sediments; and 2) magmatic intrusion into unlithified oceanic sediments off the coast of Hawaii.The Ocean Drilling Project is a wonderful resource for the types of alteration associated with magmatic intrusion of unconsolidated sediments. I might have to get back to this one, but in a nutshell, yes and no. The alteration and metamorphic effects of igneous intrusion into lithified vs. non-lithified material is dependent on many variables, such as: presence of water in the intruded material (marine seds vs. terrestrial seds), the source of the water itself (marine vs. magmatic vs. meteoric), the pre-existing mineral suite (100% quartz vs. limestone), chemistry of the igneous body and how much water it contains (wet vs. dry intrusives), duration of thermal activity (a dike vs. a laccolith), and so on.For the most part, the unconsolidated equivalents of lithified rocks will generally form similar minerals because of similar chemistry, but the variables will determine the end result (different minerals and textures, alteration suites and halos, etc.).

I understand, Moose. Anything more specific than a general mention should have it's own topic. But I think it's important to point out the geologic column is not just sediment or volcanics.

originally Message 371Hi Peg, You're welcome. That depends on how you look at it. The "column" is complete in every location - it has all the layers for that location. If we are looking for one location that has all the layers, then the "column" is the earth. Each new layer wraps around the previous layer, taking the shape of the previous layer/s as its base, and builds onto it.It also depends on what you call a layer. There is a layer called the iridium layer that covers a large proportion of the earth, and is the evidence of the meteor strike that hit the Yucatan Peninsula 65 million years ago - it has a distinctive level of iridium that is characteristic of meteors, hence it can be identified. This layer does not exist where it has been eroded away (such as where Tiktaalik was discovered), but it covers many different formations that are discontinuous layers, and it in turn is covered by many discontinuous layers. There are similar layers that contain volcanic ash, which covers a much wider area than lava, and in some cases can be found world wide. This is where the fun (for geologists) comes in. Some layers are necessarily local - volcanic lava flows do not cover the earth, but every one of them covers part of the earth, over older formations, so you may have several different sources providing material that cover different parts of other layers. Rather obviously you are not going to have lava flows from Oahu island in Connecticut, nor are you likely to find a sedimentary deposit from the Connecticut river on one of the islands in Hawaii.What you are going to have are groups of layers of the same approximate age, with different members of the groups in different places. The rock layer that exists now on the surface in Oahu and the Connecticut valley both represent the current age. Likewise the layers that existed on the surface 100 or 1000 or whatever years ago represent the age of the earth at that time. Note that in some areas the surface is eroding away to expose older layers, and in some areas it is building up new layers, and some new building layers are formed from old eroded layers, formed into new layers.Thus if you arrange the layers all over the earth in a chronological by depth order you will have a number of discontinuous layers included in different areas, and you will have something like: Where any member of the A group will be over any member of the B group that occur in the same location.You may or may not find areas where a1 and a2 both occur to see which is over the other, but you can still build up a relative chronology in every area by the layers.Geologists give groups of layers of the same relative age names according to their age, a system of relative dating of formations that is as old as the law of superposition.Is there one location that has a layer that represents every known geological age? Probably not, but that is not necessary for the "geological column" to be a valid concept of relative age.See Geologic time scale - Wikipedia
Geologic time scale(Redirected from Geological column)

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The geologic time scale is a chronologic schema (or idealized model) relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth. The table of geologic time spans presented here agrees with the dates and nomenclature proposed by the International Commission on Stratigraphy, and uses the standard color codes of the United States Geological Survey.

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Evidence from radiometric dating indicates that the Earth is about 4.570 billion years old. The geological or deep time of Earth's past has been organized into various units according to events which took place in each period. Different spans of time on the time scale are usually delimited by major geological or paleontological events, such as mass extinctions. For example, the boundary between the Cretaceous period and the Paleogene period is defined by the Cretaceous—Tertiary extinction event, which marked the demise of the dinosaurs and of many marine species. Older periods which predate the reliable fossil record are defined by absolute age.

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Each era on the scale is separated from the next by a major event or change.

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Each era is represented by a group of layers, all of which are above or below the group of layers that make up the other eras. Geologists don't expect the "geological column" to exist in its entirety in any one area, but they do expect the overall pattern of superposition of newer layers over older layers to occur in all locations, and use the term "geological column" to refer to this general pattern of superposition, rather than to a specific column.Is there any place on earth where you can link a path between layers in direct absolute chronological order representing every (known) era/age of the earth? Yes.For further reference see PRATT CD101 (Talk Origins)

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1. The existence of the entire column at one spot is irrelevant. All of the parts of the geological column exist in many places, and there is more than enough overlap that the full column can be reconstructed from those parts.

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Breaks in the geological column at any spot are entirely consistent with an old earth history. The column is deposited only in sedimentary environments, where conditions favor the accumulation of sediments. Climatic and geological changes over time would be expected to change areas back and forth between sedimentary and erosional environments.

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2. There are several places around the world where strata from all geological eras do exist at a single spot -- for example, the Bonaparte Basin of Australia (Trendall et al. 1990, 382, 396) and the Williston Basin of North Dakota (Morton 2001).

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Does that help?Enjoy.

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cheers radzHow consistent is it?ie, if we choose a random location and dig down, would the rock strata be in that sequence?and how reliable and consistent are the ages assigned to the different life-forms found in the layers?

Near-certainly they would be, except in a very few places where something has happened to disturb the order. And we can detect thos cases. Such as the Lewis Overthrust, beloved of creationists, where a huge chunk of landscape was shoved up on top of another chunk of landscape. Creationist ... um ... er ... let's say "fibs" about the Lewis Overthrust are discussed at Claim CD102.1. Extremely reliable and consistent. The few cases in which there are seeming inconsistencies have been extensively investigated, and almost all those apparent inconsistencies have been found to be consistent after all. Such as the KBS TUff story we've mentioned here.

Here's an example of what JonF means by an overthrust. First you have a region of geological layers, I'll give each layer a unique character. We're looking at the layers edge on: Now the region gets compressed from both ends because of the motion of the continents, and this causes it to sheer (break) along a diagonal line: Continued pressure from both ends causes one to slip along the fault and rise above the other: The compression and pushing from each end continues and the layers that have risen are gradually pushed on top of the other layers, giving this result: Now the youngest layer ("-") exists both at the top and several layers further down where it is just below the oldest layer ("|"). In reality many more layers are often involved, and subsequent erosion and deposition can make the situation very complex.Sometimes the sheer lines still exist and can be identified, sometimes not. Geologic processes like erosion and subduction destroy a lot of evidence.Much more complex overthrusts are common. Imagine a rug being pushed together from each end. It will gradually fold and bunch up, and bunched-up and folded portions can be folded again and can bunch up over other bunched up portions.--PercyEdited by Percy, : Minor correction.Edited by Percy, : Rendering error somehow crept in - that's weird!

Great post RAZD! But how do you find the time? :-)

Hi Peg, sorry for the delay in reply, but I wanted to give this some more detail. As others have noted, it is very consistent, and more to the point, in those places where it does not appear to be consistent, there are reasons for in the inconsistency. Thus a look in one small area may display an anomaly, however when you look at the larger picture it becomes clear. The overthrust mentioned is a clear demonstration of this. The layers that are present in that location would be in order, provided that they had not been disturbed later by some other geological process (such as an overthrust). Note that some layers could be missing whole eons due to erosion, so there could be gaps in different locations.The layers would not be out of sequence (ACB instead of ABC), and this can be further checked by that other part of the superposition law: that the first formed layer controls the shape of the bottom of the next layer: one can look at the interface and determine which is the "first formed" side and which is the "second fit" side. Thus if you did find an area with ACB layers and you looked at the interface between B and C you would see that B conformed to C rather than the other way, thus these layers had been inverted before A was added. The ages assigned to the rock layers are very reliable and consistent (see previous post). The ages assigned to the different life-forms found in the layers are the ages of the layers.When we look at the areas where fossils are discovered, they are of interest to the paleontologists because the upper layers have eroded away, and they don't have to dig as far down to uncover the ages in question. For example, where Tiktaalik was discovered:BBC NEWS | Science/Nature | Arctic fossils mark move to land

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Before these finds, palaeontologists knew that lobe-finned fishes evolved into land-living creatures during the Devonian Period.

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But fossil records showed a gap between Panderichthys, a fish that lived about 385 million years ago which shows early signs of evolving land-friendly features, and Acanthostega, the earliest known tetrapod (four-limbed animals) dating from about 365 million years ago.

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In 1999, palaeontologists Professor Neil Shubin, from the University of Chicago, and Professor Edward Daeschler, from the Academy of Natural Sciences in Philadelphia, set out to explore the Canadian Arctic in an attempt to find the "missing link" that would explain the transition from water to land.

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Why the Canadian arctic?Tiktaalik roseae: The Search for Tiktaalik

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We look to geological maps of the world to help us find areas with rocks of the right type and the right age which have not been explored yet.

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We happen to know that lobe-finned fish and the first tetrapods lived in freshwater streams because of the sediments we find them in. So we're looking for freshwater deposits, not marine. We also have pinpointed a gap in the fossil record 380-363 million years ago which is likely to produce our transitional form. That time period is known as the Middle Devonian. ...

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A geological map of North America shows which rocks are at the surface. Each color indicates a different age of rocks and there are over 900 different groups of rock mapped within those ages. The Devonian rocks we're looking for are one of the shades of blue.

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Image courtesy of the Geological Society of America and the United States Geological Survey.

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(image used above is from Geosciences and Environmental Change Science Center | U.S. Geological Survey)The big white area at the top is Greenland. The find was on Ellesmere Island which abuts Greenland at the top of the map. It is shown in green here:
Erreur HTTP 404 - Non trouv | HTTP Error 404 - Not Found - All Versions We find very few organisms that span eons of time, and those that do, still show changes - the Coelacanths for instance, where modern ones are a different genus, live in a different ecology and are much larger than any of the prehistoric ones from the age of dinosaurs. There are also few organisms that span large geological areas. Some organisms are more universal in geological area covered, while their species are also closely related to the age of the rock layer/s they are found in. For instance foraminifera are used as an index fossil:Biostratigraphy - Wikipedia

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Index fossils (also known as guide fossils or zone fossils) are fossils used to define and identify geologic periods (or faunal stages). They work on the premise that, although different sediments may look different depending on the conditions under which they were laid down, they may include the remains of the same species of fossil. If the species concerned were short-lived (in geological terms, lasting a few hundred thousand years), then it is certain that the sediments in question were deposited within that narrow time period. The shorter the lifespan of a species, the more precisely different sediments can be correlated, and so rapidly evolving types of fossils are particularly valuable. The best index fossils are common, easy-to-identify at species level, and have a broad distributionotherwise the likelihood of finding and recognizing one in the two sediments is low.

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Foramins are used as an index fossil to gauge the of the age of the rock until radiometric data can confirm it, because they are in so many layers of (marine) sedimentary rock, but each species is only found in a narrow age band.http://www.gomr.mms.gov/homepg/whatsnew/papers/biochart.pdfThis chart lists the geological time on the left, the various ages and eons under the CHRONOSTRATIGRAPHY heading and the different foramin species under the BIOSTRATIGRAPHY heading. If you search the chart for Globorotalia tosaensis tosaensis, for example, you will find that it is only listed during one of these age layers in the lower Pleistocene, or Calabrian stage, and thus finding this species of foram would indicate the rock was from this period.Curiously, not only do we have confirmation of the relative ages with radiometric ages for the rocks that foramins have been found in, we also have the full evolutionary picture of the diversity and development of the different species: Geology Dept article 3

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Drs. Tony Arnold (Ph.D., Harvard) and Bill Parker (Ph.D., Chicago) are the developers of what reportedly is the largest, most complete set of data ever compiled on the evolutionary history of an organism. The two scientists have painstakingly pieced together a virtually unbroken fossil record that shows in stunning detail how a single-celled marine organism has evolved during the past 66 million years. Apparently, it's the only fossil record known to science that has no obvious gaps -- no "missing links."

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"It's all here -- a complete record," says Arnold. "There are other good examples, but this is by far the best. We're seeing the whole picture of how this organism has changed throughout most of its existence on Earth."

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They have been able to show the evolution of almost every species of foram from generation to generation, thus validating the relative ages of the layers and the sequence of age of those layers.Not only do the layers correlate with radiometric ages, but they correlate with the changes over time of the species found in them.Enjoy.

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thanks RAZD, thats a great rundown.Charles Lyells book 'Principles of Geology' explains that all sedimentary rocks are deposited by extremely slow processes, such as rain washing loose sand down a mountain slope to a river. Is this theory still current today? Or has it changed?the other thing i want to know is why geology and evolution are so closely linked? Shouldn't they be independent of each other?