Thrust faults

by John G. Solum

Copyright © 2001

[Last Update: February 7, 2002]

Introduction

A fault is a fracture in the earth along which movement has occurred. There are several different types of faults, and the type of fault that forms is controlled by the type of stress that is applied to a rock (compression, tension or shear). Thrust faults are formed by compressive stresses, and therefore often form where two tectonic plates collide, for example where an oceanic plate is subducted (such as along the Aleutian Islands) or where two continental plates collide and a mountain range is formed (such as the Himalayas). 

Figure 1. A cross-sectional view of a normal fault (formed due to tensional stresses) and a thrust fault (formed due to compressive stresses)

While thrust faults are indeed common, Whitcomb and Morris are mistaken about the nature of the rocks associated with thrust faults.  Their claim about fossils is based on a YEC misunderstanding of how rocks are dated relative to each other, and how the geologic column was constructed. According to YECs such as Morris the ages of these divisions relative to each other are determined using circular reasoning; in other words rocks are dated using an assumed evolutionary progression:

"That is, ancient rocks contain fossils of organisms in an early stage of evolution; younger rocks contain fossils representing a more advanced stage of evolution. We know, of course, which rocks are ancient because they are the ones on the bottom, with the younger ones on top. But, then, we have just noted there are many places where this order is reversed. We know they are reversed because of the evolutionary stage of their respective fossils." (Morris, 1983).

And also:

"The rock formations of the earth do not come equipped with corner stones certifying their assumed dates of formation. How, then, do geologists determine the age of a particular rock and whether one rock is older than another?

The answer, somewhat oversimplified but nevertheless fundamentally correct, is that the date is determined by the fossils it contains. If the fossils are only simple marine organisms, then it must be dated in one of the Paleozoic systems; if it contains fossil mammals, then it must be Cenozoic. In other words, the assumption of an ages-long evolutionary development of the organic world is the basic key for identifying and dating the various components of the geologic column.

It is true, of course, that other factors (e.g., the physical characteristics of the rocks, the superposition of one layer over another, etc.) are also used for correlating and distinguishing different formations in any given locality. But whenever there is any conflict between the physical and paleontological evidence, the paleontological evidence always governs. And when it comes to correlating rocks in one region with those in some distant region, the evolutionary succession of fossils is always the main criterion." (Morris, 1967)

Morris' explanation of relative dating is not "somewhat oversimplified" it is entirely incorrect.  YECs are completely mistaken about the principles that were used to construct the geologic column, which include the principle of superposition (younger rocks are deposited on top of older rocks) and the principle of cross-cutting relationships (features such as faults are younger than the rocks they cut). YECs are also mistaken about the distribution of fossils in the geologic record. Morris, for example, stated that rocks containing only "simple" marine fossils are automatically assigned to the Paleozoic, despite the fact that there are Precambrian, Paleozoic, Mesozoic, and Cenozoic rocks that contain only "simple" marine fossils. In other words, "simple" marine fossils first appear in the Paleozoic (and Late Precambrian), however they persist to the present day.  

In an attempt to support their claim that "out of order" rock formations are commonly found Whitcomb and Morris refer their readers to a paper by two geologists (Hubbert and Rubey, 1959) for "...an extensive listing of areas of this type", referring to areas with thrust faults.  Hubbert and Rubey include a section on the history of the recognition of thrust faults in their paper and according to them,  thrust faults (a.k.a. overthrusts) were first recognized in 1826 near Dresden, Germany, where an early 19th century geologist observed a granite overlying a shale. This thrust fault was clearly not based on "out of order" fossils because granite is an igneous rock. Hubbert and Rubey discuss several other examples of thrust faults involving either igneous or metamorphic rocks including a fault near Quebec City, Canada (recognized in 1860), and the Scottish highlands (recognized in the latter half of the nineteenth century). These examples show that Whitcomb and Morris' claim that thrust faults are proposed to explain sequences of fossils that aren't in the correct "evolutionary stage" is wrong because there are many examples of thrust faults in igneous and metamorphic rocks, neither of which contain fossils. I provide these examples to demonstrate that publications dating back to the early 19th century discuss thrust faults in non-fossiliferous rocks, and yet in 1961 Whitcomb and Morris still made their claim.  

This does not mean that there are not thrust faults that place sedimentary rocks on top of other sedimentary rocks, these type of thrust faults are also common (Hubbert and Rubey provide several examples), however the fact that there are thrust faults that do not involve sedimentary rocks is a clear indication that claims that the recognition of thrust faults is based on biological evolution are incorrect.  In a case where older sedimentary rocks were thrust over younger sedimentary rocks it is true that rocks containing older fossils would be found on top of rocks containing younger fossils (assuming that both of the rocks are fossiliferous), however, I want to again emphasize that a fossil's age is not assigned due to its place in an assumed evolutionary progression (as Morris states), and that where such faults occur there is clear evidence of faulting. This evidence will be discussed later in this paper.

It is also important to note that thrust faults are usually found in mountainous areas (or areas that were once mountainous but have since been eroded), and mountains are formed where two tectonic plates collide. Clearly these collisions, which involve tectonic plates 10s of kilometers thick occurring over 100s to 1000s of kilometers, will generate high stresses, which will cause large-scale deformation, of which thrust faults are an example. Large folds (sometimes on the sable of mountain ranges) are another type of deformation that is associated with such collisions.

Whitcomb and Morris make two general claims: the stresses required to cause thrust faults are impossibly large; and there is not evidence of large motions along thrust faults.  Their statement about the amount of displacement along thrust faults (in the third quotation) is a potential source of confusion. The statement that displacements of "many miles. . . (is) required by the overthrust theory" is potentially misleading. A thrust fault is nothing more than a fault across which the hanging wall block has moved up relative to the footwall block, and the amount of displacement along a fault (regardless of the type of fault) is calculated the same way for faults of any size: the distance between a feature that has been offset and is present on either sides of the fault is measured, and that distance is equal to the amount of displacement along a fault.  In the case of large thrust faults, such features are offset by tens to hundreds of kilometers.

The absurdity of Whitcomb and Morris' claim that the deformation associated with thrust faults is only small scale (hundreds of feet) is easily shown by examining aerial and satellite images of deformed areas of the earth. Two satellite photos of different parts of the Appalachian Mountains are shown in the preceding images, and the deformation is very clearly on a large scale; the folds are on the scale of the entire mountain range. 

Engineering mechanics and the behavior of faults

Clearly large faults existed in the past, and so it must have been possible to generate the stresses required for their formation.  Whitcomb and Morris' claim that the stresses required to cause movement along a thrust fault would cause the rocks that are being moved to shatter is wrong, and they illustrate that when they state that there is evidence of at least some motion along fault planes (although they unjustifiably deny that there can be large amounts of movement). If it is possible to move a mass of rock as large as those involved in thrust fault, even for a small distance, then quite clearly the forces required to cause that movement did not shatter the rock mass.

Whitcomb and Morris' claim that engineering rock mechanics experiments accurately describe the behavior of faults is incorrect for many reasons. When a fault moves (for example during an earthquake) movement does not occur all along the fault, and those parts of the fault that do move are not in motion at the same time. An earthquake originates at a point along a fault, and the deformation caused by the earthquake propagates away from that point along the fault, until it dies out. The deformation also does not occur along the entire length of the fault. These observations are based on records of earthquake motions, such as those associated with the Great Alaskan Earthquake, recorded by seismometers. Similarly an earthquake along the San Andreas fault will not result in motion along the entire fault. The claim that the stresses required to cause movement along a thrust fault are large enough to shatter the rocks is based on the assumption that movement along the fault occurs simultaneously. This assumption is not valid, and any calculations made based on that assumption will be wrong.

Several independent observations also indicate that engineering mechanics do not accurately describe movement along a fault; in other words natural faults do not behave as predicted by laboratory experiments (for an overview of the strength of the San Andreas fault see Zoback, 2000). 

The assumptions that Whitcomb and Morris' claims are built are wrong, however, the strongest piece of evidence against Whitcomb and Morris' claim that thrust faults are physically impossible is that there are many active thrust faults across the world. This observation makes the claim that thrust faults are physically impossible unsupportable.

Figure 4.

Figure 4 shows the locations of all thrust earthquakes recorded by the National Earthquake Information Center (NEIC) from January 1998 through December 2000 (the black lines are plate boundaries). The ground motions produced by an earthquake are recorded on seismograms, and those seismograms can be used to produce what is known as a focal mechanism, and from this plot it is simple to see if the motion that produced the earthquake was thrust, normal, or strike-slip. This process is discussed at this link:

Most of the earthquakes occurred at subduction zones (where an oceanic plate is being subducted underneath either another oceanic plate or a continental plate). This is not the type of environment under which the Lewis thrust was active. The earthquakes in the Andes, the Himalayas, northern Africa, and throughout Iran occurred along faults that are similar to the Lewis thrust. There are also many active thrust faults in southern California, and the Coast and Transverse Ranges were uplifted along such faults. This figure indicates that not only are thrust faults physically possible, they are very common.

Figure 5.  A synorogenic conglomerate in northeastern Utah. This conglomerate was deposited during the Sevier Orogeny, they same event during which the Lewis thrust was formed; related thrust faults are common in the mountains in this area.

Lammerts seems to think that a contact that is parallel to bedding is conformable. This is incorrect; there is a type of unconformity (an erosional surface in the rock record) called a disconformity that is parallel to bedding. Section 5 of the following link discusses the various types of unconformities:

The Lewis thrust, however, is not an unconformity, but a fault, where older rocks have been thrust on top of younger. This movement, YEC claims notwithstanding, resulted in deformation that is readily visible.

Figure 6. The Lewis thrust in Glacier National Park. The thrust plane is at the base of the overhang that is visible in the center of the picture.	Figure 7. A close-up of the thrust plane at this location. The rocks underlying the fault plane are intensely deformed.

Figures 6 and 7 document a very well-exposed segment of the Lewis thrust in Glacier National Park. The deformation of the underlying rocks is visible in Figure 7.

Figure 8. A small fold along the fault plane formed by the injection of the fault gouge into overlying rock.	Figure 9. Another fold near the fault contact.

Figure 10. A close-up of the thrust contact (the change from light to dark rock at the center of the photograph).	Figure 11. A sample of the dark rock below the fault. Note the highly polished surfaces on the samples.

Figures 6-11 demonstrate the all the classic indicators of fault motion; intense fracturing,brecciation, polish surfaces, and slickenlines, can be found along the Lewis thrust.

Numbers (1993) reports that the outcrop that Lammerts describes is not the Lewis thrust, but is in reality an area located 200 ft above that fault. This invalidates Lammerts' claims since his descriptions of "thin layers of shale" were not made while he was examining the Lewis thrust. A similar feature, however, does exist along the Lewis thrust, and is in fact a feature that is common to many faults.

The thin "shale" layer that Lammerts describes resembles descriptions of clay fault gouge; a material that is formed along faults through a combination of abrasion of the surrounding rocks and various chemical reactions that occurred along the fault. The gouge along the Lewis thrust is shown in the overlying photographs; the dark rock is composed of clay fault gouge and highly deformed, altered shale. The shale is highly fractured, and near the fault (within approximately 1 or 2 meters) the fragments have highly polished surfaces, some of which have slickenlines (see the overlying image on the right). The gouge along the Lewis thrust has a variable thickness, but is can be up to approximately one meter thick, and has a different mineralogical composition than the undeformed shale. The changes in the clay mineral assemblages across the Lewis thrust (Vrolijk and van der Pluijm, 1999) are well-known from other geologic settings, such as the Gulf Coast, and require the input of large amounts of energy.  In the case of the Lewis thrust this energy is strain energy, which is the result of motion along the fault.

Figure 12. Deformed Cretaceous shales just outside of Glacier National Park.	Figure 13. Mt. Crandell in Waterton Lakes National Park in Alberta. Several large thrust faults are exposed, most notably at the based of the inclined beds toward the left of the photo.

Figures 12 and 13 show some of the large-scale deformation associated with the Lewis (and related) thrusts. In the left image are deformed shales that underlie the Lewis thrust. In the right image several thrust faults that are related to the Lewis thrust are shown (the clearest is at the contact between the steeply and shallowly dipping beds).  Clearly the deformation associate with the Lewis thrust is not limited to small-scale features.

To support their contention that the Lewis thrust is a bedding plane Whitcomb and Morris quote two geologists as follows:

"Ross and Rezak say: 'Most visitors, especially those who stay on the roads, get the impression that the Belt strata are undisturbed and lie almost as flat today as they did when deposited in the sea which vanished so many years ago'"(TGF p. 187)

The quote from the original paper and the following sentences are as follows:

"Most visitors, especially those who stay on the roads, get the impression that the Belt strata are undisturbed and lie almost as flat today as they did when deposited in the sea which vanished so many million years ago. Actually, they are folded, and in certain zones they are intensely so. From points on or near the trails in the park it is possible to observe places where the beds of the Belt series, as revealed in outcrops on ridges, cliffs, and canyon walls, are folded and crumpled almost as intricately as the softer younger strata in the mountains south of the park and in the Great Plains adjoining the park to the east." (Ross and Rezak 1959 p. 420) (The text quoted by Whitcomb and Morris is bold).

It is apparent that from that Whitcomb and Morris attempt to portray Ross and Rezak as stating that the rocks are undeformed, while in they are pointing out that the rocks are intensely deformed. Whitcomb and Morris also omit the word "million" from their quote. This is a clear example of an out-of-context quotation.

Morris has defended his use of this quote, brought to his attention by an article published in 1981, in an ICR publication:

From The Anti-Creationists, ICR Impact #97 (Morris, 1981)

"The author cited two alleged out-of-context quotations by creationists, one by Dr. Gary Parker supposedly intimating that Dr. Stephen Gould was "championing creationism," the other by this writer supposedly claiming that two evolutionary geologists had agreed that the strata of the great Lewis "overthrust" were all flat and undisturbed. The fact is that we are always careful not to quote out of context. Such quotations have to be brief, for reasons of space, and so cannot give the full scope of the author's thoughts on the subject, but they do not misrepresent their nature and significance. Out of the many thousands of such references that are included in our writings, critics have to search diligently to find even a handful that they can interpret as misleading. Even in the two that were cited, a careful reading of the full context in each case will demonstrate that the reporter was himself guilty of distortion. Dr. Parker made it quite clear that Dr. Gould is a committed evolutionist (in spite of his arguments against certain Darwinian tenets). In the Lewis overthrust discussion, there was ample mention of the physical evidences of disturbances, and the quote (actually appearing only in a minor footnote) certainly did not affect the evidence developed in the particular section against "overthrust" explanation. In no way did it misrepresent the beliefs of the authors quoted."

I will leave it to the reader to judge the adequacy of that response. Whitcomb and Morris' quotation of Ross and Rezak makes it appear that those geologists support Whitcomb and Morris' claim that the rocks associated with the Lewis thrust are undeformed, when quite clearly Ross and Rezak do not support that idea. To indicate otherwise is inaccurate, and I believe dishonest.

Whitcomb and Morris continue to abuse Ross and Rezak's work with the following quote:

"Another difficulty with the concept of the Lewis overthrust is that it should have produced a large mass of broken rock in front of it and along the sides. But this has not been found.

The absence of rubble or breccia is among the compelling reasons that have forced the abandonment of the long-help idea that the Lewis overthrust emerged at the surface and moved over a plain near the front of the present mountains. . . . Such a slab moving over ground as is now believed to have existed should have scarred and broken the hills and have itself been broken to a greater or less extent, depending on local conditions. No evidence of either of these things has been found (Ross and Rezak, 1959, p. 424)" (pp. 187-189)

The entire quote from the original papers is as follows:

"The fracture zone that constitutes the Lewis overthrust was inclined upward in an east and northeast direction toward the surface (reference to figure omitted). If it had reached the surface, the forward end of the moving slab of rock above the fracture zone would have been abruptly freed from the resistances that had retarded its progress underground. Motion for a time might have been rapid, comparable with the motion which takes place at the broken ends of a slab of concrete that fails in a testing machine. The eastern end of the overthrust block might have rushed forward tumultuously. If such a thing had occurred, the rock at the eastern end of the moving mass, freed from the confinement from all sides that had formerly held it together, would have broken up; as it advanced over the surface of the ground the edge would have become a great pile of rubble. Masses of broken rock assigned such an origin have been found in front of overthrusts in other regions. The absence of rubble or breccia is among the compelling reasons that have forced the abandonment of the long-help idea that the Lewis overthrust emerged at the surface and moved over a plain near the front of the present mountains . Those who held that idea assumed that the ground surface was then level enough so that the overthrust slab could move over it readily. They also thought that the relatively flat surfaces that cap ridges east of the park are remnants of the nearly level topography over which the Lewis overthrust moved after it had reached the surface of the ground.

If the advancing slab of rock had been pushed out into the air, the confining pressures that held it together would have tended to be dissipated. Such a slab moving over ground as is now believed to have existed should have scarred and broken the hills and have itself been broken to a greater or less extent, depending on local conditions. No evidence of either of these things has been found. Further, the flat uplands are regarded now as remnants of a surface much younger than, and not directly related to, the overthrust." (Ross and Rezak, 1959,p. 424) (The text quoted by Whitcomb and Morris is bold).

Ross and Rezak are discussing a scenario in which the Lewis thrust "emerged at the surface" of the earth, in which the fault plane was once an ancient ground surface. The breccia that Whitcomb and Morris mention would have been expected to form under that scenario. The absence of such a breccia does not indicate that there was no motion along the fault, it merely indicates that the fault did not emerge and move along the surface of the earth.  The idea that Ross and Rezak refute dates to a time before the theory of plate tectonics was proposed when the formation of thrust faults was unexplained. In closing, I want to reemphasize that Ross and Rezak were only refuting the idea that the Lewis thrust formed when a mass of rock was thrust across an ancient ground surface, and not the idea that the Lewis thrust moved at all.

The relationship of Chief Mountain to the Lewis thrust is shown in Figure 14.  Chief Mountain is "an entirely isolated outlier of the thrust block" because of erosion.

Figure 14.  A sketch of Chief Mountain and its relationship to the Lewis thrust.

The observation that Chief Mountain is a klippe associated with the Lewis thrust  is easily apparent from the satellite photo and the topographic map shown below

Figure 15. A satellite photo of Chief Mountain and the surrounding area (Chief Mountain is the isolated peak toward the center of the photograph). All of the mountains in this photo are remnants of a thrust sheet that was continuous before it was dissected by erosion. USGS image from TerraServer	Figure 16. A topographic map of the same area as the satellite photo to the right.
Figure 17.  Chief Mountain as seen from the north. Note the mountains in the background, they were once part of a continuous mass of rocks that included Chief Mountain, that has since been dissected by erosion.	Figure 18.  A closer view of Chief Mountain
	Figure 19. The peak in the photo to the right is Crowsnest Peak in Alberta, another example of a klippe of the Lewis thrust sheet.

Whitcomb and Morris are wrong to expect Cretaceous shales to be found on top of Chief Mountain as it is a part of the mass of rocks that was thrust over the Cretaceous shales; the observation that Chief Mountain rests on top of Cretaceous rocks is not anomalous, it is expected.

One of the early investigations of Chief Mountain was conducted by Bailey Willis in 1902. Willis describes Chief Mountain as follows:

"The detailed structure of the Algonkian mass above the Lewis overthrust is sometimes chaotic when considered in the small, yet simple when observed in the large. The chaotic structure is best exhibited in Chief mountain, where the lower massive member of the Altyn limestone is crushed (reference to figure omitted). The fractures divide the masses irregularly into blocks of all angular shapes varying from a few inches to 25 feet on a side. . .The base of massive Altyn limestone is traversed by minor thrusts which are often subparallel to bedding, so far as it can be made out. These thrusts dip 30 degrees and occupy a zone about 1,000 feet thick above the Lewis major thrust. They are limited above by an upper major thrust which is at the base of nearly horizontal thin-bedded limestones, constituting the upper member of the Altyn formation." (pp. 333-335)

The reason I use a reference that is almost 100 years old is to illustrate the point that when Whitcomb and Morris first published The Genesis Flood there was already a lot of material in the literature that dealt with the large scale deformation along the Lewis thrust and the relationship of Chief Mountain to the Lewis thrust.

To summarize, Chief Mountain is an excellent example of features that are commonly associated with thrust faults. Chief Mountain is a klippe, a remnant of a thrust sheet that has been isolated by erosion, and it is also an example of a duplex, a feature formed by a series of thrust faults. Chief Mountain is also an excellent example of the large-scale deformation associated with the Lewis thrust.