"Rock layers folded, not fractured" — or are they?

In the last of a six-part compilation of geological evidences for the Flood, Dr. Andrew Snelling argued that the absence of brittle fractures in folded strata constituted reason to believe that the sediments were laid down in rapid succession. “When solid, hard rock is bent (or folded),” he says, “it invariably fractures and breaks because it is brittle.” As an example, Dr. Snelling refers to the Tapeats Sandstone and Muav Limestone of the Grand Canyon succession, which were folded into a broad-scale monocline long after they were deposited. He claims that folding in the rocks “did not cause them to fracture and break,” and so the “only logical conclusion is that the 440-million-year delay between deposition and folding never happened!” In other words, folding took place shortly after they were laid down—within the last 5,000 years—but the sediments have since had time to lithify (transform into solid rock).

A challenge to ‘deep time’?

The lack of faults and fractures poses a potential problem to the conventional geological understanding of sedimentary strata. If you have driven through a mountainous region, you have likely seen folding in sedimentary layers, where solid rock appears to have been bent into tight—sometimes hairpin—curves without compromising the structural integrity of the individual layers. If these layers were deposited over thousands to millions of years, then given as much or more time to harden into solid rock, and finally bent under high stress at an even later time…well, shouldn’t we see some evidence for this?

Before answering this question, I should clarify part of Dr. Snelling’s reasoning. If the absence of brittle fractures in folded strata is evidence that deformation took place before the sediments had time to lithify, should the presence of brittle fractures be considered evidence of a time gap between deposition and deformation? Wouldn’t Dr. Snelling’s argument predict that we should only find fractures in the most recent deformation events, but not in rocks that were folded during or shortly after the Flood? I’ll return to this point later.

Brittle and ductile deformation—wait…what?

If these words sound foreign to you, don’t shy away. Brittle deformation simply refers to processes that break a solid—cracking a block of cement with a hammer, for example—while ductile deformation occurs when the solid stays intact, but the warping cannot be reversed. Imagine a ‘strong man’ bending a rod of iron: the metal never cracks or fractures, but neither does it return to its original shape (like a rubberband) when the force is withdrawn. This is ductile deformation.

Rocks can undergo both brittle and ductile deformation, depending on the physical conditions. When rocks are cold (less than ~300°C) and at low pressure (within a few miles below the surface), they tend to fracture under stress—like a block of concrete. On the other hand, rocks act more like a metal bar at higher pressure and temperature, and deform plastically.

But not all rocks are the same. Most limestones and diatomites, for example, have high strengths, and are quite prone to brittle deformation. Mudstones and evaporites, on the other hand, have little to no strength, and will rarely fracture. Salt diapirs in the Gulf of Mexico and elsewhere demonstrate the ability of evaporites to deform plastically under pressure. The strength of rocks depends also on the type of cement holding the grains together (silica vs. calcite vs. hematite) and the degree of cementation. Consequently, a well cemented quartzite (silica grains and cement) can only escape brittle deformation at relatively high temperature and pressure. But low redox conditions (absence of oxygen), low water:rock ratios, and the presence of hydrocarbons can prevent sandstones from lithifying—even after deep burial—so it is possible to find ancient sandstone bodies that behave as a liquid (e.g. sand injectites).

In short, there are geological reasons to expect both modes of deformation in ancient rocks. The result depends on the specific history of each rock. How deeply was it buried? What was the burial temperature? Was the rock well cemented? What is the grain composition? These questions are useful to geologists, not only when interpreting the details of Earth history, but in determining, for example, whether fractures may have formed in a rock at depth. Fractures greatly enhance the permeability of rocks, and thus their ability to carry water, oil, and gas.

In fact, one apocryphal story tells of a woman that dreamed she would find oil on her property. Nobody would take up the challenge to drill on her property, however, because it was situated on the center of Michigan Basin—a structural basin where the oil would be expected to migrate away from the center. Eventually, the drilling effort was successful, because the rocks at the center had undergone brittle deformation as a result of broad-scale folding and the fractures trapped a significant amount of hydrocarbons.

The fact of the matter is…

Nearly all rocks exposed at the surface are thoroughly fractured or faulted, particularly those that have undergone deformation. Typically, the fractures occur at small scales, and so are only visible from up close (i.e. Dr. Snelling’s photos could not possibly reveal whether brittle deformation took place). As before, the nature of brittle deformation depends on the rock properties and stresses involved, so one should not make generalizations from a single location (i.e. the Grand Canyon). Nonetheless, brittle deformation is a common process by which strain is released, so that sedimentary rock layers may continue to bend into all kinds of folds while preserving the bedding structure.

In addition to fracturing, however, many rocks can accomodate strain by slow recrystallization. In limestones, calcite components can dissolve under pressure (with the aid of water) and recrystallize at points of lower stress. The result is thousands of microcrystalline veins that run like fibers through the rock (styolites), which are only visible in hand sample or under the microscope. Sandstones and other clastic rocks can also deform slowly, through a similar method of recrystallization. As long as water can migrate through the rocks, it is entirely possible for rocks to bend into hairpin folds without a significant amount of fracturing.

The conventional explanation?

Dr. Snelling mentions another process in passing, and says the “conventional explanation is that under the pressure and heat of burial, the hardened sandstone and limestone layers were bent so slowly they behaved as though they were plastic and thus did not break.” Of course, the citation comes from a textbook on structural geology, rather than a specific treatment of his Grand Canyon example. But he continues: “…pressure and heat would have caused detectable changes in the minerals of these rocks, tell-tale signs of metamorphism. But such metamorphic minerals or recrystallization due to such plastic behavior is not observed in these rocks.”

Both the Tapeats Sandstone and Muav Limestone were deeply buried at one time (~2 miles of sediment accumulated on top of these sediments in the Grand Staircase region), but nobody would suggest that low-grade metamorphism took place (burial at these depths corresponds to ~120°C). Thus Dr. Snelling’s claim that evidence is lacking constitutes a rebuttal to a question that does not exist. Nonetheless, it is fair to ask whether Dr. Snelling has even demonstrated that these rock layers were folded without undergoing brittle deformation. If there is evidence for such, it would be visible in hand sample or thin section (under the microscope), but neither are provided for us.

Until then (or until I am able to visit these rocks myself), I can at least point out that the Muav Limestone comprises a major aquifer in the western Grand Canyon area and hosts several springs. The rock’s permeability is primarily due to faulting and connected brittle fractures (secondary porosity). Perhaps Dr. Snelling did not look close enough?

Dr. Snelling’s argument works against him

Regardless of the nature of rock layers in the Grand Canyon, there are abundant example of brittle deformation in rocks elsewhere. A Google image search for “anticlinal tension fracture” will get you started without having to leave home. But next time you do find yourself hiking or driving past folded sedimentary strata, take a close look. Most rocks will contain abundant evidence for brittle deformation as a result of folding or uplift—and now you know what to look for!

I have also provided a couple pictures at the bottom of this post. These rocks represent the equivalent of the Tapeats Sandstone and Muav Limestone in northern Utah (Ogden Canyon), where the rocks have also been folded on a broad scale (during propagation of the Sevier Fold-Thrust Belt). In the picture on the left, the brittle Tintic Quartzite (silica grains and cement) has fractured throughout and even shattered in some points. On the right, anticlinal tension fractures are visible in the Maxfield Limestone (see Dr. Snelling’s cartoon of how these form).

Now I will return to the question I originally asked: if the absence of brittle fractures in folded strata is evidence that deformation took place before the sediments had time to lithify, should the presence of brittle fractures be considered evidence of a time gap between deposition and deformation? I would answer yes. These sorts of fractures do not occur in unconsolidated sediment, so the rocks must have been well cemented at the time of deformation. In the Utah example, deformation must have occurred prior to the development of Lake Bonneville (the glacial-maximum equivalent of the Great Salt Lake). When was this, according to Dr. Snelling?

In an effort to provide evidence of deposition in rapid succession during the Flood (and deformation immediately thereafter), Dr. Snelling cites one of the most powerful arguments against his interpretation of geologic history. According to Dr. Snelling’s view of the Flood, we should not expect to find abundant evidence of brittle deformation in these rocks, but in fact we find it everywhere. Brittle faults and fractures are testament, rather, to the deep time behind geologic processes others have come to appreciate.

Brittle deformation in Cambrian strata from Ogden Canyon, northern Utah

Tintic Quartzite, Ogden Canyon, UT

Anticlinal tension fractures in the Maxfield Limestone, Ogden Canyon, UT

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