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Tuesday, May 31, 2011

Finding Noah, then and now: Part 1—"Where is Noah today?"

In the beginning

The story of Noah and his ark is one that will never lose its ability to captivate young minds. When I was a child, I regularly reenacted the scene in our bathtub with plastic figures (unbeknownst to my parents, who were paying the water bill!). Not surprisingly, it is one of the first stories taught to young children in Sunday school. Illustrations of a large, wooden boat, filled with all sorts of exotic animals from various continents around the world, are common to our Sunday-school lessons. The ark is pictured floating on an open, boundless sea that covered the whole planet, for at least half a year, until it came to rest on a high mountain peak in the new world. The animals exited peacefully to find new homes, Noah's family set up camp, offerings were made, and the world was replenished and made fruitful once again.

But then something unfortunate happened: we all grew up. Some simply drifted away from the congregation, consigning the fanciful tale to the naïveté of their youth. For those of us that remained in the church, we may have heard the narrative in passing, but rarely as the focus of any single sermon. More than 200 years of historical critical studies and scientific advances incited the world to mock our beloved Noah, and many a preacher would dare not risk controversy by recounting the narrative as historical—or worse, as ahistorical.

The capsizing of Noah's ark?

With adulthood came the responsibility of finishing school and finding jobs in the 'real' world. Most of us, and our colleagues from Sunday school, would end up in a field that cared less about whether Noah really sailed on an ark. But others, like myself, studied geology, biology, archaeology, history, and/or ancient literature. We were told early on that the Earth was never completely flooded, let alone in the course of human history. Moreover, the story of Noah was hardly the first about a man saved by an ark from impending flood waters. Was the Bible guilty of plagiarism? Unless modern scholarship was sorely mistaken about history, we could not maintain publicly our childhood belief in Noah and his ark without facing ridicule. Had the flood of intellectualism finally overcome Noah's ark, more than 4,000 years after the waters receded?

Christians have responded to this dilemma in various manners. Some, through cognizant dissonance, whereby the historical question became irrelevant. Others, through scientific dereliction, whereby the historical question would determine the facts of nature. In the latter case, Christians with scientific degrees formulated the principles of 'Flood geology' and simply reinterpreted geological and archaeological facts to concord with a multifaceted, but rigid axiom: 1) the geologic column and associated structures are the result of a catastrophic flood, ~4,500 years ago, that reshaped the face of the planet; and 2) all terrestrial life, including humans, can be traced to the ark-born survivors of that event.

The failure of Flood geology to explain geological facts has been well documented, not least by geologists in the Christian community. Despite their good intentions, promoters of Flood geology have removed the story of Noah's ark further and further from reality, and thus relevance to the modern Christian. But a high percentage of the Western population is still convinced of its validity, and the movement will, no doubt, continue to grow. While these trends are mutually exclusive, I believe they teach us that most Christians are not satisfied with consigning the Flood narrative to irrelevance. Young-Earth Creationists and Flood Geologists are right about one thing: we should not continue to call ourselves Christians if we believe the story of Noah's ark doesn't matter.

Restoring relevance to the modern Christian

If modern Christians are limited only to the two options above, then we may find ourselves in trouble. How do we approach the text of Genesis 6–9, for example, if we can't teach that it really happened? Moreover, how do we read a text that is more than 3,000 years old, and what kind of relevance could it have today? Are the New Testament analogues of Noah's flood meaningful if the historical referent never existed? These are all valid questions that must be answered by any faithful Christian that wants to remain consistent. But before I attempt to answer them in full, I want to put your minds at ease (in case you had doubts about my own intentions) with the short version.

I will propose that the events of Genesis 6–9 did, in fact, happen. I believe the characters were real people living in a real time and place on our familiar planet. Not only is the story relevant to us today, but we can bridge the cultural gap with some effort. The most difficult challenge of reading a foreign or ancient text does not lie within the text, but within the reader. Since we did not live in the ancient Near East (when the story was originally told), we must prevent our own, modern worldview from being imposed back onto the text—a difficult, if not impossible, task.

Few Christians read the Old Testament with any regularity or depth as it is, let alone the first 11 chapters, and I am willing to bet that most could not distinguish between details from scripture and details from illustrations in Sunday school. The reason is that believers and unbelievers alike have carried with them a Sunday-school version of Noah's ark, and few have reevaluated the text in light of what they know about the world as adults. We need a fresh perspective—a new look at Noah's ark that seeks to do more than stir our imaginations, and keep our attention until lunchtime.

Granted, I am not the first to offer such a perspective, and few of my thoughts here are entirely original. Nonetheless, I find it pertinent to share my perspective as a geologist commenting on faith and science issues. Hopefully, if nothing else, it will guide your thoughts in trying to answer the same questions for yourself.

The appropriateness of using science in understanding the biblical text

Young-Earth creationists will commonly object to the use of modern science in elucidating the biblical text—at least when it means 'capitulating' the face-value meaning. By way of preface, my own conviction is that science is without foundation outside of the God who reveals himself in scripture. I do not pretend that science is a means by which we may critique God, or rationalize the impact of his word. Nonetheless, I am fully aware that science—as a method of knowing the world—must play a part in our reading of his word.

For example, even to answer questions like: How long is a cubit? What are the greater and lesser lights of Genesis 1? How did the author of Genesis measure a year, and how do we convert that to our own calendar? What are the floodgates of heaven? Not to mention, we are dependent on a translation of the Hebrew text, even if we can read Hebrew ourselves. Whether in our use of an archaeological find, or simply a lexicon to look up the Hebrew word, we are dependent on at least some part of science to read and understand God's word.

I begin with these seemingly trivial examples because they are organically related to young-Earth proofs of the flood as a global catastrophe: "How did the flood cover all the mountain peaks? How did the ark land on Mt. Ararat if the flood were not global?"

Assumed in these questions is that Sunday-school image of a large wooden boat, floating on deep, epicontinental seas, which regressed across the globe, eventually to reveal the high peaks of Mt. Ararat. Now, assumptions are not bad (in fact, they are necessary), and I understand how one reasons to this picture. Nonetheless, these challenges use scientific reasoning (namely, the laws of physics and the modern geography of Turkey/Middle East) to make their case. I believe this is no different, qualitatively, from citing geological evidence that a global flood never occurred in recent Earth history.

Literary aspects of Genesis 6–9

Is Genesis myth or history? This question was a chapter title in Peter Enns' book Inspiration and Incarnation. A few friends and I recently finished the book as part of our ongoing book club, and this chapter drew a lot of discussion. It wasn't so much that we disagreed with what Dr. Enns had said—it was how he said it. Are Christians allowed even to use the word 'myth' and 'Genesis' in the same sentence?

Ongoing discussion over what genre characterizes Genesis can be misleading, and stir emotions rather quickly. The reason is that we commonly use the term 'myth' to mean: "an unfounded or false notion." But the primary meaning of 'myth' (especially in literary criticism) is:

"a usually traditional story of ostensibly historical events that serves to unfold part of the world view of a people or explain a practice, belief, or natural phenomenon." (emphasis added)

The latter definition fits Genesis rather well, and thusly Dr. Enns argued. But, understandably, most Christians would not be comfortable with saying "Genesis is myth". Dr. Enns' comments aside, I am willing to say that Genesis falls under the literary category of myth, but also that myth is not mutually exclusive to history. Rather, it is complementary thereto, so the answer to my opening question (myth or history?) is: yes.

When I say "Genesis is myth", I mean that the primary function of the text is not to recall historical events but to unfold the worldview of God's covenant people. We should not read Genesis 6–9 the same way we read Antiquities or Rise and Fall of the Roman Empire. Nonetheless, as God's word, the text is infallible in all it intends to teach us. Thus I believe those historical events were real and did happen. The challenge then, as 21st-century American Christians surrounded by a post-Enlightenment mentality, is to apply proper form criticism both to the text and the reader, that we might unravel the historical particulars and determine what exactly Genesis 'intended' to teach us about history.

In conclusion, and in passing, I do not pretend that I can do this accurately or infallibly. That is why I open my thoughts to discussion. Nonetheless, I will propose now that the 'literal' meaning of the Genesis narrative is far more elusive than others have suggested. Moreover, I am convinced that our modern understanding of the world has been written back onto the text over the centuries, removing us further from the original meaning. I hope to recover at least part of it here.

Genesis 6–9: Why was it written?

The first thing I notice about the flood narrative is its canonical relationship to Genesis 1–3. The passage begins with a rather grim description of the land (6:5): "the wickedness of man was great on the earth, and...every intent of the thoughts of his heart was only evil continually". Man's commission from God was to uphold His image to all of creation, and have dominion over it. But in failing to uphold that image, man has essentially 'undone' the pinnacle of God's creation, thereby completing the first step in a return to the chaos of Genesis 1:2. And so God commits to a process of uncreation (6:7): "I will blot out man whom I have created from the face of the land, from man to animals to creeping things and to birds of the sky."

God's judgment here is justified, in that it follows directly from His curse to Adam (3:17): "Cursed is the ground because of you...". God's covenant people, through Adam, abandoned reconciliation to their God, and brought a plague upon the land by filling it with wicked people (among other things). The curse is lifted at the end of the flood (8:21), when God says, "I will never again curse the ground on account of man...". Eventually, in God's full covenant with Noah after the flood (9:1–17), He restates the commissions given to Adam before the Fall. I argue, therefore, that the end goal of Genesis 6–9 is to return the land to a state of darkness and chaos through judgment, and then bring forth light and life to the land through Noah—God's new Adam.

Both the creation and flood narratives are quite old (primitive, if you will), and may have been around for centuries (in oral or written form) before being penned down as we find them in the received text. But we must keep in mind that each story was told as part of a much larger narrative—the Pentateuch—that was given to ancient Israel. Why, then, were these stories put into scripture? Was it to provide Israel with a divine history book, or remind them what happened long ago? Yes, they are historical narratives, but stories are not told simply to recount history. They are told to place the reader into the story.

Lessons from The Alamo and Animal Farm

My grandfather's family is from Texas, and so naturally, I spent some time reading about the events that led up to the siege of the Alamo. About this time, John Lee Hancock produced his own film portrayal of the battle. I love films about history; I loved studying about the Alamo. I watched the movie, and saw that it was good.

But Hancock's film was not the first about the unlikely birth of Texas. Neither is the Alamo an uncommon tale. In fact, I can simply say "the Alamo" and trust that you know I am referring to a battle, more than a place, and that you already know the outcome. But if we already know what happened, what's the point in making another movie? I suppose there is profit and entertainment, but these motivations are secondary to the storyteller, I believe.

In Hancock's film, we don't just see a reenactment of events. Neither do we see an effort simply to be more 'historically accurate' than others. The characters are given personalities and dialogues—words that may never have been said. Sam Houston likens Santa Anna to Napoleon, and predicts a similar downfall. Jim Bowie's slaves argue the pros and cons of running away, before Bowie sets them free temporarily. Moreover, the film depicts events before and after the main battle, but not necessarily in chronological order and without an explicit sense of the time gap. In other words, Hancock has not retold the story merely as an objectified historiography, but to unfold a particular worldview about freedom, patriotism, family, friendship, race, and empathy with the enemy at our gates.

Hancock's The Alamo is myth. And it places us directly in the story, that we might be inspired to battle our own tyrants and defend freedom at all costs. That is why it can be retold in varied forms to cultures across time and space, with great success.

So what does Animal Farm have in common with The Alamo? Not much really, but there is a common lesson. For the sake of the argument, let's call Animal Farm an allegorical tale, written to critique (negatively) Stalin's communist regime. Since it was first published in 1945 in English, the book has been translated several times into Russian. My wife's senior thesis entailed a literary comparison of three Russian translations of exactly the same English text: one published during Stalin's regime; one in the latest Soviet era; and one less than 10 years ago.

In short, the differences were astounding, despite the fact that each translator was reading the same English text. As you might imagine, the culture and worldview of each translator was evident from the specific words they chose to reflect the English. The earliest Russian translation of Animal Farm, for example, was an allegorical tale, written to critique the tyrannical capitalist policies of the West.

When the Soviet regime was on its death bed, a newer translation told a story about some animals...on a farm. The symbols had been deconstructed entirely. The latest translation, however, was an allegorical tale, written to critique the tyrannical, communist policies of Stalin.

Three lessons, I believe, can be taken from these cases in point. First, we tell stories about the past to comment on the present and prepare for the future. If we want to understand precisely stories that others have told, and particularly if we intend to deconstruct the historical referents of those stories, we must place ourselves in their shoes and ask why the story is being told. Second, the 'meaning' of a single text (or story) is as fluid over history as the worldview of the reader. We will always be inclined to read an ancient story as though it were written specifically to us and for our time. In doing so, we might benefit from the message of the text, but will be blind to its full intentions.

I understand that scripture is unique, in that God is the ultimate author and when we read the 2,000+ year old stories, He is speaking (present tense) to us. Nevertheless, we must concede that just as Christ—the living Word—was fully human and fully divine, so is the written Word (cf. Warfield, 1948, Inspiration and Authority of the Bible; Enns, 2005, Inspiration and Incarnation). The word of our God is alive, and intimately a part of His creation. We confess that God gave his word through real people, in real cultures throughout history, and the words of each author reflected his/her own culture. But we also recognize that this only magnifies our God, who brought himself down to us in such a manner that He could speak and we could listen—despite the fact that His thoughts "are higher than our thoughts."

Lastly, we should recognize that historiography is highly biased and selective. How do you tell the story of the Alamo in under two hours without cutting out 99% of the events? When we come to the biblical text, it seems more like 99.9%. What are we missing, and why were these parts preserved?

Where's Noah?

I believe that Israel, through Abrahaam, was God's answer to the theodicic problem of Adam. God's covenant people deserved judgment, even uncreation, yet He allowed His people to live and renewed His covenant through Noah, to Abrahaam—through whom all the nations would be blessed—and to Israel, Abrahaam's 'seed'. But one major dilemma remained: how could Israel be a solution to the problem if, in fact, they are part of the problem through their own wickedness? Scripture is thoroughly eschatological in this sense (cf. Wright, 1992, New Testament and the People of God).

Reading the Bible, we can find Genesis 1–3 retold again, and again, and again. As such, it is the metanarrative to all of scripture. I already mentioned the canonical relationship of the flood narrative to Gen. 1–3, so consider also how God brings light and life (Abrahaam) out of darkness (the pagan land of Ur) to raise up Jacob (who himself is exiled to darkness but returns with wealth), or to restore Israel from Egypt back to the land of Canaan (the new Eden). At the beginning of the Pentatech, Adam and Eve are exiled from a garden, to which an angel with a flaming sword guards the entrance. Yet when Israel, under Joshua, first crosses the Jordan river, they find an angel with a sword there to greet them, and lead them back to the garden.

Moreover, the promise that the seed of the serpent would always strive against the seed of the woman is fulfilled repeatedly, and God's seed always wins out by crushing the head of the serpent. After the promise is made, we find the first fulfillment in Cain and Abel. God vindicates Abel by cursing Cain and raising up Seth. Immediately after the flood, the seed of the serpent strikes at Noah, but God vindicates Noah by cursing Canaan and raising up Shem's descendants to subdue him. When Joshua leads the conquest of Canaan, he fulfills the promise by crushing the heads, quite literally, of the five kings.

Peter reminds us (2 Pet. 3:5-6) that "by the word of God the heavens existed long ago and the earth was formed out of water and by water, through which the world at that time was destroyed, being flooded with water. But by His word the present heavens and earth are being reserved for fire, kept for the day of judgment and destruction of ungodly men." As sinners ourselves, we are fallen in Adam (Rom. 5) and reserved for God's judgement. Thus when we read the flood narrative today, our primary question should be:

"Where is Noah today? And how do I get on the ark?"

Common to every 'battle of the seeds' from Cain (Gen. 4) to Jerusalem (Matt. 23:37) is that the Lord provides the means of escape, as well as the atonement (cf. Gen. 17). Peter tells us (1 Pet. 3) that Jesus is our Noah, and that by baptism in his name, we might be joined to him and survive the coming flood. Moreover, in every instance of redemption, there is an "already, but not yet" aspect of fulfillment. In other words, God has saved us, but things are not yet put to right, so we still await a future deliverance. Such was the case with Noah; so it is with us.

The Gospel writers present Jesus, I believe, as the climax to Israel's redemptive history. Jesus, the Messiah, is the new Israel. He came to accomplish what Israel failed to do: 1) uphold the image of God to all of creation so that through him the nations might be blessed, and 2) bring it under the dominion of righteousness. "He is the image of the invisible God," Paul reminds us (Col. 1). As such, he is also the new Adam—the true humanity of God—who although tempted with "equality with God" did not grasp as though toward the fruit (Phil. 2:5–7). In Daniel's apocalyptic vision, that one "like a Son of Man" subdues the other nations like beasts. In John's apocalypse, the imagery is no different, and Jesus conquers "the Beast". "All authority in Heaven and on Earth has been given" to Christ, our King, Matthew tells us. Thus Paul, a citizen of Rome, can set Christ up against Caesar (called Lord and Savior), and say "our citizenship is in heaven, from which also we eagerly await a Savior, the Lord Jesus Christ" (Phil. 3:20).

Jesus is the divine solution to the problem in Adam, above all because He was never part of the problem. We cannot, as Christians today, read the flood narrative without seeing this conclusion. We find our Noah today in Jesus the Messiah, and His church is the ark. In him alone can we find shelter and escape God's judgment and survive the flood, that we might return to "Eden"—that is, God's new creation.


Perhaps you are frustrated that I have yet to add anything new to the discussion. So far, I have only preached about redemptive themes in the Bible, and how to relate Noah's tale of survival to our own. Well, that is true, and I hope that if nothing else, my words have served satisfactorily as a devotional to you. The reason I took so much time to expound the flood narrative christologically, however, was to demonstrate how I—as one who accepts the antiquity of the Earth and limited geographic extent of the flood—read Genesis 6–9.

So this is the part where I must ask you, how different is my reading from yours? Granted, I could have elucidated more of the details, but I think my overview sufficiently reveals my hermeneutic, and what I believe is the take-away message of Noah and his ark.

At this point, however, I can almost hear you typing, "What about the details of the flood's extent? The mountains? The animals? All flesh upon the Earth?" Well yes, I have yet to expound what I believe is the 'literal reading' of the flood narrative. That is next. But until then, I wanted to demonstrate why I think those questions are inconsequential to God's message. Was the flood global or local? I don't think it matters. God's final judgment applies to all sinners that hear his message. As one of those sinners, I'm going to find an ark!

None of my theological conclusions are contingent on the exact depth/velocity of the water, sedimentation rate, identification of the pre-Flood/Flood boundary, or the exact length of a cubit. Neither does it matter whether a vapor canopy existed before the floodgates of heaven were opened. Christ's church is my ark.

Should we date the flood using the Masoretic text or the Septuagint? Was it 4,500 years ago or 9,000? Either way, the Lord is my salvation and I will run to the ark. Was Noah's ark nothing but a metaphor, plagiarized from an old, Sumerian myth to keep the Israelites in line? Regardless, I will call upon the Lord, and find rest in His Messiah. There will always be unanswered questions in scripture, but God's message has never been obscure. He alone is our help; our salvation.


Next time, part 2 of 2:

Israel retells the story of Noah: polemical historiography in the heart of Canaan

Wednesday, May 25, 2011

Young-Earth Creationists on a GSA field trip: sand injectites and Flood geology

[This article is in response to a feedback question I received some time ago. The reader brought to my attention several Geological Society of America (GSA) field trips led by a group of young-Earth creationists (YECs) last year. Although young-Earth (Flood) geology was not expressly taught on the field trips, the YEC leaders visited several sites, which they believe challenge the conventional geologic timescale. I spent some time researching the claimed examples of a young Earth, and have focused here on their presentation regarding sand injectites found along the Ute Pass Fault near Manitou Springs, Colorado. Thank you again for the feedback, and I look forward to hearing more of your questions!]

Unconsolidated Earth under pressure: sand injectites in the geologic record

What is a sand injectite? In short, it is a term applied to an irregular sand body—in the form of a pipe, dike, sill, or diapir—that formed when already deposited sand was remobilized in the subsurface. Imagine standing on a sealed tube of toothpaste, and then puncturing the container with a nail, except...while the tube is buried under a layer of mud. The toothpaste, representing unconsolidated sandy sediment, is then injected upward into the overlying sediments. The resulting intrusions have been called sand injectites, sand pipes, clastic dikes, and sand diapirs, depending on their form.

Occasionally, the remnants of injectites are visible at the surface, such as in Kodachrome Basin State Park in southern Utah, or the Panoche Hills in California (Hurst et al., 2011), and outcrop examples have been known for more than 100 years. But geologists have only recently investigated the processes behind their formation. One reason is that the kinematics behind sand injection are difficult to characterize without subsurface imaging and complex physical modeling (e.g. Huuse et al., 2010; Ross et al., 2011)—tools not available to the typical field sedimentologist. Another reason is found in the following excerpt from Schlumberger, a petroleum exploration and production group, who noted:

“Under certain conditions, unconsolidated sand is remobilized and forced upward through overlying layers. Called injectites, these sands can have high porosity and permeability and play a huge role in planning and optimizing hydrocarbon recovery.”

Hurst et al. (2005) echoed these descriptors and determined that sand injectites constitute an excellent, but relatively unexplored, play in petroleum exploration, where hydrocarbon preservation potential was high. For reference, a play in the oil industry refers to a type of deposit or structure (channel sands, dune fields, submarine canyons) that could potentially trap and preserve hydrocarbons (oil and gas). Some major sand injectites, such as in the North Sea, are comprised of well sorted, homogenous, highly porous and permeable sandstones. In the oil industry, these characteristics are of prime importance when it comes to recovering the maximum amount of oil from a reservoir. Thus, sand injectites make ideal reservoir rocks, and their irregular shape aids in trapping oil and gas.

The moral of the story is simply this: petroleum exploration companies have a lot of money, and are willing to spend that money researching aspects of geology that help them better recover oil and gas. Since Dixon et al. (1995) first explored the importance of diapiric sand in petroleum systems 16 years ago, our understanding of sand injectites has grown exponentially.

Modern understanding of sand injection: triggers and fluidization mechanisms

Sand injectites begin as relatively flat (tabular) bodies of sandy sediment, such as those deposited in coastal margins or eolian dunes (e.g. Mississippi River delta and Saharan desert, respectively). During periods of rising sea level, or high subsidence, the sand is overlain by fine-grained muds, or in some cases, evaporites, which may act as a low-permeability seal during burial. Normally, water in the pore spaces of both sediment types would escape as the rock pressure increases, allowing both the mud and sand to compact—the first step of lithification. If the geometry is just right, however, the surrounding mudstone can effectively prevent pore water from escaping the sand body during burial. Not only does this cause the sand layer to become overpressured (a condition that occurs when the pore-water pressure is higher than from the weight of overlying rock alone), but it prevents cementation—the next step of lithification.

Though sandstone lithification essentially halts in the scenario above, the surrounding mud continues to undergo diagenetic modification. First, the mudstone undergoes physical compaction, in which pore water is allowed to escape. At deeper burial (6,000–9,000 ft; 100–110°C), montmorillonite (a common clay mineral) converts to illite. The process involves loss of mineral-bound water to adjacent sedimentary units (fluid migration), as well as volume loss (since illite is smaller), causing clay-rich layers to fracture at depth (Selley, 1998).

Since both modes of compaction cause the mud to shrink, they can potentially undermine the seal that had kept the sand body overpressured. Alternatively, rising hydrostatic pressure in the underlying sandstone will inevitably fracture the mudstone when the upward normal stress overcomes the strength of the cap rock. In either case, high-pressure streams of water are forced upward into the overlying sediments, along with unconsolidated sand. At this point, the extent and geometry of sand injection is only a matter of physics, obviously dependent on the parameters of each scenario (overlying lithology, burial depth, initial hydrostatic pressure, etc.).

To add some perspective, Vigorito and Hurst (2010) reported fluid pressures of ~25 MPa, or 3,625 psi, after mobilization had occurred, and estimated that 27 MPa (~4,000 psi) was necessary to cause fracturing of the mudstone seal. Compare these pressures to the average 30–35 psi in your tires! Scott et al. (2009) estimated subsurface sandstone velocities up to 9.43 m/s, or some 21 mph. Sand injection is no gradual process.

Hurst et al. (2011) summarized a number of proposed triggers for sand mobilization: seismic events, fluid migration, igneous intrusion, and even meteor impacts. These mechanisms are not mutually exclusive to a scenario involving overpressure, however, and are more likely complementary (i.e. the straw that broke the camel’s back; see Huuse et al., 2010). For example, soft-sediment deformation is common in tectonically active regions, like the Late Cretaceous Sevier Foreland Basin of southern Utah, exposed near Cedar City (Parowan Canyon) and Gunlock. If a fluid-saturated sand body is already at high pressure and unconsolidated, even a modest earthquake could set the catastrophic dewatering process into motion.

And for the record: yes, catastrophic processes are perfectly consistent with uniformitarianism!

Sand injectites are dominantly fine to medium-grained, showing graded sedimentary structures that depend on the flow characteristics (banding in lower flow regimes; absence of structure in highest flow regimes; Hurst et al., 2011). Erosion of the surrounding bedrock may also occur. Cylindrical pipes commonly contain fine-grained sand at the core, surrounded by brecciated fragments toward the edge (Hurst et al., 2011).

Young-Earth arguments based on sand injectites

Young-Earth geologists have long argued that sand injectites are problematic for the ‘uniformitarian’ timeline, because they find it inconceivable that buried sand could remain unlithified for thousands to millions of years. Rather, they will argue that sand injectites (and other examples of soft-sediment deformation) warrant a significant rescaling of the geologic timescale—in this case, from hundreds of millions of years to less than 5,000 years. But is the argument premature, given our current understanding of post-depositional sand injection? I will examine two major cases in point here, and conclude that sand injectites are not problematic for the conventional geologic timeline.

Kodachrome Basin State Park, UT
Columnar sand pipes were cited early on as evidence against the conventional geological time scale by Roth (1992), who posited that the Jurassic sandstones of Kodachrome Basin State Park should have lithified (cemented) before the supposed remobilization. He argued that sandy sediments would have to remain unlithified for some 150 million years, based on field relationships. William Hoesch of ICR restated the case here, expressing his doubt with “quotation marks” that sediments remained unconsolidated for more than even 10 million years.

Missing overburden in the Young-Earth timeline

Roth (1992) argued erroneously, however, that movement of the sand occurred as late as Pleistocene, not realizing this would require the process to take place under only a few hundred feet of overburden (i.e. very low pressure). More likely, the sand injected later in the Jurassic (~140–150 Ma; see Netoff, 2002), long before the erosional unconformity at the base of the Upper Cretaceous Dakota Sandstone was formed (~90 Ma). The injectites did not pierce Pleistocene-age sediments, but rather those sediments were deposited on top of weather-resistant quartz arenites of the columnar sand bodies.

Hoesch argued for a Cretaceous-aged injection, based on soft-sediment deformation in the Dakota Sandstone, but the two are not necessarily related. While common in Cretaceous formations in southern Utah, soft-sediment deformation (a typical sign of seismic activity) also occurs in Jurassic units (Netoff, 2002). Both records of seismic disturbance are consistent with the Mesozoic tectonic setting of southern Utah, during which time the Sevier orogenic (fold-thrust) belt was developing to the west.

Despite the uncertain timing of sand injection, it appears to have occurred at least several million years after deposition, based on the biostratigraphic constraints of overlying Jurrasic units. Deposition of the Carmel Formation, for example, is estimated at ~170–164 Ma. Sandstone injectites sourced from the Carmel Formation cut the overlying Entrada Formation, which was in place by 161 Ma. Thus a minimum of ~3 million years passed between deposition and injection. So how did the Carmel sandstones remain unconsolidated for such a period of time?

Salt: geological Tupperware

Evaporite layers, which are impermeable, cap the Carmel Formation locally and could have served as an extremely effective seal during burial. They would also prevent circulation of meteoric water to the buried sandstone. Not only would the Carmel sandstones become overpressured, but pore waters would lack the ions and oxidation state necessary for cementation to proceed. In passive margin sequences, the geothermal gradient is also typically low, so sediments must be buried more deeply than normal to reach a given temperature. Thus quartz cementation would not have occurred before the evaporite seal was broken during burial.

Geophysicist Glenn Morton has similarly commented on the arguments of Roth (1992). He correctly points out that cementation is not simply a function of age, and cites examples from personal experience where deeply buried sediments are still unconsolidated—some below well cemented strata! I will expand on his reasoning later on, with a closer look at cementation processes.


I do not mean to suggest that sand injectites at Kodachrome Basin are not mysterious formations—even counterintuitive on some level. These incredible statues defy tangible experience, and even challenge some very old geological dogmas. But they are not, after all facts are considered, inconsistent with the accepted timing and origin of geological strata. On the contrary, a greater challenge remains to those that believe these injectites formed during or after the Flood, while still unlithified, and yet cemented well enough in the time since the Flood to be exposed as weather-resistant landforms today.

Ute Pass Fault and associated sand dikes near Manitou Springs, CO
Every summer, the picturesque, mountain town of Manitou Springs—located just west of Colorado Springs, CO—hosts a massive tourist population. In addition to the unbeatable scenery, unique shopping experience, and local dining outlets like the Wine Cellar (my personal ‘shout-out’), nearby geological attractions such as Garden of the Gods and Cave of the Winds attract visitors from across the country—myself included (in fact, I spent part of my honeymoon there)!

The structural history of Manitou Springs region is equally enticing. Over the past ~60 million years, the Ute Pass Fault (a high-angle reverse fault) has exposed the Mesoproterozoic Pike’s Peak Granite to the south of the town. Paleozoic and Mesozoic sedimentary rocks were upwarped during the Laramide Orogeny, and are now exposed along the Front Range (e.g. Garden of the Gods). Numerous sand dikes are also found within extensional fractures of the Pike’s Peak Granite. Austin and Morris (1986) note that most dikes are found in the hanging wall of reverse faults along the Front Range, and strike parallel to Laramide faults.

Sand dikes of the Front Range in Colorado are fundamentally different from examples I cited above. Rather than piercing upward into sedimentary strata, these dikes formed when unconsolidated sand moved downward to fill extensional fractures. Nonetheless, sand dikes associated with the Ute Pass Fault are incredible examples of soft-sediment deformation (i.e. remobilization of unconsolidated sand), and are worth exploring further.

Young-Earth Creationists lead a GSA field trip to the Front Range

William Hoesch and other young-Earth geologists led a field trip at the Geological Society of America annual meeting held in Denver last year (Ross et al., 2010; abstract available here). They argued that the Cambrian Sawatch Sandstone injected into Pike’s Peak granite, which was fractured during the Laramide Orogeny and thrust on top of the Cambrian sandstone, some 430 million years after deposition. How did it turn out? One sympathetic spectator noted:

“...a bunch of PhD creationist geologists led a field trip for the premier, annual secular geology meeting. I was there on that trip...and it was like music to my ears to have 16 PhD geologists stumped.”

Austin and Morris (1986) originally advanced the argument that the timing and distribution of the sandstone dikes challenged the conventional geologic timescale. Following Kost (1984), they determined the Cambrian Sawatch Formation (~500 Ma) to be the sediment source based on similarities in textural and compositional maturity (although grains within the sand dikes were better sorted and cemented by hematite, rather than dolomite).

Most peculiar about the sand dikes is that they intrude older igneous and metamorphic rocks (Harms, 1965). Thus extensional faulting (pulling apart) of the crystalline rock was necessary for injection to take place, rather than failure of an overlying seal or cap rock. If the timing of fault formation can be constrained, however, so can the timing of sand injection.

Most injectites are found within proximity to the Ute Pass Fault, a dominantly Laramide structure, and so the timing of injection has been argued to be Cretaceous or later (less than 65 Ma) by Austin and Morris (1986). But if injection occurred as a result of Laramide movement on the Ute Pass Fault, one must explain how sandstone could remobilize after more than 430 million years of burial.

An unrealistic timeline: burial history of the Sawatch Formation

Although no geologist would suggest that lithification is simply a function of time (e.g. Selley, 1998), the proposed 430 million-year time gap of Austin and Morris (1986) would constitute a daunting challenge to the conventional age assignments. The Cambrian Sawatch Formation is not simply old, but it has since been buried by more than 2 miles of sediment. Moreover, there is no impermeable cap rock that would cause overpressuring or prevent circulation of diagenetic fluids.

Austin and Morris (1986) are correct about one thing: the Sawatch Formation could not have remained unlithified until the Laramide Orogeny, unless we are hopelessly mistaken about the age of either event. But the assertion that deposition and injection all took place during or shortly after the Flood is not the only alternative hypothesis. In fact, that scenario is falsified rather easily.

Genetic link between the Sawatch and Fountain formations

The Fountain Formation, also exposed near Manitou Springs, was deposited between the Late Pennsylvanian and Early Permian (Sweet and Sorreghan, 2010). Though dominantly sandstone, the unit is stratigraphically complex, characterized by numerous shallowing-upward cycles. Lithologies range from fine-grained mud, silt and sand to coarse, pebble conglomerates. Sweet and Sorreghan (2010) interpreted both marine and terrestrial depositional environments, and concluded that deposition took place in a fan-delta system, in which uplift to the west drove progradation of sediments toward the marine basin that covered the modern Great Plains.

Based on the geometry of the Fountain Formation, along with clast-size distribution, Sweet and Sorreghan (2010) also concluded that cyclic deposition of the Fountain Formation was driven by movement along the ancestral Ute Pass Fault, during uplift of the ancestral Rocky Mountains. While the Ute Pass Fault exposed near Manitou Springs today is a Laramide feature, the region has been tectonically active since the Cambrian (Myrow et al., 2003).

Conglomerate facies of the Fountain Formation provide further evidence for this depositional model. Sweet and Sorreghan (2010) used petrography to identify earlier Paleozoic clasts within the Fountain Formation, including weathered pebbles from the Sawatch Formation. In other words, the ancestral Ute Pass Fault, also a reverse fault, exposed older Paleozoic rocks as the Fountain Formation was being deposited to the northeast.

The occurrence of Sawatch-sourced pebbles in the Fountain Formation has significant implications for the timing of sand injection, since we may conclude that emplacement of the sand injectites occurred after the deposition of the Sawatch Formation (496 Ma), but prior to deposition of the Fountain Formation (~305 Ma). Moreover, the Sawatch Formation had to be lithified—at least on the upthrown block—before it could erode into pebbles and be deposited in conglomerates of the Fountain Formation. Sand injection did not occur during the Laramide Orogeny, because the Sawatch Formation was already lithified by the late Middle Paleozoic, more than 200 million years earlier.

Syntectonic deposits in a Flood model?

This sedimentological constraint constitutes a major challenge to Austin and Morris’ interpretation of the geologic history, since they must regard both the Sawatch and Fountain formations as Flood deposits. How did the Sawatch Formation lithify within less than a year? And if it did, then how was it injected into the Pikes Peak Granite later in the Flood, during ‘Laramide’ movement along the Ute Pass Fault? Austin and Morris thus face the same challenge they raise, and their interpretation of the sand dikes is simply not tenable in light of all geological data.

But the question still remains: when did sand injection occur? And how did it happen? Not considering the paleogeography and seismic history of the region, Austin and Morris (1986) glanced over the answer in their original paper:

 “Some workers...recognize the fundamental impossibility of keeping the Sawatch
Sandstone...unlithified and deeply buried for 430 million years until the Laramide Orogeny...These workers tend to negate the important field relationships and suggest that the dikes were actually intruded in the Cambrian while the Sawatch Sandstone was unconsolidated. Evidence of Cambrian or Ordovician tectonics of a magnitude able to open up extension fractures hundreds of feet wide, however, has not been found on the Ute Pass Fault.” (emphasis added)

Austin and Morris (1986) thus ruled out the possibility that sand injection occurred in the early Paleozoic (Cambrian/Ordovician) because 1) sand dikes are found along the Ute Pass Fault—a Cenozoic structure; and 2) they believe that only the Laramide Orogeny was powerful enough to form the wide extensional fractures now hosting the Cambrian sand. But there are a few fatal flaws in this line of reasoning.

Tectonic blunders in the arguments of Austin and Morris

Sand injection could not have taken place during the Cenozoic, because uplift of the modern Rocky Mountains was driven by contractional deformation—namely, the Laramide Orogeny. The Ute Pass Fault is a reverse fault, which forms when rocks are compressed together, but sand dikes occur within extensional faults. In the latter case, rocks are pulled apart, so the tectonic features are mutually exclusive. Austin and Morris‘ suggestion that Laramide tectonism was “of sufficient magnitude to open up the large extension fractures” is blatantly contradicted by the field evidence they had already cited. A more parsimonious conclusion is that extensional faulting occurred early in the Paleozoic (Cambrian–Ordovician), allowing for sand injection. Sand dikes were then exposed by uplift and erosion, driven by tectonic contraction, during the Cenozoic.

Austin and Morris (1986) argue that “the coincidence of the dikes along the Ute Pass Fault, a proven Laramide structure, cannot be accidental...”—and they are right. So why should sand dikes be found in proximity to and strike along Laramide faults if they were not formed at the same time? One could answer this question by a simple experiment. All you need to do is take a hammer to a brick, so that it cracks from top to bottom. Then, use a vice to squeeze the fractured brick together until the pieces break and move past each other. As you might expect, the brick will break along already formed fractures (i.e. where it is already weak).

In geological systems, this phenomenon is known as reverse-reactivation of normal faults (e.g. Kelly et al., 1999). During periods of tectonic extension, normal faults and extensional fractures form. Later, when the same rocks undergo compression, reverse faults form preferentially along older fault planes. This process not only explains the association of early Paleozoic sand dikes with Cenozoic reverse faults (namely why sand dikes run parallel to the Laramide Ute Pass Fault) and the high angle of the Ute Pass Fault (in contrast to a low-angle thrust fault), but also solves the apparent time gap of Austin and Morris (1986).

In the citation above, Austin and Morris state that “evidence of Cambrian or Ordovician tectonics...has not been found on the Ute Pass Fault.” I would argue, however, that the sand dikes are themselves evidence of Cambro-Ordovician tectonics! Although most offset on the Ute Pass Fault occurred during the Laramide Orogeny, the fault zone is primarily a Paleozoic structure that also produced thick, syntectonic deposits during the Pennsylvanian (Sweet and Soreghan, 2010) and was simply reactivated in the latest Mesozoic to early Cenozoic.


Austin and Morris (1986) accused earlier workers (e.g. Kost, 1984) of ignoring vital field evidence to save the old-Earth paradigm, but after closer examination, it appears Austin and Morris are guilty the same to support their own claims. In fact, Kost (1984) also used paleomagnetic data from the sand dikes to argue for an early Paleozoic sand injection, but these data were conveniently overlooked.

Overall, sand injectites near Manitou Springs are not evidence for a faulty geologic timescale, as suggested by Austin and Morris (1986). Reinterpretation of the depositional and structural history of the Front Range on a ~5,000 year timeline would create countless geological problems in an effort to solve one or two problems that do not actually exist. In fact, it does not even solve this one or two!

Appendix: Cementation of sandstone
All clastic sedimentary rocks lose both porosity and permeability with depth. Understanding this phenomenon is crucial to the oil industry, since these characteristics may determine whether or not an oil reserve is recoverable. Selley (1998) notes that 1) the geothermal gradient, and 2) the pressure regime are the primary factors controlling cementation during burial.

The sandstone layers that sourced the Kodachrome Basin sand pipes and the clastic dikes near Manitou Springs were deposited in a passive margin and intracratonic setting, respectively. In both cases, the geothermal gradient and sedimentation rate are relatively low, implying that sediments could remain unconsolidated for a very long time.

Cementation also depends on the ion composition and oxidative state of pore waters. Since silica is relatively insoluble at low temperature and neutral pH, sandstone cementation does not occur until deep burial unless ample groundwater is allowed to circulate through the sediments. In some cases, particularly near faults, oxygen-poor waters with high amounts of dissolved iron are introduced to porous sandstones that are already saturated with oxygen-rich, meteoric water. Iron is insoluble in oxidative environments, so the result is a hematite-cemented sandstone, such as in Kodachrome Basin State Park.

In other cases, carbonate-rich waters may circulate down into porous sandstone. Since acidity is lost in the process, the carbonate ions precipitate within pore spaces of the sand, forming carbonate cements. The Cambrian Sawatch Formation was cemented by dolomite, apparently sourced from the overlying Ordovician limestone/dolomite. Sand dikes along the Ute Pass Fault, however, are cemented with hematite—evidence of hydrothermal fluid interaction.

The importance of oil in cementation

If hydrocarbons migrate through unconsolidated or poorly-cemented sandstone, they may prevent further cementation, or even dissolve certain cements already in place (namely hematite). In the American southwest, white, bleached horizons in otherwise red sandstone cliffs reflect this very process. Thus the prevalence of sand injectites as hydrocarbon reservoirs is not entirely coincidental.

Early charges of hydrocarbons are sometimes responsible for exceptionally high porosity and permeability in sandstones. The Coalinga Oil Field of California, for example, yielded far more oil that its counterpart field at Kettleman Dome, because cementation was prevented by an early hydrocarbon charge in the former. If sand injectites were to lack a sufficient seal to preserve hydrocarbons, however, microbially mediated degradation of the oil could lead to rapid carbonate cementation in oil-bearing injectites as they are exhumed (Jonk et al., 2005). Thus many sand injectites and sand pipes are exposed today as weather-resistant structures.

References Cited:

Austin, S.A., and Morris, J.D., 1986, Tight Fold and Clastic Dikes as Evidence for Rapid Deposition and Deformation of Two Very Thick Stratigraphic Sequences, in Walsh, R.E., Brooks, C.L., Crowell, R.S. (editors), Proceedings of the First International Conference on Creationism, Pittsburgh, p. 3–13.

Dixon, R.J., Schofield, K., Anderton, R., Reynolds, A.D., Alexander, R.W.S., Williams, M.C., Davies, K.G., 1995, Sandstone diapirism and clastic intrusion in the Tertiary
submarine fans of the Bruce-Beryl Embayment, Quadrant 9, UKCS, in Hartley, A.J.,
Prosser, D.J. (editors), Characterisation of deep-marine clastic systems: Geological Society of London Special Publication, v. 94., p. 77–94.

Harms, J.C., 1965, Sandstone Dikes in Relation to Laramide Faults and Stress Distribution in the Southern Front Range, Colorado: Geological Society of America Bulletin, v. 76, p. 981–1002.

Hurst, A., Cartwright, J.A., Duranti, D., Huuse, M., Nelson, M., 2005, Sand injectites: an emerging global play in deep-water clastic environments: Petroleum Geology Conference Series, v. 6, p. 133–144.

Hurst, A., Scott, A., Vigorito, M., 2011, Physical characteristics of sand injectites: Earth-Science Reviews, v. 106, p. 215–246.

Huuse, M., Jackson, C.A., Van Rensbergen, P., Davies, R.J., Flemings, P.B., Dixon, R.J., 2010, Subsurface sediment remobilization and fluid flow in sedimentary basins: an overview: Basin Research, v. 22, p. 342–360.

Jonk, R., Hurst, A., Duranti, D., Parnell, J., Mazzini, A., Fallick, A.E., 2005, Origin and timing of sand injection, petroleum migration, and diagenesis in Tertiary reservoirs, south Viking Graben, North Sea: American Association of Petroleum Geologists, v. 89, p. 329–357.

Kelly, P.G., Peacock, D.C.P., Sanderson, D.J., McGurk, A.C., 1999, Selective reverse-reactivation of normal faults, and deformation around reverse-reactivated faults in the Mesozoic of the Somerset coast: Journal of Structural Geology, v. 21, p. 493–509.

Kost, L. S., 1984, Paleomagnetic and petrographic study of sandstone dikes and the Cambrian Sawatch Sandstone, east flank of the southern Front Range, Colorado: Master’s Thesis, University of Colorado, Colorado, 173 p.

Myrow, P.M., Taylor, J.F., Miller, J.F., Ethington, R.L., Ripperdan, R.L., Allen, J., 2003, Fallen arches: Dispelling myths concerning Cambrian and Ordovician paleogeography of the Rocky Mountain region: Geological Society of America Bulletin, v. 115, p. 695–713.

Netoff, D., 2002, Seismogenically induced fluidization of Jurassic erg sands, south-central Utah: Sedimentology, v. 49, p. 65–80.

Ross, J.A., Peakall, J., Keevil, G.M., 2011, An integrated model of extrusive sand injectites in cohesionless sediments: Sedimentology, v. 58.

Ross, M.R., Hoesch, W.A., Austin, S.A., Whitmore, J.H., Clarey, T.L., 2010, Garden of the Gods at Colorado Springs: Paleozoic and Mesozoic Sedimentation and Tectonics: Geological Society of America Field Guides, v. 18, p. 77–93.

Roth, A., 1992, Clastic Pipes in Dikes in Kodachrome Basin: Origins, v. 19, p. 44–48.

Scott, A., Vigorito, M., Hurst, A., 2009, The process of sand injection: internal structures and relationships with host strata (Yellowbank Creek Injectite Complex, California, U.S.A.): Journal of Sedimentary Research, v. 79, p. 568 – 583.

Selley, R.C., 1998, Elements of Petroleum Geology: Academic Press, San Diego, 470 p.

Vigorito, M., and Hurst, A., 2010, Regional sand injectite architecture as a record of pore-pressure evolution and sand redistribution in the shallow crust: insights from the Panoche Giant Injection Complex, California: Journal of the Geological Society of London, v. 167, p. 889–904.

Sunday, May 15, 2011

How old is Carlsbad Cavern (Guadalupe Mountains, New Mexico)?

The Guadalupe Mountains of New Mexico and Texas are home to more than 300 caves, including those of Carlsbad Caverns National Park. If you are not familiar with the geology of the region, the National Park Service has already published a number of brochures describing the intricate, and well decorated cave system (I would recommend starting with this PDF on the development of the caves).

Many visitors and researchers alike have wanted to know, how old are these caves? In the last post, I described the most common method of dating speleothems: uranium-thorium (U-Th) disequilibrium dating. Some of the younger speleothems at Carlsbad Caverns have been dated using the U-Th method (e.g. Polyak et al., 2004; Brook et al., 2006), and cover the past 12,500 years and 164,000 years, respectively. Forty-six U-Th ages were analyzed in the latter case, and were used to model highly variable stalagmite growth (0–70 mm/kyr) and climate over the last two glacial cycles.

But this only address part of the question, because it tells us when precipitation of speleothems began, and not when the caverns were actually carved out. Unfortunately, it is much more difficult to date the removal of something in geology than its appearance (e.g. erosion of the Grand Canyon vs. the sediments being eroded).

The curious case of Carlsbad Cavern: sulfuric acid dissolution

Several researchers in the region devised a novel solution to this question (Polyak et al., 1998). As it turns out, some of the larger caves of the Guadalupe Mountains were dissolved with the help of sulfuric acid (as opposed to just carbonic acid). The unique dissolution process left its mark in the form of sulfate minerals, such as alunite, that formed residues on the cave walls, and in small cavities. Alunite is a potassium-bearing mineral, which means that it can be dated using the 40Ar/39Ar method. Since alunite forms as a byproduct of dissolution, the model age should reflect the time of cave dissolution.

Polyak et al. (1998) obtained 15 ages from the purest alunite samples (determined by XRF), representing 5 different caves in the region. Model ages ranged from 3.89–12.26 million years (precision better than 3%) and were reproducible across multiple rooms from each cave. Moreover, clay minerals from the Permian bedrock were dated by the same method, and estimated to be 278±3 Ma. Several clay-rich samples of alunite, with unusually high K/Ca ratios, yielded anomalously old ages (~30 Ma), as expected. Thus contamination could be ruled out in the primary data set by analyzing for clay content and elemental ratios (K/Ca).

40Ar/39Ar model ages, tectonic uplift of the Guadalupe Mountains, and the age of Carlsbad Cavern

Model ages from each cave were also plotted against elevation, revealing a strong correlation. This result corroborates the current understanding of cave dissolution, which is thought to occur from groundwater interaction near the water table. As the mountains were uplifted, the water table dropped, and so caves were carved out at lower and lower elevations. In other words, the oldest caves are now found at the highest elevation, and the youngest caves are found much lower.

Carlsbad Cavern, currently at ~1,100 meters above sea level, was carved out about 4 million years ago, according to alunite model ages. Speleothems would have begun long after, however, and some are still forming today.

Sulfuric acid dissolution: mechanism of rapid cave formation in a young Earth?

Back in 1998, young-Earth creationist Michael Oard tried to work the results of Polyak et al. (1998) in his favor (original article here; responding to YEC-critic Art Strahler). Mr. Oard suggested that since sulfuric acid is a much stronger acid, it could have formed caves rapidly during or after the Flood, allowing more time for speleothem formation (~4,500 years versus...4,000 years?). Currently, some 10% of the world's caves are thought to have formed by sulfuric-acid dissolution, but Mr. Oard posits that number might be larger, and the evidence has since washed away.

Greg Neyman (Answers in Creation) has already responded to the article here, showing that Mr. Oard's optimism is hardly warranted, so I will address the remaining errors here.

1) Syn-Flood vs. Post-Flood: Mr. Oard suggests that cave dissolution might have occurred during the Flood, contra his critic that deemed caves as "post-Flood" features:

"...cave formation is not necessarily a post-Flood phenomenon as Strahler thought. It could have formed anytime after the limestone was first deposited in the Flood, since hydrothermal water would be expected to begin moving through the limestone soon after deposition."

This point is hardly worth discussing, since it only moves the possible age of the cave back by one year at most. Nonetheless, I'll mention that evidence of hydrothermal fluids is common in limestone bedrock (e.g. Tritlla et al., 2001). Hydrothermal fluids typically move through fractures in the bedrock and deposit calcite veins in their path. The calcite is a mixture of dissolved bedrock and CO2 from thermally altered organic matter. Hydrothermal fluids also contain trace elements, like strontium, that are incorporated into the recrystallized calcite. Overall, hydrothermal activity is very easy to detect in carbonates, because it shifts the chemistry on every level: 87Sr/86Sr ratios drop, along with δ18O and δ13C values. Mr. Oard's hypothesis can thus be tested, but I suspect that most of his readers will rest on his 'just-so' story.

2) Biogenic sulfur: Mr. Oard contradicts himself after he confuses the origin of sulfuric acid in the Polyak et al. (1998) study.

"The sulfuric acid is formed by the oxidation of hydrogen sulfide in hydrothermal water...The 34S/32S ratio indicates the hydrogen sulfide is biogenic."

Polyak et al. (1998) mention sulfur input from hydrothermal fluids as a factor for some caves, but not in the case of Carlsbad Cavern. The significance of isotopically light sulfur is that the sulfuric acid was ultimately sourced from decaying organic matter—not H2S in hydrothermal fluids. Hill (1990), cited by Mr. Oard, linked the biogenic sulfur signal to hydrocarbons (oil) in the underlying strata. In other words, sulfur-bearing oil was oxidized in the subsurface to produce small quantities of H2S, and that H2S was oxidized to sulfuric acid (H2SO4) as it was carried through the groundwater to the site of cave dissolution.

Now, I do not highlight this mistake for the sake of trivial amendment. The fact that sulfuric acid responsible for carving out Carlsbad Cavern was a byproduct of oil degradation raises a serious challenge to Mr. Oard's young-Earth timeline, for it requires that sedimentary organic matter had already matured to oil by the time Carlsbad Cavern was forming. But outside of controlled, high-temperature and high-pressure laboratory conditions, oil does not mature overnight! At the current rock temperature beneath Carlsbad Cavern, the process would have taken many thousands to millions of years. Thus Mr. Oard's assertion that cave dissolution might have taken place during the Flood is entirely contrary to the facts.

In summary, Mr. Oard's timelines does not allow enough time 1) for oil to have matured; 2) for oil to have chemically degraded; 3) for sulfuric acid to be transported to the site of dissolution, let alone dissolve the massive caverns; 4) for the water table to drop substantially, creating a vadose zone environment; and 5) for decorative speleothems (some the size of trees!) to have precipitated.

3) Geochronological mishap: Since my focus here is on the age of Carlsbad Cavern, I will conclude with Mr. Oard's misunderstanding of the available geochronological data. Since Mr. Oard must reject all radiometric dates from cave samples—though he does not explain why, scientifically, we should—he ends the article by blankly asserting that the available data is contradictory:

"It is of further interest that the dating of alunite resulted in significantly older dates for...caves in the Guadaloupe Mountains. The new dates range from 4 to 12 million years (Ma)...Previously, the cavern was dated at 1.2–0.75 Ma, or as much as 3 Ma based on the timing of mountain uplift. The younger dates were not only based on field evidence, but also on paleomagnetic, uranium-series, and electron-spin-resonance dating...This does not give one much confidence in dating methods." (emphasis added)

If you also read my last post, then Mr. Oard's error might seem obvious. Polyak et al. (1998) did not introduce 'new dates' for the cave, as though to correct available ones. Rather, the various studies were dating entirely different events.

Paleomagnetic, U-series, and electron-spin-resonance methods are applied to speleothems or sediments within the caves. The 40Ar/39Ar ages of Polyak et al. (1998) were applied to alunite formed during cave dissolution. Obviously, speleothems and cave sediments cannot form until the cave has actually been carved out, so we would expect these dates to be younger than those for the alunite. Despite the confidence in Mr. Oard's sarcastic assessment, it remains a non sequitur.


The available geochronological data are thus perfectly consistent with conventional understanding of Carlsbad Cavern's geological history. Uplift of the Guadalupe Mountains began some time in the early Cenozoic. In the mid-Miocene, H2S was introduced to the groundwater, was oxidized to sulfuric acid, and began dissolving caverns near the water table. The water table dropped slowly over the rest of the Miocene, and into the Pliocene, carving out Carlsbad Cavern around 4 million years ago. Since that time, continued fall of the water table created a vadose zone within the cavern, allowing for the precipitation of speleothems (as early as 1.2 Ma or more), and that process continues today.

References Cited:
Brook, G.A., Ellwood, B.B., Railsback, L.B., Cowart, J.B., 2006, A 164 ka record of environmental change in the American Southwest from a Carlsbad Cavern speleothem: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 237, p. 483–507.

Hill, C.A., 1990, Sulfuric acid speleogenesis of Carlsbad Cavern and its relationship to hydrocarbons, Delaware Basin, New Mexico and Texas: American Association of Petroleum Geologists Bulletin, v. 74, p. 1685–1694.

Polyak, V., McIntosh, W.C., Güven, N., Provencio, P., 1998, Age and Origin of Carlsbad Cavern and Related Caves from 40Ar/39Ar of Alunite: Science, v. 279, p. 1919–1921.

Polyak, V., Rasmussen, J.B.T., Asmeron, Y., 2004, Prolonged wet period in the southwestern United States through the Younger Dryas: Geology, v. 32, p. 5–8.

Tritlla, J., Cardellach, E., Sharp, Z.D., 2001, Origin of vein hydrothermal carbonates in triassic limestones of the Espadán Ranges (Iberian Chain, E Spain): Chemical Geology, v. 172, p. 291–305.

Saturday, May 14, 2011

How to put the 'paleo' in paleoclimatology: isotopic records from speleothems

Caves are perhaps the most fascinating recorders of Earth's recent climate. Though not the most popular proxy—being stuck in a world of paleoclimatology where tree rings and ice, lake, and marine cores make all of the headlines—caves have the potential to record rainfall and soil data at high resolution for thousands of years. The results are not only locked away in dark rooms, safe from the elements, but are contained within some of the most beautiful rock formations known to us: speleothems.

And that is why we take hammers to them, saw them in half, and mount them on a micro-drilling stage in the isotope geochemistry lab.

Paleoclimate records from stalagmites

By way of preface, I am slightly biased in my attitude, because I've spent the past year analyzing isotopic records from stalagmites around North America. But if you were to consider my position for a moment, I don't think you would disagree. Consider, for example, how a cave forms. Precipitation (or spring meltwater) trickles down through a carbonate aquifer, picking up metal cations (like calcium) and bicarbonate anions along the way. Steady drips of groundwater quickly lose their carbonate concentration to the cave atmosphere by CO2-degassing as they hang from the cave roof (or from stalactites). When the drip hits the floor, further degassing initiates the precipitation of aragonite or calcite (CaCO3). Give the process tens to hundreds to thousands of years, and you have a stalagmite with concentric laminae that reach toward the apex.

As it turns out, the carbon and oxygen isotopic chemistry of the laminae depends primarily on rainfall source and amount, as well as soil activity. We can test these hypotheses by comparing isotopic records from very recently formed stalagmites with human/instrumental climate records, or by comparing the isotopic chemistry of rainwater to dripwater to aragonite in stalagmites over several years. In general, oxygen isotopes are depleted in 18O (heavy oxygen) during wet periods and enriched in 18O during dry periods, but the source of precipitation also plays a role (high vs. low latitude; Atlantic vs. Pacific). Therefore, speleothem records from North America record not only rainfall amount, but migration of the Gulf Stream, El Niño cycles, and other multidecadal oscillations.

Depending on the residence time of the aquifer (i.e. how long, on average, the water takes to get from rainfall to 'cave'-fall), the groundwater will mix thoroughly with that from the past month to the past several years. This means that isotopic inputs from rainfall represent a weighted average for that time interval—good news for the paleoclimatologist. Also, most carbonate ions in groundwater are dissolved within the upper soil horizons during the wet season, so one may track soil processes as well.

Both the hydrological and geochemical processes behind speleothem formation are now very well understood. With few exceptions, stalagmites have been proven faithful proxies of climate. If the sampling process were not so destructive, I believe they would also gain some popularity.

High-resolution age dating of speleothems: answering the 'when' of cave formation

Understanding the climatic significance of isotopic ratios in stalagmites is great, but unless we know when each laminae formed, the records are quite useless. So how does one discern the 'paleo' in paleoclimate? If you've ever had the opportunity to visit a cave set up for guided tours (Cave of the Winds, Colorado and Timpanogos Cave, Utah are on my list), the tour guide likely pointed out a speleothem that had been measured over time: "You see, 50 years ago, this guy was 5 cm shorter! So stalagmites grow about 1 mm per year, and since now it's 105 cm tall, it must have been growing for...1,050 years!"

This approach is simple and intuitive, and in some cases may provide a decent approximation of stalagmite growth. But the fact is, the rate of growth for individual stalagmites can vary over time, due to fluctuations in climate. For example, high amounts of rainfall and soil activity can promote speleothem growth. Low ambient CO2 and high ambient temperature in the cave can also promote growth by increasing the rate of precipitation in each drop. Since we know all of these factors will change over the life of a speleothem, we need a more precise method of dating.

Unfortunately, the popular notion that stalagmite growth-rates are simply extrapolated, like above, has caused young-Earth critics to focus on examples of rapid stalactite growth—some rather odd—to make that case that limestone caves are compatible with a young-Earth, Flood model. But the arguments typically go like this: we know that speleothems can form rapidly under favorable conditions; therefore, all speleothems formed rapidly under favorable conditions. The informal logical fallacy is rarely challenged, because few people are familiar with actual method used to date speleothems.

Uranium-thorium (U-series) dating of speleothems

Most speleothems are originally precipitated as aragonite (calcium carbonate). But like any mineral, the aragonite is bound to contain some impurities. Magnesium, strontium, sodium, barium, and lithium are incorporated in trace amounts. As an aside, the ratio of calcium to these trace elements serves as an independent proxy of climate, occasionally used by ambitious geochemists. One of the most important trace elements, however, is uranium.

Why uranium? Because uranium is radioactive, and decays into thorium at a constant, known rate. By analyzing the current ratio of uranium and thorium isotopes, one can estimate the absolute age of laminae in speleothems. More specifically, the ratio of 234U (parent) to 230Th (daughter) is measured. But the ratio does not change like an hourglass model with time (as in the radiocarbon, K-Ar, and U-Pb systems), since the daughter product is also radioactive, and decays even faster than the parent. Let's take a closer look.

Money matters: a financial analogy
Imagine that you set up a bank account with $1,000 in savings and $0 in checking. Every month, 1% of the savings amount is transferred to checking, but 5% of the checking amount is...donated to charity. In this scenario, the money in savings represents 234-Uranium, and the money in checking represents 230-Thorium. Both accounts are constantly decaying at a constant rate, unique to each account, that depends on the residual balance. The money spent to charity represents the daughter product of thorium decay, which is neither measured in the rock nor this analogy.

At the end of the first month, zero dollars are donated to charity, because the checking account has zero dollars available. But 1%, or $10, will be transferred from savings to checking. The new balance: $990 in savings; $10 in checking. So at the end of the second month, 5% of $10, or 50 cents, will be donated to charity, and $9.90 transferred from savings to checking. The new balances: $980.10 in savings; $19.40 in checking. Easy enough?

In geology, we actually measure the ratio between the isotopes (i.e. $ in savings divided by $ in checking). If we know the rate of decay (what % is lost each month), and the original balance in at least one of the accounts, we can back calculate the time that has passed since the experiment started. Below, I have plotted the experiment over 100 months:

The yellow line represents the ratio between the two accounts. As you can see, the ratio changes very quickly at first, but eventually flattens out to equilibrium (hence the name "Uranium-Thorium Disequilibrium Dating"). This means that if one were to estimate the time passed based on the current ratio between the accounts, that estimate would be more precise at time = 0–30 months than at time = 30–100 months. Correspondingly, U-Th disequilibrium ages are most precise up to ~500,000 years, after which the change in 234U/230Th is too small to be detected.

Another limit occurs in very young samples, since the mass spectrometer is unable to detect thorium at exceedingly low concentrations. Thus ideal samples are uranium-rich to begin with, and are at least several years to several thousand years old. Personally, I have seen very precise (±1%) age estimates from U-rich samples, however, even between 0 and 100 years old.

Depending on the scientific importance of the sample, and given that each age datum costs ~$500 to analyze, between 2 and 20 U-Th dates are taken along the growth axis. This allows the paleoclimatologist to construct an age model for each speleothem, and attach real ages to isotopic records.

But aren't there a few assumptions involved?

Yes, some assumptions are made. That is how science progresses. But fortunately for us, most of those assumptions can be falsified/verified independently.

1) How do we know the initial ratio of U/Th isotopes? In oxic environments, uranium is fairly soluble and thorium is very insoluble. Since stalagmites form out of dissolved constituents of groundwater, we should expect very little, if any, thorium to be originally present (i.e. $0 in checking).

2) Does this assumption always hold? On the contrary, we expect this assumption never to hold, in the absolute sense. There will always be at least some thorium present. So to account for this, we measure the ratio of 238U to 232Th (two common isotopes). Both isotopes are radioactive, but their half-lives (4.5 and 14.05 billion years, respectively) are much longer than that of 230Th (75,380 years), and may be considered stable on shorter geologic timescales. Using the 238U/232Th ratio, the 232Th/230Th ratio, and the total concentration of uranium, we can estimate the initial concentration of 230-thorium. Typically, this value is insignificant, and will only change the age estimates by a maximum of 1% if left uncorrected. To put this in perspective, imagine that I started the experiment above with $1.50 in checking. In this case, the age estimate would be off by less than a few days.

3) How do we know whether any uranium or thorium was lost since crystallization? In speleothems, this is rarely a concern, since most ages fit very well into a growth model (i.e. they get progressively older along the axis, and result in globally correlated paleoclimate records). But if this assumption were challenged, one could use trace element data, petrography, and cathodoluminescence to test whether recrystallization of the speleothem caused a loss of soluble trace-elements. Also, any loss of uranium is likely to be localized, through microfractures in the speleothem. In this case, model ages taken from those points will show up as anomalous, and result in an unrealistic growth-rate curve. It is simply unreasonable to expect that uranium loss occurred systematically, shifting all the ages by a proportional amount.

4) How do we know the decay rates for both isotopes has remained the same? This is a matter of quantum physics, and a sound one at that. There is no reason to expect decay rates to change. If this were to happen, however, during the life of the speleothem, then the growth model would shift dramatically at a point, making it appear as though the speleothem started to grow many times faster or slower.

Are caves and speleothems consistent with the Flood model?

In short, no. The Flood model must consider modern caves and speleothems as post-Flood features. Even if one were to allow for the unrealistic scenario of accelerated nuclear decay during, the caveat would not apply to speleothems. Since thousands of speleothems have been dated beyond 5,000 years, there remains a significant challenge to young-Earth Flood geologists.

We can also consider speleothem records in the larger climatic context. For example, speleothem records match up very well with ice core records (dated by counting annual layers), marine/lake core records (dated by counting annual layers and radiocarbon methods), and tree ring records (same as above). Thus we have multiple independent methods yielding essentially the same result. Such concordance highly corroborates the use of each method to track the Earth's climate history, and thoroughly falsifies the Flood model.