Reefs and Young-Earth Creationism

last updated: 04/07/2002

Eniwetok Atoll as a Post-Flood Reef

The Eniwetok atoll is a reef in the Marshall Islands. The US detonated hydrogen bombs there in the 1960's. Drill cores show that this reef is about 4600ft thick, and rests atop the surface of a submerged volcanic seamount. The entire thing is composed of corals, calcerous algae, foraminifera, echinoderms, oysters and so forth, which are cemented together. In terms of texture and composition, this reefs is very similar to buried reef strucures in the fossil record. How quickly could it form? Could it form in the 4500 year post-flood period?

Doing research on the Eniwetok atoll, I decided to visit some creationist websites and see how they explained these structures in terms of an earth less than 10,000 years old. According to the "Stand for Jesus" web page, the oldest living coral reef is only 4200 years old. This claim can be found on dozens of creationist web pages, and is evidently widely accepted as an accurate estimate. Answers in Genesis makes the same claim: ". . . reef growth rates have been reported as high as 414 millimetres per year in the Celebes. At such a rate, the entire thickness of the Eniwetok Atoll could have been formed in less than 3,500 years. To maintain that Eniwetok Atoll could have formed in the time-span since the Flood recorded in Genesis is not at all inconsistent with real-world evidence." I could not find any articles at ICR addressing the issue.

The Evidence for Rapid Reef-Building

Let's examine the "real-world evidence" cited for this conclusion. Every one of the creationist web pages I found seem to be relying, directly or indirectly, on two papers, one by Arthur Chadwick, and an Origins paper by A. A. Roth. These papers list various estimates of reef growth rates from a variety of methods. Most of the estimates cited by Chadwick and Roth give long ages for the growth of a 1,400m coral reef. However, both authors include a single anamalously high estimate rate of 414mm(!)/yr. These estimates were based on "soundings" done in the early 1930's. They cite only a single source for this astounding rate, a 1932 paper by J. Verstelle, 'The Growth Rate at Various Depths of Coral Reefs in the Dutch East-Indian Archipelago', Treubia 14:117-126, 1932.

Virtually all of the other estimates in Chadwick's paper yielded rates of reef growth of 0.8-30mm or so, requiring many thousands or even millions of years to form a reef 1400m thick. For instance, Hubbard et al. (1990), estimated growth rates of 0.7 tp 3.3mm per year. Davies and Hopley (1983) estimated a *maximum* of 20mm/yr. Smith and Kinsey (1976) listed rates of 2-5mm/yr. Smith and Harrison (1977) listed rates of 0.8-1.1mm/yr, and so on. Many additional studies indicate Holocene reef growth histories on the order of 1-15mm/yr, with the upper range only being attained in reefs dominated by the fast-growing Acropora corals (e.g. Aronson et al., 1998; Hubbard, 2001). While Chadwick's paper included many reasonable estimates, his readers predictably siezed upon the one rate reported by Verstelle over 60(!) years ago, ignoring a massive body of more recent research on the subject.

Another odd thing is that both Roth and Chadwick's papers also included estimates of the growth rates of *individual corals,* and they showed that even most individual corals cannot grow nearly that fast (i.e. ~400mm/yr)! Most studies document maximum *coral* growth rates of only 10-50mm per year.

How Fast Can Reefs Really Grow?

By far the most contentious isse here is the rate at which reefs can grow. Studies of reef growth in the modern Pacific show that even under ideal conditions, the growth of the actual reefs is only on the order of 8-10mm a year (see below). Note that individual corals can grow a bit faster than this, but this cannot be used to estimate the growth rate of the *reef* itself, since the reef is not one giant coral, but is largely composed of billions of coral fragments that are broken by waves and cemented to the growing mass (see below).

So, assuming an average 10mm per yr growth rate, the Eniwetok Reef would require 140,000 years to grow to its present thickness. And this assumes no compaction, no destruction by storms, no temporal breaks in growth, continuous optimal growth rates, and adequate subsidence rates. All of these assumptions are entirely unreasonable, and thus any estimate based on extrapolation of optimal reef growth rates is clearly a minimum.

For instance, we know that there are at least 3 major weathered unconformities within the Eniwetok, at 300ft, 1000ft, and 2,800ft depth. These unconformities not only show the type calcite cementation which develops on exposed reef surfaces, they are also extremely enriched in pollen, most of which appears to be from Mangrove trees. Mangrove trees are growing on many exposed reefs in the Pacific today. In some cases, the pollen is so abundant that there are an estimated 10,000 or more pollen grains per gram (Leopold, E. B., 1969, "Bikini and Nearby Atolls, Marshall Islands, Miocene Pollen and Spore Flora of Eniwetok Atoll, Marshall Islands," U. S. Geological Survey Professional Paper 260-II , U. S. Government Printing Office, 53 pp). This shows that at each of these unconformities, the reef surface remained exposed for an extended period of time, although exactly how long is not known.

Subsidence as a Limiting Factor of Reef Growth

And there is one more simple reason why such high estimates assumed by AIG and others are entirely unreasonable. The reason is this -- the net growth of the reef can only be as fast as the net subsidence of the seamount or platform on which it is growing. This is a limiting factor. Thus, even if a reef could grow at, say, 3cm per year rather than around 1cm or less as virtually all of the empirical estimates show, the reef can still only grow to the surface of the water. Where rates of subsidence of seamounts can be measured, it is only a few mm per year. Subsidence rates have been estimated with high precision for the Hawaiian Islands, which are similar in most respects to the submerged seamount atop which the Eniwetok atoll rests. These islands are subsiding at only a few mm per year.

Carbon dating of drowned reefs on the side of Hawaii show that it has subsided at this slow rate for hundreds of thousands of years. In fact, its a little more interesting than that. You can actually predict the radiometric ages of a drowned coral reef, with considerable accuracy, simply by dividing the depth in mm by the observed subsidence rates in mm per year.

Radiometric ages of Hawaiian corals compared to ages predicted by extrapolating observed subsidence rate of 2.7mm per year. Judging by the close correlation between predicted age and actual age, the rate of subsidence for the island of Hawaii has remained very close to 2.7mm per year throughout at least the last half-million years.

But for agument's sake, let's disregard the radiometric dates. Do any YECs have a plausible explanation for the growth of a 4600ft thick reef in 4500 years of post-flood time? And if YECs really think reefs can grow at rates of 100-400mm per year or more, when can we expect to see the research documenting this, and the evidence showing that the required conditions for this were somehow satisfied throughout post-flood times, while not being satisfied anywhere today? Remember, even if we multiply the fastest observed reef growth rates by a factor or 10, and assume *continuous* maximum growth rates, and assumed *no* erosional breaks or storm damage, and assumed that subsidence was somehow *greatly* accelerated, we would *still* need 14,000 years for the growth of Eniwetok.


The Capitan Reef: A Flood Deposit?

Virtual Field Trip to Permian Reef Complex
The Permian Reef and the Guadalupe Mountains
Midland Basin Salts
A giant Permian sponge-algae reef from China

The Capitan Reef is a giant sponge/algae/bryozoan reef or organic bank which grew around the margins of the Delaware Basin during the late Permian. It has a composite length of ~350 miles, and is over 1000ft thick in places. It can be seen exposed in the Guadalupe mountains, but further north the structure is buried by thousands of feet of Permian, Triassic, and Quaternary sediments. Deep well cores show that the Capitan strata are underlain by over 3000ft of Permian, Pennsylvanian, Mississippian, Silurian and Ordovician limestones and shales (e.g. Hughes, 1954). Numerous well cores have been taken through the reef, and these show numerous bryozoans and sponges, many in "life position," cemented together by encrusing algae, microbial crusts (Kirkland et al., 1998) and carbonate cement.

Fagerstrom and Weidlich (1999) indicate that ~70-80% of the sponges with erect growth habits are preserved in growth position.

"On horizontal polished surfaces of 45 randomly distributed quadrats (areas = 200 - 400 cm2) from two localities (areas = 450 m2 and 5400 m2) near the northeast end of the Capitan outcrop belt, 74% of the sponges are preserved in their erect life positions and 26% are toppled fragments (n = 672). Most sponges are small; fragments of those with the weakest skeletons are randomly arranged, not current aligned. Successive generations of erect sponges built the initial accretionary reef framework. Many sponges were subsequently supported in life position by very weakly skeletonized encrusters and/or syndepositional cement."

They conclude that:

"The data presented here indicate that the upper Capitan-Massive is a biological reef. It is not a 'garbage-pile' of cemented skeletal debris nor a 'hydrodynamic reef.' It has a skeletal framework built by the upward growth and accretion of erect sponges supported in growth position by other organisms. . ." (p. 175).

Immediately behind the boundstone "reef" core, we find richly fossiliferous grainstones. Kirkland and Moore note that "these dasyclad dominated back- reef sediments and their associated biota are indicative of shallow, hypersaline conditions. Few of these dasyclads exhibit broken or abraded segments and some thallus sections are still articulated suggesting that low-energy, hypersaline conditions occurred immediately shelfward of the reef. In addition, large-scale topographic features, such as possible spur and groove structures between Walnut Canyon and Rattlesnake Canyon, and facies geometries, such as the reef to shelf transition, resemble those found in modern shallow-water reefs. The organisms that formed the Capitan Reef appear to have lived in, and responded to, physical and chemical conditions similar to those that control the geometry of modern shallow-water reefs. Like their modern counterparts, they seem to have strongly influenced adjacent environments."

Dasycladales are a type of calcerous alga. They are exceedingly delicate, and thus are easily obliterated by turbulent water. The fact that so many articulated dasyclads are found in the backreef setting therefore is strong evidence against catastrophic "mass transport" of these sediments.

Further back, towards the shoreline facies (the Seven Rivers Formation), these grade into fossil-poor sediments containing stromatolites, "cryptalgal structures," teepee structures, nodular gypsum and gypsum "rosettes," mudcracks, and occasional thin layers of windblown sand, just like you find in some back reef environments and coastal sabkhas today. At the "shoreline" facies, these grade into terrestrial "redbeds."

On the forereef slope, we find a talus slope of reef debris grading basinward into marine sands and silts which contain minor layers of limestone. These diverse sedimentary and "facies" relationships are seen in modern fringing reefs enclosing restricted marine bains. Thus, we need to explain not only the Capitan Limestone "reef," but the whole set of sedimentary facies in which the reef is found.

The Castile/Saludo Formations - Ochoan Series

Above the reef complex exist about 260,000 thin layers of anhydrite and calcium carbonate (collectively the Castille Formation), each only about 1-1.5mm thick, which can be correlated over dozens of miles throughout the Delaware Basin (Anderson, 1982). There are about 1300ft worth of these thin, repetitive layers filling the Delaware Basin. Some of the couplets also contain tiny layers of organic rich shale. These bedded layers of salt are thought to be evaporites formed as the Delaware basin was periodically replinished with seawater, which evaporated, each time formed a thin couplet of carbonate and anhydrite. The thin organic shale layers are interpreted to have been deposited during brief periods of reduced salinity and thus higher biologic productivity, for instance periods when the basin was exceptionally full. These thin, laterally extensive "triplets" may be annual ('varves'), and Anderson (1984) claims that the laminae variation reflect Milankovitch-scale precession (circa 20,000 year) and eccentricity (100,000 year) cycles.

Another interesting fact about these thin carbonate/anhydrite couplets in the Castile is that the proportions of them to each other is just right for what you would expect from the evaporation of a pool of seawater of normal salinity.

Both above and adjacent to the delicately layered salts of the Castile Formation lies the massive Salado Formation, consisting of about 600 meters worth of bedded halite and other salts. At its thickest, these Ochoan series salts together have a thickness of around 1300m, a lateral subsurface extent of 150,000km2, and a volume of about 65,000km2 (Blatt and Tracy, Petrology, p. 329)! These salts show a concentric arrangement, as would be expected from a dessicated basin. Blatt and Tracy (Petrology, 1996, p. 330) write:

The distribution of sedimentary rock types in the Deleware Basin shows a crude concentric zonation, characteristic of a dessicating basin. Along the outer fringe are either fine-grained clastics or carbonate rocks, depending on the location of nearby land areas. Within this outer fringe are gypsum and/or anhydrite, followed by halite, and finally by the more soluable salts in the center of the dessicated area - salts such as polyhalite, langbeinite, carnallite, and sylvite.

Kirkland, B.L.; Moore, C.H. Jr. 1997. New evidence for the barrier reef model, Permian Capitan Reef complex, New Mexico. AAPG Annual Meeting Abstract, p. 696.

"Recent paleontologic and petrologic observations suggest that the Capitan Formation was deposited as an organic or ecologic reef that acted as an emergent barrier to incoming wave energy. In outcrops in the Guadalupe Mountains and within Carlsbad Caverns, massive reef boundstone contains a highly diverse assemblage of frame-building and binding organisms. In modern reefs, diversity among frame builders decreases dramatically with depth. Marine cement is abundant in reef boundstone, but limited in back-reef grainstone and packstone. This cementation pattern is similar to that observed in modern emergent barrier reef systems. Based on comparison with modern analogs, these dasyclad- dominated back- reef sediments and their associated biota are indicative of shallow, hypersaline conditions. Few of these dasyclads exhibit broken or abraded segments and some thallus sections are still articulated suggesting that low-energy, hypersaline conditions occurred immediately shelfward of the reef. In addition, large-scale topographic features, such as possible spur and groove structures between Walnut Canyon and Rattlesnake Canyon, and facies geometries, such as the reef to shelf transition, resemble those found in modern shallow-water reefs. The organisms that formed the Capitan Reef appear to have lived in, and responded to, physical and chemical conditions similar to those that control the geometry of modern shallow-water reefs. Like their modern counterparts, they seem to have strongly influenced adjacent environments."


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