Volcanic Ash Beds

"In view of their enormous size and continent-wide distribution, it is surprising that these ash beds are not directly associated with any notable faunal extinction event or any significant lithologic change in the sedimentary record." — Stig Bergström and colleagues, on the Ordovician Deicke, Millbrig and Kinnekulle ash beds, 2004¹

"A major difficulty in correlating these beds results from the diachronous age of the sub-Tippecanoe unconformity and the equally diachronous nature of the overstepping Tippecanoe sequence." — Dennis Kolata, Warren Huff and Stig Bergström, 1996²

Summary

Volcanic ash beds are layers of ash from explosive eruptions, found through the rock record as tuffs, as bentonite clays in marine and lake rock, as K-bentonites where burial has changed the clay, and as tonsteins inside coal.  This article asks what they show about how the rock record formed, and how fast.

The verdict:  each ash bed is one short event, as young-earth geologists say, but the record holds dozens to hundreds of them stacked in single sections with sediment made by living things between them, and where fingerprinted ash beds have been traced against unconformities, the surfaces were cut at different times in different places.  Young-earth geologists are right about the bed and wrong, so far as the published evidence goes, about the stack.

1. One eruption, one bed, in hours to days. Mount St. Helens spread ash over 57,372 km² in a day, Pinatubo's ash reached a trap 3,730 m down in the South China Sea within about 58 hours, and the largest ancient falls covered millions of square kilometres. Andrew Snelling calls ash beds "event horizons," and both sides use them as time lines.³⁴⁵
2. The glass-to-clay reaction is not a clock here. Hot water turns glass to clay in years, cool lake beds keep glass far longer, and no model needs the clay to form fast, since a buried glass bed can alter at any time afterwards. None of the young-earth sources read gives a rate.
3. The stack is the evidence. More than 60 Ordovician ash beds in North America and more than 150 in Baltoscandia; up to 80 or more in the Lower and Middle Devonian of the Appalachians; more than 100 in 181.8 m of the Smoky Hill Chalk; over 40 in 70 m at Hell Creek; 179 in 60 m of Danish diatomite.⁶⁷²¹⁸⁹ Between the falls lie limestone, coccolith chalk, diatom ooze or peat, and in places a hardground.
4. Priced on the young-earth model's own numbers, the gaps shrink to hours. This article's arithmetic on Clarey and Werner's calendar and average thicknesses puts the Deicke and Millbrig ash beds, two of the largest falls in the rock record, 3.5 to 4.6 hours apart, a fall every 2.5 hours through the Smoky Hill Chalk, and two Smoky Hill falls four minutes of chalk apart.¹⁰ No young-earth source read for this article gives a count of Flood eruptions, and two young-earth treatments, Tyler's on the chalk and Whitmore and Garner's general criterion, treat many well-kept ash horizons as a sign of rock laid down outside the Flood.¹¹¹²
5. Ash fell into the sea, onto peat and onto bare rock. Marine beds are graded and sharp-based. Tonsteins are ash on peat swamps, kept because nothing else was settling there. At the base of the Tippecanoe megasequence, ash lies in hollows and in a 15 m bed in a sinkhole on limestone exposed before the sea returned, which is hard to square with Tim Clarey's reading that the water "may never have drained" there.²¹³
6. Tonsteins answer the floating-mat question. Roots grew into the ash after each fall, and the coal above records plants coming back. That rules out a dead floating mat. A living mat is not ruled out by tonsteins alone, and the rooted soils under the coal decide it.¹⁴
7. The unconformities overview's test has been made inside the megasequences, not at their bases. Fingerprinted Ordovician ash beds pinch out on the Kankakee Arch, are eroded off the Nashville Dome and the Cincinnati Arch, and converge at the Black River-Trenton unconformity where most rock is missing, while basinward the surface fades and the beds run on.²²¹⁵ At the megasequence bases no fingerprinted ash bed has been traced, though the specialists call the Tippecanoe base diachronous.²
8. Ash-bed dating has its own article. Radiometric Concordance takes it up. This article uses no radiometric age.

Part 1: Each ash bed is one short event

What the words mean

An explosive eruption shatters magma into glass shards and crystals called tephra, or ash when the grains are fine.  Where the ash settles and hardens into rock it is a tuff.  Over time the glass reacts with water and turns to clay.  A bed of ash turned to smectite clay, usually in marine or lake rock, is a bentonite.  A K-bentonite is an old bentonite whose clay has been changed by burial into a potassium-rich mixed clay of illite and smectite.²  A tonstein is a thin bed of kaolinite clay inside coal, made from ash that fell on a peat swamp, where acid water altered it.¹⁴  These are one thing in different settings.  Bruce Bohor and Donald Triplehorn note that Masek "traced the lateral transformation from bentonites to coal tonsteins in the central Bohemian basin," and that Waage traced kaolinite tonsteins in Colorado "into marine smectitic bentonites."¹⁴

How far and how fast ash falls

The best measured modern fall is Mount St. Helens on 18 May 1980.  The ash cloud's front "advanced rapidly to the northeast at an average velocity of about 250 km/hr during the first 13 min after eruption," and then at "about 100 km/hr over the first 1,000 km."  It passed Yakima, 135 km away, by 9:45 in the morning, and Spokane and Moscow, Idaho, about 400 km away, by about noon.  The eruption dropped at least 1.1 km³ of uncompacted tephra, and the ash heavier than 0.1 gram per square centimetre covered 57,372 km².³³³

The 1991 eruption of Pinatubo in the Philippines shows what happens when ash falls into deep water.  Sea-floor cores show the ash "blankets an area of at least 37 x 10⁴ square kilometers," and "Thickness varied from 6.2 centimeters close to Luzon Island to <0.1 centimeter at the continental slope off southeastern Vietnam."⁴  Ash reached a sediment trap moored at 3,730 m depth, 586 km from the volcano, about 58 hours after the eruption, so it sank at "greater than 1,550 m/day."⁴  That is far faster than single grains sink.  Fine grains clumped together, and loaded water sank as a current, which can move ash down "1–3 orders of magnitude faster than possible by Stokesian settling."¹⁶¹⁷  Andrew Snelling, in his two-volume young-earth geology text Earth's Catastrophic Past, cites this case:  the ash layer "formed on the sea-bed within just three days!"⁵  He is right about the speed.¹⁸

Larger eruptions spread farther.  Yellowstone's Huckleberry Ridge Tuff is "more than 2,450 km³," and the windblown ash of the Yellowstone eruptions "can be found in Pleistocene deposits from California to Iowa, and Canada to Mexico."¹⁹¹⁹  The Toba eruption in Sumatra put "at least 800 km³" of ash in the air, and its glass has been found in Lake Malawi, "∼7,300 km from the caldera."²⁰²¹

So one eruption lays a single bed over tens of thousands to millions of square kilometres in hours to days, on land and on the deep sea floor.  Young-earth and mainstream geologists agree on this.  Snelling calls ash beds "'event horizons,' because of each being laid down essentially instantaneously by single volcanic eruptions."⁵

What a fall into water looks like

Richard Fisher and Hans-Ulrich Schmincke's textbook Pyroclastic Rocks gives the signs.  "The lower contacts of submarine fallout ash layers are generally quite sharp in contrast to the more diffuse upper boundaries."  The heavy crystals sit at the base and the light pumice at the top.  The fuzzy top "is explained by most workers as due to bioturbation," animals burrowing into the ash after it landed.⁷⁷  At Pinatubo, ash layers thinner than about 0.1 cm were already full of "small-scale burrows," while layers thicker than 2 cm were "undisturbed" when they were cored.⁴  An ash bed laid by a current instead of a fall shows "no density or size grading" and is mixed "with foraminifera and terrigenous debris throughout."⁷  Ash that fell into a peat swamp is not graded, because the water was shallow, while "marine bentonites almost always show graded bedding because of the thick water column through which the ash must settle."¹⁴

How glass turns to clay, and why this article does not use the rate

Glass reacts with water.  "Bentonites generally form by diagenetic or hydrothermal alteration under the influence of fluids with high-Mg content and that leach alkali elements," in Warren Huff's summary.²²  In a peat swamp, acids from rotting plants turn the glass to kaolinite instead.¹⁴  Burial heat later turns smectite into the illite-smectite of a K-bentonite.²

The speed of the reaction depends on heat and water, and it covers a huge range.  Richard Hay wrote that "Reaction rates of glass range from a few hundred years to tens of millions of years, depending on composition of the glass and nature of the chemical environment."²³  At Surtsey, the Icelandic island that rose from the sea in 1963, a drill core recorded "12 yr of hydrothermal alteration of basaltic tephra":  "At 60 °C, <40% of the glass is palagonitized, but above 100 °C, >90% is palagonitized."²⁴  Hot water alters glass in years.  In cool lake beds of southwestern Idaho, by contrast, the tephra beds "are unaltered or altered to smectite," and "some tephra consists of about 90 percent glass."²⁵

None of the young-earth sources read for this article gives a rate for bentonite formation.  Snelling says the more than 100 bentonites of the American chalk come from explosive eruptions "late in the Flood year," and that "the bentonite is derived from in situ decomposition of volcanic ash."⁵  He gives no time for the decomposition.  Carl Froede writes that "Changing environmental conditions (e.g., marine to freshwater) resulted in the further alteration of the bentonite clay to a montmorillonitic clay," also without a time.²⁶

This article sets the alteration rate aside, for a plain reason.  No model needs the clay to form fast.  A glass bed buried during a Flood year could have turned to clay at any time since, in burial heat, and the young-earth timeline allows thousands of years for that.  The glass-to-clay reaction is therefore not a clock that separates the two accounts.  What does separate them is how many falls are stacked in one place and what lies between them, which Part 3 counts.

Part 2: Ash beds are time lines, and both sides use them that way

An ash fall reaches the ground or the sea floor over a wide area within hours to days of the eruption, as Part 1 showed.  So one ash bed, traced from place to place, marks very nearly one moment wherever it is found.  Mainstream stratigraphers call such beds event beds, and they use them as the most exact time lines the rock record holds.  Young-earth geologists use them the same way.  Tim Clarey of the Institute for Creation Research cites ash-bed dates to argue that the base of the Hell Creek Formation in Montana and the Dakotas "is thought to be significantly diachronous," meaning that it was laid down at different times in different places.²⁷  That is the same logic this Part uses.

How a bed is shown to be one bed

Two clay layers can look alike and be different falls.  So the bed is matched by chemistry, not by looks.  Dennis Kolata, Joyce Frost and Warren Huff measured 26 elements in the Ordovician ash beds of the upper Mississippi Valley in 1986.  Each bed carries its own fingerprint, and "The distinctive chemical signatures of the Deicke and Millbrig have been measured in outcrop and subsurface samples between southeastern Minnesota and southeastern Missouri, a distance of about 900 km."²⁸  Later work matched the crystals inside the beds.  Charles Mitchell and colleagues found that apatite and glass trapped in quartz from the Millbrig at eight sites in Kentucky, Missouri, Virginia and Pennsylvania match a bed at Dexter, New York, and called the Millbrig "a key stratigraphic marker horizon that is regionally synchronous over much of eastern and central North America."²⁹

The largest ash falls known

Two Ordovician ash beds, the Deicke and the Millbrig, run through the limestones and shales of eastern and central North America.  A third, the Kinnekulle, runs through Scandinavia and the Baltic.  Stig Bergström, Warren Huff, Dennis Kolata and two colleagues, the people who traced them, summarized them in 2004.  The beds "are locally 1-2 m or more thick and before compaction, they apparently represented ash layers with an original thickness of at least four times that figure."  The Millbrig covers "at least 2.2x10⁶ km²" of North America, and the Kinnekulle at least 690,000 km² of northwestern Europe.¹  The erupted magma is estimated at 1,509 km³ for the Millbrig and 972 km³ for the Kinnekulle, against 0.2 km³ for Mount St. Helens in 1980.¹  The Millbrig alone is about 7,500 times the 1980 eruption.¹⁰  Both beds thicken toward the southeast, from a few centimetres in the Mississippi Valley to 1 or 2 metres in the southern Appalachians, so the volcanoes lay off the old east coast.¹

Two points here go to the young-earth side.  First, the Millbrig and the Kinnekulle are not single blasts.  Bergström and colleagues report that "both Millbrig and Kinnekulle include multiple ash beds that apparently represent separate, in time very closely spaced, eruptions."¹  A metre of ash can be several eruptions a short time apart.  Second, the same authors say that radiometric dates on these beds scatter badly.  About a dozen ages have been published for each bed, with "a considerable spread (more than 10 million years for each bed)," and they call the radiometric evidence "inconclusive" on whether the two beds are one fall.¹  The correlation rests on fossils and on a carbon-isotope shift found just above both beds, not on the dates.  Nothing in this article depends on those dates.

What an ash bed shows that a rock boundary cannot

Rock types change from place to place, and geologists draw formation boundaries where the rock changes.  An ash bed ignores those changes.  Kolata, Huff and Bergström found the same kind of altered ash in "shallow marine carbonate platform, carbonate slope facies, deep-water turbidites, black shale facies, and near-shore red-bed siliciclastics."²  Wherever one fingerprinted bed passes from limestone into shale, the limestone and the shale were forming side by side at that moment.

That lets an ash bed test whether a rock boundary is one moment.  The Black River Group of limestones lies below the Trenton Group across much of eastern North America, and the change between them is sharp.  In the Mississippi Valley the Millbrig lies above that change, in the Trenton.  But "in the area of southwestern Ohio, as throughout most of the Illinois Basin, the Millbrig lies in the upper part of the Tyrone Limestone (=Black River Group), overlain by as much as 2 m of pure micritic limestone."  So "the micritic limestones in the upper part of the Tyrone were deposited in southern Ohio at the same time that basal Trenton shales were deposited in the Mississippi Valley," and the hard, bored surface at the top of the Tyrone "is either diachronous … or, more likely, there are multiple hardgrounds."²  A prominent rock boundary that looks like one surface is, by the ash bed, two or more surfaces at different times.

The same in younger rock

The pattern is not special to the Ordovician.  Cretaceous bentonites in the marine shales of Wyoming include a bed 3 cm thick traced about 160 km over an area of 2,540 km², according to Slaughter and Early, as Fisher and Schmincke report them.⁷  William Elder of the U.S. Geological Survey wrote in 1988 that "Four bentonite beds near the Cenomanian-Turonian Stage boundary … can be traced through much of the western interior of the United States," and he used their thickness maps to place the volcanoes northwest and southwest of the seaway.³⁰  Bradley Sageman and colleagues add a caution that applies to every such claim.  Some bentonites "are observed to vanish and reappear in correlated stratigraphic sections spanning significant distance," and without chemical, mineral or radiometric support "most correlations are hypotheses."³¹  The Ordovician beds above meet that standard, because they were fingerprinted.  Many Cretaceous correlations have not been.

In the Hell Creek region of Montana, at the Cretaceous-Paleogene boundary, Courtney Sprain and colleagues sampled ash beds from ten sections over about 5,000 km² and found that "Several distinctive tephras can be correlated between sections separated spatially by as much as ~60 km."⁹

Part 3: How many falls, and what lies between them

One ash bed says nothing about time.  It fell in hours or days, on any account.  The question is what lies between one fall and the next, and how many falls are stacked in one place.  Those can be counted.

The counts

The day ranges are Clarey and Werner's, from their 2023 Flood model, which assigns the first three megasequences to "Days 1-40," the Tippecanoe to "Days 20?-30?" and the Zuni to "Days 90?-150."³²  The counts are the authors' own.⁶⁷²¹⁸⁹

What lies between them

Between the Deicke and the Millbrig in central Tennessee lie "Approximately 6 m to 8 m of limestone."  In Johnson County, Kentucky, the gap "thickens from 8 m to 12 m" within 20 km.²²  Near South Carthage, Tennessee, a third ash bed 15 cm thick lies 0.6 m below the Millbrig.  "In an outcrop situated 4 km to the south, this bed is absent, but its position is marked by a prominent hardground."²  A hardground is a sea floor that was cemented to rock while it lay exposed, and the one at the top of the Tyrone Limestone in Ohio carries "filled borings that penetrate 3 cm into the Tyrone."²

In the Smoky Hill Chalk the material between the bentonites is chalk, which is made of the plates of microscopic algae called coccoliths.  The spacing can be tight.  Donald Hattin's first marker unit is "Three bentonite seams in a 22 cm (0.72 ft) interval, separated by 5.2 cm (0.17 ft) and 12.8 cm (0.42 ft) beds of chalk," and the Smoky Hill has no hardgrounds:  "Hardgrounds, such as those recorded commonly in European chalk deposits, are lacking."⁶  In the Hell Creek region each ash bed sits in a lignite, a bed of compacted peat, and the lignites alternate with river sands and muds that carry successive faunas of dinosaurs and mammals.⁹  In Denmark the 179 ash layers lie in diatomite, the silica shells of microscopic algae, and "have vertical grading typical of marine fallout tephra … and lack current-induced sedimentary structures."⁷

What the Flood calendar asks of them

Clarey and Werner publish both a calendar and an average thickness for each megasequence on each continent.  Dividing one by the other gives the average rate at which their own model lays down rock.  For North America the Tippecanoe averages 0.417 km thick and the Zuni 1.027 km.³²  That is about 42 m a day for the Tippecanoe in ten days, or about 10 m a day if it is given all of the first forty, and about 17 m a day for the Zuni.  At those rates:

These figures are this article's arithmetic on Clarey's own numbers, done in research/ash-pricing.ts.¹⁰  They are averages.  Clarey's model lays rock down in pulses, so some intervals would be shorter and some longer.  But the averages show the size of the demand.  Between two of the largest eruptions in the rock record, each hundreds of cubic kilometres of magma, the sea had to lay down several metres of limestone in a few hours.  At South Carthage the sea floor had to be cemented hard enough to hold a hardground within the time it takes to lay down 60 centimetres of rock.  In the Smoky Hill a new eruption had to arrive every two or three hours for eleven days, each leaving its own clean layer, and in one place two falls came four minutes of chalk apart.

The young-earth answers, and what they leave

Young-earth geologists do not all read these beds as Flood deposits.  David Tyler, then of the Biblical Creation Society, wrote in 1996 that "Like hardgrounds in the European chalks, bentonites in the Niobrara Chalk identify stationary surfaces."  If the chalk was laid in deep, quiet water, "the bentonites provide evidence for over 100 stationary surfaces within the Niobara Chalk which, in turn, is evidence against catastrophic scenarios involving turbulent waters and few cycles of deposition."¹¹  Tyler argued against long times too:  "Since these beds were not destroyed by burrowing or by bottom currents reworking the sediment, long timescales are improbable."  He moved the chalk after the Flood, into "a period measured in decades."¹¹  The Chalk and Limestone article prices that move.  Clarey's model keeps the Smoky Hill in the Zuni, inside the Flood.

Hardgrounds have a published young-earth answer.  Tas Walker argues that they are sea floor cemented during dewatering and that their borings are moulds pressed in during compaction, and John Woodmorappe asks whether the clean cut through hard grains proves that the whole layer was rock.  The Flat Gaps article sets out that exchange.  It finds that the hardground test survives only in a narrow form, a boring that cuts cement bridging two grains, and nobody has published that thin section for these beds.  So this article does not rest its case on the hardgrounds.

What does not depend on hardgrounds is the count itself and what each interval holds.  The intervals hold coccolith chalk, diatom ooze and peat, each of which is made by living things growing in place, and the falls are separate, graded layers that did not run into one another.  A model that puts these packages in the Flood has to supply dozens to hundreds of separate eruptions, a fall every few hours, and the growth or delivery of the material between them, in each package.  None of the young-earth sources read for this article gives that count.  Jerry Akridge and Carl Froede write of "subsequent short-spaced eruptive volcanic events" at Ashfall Fossil Beds in Nebraska, which they place after the Flood, and Snelling of "numerous volcanic eruptions" during the Green River shales.³³⁵  John Whitmore and Paul Garner give the one young-earth prediction about counts that can be checked.  They expect ash beds to survive better after the Flood than during it:  "Ash beds might not be as well-preserved during the Flood because ash may have been easily mixed into other sediments during aqueous turbulence.  Therefore, we might expect more ash horizons following the Flood than during the Flood."¹²  On their own placement of the end of the Flood, near the Cretaceous-Paleogene boundary in Wyoming, every bed in the table above except the Hell Creek and Danish ones lies inside the Flood, and those beds were not mixed into the sediment.¹²

Part 4: Where the ash landed: sea, swamp and bare rock

The signs from Part 1 sort the ancient beds by where they fell, the same way they sort modern ones.

Into the sea.  The Ordovician K-bentonites lie in marine limestones and shales, in settings that Kolata, Huff and Bergström list as platform, slope, turbidite, black-shale and near-shore red beds.²  The Millbrig in Tennessee "locally consists of two or three graded beds."²  The 179 Danish ash layers are graded and lie in marine diatomite.⁷

Into a peat swamp.  Tonsteins are the ash that fell on peat.  Bohor and Triplehorn explain why peat keeps thin falls:  "The coal-forming environment is well suited for preservation of thin air-fall deposits because it features low depositional energy, topographic depression, rapidity of burial by organic matter, and lack of detrital input due to the baffling effect of plant growth."¹⁴  In the Hell Creek region the ash beds "are almost exclusively found within lignite beds, probably due to preservational bias."⁹  In Kentucky the Fire Clay tonstein is missing in some places, which William Outerbridge of the U.S. Geological Survey reads as ash that "was not preserved, probably because it floated downstream as pumice."³⁴

Onto bare rock.  The surface at the base of the Tippecanoe megasequence, called the sub-Tippecanoe or Knox unconformity in the eastern United States, carries ash that fell before the Tippecanoe sea covered it.  Near Utica, Illinois, clay beds that may be K-bentonites rest "on the sub-Tippecanoe unconformity where a significant part of the Whiterockian Series is absent as a result of subaerial erosion," and Kolata, Huff and Bergström suggest they "may represent the residuum of several ash falls that accumulated locally in depressions on the exposed carbonate rocks of the Sauk Sequence prior to the transgressive cycle that began with deposition of the St. Peter Sandstone."²  At Douglas Dam in eastern Tennessee, "One of the oldest K-bentonites is in a sinkhole in the Beekmantown Formation of the Knox Group on the sub-Tippecanoe unconformity," and "the 15 m thick bed was deposited in a depression on the unconformity … prior to deposition of the regionally extensive Lenoir Limestone."²  A sinkhole is a hole dissolved in limestone.  An ash bed 15 m thick is far thicker than any single fall, and Kolata and colleagues read it as "the accumulation and concentration of volcanic ash in a sinkhole."²  In the Devonian of the Appalachian Basin, Charles Ver Straeten found single K-bentonites that "occur variously on sequence-bounding unconformities."³⁵

What this asks of each account

The mainstream account expects all three settings, since the sea rose and fell across the continent and swamps grew on its edges.

Clarey's Flood calendar has a specific problem with the Tennessee sinkhole.  He reads the contact between the Sauk and the Tippecanoe in the eastern United States, limestone on limestone, as a sign that "the floodwaters may never have drained off these areas between the Sauk and Tippecanoe Megasequence cycles."¹³  The Douglas Dam sinkhole lies on that surface in that region, and on Kolata and colleagues' reading it gathered ash before the next sea arrived.  A young-earth geologist has a published answer for sinkholes in general.  Emil Silvestru argues that "rapidly accumulating Flood sediments periodically emerged," and that degassing and dewatering "would have developed a wide range of negative relief in a matter of days."³⁶  That answer would also let ash fall on the briefly exposed surface.  But it needs the surface to have been out of the water, which is the opposite of "never drained," and nobody has worked out whether a 15 m pile of ash can gather in such a hole in the days Silvestru allows.  One sinkhole is a single site, and this article does not rest a verdict on it.  It does show that the ash beds at the base of the Tippecanoe record exposure, which is the question Part 6 asks of every megasequence base.

Part 5: Tonsteins and the floating mat

The Coal article tests the young-earth models of coal formation in full.  This Part takes only what tonsteins add.

The young-earth positions

Steven Austin proposed in his 1979 doctoral thesis that some Carboniferous coal formed from a mat of plants floating on water, which later sank and was buried.  In his and Roger Sanders' own words, Austin "introduced the term 'floating mat model' for the origin of coal and left the terminology broad enough to include either living or dead mats."³⁷  Their 2018 history of the model cites a question that William Gresley asked in 1894 about the Pittsburgh coal:  "How could a single three-eighths-inch-thick shale parting be deposited within the Pittsburgh Coal Bed throughout a 15,000 square mile area?"  And "How could the continuity of that parting be preserved as an equally widespread bench of vegetation was formed directly above that parting?"  Gresley's answer was "vegetable matter sinking down from floating 'islands' of vegetation."³⁷  A tonstein poses the same question, and neither that paper nor Sanders and Austin's companion paper on the model's botany discusses tonsteins.³⁸

Snelling accepts that tonsteins are ash.  They "are widely regarded as having originated as ash-fall tuffs," and he uses their clay to argue that coal formed below 200 °C.⁵  Kurt Wise, who defends a Flood origin for every Carboniferous fossil forest, grants that "a systematic study of in situ fossil forest claims will certainly include some challenges for creationists (e.g., in situ ash-fall claims," among others.³⁹  Warren Johns, writing in the same journal, takes up one such claim, a Permian forest buried by ash in Inner Mongolia, and answers that "Even if the air-fall volcanic ash had descended into Flood waters, the catastrophic movement of the waters would not have allowed much of the ash to preserve the plant life as it descended through the water column," and that "the Mongolian ash-fall interpretation is just an interpretation and needs independent verification."⁴⁰

What tonsteins show

Bohor and Triplehorn's monograph on tonsteins makes four observations that bear on Gresley's question.

1. They are sheets. "Tonstein layers are usually thin, continuous, widespread, and have sharp contacts with the enclosing beds." The Fire Clay tonstein of the central Appalachians covers about 37,000 km² inside one coal bed.¹⁴³⁴
2. They are not graded, because the water was shallow. "Shallow water depths in peat swamps are substantiated by the lack of graded bedding in most tonsteins. Conversely, marine bentonites almost always show graded bedding because of the thick water column through which the ash must settle."¹⁴ The Fire Clay is an exception: Paul Lyons and colleagues found "Several normal graded cycles" in it, from repeated eruptions, but almost no detrital quartz or clay, "which indicates rapid deposition in a mire."⁴¹
3. Roots grow into them. "Resumption of plant growth following an ash fall often results in root penetration of the nascent tonstein. Larger roots are usually carbonized and are often visible in outcrop." Some rootlets are filled with kaolinite, "implying early decay of the organic material and rapid filling by chemically precipitated kaolinite."¹⁴
4. The coal above records plants coming back. "In peat beds, this takes place by resumption of plant growth, probably within a year or so," and "organic petrology of the overlying peat reflects sequential stages in the reestablishment of plant growth."¹⁴ The year is their estimate, reported here as theirs.

The Permian forest that Johns answers is a large example of the same thing.  Jun Wang and colleagues dug out about 1,000 m² of a tuff that is now 66 cm thick, lying between two coal seams, and recorded every plant where it lay.  "The vegetation preserved in the tuff grew on the peat that later formed coal No. 7."  The ash fall "buried and killed the plants, broke off twigs and leaves, toppled trees, and preserved the forest remains in place within the ash layer."⁴²

What this asks of each account

Gresley's question has an observed answer.  The clay parting stays continuous even though roots grow through it, because the roots enter after the ash has settled and the plants then build the next bench of peat on top.  That is what a swamp that kept growing through an ash fall would leave.

A dead floating mat cannot do it.  Plant debris that sinks onto an ash layer from a mat above lays material on top, but nothing in it grows roots down into the ash.  A living mat could, which is why Austin's wording leaves room for one.  Ash falling on a living floating mat could be rooted into by the mat's plants as they kept growing.  So tonsteins alone do not rule out every floating-mat model.  They rule out the dead-mat version, and they require any living-mat version to keep one mat, or many joined mats, intact across tens of thousands of square kilometres while ash fell on it, roots grew into it, and a new bench of peat grew above it.  Whether the coal below the ash grew in rooted soil or on a raft is decided by the rooted underclays beneath the seams, which the Coal article covers.

Johns' answer, that turbulent Flood water would not let ash preserve plants, concedes the main point.  If the Wuda forest was buried by an ash fall in place, it grew there.  His reply is that the in-place reading is "just an interpretation."  The interpretation rests on mapped positions of individual plants over 1,000 m², on a single tuff layer of consistent thickness, and on the coal beneath it.  A young-earth reply would need to show that these plants were transported, for example by mapping their orientation and their roots.  None of the young-earth sources read for this article has done that for this site.

Part 6: The test at the megasequence boundaries

The proposal

The Unconformities and Megasequences overview proposed a test.  An ash bed is a moment.  If the base of a megasequence was laid down at one moment everywhere, every ash bed in the package above it should run right across the old surface.  If the sea instead crept across the surface over time, as Laurence Sloss held, the lowest ash beds should be found only in the low places that were already under water, and should pinch out toward the old high ground.

First, what the young-earth model actually claims.  Clarey does not say a megasequence base is one moment.  His model is a progressive Flood, rising in pulses.  Of the Kaskaskia, for example, he writes that "the tsunami-like waves of another series of megasequence advanced across the continents," so each package arrives first in some places and later in others, over days.³²  Onlap as such fits his model.  What the ash beds can add is two things:  whether the surface was cut or exposed while ash fell elsewhere, and how many separate falls the advance had to hold.

At the base of the Tippecanoe

This is the one megasequence base for which the ash-bed literature speaks directly.  Kolata, Huff and Bergström wrote that "A major difficulty in correlating these beds results from the diachronous age of the sub-Tippecanoe unconformity and the equally diachronous nature of the overstepping Tippecanoe sequence."  In the upper Mississippi Valley the St. Peter Sandstone, "with a K-bentonite at its base," lies on Lower Ordovician dolomite across "A major hiatus, spanning most of Whiterockian time," so "the precise age of the basal St. Peter K-bentonite is unknown and its correlation with Whiterockian K-bentonites elsewhere in eastern North America is uncertain."²

So the test has not been made at this boundary in the form the overview proposed.  The ash beds near the base are few, and nobody has fingerprinted one across the surface to see whether it pinches out.  The workers who know these beds best do say the base and the package above it are diachronous, but they say so from fossils, not from a traced ash bed.  What the ash beds do show at this base is Part 4's evidence:  ash residues in hollows and a 15 m ash bed in a sinkhole on the exposed surface, deposited before the sea returned.²²

Inside the Tippecanoe: the test has been made, many times

Higher in the same package the test has been run on smaller unconformities, and the results are consistent.

• The Deicke pinches out on an arch. "The Deicke pinches-out on the Kankakee Arch in northern Illinois and northern Indiana, but it is present north of the arch in the Michigan Basin."²
• Erosion cut both beds out of the highs. "In the region of the Cincinnati Arch in north-central Kentucky, the Millbrig is locally absent, apparently resulting from pre-Lexington erosion," and "the Millbrig and, locally, the Deicke are absent near the crest of the Nashville Dome … as a result of pre-Nashville (pre-Trenton) erosion."²
• Two ash beds converge at one surface. Kolata, Huff and Bergström's 1998 study of the unconformity between the Black River and Trenton groups found it "diachronous and … an amalgamated surface," and its gap "is greatest in southern Wisconsin, northern Illinois, and northern Indiana, where the Deicke and Millbrig K-bentonite Beds converge at the unconformity."¹⁵ Two ash beds that lie metres apart elsewhere meet at the surface where the most rock is missing. That is the signature the overview predicted, measured.
• A unit holding an ash bed is bevelled beneath a surface. John Hohman traced the Decorah unit that holds the Millbrig from the Ozark Dome to the Cincinnati Arch and found that it "is progressively truncated beneath the unconformity towards the east and is not present in the Cincinnati Arch area," while an older ash bed, the Pencil Cave, "pinches out to the west in the subsurface of the Illinois Basin."⁴³
• Basinward, the surface disappears and the ash beds continue. "the unconformity between the Black River and Trenton Limestones in Kentucky and Tennessee merges with the conformable succession of strata" in West Virginia, Virginia and northern Alabama.²

A young-earth geologist has an answer to the cut-outs themselves.  Waves crossing a shallow arch during the Flood could strip off sediment there while deeper water nearby kept it, so the geometry alone does not measure time.  Two things go beyond geometry.  The specialists read exposure on these surfaces:  Kolata and colleagues call the Black River-Trenton surface the result of "local late Turinian lowstand exposure," and on the Wisconsin Arch they report "significant topographic relief at the top of the Quimbys Mill" that "suggests local subaerial erosion."²¹⁵  And in Clarey's calendar all of this happened between about Day 20 and Day 30:  the arches lost two of the largest ash falls in the record to erosion, while a few hundred kilometres away the same falls settled into limestone a few hours apart on his average rates.

At the base of the Kaskaskia

The Devonian Tioga ash beds of the Appalachian Basin lie in the Onondaga Limestone, which rests on the Wallbridge unconformity, the base of the Kaskaskia in the east.⁴⁴  Charles Ver Straeten and Carlton Brett describe them as "a second interval of Devonian pyroclastic-rich strata above the Wallbridge Unconformity."  But they lie in the upper Onondaga, well above the base, and what is reported is a cut-out at a younger surface:  in eastern New York the beds "appear to be cutout at a submarine unconformity at the top of the Onondaga."  The same authors then report two ash beds near Albany that "could potentially be" the main Tioga bed, so even that cut-out is not settled.⁴⁵  No traced ash bed tests the Wallbridge surface itself.

Higher in the column

In the Cretaceous of the Western Interior, bentonites serve as the reference lines for cross-sections, as in the Ardmore Bentonite datum of the eastern Williston Basin, and the formations between them are bounded by unconformities.⁴⁶  But no source found for this article maps a bentonite ending against the base of the Zuni, and Sageman's caution applies:  without chemistry, a bed traced across a basin is a hypothesis.³¹  In the Hell Creek region the ash beds run across the Cretaceous-Paleogene boundary, which Clarey and Werner put "about" Day 150, in sections where the contact is conformable.⁹³²  Both accounts expect that in the middle of a basin, so it decides nothing.

What the test shows, and what it does not

The overview asked whether published correlations already answer its test.  They answer it at the smaller unconformities inside the megasequences, many times over:  the surfaces are diachronous, they cut out fingerprinted ash beds over the old highs, and they fade into continuous rock toward the basins.  At the megasequence bases themselves the fingerprinted test has not been made.  The specialists call the Tippecanoe base diachronous on other grounds, and the ash on that base lies in hollows on exposed rock.

Two cautions keep this from being stronger.  An ash bed can be missing because it never fell there, because it fell and was eroded, or because it fell and was never kept.  Outerbridge's floating pumice and Ver Straeten's finding that "Six of them yield no volcanic ash layers," of eleven Devonian sequences, are reminders that absence is weak evidence.³⁴³⁵  The cases above are strong because the beds are present on both sides of the gap and are cut out in between, which is not a preservation accident.  And the test needs a fingerprinted ash bed close to the base, which most megasequence bases lack.  The Whiterockian beds of the southern Appalachians and the lowest Devonian beds of New York are the places where it could be done.

Part 7: Dating, in outline

Ash beds carry the crystals, sanidine and zircon, from which most numeric ages in the geologic timescale come, and their dating has its own article.  Radiometric Concordance tests seven ash beds in the Hell Creek coals of Montana, where argon-argon ages on sanidine and uranium-lead ages on zircon from the same beds agree closely and put the beds in the same order.  Orbital Cycles in Rock covers ash beds used to check counts of sedimentary cycles.  Two points from the ash-bed literature belong here.  The radiometric ages for the Millbrig and the Kinnekulle scatter by more than 10 million years per bed, and the specialists who traced them call the dates inconclusive for correlation.¹  And the clay in a K-bentonite can give an age that records burial, not the eruption:  in the Kinnekulle, illite in the clay gave potassium-argon ages of 336 to 300 million years against 455 million for the bed's biotite, which Kolata and colleagues say "do not record depositional or early diagenetic events."²  Nothing in this article's argument rests on any of these ages.

Objections and responses

"Each ash bed fell in hours.  That is rapid deposition, which is what the Flood needs." Granted for each bed, and Part 1 says so.  But a stack of beds is not one rapid event.  It is many rapid events with something else between them.  The question is what the gaps hold, and Part 3 counts them.

"The Flood had far more volcanism than today.  Hundreds of eruptions in a year are no problem." None of the young-earth sources read for this article gives a number.  Clarey's own calendar and thicknesses supply one:  in the Smoky Hill, a fall every 2.5 hours for 11 days, and in the Ordovician of eastern North America, sixty falls in about ten days, two of them hundreds of cubic kilometres each and hours apart.¹⁰  The number of eruptions is only half the demand.  Between the falls the sea had to lay down limestone or chalk, peat had to grow, or diatoms had to bloom, each time, and every fall had to settle as its own graded layer without the next one landing in it.

"The bentonites were not burrowed, so they were not exposed for long." David Tyler makes this argument.¹¹  His own explanation of why the Smoky Hill bentonites were not burrowed is that the bottom water "had less oxygen and nutrients to support life."¹¹  That stops burrowers whatever the length of time.  At Pinatubo, ash thicker than 2 cm on the deep sea floor was still undisturbed years later, so an unburrowed bed sets no upper limit on the time it lay there.⁴  And unburrowed beds do not change the count.

"The correlations are circular.  Beds are matched by their ages, and the ages are assumed." The Ordovician beds were matched by chemistry:  26 elements in the clay, then apatite and glass inside the crystals.²⁸²⁹  For beds that have not been fingerprinted the objection has force, and Sageman and colleagues say so themselves.³¹  This article's cut-out cases use fingerprinted Ordovician beds.

"Hardgrounds between the beds do not prove time.  Walker and Woodmorappe have answered that." Granted as a limit on this argument.  The Flat Gaps article finds that the hardground test survives only in a narrow form that nobody has yet published for these beds.  Part 3 does not rest on hardgrounds.  The Smoky Hill has none, and its hundred-plus falls still need chalk between them.

"Ash missing over an arch only means it was not preserved there." Sometimes, which is why Part 6 states the caution.  But in the cases cited the same fingerprinted beds lie on both sides of the arch, and the specialists trace the gap to erosion beneath a named surface, which bevels a whole ash-bearing unit.²⁴³  A preservation accident does not bevel a unit.

"Clarey's Flood advances across the continent.  Onlap fits it." Agreed, and Part 6 says so.  Geometry alone cannot tell days of advance from long ages of advance.  What the ash beds add is what happened inside the advance:  arches that lost ash beds to erosion while the same beds settled into limestone nearby, two of the largest falls known converging at one eroded surface, and dozens of falls each with its own sediment above it, all inside Clarey's ten days.

"A living floating mat explains rooted tonsteins." It can explain roots in one tonstein.  Part 5 grants that.  It still has to keep one connected mat across tens of thousands of square kilometres through the ash fall and the regrowth, and the rooted soils under the coal, covered in the Coal article, are the evidence that decides whether the plants grew on rafts at all.

"The Smoky Hill and the Hell Creek may be after the Flood." Tyler puts the Smoky Hill after the Flood, and Whitmore and Garner place the end of the Flood near the top of the Cretaceous in Wyoming.¹¹¹²  Moving those packages out of the Flood removes them from this argument.  It does not remove the Ordovician beds, which lie inside the Flood on every young-earth placement of its start and end, and which hold sixty and more falls with limestone between them.

From the other side:  "This article uses Clarey's averages, but his model lays sediment in pulses." True.  The figures are averages, labelled as such.  Pulses make some intervals shorter and others longer.  Spreading the Tippecanoe over all of the first forty days instead of ten still leaves the Deicke and the Millbrig 14 to 18 hours apart.¹⁰

"The radiometric dates on these beds scatter by ten million years.  Why trust any ash-bed date?" This article uses none.  The scatter on the Millbrig is in older work, and the specialists say so.¹  Whether modern ash-bed dates agree is the subject of Radiometric Concordance.

Issues and unanswered questions

• The fingerprinted test at a megasequence base has not been made. No source found for this article traces a chemically fingerprinted ash bed across or against the base of any of Sloss's packages. The places to try are the few Whiterockian ash beds of the southern Appalachians near the base of the Tippecanoe, and the Tioga and older Devonian beds of New York and Pennsylvania near the Wallbridge surface.
• Sources not obtained. The body of Kolata, Huff and Bergström's 1998 GSA Bulletin paper on the Black River-Trenton unconformity, which holds the convergence maps; Huff and Kolata 1990 (AAPG Bulletin) and Haynes 1994 (GSA Special Paper 290), which hold the original cross-sections of the Deicke and Millbrig; the body of Elder 1988 with its isopach maps; the body of Ver Straeten 2004; Kauffman and Caldwell 1993 and Obradovich 1993 on Western Interior event beds; Witzke and Ludvigson 1994 on the seaway's eastern margin; Spears 2012 on tonsteins; Snelling and Mackay 1984, "Coal volcanism and Noah's Flood"; and Buchheim and Biaggi 1988, the Green River laminae counts between two tuffs that Snelling and Paul Garner cite.
• No young-earth count or rate. None of the young-earth sources read gives the number of Flood-year eruptions a package needs, or a rate at which glass becomes bentonite. Whitmore and Garner's expectation, that ash beds should be more common after the Flood than during it, could be tested with a count of named ash beds by system.
• Three errors in Snelling's text. He gives the Millbrig's volume as "in the order of a million cubic kilometers," against Bergström and colleagues' estimate of 1,509 km³ of magma.¹⁵ He credits Wiesner with the "two to three orders of magnitude" speed-up, a figure that comes from Manville and Wilson, and the Pinatubo ash he says formed "on the sea-bed" within three days was caught in traps in the water column.¹⁸ And he cites Hattin's 1982 bulletin for the bentonites being "derived from in situ decomposition of volcanic ash," though Hattin's text does not discuss their origin. None of the three changes his main points, which are that ash beds are real, numerous and fast.
• Measurements nobody has made. A thin section across the hardground that replaces an ash bed at South Carthage, Tennessee, looking for borings that cut cement between grains. A modern look at the Douglas Dam sinkhole ash, described in 1944. Root orientation and rooting depth at the Wuda forest, which would test the in-place reading Johns doubts.
• The Smoky Hill's clay is mostly kaolinite. Hattin found kaolinite dominant in 23 of 35 bentonite samples, a clay usually made in acid fresh water, in a marine chalk.⁶ Neither side's literature read here explains it.

Verdict

Young-earth geologists are right about each ash bed.  One eruption spreads a single layer over tens of thousands to millions of square kilometres in hours to days, on land and on the deep sea floor, and the layer is a moment that both sides use as a time line.  The glass-to-clay reaction is not a clock that separates the two accounts, because no model needs it to be fast.

But one ash bed is not the evidence.  The evidence is the stack.  A single section holds dozens to more than a hundred separate falls, and between them lie limestone, chalk made of algal plates, diatom ooze or peat, the last three made by living things, with hardgrounds in places and with roots grown into the ash in coal.  On Clarey and Werner's own calendar and thicknesses, that asks for a separate eruption every few hours, and in places minutes of sediment between two falls, through whole formations.  No young-earth source read for this article gives the count or the mechanism, and young-earth geologists themselves read many well-kept ash horizons as a mark of rock laid down outside the Flood:  Tyler for the chalk, and Whitmore and Garner as a general rule.

On the overview's proposed test the answer is partial.  At the smaller unconformities inside the Tippecanoe, fingerprinted ash beds pinch out on arches, are cut out beneath eroded surfaces over the highs, converge where the most rock is missing, and run on through continuous rock in the basins.  At the megasequence bases themselves the fingerprinted test has not been made, though the base of the Tippecanoe carries ash in hollows and a sinkhole on rock that was exposed before the sea came back.  Every surface the ash beds have tested so far was made at different times in different places, and on the specialists' reading with ground exposed between the seas.  Flood waves can account for the geometry of the cut-outs, but not for the dozens of separate falls, each with its own limestone above it, inside a few days.

Sources