The Great Unconformity

Sharp, Robert P.  “Ep-Archean and Ep-Algonkian erosion surfaces, Grand Canyon, Arizona.”  Geological Society of America Bulletin 51(8):1235–1270.  Aug 1, 1940.  A study of two ancient erosion surfaces in the Grand Canyon, Arizona, and the weathered rock beneath them.  Sharp's lower "Ep-Archean" surface is what is now called the Great Nonconformity, and his upper "Ep-Algonkian" surface is the Great Unconformity proper.  The article uses it for Sharp's mapping, his estimate of the time the upper surface took to form, and his own warning that the estimate is only an approximation. ↩

1. 1a.

   Section Abstract, page 1236:  “The maximum relief of the Ep-Archean surface is less than 50 feet, and monadnocks rise a maximum of 800 feet above the level of the Ep-Algonkian surface, about 95 per cent of which is relatively flat.” ↩

2. 1b.

   Page 1245:  “On Crystal Creek the Tapeats sandstone rests on Algonkian beds (Fig. 3).  The rocks below the contact show little evidence of weathering, and this appears to be the case in other localities where the Tapeats-Algonkian contact has been observed.  The Algonkian rocks show only slight weathering, probably because they are composed of materials which have already survived at least one cycle of weathering.”  Austin's fresh contact in Figure 3.22 is Tapeats on Dox Sandstone, an Algonkian (Grand Canyon Supergroup) sedimentary unit, so this is the case Sharp is describing. ↩

3. 1c.

   Page 1244:  “The relief of the Ep-Algonkian surface is controlled by the nature of the underlying rocks, for the highest monadnocks are composed of Shinumo quartzite (Pl. 7, fig. 1) and massive granite.” ↩

4. 1d.

   Page 1261:  “If 150 feet per million years is used as an approximate mean figure, removal of 15,000 feet of rock to form the Ep-Algonkian surface would require 100 million years.  Obviously this figure is only an approximation, for variations in climate, topographic relief, rock types, and stage of the erosion cycle are all unevaluated.  Furthermore, if the surface were barren of vegetation, the rate of erosion may have been considerably greater and the elapsed time correspondingly shorter.” ↩

5. 1e.

   Figure 4, page 1248:  The caption, to a photograph at Elves Chasm, gives the section, listing it from the top down:  “(1) Gritty Tapeats sandstone.  (2) Reworked weathered detritus.  (3) Weathered zone with boulders of decomposition.  (4) Fresh Archean granite.” ↩ ↩

6. 1f.

   Page 1252:  “Lenses of grit and conglomerate or breccia are abundant in the lower Tapeats.  The grits are usually arkosic and consist of angular quartz and feldspar fragments such as might have been derived from a pegmatite.  The conglomerate lenses or pockets consist predominantly of a ferruginous sandy matrix containing angular quartz fragments half an inch to 8 inches [in diameter].” ↩

7. 1g.

   Page 1242:  On the basal Grand Canyon Supergroup conglomerate resting on the lower erosion surface, Sharp writes:  “In Hotauta Canyon at the locality from which the formation was named by Noble (1914, p. 42) the Hotauta is 2 feet thick and consists chiefly of reworked arkosic detritus derived from underlying weathered Archean quartz diorite (Fig. 2).  Within the reworked material are fragments of quartz diorite several inches in diameter.” ↩

8. 1h.

   Page 1263:  “The initial Tapeats sea must have been a shallow sea above whose surface rose numerous islands.  Some of these islands were so high that they were not completely submerged until well into Bright Angel time.” ↩

9. 1i.

   Page 1244:  “Hinds (1935, p. 27) reports a maximum relief of 250 feet in the Bright Angel and Vishnu quadrangles, and Noble (1914, p. 51) records a relief of 600 feet in Monadnock Amphitheater in the Shinumo quadrangle.  A large monadnock on the north side of the Grand Canyon between Bright Angel and Ninetyone Mile creeks (Pl. 6, fig. 2) is almost 800 feet high (Wheeler and Kerr, 1936, p. 5), and this is the highest known point on the Ep-Algonkian surface in the Grand Canyon, where more than 95 per cent of the Ep-Algonkian surface has a relief of less than 150 feet and a large part is essentially flat.” ↩ ↩

10. 1j.

    Page 1261:  “By no means should the inference be drawn that 100 million years of erosion are required to produce a peneplain, for it is well known that many peneplains have been formed in a small fraction of that time.” ↩ ↩

11. 1k.

    Page 1251:  Sharp gives his reasons that the weathering is ancient rather than modern, numbered 3 to 5:  “(3) The beds overlying the Ep-Archean surface contain fragments of gossanlike material derived from the underlying weathered zone.  (4) Residual quartz fragments on hillocks and surficial creep indicate ancient weathering on at least the Ep-Algonkian surface.  (5) Recent weathering has developed caves and alcoves along the weathered zone, it has not produced that zone.”  His reason (2), on the same page, is that the weathered mantle was.  “reworked and incorporated in the overlying sedimentary deposits, hence it must have been in existence prior to encroachment of the seas in which those deposits were formed.” ↩ ↩ ↩

12. 1l.

    Page 1253:  “These beach shingles, if they may be called such, consist of large angular blocks close to the monadnock and pass gradationally outward into material consisting of smaller and more rounded fragments until the conglomeratic nature is entirely lost.  Noble … Walcott … Ransome … Hinds … and others have noted this relation.  It has been observed on the flanks of many Ep-Algonkian monadnocks. …  Dake and Bridge (1932, p. 630–636) report similar conditions in the Ozarks.” ↩

13. 1m.

    Page 1254:  “The encroaching Tapeats sea lapped over the relatively flat Ep-Algonkian surface and against the southwest flank of a monadnock of Shinumo quartzite (Pl. 6, fig. 2).  The detritus mantling the surface was reworked to form the relatively fine basal Tapeats.  Wave erosion oversteepened the slopes of the monadnock to such an extent that a great mass of material broke loose, slid down into the sea, and moved southwestward out over the fine beds, deforming them locally.” ↩

14. 1n.

    Page 1262:  “Modification of the Grand Canyon surfaces by marine processes has been so slight that submergence of these surfaces must have been moderately rapid.” ↩

15. 1o.

    Page 1261:  “Using Noble's section CC' (1914, Pl. 1) as a basis, the thickness of Archean rocks removed by Ep-Algonkian erosion has been calculated as approximately 2000 feet.  Therefore, the total thickness of rock eroded during the Ep-Algonkian interval is close to 15,000 feet.  This is a conservative calculation, and in many places the thicknesses were probably considerably greater.” ↩

16. 1p.

    Page 1264:  “Both surfaces show evidence of subaerial weathering, and this weathered mantle has been studied in considerable detail.  The greatest depth of weathering is 10 feet beneath the Ep-Archean surface;  it is 50 feet beneath the Ep-Algonkian surface, but only the uppermost 5 to 10 feet is greatly altered. …  Biotite changes first to a green chlorite and then to a colorless chloritelike material in which are dispersed small grains of iron oxide.  Eventually, biotite is entirely eliminated, leaving hydrated iron oxide.  Feldspars show some kaolinization even at considerable depth, and plagioclase is almost entirely decomposed in an early stage of the weathering. …  Quartz and muscovite with hydrated iron oxides and clay constitute most of the residual regolith produced by extended weathering;  the amount of iron oxides ranges from 0.9 to 12.8 per cent. …  Insoluble residues constitute an average of 88 per cent of the most maturely weathered material.  The evidence of chemical weathering on these surfaces is far greater than the evidence of mechanical weathering.” ↩ ↩ ↩ ↩

Snelling, Andrew A.  “The Petrology of the Tapeats Sandstone, Tonto Group, Grand Canyon, Arizona.”  Answers Research Journal 14:159–254.  2021.  A 2021 petrology study, which is a study of rock composition and texture, by Andrew Snelling of Answers in Genesis, a young-earth creationist ministry that publishes the journal.  The paper runs 96 pages and examines 26 thin sections, which are slices of rock viewed under a microscope, from the Tapeats Sandstone, the Cambrian sandstone at the base of the Tonto Group in the Grand Canyon.  The article uses it as the most detailed young-earth treatment of this surface in print. ↩

1. 2a.

   Page 170:  “the time interval at the Great Unconformity could be <200 Ma.”  Snelling is arguing that the gap is smaller than usually stated, which concedes the framing. ↩

2. 2b.

   Page 240:  “However, before the Tapeats Sandstone was deposited there had to be a prolonged period (days or more) in which there was a significant amount of continental-scale erosion to bevel the Precambrian (pre-Flood) land surface to produce the Great Unconformity.  In the Grand Canyon region this involved intensive catastrophic erosion to remove several thousand meters of Grand Canyon Supergroup strata (which appear to only have survived in several down-faulted blocks) and then to bevel the underlying metamorphic schists and granite plutons.” ↩ ↩ ↩ ↩ ↩

3. 2c.

   Page 170:  “The surface on which the Tonto Group accumulated was fairly irregular, though it is also flat at many locations.  Where irregular it was characterized by a rolling topography of resistant bedrock 'hills' (often Unkar Group Shinumo Quartzite) and 'lowlands.'  The Precambrian bedrock appears to have been extensively weathered in places and eroded during the claimed prolonged period of subaerial exposure.” ↩

4. 2d.

   Page 173:  “An apparently highly weathered horizon occurs on top of the Precambrian surface in several places in the Canyon.  The only effort to understand the genesis of that potentially significant horizon is that of Sharp (1940).  His study suggested that extensive chemical weathering of Precambrian rocks occurred prior to deposition of Cambrian sediments.  In places that apparently highly weathered surface or potential regolith is up to 15.3 m (50 ft) thick, but elsewhere is generally less than 3.1 m (10 ft) thick.”  Snelling's objection, on the same page, is that.  “there have been no petrologic and geochemical studies that could substantiate that hypothesis…  so a humid climate interpretation is quite tenuous.” ↩ ↩

5. 2e.

   Page 195:  “The basal sediments were deposited on a Precambrian surface that had been exposed for possibly long periods of time.  There was considerable relief on that surface.  The 'hills' have a relief as great as 244 m (800 ft) (McKee 1945).  Generally, however, the relief is considerably less.” ↩

6. 2f.

   Page 173:  Snelling names Sharp 1940 as the source of this statement:  “The only effort to understand the genesis of that potentially significant horizon.”  That remains true at the Grand Canyon, and it is why this article leans on an eighty-six-year-old paper there.  It is not true in Colorado, where Flowers et al. 2020 is a peer-reviewed petrologic study of the same feature. ↩

7. 2g.

   Page 173:  Snelling reports Sharp's own explanation for the places with no regolith: where the Tapeats Sandstone sits on unaltered Precambrian basement, that regolith was probably removed by the wave erosion associated with the initial Cambrian transgression. ↩

8. 2h.

   Page 241:  “Austin (1994) diagrammatically envisaged a fining upwards model for the time transgressive rapid deposition of the Tonto Group strata as the powerful westward back under-flow of the advancing Flood waters at a water flow speed of >2 m/sec intensely scoured and catastrophically eroded all pre-Flood rocks to produce the Great Unconformity before sequentially depositing their load of sediments as horizontally segregated facies in the vertically stacked Tonto Group strata (fig. 40).”  Austin's printed text gives no velocity for the erosive zone, only 1.5, 1.0, 0.5 and less than 0.5 m/s for Zones 2, 3, 5 and 6, so the >2 m/sec speed is attributed to Snelling and not to Austin. ↩

Flowers, Rebecca M. et al.  “Diachronous development of Great Unconformities before Neoproterozoic Snowball Earth.”  Proceedings of the National Academy of Sciences 117(19):10172–10180.  2020.  Section Abstract:  The abstract says:  “Our results provide evidence that most erosion below the Great Unconformity in Colorado occurred before the first Neoproterozoic Snowball Earth and therefore cannot be a product of glacial erosion.  We propose that multiple Great Unconformities developed diachronously and represent regional tectonic features rather than a synchronous global phenomenon.”  A research paper by four geologists that studies the Pikes Peak granite in Colorado and the sandstone that was injected into it.  It argues that there are several Great Unconformities, formed at different times as regional tectonic features rather than one global event.  The article sets it against Keller and colleagues, who attribute the same surface to Neoproterozoic glaciation. ↩

1. 3a.

   Section Constraints on the Great Unconformity in Colorado:  “Locally, the basal Cambrian beds above the Great Unconformity drape over relief induced by variably resistant, meter-scale core stones in an ∼100-m-thick weathered zone of the Pikes Peak granite (Fig. 3A).  This is clear evidence that a Pikes granite regolith was also present in the Cambrian.” ↩ ↩ ↩

2. 3b.

   Section Abstract:  “We propose that multiple Great Unconformities developed diachronously and represent regional tectonic features rather than a synchronous global phenomenon.” ↩

3. 3c.

   Figure 3:  The figure caption reads:  “(A) Great Unconformity near Manitou Springs, Colorado.  Pikes Peak basement with ∼1.5-m-diameter core stones (marked with the yellow arrow) onlapped by sandstone of the Sawatch Formation.” ↩ ↩

4. 3d.

   Section Abstract:  “Fractured, weathered wall rock around Tavakaiv bodies and intensely altered basement fragments within unweathered injectites imply still earlier regolith development.  These observations provide evidence that the granite was exhumed and resided at the surface prior to sand injection, likely before the 717-Ma Sturtian glaciation.” ↩

5. 3e.

   Section Constraints on the Great Unconformity in Colorado:  “If substantial exhumation had occurred, then the shallowly emplaced injectites would have been removed by erosion.” ↩

Peters, Shanan E., and Robert R. Gaines.  “Formation of the 'Great Unconformity' as a trigger for the Cambrian explosion.”  Nature 484(7394):363–366.  Apr 19, 2012.  A research letter in Nature arguing that the Great Unconformity, the surface under the Cambrian sandstones, was formed by a long wearing-down of the continents and may have helped trigger the Cambrian explosion of animal life.  The authors used stratigraphic and lithologic data for 21,521 rock units from 830 regions of North America, with carbon and oxygen isotopes on 220 mudstone samples, to explore that hypothesis.  The article uses it because young-earth authors cite it for the surface's near-global extent, and it says what they say it says.  Mirror:  Strata.geology.wisc.edu ↩

1. 4a.

   Section Methods Summary, page 366:  “This approach is conservative with respect to the Great Unconformity because a large fraction of Precambrian sedimentary rock is structurally deformed and laterally adjacent to basement rocks.  Thus, the Great Unconformity often cuts across all older rock units at each location.” ↩

2. 4b.

   Section Abstract, page 363:  “The resultant globally occurring stratigraphic surface, which in most regions separates continental crystalline basement rock from much younger Cambrian shallow marine sedimentary deposits, is known as the Great Unconformity.” ↩ ↩

3. 4c.

   Page 363, column 2:  “Continental-scale marine transgression during the Cambrian–Early Ordovician accentuated rates of weathering on the Great Unconformity by shifting landward the position of the erosive transgressive shoreface system, often called the 'wave-base razor', as well as adjacent transitional backshore, aeolian and fluvial systems.  As a result, much of the soil and weathered basement rock (regolith) that covered low-relief continental interiors was eroded and mobilized during the transgression.” ↩

4. 4d.

   Page 363, column 2:  “The Cambrian- to Early Ordovician-aged sediments of the Sauk Sequence that overlie the Great Unconformity are time-transgressive, such that Early Cambrian sediments occur on the margins of the palaeocontinents and Late Cambrian sediments overlie the Great Unconformity in continental interiors (Fig. 1).” ↩ ↩

5. 4e.

   Page 366, column 1:  “The palaeogeomorphic surface represented by the Great Unconformity is unique in at least the past 900 Myr of Earth history, but similar episodes of widespread continental denudation followed by large-scale marine transgression and sedimentation may have occurred before 900 Myr ago.” ↩

Grand Canyon: Monument to Catastrophe.  Institute for Creation Research, Santee, California.  Edited by Steven A. Austin.  1994.  An edited book of chapters on the geology of the Grand Canyon, published by the Institute for Creation Research.  The article uses its chapter 3 (pp. 45–47) and chapter 4 (pp. 57 and 66–70) as the young-earth side's own account of the Great Unconformity. ↩

1. 5a.

   Page 47:  “Is there evidence for catastrophic erosion on the Great Unconformity?  Many creationists believe there is.  Large boulders of Shinumo Quartzite fill great channels of boulders which, in places, occur directly above the Great Unconformity in the base of the Tapeats Sandstone (figure 3.23). …  Arthur Chadwick surveyed hills of bedrock covered with boulder and sand beds.  These were interpreted by Chadwick as catastrophic underwater debris flows, which were able to move boulders ten feet in diameter more than a quarter mile.  Such processes require conditions which would be very erosive to bedrock. …  The best theory seems to be that significant erosion occurred on the Great Unconformity while it was under water, not while it was [subaerial]”. ↩ ↩

2. 5b.

   Figure 3.22, page 46:  The caption, which reads:  “Detail of the Great Unconformity in Grand Canyon.  At this location, Tapeats Sandstone (Cambrian) overlies Dox Sandstone (Precambrian).  Evidences of extensive chemical weathering are not obvious.  Instead, feldspar-rich pebbles of Tapeats overlie the unaltered surface of Dox Sandstone.  Does the surface of erosion represent one-half billion years?  We marvel at the fresh appearance of the contact.”  Page 45:  On the preceding page Austin sets out the dispute:  “Has evidence of 'gentle weathering' been documented at the Great Unconformity?  Geologists have been divided on this point.”  Page 46:  His witness against Sharp is N. E. A. Hinds, who.  “could not find significant evidence of chemical weathering of bedrock, or of the debris incorporated into the base of the Tapeats Sandstone”. ↩

3. 5c.

   Page 57:  “Everywhere in northern Arizona these strata occur, they are bounded above by a very conspicuous planar surface of erosion (the 'Great Unconformity'), believed to represent early erosion and the onset of Noah's Flood.”  Page 67:  He generalises:  “Most creationist geologists regard the Great Unconformity as the feature formed during the tectonic and erosive catastrophe at the onset of Noah's Flood.” ↩ ↩ ↩

4. 5d.

   Page 67:  “Overall, when viewed on a regional scale, the Great Unconformity is a very flat surface.  Locally, however, the Great Unconformity displays as much as 300 feet of topographic relief around resistant ridges of Unkar Group rocks (Shinumo Quartzite, Cardenas Basalt, and Diabase sills).” ↩

5. 5e.

   Page 69:  “Zone 1 is the highest elevation area of the continent, where shallow, fast floodwaters are causing intense scouring and erosion of the pre-Flood rocks.”  No velocity is given for Zone 1 in the printed text. ↩

6. 5f.

   Page 69, figure 4.12:  The zone descriptions accompanying Figure 4.12.  Zone 2:  “intense bottom-surging current (velocity about 1.5 meters per second)”.  Zone 3:  “the water velocity is about 1.0 meter per second”.  Zone 5:  “about 0.5 meter per second”.  Zone 6:  “the water current velocity is less than 0.5 meter per second”.  The figure caption reads:  “A model for the formation of sedimentary deposits beneath advancing floodwaters in Nevada, Arizona, and New Mexico. …  The Flood model explains erosion of the Great Unconformity and simultaneous deposition of the Tapeats Sandstone, Bright Angel Shale, and Muav Limestone.” ↩

Oard, Michael J.  “The Puzzle of Planation Surfaces (Part VII, chapters 32 and 49).”  Michael Oard's online Flood-runoff monograph.  Apr 30, 2014.  Two chapters from Oard's online book on the Flood's runoff, about the flat erosion surfaces called planation surfaces that cut across the continents.  Chapter 32 defines them, and chapter 49 summarizes the survey evidence that they are common on all continents, which Oard attributes to sheet erosion during the Flood.  The article uses it for his mechanism, sheet flow off a rising continent during the Retreating Stage of the Flood; the phrase "Great Unconformity" does not appear in either chapter.  Mirror:  Michael.oards.net ↩

1. 6a.

   Chapter 49, page 1:  On the general sequence he reads from planation surfaces, Oard writes:  “Second, the rough, deformed terrain that consisted of various types of rocks of varying hardness, was planed into a flat surface.  Tilted sedimentary rocks and granite were commonly beveled to the same grade.  Third, often a thin layer of mostly rounded rocks blanketed the planation surfaces.” ↩

2. 6b.

   Chapter 32, page 2:  “Today, comparatively small planation surfaces (strath terraces) are formed when a river floods, overflows its banks, and planes bedrock to a horizontal or near horizontal surface.  But, present processes do not form planation surfaces of any significant size.  The large surfaces that frequent the Earth's surface are contrary to the principle of uniformitarianism.”  His chapter 49 supports the claim with mainstream geomorphologists including King, Twidale, and Ollier and Pain.  The article grants the point. ↩

3. 6c.

   Chapter 32, page 1, section Part VII opening:  “During the Retreating Stage of the Flood, the mountains rose and the valleys (basins) sank (Psalm 104:8) and the Floodwater receded off the continents. …  Great sheet erosion of the rising continent ensued during the Sheet Flow Phase of the Flood, leaving behind escarpments, tall erosional remnants, arches, large natural bridges, long-transported gravel, and other features.  At the same time, this great erosion scoured the land and formed erosion and planation surface.” ↩

Corsetti, Frank A., and James W. Hagadorn.  “Precambrian-Cambrian transition: Death Valley, United States.”  Geology 28(4):299–302.  Apr 2000.  A research paper that places the Precambrian-Cambrian boundary in the Death Valley rocks of California, using the trace fossil Treptichnus pedum and a carbon-isotope profile.  The article uses it because the boundary falls inside the lower member of the Wood Canyon Formation, an ordinary succession with no Great Unconformity. ↩

1. 7a.

   Page 300:  “Interbedded siltstone and sandstone units of the third parasequence, overlying the second major carbonate unit at most sections, contain an easily recognizable suite of bed-parallel trace fossils, as well as several forms demonstrating a vertical burrowing component, including T. pedum (Fig. 2D).  Thus, the Precambrian-Cambrian boundary can be correlated to the basal siliciclastic units of the third parasequence in the lower member of the Wood Canyon Formation.” ↩ ↩

2. 7b.

   Page 300:  “the lower member contains rare Ediacaran-style body fossils (including Ernietta [Horodyski, 1991], Swartpuntia, and a variety of tubular forms [Hagadorn and Waggoner, 2000]) in the lowest parasequence of the unit.  In rare cases, Ediacaran-style fossils occur in Cambrian strata, but Ernietta is known only from terminal Proterozoic deposits.” ↩

3. 7c.

   Page 301:  “A pronounced negative carbon isotope excursion to ~ –4‰ occurs in the lower member of the Wood Canyon Formation directly below the Precambrian-Cambrian boundary interval in both sections.” ↩

4. 7d.

   Page 299:  “Each broadly reflects deposition in cratonal, craton-margin, proximal-shelf, and outer-shelf environments, respectively …  The Cratonal and Mojave successions contain an erosional disconformity that has removed the Precambrian-Cambrian boundary interval (Diehl, 1979;  Fedo and Cooper, 1990).  The White-Inyo succession is thickest but is poorly fossiliferous with respect to earliest Cambrian index fossils …  The Death Valley succession contains both lowest Cambrian index fossils and sufficient carbonate rocks, providing an ideal combination of data to characterize the Precambrian-Cambrian transition.” ↩

Nelson, Lyle L. et al.  “Cambrian explosion condensed: High-precision geochronology of the lower Wood Canyon Formation, Nevada.”  Proceedings of the National Academy of Sciences 120(30):e2301478120.  Jul 17, 2023.  A 2023 paper by six authors that dates a siltstone in the lower Wood Canyon Formation of the Spring Mountains in Nevada, using zircon crystals.  The authors analyzed detrital zircon grains (grains washed in from older rocks) with a laser, then used a more precise isotope-dilution method on the youngest ones.  They conclude that the base of the Cambrian is younger than 533 million years and that the early animal radiation was faster than previously recognized.  The article uses it for the dated siltstone that sits at the boundary between the Precambrian and the Cambrian in the Wood Canyon Formation. ↩

1. 8a.

   Section Results:  “Sample L2005-27.1 was collected from a <0.1 m micaceous siltstone bed within the second dolostone marker unit of the lower member of the Wood Canyon Formation. …  The five youngest ID-TIMS dates define a mode with a ²⁰⁶Pb/²³⁸U age of 532.83 ± 0.98/1.00/1.14 Ma”.  The zircons are detrital, so this is a maximum depositional age, meaning the rock cannot be older than it.  Section Abstract:  Their abstract concludes that.  “the base of the Cambrian Period, as defined by both ichnofossil biostratigraphy and carbon isotope chemostratigraphy, was younger than 533 Mya, at least 6 My later than currently recognized.” ↩ ↩

Clarey, Timothy L., and Davis J. Werner.  “The Sedimentary Record Demonstrates Minimal Flooding of the Continents During Sauk Deposition.”  Answers Research Journal 10:271–283.  2017.  Page 271:  From the abstract, its conclusion is that.  “the Sauk megasequence represented only a partial, but violent, start to the global Flood”.  The abstract also says.  “Africa and South America exhibit very little evidence of continental flooding during the deposition of the Sauk megasequence.”  A study of Lower Paleozoic rock across North America, South America and Africa, built from about 1,500 stratigraphic columns, which measured the volume of rock in the Sauk megasequence.  The article uses it as the best quantitative dataset the young-earth movement has, and its own conclusion, that the Sauk sea was partial and limited, is in tension with a continent-stripping erosional event immediately beneath the Sauk, since a partial, limited sea does not plane a continent. ↩ ↩

1. 9a.

   Page 278:  Clarey and Werner, arguing against large erosion between megasequences:  “Secondly, we do not observe significant numbers of reworked fossils and mixed fossil debris in younger, Cretaceous and Cenozoic strata.  Massive late Flood or post-Flood erosion should have transported vast amounts of fossil material and microfossils from the earlier megasequences.”  Their first argument on the same page is that.  “the consistent internal stratigraphy of each megasequence testifies against significant erosion.” ↩

2. 9b.

   Table 1, page 282:  The Sauk megasequence, summed over North America, South America and Africa: 22,594,600 km² of surface area and 10,436,090 km³ of rock.  Sauk, Tippecanoe and Kaskaskia together on the same three continents come to about 35 million km³.  The article's own mass-balance arithmetic, in Part 5, is computed from those two published figures; no number in it is disputed by the authors. ↩ ↩

Oard, Michael J.  “Analysis of Walt Brown's Flood model.”  Creation Ministries International.  2013.  “There are many more specific problems that can be brought forth against Brown's version of the dam-breach hypothesis, but the above are enough to show that his hypothesis won't work.”  On Brown's block-faulting of the Grand Staircase and Book Cliffs, Oard writes:  “are obviously erosional escarpments … They are not fault scarps”.  He also says the lakes did not breach at the low points of the Kaibab Plateau, an objection that hits Austin equally.  A commissioned critique of Walt Brown's hydroplate model of the Flood, written by Michael Oard, a full-time researcher in field geology and a board member of the Creation Research Society, at the request of Creation Ministries International.  It summarizes Brown's model, then tests its Grand Canyon and woolly mammoth claims, finding questionable starting conditions, data fitted to the model, and a dam-breach explanation of the canyon that cannot account for its long, deep tributary canyons.  The article uses it for Oard's own water-to-rock arithmetic from the Missoula floods and for his Bonneville erosion rate. ↩

1. 10a.

   On the Bonneville flood, Oard writes:  “It is estimated that about 100 m (330 ft) of rock was eroded in about 8 weeks before the flood ended.”  He adds that although the estimate is a uniformitarian one, he believes it, because the flood landforms in the Snake River Valley are small.  The article's rate of 6.5 × 10⁵ mm/yr is its own arithmetic on this figure: 100 m in 8 weeks. ↩

2. 10b.

   “the total volume of rock eroded by sheet flow would be 8,500 km³ (2,000 mi³).  The volume of Brown's two lakes east of Grand Canyon was only about 12,000 km³ (2,930 mi³).  That is a little more than a cubic km of water to erode a cubic km of sediment, which seems like too little water, just to erode the 300 m (1,000 ft) of sediments before Grand Canyon was even carved!”  “that much water only eroded about 200 km³ (50 mi³) of soft silt and hard basalt along the flood path.  That is about a 10 to 1 ratio of water to erosion.” ↩ ↩

Karlstrom, Karl E. et al.  “Telling Time at Grand Canyon National Park: 2020 update.”  Natural Resource Report NPS/GRCA/NRR-2021/2246.  National Park Service, Fort Collins.  2021.  A National Park Service report on the ages of the rock layers in Grand Canyon National Park, with a table of numeric ages for them.  The Park Service's web version of that table was last updated on 12 March 2024.  The article uses it for the three unconformities the Park Service names in the canyon and for the revised date of the Cardenas Basalt. ↩

1. 11a.

   Section Missing Time, page 14:  The Great Nonconformity spans this much missing record:  “up to 500 million years of missing record”.  The Great Angular Unconformity:  “can span up to 750 million years of missing rock record”.  Powell's Great Unconformity, where Paleozoic rests directly on basement, is:  “approximately 1.2 billion years (or about 30 percent) of Earth history missing.” ↩ ↩

Thurston, Olivia G. et al.  “Zircon (U-Th)/He thermochronology of Grand Canyon resolves 1250 Ma unroofing at the Great Unconformity and <20 Ma canyon carving.”  Geology 50(2):222–226.  2022.  Page 222:  “the sub-Tonto Group unconformity has between 200 and 1300 Ma of time 'missing'.”  “Fault blocks of the Grand Canyon Supergroup show that the GU is a composite erosion surface that records exhumation of Proterozoic crystalline basement during several pulses of intracratonic tectonism.”  A 2022 study that dated basement rock under the Great Unconformity in the eastern Grand Canyon with zircon (U-Th)/He, a method that shows when a rock cooled through about 200 °C.  It used 37 single zircon grain aliquots from seven locations and modeled the cooling history, and it found the main Precambrian cooling between 1300 and 1250 Ma and canyon carving under 20 Ma.  The article uses it for the spread of missing time along one canyon, from 200 to 1300 million years. ↩ ↩

Powell, John Wesley.  Exploration of the Colorado River of the West and its Tributaries, Explored in 1869, 1870, 1871, and 1872.  Government Printing Office, Washington DC.  1875.  The report of John Wesley Powell's 1869 to 1872 expeditions down the Colorado River and its tributaries, made under the direction of the Smithsonian Institution and submitted to Congress.  Powell calls the contact between the tilted older beds and the overlying Carboniferous rocks "non-conformable," and never uses the phrase "Great Unconformity"; his Fig. 79, "Section of wall in the Grand Canon," is the first published drawing of the surface.  The article uses it because Powell described the surface first, in this report; his 1876 Uinta report does use "unconformity" freely, but that is Utah. ↩

1. 13a.

   Page 212:  “The beds themselves are non-conformable with the overlying Carboniferous rocks;  that is, the Carboniferous rocks are spread over their upturned edges.”  “Doubtless, at some time before the Carboniferous rocks C, C were formed, the beds B, B extended off to the left, but between the periods of deposition of the two series, B, B and C, C there was a period of erosion.  The beds, themselves, are records of the invasion of the sea;  the line of separation, the record of a long time when the region was dry land.” ↩

2. 13b.

   Page 213:  “the metamorphosed sandstones and shales, and the beds of granite, present evidences of erosion subsequent to the periods just mentioned, yet antecedent to the deposition of the non-conformable sandstones.  Here, then, we have evidences of another and more ancient period of erosion, or dry land.  Three times has this great region been left high and dry by the ever shifting sea;  three times have the rocks been fractured and faulted;  three times have floods of lava been poured up through the crevices”.  On the same page he notes that the lava.  “was doubtless poured out on the dry land, for it bears evidence of being eroded by rains and streams prior to the deposition of the overlying rocks.” ↩ ↩

Keller, C. Brenhin et al.  “Neoproterozoic glacial origin of the Great Unconformity.”  Proceedings of the National Academy of Sciences 116(4):1136–1145.  2019.  Section Abstract:  The abstract says that the isotope excursions and the unconformity.  “can together be explained by spatially heterogeneous Neoproterozoic glacial erosion totaling a global average of 3-5 vertical kilometers.”  A 2019 paper by nine authors that combines three records: oxygen and hafnium isotope measurements in zircon crystals, the impact craters found on Earth, and how much sediment covers the continents through time.  The authors argue that Neoproterozoic glacial erosion can explain all three together, with a global average of 3-5 vertical kilometers of rock removed.  The article uses it as the strongest case for a single glacial cause. ↩

1. 14a.

   Section Inferences and Conclusions:  “While nonconformity between sediment and crystalline basement is ubiquitous on all continents, it is highly diachronous (6).  This diachroneity of amalgamated unconformities has helped to obscure the global s[ignal]…”  Their reference 6 is Karlstrom and Timmons 2012. ↩

2. 14b.

   Section Neoproterozoic Glaciation and Erosion:  “Modern glacial erosion rates are highly variable, estimated to span some four orders of magnitude from ∼0.01 mm/y to ∼100 mm/y (54).  For comparison, 4 km of erosion over 64 Ma of Neoproterozoic glaciation would require an average erosion rate of only 0.0625 mm/y — nearly two orders of magnitude slower than recent direct estimates for the modern Greenland ice sheet (55).”  The same paper offers an independent test that comes out in its favour.  Impact craters are shallow features, so kilometre-scale erosion should destroy all but the largest, and the authors report that.  Section The Terrestrial Bolide Impact Record:  “only two craters matching the criteria of Fig. 3 predate the onset of Sturtian glaciation, both deeply eroded remnants of massive craters:  Sudbury and Vredefort, eroded to depths of 4.2–5.8 km and 8–11 km, respectively,”.  The paper also reports.  “an abrupt truncation of <100-km diameter craters before 700 Ma and <10-km diameter craters before 600 Ma.”  A Flood that stripped the continents in a year predicts a truncation too, but not one that arrives in size order across 100 million years. ↩ ↩

Zhan, Rong-Ruo et al.  “Tectonism rather than 'snowball Earth' glaciation is responsible for the Great Unconformity.”  PNAS 123(9):e2523891123.  Feb 23, 2026.  A 2026 study, published on 23 February 2026, that dated basement rock beneath the Great Unconformity at five North China locations, three inside the craton and two near its margin, with zircon and monazite U-Pb, biotite and muscovite Rb-Sr and zircon (U-Th)/He, and argues that plate tectonics, not snowball Earth glaciation, drove most of the exhumation below the unconformity.  Nicholas Christie-Blick, a co-author, is a long-standing critic of catastrophic snowball interpretations, so this is not a consensus restatement.  The article cites it for its finding that most of the exhumation came 2,100 to 1,600 million years ago, far earlier than any glacial model allows. ↩

1. 15a.

   Section abstract, page 1:  “Dates from multichronometers and thermal history inversions show that the most substantial cooling of continental basement took place from ~2,100 to 1,600 Ma.  Comparison with thermal history data from Laurentia, Baltica, and Amazonia suggests that protracted plate tectonics broadly modulated by supercontinent cycles, and not 'snowball Earth' glaciation, is responsible for crustal exhumation below the unconformity.” ↩

2. 15b.

   Section Discussion, page 7:  “Unlike previously documented thermochronologic constraints on the origin of the GUn in the southern Rocky Mountains and Canadian Shield of Laurentia, evidence from multiple thermochronometers synthesized here strongly suggests that mechanisms driving most of the GUn denudation date from the late Paleoproterozoic, much earlier than the Cambrian Explosion of life or the onset of modern plate tectonics.” ↩

3. 15c.

   Page 3:  “The major cooling trend from ~2,100 Ma to ~1,600 Ma revealed by dates of higher temperature isotopic systems indicates at least ~370 °C of cooling during this period, and requires a ∼12.3 km average exhumation within cratonic interior of the North China assuming a geothermal gradient of 30 °C/km.” ↩

Clarey, Timothy.  “Great Unconformity Best Solved by Global Flood.”  Creation Science Update, Institute for Creation Research.  2021.  An ICR news reply to Peak et al. 2021, which answers it while citing Keller et al. 2019 and Flowers et al. 2020.  The article uses it for the flatness argument, that the surface is too flat to have been carved over a long interval. ↩

1. 16a.

   On Keller et al. 2019 against Flowers et al. 2020:  “Whenever conclusions contradict, it's a good bet that neither conclusion holds any water.” ↩

2. 16b.

   “There couldn't have been much time between the erosion and the deposition, since the Great Unconformity surface is fairly flat in most places.  And in many cases, it contains broken pieces of the underlying material.  There are no gullies, ravines, channels or any other expected types of long-term erosion along the surface.  The surface looks fairly flat and appears as if it was only planed off hours or days before the sediments were deposited on top.”  His closing line is:  “It takes a global cause to produce a global effect, and the Flood fits the bill.” ↩

Clarey, Timothy.  “Conventional Science Still Struggling to Exhume the Great Unconformity.”  Creation Science Update, Institute for Creation Research, article 15828.  2026.  Its references are marked.  “accessed February 27, 2026”.  The byline at the foot of the body reads:  “Dr. Clarey is the director of research at the Institute for Creation Research.”  No publication date is printed on the page, so it was posted on or after the date its references were accessed.  It is a reply to Zhan et al. 2026, and the article uses it because it moves the Flood's onset down to the Great Nonconformity, one surface below the Great Unconformity. ↩

1. 17a.

   “But the results of this study do support an earlier beginning to the massive erosional event that likely marked the onset of the global Flood.  This earlier erosional surface is known as the Great Nonconformity at Grand Canyon, possibly marking the beginning of the Flood. …  Furthermore, this suggests that many Proterozoic (Precambrian) sediments may have also been part of the Genesis Flood.” ↩ ↩

Berean Archive.  The Grand Canyon.  n.d.  An article in this archive on the Grand Canyon's rock layers and their thicknesses, the eight things the Grand Canyon Supergroup requires before the Flood begins, the Sauk transgression inside the canyon, the carving debate, and the RATE radiometric arguments.  This article uses it for the canyon's own stratigraphy and for the Supergroup figures used in Part 6 of this article, which are documented there. ↩ ↩ ↩

Karlstrom, Karl E., and J. Michael Timmons.  “Many unconformities make one 'Great Unconformity'.”  Grand Canyon Geology: Two Billion Years of Earth's History (Geological Society of America Special Paper 489), 73–79.  Edited by J. Michael Timmons and Karl E. Karlstrom.  2012.  A chapter in a collected volume on the geology of the Grand Canyon.  The article uses its title, which says that many separate unconformities make up the one 'Great Unconformity'. ↩

DeLucia, Michael S. et al.  “Thermochronology links denudation of the Great Unconformity surface to the supercontinent cycle and snowball Earth.”  Geology 46(2):167–170.  2018.  Page 29:  The abstract states the general figure:  “The Great Unconformity (GU), a global erosion surface separating Precambrian and Paleozoic rocks, represents ~100–1000 m.y. of missing geologic time.”  A study of how granite and rhyolite in the St. Francois Mountains of Missouri cooled, using zircon and apatite (U-Th)/He dating and apatite fission-track dating, which record when rock cooled through temperatures near the surface, with radiation-damage-corrected t-T modelling in HeFTy.  The rock had been at least about 6 km down and was brought up by erosion between roughly 850 and 680 million years ago, and the authors link that erosion to the break-up of the supercontinent Rodinia.  The article uses it for the Missouri case, where Cambrian sandstone lies directly on the granite and rhyolite. ↩

1. 20a.

   Page 41:  Printed page of the 2020 dissertation chapter, which reproduces the paper.  “Subsequent cooling occurs between ca. 850 and ca. 680 Ma (dark gray box in Fig. 11) to temperatures between ~100 and 20 °C, or ~6.4 and 9.6 km of exhumation using a geothermal gradient of 25 °C/km.  A second, slower phase of cooling appears to occur from ca. 680 to 500 Ma in 7 of the 11 good paths, although this phase is subtle.” ↩

2. 20b.

   Page 33:  Printed page of the 2020 dissertation chapter, which reproduces the paper.  “The U/Pb ages for the granites and rhyolites in the St. Francois Mountains range from 1470 to 1380 Ma (Van Schmus et al., 1996).  The granites intruded the rhyolites and therefore crystallized at shallow crustal levels …  The oldest Paleozoic unit in the region, the Cambrian Lamotte Sandstone, was deposited at ~500 Ma (Ojakangas, 1963).” ↩

Clarey, Timothy.  “Still Trying to Explain the Great Unconformity.”  Creation Science Update, Institute for Creation Research.  2020.  A short news commentary answering Flowers et al. 2020, citing Keller et al. 2019 as its reference 3.  The article uses it as the young-earth answer to Flowers and colleagues. ↩

1. 21a.

   Paragraph closing paragraphs:  “So, it appears that uniformitarian scientists still cannot agree on what formed the global Great Unconformity.  It remains one of the largest and most extensive enigmas in geology.  Is it simply because they do not want to believe there was a global Flood?” ↩

2. 21b.

   “To make this extensive erosional surface, a significant portion of the Precambrian surface material, and some of the pre-Flood sedimentary rocks, must have been stripped off a majority of the world's continents, simultaneously, before the deposition of the overlying Sauk megasequence (Cambrian rocks).  This may have been caused by the torrential rains that occurred in the first 40 days of the Flood and/or by the erosive action of tsunami-like waves propagating across parts of the continents.” ↩

McDannell, Kalin T. et al.  “Thermochronologic constraints on the origin of the Great Unconformity.”  Proceedings of the National Academy of Sciences 119(29):e2118682119.  2022.  A 2022 paper by five authors that applied Bayesian inverse t-T modelling, which fits computer models of a rock's temperature history to its measured ages, to published thermochronology from four cratonic-interior locations: East Lake Athabasca, the Minnesota River Valley, the Ozark Plateau and the Pikes Peak batholith.  The authors report rapid cooling of 120 to 200 °C during the Cryogenian (717 to 635 million years ago), which they read as 3 to 5 km of erosion during the snowball Earth glaciations, and they argue that in these stable interiors glaciation is the only plausible cause.  The article uses it because it reworks Flowers' Pikes Peak data and reaches the opposite conclusion. ↩

1. 22a.

   Section Results:  The authors write:  “To better understand the thermal history of the Pikes Peak region, we remodelled the Flowers et al. (29) Pikes Peak ZHe [data].”  Section Abstract:  The abstract's conclusion runs the other way from Flowers': the models.  “imply widespread, synchronous cooling consistent with at least ∼3–5 km of unroofing during snowball Earth glaciations.” ↩

2. 22b.

   Section Discussion:  “A scenario where modest continental ice sheet incision rates are effectively constant at 0.05 to 0.1 km Myr⁻¹ yields 2.9–5.8 km of exhumation over the Sturtian glacial interval alone. …  Cowton et al. (113) indicated that the modern Greenland ice sheet erosion rate is ∼2.2–7.4 km Myr⁻¹ (from the ice margin to >50 km inland) during the deglacial phase, which is at least an order of magnitude higher than previously established ice sheet erosion rate estimates (114), and places incision rates on par with empirical estimates of ∼1 to >10 km Myr⁻¹ for temperate glaciers (115).” ↩

Peak, Barra A. et al.  “Zircon (U-Th)/He thermochronology reveals pre-Great Unconformity paleotopography in the Grand Canyon region, USA.”  Geology 50(3):e544.  2022.  Page e544:  “The Comment by Karlstrom et al. (2022) … makes false statements about our work and presents time-temperature (t-T) models that should not be interpreted because of invalidation by basic Grand Canyon geology … Reliable interpretations cannot be drawn from a model that is irreconcilable with geologic facts.”  A forum reply in the journal Geology from the team that first reported these zircon helium ages from Grand Canyon basement.  It answers a comment by Karlstrom, Guenthner, Thurston, Heizler, Ricketts and Timmons (Geology 50(3):e543, doi:10.1130/G49843C.1), which modelled the same data, and the article quotes its verdict that the comment's models are irreconcilable with geologic facts. ↩

Thurston, Olivia G. et al.  “Deep-time thermal history of the Great Unconformity in the Grand Canyon, USA: Combined zircon (U-Th)/He and K-feldspar 40Ar/39Ar thermochronometers.”  GSA Bulletin 136(11-12):4815–4835.  2024.  Section Abstract:  “two regional basement unroofing events … A ca. 1350–1250 Ma cooling event … and a second cooling episode … between ca. 600 Ma and 500 Ma.”  A 2024 modeling study that combined 26 new zircon (U-Th)/He results and 4 new K-feldspar 40Ar/39Ar data sets with 77 published zircon (U-Th)/He results to reconstruct how Grand Canyon basement cooled and was exhumed, meaning brought up toward the surface by erosion.  It found two episodes: a ca. 1350–1250 Ma event that records exhumation from about 10 km deep, and a second episode between ca. 600 and 500 Ma that raised rock from about 3 to 7 km deep to near the surface.  The article calls it the most recent synthesis of Grand Canyon thermochronology, and the two events it resolves are 750 million years apart. ↩

Billingsley, George H.  “Geologic Map of the Grand Canyon 30' x 60' Quadrangle, Coconino and Mohave Counties, Northwestern Arizona.”  Geologic Investigations Series (I-2688).  U.S. Geological Survey.  2000.  A geologic map at a scale of 1:100,000, issued with a 16-page pamphlet of unit descriptions.  The article uses the pamphlet as its authority for the lithology and thickness of each unit, since its Description of Map Units gives an east-to-west thickness range for every unit.  The map covers the central and western canyon but not the far eastern canyon, so the Cardenas Basalt, Nankoweap, Chuar and Sixtymile lie outside its area. ↩

1. 25a.

   Section Description of Map Units, Early Proterozoic metamorphic rocks, unit Xo:  “Orthoamphibole-bearing gneiss—Regolith.  An interval several meters thick of weathered detritus eroded from older plutonic rocks. …  Very small outcrops along Colorado River within Granite Gorge.”  The plutonic rocks in question are the ~1.84 Ga Elves Chasm pluton, so this is a buried weathering profile inside the basement, older than both canyon unconformities, and not the sub-Supergroup surface.  The unit descriptions are keyed by unit symbol rather than by page. ↩

Karlstrom, Karl E. et al.  “Redefining the Tonto Group of Grand Canyon and recalibrating the Cambrian time scale.”  Geology 48(5):425–430.  2020.  A 2020 paper by ten authors that redefines the Tonto Group, a set of rock layers in the Grand Canyon, and resets the dates of the Cambrian time scale.  The authors ran laser-ablation screening of 100-300 zircon grains per sample, a laser that burns a small pit in each grain, followed by chemical-abrasion isotope-dilution mass spectrometry, which measures uranium and lead isotopes, on the youngest grains plucked off the mount.  The article uses it for two things: the relief of the rock islands that stood up before the Tapeats Sandstone covered them, and the ages of the zircon grains in the Tonto Group. ↩

1. 26a.

   Figure 3, page 428:  Figure 3 caption:  “islands (monadnocks) of tilted Unkar Group strata (resistant Shinumo Sandstone) created up to 200 m of relief and were not covered until Bright Angel time.”  Billingsley's map records the same relationship: "The Tapeats fills in lowland areas and thins across or pinches out against young Proterozoic highlands," thickness 0-122 m. ↩

2. 26b.

   Figure 2, page 427:  The Figure 2 caption says the Tonto Group's detrital zircon spectrum (the ages of zircon grains washed in from older rocks) shows.  “peaks at 1.7, 1.4, and 1.1 Ga that reflect unroofing of older Precambrian basement and the Grand Canyon Supergroup, and a strong Cambrian peak.” ↩

Dalziel, Ian W. D., and Robert H. Jr. Dott.  “Geology of the Baraboo District, Wisconsin: A Description and Field Guide Incorporating Structural Analysis of the Precambrian Rocks and Sedimentologic Studies of the Paleozoic Strata.”  Information Circular (14).  Wisconsin Geological and Natural History Survey.  1970.  A field guide to the Baraboo Hills of Wisconsin, with a description of the Precambrian quartzite hills and the Cambrian rocks that bury them.  The scan's optical character recognition did not capture the printed page numbers, so the page numbers cited are PDF pages of the file.  The article uses it for the quartzite hills that stood above the Cambrian sea, and for a table of pebble size against distance from those hills. ↩

1. 27a.

   Page 12:  “Irving and Weidman recognized the profound unconformity between the two sequences and noted the spectacular coarse basal Paleozoic conglomerates.  Weidman had a clear appreciation of profound mountain building and deep erosion prior to Cambrian deposition.  He noted that the most resistant Precambrian rocks in Wisconsin remained as islands or monadnocks, and estimated that the Baraboo monadnocks must have been from 1000 to 1600 feet above the surrounding plain.”  Page 10:  “The Baraboo Ranges are exhumed monadnocks of massive, pink, maroon or purple-colored Baraboo Quartzite.  This conspicuous rock unit is certainly more than 4,000 feet thick.” ↩

2. 27b.

   Page 54, section Paleozoic stratigraphy:  “In addition, the topographically highest quartzite-conglomerate facies probably contains St. Peter age-equivalents, but they are impossible to differentiate from Jordan equivalents.”  The St. Peter Sandstone is Middle Ordovician. ↩

3. 27c.

   Table VI, page 7:  “Conglomerate-size data for lower Paleozoic rocks”.  Page 45:  The quartzite-island conglomerate plate caption:  “Typical crudely-stratified conglomerate of rounded quartzite … near the outer side of a quartzite island.”  Their Fig. 13 maps the Baraboo islands. ↩

Fenton, Cassandra R. et al.  “Peak discharge of a Pleistocene lava-dam outburst flood in Grand Canyon, Arizona, USA.”  Quaternary Research 65:324–335.  2006.  Section Abstract, page 324:  The abstract states:  “The Hyaloclastite Dam was up to 366 m high … Failure of the Hyaloclastite Dam released a maximum 11 × 10^9 m3 of water in 31 h.  Peak discharges … ranged from 2.3 to 5.3 × 10^5 m3 s−1 … This discharge is an order of magnitude greater than the largest known discharge on the Colorado River (1.4 × 10^4 m3 s−1) … and in the top ten largest floods in North America.”  A research paper that estimates the size and speed of a flood from a lava dam in the Grand Canyon during the Pleistocene.  The dam was made of hyaloclastite, a glassy rock that forms when lava meets water, and the authors compare the flood with the largest known flow on the Colorado River.  The article uses it for the size of that flood and for the authors' conclusion that such floods did little erosion. ↩

1. 28a.

   Page 334:  “Floods with large peak stream power, but of short duration and low total energy expenditure are ineffective agents of geomorphic change in alluvial or bedrock channels … lower incision rates are reported … in western Grand Canyon relative to eastern Grand Canyon for the past 630,000 yr, the time during which lava dams periodically existed in the western canyon.  The difference in incision rates may reflect the ineffective erosive power of lava-dam outburst floods in western Grand Canyon.” ↩