Trouble with Model

We had been trying to do this ourselves but found this fun model:


We can attest that the model parameters agree with our own incomplete efforts. It has lots of fun stuff to play with, and you can test the sensitivities of all the variables. We disagree with the commonly assumed R(initial) value ~2.5. The table of calculated values on the site has an average of 4.5. An excellent paper in review, Sanche et al at Los Alamos available on the CDC website finds Ri over 5. This model goes completely off the rails at these values so we set close to 3. We also disagree with a short infectious duration. Symptomatic spread alone is at least 5 days and there are at least 3 days of asymptomatic. Surprisingly, the model is insensitive to infectious duration, merely shifting the timing. Above we set the model to as close as possible to N=1 million so for the US you multiply by 327. The model seems excessively sensitive to initial infections. By limiting to 1 million and 1 initial behavior improved. Hospitalizations are a reasonable match, but deaths are too low. What we like about this is that contrary to the IHME model which predicts a decline that has not materialized, this shows we are going to be dealing with this for a while.

Above we tried to coax the model to replicate data we have for deaths and hospitalizations. We know from the Covid Tracking Project and Worldometers that daily hospitalization accelerated to 79,000 about April 15 and have declined only slightly since  ever since, defying the IHME model’s projected decline. Daily deaths reached a high of 2800 about April 20, and have likewise failed to decline according to IHME.

We were able to get a reasonably sensible approximation of actual US hospitalization and death only by removing intervention altogether. This makes no sense as intervention must surely be a factor. The model also takes way too long to reach appropriate values. We are seemingly only two months in.

We have developed some sympathy for the difficulty of modeling, but are forced to conclude that important variables are not yet included.



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The Possible Origins of 2019-nCoV Coronavirus

The possible origins of 2019-nCoV coronavirus
Botao Xiao1,2* and Lei Xiao3
1 Joint International Research Laboratory of Synthetic Biology and Medicine, School
of Biology and Biological Engineering, South China University of Technology,
Guangzhou 510006, China
2 School of Physics, Huazhong University of Science and Technology, Wuhan
430074, China
3 Tian You Hospital, Wuhan University of Science and Technology, Wuhan 430064,
* Corresponding author:
Tel / Fax: 86-20-3938-0631

The 2019-nCoV coronavirus has caused an epidemic of 28,060 laboratory-confirmed
infections in human including 564 deaths in China by February 6, 2020. Two descriptions
of the virus published on Nature this week indicated that the genome sequences from
patients were 96% or 89% identical to the Bat CoV ZC45 coronavirus originally found in
Rhinolophus affinis (1,2). It was critical to study where the pathogen came from and how it
passed onto human.

An article published on The Lancet reported that 41 people in Wuhan were found to
have the acute respiratory syndrome and 27 of them had contact with Huanan Seafood
Market 3. The 2019-nCoV was found in 33 out of 585 samples collected in the market after
the outbreak. The market was suspicious to be the origin of the epidemic, and was shut
down according to the rule of quarantine the source during an epidemic.
The bats carrying CoV ZC45 were originally found in Yunnan or Zhejiang province,
both of which were more than 900 kilometers away from the seafood market. Bats were
normally found to live in caves and trees. But the seafood market is in a densely-populated
district of Wuhan, a metropolitan of ~15 million people. The probability was very low for the bats to fly to the market. According to municipal reports and the testimonies of 31 residents and 28 visitors, the bat was never a food source in the city, and no bat was traded in the market. There was possible natural recombination or intermediate host of the coronavirus, yet little proof has been reported.
Was there any other possible pathway? We screened the area around the seafood
market and identified two laboratories conducting research on bat coronavirus. Within ~280 meters from the market, there was the Wuhan Center for Disease Control & Prevention (WHCDC) (Figure 1, from Baidu and Google maps). WHCDC hosted animals in laboratories for research purpose, one of which was specialized in pathogens collection and identification (4-6).

In one of their studies, 155 bats including Rhinolophus affinis were captured in Hubei
province, and other 450 bats were captured in Zhejiang province (4). The expert in collection was noted in the Author Contributions (JHT). Moreover, he was broadcasted for collecting viruses on nation-wide newspapers and websites in 2017 and 2019 (7,8). He described that he was once by attacked by bats and the blood of a bat shot on his skin. He knew the extreme danger of the infection so he quarantined himself for 14 days (7).

In another accident, he quarantined himself again because bats peed on him. He was once thrilled for capturing a bat carrying a live tick (8). Surgery was performed on the caged animals and the tissue samples were collected for DNA and RNA extraction and sequencing (4, 5). The tissue samples and contaminated trashes were source of pathogens. They were only ~280 meters from the seafood market. The WHCDC was also adjacent to the Union Hospital (Figure 1, bottom) where the first group of doctors were infected during this epidemic. It is plausible that the virus leaked around and some of them contaminated the initial patients in this epidemic, though solid proofs are needed in future study.
The second laboratory was ~12 kilometers from the seafood market and belonged to
Wuhan Institute of Virology, Chinese Academy of Sciences (1, 9, 10). This laboratory
reported that the Chinese horseshoe bats were natural reservoirs for the severe acute
respiratory syndrome coronavirus (SARS-CoV) which caused the 2002-3 pandemic (9).
The principle investigator participated in a project which generated a chimeric virus using
the SARS-CoV reverse genetics system, and reported the potential for human emergence (10). A direct speculation was that SARS-CoV or its derivative might leak from
the laboratory.
In summary, somebody was entangled with the evolution of 2019-nCoV coronavirus.
In addition to origins of natural recombination and intermediate host, the killer coronavirus probably originated from a laboratory in Wuhan. Safety level may need to be reinforced in high risk biohazardous laboratories. Regulations may be taken to relocate these laboratories far away from city center and other densely populated places.

BX designed the comment and performed literature search. All authors performed data
acquisition and analysis, collected documents, draw the figure, and wrote the papers.
This work is supported by the National Natural Science Foundation of China (11772133,
Declaration of interests
All authors declare no competing interests.
1. Zhou P, Yang X-L, Wang X-G, et al. A pneumonia outbreak associated with a new
coronavirus of probable bat origin. Nature 2020.
2. Wu F, Zhao S, Yu B, et al. A new coronavirus associated with human respiratory disease
in China. Nature 2020.
3. Huang C, Wang Y, Li X, et al. Clinical features of patients infected with 2019 novel
coronavirus in Wuhan, China. The Lancet 2019.
4. Guo WP, Lin XD, Wang W, et al. Phylogeny and origins of hantaviruses harbored by bats,
insectivores, and rodents. PLoS pathogens 2013; 9(2): e1003159.
5. Lu M, Tian JH, Yu B, Guo WP, Holmes EC, Zhang YZ. Extensive diversity of rickettsiales
bacteria in ticks from Wuhan, China. Ticks and tick-borne diseases 2017; 8(4): 574-80.
6. Shi M, Lin XD, Chen X, et al. The evolutionary history of vertebrate RNA viruses. Nature
2018; 556(7700): 197-202.
7. Tao P. Expert in Wuhan collected ten thousands animals: capture bats in mountain at night.
Changjiang Times 2017.
8. Li QX, Zhanyao. Playing with elephant dung, fishing for sea bottom mud: the work that will
change China’s future. thepaper 2019.
9. Ge XY, Li JL, Yang XL, et al. Isolation and characterization of a bat SARS-like coronavirus
that uses the ACE2 receptor. Nature 2013; 503(7477): 535-8.
10. Menachery VD, Yount BL, Jr., Debbink K, et al. A SARS-like cluster of circulating bat
coronaviruses shows potential for human emergence. Nature medicine 2015; 21(12): 1508-13.

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Pandemic Persistence

We labor under a serious misconception that Corona can be eliminated, like polio. The history of pandemics tells us otherwise. The H2N2 virus likely caused the pandemic of 1890. It became the seasonal flu until it was supplanted by H3N2 during the pandemic of 1900. H3N2 was in turn supplanted by the H1N1 virus that caused the 1918 pandemic,which became the seasonal flu until the pandemic of 1957, when it was supplanted by an evolved H2N2. Of course, this became the seasonal flu until 1968, when it was supplanted by a new and improved H3N2 during the pandemic of that year. Vaccination became routine in the U.S. in the 1990’s, but none of these viruses has been eliminated.

The graphic above by Ed Rybiki illustrates this game of virus leap frog. An H1N1 genetically identical to laboratory samples from 1918 caused an epidemic in 1977, but many Americans had immunity. There can be little doubt the critter escaped. Another H1N1 variant caused an epidemic in 2009 that caused fewer U.S. deaths because older Americans still had immunity.

Corona is the new lead dog pulling this sled. It may abate as the weather warms, but it is not going away. We will get antibodies from exposure or vaccine, or succumb. Let’s hope seasonality drums it down and gives us time to develop a vaccine.

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Pandemic Seasonality

We do not yet understand seasonality in viruses. There are ideas about UV from sunlight zapping them. There are ideas about elevated vitamin D in humans during the warm season. There are ideas that warm weather just dries them out, that they can’t handle the osmotic pressure of higher humidity, and that melatonin based human immune seasonality and virus seasonality co-evolved.

In general, coated viruses are seasonal. Covid-19 is coated. Three human coated corona viruses that commonly circulate as colds are strongly seasonal. We show below  the seasonality of past U.S. Pandemics.

These deaths are not adjusted per capita, as that has no effect on seasonality and separates the curves. Clearly, prior pandemic deaths are strongly seasonal. The 1967-68 year looks like it may have been pretty bad. Unfortunately, CDC has no monthly data except for 68-69.

Corona got off to a very late start in the U.S. Will it go “away in May”? Nobody will write a guarantee as this virus has been breaking rules. If it does, it may be back very strong next fall. We should have a vaccine by then.

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The Shapes of Pandemic Curves

Getting monthly data for even 1957 and 1968 is tough sledding. We finally found in the CDC Vital Statistics Archives monthly data for these pandemics. Monthly data for surrounding years is available for 1968, but only 1957 and 58 for that period. Influenza is a separate line immediately above pneumonia. Our interest was the shapes of the curves, so rather than get into the modern morass of adding flu and pneumonic deaths and looking for “excess”, we report here only deaths ascribed solely to flu.

Corona deaths are the crude totals from Worldometers and there has only been one complete monthly bin so far. CDC will eventually parse these crude deaths into flu and pneumonic, likely reducing the trend. Germany recently reduced its corona deaths nearly 50%. It appears corona will be worse than ’57 and ’68, but nowhere near as bad as 1918.

We show here San Francisco data as a proxy for the entire US based on the following:

We got monthly data by tracing in Autocad according to the monthly grid and apportioning the areas under the curve. We originally were going to use Boston as more representative, but population data proved difficult and SF had a nice round 500k population in 1918.

The graph above is for all causes of deaths. We had previously determined that the shapes of the curves for all causes in ’57 and ’68 closely matched the influenza only curves. On this basis, we apportioned our SF data to match 670k US flu and pneumonia deaths and multiplied it by the ratio of flu only to pneumonia deaths in 1968 (.074) to get flu only deaths in 1918. We then subtracted 1000 to roughly align the start points.

Obviously this is not ideal, but it is at least a rational basis for comparing the shapes.

There is a notable similarity of the shapes, reaching initial peaks in about a month and a half. It is also notable that the fall from initial highs seems much faster than IHME projects.

We have shown above only the second and third peaks of the widely circulated triple whammy from England shown above. US data for the first wave is dismal. A handful of deaths at an army base and nearby towns. The CDC offers this curve as anecdotal without axis data.There is an interesting paper (Olsen et al 2005) arguing for a US beginning in New York as early as 1916.

Sobering image of a ravaged lung from a soldier who died from the 1918 flu from Smithsonian Magazine:

We now feel trying to force everything to actual deaths for influenza only was an error that distorts the true historical perspective, so we make this addendum April 12. Below we have converted everything to deaths per capita and added the IHME model in monthly bins.


From this perspective, it appears very unlikely that Corona will ever make the big time in the US. be about the same as 68-69. Current data suggests that US cases and deaths are at or very near their peaks, somewhat earlier than IHME prediction.

A separate axis is required for 1918. It is a completely different animal. US population was 1/3 current, and deaths were six times higher. Let’s not go there, ever.

Note* We made a spreadsheet error from prior dithering with virus only that incorrectly reduced the IHME model. The graphic and text were modified 4-16-20.

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Unified Geological Map of the Grand Canyon

We were puzzled about the Supergroup so we bought a pdf map from the Geological Society of America that covered the eastern part. We found that a forest of inconsequential faults, strikes and dips, and other notations was distracting us from the trees. We converted it to Autocad with the notion of moving these nuisances to a different layer. This tediously done, we still did not like the hatches so we set about creating our own with better contrast.

This proved to be astonishingly difficult as the unit boundaries proved to be multiple crudely overlapping splines and polylines that confounded our new hatches. We wound up erasing duplicates and retracing the boundaries. Lots of Supergroup exposures lie west of our GSA map, so we used a similar approach with scaled screen captures from the USGS “Mapview”. These we positioned in

Arcmap to create the previously posted image below.

Arcmap allows crude two point geolocation of Autocad linework that is good enough for views from the stratosphere as above, but when we dug into the schists we really wanted more. We had been unable to accurately position the GSA map in Autocad. Autocad warps the underlying Bing image to match the linework from a single geolocation point, and none of their projections matched. 

During the schist work we realized that the Autocad imagery was good enough that we could SEE the layers and began drawing directly on the imagery. 

Thus the Unified Map of the Grand Canyon was born.

It was a lot of work. It is a completely different kind of geological map based on the river runner’s encounter with the TOP of each layer. Top means when you can’t see it any more because it is buried by the layer above, not when there is air above it. If there is air above it, you are somewhere below the top and above the bottom; which here is the top of the layer below. Using only the top forces constant mindfulness of the stratigraphy. 

We use no regions or hatches. The imagery itself becomes the hatch, true to the nature of the layer. We ignore land slides and faults not critical for understanding. Recent lava is a distraction. It is plainly visible. We die into it when it is thick, but often find a line that telegraphs through.

The map is unified in that the USGS Mapview uses many different maps compiled over half a century with different groupings and different names. Our interpretation groups Esplanade with Supai, Surprise Canyon with Redwall, and Temple Butte with Muav. The latter two are discontinuous, and well, we didn’t need any more lines.

We will get further into the features of this map in the next post. 








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A River Runner’s Guide to Grand Canyon Geology VI: The Schists

Geologists have great fun with puns on the term “schist”. Technically, it refers to metamorphic rock; rock that has been altered by high temperature and pressure. There are several grades of schist, our former favorite was “blue schist” as a double pun. You can imagine our surprise to find a camp in the Grand Canyon called “Bull Schist”, dispensing with subtlety.

Bull Schist

We camped just below and across the river at a camp called “Schist”, but you can see the intrusion across the river at the “Bull Schist” camp. This striking basaltic schist is what piqued our interest in the schists, and prompted this post.

The first schist encountered by river runners is the Vishnu schist about mile 78. This is also the first Paleoproterozoic rock encountered. The overlying Bass formation, the lowest of the Mesoproterozoic and Neoproterozoic Supergroup, is about 1.25 billion years old. The Vishnu schist shows multiple episodes of folding and metamorphism, but it is shot through and through with granite that has been dated about 1.68 billion years old, so there is a very significant unconformity here, a time lapse of some 430 million years.

We originally intended to ignore the granites and focus on the schists, but it is telling that the three gorges in the Grand Canyon that expose Paleoproterozoic rocks are called the upper, middle, and lower granite gorges.

Above the top of the Vishnu is shown as a green line in the first river encounter, just below Hance Rapid. Granite intrusions are shown in pink. The Bass Formation extends to the top of the red cliff face above the Vishnu/granite.

The schists can be seen above in the “W” of the Grand Canyon. They are found on the downstream sides of two modern uplifts the river detoured around to create the “W”. Perhaps the downstream sides were uplifted a bit more.

Current thinking is that the Paleoproterozoic Grand Canyon area was something like  current Indonesia, shown below; a complex subduction trench, island arc, back arc basin arrangement.

The Vishnu Schist (green) would have been intermediate back arc basin sediments from the primary island arc volcanic mountains. The Rama Schist (purple), with more silica and aluminum, would have been basin sediments from more inboard volcanics; something like the current Mono volcanic field. The Brahma Schist (blue, and the dark Bull Schist above), loaded with Iron and Manganese, would have been essentially mid ocean ridge basalts from back arc basin spreading.

Granite forms deep in the wet conditions beneath subduction related volcanic mountain ranges and island arcs. It cools slowly, and varies considerably in composition and crystalline structure depending on the exact conditions of temperature and pressure. Many different plutons (blobs) of granite can be identified, notably the Elves Chasm pluton of (maroon) granodiorite above. It is the oldest rock exposed in Western United States.

We intend a separate post on these plutons, but above we have simplified.

The (pink) 1.685 to 1.68 Ga granite is what we found  intruding the Vishnu at the first river encounter above. This stuff intrudes just about everything down the granite gorges with veins too small to draw. It seems to increase in tendency to form larger intrusions as we proceed downriver. Some folks consider this time period to be the peak of metamorphism.

The (maroon) granodiorite spans a lot of time from the Elves Chasm 1.84 to 1.71 Ga. It is far more foliated (showing layers), and expresses as plutons more than micro intrusions. It probably represents a series of main island arc mountain ranges.

Farthest downriver we have the (salmon) 1.375 Ga granite. This is granular (not foliated) and is actually of Mesoproterozoic age, but it is over 100 million years older than the Mesoproterozoic Supergroup members upstream. This is the Quartermaster pluton and it tends to look more like Sierra Nevada granite.

The reality is the granites and schists of the Grand Canyon Paleoproterozoic gorges represent an inseparable dance of island arcs and back arc basins pressed against the North American Continent.

We have done enough hard work to earn a flight of fancy.

Well, there you have it. A fanciful attempt to reconstruct geography 200 million years before eukaryotic (with a nucleus) cells evolved. Our most serious suggestion is that the distribution of Vishnu suggests two uplifts that dictate the “W” of the Grand Canyon may be ancient basins.


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A River Runner’s Guide to Grand Canyon Geology V: Transects

River runners follow the water. The water is in our blood, and following it is what we do. We began this series by using the Colorado River as a transect, and following the drainages up to the South Rim as lateral transects showing the elevations of the layers.

We had promised at the end of the last post to next explore the schists, but we had an idea to follow the water from the last Supergroup exposure at Tapeats Creek up and over the Kaibab uplift. The original notion was to illuminate the Supergroup. We followed Tapeats Creek up to the North Rim and then up Quaking Aspen Creek to the divide or watershed high point. From there, the water did not naturally take us back to the southeast across the Supergroup as intended. It took us down North Canyon, continuing to the northeast.

We followed it.

The dark blue transect is quite natural, and the water may eventually cut through the Kaibab Uplift along this line. This would leave the first dogleg of the Grand Canyon “W” as a cutoff meander.

As we followed the water we first encountered a puzzlement in the extra layers of Toroweap and Kaibab Limestone near the top. This appears to be the result of complex faulting and folding that may or not extend to deeper layers. We may eventually dig into this at an appropriate scale. We found the elevations of the strata at significantly higher elevations as we followed the water down North Canyon. Where the grade leveled off we were surprised to find an inverted sequence, where as we went down we encountered the sequence one would expect going up.

The river follows a very different (and much longer) path. It has been known since the Geological Survey in 1923 that the river is pretty much in equilibrium, and can be approximated closely with a straight grade as we have done here. Distances of the members at river level are apportioned according to the actual river length and position.

We are unaware of any published transects approximating ours, and offer here a reasonable hypothesis accounting for the data. The Butte Fault, which separates the Neoproterozoic Supergroup members from the river, transitions to the East Kaibab Monocline, which our transect crosses nearly perpendicular.

The folding of the East Kaibab Monocline must have taken place after Kaibab time, so Supergroup members may also have been folded. We find it interesting that the Escalante Creek member, the highest exposure “around the corner” and where we leave it in Tapeats Creek, is also the first Mesoproterozoic member the Colorado River encounters, even though it is not the youngest Mesoproterozoic member.

This post will be updated as we follow the water in future transects. Hopefully they will shed some light. Likely they will require some modifications to our effort here.






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A River Runner’s Guide to Grand Canyon Geology IV: Whither the Supergroup?

We left off the last post having seen the complete Supergroup sequence of over two miles of Neoproterozoic and Mesoproterozoic sediments. The river never encounters the Neoproterozoic part, roughly half. These lie above the river on the North Rim side along the northeast shoulder of the Kaibab uplift that defines the first leg of the “W” of the Grand Canyon.

The river essentially makes an end run around the southern end of the Kaibab uplift. Where it turns the corner and heads towards the northwest, the river first encounters the Paleoproterozoic felsic intruded schists of the upper “Granite Gorge”. We don’t know how old these are. They have been baked at high temperature at a very considerable depth, possibly in several episodes. Each melt overprints the isotopic information.

We show above the river leaving the colored and hatched Mesoproterozoic Supergroup and entering the first Granite Gorge. The granite intrusions look like swimming amabae. Red Cardenas Basalt intrusions can be seen scattered about the Supergroup.This sequence from the green Escalante Creek member to Cardenas intruded Bass Formation foreshadows the rest of the Supergroup in the Grand Canyon.

Below we zoom in to the strange relationship between the Bass and the Cardenas intrusion. It is like there is some weak layer in the Bass the Cardenas easily intruded. We will see this same relationship at the very last Supergroup exposure in the Grand Canyon. A date of 1741 million years has been found the most recent melt of the Rama Schist near the left of the image.


The solid hatched Cardenas Basalt (Yc) can be seen sandwiched within the Bass. The Hatakai Shale lies above it; and finally the outlining top of Paleozoic Tapeats.

After turning the corner, the river never encounters the Supergroup again until Shinumo Creek; but up side canyons, particularly on the North Rim side, Supergroup rocks can be found. The shallower canyons have only the lowest Bass and Shinumo members, with maybe some Cardenas Intrusion. The deeper canyons expose the green Escalante Creek, but nothing higher in the Mesoproterozoic sequence is ever exposed in the Grand Canyon again.

Despite the names Bass Rapid and Bass Camp, the Bass Formation only just barely manages to reach the river at the Shinumo Creek Supergroup exposure below. The Bass lies over waning Vishnu Schist near the end of the Upper Granite Gorge, and only reaches the river with the help of a fault.

The Shinumo Creek exposure is tectonically complex. We have shown only the faults that control Supergroup extents. Here the Cardenas has intruded between the Bass and the Hatakai Shale. Over the Hatakai we get the namesake Shinumo and Escalante Creek (greenish blue here). A fault system has left more Shinumo above the Escalante Creek (Dox), including an outlier in the “Mordred Abyss” beyond the usual Tapeats boundary.


Below we zoom into the final Supergroup exposure in the Grand Canyon. Fittingly, it extends down to the river, where river runners may bid it proper farewell. You may recall a couple graphics back how the Cardenas intruded the bass in a ribbon, seemingly in some weak layer, next to the older Paleoproterozoic schists. Here the river decided to follow the ribbon of Cardenas.

The Middle Granite Gorge begins just below Specter Rapid, near the bottom of the graphic. We will explore the relationship between the Supergroup and the older schists and granites in the next post.

When we step back and contemplate the distribution of the Supergroup rocks in the Grand Canyon, we still find ourselves asking the same question that drove us to this exercise: What’s going on here?

Do the Supergroup rocks extend over the top of the Kaibab uplift where they will be exposed when the Paleozoic overburden eventually erodes away? We find no reason to believe they do not. The Mesoproterozoic members, sometimes called the Unkar Group, have no unconformities or intervals of time and erosion. They extend the entire length of the second leg of the Grand Canyon “W” at fairly consistent elevations up the southwest side of the Kaibab Uplift.

Do the Neoproterozoic members overlie the Mesoproterozoic rocks beneath the Paleozoic rocks in the Kaibab uplift? Maybe. Both Karlstrom (2012) and Huntoon (1999) draw sections that have the Neoproterozoic pinch out at the North Rim.

The above is from Karlstrom. It is a transect at about Nankoweap. It shows both the Mesoproterozoic (Y) and Neoproterozoic (Z) both pinching out somewhat up the Kaibab uplift towards the North Rim. It is unlikely that anyone has drilled to verify this and it strikes us as relying heavily on the notion of a flat surface before Paleozoic deposition.

We find the top of the Mesoproterozoic exposures up the creeks on the western side of the uplift routinely at 4200 feet, some 2000′ higher than shown for the Escalante and Shinumo members here.

Do the Supergroup members continue dipping down beneath the Paleozoic members on river left? The Karlstrom section suggests they do.

The next post will tackle another river runner’s bewilderment; the schists.





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A River Runner’s Guide to Grand Canyon Geology III: The Supergroup

A typical visitor to the Grand Canyon looks down from the rim through about a mile of sediments to the river. Most of these are Paleozoic sediments extending back about 515 million years. They appear to be level, although in a prior post we showed this levelness is an illusion of limited perspective.

This post is about over two miles of older sediments the typical visitor rarely sees. The Supergroup sediments are sloped at about 15 degrees due to uplift prior to the Paleozoic sediments deposited on top of them. River runners encounter these rocks in a very bewildering sequence we resolved to clarify on our last trip.

Above we show the eastern distribution of Supergroup rocks on an Arcmap image showing the grand “W” of the Grand Canyon. It can be seen that all of the Supergroup exposures are on the shoulders of the Kaibab Uplift, which reads dark green from the forest. The North and South Rim Visitor Centers are roughly centered on the eastern Supergroup.

Above we zoom into the first iteration on the river, and complete sequence of the Supergroup. This corresponds to the right hand first leg of the “W” before the river turns northwest in the first image. The Supergroup is composed of 17 members. Nine are Neoproterozoic (hatched horizontal) and eight are Mesoproterozoic (hatched diagonal). The colors follow the spectrum from red to violet

Sediments are difficult to date in general and Proterozoic sediments in particular because complex critters used for markers had not yet  evolved. A tiny volcanic ash deposit in the Walcott, the second Neoproterozoic member, dates to 742 million years ago. The Walcott is separated from the Sixty Mile formation above by an unknown amount of missing time and an unknown amount of erosion. The Sixty Mile Formation, currently a maximum of 200 feet thick, is preserved rarely, and is separated from Paleozoic rocks above by  unknown intervals of time and erosion as well.

The oldest and lowest Neoproterozoic member, the Nankoweap Formation, is also bounded by unknown intervals of time and erosion. Interestingly, the lowest Nankoweap contains wisps of sediments derived from the latest Mesoproterozoic Cardenas Basalt, showing that these intrusions got off to an early start.

The river never encounters the Neoproterozoic section (Sixty Mile through Nankoweap). These rocks lie up the Kaibab monocline and are separated at about the top of the Redwall from the river sequence by a large vertical offset along the Butte Fault. Like other places in the Grand Canyon, you can get multiple copies of the sequences where faults have made a mess of things. From the river, the Paleozoic sequence goes from Tapeats to top of Redwall. Above the top of Redwall and the Butte Fault lie members of Neoproterozoic Supergroup. Above the Supergroup it starts over again with Tapeats and climbs up the entire sequence to the North Rim.

The river first encounters the Supergroup in the Mesoproterozoic Escalante Creek Formation, which is not even the youngest. This is because a vertical offset along the Palisades Fault has allowed the younger strata to erode away. Below the fault the river marches through each of the inclined sedimentary strata beginning with the Ochoa Point Formation in turn.

The youngest Mesoproterozoic member, the Cardenas Basalt, is an intrusive rather than sedimentary layer. Below the Palisades Fault it intrudes all the sedimentary layers and only meets the river in dikes intruding the Bass and Shinumo members near the bottom of the second graphic above. The Cardenas is generically dated about 1.1 billion years ago. The oldest Mesoproterozoic member, the Bass Formation, contains some ash dated at 1.254 billion years ago.

In summary, the Supergroup extends from 1.25 billion years ago to some unknown time between 742 and 515 million years ago. Its current aggregate thickness is over two miles. It contains four unconformities, intervals of erosion, where an unknown amount of additional thickness was lost.

The lowest Paleozoic member, The Tapeats Sandstone, overlies the Supergroup and provides an outline. The bottom of the Tapeats is about 515 million years old. We show the top of the Tapeats as a tan line (close to its actual color). We extend it through the entire distribution of Supergroup rocks, even where it overlies even older schists and granites rather than the supergroup, because we feel it ties the narrative of Paleozoic deposition over a highly eroded Proterozoic surface together.

We have found many places where the Tapeats pinches out against the Supergroup, and also against older Paleoproterozoic rocks. We will argue that the Proterozoic surface was not entirely flat, and that these places where the Tapeats pinches out represent islands in the Tapeats Sea.

For context, we show above the distribution of middle and late Proterozoic rocks in the western United States. These formed at the same time as the Supergroup. The warmer colors are igneous granites and volcanics and the cooler colors are sediments. The “W” of the Grand Canyon is shown as a white path in the lower left. The large area of sediments at the top of the image extends well into Canada and is known as the “Belt Supergroup”. Correlation of these units with the Grand Canyon Supergroup is hindered by the same difficulties of dating sediments.

In the next post we will follow the river down through the remaining Supergroup exposures.





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