Mancos Group Field Trip Guide

 

Revisiting the Cretaceous Mancos Group in Utah—problems, previous methods, and new perspectives on a world-class Cretaceous marine section.  James I. Kirkland, M. Ryan King, Kevin G. Bylund, 2025 

The Canadian System (Period) as proposed by Flower (1957)

Because the Cephalopods were so different, Rousseau H. Flower wrote proposing the Canadian System with four divisions of unspecified rank (Flower 1957 p. 17).  Quoting from Flower:

"Faunally, the Canadian is relatively isolated from the Ordovician above and is characterized by stocks of its own. In the cephalopods..., the Canadian-Ordovician boundary involves changes never lower than of generic rank, and generally of the rank of families and orders."

Someone looking at only, or mostly Cephalopod fossils could see the column this way. The four divisions are areas where Flower collected cephalopods. The Cassinian from the Ft. Cassin area in Vermont, the Jeffersonian from the Adirondacks in NY, the Demingian from the Florida Mts. in New Mexico, and the Gasconadian from the Ozark Mt. area of Missouri. I don't think his later collections in Utah and Nevada changed anything.  His boundary is just above Zone K, which is basically the Hesperonomiella minor bed (e.g. Li and Droser 1999) or the base of the Whiterockian Stage of the Ordovician.

Chart modified from Flower 1964 (p. 23, fig. 3) Ross-Hintze Zones on the right.

These days, the Canadian System of Flower (later referred to as the Canadian Series) has been replaced with the Ibexian Series (Ross et al., 1997) and the Lower Ordovician Series of the ICS.

References:

Flower, R.H., 1957, Studies of the Actinoceratida, Memoir 2, New Mexico Bureau of Mines and Mineral Resources, Socorro, NM.

Flower, R.H., 1964, The Nautiloid Order Ellesmeroceratida (Cephalopoda), Memoir 12, New Mexico Bureau of Mines and Mineral Resources, Socorro, NM.

Li, X., and Droser, M.L., 1999, Lower and Middle Ordovician Shell Beds from the Basin and Range Province of the Western United States (California, Nevada, and Utah) PALAIOS, V. 14.

Ross, R.J., Jr, Hintze, L.F., Ethington, R.L., Miller, J.F., Taylor, M.E. & Repetski, J.E., 1997, The Ibexian, lowermost series in the North American Ordovician. United States Geological Survey Professional Paper, 1579-A.

Lower Ferron Sandstone and Juana Lopez Members of the Mancos Shale around the north side of the San Rafael Swell

In an attempt to show that the Juana Lopez Member of the Mancos Shale really does expose itself on the west side of the San Rafael Swell, I introduce some photos to help.

Lower Ferron east of Huntington (visible upper right).

Lower Ferron east of Huntington, these beds contain Prionocyclus hyatti near Mounds.  They also form a small cliff under the Ferron Sandstone south of here from Ferron south to Last Chance Creek.

Juana Lopez Member east of Huntington (visible upper left)  Prionocyclus macombi concretions in middle of cliff  (right) and P. wyomingensis concretions at top of cuesta across wash.

Juana Lopez Member east of Huntington.  The same thin platy siltstone beds that appear on the east side of the swell appear here with the same platy rubble littering the slopes.  The concretion beds are also the same.

Two beds of the Lower Ferron Sandstone with large round concretions just north of Mounds.  Lower bed contains the ammonite Prionocyclus hyatti along with many other mollusks.

Around the north side the Juana Lopez is still there above the Lower Ferron.

Juana Lopez Member just west of Cat Canyon where Highway 6 and 191 cut through the Farnham Dome just east of Wellington.  Prionocyclus wyomingensis beds at top of cuesta in middle distance (Light cliff), P. macombi concretions in middle of slope.  Farnham Unit of Lower Ferron Sandstone in foreground.  Some minor faults also in foreground, one duplicating the orange bed in center.

The same thin siltstone beds, the same platy rubble.

Lower Ferron Sandstone just below dark Juana Lopez Member, 1 mile southwest of Grassy Siding.  Coon Spring Sandstone Bed at base.  Brown concretion to left center is what's left of the P. hyatti beds at Mounds.

On the east side of the Swell, the beds above the Lower Ferron have been refered to the Juana Lopez.  The only real difference I can see is a couple (2) of thin (2cm max) calcarenite beds.  South and east of Green River the Juana Lopez has more and thicker calcarenite beds.

Juana Lopez Member just west of Grassy Siding, Mt. Elliot in right distance.  Prionocyclus macombi concretions form edge of middle cuesta, P. wyomingensis concretions form orange lip of upper cuesta.

 Here on the east side are the same thin bedded siltstone beds, the same platy rubble, and the same concretion beds with the same fossils.  The siltstone beds on the west side maybe get a bit thicker, up to 3 or 4 cm, even more reason not to refer them to the Blue Gate Shale.

References:

Dane, C. H., Cobban, W. A., and Kauffman, E. G., 1966, Stratigraphy and Regional Relationships of a Reference Section for the Juana Lopez Member, Mancos Shale, in the San Juan Basin, New Mexico, U.S.G.S. Bulletin 1224-H

Edwards, C., D. Hodgson, S. Flint, and J. Howell, 2005, Contrasting styles of shelf sediment transport and deposit in a ramp margin setting related to sea-level change and basin floor topography, Turonian (Cretaceous) Western Interior of central Utah, USA: Sedimentary Geology, v. 179

Molenaar, C. M., and Cobban, W. A., 1991, Middle Cretaceous Stratigraphy on the South and East Sides of the Uinta Basin, Northeastern Utah and Northwestern Colorado,   U.S.G.S. Bulletin 1787-P

Ugly Map Colors

Too bad modern geology is taking a step backward with their geologic mapping colors.  I have yet to see an official standard calling out the new colors. You used to get a choice at stratigraphy.org, but no more.  Are they using a traditional system for the sake of tradition under the guise of priority.  This is almost as bad as illustrating ammonoids upside down of their assumed life position (again, mainly tradition).  It is like moving away from Metric Units back to Imperial feet and inches.  Why random colors?  The divisions are called Systems or in the case of rock units, Series.  Why wouldn't the colors look better in order or series?

CGMW		USGS
	Quarternary
	Neogene
	Paleogene
	Cretaceous
	Jurassic
	Triassic
	Permian
	Pennsylvanian
	Mississippian
	Devonian
	Silurian
	Ordovician
	Cambrian
	“preCambrian”

I tried to match the colors from the latest time scale from www.stratigraphy.org for the CGMW colors, and from the pdf linked below for the USGS colors

Hopefully no rocks on your map from the Cretaceous, Mississippian, or Cambrian come in contact with each other, they would be difficult to separate.

CGMW		USGS
	Cretaceous
	Mississippian
	Cambrian

How about Jurassic, Pennsylvanian, and Silurian?

CGMW		USGS
	Jurassic
	Pennsylvanian
	Silurian

Why even use colors to distinguish different Formations or Series if they are so similar to others?

Are the old Standards to be changed?
The USGS published some suggestions back in 2005.

USGS Colors (pdf)

And the Geologic Data Subcommittee (GDS) of the Federal Geographic Data Committee (FGDC)

published standards for GIS in 2008.
Are these going to change?  Will they use the random color system of the CGMW?

Some pages (just a few I've run across so far) already using the CGMW colors:
This map (from SVP) was modified from an existing map and strat column with the new colors.
Macrostrat using the new colors.

I think it is unfortunate that these new colors are being adopted, and it seems to me a step backwards.

Whine over :(

Early Triassic Red Beds

Red beds between the lowest ammonoid bearing limestones and the basal conglomerates.  Commonly referred to the Black Dragon Formation (previously a member of the Moenkopi Fm.) or the Woodside Shale.  Exposed all over Utah, SE Idaho and SW Wyoming.

In the San Rafael Swell the lowest (and only) Triassic Limestone contains the Anasibirites Fauna, so the red beds below are older than Late Smithian age.

Lone Rock (right) above ridge of Sinbad Limestone with yellow and red Black Dragon Fm. below.  Foreground is Permian Black Box Dolomite.  On the road to the Black Box, northern San Rafael Swell.

In Weber Canyon the red beds overlie the Dinwoody Fm. and are below beds containing Meekoceras so these beds are either Dienerian or Early Smithian,

Woodside Shale with "Meekoceras Limestone" to the right.  In the canyon of the Weber River, just east of Morgan.

In the Confusion Range of western Utah.  A bed of limestone with large chert nodules and a chert pebble conglomerate separate the two sets of red beds shown (see this old post).  Kashmirites is found just above the calcarenites here and the brachiopod Xestotrema is found in limestones below the Permian red beds so these are probably Dienerian, or earliest Smithian.

Gerster Fm. redbeds (right), Thaynes red beds (center) and calcarenite (left).  Just north of Cowboy Pass in the northern Confusion Range.

Down south near Minersville the red beds are below limestones that contain the Early Smithian ammonoid Vercherites, so the beds here are probably Dienerian.

Moenkopi red beds below microbial limestones near Minersville.

  Farther south, around St. George, the limestones rest directly on the Permian and redbeds of this age are missing.

Early Triassic Thaynes Group Isotopes

A diagenetic control on the Early Triassic Smithian–Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)

C. Thomazo, E. Vennin, A. Brayard, I. Bour, O. Mathieu, S. Elmeknassi, N. Olivier, G. Escarguel, K. G. Bylund, J. Jenks, D. A. Stephen, E. Fara

In the aftermath of the end-Permian mass extinction, Early Triassic sediments record some of the largest Phanerozoic carbon isotopic excursions. Among them, a global Smithian-negative carbonate carbon isotope excursion has been identified, followed by an abrupt increase across the Smithian–Spathian boundary (SSB; ~250.8 Myr ago). This chemostratigraphic evolution is associated with palaeontological evidence that indicate a major collapse of terrestrial and marine ecosystems during the Late Smithian. It is commonly assumed that Smithian and Spathian isotopic variations are intimately linked to major perturbations in the exogenic carbon reservoir. We present paired carbon isotopes measurements from the Thaynes Group (Utah, USA) to evaluate the extent to which the Early Triassic isotopic perturbations reflect changes in the exogenic carbon cycle. The δ13Ccarb variations obtained here reproduce the known Smithian δ13Ccarb-negative excursion. However, the δ13C signal of the bulk organic matter is invariant across the SSB and variations in the δ34S signal of sedimentary sulphides are interpreted here to reflect the intensity of sediment remobilization. We argue that Middle to Late Smithian δ13Ccarb signal in the shallow marine environments of the Thaynes Group does not reflect secular evolution of the exogenic carbon cycle but rather physicochemical conditions at the sediment–water interface leading to authigenic carbonate formation during early diagenetic processes.

Basal Triassic Conglomerate

The Permian-Triassic boundary in central and southern Utah is marked with Conglomerates.  Some are probably Permian, those deep in paleo channels, and some are earliest Triassic, those mixed in with the sand and silt at the base of the Black Dragon Formation red beds.

In the East, there is a nice outcrop in Black Dragon Canyon coming off the San Rafael Swell.

Close-up of conglomerate in Black Dragon Canyon.

Outcrop of conglomerate (~1 meter thick here) in Black Dragon Canyon.  Above the yellowish Permian Black Box Dolomite "Kaibab Limestone", and below the yellowish Black Dragon Formation, the gray Sinbad Formation.  The Torrey, Moody Cyn., Chinle, and Wingate Formations continue the section.

At Minersville, the beds are much like those in Black Dragon Canyon.  The chert gravel is a little more rounded.

Close-up of conglomerate at the Minersville section.

Conglomerate, lower left, under the "Black Dragon" red beds in Minersville Canyon.

In the Confusion Range, three forms of the conglomerate are present; A chert pebble, a breccia, and a boulder.

Chert pebble conglomerate under "Woodside/Black Dragon" red beds on the eastern exposures at Disappointment Hills and Cowboy Pass.

Breccia in karstic crevices under "Reef limestones (Sinbad?)" on the west side exposures in the Disappointment Hills.

Boulder conglomerate under "Reef limestones (Sinbad?)" in the SW corner of the Cowboy Pass exposure.

Down in southern Utah, the only place where the conglomerate has an official name, the Rock Canyon Conglomerate crops out between the Sinbad and Permian rocks from Cedar City down into Arizona.

Close-up of the Rock Canyon Conglomerate in Spring Creek Canyon.

Two new papers on the Early Triassic rocks in Utah

Evolution of depositional settings in the Torrey area during the Smithian (Early Triassic, Utah, USA) and their significance for the biotic recovery; Olivier, N., Brayard, A., Vennin, E., Escarguel, G., Fara, E., Bylund, K.G., Jenks, J.F., Caravaca G. and Stephen, D.A.; 2015, Geological Journal

and

Microbial deposits in the aftermath of the end-Permian mass extinction: A diverging case from the Mineral Mountains (Utah, USA); Vennin, E., Olivier, N., Brayard, A., Bour, I., Thomazo, C., Escarguel, G., Fara, E., Bylund, K.G., Jenks, J.F., Stephen, D.A. and Hofmann, R.; 2015, Sedimentology

The Sinbad Formation as exposed just west of Capitol Reef National Park (just East of Torrey)

View of the Early Triassic rocks exposed just East of Minersville

9ISCPP in Zurich

Zurich and the Limmat River

Symposium signage

The Poster Hall

A colorful Poster

Recovery of benthic marine communities from the end‐Permian mass extinction at the low latitudes of eastern Panthalassa

Richard Hofmann, Michael Hautmann, Arnaud Brayard, Alexander Nützel, Kevin G Bylund, James F Jenks, Emmanuelle Vennin, Nicolas Olivier, Hugo Bucher

Early View (Online Version of Record published before inclusion in an issue)

Fossils from the Early Spathian "Eumorphotis Bioevent".  These were found in the Confusion Range.

More of our work on the Early Triassic of Utah and other Western States.

Smithian shoreline migrations and depositional settings in Timpoweap Canyon (Early Triassic, Utah, USA)

NICOLAS OLIVIER,ARNAUD BRAYARD,EMMANUEL FARA,KEVIN G. BYLUND,JAMES F. JENKS,EMMANUELLE VENNIN,DANIEL A. STEPHEN and GILLES ESCARGUEL

Geological Magazine FirstView Articles

Triassic Rock Canyon Conglomerate and Sinbad Formations
(formerly Timpoweap) in Timpoweap Canyon

More from our work in the Triassic of Utah.

Paleontological Resources Preservation US Forest Service

Amateurs will not be allowed to do research?

Amateurs and/or non-professionals will need a permit (if they can get one) to collect fossils for research.   Casual collecting just will not fit the bill if these regulations go into effect.  Who can do research collecting only 5 specimens of each type of fossil per year?  And what is a type of fossil?  Can I only collect 5 cephalopod fossils per year?
  In fact, even professionals and academics will need a permit to collect invertebrate fossils for research (which is what they all collect for) on any public land (the BLM will adopt the same regs as the USFS), which has not been necessary before.

From the Definitions Section:

4. The term casual collecting would restate the definition contained in 16 U.S.C. 470aaa of the Act. To be considered casual collecting, the activity would mean all of the following: Collecting of a reasonable amount of common invertebrate or plant paleontological resources for non-commercial personal use, either by surface collection or the use of non-powered hand tools, resulting in only negligible disturbance to the Earth's surface and other resources.

 14. The term non-commercial personal use as used in the definition of casual collecting would clarify the types of use allowed under casual collection, and would mean uses other than for purchase, sale, financial gain, or research. Common invertebrate and plant paleontological resources collected for research purposes is not personal use and would need to be authorized under a permit in accordance with Sections 291.13 through 291.20. Exchange of common invertebrate and plant paleontological resources among casual collectors would be permissible as long as such resources were collected in accordance with the Act and the proposed regulations.

 18. The term reasonable amount as used in the definition of casual collecting would quantify the maximum amount of common invertebrate and plant paleontological resources that could be removed from Federal lands. A person may remove up to one gallon of material in volume or 25 pounds in weight, and up to five specimens of each type of fossil per calendar year. If the fossil specimens are contained within rock slabs, the reasonable amount would be limited to a slab that can be hand-carried by one person without the aid of mechanical devices. The authorized officer may modify the amount that is reasonable in order to preserve fossil-bearing locations that may be at risk of being depleted, thereby preserving paleontological resources in accordance with the Act.

I think I'll post a comment to this one...

If I can make the July 22, 2013 deadline...


Paleontological Resources Preservation US Forest Service

For a cold, snowy, December day

San Rafael River cutting through the Swell

Just to remember those hot days of summer and early fall in the desert.  The Sinbad Formation of the Thaynes Group slopes down to river level on the left, bleached rocks of the Moenkopi Group up to the maroon Chinle Formation on the slopes of Assembly Hall Peak, with a cap of Wingate Sandstone, and Kayenta and Navajo above that on the cliffs beyond.  The leaves of the Fremont Cottonwoods just starting to foretell the cold and snow of today.

Silica Replacement

An update for this old Calcite Replacement post.

 After finding another small ammonoid (above) in the same beds, and a discussion on TONMO, I've realized the pattern on the two fossils is that of "Beekite".  Not having a lot of experience with silicified cephalopod fossils around here, I got out the acid bottle, fizz on the matrix, no fizz on the fossil.  So instead of a Calcite replacement, they are replaced with Silica.  Beekite may be a mineral, but the word is more commonly used as a descriptive term for the concentric rings of the replacement material.  

The fossil from the first post showing the "Beekite Rings".

Conglomerate again

On the south end of the outcrop is this conglomerate with some very large cobbles. There are few places where this bed rests on a limestone bed full of chert nodules, and a place where the calcarenite beds rest directly on top of this bed. The matrix looks like the calcarenite but a little more analysis is needed to verify.

The hammer is sitting on top of the Conglomerate, the beds above are the calcarenite. The hill in the middle distance is capped with the conglomerate (the dark rock), it was mapped as the Thaynes Formation back in the last century, all the rest is Permian.


The conglomerate on top of the hill. Limestone with chert in foreground. Both dip toward the NE, toward the axis of the syncline. The beds in the previous picture dip north, along the axis.

Permian/Triassic Transition

CP1

CP1 conglomerate

DH1

DH1 breccia

Just a few pics to ponder as the details are yet to be worked out.

Groups, Formations, Beds, Horizons and Zones

A little snippet (edited) from an email to Dan:

Lucas et al 2007 (on the Timpoweap) raised the Thaynes and Moenkopi Formations to Group status. If we dont accept Lucas et al, do we extend the Sinbad Member into the Confusion Range or extend the Thaynes Formation into the Pahvant Range. To me the rocks in the Pahvant Range, a few thin limestone beds in a fairly thick shale sequence, are more like the rocks in the Confusion Range than they are to the rocks in the San Rafael Swell (type Sinbad) where you get a fairly thin set of limestone beds with very little shale. Having hiked up to the Virgin in Dog Valley with Arnaud and Dawn, we noticed alot more thin limestone beds above the anasibirites beds, I didnt notice a clear contact to separate the Sinbad from the "Middle Red Formation" unless you just use the first set of red beds, the Virgin could probably be mapped. Ideally a new name for the rocks in Dog Valley and the Confusion range would make me happy, but that is beyond the scope of our abstract. So I was thinking of just calling them both the lower part of the Thaynes Group. Arnaud put Sinbad Formation on his strat sections for Dog Valley, and Thaynes Group for the DH sections. I think he used Sinbad Formation because the geologic map of the Richfield Quad and The Geology of Millard County both call it Sinbad* (or we discussed it in the field?). I really dont think it should be called Sinbad.

A formation is a mappable unit of rocks, a group is a set of similar formations, what separates one formation from another?

Jim asked me yesterday if I had heard of the Claraia Zone. I remembered seeing it somewhere like in Silberling & Tozer 1968, but Jim corrected me and read it as the Claraia Beds. It seems that Hintze used it in the Geologic History of Utah and/or The Geology of Millard County* (I will have to check on these). Is there a Claraia Zone? I also remember seeing Xxxxxx Horizon on a few papers. I think "Zone" is a formally defined unit, whereas Beds and Horizon are informal, can they be used interchangeably? Is an Horizon just a little thicker than a set of Beds?

*after reading the Geology of Millard County and the Richfield Map, It seems Hintze didn't refer to the Sinbad, he only calls it Moenkopi.