Saturday, December 31, 2016

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 Lower 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.



Monday, February 22, 2016

Early Triassic Thaynes Group Isotopes

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.

Sunday, May 17, 2015

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.


Thursday, March 5, 2015

Jim Jenks gets the 2014 Katherine Palmer Award


My Friend and colleague Jim Jenks received PRI's 2014 Katherine Palmer Award.

It is a pleasure working with Jim and I congratulate him on getting this well deserved award.

Tuesday, March 3, 2015

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

Tuesday, September 16, 2014

Thursday, April 3, 2014

Types on loan from USNM to NHMU

After a request to the US National Museum, they sent the first of three loans of Type Specimens to the Natural History Museum of Utah.  Types are the specimens used to compare to other specimens to verify the others are typical of the type.  Syntypes are usually from a series of types where neither a Holotype or Lectotype have been designated.
Syntype of Wyomingites aplanatus (White 1879)

paperwork

Holotypes are single specimens showing what all other specimens of that species should look like.

Holotype for Danubites strongi  Hyatt & Smith 1905

Paperwork in the box



Jim and I will be examining these types over the next few weeks or months as they come in.  There is a lot of revising and/or synonymizing to do.  What was thought to be typical may actually be atypical of the type.


Holotype of Xenoceltites cordilleranus (Smith 1932)

Paperwork



Thanks to Dan Levin at the Smithsonian Institute, and Randy Irmis and Carrie Levitt-Bussian at the NHMU for helping and facilitating the loan from the USNM, we really appreciate their help and hospitality.