This is a new paper written by a group of geologists who are largely responsible for conducting much of the current geological mapping in New Mexico, and is an attempt to standardize the nomenclature used for Phanerozoic rocks especially the Triassic. Key recommendations regarding the Triassic rocks are abandonment of the Chinle as a Group and keeping it at the formation level, removal of the Dockum from the "Chinle Group" and reinstatement as the Dockum Group as traditionally used, and a suggestion where to divide strata between the Chinle and Dockum. Consideration of the Chinle as a group and subsuming the Dockum has been controversial and never fully accepted since it was first proposed in the early 1990s. Thus, this paper suggests abandonment of much of the nomenclature proposed by Spencer Lucas and colleagues over the last couple of decades.
Cather, S. M., Zeigler, K. E., Mack, G. H., and S. A. Kelley. 2013. Toward standardization of Phanerozoic stratigraphic nomenclature in New Mexico. Rocky Mountain Geology 48:101-124. doi:10.2113/gsrocky.48.2.101
Abstract - Nomenclature for Phanerozoic strata in New Mexico has been rapidly evolving, but not all proposed changes have been widely accepted. From a perspective of geologic mapping, we evaluate some recent nomenclatural proposals for Pennsylvanian, Permian, Triassic, Jurassic, and Paleogene units. Because of the long shelf-life of geologic quadrangle maps and the desirability of minimizing nomenclatural diversity among them, we present guidelines with which we argue for a conservative approach to changes in stratigraphic nomenclature.
Showing posts with label Stratigraphic Nomenclature. Show all posts
Showing posts with label Stratigraphic Nomenclature. Show all posts
Revised Stratigraphy of the Sonsela Member (Chinle Formation) in the Southern Part of Petrified Forest National Park, Arizona
One of the immediate problems facing me when I started working at Petrified Forest National Park in 2001 was the inability to often locate myself stratigraphically using existing lithostratigraphic models. This became particularly irksome in the winter of 2001 when I recovered a partial skeleton of the aetosaur Calyptosuchus wellesi from just below a prominent sandstone ledge in the central portion of the park. Calyptosuchus (=Stagonolepis) has been proposed as a biochronological index fossil of the Adamanian land vertebrate faunachron, which at that time was considered to represent the latest Carnian. The existing lithostratigraphic scheme divided the Petrified Forest Member of the Chinle Formation into upper and lower parts using a local sandstone called the Sonsela Sandstone bed. A major part of the problem was that various researchers differed on exactly what sandstone ledges in the park (and there are many) represented the Sonsela. Revisions by Andrew Heckert and Spencer Lucas in the Spring of 2003 (Heckert & Lucas, 2003 [imprint 2002]) and later that year by NAU graduate student Daniel Woody (Woody 2003, 2006) looked to address this problem by expanding the Sonsela Member to include more of these beds and to provide hypotheses of correlation. Unfortunately, attempts to map the park in 2006 at the 1:24000 scale realized that the new proposed correlations looked great on paper, but didn't work at the outcrop or on the map (Raucci et al., 2006). This reinforced doubts I was already having because of difficulty using the new scheme in the field, and simply stating that it represented a complex fluvial system wasn't helping.
In 2008 Jeff Martz was hired in a seasonal position at the park. Jeff had just completed his dissertation at Texas Tech University solving similar problems in the Upper Triassic Dockum Group of west Texas. Realizing that this was a perfect opportunity to examine and hopefully solve this problem once and for all I dragged him out to an area of the park known as the Flattops, near the center of one of the more stratigraphically challenging areas of the park. The Flattops area contains three prominent sandstone horizons termed the Flattops Sandstones #2-4 (Billingsley, 1985) which are only found in this area and restricted in their lateral extent. One of the points Jeff had stressed in his dissertation was the need to completely walk out beds in areas with complex stratigraphy in order to ascertain the proper superpositional relationships and correlations of beds. In the past a lot of this had been done using correlated measured sections or seemingly by 'eyeballing it'. I placed us on top of what was unambiguously Flattops Sandstone #2 and we proceeded to walk out numerous beds in the Sonsela Member. At first we assigned alpha names to each bed (e.g., A, B, C) and did not change these to existing bed level names until we could directly correlate to the 'type sections' for those beds. Fairly quickly we were able to work out most of the major correlations and superpositional relationships. We also were able to directly tie in all of our known fossil sites, including the site that had given me so much trouble since 2001.
The results of this work, which differs in significant ways from that of all previous workers, will be published on Friday, February 19th in the open access journal PLoSONE - Martz & Parker 2010. The media embargo ended today (Feb. 18th) and the paper is actually available now.
Figuring out the stratigraphic relationships of the southern portion of the park has allowed us to see support for various hypothesis regarding the depositional systems and biostratigraphy of the park, including the position of the Adamanian-Revueltian boundary (a proposed faunal and possibly floral turnover event; Parker & Martz, 2009). We have also been successful in correlating the northern and southern ends of the park, something that no previous researcher has been able to do conclusively. This allows us to amalgamate biostratigraphic data from both areas, allowing for a more robust biostratigraphic hypothesis. We are currently working on correlating other Chinle Formation outcrops in Arizona back to the park in hopes of developing regional lithostratigraphic and biostratigraphic models. A paper detailing our biostratigraphic hypotheses has been submitted and a paper discussing the north end stratigraphy and another on regional correlations are in the works.
One of the things we have tried to do with the PLoS ONE paper is to make our study completely reproducible. This was a problem we had with many of the past studies, rendering much of their data unusable. For example, stratigraphic measured sections can be highly subjective both in terms of where on the outcrop it was measured as well as how the individual units were broken out. In complex fluvial systems where beds can thicken, thin, or pinch out laterally over very short distances the ability to precisely relocate where a section was done is very important. To this end we have provided (and advocate that all future studies also do this) GPS coordinates as well as photos of all measured outcrops, showing not only the location but how the outcrop was separated into units. We also provide a copy of our geological map. Mapping was crucial to the determining of correlations, and as is stated in the paper, we have doubts about stratigraphic correlations made without the tool of geological mapping. Furthermore, any proposed mistakes in our work can be easily verified or refuted by future workers by using the map. Very important!
This project has been a lot of work, but also a lot of fun and it is refreshing that I can pretty much accurately place myself stratigraphically anywhere in the park. This is crucial for accurate plotting of fossil sites and for determining stratigraphic ranges of organisms. I hope that our colleagues find this work extremely useful for their own studies on the Chinle Formation as well.
Martz, J.W., and W.G. Parker. 2010. Revised lithostratigraphy of the Sonsela Member (Chinle Formation, Upper Triassic) in the southern part of Petrified Forest National Park, Arizona. PLoSONE 5(2)e9329. doi:10.1371/journal.pone.0009329
ABSTRACT
Background: Recent revisions to the Sonsela Member of the Chinle Formation in Petrified Forest National Park have presented a three-part lithostratigraphic model based on unconventional correlations of sandstone beds. As a vertebrate faunal transition is recorded within this stratigraphic interval, these correlations, and the purported existence of a
depositional hiatus (the Tr-4 unconformity) at about the same level, must be carefully re-examined.
Methodology/Principal Findings: Our investigations demonstrate the neglected necessity of walking out contacts and mapping when constructing lithostratigraphic models, and providing UTM coordinates and labeled photographs for all measured sections. We correct correlation errors within the Sonsela Member, demonstrate that there are multiple Flattops
One sandstones, all of which are higher than the traditional Sonsela sandstone bed, that the Sonsela sandstone bed and Rainbow Forest Bed are equivalent, that the Rainbow Forest Bed is higher than the sandstones at the base of Blue Mesa and Agate Mesa, that strata formerly assigned to the Jim Camp Wash beds occur at two stratigraphic levels, and that there are
multiple persistent silcrete horizons within the Sonsela Member.
Conclusions/Significance: We present a revised five-part model for the Sonsela Member. The units from lowest to highest are: the Camp Butte beds, Lot’s Wife beds, Jasper Forest bed (the Sonsela sandstone)/Rainbow Forest Bed, Jim Camp Wash beds, and Martha’s Butte beds (including the Flattops One sandstones). Although there are numerous degradational/
aggradational cycles within the Chinle Formation, a single unconformable horizon within or at the base of the Sonsela Member that can be traced across the entire western United States (the ‘‘Tr-4 unconformity’’) probably does not exist. The shift from relatively humid and poorly-drained to arid and well-drained climatic conditions began during deposition of the Sonsela Member (low in the Jim Camp Wash beds), well after the Carnian-Norian transition.
REFERENCES
Billingsley, G. H.,1985. General stratigraphy of the Petrified Forest National Park, Arizona. Museum of Northern Arizona Bulletin 54:3-8.
Heckert, A.B., and S.G. Lucas. 2002. Revised Upper Triassic stratigraphy of the Petrified Forest National Park. New Mexico Museum of Natural History and Science Bulletin 21:1-36.
Martz, J.W., and W.G. Parker. 2010. Revised lithostratigraphy of the Sonsela Member (Chinle Formation, Upper Triassic) in the southern part of Petrified Forest National Park, Arizona. PLoSONE 5(2)e9329. doi:10.1371/journal.pone.0009329
Parker, W. G., and J. W. Martz. 2009. Constraining the stratigraphic position of the Late Triassic (Norian) Adamanian-Revueltian faunal transistion in the Chinle Formation of Petrified Forest National Park, Arizona. Journal of Vertebrate Paleontology 29(3):162A.
Woody, D. T., 2003. Revised geological assessment of the Sonsela Member, Chinle Formation, Petrified Forest National Park, Arizona. Unpublished M. S. Thesis, Northern Arizona University, Flagstaff.
Woody, D. T., 2006. Revised stratigraphy of the lower Chinle Formation (Upper Triassic) of Petrified Forest National Park, Arizona. Museum of Northern Arizona Bulletin 62:17-45.
In 2008 Jeff Martz was hired in a seasonal position at the park. Jeff had just completed his dissertation at Texas Tech University solving similar problems in the Upper Triassic Dockum Group of west Texas. Realizing that this was a perfect opportunity to examine and hopefully solve this problem once and for all I dragged him out to an area of the park known as the Flattops, near the center of one of the more stratigraphically challenging areas of the park. The Flattops area contains three prominent sandstone horizons termed the Flattops Sandstones #2-4 (Billingsley, 1985) which are only found in this area and restricted in their lateral extent. One of the points Jeff had stressed in his dissertation was the need to completely walk out beds in areas with complex stratigraphy in order to ascertain the proper superpositional relationships and correlations of beds. In the past a lot of this had been done using correlated measured sections or seemingly by 'eyeballing it'. I placed us on top of what was unambiguously Flattops Sandstone #2 and we proceeded to walk out numerous beds in the Sonsela Member. At first we assigned alpha names to each bed (e.g., A, B, C) and did not change these to existing bed level names until we could directly correlate to the 'type sections' for those beds. Fairly quickly we were able to work out most of the major correlations and superpositional relationships. We also were able to directly tie in all of our known fossil sites, including the site that had given me so much trouble since 2001.
The results of this work, which differs in significant ways from that of all previous workers, will be published on Friday, February 19th in the open access journal PLoSONE - Martz & Parker 2010. The media embargo ended today (Feb. 18th) and the paper is actually available now.
Figuring out the stratigraphic relationships of the southern portion of the park has allowed us to see support for various hypothesis regarding the depositional systems and biostratigraphy of the park, including the position of the Adamanian-Revueltian boundary (a proposed faunal and possibly floral turnover event; Parker & Martz, 2009). We have also been successful in correlating the northern and southern ends of the park, something that no previous researcher has been able to do conclusively. This allows us to amalgamate biostratigraphic data from both areas, allowing for a more robust biostratigraphic hypothesis. We are currently working on correlating other Chinle Formation outcrops in Arizona back to the park in hopes of developing regional lithostratigraphic and biostratigraphic models. A paper detailing our biostratigraphic hypotheses has been submitted and a paper discussing the north end stratigraphy and another on regional correlations are in the works.
One of the things we have tried to do with the PLoS ONE paper is to make our study completely reproducible. This was a problem we had with many of the past studies, rendering much of their data unusable. For example, stratigraphic measured sections can be highly subjective both in terms of where on the outcrop it was measured as well as how the individual units were broken out. In complex fluvial systems where beds can thicken, thin, or pinch out laterally over very short distances the ability to precisely relocate where a section was done is very important. To this end we have provided (and advocate that all future studies also do this) GPS coordinates as well as photos of all measured outcrops, showing not only the location but how the outcrop was separated into units. We also provide a copy of our geological map. Mapping was crucial to the determining of correlations, and as is stated in the paper, we have doubts about stratigraphic correlations made without the tool of geological mapping. Furthermore, any proposed mistakes in our work can be easily verified or refuted by future workers by using the map. Very important!
This project has been a lot of work, but also a lot of fun and it is refreshing that I can pretty much accurately place myself stratigraphically anywhere in the park. This is crucial for accurate plotting of fossil sites and for determining stratigraphic ranges of organisms. I hope that our colleagues find this work extremely useful for their own studies on the Chinle Formation as well.
Martz, J.W., and W.G. Parker. 2010. Revised lithostratigraphy of the Sonsela Member (Chinle Formation, Upper Triassic) in the southern part of Petrified Forest National Park, Arizona. PLoSONE 5(2)e9329. doi:10.1371/journal.pone.0009329
ABSTRACT
Background: Recent revisions to the Sonsela Member of the Chinle Formation in Petrified Forest National Park have presented a three-part lithostratigraphic model based on unconventional correlations of sandstone beds. As a vertebrate faunal transition is recorded within this stratigraphic interval, these correlations, and the purported existence of a
depositional hiatus (the Tr-4 unconformity) at about the same level, must be carefully re-examined.
Methodology/Principal Findings: Our investigations demonstrate the neglected necessity of walking out contacts and mapping when constructing lithostratigraphic models, and providing UTM coordinates and labeled photographs for all measured sections. We correct correlation errors within the Sonsela Member, demonstrate that there are multiple Flattops
One sandstones, all of which are higher than the traditional Sonsela sandstone bed, that the Sonsela sandstone bed and Rainbow Forest Bed are equivalent, that the Rainbow Forest Bed is higher than the sandstones at the base of Blue Mesa and Agate Mesa, that strata formerly assigned to the Jim Camp Wash beds occur at two stratigraphic levels, and that there are
multiple persistent silcrete horizons within the Sonsela Member.
Conclusions/Significance: We present a revised five-part model for the Sonsela Member. The units from lowest to highest are: the Camp Butte beds, Lot’s Wife beds, Jasper Forest bed (the Sonsela sandstone)/Rainbow Forest Bed, Jim Camp Wash beds, and Martha’s Butte beds (including the Flattops One sandstones). Although there are numerous degradational/
aggradational cycles within the Chinle Formation, a single unconformable horizon within or at the base of the Sonsela Member that can be traced across the entire western United States (the ‘‘Tr-4 unconformity’’) probably does not exist. The shift from relatively humid and poorly-drained to arid and well-drained climatic conditions began during deposition of the Sonsela Member (low in the Jim Camp Wash beds), well after the Carnian-Norian transition.
REFERENCES
Billingsley, G. H.,1985. General stratigraphy of the Petrified Forest National Park, Arizona. Museum of Northern Arizona Bulletin 54:3-8.
Heckert, A.B., and S.G. Lucas. 2002. Revised Upper Triassic stratigraphy of the Petrified Forest National Park. New Mexico Museum of Natural History and Science Bulletin 21:1-36.
Martz, J.W., and W.G. Parker. 2010. Revised lithostratigraphy of the Sonsela Member (Chinle Formation, Upper Triassic) in the southern part of Petrified Forest National Park, Arizona. PLoSONE 5(2)e9329. doi:10.1371/journal.pone.0009329
Parker, W. G., and J. W. Martz. 2009. Constraining the stratigraphic position of the Late Triassic (Norian) Adamanian-Revueltian faunal transistion in the Chinle Formation of Petrified Forest National Park, Arizona. Journal of Vertebrate Paleontology 29(3):162A.
Woody, D. T., 2003. Revised geological assessment of the Sonsela Member, Chinle Formation, Petrified Forest National Park, Arizona. Unpublished M. S. Thesis, Northern Arizona University, Flagstaff.
Woody, D. T., 2006. Revised stratigraphy of the lower Chinle Formation (Upper Triassic) of Petrified Forest National Park, Arizona. Museum of Northern Arizona Bulletin 62:17-45.
Revised Chinle Stratigraphy of the Chama Basin
Zeigler, K. E., Kelley, S., and J. W. Geissman. 2008. Revisions to stratigraphic nomenclature of the Upper Triassic Chinle Group in New Mexico: New insights from geologic mapping, sedimentology, and magnetostratigraphic/ paleomagnetic data. Rocky Mountain Geology 43:121-141. DOI: 10.2113/gsrocky.43.2.121
This is a recent paper with some interesting and possibly key implications for stratigraphic correlations in the Chinle Formation. Historically, stratigraphic correlation for Late Triassic non-marine rocks in western North America has been accomplished mainly through the use of biostratigraphy (e.g., Camp, 1930 [phytosaurs]; Colbert and Gregory, 1957 [vertebrates]; Litwin et al., 1991 [palynomorphs]; Good, 1993 [invertebrates], Lucas, 1993 [vertebrates]); however, these biostratigraphic-based correlations have not been unambiguous and are often contested and revised (e.g., Long and Murry, 1995; Langer, 2005; Rayfield et al., 2005; Hunt et al. 2005; Parker, 2006). More recent studies (e.g., Riggs et al. 1996; Zeigler, 2008; Irmis and Mundil, 2008; Dickinson and Gehrels, 2008) generating isotopic dates as well as magnetostratigraphic data may be more reliable to provide correlations and reconstruct Late Triassic paleogeography. However, much of this work is in preliminary stages and/or unpublished outside of dissertations and/or abstracts. Nonetheless, some important resolutions have been made regarding the Late Triassic of the southwest U. S. such as confirming that the lower portion of the Glen Canyon Group is Triassic in age and not Jurassic (Molina-Garza et al. 2003), providing isotopic ages for the Chinle Formation (Riggs et al., 2003; Irmis and Mundil, 2008); and reconstructing the Chinle-Dockum River systems (Riggs et al. 1996; Dickinson and Gehrels, 2008).
Zeigler et al. (2008) examine the sedimentology and magnetostratigraphy of the Chinle Formation in the Chama Basin of north central New Mexico. This area is well known for its paleontology containing no less than four major vertebrate quarries (Canjilon, Snyder, Coelophysis, and Hayden) and the areas have produced the type materials of several taxa including Coelophysis bauri, Eucoelophysis baldwini, Typothorax coccinarum, and Dromomeron romeri (e.g., Colbert, 1989; Hunt and Lucas, 1993; Long and Murry, 1995; Sullivan and Lucas, 1999; Zeigler et al., 2003; Irmis et al., 2007). Furthermore, this area has produced the vast majority of known dinosauromorph (including dinosauriforms and dinosaurs) material from the Late Triassic (e.g., Colbert, 1989; Irmis et al., 2007). Thus, correlating these deposits to the rest of the Chinle Basin is of extreme importance.
In the Chama Basin, the members of the Chinle from oldest to youngest are the “Mottled Strata”, Agua Zarca Sandstone, Salitral Shale tongue, Poleo Sandstone Lentil, Petrified Forest Member, and the Siltstone Member (Stewart et al. 1972). Lucas (1993) raised the Chinle Formation to group status and correlated the Agua Zarca “Formation” to the Shinarump “Formation” and the siltstone member (erroneous termed the Red Siltstone Member by Zeigler et al. 2008) to the Rock Point “Formation”. This last correlation has been highly contested with other workers (e.g., Dubiel, 1989) suggesting correlation with the Owl Rock Member instead. In later papers, Lucas and colleagues (e. g., Lucas et al., 2003) separated out various members of the Salitral “Formation” and the Petrified Forest “Formation”. It is important to note that the Coelophysis Quarry is situated in the siltstone member; whereas the Snyder, Canjillon, and Hayden Quarries are in the Petrified Forest Member. Based on stratigraphic position and vertebrates Lucas (1993) correlated the siltstone member (his Rock Point) with the Redonda Formation (Dockum Group) in eastern New Mexico and the Poleo Sandstone to the Sonsela Sandstone of northeastern Arizona. Finally, Heckert and Lucas (2003) formally named the “Mottled Strata” the Zuni Mountains Formation.
One of the goals of Zeigler et al. (2008) was to test some of these correlations using geological mapping magnetostratigraphy and provide the following results:
1) The Zuni Mountain Formation is not mappable at the 1:24000 scale and thus is not a valid formation.
2) The various proposed members of the Salitral and Petrified Forest “Formations” cannot be distinguished by mapping and therefore are rejected.
3) The Poleo Sandstone is of almost entirely reverse polarity whereas the Sonsela Sandstone bed is of normal polarity and therefore cannot be correlative. [Note that this is the same bed which Jeff Martz and I now call the Jasper Forest bed of the Sonsela Member].
4) The siltstone member is predominantly of normal polarity whereas the type Rock Point (in Utah) and the Redonda Formation are of reverse polarity. Thus the siltstone member is not assignable to the Rock Point, nor is it correlative with the Redonda.
5) The siltstone member (and thus the Coelophysis Quarry) shares a paleo pole position with the lower part of the Moenave Formation of the Glen Canyon Group, which has alternatively been considered to be Triassic or Jurassic.
These conclusions reveal limitations of relying solely on biostratigraphy to correlate non-marine stratigraphic units. Late Triassic terrestrial fossils do have biostratigraphic utility, however, more work needs to be done (e.g., larger sample sizes) to determine accurate stratigraphic ranges of taxa, and this work needs to be done in concert with detailed palynology, magnetostratigraphic, stratigraphy, and anchored with robust isotopic dates.
One aspect of the Zeigler et al. (2008) paper that confuses me is the rank of the Chinle (and Kate and I have discussed this numerous times). In the beginning of the paper they suggest that because Spencer Lucas did not propose his change in rank for the Chinle in peer-reviewed literature, usage of Chinle Group for all non-marine Upper Triassic strata in the western U. S. is not valid. However, without any real justification or explanation they then ‘formally’ raise the Chinle to group rank only in the Chama Basin. When I mentioned this to a Chinle Formation veteran colleague of mine he exclaimed that this would only make things more confusing and Chinle nomenclature was already confusing enough. I have to agree. I really do not see the utility in raising the Chinle to group rank at all, nevermind in such a small portion of the formation. Now if one uses Chinle Group they will have to state whether this is sensu Lucas (1993) or sensu Zeigler et al. (2008). I am really not sure how any of this will be resolved.
Overall the new paper by Zeigler et al. (2008) provides intriguing hypotheses regarding the Chinle Formation and emphasizes how much work is left to do on that unit.
The photo above is of the Hayden Quarry in the Petrified Forest Member and is from here.
REFERENCES
Camp, C. L. 1930. A study of the phytosaurs with description of new material from western North America. Memoirs of the University of California, 10:1-174.
Colbert, E. H. 1989. The Triassic dinosaur Coelophysis. Museum of Northern Arizona Bulletin 57:1-160.
Colbert, E. H., and J. T. Gregory. 1957. Correlation of continental Triassic sediments by vertebrate fossils. Geological Society of America Bulletin 68:1458-1467.
Dickinson, W. R., and G. E. Gehrels. 2008. U-Pb ages of detrital zircons in relation to paleogeography: Triassic paleodrainage networks and sediment dispersal across southwest Laurentia. Journal of Sedimentary Research 78:745-764.
Dubiel, R.F. 1989. Depositional environments of the Upper Triassic Chinle Formation in the eastern San Juan Basin and vicinity, New Mexico. U.S. Geological Survey Bulletin 1801B:1-22.
Good, S. 1993. Molluscan paleobiology of the Upper Triassic Chinle Formation, Arizona and Utah. Unpublished PhD Dissertation, University of Colorado, Boulder.
Heckert, A. B., and S. G. Lucas. 2003. Triassic stratigraphy in the Zuni Mountains, west-central New Mexico. New Mexico Geological Society Guidebook 54:245-262.
Hunt, A. P. and S. G. Lucas, S.G. 1993. Stratigraphy and vertebrate paleontology of the Chinle Group (Upper Triassic), Chama Basin, north-central New Mexico. New Mexico Museum of Natural History Bulletin 2:61-69.
Hunt, A. P., Lucas, S. G., and A. B. Heckert. 2005. Definition and correlation of the Lamyan: A new biochronological unit for the non-marine late Carnian (Late Triassic). New Mexico Geological Society Guidebook, 56:357-366.
Irmis, R. B., and R. Mundil. 2008. New age constraints from the Chinle Formation resolve global comparisons of Late Triassic vertebrate assemblages. Journal of Vertebrate Paleontology 28:95A.
Irmis, R. B, Nesbitt, S. J., Padian, K., Smith, N. D., Turner, A. H, Woody, D., and A. Downs. 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317:358–361.
Langer, M. C. 2005. Studies on continental Late Triassic tetrapod biochronology. II. The Ischigualastian and a Carnian global correlation. Journal of South American Earth Sciences, 19:219-239.
Litwin, R. J., Traverse, A., and S. R. Ash. 1991. Preliminary palynological zonation of the Chinle Formation, southwestern U.S.A. and its correlation to the Newark Supergroup (eastern U.S.A.). Review of Palaeobotany and Palynology 68:269-287.
Long, R. A., and P. A. Murry. 1995. Late Triassic (Carnian and Norian) tetrapods from the southwestern United States. New Mexico Museum of Natural History and Science Bulletin, 4:1-254.
Lucas, S. G. 1993. The Chinle Group: Revised stratigraphy and chronology of Upper Triassic non-marine strata in the Western United States. Museum of Northern Arizona Bulletin 59:27-50.
Lucas, S. G., Zeigler, K. E., Heckert, A. B. and A. P. Hunt. 2003. Upper Triassic stratigraphy and biostratigraphy, Chama Basin, north-central New Mexico: New Mexico Museum of Natural History and Science Bulletin 24:15-39.
Molina-Garza, R. S., Geissman, J. W., and S. G. Lucas. 2003. Paleomagnetism and magnetostratigraphy of the lower Glen Canyon and upper Chinle Groups, Jurassic-Triassic of northern Arizona and northeast Utah. Journal of Geophysical Research 108, B4, 2181: 1-24.
Parker, W. G. 2006. The stratigraphic distribution of major fossil localities in Petrified Forest National Park, Arizona. Museum of Northern Arizona Bulletin 62:46-61.
Riggs, N. R., Lehman, T. M., Gehrels, G. E., and W. R. Dickinson. 1996. Detrital zircon link between headwaters and terminus of the Upper Triassic Chinle-Dockum paleoriver system. Science 273:97-100.
Riggs, N. R., Ash, S. R., Barth, A. P., Gehrels, G. E., and J. L. Wooden. 2003. Isotopic age of the Black Forest Bed, Petrified Forest Member, Chinle Formation, Arizona: An example of dating a continental sandstone. Geological Society of America Bulletin 115:1315-1323.
Stewart, J. H., Poole, F. G. and R. F. Wilson. 1972. Stratigraphy and origin of the Chinle Formation and related Upper Triassic strata of the Colorado Plateau region, U.S. Geological Survey Professional Paper 690, 336 p.
Sullivan, R. M. and S. G. Lucas. 1999. Eucoelophysis baldwini, a new theropod dinosaur from the Upper Triassic of New Mexico, and the status of the original types of Coelophysis. Journal of Vertebrate Paleontology 19:81-90.
Zeigler, K.E. 2008. Stratigraphy, paleomagnetism, and magnetostratigraphy of the Upper Triassic Chinle Group, North-central New Mexico and preliminary magnetostratigraphy of the Lower Cretaceous Cedar Mountain Formation, Eastern Utah. Unpublished PhD dissertation, University of New Mexico, 224p.
Zeigler, K.E., and J.W. Geissman. 2008. Magnetostratigraphy of the Upper Triassic Chinle Group and Implications for the Age and Correlation of Upper Triassic Strata in North America. Geological Society of America Abstracts with programs (online).
http://a-c-s.confex.com/crops/2008am/webprogram/Paper47897.html
K. E. Zeigler, S. Kelley, J. W. Geissman (2008). Revisions to stratigraphic nomenclature of the Upper Triassic Chinle Group in New Mexico: New insights from geologic mapping, sedimentology, and magnetostratigraphic/paleomagnetic data Rocky Mountain Geology, 43 (2), 121-141 DOI: 10.2113/gsrocky.43.2.121
Zeigler, K. E., Heckert, A. B. and S. G. Lucas. 2003. Paleontology and Geology of the Upper Triassic Snyder Quarry (Revueltian), North-Central New Mexico: New Mexico Museum of Natural History and Science Bulletin 24, 132 p.
Chinle Confusion
The word 'nomenclature' (syn: terminology) is defined as “a system of terms used in a particular science” and allows for more precise communication and understanding of ideas. All scientific disciplines have established nomenclature (called ‘jargon’ by those outside of the discipline) and many have rules regarding the establishment of nomenclature. The Chinle Formation (mainly) of Arizona, Utah, and western New Mexico and the Dockum Group (mainly) of eastern New Mexico and western Texas are Late Triassic terrestrial units that are often correlated to each other on the basis of similar fossil content. Both have been widely studied by geologists and paleontologists since the beginning of last century and it is still debated whether the units were deposited within separate basins. Current thinking shows that the two depocenters may have been connected early in their history (Riggs et al., 1996) and separated later (Lehman and Chatterjee, 2005). The Dockum was named in 1890, the Chinle in 1917.
In 1993 Spencer Lucas advocated raising the name Chinle to Group status (and thus all of its constituent members to Formation rank). In doing so he reduced to Dockum in Texas to formational rank and included it within his Chinle Group. His rationale was that both units were the same age (based on fossils) and deposited in the same basin. It is important to note that he included all Late Triassic terrestrial rocks (including the Popo Agie Fm. of Wyoming) in his newly established group and eliminated some other older names (e.g., Dolores Fm. of Colorado). In later papers Lucas and colleagues completely abandoned use of the name Dockum as well. Lucas et al. (1985) argued that the term Dockum was meaningless, having been widely applied and lacks specificity as it used to include strata later determined to be Middle Triassic in age (Anton Chico Formation). Lucas argued that the term Chinle was better established; however, when originally defined, the Chinle contained units that are now considered to be Jurassic in age (Glen Canyon Group). Nonetheless, this is irrelevant as lithostratigraphic units can be time transgressive and do not need to be restricted by chronstratigraphic boundaries. Moreover, revising lithostratigraphic units does not invalidate them.
Furthermore, the term Dockum has long (since the 1890s) been generally understood to be restricted to Upper Triassic strata exposed around the southern High Plains in eastern New Mexico and west Texas. However, the term “Chinle” has been applied in a much more varied fashion, not only to the upper Triassic strata of the Colorado Plateau, but to strata in northern Utah and Colorado (e.g., Eagle Basin) deposited in a separate basin, and to strata within the Dockum Group which is probably only equivalent to parts of the Chinle Formation on the Colorado Plateau. However, by 1993 the scope of the term “Chinle” was well understood. Ironically the most confusing application of the term “Chinle” has been its extension to all Upper Triassic strata in the southwest by Lucas (1993), which has created two very different understandings of the term in the literature. Given that Lucas (1993) argued that the term Dockum should only be restricted to its type area in Texas, his radical extension of the term “Chinle” through the whole western U.S. is puzzling.
Nonetheless, since first being proposed in 1993, the use of Chinle as a Group has been published in hundreds of papers and abstracts by Lucas and colleagues and has also been used by a few other workers as well. There is also a large group of researchers who insist on leaving the Chinle at Formational rank, as well as researchers from Texas who refuse to abandon the term Dockum. Arguments as to why the Chinle should not subsume the Dockum were provided by Lehman (1994) and Dubiel (1994) and most recently addressed by Carpenter (1997) who wrote: “substituting one name for another (Chinle Group for Dockum Group) violates nomenclatural stability. Furthermore, as a stratigraphic unit, the Dockum Group is not defined by time” making the arguments by Lucas and colleagues “meaningless”. He then writes “the term Dockum Group must be retained, and because it has priority, can be used to encompass the Upper Triassic formations of the American southwest”. He also notes that because Upper Triassic formations in Colorado, Wyoming, and Idaho were most likely not deposited in the same basins as the Chinle or Dockum they should be left alone.
Although Carpenter (1997) was just making a point and not really advocating using the term Dockum in Arizona and Utah, this is where the issue of nomenclatural utility comes to play. Admittedly these names were erected at different times by different researchers who may not have been looking at all of the Triassic rocks in the western U.S. as a whole, but this does not negate their utility. When we hear the term Dockum we think Texas, whereas Chinle suggests Arizona., to mix the two only causes confusion. Even more so IMHO combining all of these units under a single name tells us nothing new scientifically, we already knew that they were roughly of the same age. In fact, again IMHO, “Chinle Group” appears to basically be synonymous with “Upper Triassic” and tells us nothing about local lithostratigraphic variation. This is contrary to Lucas’ (1993) stated intent to “simplify” the basic nomenclatural framework. Essentially, you have two groups of workers, one producing a plethora of papers in in-house bulletins and geological society guidebooks, independently utilizing two differing schemes. In summary, not only is one scheme considered to be against the North American Stratigraphic Code, the situation also creates serious confusion especially among outside researchers, as I will document next with a couple cases.
Weishampel et al. (2004) provide a listing of all known dinosaur occurrences along with their stratigraphic information. Under their Triassic section for North America they refer to the Chinle Formation, but also refer to the members within it also as formations (e.g., “Chinle Formation/Petrified Forest Fm”.). This is non-sensical as they are actually referring to the Petrified Forest Member of the Chinle Formation. Furthermore they list “Chinle Formation/Santa Rosa Fm” regardless of the fact that the Santa Rosa has never been considered a member of the Chinle Formation. Again this makes no sense and would only confuse workers with no familiarity with the conflicting schemes. It certainly does appear that Weishampel et al. (2004) were confused.
Cleveland et al. (2007, 2008a, 2008b) have recently published a series of papers documenting Late Triassic paleosols from New Mexico. The earliest paper (Cleveland et al., 2007) explicitly states that they prefer the nomenclature of Lucas (1993), and in the second paper (Cleveland et al., 2008a) this is implied. However, in the third paper (Cleveland et al., 2008b) they drop the Chinle back to Formational rank, presumably to move away from the Lucas nomenclature (although they do not state why), and return all lesser units back to member rank. Unfortunately, it is not this simple. For example, Cleveland et al. (2008b) now list one of their units as the Painted Desert Member of the Chinle Formation. No such member has ever been proposed. This is the Painted Desert Member of the Petrified Forest Formation of the Chinle Group according to Lucas (1993). Thus, Cleveland et als. (2008b) unit is actually the Petrified Forest Member (Chinle Formation). Likewise, upon dropping Chinle Group they do not appear to resurrect the term Dockum for their units in eastern New Mexico. This provides a similar scheme to that of Weishampel et al. (2004) where the Santa Rosa and Redonda Formations are considered part of the Chinle Formation (equal rank?). Clearly Cleveland and colleagues are confused by the changes in nomenclature and are possibly propagating more confusion. By the way, this is not meant to be a criticism of their paleosol work or general conclusions, I’m just pointing out the stratigraphic nomenclature confusion. Obviously I support their switch back to Chinle as a formational name. I have provided the nomenclature from thier 2007 (top center) and 2008b (bottom left) papers below as well as a rough correction of the 2008b figure (bottom right) below.
In 1993 Spencer Lucas advocated raising the name Chinle to Group status (and thus all of its constituent members to Formation rank). In doing so he reduced to Dockum in Texas to formational rank and included it within his Chinle Group. His rationale was that both units were the same age (based on fossils) and deposited in the same basin. It is important to note that he included all Late Triassic terrestrial rocks (including the Popo Agie Fm. of Wyoming) in his newly established group and eliminated some other older names (e.g., Dolores Fm. of Colorado). In later papers Lucas and colleagues completely abandoned use of the name Dockum as well. Lucas et al. (1985) argued that the term Dockum was meaningless, having been widely applied and lacks specificity as it used to include strata later determined to be Middle Triassic in age (Anton Chico Formation). Lucas argued that the term Chinle was better established; however, when originally defined, the Chinle contained units that are now considered to be Jurassic in age (Glen Canyon Group). Nonetheless, this is irrelevant as lithostratigraphic units can be time transgressive and do not need to be restricted by chronstratigraphic boundaries. Moreover, revising lithostratigraphic units does not invalidate them.
Furthermore, the term Dockum has long (since the 1890s) been generally understood to be restricted to Upper Triassic strata exposed around the southern High Plains in eastern New Mexico and west Texas. However, the term “Chinle” has been applied in a much more varied fashion, not only to the upper Triassic strata of the Colorado Plateau, but to strata in northern Utah and Colorado (e.g., Eagle Basin) deposited in a separate basin, and to strata within the Dockum Group which is probably only equivalent to parts of the Chinle Formation on the Colorado Plateau. However, by 1993 the scope of the term “Chinle” was well understood. Ironically the most confusing application of the term “Chinle” has been its extension to all Upper Triassic strata in the southwest by Lucas (1993), which has created two very different understandings of the term in the literature. Given that Lucas (1993) argued that the term Dockum should only be restricted to its type area in Texas, his radical extension of the term “Chinle” through the whole western U.S. is puzzling.
Nonetheless, since first being proposed in 1993, the use of Chinle as a Group has been published in hundreds of papers and abstracts by Lucas and colleagues and has also been used by a few other workers as well. There is also a large group of researchers who insist on leaving the Chinle at Formational rank, as well as researchers from Texas who refuse to abandon the term Dockum. Arguments as to why the Chinle should not subsume the Dockum were provided by Lehman (1994) and Dubiel (1994) and most recently addressed by Carpenter (1997) who wrote: “substituting one name for another (Chinle Group for Dockum Group) violates nomenclatural stability. Furthermore, as a stratigraphic unit, the Dockum Group is not defined by time” making the arguments by Lucas and colleagues “meaningless”. He then writes “the term Dockum Group must be retained, and because it has priority, can be used to encompass the Upper Triassic formations of the American southwest”. He also notes that because Upper Triassic formations in Colorado, Wyoming, and Idaho were most likely not deposited in the same basins as the Chinle or Dockum they should be left alone.
Although Carpenter (1997) was just making a point and not really advocating using the term Dockum in Arizona and Utah, this is where the issue of nomenclatural utility comes to play. Admittedly these names were erected at different times by different researchers who may not have been looking at all of the Triassic rocks in the western U.S. as a whole, but this does not negate their utility. When we hear the term Dockum we think Texas, whereas Chinle suggests Arizona., to mix the two only causes confusion. Even more so IMHO combining all of these units under a single name tells us nothing new scientifically, we already knew that they were roughly of the same age. In fact, again IMHO, “Chinle Group” appears to basically be synonymous with “Upper Triassic” and tells us nothing about local lithostratigraphic variation. This is contrary to Lucas’ (1993) stated intent to “simplify” the basic nomenclatural framework. Essentially, you have two groups of workers, one producing a plethora of papers in in-house bulletins and geological society guidebooks, independently utilizing two differing schemes. In summary, not only is one scheme considered to be against the North American Stratigraphic Code, the situation also creates serious confusion especially among outside researchers, as I will document next with a couple cases.
Weishampel et al. (2004) provide a listing of all known dinosaur occurrences along with their stratigraphic information. Under their Triassic section for North America they refer to the Chinle Formation, but also refer to the members within it also as formations (e.g., “Chinle Formation/Petrified Forest Fm”.). This is non-sensical as they are actually referring to the Petrified Forest Member of the Chinle Formation. Furthermore they list “Chinle Formation/Santa Rosa Fm” regardless of the fact that the Santa Rosa has never been considered a member of the Chinle Formation. Again this makes no sense and would only confuse workers with no familiarity with the conflicting schemes. It certainly does appear that Weishampel et al. (2004) were confused.
Cleveland et al. (2007, 2008a, 2008b) have recently published a series of papers documenting Late Triassic paleosols from New Mexico. The earliest paper (Cleveland et al., 2007) explicitly states that they prefer the nomenclature of Lucas (1993), and in the second paper (Cleveland et al., 2008a) this is implied. However, in the third paper (Cleveland et al., 2008b) they drop the Chinle back to Formational rank, presumably to move away from the Lucas nomenclature (although they do not state why), and return all lesser units back to member rank. Unfortunately, it is not this simple. For example, Cleveland et al. (2008b) now list one of their units as the Painted Desert Member of the Chinle Formation. No such member has ever been proposed. This is the Painted Desert Member of the Petrified Forest Formation of the Chinle Group according to Lucas (1993). Thus, Cleveland et als. (2008b) unit is actually the Petrified Forest Member (Chinle Formation). Likewise, upon dropping Chinle Group they do not appear to resurrect the term Dockum for their units in eastern New Mexico. This provides a similar scheme to that of Weishampel et al. (2004) where the Santa Rosa and Redonda Formations are considered part of the Chinle Formation (equal rank?). Clearly Cleveland and colleagues are confused by the changes in nomenclature and are possibly propagating more confusion. By the way, this is not meant to be a criticism of their paleosol work or general conclusions, I’m just pointing out the stratigraphic nomenclature confusion. Obviously I support their switch back to Chinle as a formational name. I have provided the nomenclature from thier 2007 (top center) and 2008b (bottom left) papers below as well as a rough correction of the 2008b figure (bottom right) below.
To wrap this up (it is already much longer than I planned). IMHO the scheme presented by Lucas (1993) has caused more confusion than clarification regarding the stratigraphic nomenclature of the Upper Triassic rocks in the western U.S. Also, others have argued that his scheme is against the North American Stratigraphic Code. I am not adverse to the Chinle Formation being raised to group rank, but I cannot do so at the expense of the name Dockum. Moreover, given how radically the meaning of the term “Chinle” was stretched by Lucas (1993), this might propagate more confusion. I am certain that my colleagues in Texas will not call their rocks “Chinle”, and rightfully so. Likewise, I would never dream of calling the rocks in Arizona “Dockum”, because of the confusion it would introduce. Maybe this calls for a special symposium to straighten out the issue, or maybe we should all just stop using Chinle Group. Many of the southwestern U.S. Triassic workers already have (or never adopted it to begin with) but it is important that this issue is brought to the attention of outside workers to help cease the confusion.
REFERENCES
Carpenter, K. 1997. A giant coelophysoid (Certosauria) theropod from the Upper Triassic of New Mexico, USA. N. Jb. Geol. Palaeont. Abh. 205:189-208.
Cleveland, D.M., Atchley, S.C., and L.C. Nordt. 2007. Continental sequence-stratigraphy of the Late Triassic (Norian-Rhaetian) Chinle strata, northern New Mexico: Allo- and autocyclic origins of paleosol-bearing alluvial successions: Journal of Sedimentary Research 77:909–924.
Cleveland, D.M., Nordt, L.C., and S.C. Atchley. 2008a. Paleosols, trace fossils, and precipitation estimates of the uppermost Triassic strata in northern New Mexico: Palaeogeography, Palaeoclimatology, Palaeoecology 257:421–444.
Cleveland, D.M., Nordt, L.C., Dworkin, S.I., and S.C. Atchley. 2008a. Pedogenic carbonate isotopes as evidence for extreme climatic events preceding the Triassic-Jurassic boundary: Implications for the biotic crisis? GSA Bulletin 120:1408-1415.
Dubiel, R. F. 1994. Triassic deposystems, paleogeography, and paleoclimate of the western interior; pp. 133-168 in Caputo, M.V., Peterson, J.A., and K.J. Franczyk (eds.) Mesozoic systems of the Rocky Mountain Region, USA. RMS-SEPM.
Lehman, T.M. 1994. Save the Dockum Group. West Texas Geological Society Bulletin 34:5–10.
Lehman, T. and S. Chatterjee. 2005. Depositional setting and vertebrate biostratigraphy of the Triassic Dockum Group of Texas. Journal of Earth System Science 114:325-351.
Lucas, S.G. 1993. The Chinle Group: Revised stratigraphy and biochronology of Upper Triassic non-marine strata in the western United States. Museum of Northern Arizona Bulletin 59:27-50.
Lucas, S.G., Hunt, A.P., and M. Morales. 1985. Stratigraphic nomenclature and correlation of Triassic rocks in east-central New Mexico, a preliminary report. New Mexico Geological Society Guidebook 36:171-184.
Weishampel, D. B., Barrett, P. M., Coria, R. E., Le Loeuff, J., Gomani, E. S., Zhao Z., Xu X., Sahni, A., and C. Noto. 2004. Dinosaur Distribution, pp. 517-606 in Weishampel D. B., Dodson, P., and H. Osmólska, H. (eds.) The Dinosauria. 2nd edition. Univ. California Press, Berkeley.
Cleveland, D.M., Atchley, S.C., and L.C. Nordt. 2007. Continental sequence-stratigraphy of the Late Triassic (Norian-Rhaetian) Chinle strata, northern New Mexico: Allo- and autocyclic origins of paleosol-bearing alluvial successions: Journal of Sedimentary Research 77:909–924.
Cleveland, D.M., Nordt, L.C., and S.C. Atchley. 2008a. Paleosols, trace fossils, and precipitation estimates of the uppermost Triassic strata in northern New Mexico: Palaeogeography, Palaeoclimatology, Palaeoecology 257:421–444.
Cleveland, D.M., Nordt, L.C., Dworkin, S.I., and S.C. Atchley. 2008a. Pedogenic carbonate isotopes as evidence for extreme climatic events preceding the Triassic-Jurassic boundary: Implications for the biotic crisis? GSA Bulletin 120:1408-1415.
Dubiel, R. F. 1994. Triassic deposystems, paleogeography, and paleoclimate of the western interior; pp. 133-168 in Caputo, M.V., Peterson, J.A., and K.J. Franczyk (eds.) Mesozoic systems of the Rocky Mountain Region, USA. RMS-SEPM.
Lehman, T.M. 1994. Save the Dockum Group. West Texas Geological Society Bulletin 34:5–10.
Lehman, T. and S. Chatterjee. 2005. Depositional setting and vertebrate biostratigraphy of the Triassic Dockum Group of Texas. Journal of Earth System Science 114:325-351.
Lucas, S.G. 1993. The Chinle Group: Revised stratigraphy and biochronology of Upper Triassic non-marine strata in the western United States. Museum of Northern Arizona Bulletin 59:27-50.
Lucas, S.G., Hunt, A.P., and M. Morales. 1985. Stratigraphic nomenclature and correlation of Triassic rocks in east-central New Mexico, a preliminary report. New Mexico Geological Society Guidebook 36:171-184.
Weishampel, D. B., Barrett, P. M., Coria, R. E., Le Loeuff, J., Gomani, E. S., Zhao Z., Xu X., Sahni, A., and C. Noto. 2004. Dinosaur Distribution, pp. 517-606 in Weishampel D. B., Dodson, P., and H. Osmólska, H. (eds.) The Dinosauria. 2nd edition. Univ. California Press, Berkeley.
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