CAMP Magnetostratigraphy Revisited

New paper in which the results suggest that either the SA5.r magnetozone from St. Audrie's Bay is not recorded in North American and Moroccan CAMP deposits or that the SA5.r is not reliable or useful for global-scale correlations. This has implications on the timing of the CAMP eruptions in relation to the Triassic-Jurassic boundary as well as correlations into non-marine sequences. This paper also provides a new paleo pole hypothesis for CAMP deposits in Morocco, which is more similar than past poles recovered for that unit to those determined for the North American sequence.

Font, E., Youbi, N., Fernandes, S., El Hachimi, H., Kratinova, Z., and Y. Hamim. 2011. Revisiting the magnetostratigraphy of the Central Atlantic Magmatic Province (CAMP) in Morocco. Earth and Planetary Science Letters, corrected proof. doi:10.1016/j.epsl.2011.07.007

Abstract - The origin of the Triassic–Jurassic (Tr–J) mass extinction is still a matter of debate: proponents of the idea that continental flood basalts of the Central Atlantic Magmatic Province (CAMP) are responsible for the crisis are opposed by those who favor an extraterrestrial origin linked to the impact of meteorite. Principal limitations reside in the difficulty to date and correlate CAMP lavas with the marine realm turnover. One argument widely used to suggest that CAMP lavas pre-dated the Tr–J boundary in Morocco is based on the presence of two brief magnetic reversals in the intermediate units of the Tiourjdal and Oued Lahr sections (Morocco) that were correlated to the E23r chron from the Newark basin and to the SA5n.2r/3r and SA5r chrons of the Saint Audrie Bay [Knight, K.B., Nomade, S., Renne, P.R., Marzoli, A., Betrand, H., Youbi, N., 2004. The Central Atlantic Magmatic Province at the Triassic–Jurassic boundary: paleomagnetic and ⁴⁰Ar/³⁰Ar evidence from Morocco for brief, episodic volcanism. Earth and Planetary Science Letters 228, 143–160]. However the primary origin for these negative (reverse) magnetic components is questionable since no field or reversal test was provided to constrain the primary character of the remanence as well as because the small number of samples. Here we have conducted a detailed paleomagnetic and magnetic mineralogy study of the interbedded limestones of the Tiourjdal section and of other CAMP lavas sections where the intermediate unit is complete, namely the Tizi El Hajaj, Jbel Imzar and Aït Ourir sections, to better constrain the origin and stratigraphic location of these negative magnetic components. We show that the interbedded limestones of the Tiourjdal section were entirely remagnetized by chemical processes via acid and oxidizing hydrothermal fluids generated by eruptions of CAMP lavas. In addition, magnetostratigraphic data of the Tizi El Hajaj, Jbel Imzar and Aït Ourir sections show that the entire intermediate unit encompassed a positive (normal) magnetic interval. A good quality paleomagnetic pole for the CAMP lava in Morocco is then provided (Plat = 60.0°; Plong = 241.6°; A95 = 2.6; N = 99) that is now in better agreement with its trans-Atlantic counterpart.

New Magnetostratigraphy Data for the Upper Triassic Chinle Formation and Dockum Group of New Mexico

Lots of good new data in this paper that are very useful.  Unfortunately it is victimized by having to rely on previously published stratigraphic correlations that are generally erroneous and unsupported by radioisotopic dates, which especially affects some of the key conclusions of the paper. I also still get really confused with the "Chinle Group" terminology especially units like the "Petrified Forest Formation" which is not equivalent to the currently recognized Petrified Forest Member of the Chinle Formation. Trying to go back and forth between the two schemes (Chinle Formation vs. Chinle Group) is very confusing and often leads to mistakes unless one is extremely careful. Still I extend my congratulations to Kate Zeigler in getting this body of work out there. The correlations can be fine-tuned later.

Zeigler, K. E., and J. W. Geissman. 2011. Magnetostratigraphy of the Upper Triassic Chinle Group of New Mexico: Implications for regional and global correlations among Upper Triassic sequences. Geosphere 7:802–829; doi:10.1130/GES00628.1
Abstract - A magnetic polarity zonation for the Upper Triassic Chinle Group in the Chama Basin, north-central New Mexico (United States), supplemented by polarity data from eastern and west-central New Mexico (Mesa Redonda and Zuni Mountains, respectively), provides the most complete and continuous magnetic polarity chronology for the Late Triassic of the American Southwest yet available. Most of the Chinle Group sequence is composed of hematitic mudrocks that typically carry a well-defined, well-grouped magnetization (residing in both pigmentary and detrital hematite), with laboratory unblocking temperatures as high as 680 °C. Demagnetization experiments isolate magnetizations of south- or north-seeking declination and shallow inclination, which are interpreted as early acquired, Late Triassic magnetizations. Our proposed polarity correlations, coupled with biostratigraphic observations and recent U-Pb age determinations on detrital zircon–bearing strata in the Chinle Group in western New Mexico, West Texas, and Arizona, indicate that deposition of Chinle strata likely spanned a much shorter time span than previously considered. If this interpretation is correct, the Chinle Group can be correlated with only part of the Newark Supergroup or the Upper Triassic Tethyan sections. On a local scale, lower Chinle strata in the Chama Basin are significantly older than the Bluewater Creek Formation in western New Mexico, and the base of the Poleo Formation represents a disconformity of >13 m.y. duration. Magnetic polarity chronologies from upper Chinle strata in New Mexico and Utah suggest that strata considered to be part of the Rock Point Formation in north-central New Mexico are not time equivalent to type Rock Point strata in Utah or to the Redonda Formation of eastern New Mexico.

More Evidence for Long Norian and Rhaetian Stages

This is a new paper looking at Triassic magnetostratigraphic correlations between Europe and North America.  The findings essentially support the early conclusions of Muttoni et al. (2004; 2010) arguing for long Norian and Rhaetian stages.  Correlations between the Steinbergkogel sections in Austria and the Newark Supergroup in the eastern U.S.A., suggest the following timescale revisions:

Carnian-Norian boundary: ~226.6 Ma;
Lacian-Alaunian boundary: ~216.4 Ma (fairly equivalent to the old Carnian/Norian boundary);
Alaunian-Sevatian 1 boundary: 211.8 Ma;
Norian Rhaetian boundary: ~209.8 Ma.

Thus according to these data the early Norian is approximately 10 million years long, the middle Norian is 4.5 million years old, and the late Norian is 2 million years old for an approximately 17 million year long Norian stage.  The Rhaetian is approximately 9 million years long.

Proposed biostratigraphic data from palynomorphs and conchostracans suggesting a shorter Norian are refuted.

Hüsing, S. K., Deenen, M. H. L., Koopmans, J. G., and W. Krijgsman. 2011. Magnetostratigraphic dating of the proposed Rhaetian GSSP at Steinbergkogel (Upper Triassic, Austria): Implications for the Late Triassic time scale.  Earth and Planetary Science Letters 302: 203-216

Abstract - The Global Stratotype Section and Point (GSSP) for the Rhaetian Stage has recently been proposed at Steinbergkogel in Austria. We re-sampled the Steinbergkogel sections (STK-A and STK-B + C) in high-resolution to establish a robust magnetostratigraphy that allows global correlation. The palaeomagnetic signal at Steinbergkogel is composed of three components, which can be separated by thermal demagnetization. The highest temperature component, revealed between 280/300 and maximum 600 °C is of dual polarity and is interpreted as primary. Rock magnetic experiments showed that the signal is carried by magnetite. Our results allow correlation between the two individual Steinbergkogel outcrops. Subsequently, we correlate the two key biostratigraphic horizons for the base of the Rhaetian, the FO of M. hernsteini and the FAD of M. posthernsteini to other sections of the Tethys domain. The correlation to the astronomically dated continental successions of the Newark basin indicates that these positions for the base of the Rhaetian are most likely determined in chrons E16n and E16r, respectively. This correlation is confirmed by cyclostratigraphic control on the marine Pizzo Mondello (Italy) section, where a combination of long period Milankovitch cycles (~ 175-Myr) and short-eccentricity cycles (~ 100-kyr) provide additional correlation constraints, respectively supporting a long duration of the Rhaetian. Our study implies that the Norian and Rhaetian Stages have durations of ~ 17 and ~ 9 Myr.


REFERENCES

Muttoni, G., Kent, D.V., Jadoul, F., Olsen, P.E., Rigo, M., Galli, M.T., and A. Nicora. 2010. Rhaetian magneto-biostratigraphy from the Southern Alps (Italy): constraints on Triassic chronology. Palaeogeography, Palaeoclimatology, Palaeoecology 285: 1–16.

Muttoni, G., Kent, D.V., Olsen, P.E., Di Stefano, P., Lowrie, W., Bernasconi, S.M., and F. M. Hernandez. 2004. Tethyan magnetostratigraphy from Pizzo Mondello (Sicily)and correlation to the Late Triassic Newark astrochronological polarity time scale. Geological Society of America Bulletin 116: 1043–1058.

Rhaetian Magneto-biostratigraphy from the Southern Alps (Italy): Constraints on Triassic Chronology

This is fairly significant as it argues for quite a long Rhaetian Stage of the latest Triassic. If this is correct it means that a sizable portion of the upper part of the Chinle Formation could actually be Rhaetian in age. Not bad considering not too long ago workers were arguing if the Rhaetian was really even applicable outside of the marine realm.

Muttoni, G., Kent, D.V., Jadoul, F., Olsen, P.E., Rigo, M., Galli, M.T., and A. Nicora. 2009. Rhaetian magneto-biostratigraphy from the Southern Alps (Italy): Constraints on Triassic chronology. Palaeogeography, Palaeoclimatology, Palaeoecology. doi: 10.1016/j.palaeo.2009.10.014.

ABSTRACT: New Late Triassic-earliest Jurassic magneto-biostratigraphic data have been obtained from three overlapping sections in the Southern Alps, Italy (Costa Imagna, Brumano, Italcementi Quarry), comprised of ~ 520 m of shallow marine carbonates outcropping in stratigraphic continuity. Characteristic magnetic components of presumed depositional age record a sequence of 9 normal and reverse polarity magnetozones (as defined by at least three stratigraphically superposed samples) linked by conodont and palynofloral evidence from this study and the literature to Rhaetian to Triassic–Jurassic boundary age. This represents a significantly larger number of polarity zones than previously recognized in more condensed
Rhaetian sections from the literature, and by inference represents more time. These data are placed in a broader Late Triassic temporal framework by means of correlations to published magneto-biostratigraphic data from the Tethyan marine Pizzo Mondello section and the Newark astronomical polarity time scale (APTS). This framework is consistent with a position of the
Norian–Rhaetian boundary (as defined at Brumano and Pizzo Mondello by the first appearance of Misikella posthernsteini) within Newark magnetozones E17r–E19r in the ~ 207–210 Ma time interval, in basic agreement with the position originally estimated in the Newark using pollen biostratigraphy (E18 at 208–209 Ma). This framework is also consistent with the position of
the Triassic–Jurassic boundary interval (placed at Italcementi Quarry at the acme of Kraeuselisporites reissingeri coincident with a negative carbon isotope excursion) correlative to just above Newark magnetozone E23r and just below the oldest CAMP lavas dated at ~ 202 Ma. Hence, we estimate the duration of the Rhaetian to be ~ 5.5–8.5 Myr (or even longer if the
Triassic–Jurassic boundary is instead placed above the negative carbon isotope excursion as at Kuhjoch, which is the designated GSSP for the base of the Hettangian), and encompassing 9 magnetozones. This duration contrasts with a duration of ~ 2 Myr and only ~ 4 magnetozones in several alternative published magneto-biostratigraphic schemes.

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.