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Albuquerque, NM, United States

Lucas S.G.,New Mexico Museum of Natural History and Science
Geological Society Special Publication | Year: 2010

German geologists began to study rocks now recognized as Triassic during the late 1700s. In 1823, one of those German geologists, a very astute mining engineer named Friedrich August von Alberti (1795-1878), coined the term 'Trias formation' for an c. 1 km thick, tripartite succession of strata in southwestern Germany - the Bunten Sandsteins, Muschelkalk and Keuper of the German miners. Alberti also recognized Triassic rocks outside of Germany, throughout much of Europe and as far away as India and the United States. By the end of the nineteenth century, Triassic rocks had been identified across Europe and Asia, and in North America, South America and Africa. Indeed, in 1895, the Austrian geologist Edmund von Mojsisovics (1839-1907) and his collaborators published a complete subdivision of Triassic time based on ammonoid biostratigraphy and, in so doing, introduced many of the Triassic chronostratigraphic terms still used today. The twentieth century saw the elaboration of an ammonoid-based Triassic timescale, especially due to the work of Canadian palaeontologist E. Timothy Tozer (1928-). During the last few decades, work also began on developing a global magnetic polarity timescale for the Triassic, a variety of precise numerical ages tied to reliable Triassic biostratigraphy have been determined, and conodont biostratigraphy has become an important tool in Triassic chronostratigraphic definition and correlations. The current Triassic chronostratigraphic scale is a hierarchy of three series (Lower, Middle, Upper) divided into seven stages (Lower = Induan, Olenekian; Middle = Anisian, Ladinian; and Upper = Carnian, Norian, Rhaetian) further divided into 15 substages (Induan = upper Gries-bachian, Dienerian; Olenekian = Smithian, Spathian; Anisian = Aegean, Bithynian, Pelsonian, Illyrian; Ladinian = Fassanian, Longobardian; Carnian = Julian, Tuvalian; Norian = Lacian, Alaunian, Sevatian). Ammonoid and conodont biostratigraphies provide the primary basis for the chronostratigraphy. A sparse but growing database of precise radioisotopic ages support these calibrations: base of Triassic c. 252 Ma, base Olenekian c. 251 Ma, base Anisian c. 247 Ma, base Ladinian c. 242 Ma, base Jurassic c. 201 Ma. A U/Pb age of c. 231 Ma from the Italian Pignola 2 section is lower Tuvalian, and U/Pb ages on detrital zircons from the non-marine Chinle Group of the western USA of c. 219 Ma are in strata of late Carnian (Tuvalian) age based on the biostratigraphy of palynomorphs, conchostracans and tetrapods. These data support placement of the Norian base at c. 217 Ma, and indicate that the Tuvalian is more than 10 million years long and that the Carnian and Norian are the longest Triassic stages. Magnetostratigraphic data establish normal polarity for all of the Triassic stage bases except Anisian and Ladinian. An integrated biostratigraphic correlation web for the marine Triassic consists of ammonoids, bivalves, radiolarians and conodonts, whereas a similar web exists for the nonmarine Triassic using palynomorphs, conchostracans and tetrapods. Critical to cross correlation of the two webs is the Triassic section in the Germanic basin, where a confident correlation of nonmarine biostratigraphy to Triassic stage boundaries has been achieved. The major paths forward in development of the Triassic timescale are: finish formal definition of all Triassic stage boundaries, formally define the 15 Triassic substages, improve the integration of the Triassic biostratigraphic webs and develop new radioisotopic and magnetostratigraphic data, particularly for the Late Triassic. © The Geological Society of London 2010.

D'Emic M.D.,University of Michigan | Wilson J.A.,University of Michigan | Williamson T.E.,New Mexico Museum of Natural History and Science
Journal of Vertebrate Paleontology | Year: 2011

Complete sauropod pedes are rare in the fossil record, which has limited their use in systematics. We describe a nearly complete, large sauropod pes from the Maastrichtian-age Naashoibito Member of the Kirtland Formation of New Mexico, U.S.A., that bears synapomorphies of some eusauropod clades, such as the presence of metatarsal I with a wide shaft and laterally deflected pedal unguals. Novel pedal characters presented herein, such as the presence of an embayment on the proximomedial corner of metatarsal IV, suggest that the Naashoibito specimen likely belongs to a titanosauriform. Based on its provenance, the Naashoibito specimen likely belongs to the derived titanosaur Alamosaurus sanjuanensis, which is the only recognized Late Cretaceous titanosaur in North America. However, formal referral to Alamosaurus awaits discovery of overlapping materials with the holotype or definitively referred remains. The holotypic scapula of Alamosaurus sanjuanensis is diagnostic, providing a basis for referral of some other Maastrichtian North American titanosaur specimens to the genus. Confirmation of these referrals and the description of the pes presented herein augment the data relevant to the systematic problems that have historically surrounded Alamosaurus. © 2011 by the Society of Vertebrate Paleontology.

Lucas S.G.,New Mexico Museum of Natural History and Science
Geological Society Special Publication | Year: 2010

The Triassic chronostratigraphic scale is a hierarchy of three series, seven stages and 15 substages developed during nearly two centuries of research. The first geological studies of Triassic rocks began in Germany in the late 1700s and culminated in 1834 when Friedrich August von Alberti coined the term 'Trias' for the Bunten Sandsteins, Muschelkalk and Keuper, a thick succession of strata between the Zechstein and the Lias. Recognition of the Trias outside of Germany soon followed, and by the 1860s Austrian geologist Edmund von Mojsisovics began constructing a detailed Triassic chronostratigraphy based on ammonoid biostratigraphy. In 1895, Mojsisovics and his principal collaborators, Wilhelm Waagen and Carl Diener, published a Triassic timescale that contains most of the stage and substage names still used today. In 1934, Leonard Spath proposed a Triassic ammonoid-based biochronological timescale that differed little from that of Mojsisovics and his collaborators. In the 1960s, E. Timothy Tozer proposed a Triassic ammonoid-based timescale based on North American standards, and his timescale included proposal of four Lower Triassic stages (Griesbachian, Dienerian, Smithian and Spathian). The work of the Subcommission on Triassic Stratigraphy began in the 1970s and resulted in current recognition of seven Triassic stages in three series: Lower Triassic-Induan, Olenekian; Middle Triassic-Anisian, Ladinian; Upper Triassic-Carnian, Norian and Rhaetian. The 1990s saw the rise of Triassic conodont biostratigraphy so that four intervals that have agreed on Triassic GSSPs use conodont occurrences as defining features: bases of Induan, Olenekian, Anisian and Rhaetian. The bases of the Ladinian and Carnian are defined by ammonoid events. The base of the Norian remains undefined, but will most likely be defined by conodonts. Except for the Rhaetian, the Middle and Upper Triassic stages and substages have been fairly stable for decades, but there has been much less agreement on Lower Triassic chronostratigraphic subdivisions. Issues in the development of a Triassic chronostratigraphic scale include those of: stability and priority of nomenclature and concepts; disagreement over and changing taxonomy; the use of ammonoid v. conodont biostratigraphy; differences in the perceived significance of biotic events for chronostratigraphic classification; disagreements about the utility of relatively short stages; correlation problems between the Tethyan and Boreal realms (provinces); and competing standards from the Old and New worlds. Most of these issues have been resolved in the recognition of three Triassic series and seven stages. Further development of the Triassic chronostratigraphic scale needs to focus on definition and characterization of the 15 Triassic substages as these will provide a much more detailed basis for subdivision of Triassic time than do the seven stages. © The Geological Society of London 2010.

Lucas S.G.,New Mexico Museum of Natural History and Science
Geological Society Special Publication | Year: 2010

The Triassic timescale based on nonmarine tetrapod biostratigraphy and biochronology divides Triassic time into eight land-vertebrate faunachrons (LVFs) with boundaries defined by the first appearance datums (FADs) of tetrapod genera or, in two cases, the FADs of a tetrapod species. Definition and characterization of these LVFs is updated here as follows: the beginning of the Lootsbergian LVF = FAD of Lystrosaurus; the beginning of the Nonesian = FAD Cynognathus; the beginning of the Perovkan LVF = FAD Eocyclotosaurus; the beginning of the Berdyankian LVF = FAD Mastodonsaurus giganteus; the beginning of the Otischalkian LVF = FAD Parasuchus; the beginning of the Adamanian LVF = FAD Rutiodon; the beginning of the Revueltian LVF = FAD Typothorax coccinarum; and the beginning of the Apachean LVF = FAD Redondasaurus. The end of the Apachean (= beginning of the Wasonian LVF, near the beginning of the Jurassic) is the FAD of the crocodylomorph Protosuchus. The Early Triassic tetrapod LVFs, Lootsbergian and Nonesian, have characteristic tetrapod assemblages in the Karoo basin of South Africa, the Lystrosaurus assemblage zone and the lower two-thirds of the Cynognathus assemblage zone, respectively. The Middle Triassic LVFs, Perovkan and Berdyankian, have characteristic assemblages from the Russian Ural foreland basin, the tetrapod assemblages of the Donguz and the Bukobay svitas, respectively. The Late Triassic LVFs, Otischalkian, Adamanian, Revueltian and Apachean, have characteristic assemblages in the Chinle basin of the western USA, the tetrapod assemblages of the Colorado City Formation of Texas, Blue Mesa Member of the Petrified Forest Formation in Arizona, and Bull Canyon and Redonda formations in New Mexico. Since the Triassic LVFs were introduced, several subdivisions have been proposed: Lootsbergian can be divided into three sub-LVFs, Nonesian into two, Adamanian into two and Revueltian into three. However, successful inter-regional correlation of most of these sub-LVFs remains to be demonstrated. Occasional records of nonmarine Triassic tetrapods in marine strata, palynostratigraphy, conchostracan biostratigraphy, magnetostratigraphy and radioisotopic ages provide some basis for correlation of the LVFs to the standard global chronostratigraphic scale. These data indicate that Lootsbergian = uppermost Changshingian, Induan and possibly earliest Olenekian; Nonesian = much of the Olenekian; Perovkan = most of the Anisian; Berdyankian = latest Anisian? and Ladinian; Otischalkian = early to late Carnian; Adamanian = most of the late Carnian; Revueltian = early-middle Norian; and Apachean = late Norian-Rhaetian. The Triassic timescale based on tetrapod biostratigraphy and biochronology remains a robust tool for the correlation of nonmarine Triassic tetrapod assemblages independent of the marine timescale. © The Geological Society of London 2010.

Donohoo-Hurley L.L.,University of New Mexico | Geissman J.W.,University of New Mexico | Lucas S.G.,New Mexico Museum of Natural History and Science
Bulletin of the Geological Society of America | Year: 2010

A composite magnetostratigraphy based on the magnetic polarity data from four sections of the uppermost Triassic and lowermost Jurassic Moenave Formation, Utah and Arizona, USA, can be correlated to the marine successions at Saint Audrie's Bay (UK), Oyuklu, Turkey, and the Southern Alps, Italy, and to the nonmarine sections in Morocco, northern Africa, and the Newark Basin, eastern North America, all deposited across the Triassic-Jurassic boundary. Our proposed correlation provides a stratigraphic framework to tie Triassic-Jurassic sedimentation in the American Southwest to the marine UK, Turkey, and Italy sections, and to the Pangea rift history, including extrusive igneous rocks, preserved in Morocco and in the Newark Basin. The Moenave polarity record is characterized by mostly normal polarity, as is consistent with other polarity records across the Triassic-Jurassic boundary, and is interrupted by at least two well-defined reverse-polarity magnetozones. On the basis of available paleontologic information, we interpret the oldest well-defined , reverse-polarity magnetozone, M2r of the Moenave Formation, to correlate with SA5n.2r or SA5n.3r of the Saint Audrie's Bay record, H- of the Oyuklu record, BIT5n.1r of the Italcementi Quarry record, the oldest reverse magnetozone in sedimentary rocks in Morocco, and with reverse magnetozone E23r of the Newark Basin. The youngest reverse magnetozone of the Moenave Formation, M3r, is correlated to the latest Triassic magnetozones SA5n.5r of the Saint Audrie's Bay record, J- of the Oyuklu record, and with the interval of reverse polarity in the "intermediate unit" of the Morocco record. Magnetostratigraphic correlations and marine biostratigraphic information support placement of the Triassic-Jurassic boundary in the middle to upper Whitmore Point Member of the Moenave Formation, the Lias Group of the Saint Audrie's Bay section, the chert-rich limestone of the Oyuklu section, above the Zu Limestone in Italy, and in the central Atlantic magmatic province extrusive zone in the Morocco and the Newark records. © 2010 Geological Society of America.

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