High Latitute Triassic Flora from Antarctica

Escapa, I. H., Taylor, E. L., Cúneo, R., Bomfleur, B., Bergene, J., Serbet, R., and  T. N. Taylor. 2011. Triassic floras of Antarctica: plant diversity and distribution in high paleolatitude communities. Palaios 26:522-544.

Abstract - Continental Triassic sequences in Antarctica are among the most continuous and best represented in Gondwana. Triassic fossil plants have been collected sporadically from Antarctica since the beginning of the twentieth century, but our knowledge of the vegetation during this time has dramatically increased during the last three decades. Here we review the fossil record of Triassic plants as representatives of natural groups from sites along the Transantarctic Mountains, using the fossils as evidence for successive vegetational changes through the Triassic, taking into account that these plant communities were living under particular high-latitude (70° or higher) paleoclimatological conditions, including a polar light regime. Even though our knowledge of the Triassic floras of Antarctica is still incomplete, this survey shows that these floras were remarkably diverse. Lycopsids, equisetaleans, ferns, seed ferns, ginkgoaleans, and conifers were major components of the landscape in Antarctica during this time. The diversity of gymnosperms is exceptional, with almost every major clade of seed plants present, despite the high paleolatitude; however, each clade is often represented by only one or a few genera. The occurrence of permineralized peat, along with compression-impression floras, has increased our knowledge of the morphology, reproductive biology, and evolution of many of the plants in these floras. In general, floral changes in Antarctica during the Triassic can be recognized elsewhere in Gondwana, especially in South America, although a strict correlation based on macrofossils is still not possible. Thus, this contribution represents the first attempt to bring together information on Triassic floras from continental Antarctica (excluding the Antarctic Peninsula) within a biostratigraphic framework and thereby to compare these floras with those from lower latitudes.

Two New Papers on the Triassic/Jurassic Boundary

Kent, D. V., and E. Irving. 2010. Influence of inclination error in sedimentary rocks on the Triassic and Jurassic apparent pole wander path for North America and implications for Cordilleran tectonics. Journal Of Geophysical Research 115: B10103, doi:10.1029/2009JB007205



Abstract - Because of paleomagnetic inclination error (I error) in sedimentary rocks, we argue that previous estimates of Triassic and Jurassic paleolatitudes of the North American craton have generally been too low, the record being derived mostly from sedimentary rocks. Using results from all major cratons, we construct a new composite apparent pole wander (APW) path for Triassic through Paleogene based on 69 paleopoles ranging in age from 243 to 43 Ma. The poles are from igneous rocks and certain sedimentary formations corrected for I error brought into North American coordinates using plate tectonic reconstructions. Key features of the new APW path are a 25° northward progression from 230 to 190 Ma to high latitudes (off northernmost Siberia) where the pole lingers until 160 Ma, a jump to the Aleutians followed by a hook in western Alaska by ∼145 Ma that leads to the 130–60 Ma stillstand, after which the pole moves to its present position. As an example of the application of this new path we use paleomagnetic results to determine that southern Wrangellia and Stikinia (W/S), the two most westerly terranes in the Canadian Cordillera, lay 630 to 1650 km farther south than at present relative to the craton during the Late Triassic and Early Jurassic. This is consistent with an exotic Tethyan origin as paleontological and mantle geochemical evidences imply. During the Late Triassic through Early Cretaceous, W/S moved northward more slowly than the craton, implying oblique sinistral net convergence over this 130 Myr interval. This was followed by dextral shear in latest Cretaceous through Eocene.


Donohoo-Hurley, L. L., Geissman, J. W., and S. G. Lucas. 2010. Magnetostratigraphy of the uppermost Triassic and lowermost Jurassic Moenave Formation, western United States: Correlation with strata in the United Kingdom, Morocco, Turkey, Italy, and eastern United States. Geological Society of America Bulletin 122: 2005-2019; doi: 10.1130/B30136.1


Abstract - 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.