scholarly journals Slow apparent polar wander for North America in the Late Triassic and large Colorado Plateau rotation

Tectonics ◽  
1993 ◽  
Vol 12 (1) ◽  
pp. 291-300 ◽  
Author(s):  
Dennis V. Kent ◽  
William K. Witte
Keyword(s):  
North America ◽  
Colorado Plateau ◽  
Late Triassic ◽  
Polar Wander

Displacement of Vancouver Island: paleomagnetic evidence from the Karmutsen Formation

1980 ◽  
Vol 17 (9) ◽  
pp. 1210-1228 ◽  
Author(s):  
R. W. Yole ◽  
E. Irving
Keyword(s):  
North America ◽  
Vancouver Island ◽  
Late Triassic ◽  
Polar Wander ◽  
Apparent Polar Wander Path ◽  
Individual Site ◽  
Anticlockwise Rotation ◽  
Oriented Samples ◽  
Geomagnetic Fields ◽  
The Mean

New paleomagnetic results from the Karmutsen Formation (Late Triassic) of Vancouver Island confirm the presence of two families of magnetizations (X and Y), both of which are inconsistent with known Mesozoic and Cenozoic geomagnetic fields of cratonic North America. The X magnetizations have coherent directions with the exception of a subset of five sites (the B subset). We argue that the deviation of the B subset is caused either by a 31 ± 13 °anticlockwise rotation of a small block relative to the main sampling areas or by a short-term excursion of the field. The X magnetization has an overall mean direction 008°, −33 °α95 = 6 °based on results from 147 oriented samples (usually 2 specimens from each) collected at 28 sites spanning about 6000 m stratigraphically. We interpret this as the original Late Triassic magnetization. The corresponding X paleopole (21°N, 44°E A95 = 6°) is strongly far-sided and right-handed with respect to the Mesozoic apparent polar wander path for cratonic North America. The paleolatitude indicated for Vancouver Island in the Late Triassic is either 18°N or 18°S, the latter being preferred on the grounds that it yields a more consistent pattern for Cordilleran magnetizations, but the ambiguity is still not settled. In either case the results show that Vancouver Island was far south of its present position relative to North America in the Late Triassic, thus confirming the previous results of Irving and Yole. The Y magnetizations, with more heterogenous properties, occur at 14 sites (66 oriented cores, usually 2 specimens each). Y magnetizations are generally softer than X and for this and other reasons we regard them as secondary and post-Triassic in age. Individual site poles for the Y magnetization are, with minor exceptions, right-handed and slightly far-sided with respect to the apparent polar wandering path for cratonic North America. The mean paleopole for Y magnetizations is situated at 70°N, 15°W A95 = 11°. Both the X and Y magnetizations are consistent with either northward motion of the westernmost Cordilleran elements accompanied by clockwise rotation, or with oblique translation from the southwest. The northward component of motion derived from X directions would be the same in both instances and amounts to 1300 or 4900 km depending on whether the northern or the southern paleolatitude option is chosen. Our preference is for the latter and we present arguments which suggest that Vancouver Island may have been originally derived from a region near to eastern Gondwana or from a block east of Gondwana that might have included Malaysia. The procedures used for the tectonic analysis of aberrant paleopoles are described in the Appendix.

scholarly journals Colorado Plateau Coring Project, Phase I (CPCP-I): a continuously cored, globally exportable chronology of Triassic continental environmental change from western North America

2018 ◽  
Vol 24 ◽  
pp. 15-40 ◽  
Author(s):  
Paul E. Olsen ◽  
John W. Geissman ◽  
Dennis V. Kent ◽  
George E. Gehrels ◽  
Roland Mundil ◽  
...  
Keyword(s):  
North America ◽  
Environmental Change ◽  
National Park ◽  
Colorado Plateau ◽  
Global Environmental Change ◽  
Magnetic Polarity ◽  
Late Triassic ◽  
Western North America ◽  
Petrified Forest National Park ◽  
Petrified Forest

Abstract. Phase 1 of the Colorado Plateau Coring Project (CPCP-I) recovered a total of over 850 m of stratigraphically overlapping core from three coreholes at two sites in the Early to Middle and Late Triassic age largely fluvial Moenkopi and Chinle formations in Petrified Forest National Park (PFNP), northeastern Arizona, USA. Coring took place during November and December of 2013 and the project is now in its post-drilling science phase. The CPCP cores have abundant detrital zircon-producing layers (with survey LA-ICP-MS dates selectively resampled for CA-ID-TIMS U-Pb ages ranging in age from at least 210 to 241 Ma), which together with their magnetic polarity stratigraphy demonstrate that a globally exportable timescale can be produced from these continental sequences and in the process show that a prominent gap in the calibrated Phanerozoic record can be filled. The portion of core CPCP-PFNP13-1A for which the polarity stratigraphy has been completed thus far spans ∼215 to 209 Ma of the Late Triassic age, and strongly validates the longer Newark-Hartford Astrochronostratigraphic-calibrated magnetic Polarity Time-Scale (APTS) based on cores recovered in the 1990s during the Newark Basin Coring Project (NBCP). Core recovery was ∼100 % in all holes (Table 1). The coreholes were inclined ∼60–75∘ approximately to the south to ensure azimuthal orientation in the nearly flat-lying bedding, critical to the interpretation of paleomagentic polarity stratigraphy. The two longest of the cores (CPCP-PFNP13-1A and 2B) were CT-scanned in their entirety at the University of Texas High Resolution X-ray CT Facility in Austin, TX, and subsequently along with 2A, all cores were split and processed at the CSDCO/LacCore Facility, in Minneapolis, MN, where they were scanned for physical property logs and imaging. While remaining the property of the Federal Government, the archive half of each core is curated at the NSF-sponsored LacCore Core Repository and the working half is stored at the Rutgers University Core Repository in Piscataway, NJ, where the initial sampling party was held in 2015 with several additional sampling events following. Additional planned study will recover the rest of the polarity stratigraphy of the cores as additional zircon ages, sedimentary structure and paleosol facies analysis, stable isotope geochemistry, and calibrated XRF core scanning are accomplished. Together with strategic outcrop studies in Petrified Forest National Park and environs, these cores will allow the vast amount of surface paleontological and paleoenvironmental information recorded in the continental Triassic of western North America to be confidently placed in a secure context along with important events such as the giant Manicouagan impact at ∼215.5 Ma (Ramezani et al., 2005) and long wavelength astronomical cycles pacing global environmental change and trends in atmospheric gas composition during the dawn of the dinosaurs.

Taxonomic affinities and paleogeography of Stromatomorpha californica Smith, a distinctive Upper Triassic reef-adapted demosponge

2009 ◽  
Vol 83 (5) ◽  
pp. 783-793 ◽  
Author(s):  
B. Senowbari-Daryan ◽  
G. D. Stanley
Keyword(s):  
North America ◽  
Shallow Water ◽  
Type Species ◽  
Upper Triassic ◽  
Northern Calcareous Alps ◽  
Late Triassic ◽  
Separate Species ◽  
Northern Calcareous ◽  
Siliceous Spicules ◽  
Horizontal Layers

Stromatomorpha californica Smith is a massive, calcified, tropical to subtropical organism of the Late Triassic that produced small biostromes and contributed in building some reefs. It comes from the displaced terranes of Cordilleran North America (Eastern Klamath terrane, Alexander terrane, and Wrangellia). This shallow-water organism formed small laminar masses and sometimes patch reefs. It was first referred to the order Spongiomorphidae but was considered to be a coral. Other affinities that have been proposed include hydrozoan, stomatoporoid, sclerosponge, and chambered sponge. Part of the problem was diagenesis that resulted in dissolution of the siliceous spicules and/or replaced them with calcite. Well-preserved dendroclone spicules found during study of newly discovered specimens necessitate an assignment of Stromatomorpha californica to the demosponge order Orchocladina Rauff. Restudy of examples from the Northern Calcareous Alps extends the distribution of this species to the Tethys, where it was an important secondary framework builder in Upper Triassic (Norian-Rhaetian) reef complexes. Revisions of Stromatomorpha californica produce much wider pantropical distribution, mirroring paleogeographic patterns revealed for other tropical Triassic taxa. Review of Liassic material from the Jurassic of Morocco, previously assigned to Stromatomorpha californica Smith var. columnaris Le Maitre, cannot be sustained. Species previously included in Stromatomorpha are: S. stylifera Frech (type species, Rhaetian), S. actinostromoides Boiko (Norian), S. californica Smith (Norian), S. concescui Balters (Ladinian-Carnian), S. pamirica Boiko (Norian), S. rhaetica Kühn (Rhaetian), S. stromatoporoides Frech, and S. tenuiramosa Boiko (Norian). Stromatomorpha rhaetica Kühn described from the Rhaetian of Vorarlberg, Austria shows no major difference from S. californica. An example described as S. oncescui Balters from the Ladinian-Carnian of the Rarau Mountains, Romania, is very similar to S. californica in exhibiting similar spicule types. However, because of the greater distance between individual pillars, horizontal layers, and the older age, S. oncescui is retained as a separate species. The net-like and regular skeleton of Spongiomorpha sanpozanensis Yabe and Sugiyama, from the Upper Triassic of Sambosan (Tosa, Japan), suggests a closer alliance with Stromatomorpha, and this taxon possibly could be the same as S. californica.

scholarly journals Evolution of the early Mesozoic Cordilleran arc: The detrital zircon record of back-arc basin deposits, Triassic Buckskin Formation, western Arizona and southeastern California, USA

Geosphere ◽  
2020 ◽  
Vol 16 (4) ◽  
pp. 1042-1057
Author(s):  
N.R. Riggs ◽  
T.B. Sanchez ◽  
S.J. Reynolds
Keyword(s):  
North America ◽  
Detrital Zircon ◽  
Colorado Plateau ◽  
Depositional Environments ◽  
Coarse Grained ◽  
Land Bridge ◽  
Magmatic Arc ◽  
Early Mesozoic ◽  
Northern Nevada ◽  
Back Arc

Abstract A shift in the depositional systems and tectonic regime along the western margin of Laurentia marked the end of the Paleozoic Era. The record of this transition and the inception and tectonic development of the Permo-Triassic Cordilleran magmatic arc is preserved in plutonic rocks in southwestern North America, in successions in the distal back-arc region on the Colorado Plateau, and in the more proximal back-arc region in the rocks of the Buckskin Formation of southeastern California and west-central Arizona (southwestern North America). The Buckskin Formation is correlated to the Lower–Middle Triassic Moenkopi and Upper Triassic Chinle Formations of the Colorado Plateau based on stratigraphic facies and position and new detrital zircon data. Calcareous, fine- to medium-grained and locally gypsiferous quartzites (quartz siltstone) of the lower and quartzite members of the Buckskin Formation were deposited in a marginal-marine environment between ca. 250 and 245 Ma, based on detrital zircon U-Pb data analysis, matching a detrital-zircon maximum depositional age of 250 Ma from the Holbrook Member of the Moenkopi Formation. An unconformity that separates the quartzite and phyllite members is inferred to be the Tr-3 unconformity that is documented across the Colorado Plateau, and marks a transition in depositional environments. Rocks of the phyllite and upper members were deposited in wholly continental depositional environments beginning at ca. 220 Ma. Lenticular bodies of pebble to cobble (meta) conglomerate and medium- to coarse-grained phyllite (subfeldspathic or quartz wacke) in the phyllite member indicate deposition in fluvial systems, whereas the fine- to medium-grained beds of quartzite (quartz arenite) in the upper member indicate deposition in fluvial and shallow-lacustrine environments. The lower and phyllite members show very strong age and Th/U overlap with grains derived from Cordilleran arc plutons. A normalized-distribution plot of Triassic ages across southwestern North America shows peak magmatism at ca. 260–250 Ma and 230–210 Ma, with relatively less activity at ca. 240 Ma, when a land bridge between the arc and the continent was established. Ages and facies of the Buckskin Formation provide insight into the tectono-magmatic evolution of early Mesozoic southwestern North America. During deposition of the lower and quartzite members, the Cordilleran arc was offshore and likely dominantly marine. Sedimentation patterns were most strongly influenced by the Sonoma orogeny in northern Nevada and Utah (USA). The Tr-3 unconformity corresponds to both a lull in magmatism and the “shoaling” of the arc. The phyllite and upper members were deposited in a sedimentary system that was still influenced by a strong contribution of detritus from headwaters far to the southeast, but more locally by a developing arc that had a far stronger effect on sedimentation than the initial phases of magmatism during deposition of the basal members.

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