Magnétochronologie des formations rocheuses du Mont Mégantic et des environs, Québec méridional

1985 ◽  
Vol 22 (4) ◽  
pp. 487-497 ◽  
Author(s):  
Maurice K.-Seguin ◽  
B. St-Hilaire
Keyword(s):  
Late Cretaceous ◽  
The Other ◽  
Field Observations ◽  
Magnetization Component ◽  
Paleomagnetic Study ◽  
Intrusive Rocks ◽  
Normal Polarity ◽  
Reversed Polarity ◽  
Radiometric Ages ◽  
Devonian Age

A paleomagnetic study was made to elucidate the ambiguities of the radiometric ages of Mont Megantic intrusions in relation to field observations and to determine the magnetochronology of the intruded rocks. Some 179 samples (550 specimens) were collected over 58 sites, and their magnetization was cleaned by thermal and (or) alternating field treatment. The paleopoles obtained for the Compton Formation metasediments indicate an Early to Middle Devonian age and for the overlying Frontenac Formation metavolcanics indicate an age definitely different from that for the intrusive rocks. The baked contact test on the hornfels forming the contact metamorphic aureole is positive, and the magnetization component was acquired in the Early to Late Cretaceous interval. Syenite contains two components: one with normal polarity, the other with reversed polarity; their ages are Juro-Cretaceous. The gabbro contains only one magnetization component (reversed), which was acquired in the Early Cretaceous, whereas the granite bears one component with a mostly normal polarity; its intrusive age is Late Cretaceous.The paleomagnetic ages for the intrusive rocks support the multiple intrusion interpretation; it appears that the emplacement of the intrusive bodies is Juro-Late Cretaceous. [Journal Translation]

Paleomagnetism and geochronology of St. Matthew Island, Bering Sea

1989 ◽  
Vol 26 (10) ◽  
pp. 2116-2129 ◽  
Author(s):  
Paul R. Wittbrodt ◽  
David B. Stone ◽  
Donald L. Turner
Keyword(s):  
Late Cretaceous ◽  
Bering Sea ◽  
Large Scale ◽  
Flow Units ◽  
Intrusive Rocks ◽  
Normal Polarity ◽  
Reversed Polarity ◽  
Shelf Region ◽  
Bering Sea Shelf ◽  
The Bering Sea

Oriented samples from a series of flow units, pyroclastics, tuffs, tuff breccias, and some intrusive rocks from St. Matthew Island were studied paleomagnetically in an attempt to constrain possible paleolatitudes of the Bering Sea shelf. The volcanic sequences have apparently stable magnetic directions and contain a reversed–normal–reversed–normal polarity succession.The Late Cretaceous paleolatitude deduced from the paleomagnetic data was 67°N, and the island has rotated in a clockwise sense by a nominal 10°. This implies that the rocks analyzed were formed about 12 °south of their present location with respect to cratonic North America. These data argue against tectonic models for the Bering Sea shelf region that require large-scale Late Cretaceous and Tertiary latitude changes.New K–Ar age dates combined with previously reported K–Ar ages give a best estimate of the age of the St. Matthew volcanic units of about 78.7 ± 0.4 Ma. The reversed–normal–reversed polarity changes are thought to represent part of the sequence seen between marine anomalies 32 and 33 that are usually assigned an age of about 74 Ma, which appears to be about 5 Ma too young.

scholarly journals Chronological implications of the paleomagnetic record of the Late Cenozoic volcanic activity along the Moravia-Silesia border (NE Bohemian Massif)

2012 ◽  
Vol 63 (5) ◽  
pp. 423-435 ◽  
Author(s):  
Vladimír Cajz ◽  
Petr Schnabl ◽  
Zoltan Pécskay ◽  
Zuzana Skácelová ◽  
Daniela Venhodová ◽  
...  
Keyword(s):  
Bohemian Massif ◽  
Multidisciplinary Approach ◽  
Field Survey ◽  
Volcanic Field ◽  
Late Cenozoic ◽  
Paleomagnetic Study ◽  
Normal Polarity ◽  
Reversed Polarity ◽  
Scoria Cones ◽  
Age Determinations

Abstract This paper presents the results of a paleomagnetic study carried out on Plio-Pleistocene Cenozoic basalts from the NE part of the Bohemian Massif. Paleomagnetic data were supplemented by 27 newly obtained K/Ar age determinations. Lavas and volcaniclastics from 6 volcanoes were sampled. The declination and inclination values of paleomagnetic vectors vary in the ranges of 130 to 174 and -85 to -68° for reversed polarity (Pleistocene); or 345 to 350° and around 62° for normal polarity (Pliocene). Volcanological evaluation and compilation of older geophysical data from field survey served as the basis for the interpretation of these results. The Pleistocene volcanic stage consists of two volcanic phases, fairly closely spaced in time. Four volcanoes constitute the Bruntál Volcanic Field; two others are located 20 km to the E and 65 km to the NW, respectively. The volcanoes are defined as monogenetic ones, producing scoria cones and lavas. Exceptionally, the largest volcano shows a possibility of remobilization during the youngest volcanic phase, suggested by paleomagnetic properties. The oldest one (4.3-3.3 Ma), Břidličná Volcano, was simultaneously active with the Lutynia Volcano (Poland) which produced the Zálesí lava relic (normal polarity). Three other volcanoes of the volcanic field are younger and reversely polarized. The Velký Roudný Volcano was active during the Gelasian (2.6-2.1 Ma) and possibly could have been reactivated during the youngest (Calabrian, 1.8-1.1 Ma) phase which gave birth to the Venušina sopka and Uhlířský vrch volcanoes. The reliability of all available K-Ar data was evaluated using a multidisciplinary approach.

scholarly journals Remagnetization of Upper Jurassic limestones from the Danubian Unit (Southern Carpathians, Romania): tectonic implications

2012 ◽  
Vol 63 (6) ◽  
pp. 453-461 ◽  
Author(s):  
Panaiotu Cristian G. ◽  
Panaiotu Cristina E. ◽  
Lazăr Iuliana
Keyword(s):  
Remanent Magnetization ◽  
Upper Jurassic ◽  
Relative Rotation ◽  
Clockwise Rotation ◽  
Magnetization Component ◽  
Diagenetic Processes ◽  
Tectonic Implications ◽  
Paleomagnetic Study ◽  
Normal Polarity ◽  
Southern Carpathians

Abstract We present a pioneering paleomagnetic study on Upper Jurassic limestones from the Danubian Unit (Southern Carpathians, Romania). Thermal and alternating field demagnetizations were applied to define the characteristic remanent magnetization component in all six localities (81 samples). All samples have a normal polarity characteristic remanent magnetization. Negative regional and local fold tests suggest that this remanent magnetization is in fact a remagnetization produced by late diagenetic processes. The studied limestones were probably remagnetized during the collision of the Getic Unit and Danubian Unit which took place during the long normal polarity Chron C34 (82-118 Ma). The area mean direction (D = 75.5°, I = 50.0°, α95 = 10.2°, k = 44) implies about 75° clockwise rotation post remagnetization. Our paleomagnetic results further indicate the absence of significant relative rotation between the Getic Unit and the Danubian Unit during the Cenozoic.

Paleomagnetism of the Notre Dame Bay lamprophyre dikes, Newfoundland, and the opening of the North Atlantic Ocean

1979 ◽  
Vol 16 (9) ◽  
pp. 1823-1831 ◽  
Author(s):  
P. L. Lapointe
Keyword(s):  
Thermal Treatment ◽  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Tectonic Setting ◽  
The Other ◽  
The North ◽  
Paleomagnetic Study ◽  
Normal Polarity ◽  
The North Atlantic

Lamprophyre dikes and the Leading Tickles dunite from Notre Dame Bay. Nfld., were sampled for a paleomagnetic study to define their age relationships and the tectonic implications of their emplacements. A single normal polarity direction (328°, +62°) was obtained by alternating field and thermal treatment, from 10 Cretaceous lamprophyre dikes. The paleopole (2I2°E, 67°N) derived from these dikes agrees with the cluster of North American Cretaceous paleopoles. On the other hand. I he Leading Tickles dunite recorded two magnetizations: one (206°, +32°) related to the time of intrusion and interpreted to be Ordovician; the second one (000°, +66°). an overprint, is related to the intrusion of the lamprophyre dikes and interpreted to be Cretaceous. The polarity, paleopole, radiometric age, and tectonic setting of the lamprophyre dikes when compared with the Isachsen dikes. N.W.T., suggest the opening of the North Atlantic Ocean was initiated in the Lower Cretaceous.

Paleomagnetism of tills and associated paleosols in southwestern Alberta and northern Montana: evidence for Late Pliocene–Early Pleistocene glaciations

1995 ◽  
Vol 32 (5) ◽  
pp. 555-564 ◽  
Author(s):  
M. T. Cioppa ◽  
E. T. Karlstrom ◽  
E. Irving ◽  
R. W. Barendregt
Keyword(s):  
North America ◽  
Early Pleistocene ◽  
Pleistocene Glaciations ◽  
Glacial Deposits ◽  
Late Pliocene ◽  
Carbonate Cement ◽  
Paleomagnetic Study ◽  
Normal Polarity ◽  
Reversed Polarity ◽  
Initial Deposition

Sequences of pre-Wisconsinan till and intercalated paleosols were sampled for paleomagnetic study. The tills were deposited during successive glaciations and the paleosols formed during interglacial intervals. Paleoargillic horizons of the paleosols and the carbonate cement (calcrete) found in some till–paleosol units generally yielded excellent data. Magnetizations of paleosols probably were acquired during the formation of the paleosols rather than during initial deposition of the tills in which they were developed. At Mokowan Butte (Alberta), the lowest paleosol has normal polarity, two of the middle tills have reversed polarity, and the uppermost till–paleosol unit has normal polarity. At Saint Mary Ridge (Montana), three of the lower tills have reversed polarity, and the upper two till–paleosol units have normal polarity. At Two Medicine Ridge (Montana), the lowest three tills are reversed, but the paleoargillic horizon on the uppermost (fourth) till is normal. Magnetostratigraphic correlation indicates that at least six glacial and six interglacial episodes are represented in the Kennedy Drift. The upper normal polarity units are interpreted as having been developed during the Brunhes Normal Chron, the underlying reversed polarity sediments during the Matuyama Reversed Chron, and the lowest normal polarity unit at Mokowan Butte during the Gauss Normal Chron. The oldest glaciations here extend into the Pliocene (2600 ka), making these sediments among the oldest glacial deposits in North America. Alternatively, the lowest normally magnetized paleosol at Mokowan Butte may have formed during either the Jaramillo or the Olduvai subchrons, although this is considered less likely.

Defining a paleomagnetic polarity pattern in the Monteregian intrusives

1979 ◽  
Vol 16 (9) ◽  
pp. 1716-1725 ◽  
Author(s):  
J. Foster ◽  
D. T. A. Symons
Keyword(s):  
Stability Index ◽  
Pole Position ◽  
End Points ◽  
Paleomagnetic Study ◽  
Normal Polarity ◽  
Reversed Polarity ◽  
Remanence Direction

Oka and nearby small plutons on the western end of the Monteregian Hills were sampled for paleomagnetic study at 43 sites (569 specimens). Every specimen was AF step demagnetized in 4 kA/m increments to 20 or 24 kA/m. Consistent remanence directions were found for 36 sites (452 specimens). Use of a stability index to select only those specimens with the best defined end points does not improve the site statistics. The Oka, Brilund, Carillon, and Ile Cadieux plutons have statistically similar mean remanence direction populations which are different from the Ste. Dorothée sill direction. Except for one Carillon site, all site mean directions are normally polarized, whereas all nine plutons, except for Mt. Johnson, from the middle and eastern end of the Monteregian Hills are reversely polarized. Normally and reversely polarized plutons give statistically similar but antiparallel pole positions, giving a combined pole position of 169.0°W, 72.4°N (δp = 2.8°, δm = 3.7°), which is consistent with the 120 ± 4 Ma radiometric age. The polarity pattern evidence suggests that Oka and adjacent plutons were emplaced rapidly during one normal polarity interval, and that the Monteregian Hills plutons were emplaced progressively from west to east during two normal and two reversed polarity intervals lasting ~ 2 Ma. This leads to some speculations on the plume and rift modes of emplacement.

Multi-Aged Small Pterosaur Track Assemblage from the Upper Cretaceous of Korea

2021 ◽  
Author(s):  
Jongyun Jung ◽  
Min Huh ◽  
Koo-Geun Hwang ◽  
Hyun-Joo Kim ◽  
Byung-Do Choi ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
Korean Peninsula ◽  
Upper Cretaceous ◽  
Global Distribution ◽  
The Other

Abstract The pterosaur is the earliest and largest powered flying vertebrate, even earlier and larger than the other extant archosaurian group, birds. However, evidence for this flying reptile, including the diversity of the small-sized pterosaur after the mid-Cretaceous, and their ecology, has remained elusive. Here we present numerous and dense pterosaur track assemblages from the Hwasun Seoyuri tracksite in the Upper Cretaceous Jangdong Formation of the Neungju Basin in Korea. The pterosaur track assemblage, assigned to Pteraichnus isp., consists of various sized, randomly oriented manus-dominated tracks with several pes claw marks. These features commonly indicate the semi-aquatic behavior and multi-age gregariousness of pterosaurs. The supposed trackmaker of pterosaur tracks would be the small-sized pterodactyloid that inhibited the Late Cretaceous Korean Peninsula, but that has not previously been reported. This ichnological evidence for the global distribution of small-sized pterosaurs could be interpreted to mean that the pterosaur fauna in the Late Cretaceous was more distributed and diverse than was previously known.

scholarly journals Tectonic influence on axial-transverse sediment routing in the Denver Basin

2022 ◽  
Author(s):  
Glenn R. Sharman ◽  
Daniel F. Stockli ◽  
Peter Flaig ◽  
Robert G. Raynolds ◽  
Marieke Dechesne ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
Detrital Zircon ◽  
Foreland Basin ◽  
The Other ◽  
Front Range ◽  
Denver Basin ◽  
Dispersal Patterns ◽  
Magmatic Arc ◽  
Sedimentary Sequences ◽  
Basin Fill

ABSTRACT Detrital zircon U-Pb and (U-Th)/He ages from latest Cretaceous–Eocene strata of the Denver Basin provide novel insights into evolving sediment sourcing, recycling, and dispersal patterns during deposition in an intracontinental foreland basin. In total, 2464 U-Pb and 78 (U-Th)/He analyses of detrital zircons from 21 sandstone samples are presented from outcrop and drill core in the proximal and distal portions of the Denver Basin. Upper Cretaceous samples that predate uplift of the southern Front Range during the Laramide orogeny (Pierre Shale, Fox Hills Sandstone, and Laramie Formation) contain prominent Late Cretaceous (84–77 Ma), Jurassic (169–163 Ma), and Proterozoic (1.69–1.68 Ga) U-Pb ages, along with less abundant Paleozoic through Archean zircon grain ages. These grain ages are consistent with sources in the western U.S. Cordillera, including the Mesozoic Cordilleran magmatic arc and Yavapai-Mazatzal basement, with lesser contributions of Grenville and Appalachian zircon recycled from older sedimentary sequences. Mesozoic zircon (U-Th)/He ages confirm Cordilleran sources and/or recycling from the Sevier orogenic hinterland. Five of the 11 samples from syn-Laramide basin fill (latest Cretaceous–Paleocene D1 Sequence) and all five samples from the overlying Eocene D2 Sequence are dominated by 1.1–1.05 Ga zircon ages that are interpreted to reflect local derivation from the ca. 1.1 Ga Pikes Peak batholith. Corresponding late Mesoproterozoic to early Neoproterozoic zircon (U-Th)/He ages are consistent with local sourcing from the southern Front Range that underwent limited Mesozoic–Cenozoic unroofing. The other six samples from the D1 Sequence yielded detrital zircon U-Pb ages similar to pre-Laramide units, with major U-Pb age peaks at ca. 1.7 and 1.4 Ga but lacking the 1.1 Ga age peak found in the other syn-Laramide samples. One of these samples yielded abundant Mesozoic and Paleozoic (U-Th)/He ages, including prominent Early and Late Cretaceous peaks. We propose that fill of the Denver Basin represents the interplay between locally derived sediment delivered by transverse drainages that emanated from the southern Front Range and a previously unrecognized, possibly extraregional, axial-fluvial system. Transverse alluvial-fluvial fans, preserved in proximal basin fill, record progressive unroofing of southern Front Range basement during D1 and D2 Sequence deposition. Deposits of the upper and lower D1 Sequence across the basin were derived from these fans that emanated from the southern Front Range. However, the finer-grained, middle portion of the D1 Sequence that spans the Cretaceous-Paleogene boundary was deposited by both transverse (proximal basin fill) and axial (distal basin fill) fluvial systems that exhibit contrasting provenance signatures. Although both tectonic and climatic controls likely influenced the stratigraphic development of the Denver Basin, the migration of locally derived fans toward and then away from the thrust front suggests that uplift of the southern Front Range may have peaked at approximately the Cretaceous-Paleogene boundary.

scholarly journals Age of the Post-rift Sequence I from the Araripe Basin, Lower Cretaceous, NE Brazil: implications for spatio-temporal correlation

2021 ◽  
Vol 24 (1) ◽  
pp. 37-46
Author(s):  
João Carlos Coimbra ◽  
Tiago Menezes Freire
Keyword(s):  
Critical Review ◽  
Lower Cretaceous ◽  
Temporal Correlation ◽  
Isotopic Analysis ◽  
The Other ◽  
Stratigraphic Framework ◽  
Spatio Temporal ◽  
Radiometric Ages ◽  
The One ◽  
Do So

A robust biostratigraphic zonation based on microfossils supports the stratigraphic framework and correlation of the interior basins of the Lower Cretaceous of NE Brazil. This zonation has also allowed correlations with coeval sections in the Brazilian marginal basins and in the Gabon and Congo basins (central-west Africa). These records, consisting mainly of non-marine sediments, were a great challenge with regard to the correlation with the International Chronostratigraphic Chart. Therefore, local stages were used, the most recent being the Alagoas local Brazilian Stage, with which the Post-rift Sequence I of the Araripe Basin is related. Regarding lithostratigraphy, this sequence includes the Rio da Batateira (Barbalha for some authors) and Santana formations, the last one with the famous Crato, Ipubi, and Romualdo members, from the base to the top. Although currently there is a consensus on the age of the Alagoas local Brazilian Stage in the Araripe Basin, recently a new age for at least part of the Post-rift Sequence I was proposed. This new proposal, based on isotopic analysis of Re-Os, arose as a panacea to correlate the Rio da Batateira Formation and the Crato and Ipubi members with the international stages. Surprisingly, their authors, although on the one hand, they seem to underestimate biostratigraphic results, on the other they seek to support their proposal from microfossils studied by previous authors, but they do so in an inappropriate way, leading readers to misinterpret their results. Therefore, this paper presents a critical review on the age of the Alagoas local Brazilian Stage in the Araripe Basin and nearby basins, refuting a Barremian age for part of the Post-rift Sequence I. Keywords: Alagoas local Brazilian Stage, biostratigraphy, ostracods, palynomorphs, radiometric ages.

Magnetostratigraphic dating of late Miocene megalake regressions in Central Eurasia 

2021 ◽  
Author(s):  
Wout Krijgsman ◽  
Dan Palcu ◽  
Irina Patina ◽  
Ionuț Șandric ◽  
Sergei Lazarev ◽  
...  
Keyword(s):  
Late Miocene ◽  
Salt Lake ◽  
Global Ocean ◽  
Water Volume ◽  
Forest Steppe ◽  
Short Term ◽  
Central Eurasia ◽  
Normal Polarity ◽  
Partial Desiccation ◽  
Reversed Polarity

<p>The largest megalake in the record formed in Eurasia during the late Miocene, when the epicontinental Paratethys Sea became tectonically-trapped and disconnected from the global ocean. The Paratethys megalake was characterized by several episodes of hydrological instability and partial desiccation, but the chronology, magnitude and impacts of these paleoenvironmental crises are poorly known. The Panagia section on the Taman Peninsula of Russia is the only place known to host a continuous sedimentary record of the late Miocene hydrological crises of Paratethys. Paleomagnetic measurements allow the development of a polarity pattern that can be used to date the regression events. The Panagia polarity pattern consists of 17 polarity intervals, 9 of normal polarity and 8 of reversed polarity, plus 4 additional short-term polarity fluctuations, that are inferred to correspond to the 11-7.5 Ma interval. We identified four major regressions that correlate with aridification events, vegetation changes and faunal turnovers in large parts of Europe. Our paleogeographic reconstructions reveal that Paratethys was profoundly transformed during the regression episodes, losing ~1/3 of the water volume and ~70% of its surface during the most extreme events. The remaining water was stored in a central salt-lake and peripheral desalinated basins while vast regions (up to 1.75 million km2) became emerged land, suitable for the development of forest-steppe landscapes. The dry episodes of the megalake match with climate, food-web and landscape changes throughout Eurasia but the exact triggers and mechanisms remain to be resolved.</p>

Sign in / Sign up

Export Citation Format

Share Document