Magnetostratigraphy Dating and Correlation of the Lower Doig and Upper Montney Formations (Lower Triassic), Northeastern British Columbia, Western Canada (original) (raw)
Related papers
Earth and Planetary Science Letters, 1991
Stratotypes defining the stages of the Early Triassic (Griesbachian, Dienerian, Smithian and Spathian) are located on Ellesmere and Axel Heiberg islands in the northern Canadian Arctic. Ammonite-rich horizons are within a clastic outer shelf-to-slope facies of thick progradational wedges of mudstones and siltstones. Three sections were sampled for magnetostratigraphy and interpreted for transgressive and regressive pulses of sedimentation. Using the ammonite zonation as a guide, the transgressive-regressive cycles and magnetostratigraphies have been correlated among the sections and to the published Triassic sequence stratigraphy time scale, thus enabling definition of the magnetic polarity pattern for the upper Griesbachian to Smithian stages in multiple sections. The magnetic polarity and associated sequence stratigraphy pattern for the lower Griesbachian and for the Spathian were derived from single sections. The Griesbachian and Dienerian stages each have two pairs of normal-and reversed-polarity chrons; the Smithian is predominantly of normal polarity, and the Spathian is predominantly of reversed polarity. This magnetic polarity time scale may help to resolve age correlations of North American redbed facies and to define the Permian-Triassic boundary.
Canadian Journal of Earth Sciences, 2001
Three classic sections of Middle and Late Triassic fossiliferous limestones cropping out around Williston Lake in British Columbia, Canada, were sampled for paleomagnetic study. The objective was to test the suitability of these units for detailed magnetobiostratigraphic study with the aim of improving the reference Triassic geomagnetic polarity time scale. The Williston Lake characteristic magnetizations differ, however, from any Triassic North America cratonic reference directions. A satisfactory agreement is found instead with Cretaceous -early Cenozoic North America cratonic reference directions. The exclusive occurrence of normal polarity suggests that remagnetization likely occurred during the Cretaceous long normal superchron. Remagnetizations may have been triggered by connate brines, which moved along aquifers of porous sandstones and carbonates in the early stages of Laramide folding.
Three classic sections of Middle and Late Triassic fossiliferous limestones cropping out around Williston Lake in British Columbia, Canada, were sampled for paleomagnetic study. The objective was to test the suitability of these units for detailed magnetobiostratigraphic study with the aim of improving the reference Triassic geomagnetic polarity time scale. The Williston Lake characteristic magnetizations differ, however, from any Triassic North America cratonic reference directions. A satisfactory agreement is found instead with Cretaceous -early Cenozoic North America cratonic reference directions. The exclusive occurrence of normal polarity suggests that remagnetization likely occurred during the Cretaceous long normal superchron. Remagnetizations may have been triggered by connate brines, which moved along aquifers of porous sandstones and carbonates in the early stages of Laramide folding.
Journal of Geophysical Research, 1995
Paleomagnetic study of about 2400 samples from nearly 7 km of core recovered at seven drill sites in the Newark continental rift basin of eastern North America provides a derailed history of geomagnetic reversals and paleolatitudinal motion for about 30 m.y. of the Late Triassic and earliest Jurassic (Carnian to Hettangian). Northward drift of only about 7 ø is recorded in the continental sediments and minor interbedded basaltic lavas in the basin, from 2.5 ø to 6.5 ø north paleolatitude in the Carnian and from 6.5 ø to 9.5 ø north paleolatitude over the Norian-"Rhaetian" and the early Hettangian. A total of 59 polarity intervals, ranging from about 4 m to over 300 m in thickness, have been delineated in a composite stratigraphic section of 4660 m. The lateral continuity and consistent relationship of lithological lake level cycles and magnetozones in the stratigraphically overlapping sections of the drill cores demonstrate their validity as time markers. A geomagnetic polarity timescale was constructed by scaling the composite section assuming that lithostratigraphic members in the predominant lacustrine facies represent the 413-kyr orbital periodicity of Milankovitch climate change and by extrapolating a sedimentation rate for the fluvial facies in the lower part of the section; a 202 Ma age for the palynological Triassic/Jurassic boundary was used to anchor the chronology based on published concordant radiometric dates linked to the earliest Jurassic igneous extrusive zone. Geomagnetic polarity intervals range from about 0.03 to 2 m.y., have a mean duration of about 0.5 m.y., and show no significant polarity bias. The cyclostratigraphically calibrated record provides a reference section for the history of Late Triassic-earliest Jurassic geomagnetic reversals. Correlations are attempted with available magnetostratigraphies from nonmarine sediments from the Chinle Group of the southwestern United States and marine limestones from Turkey. Recent and is based on the analysis of marine magnetic anomaly profiles from the global ocean [e.g., Cande and Kent, 1992; Gradstein et al., 1994]. The relative spacing of polarity intervals is established from the anomaly patterns and is calibrated in time by correlation to magnetostratigraphic sections with biostratigraphy, radiometric dates, and now by cyclostratigraphy [e.g., Shackleton et al., 1990; Hilgen, 1991]. Because of the absence of seafloor and hence marine magnetic anomalies, a geomagnetic polarity reference scale for pre-Jurassic time is much less well developed and requires long, continuous magnetostratigraphic sections with good chronostratigraphic control from the continents. A very thick sequence of lacustrine and fluvial sediments is represented in the Newark Basin, one of the largest of a chain 1Now at Paper number 95JB01054. 0148-0227/95/95 JB-01054505.00 of Mesozoic rift basins that developed along the margin of eastern North America in the early stages of formation of the Atlantic Ocean [Manspeizer, 1988]. Deposition in the basin is now known to span much of the the Late Triassic to earliest Jurassic [Cornet and Olsen, 1985] and was punctuated only by a brief igneous intrusive and extrusive episode just after the Triassic/Jurassic boundary [Olsen and Sues, 1986; Fowell et al., 1994] and dated at 201-202 Ma [Sutter, 1988; Dunning and Hodych, 1990]. The lacustrine sediments that constitute much of the Newark Basin section record climatically induced lake level variations reflecting Milankovitch orbital forcing [Van Houten, 1964; Olsen, 1986]. These climatic cycles constitute a basis for detailed lithostratigraphic correlation as well as chronological scaling. Early paleomagnetic work on Newark Supergroup rocks focused on the igneous units and found mostly normal polarity magnetizations [e.g., DuBois et al., 1957; Opdyke, 1961; Smith and Noltmier, 1979]. This contributed to the concept of a quiet or long normal polarity interval in the Late Triassic and Early Jurassic [McElhinny and Burek, 1971; Perchesky and Khramov, 1973; Irving and Pullaiah, 1976; Haq et al., 1988]. More extensive sampling of the Newark Basin sedimentary section has revealed the presence of numerous polarity reversals [Mclntosh et al., 1985; Witte and Kent, 1989, 1990; Witte et al., 1991]. The Newark Basin section thus provides an opportunity to obtain a cyclostratigraphically scaled, high-resolution timescale of 14,965 14,966 KENT ET AL.: NEWARK MAGNETOSTRATIGRAPHY AND PALEOLATITUDES .E••North America •ewark Basin: Africa (Pang•ea position) NBCP drill sites projected onto A-A' and B-B' of Figure lb. Late Triassic and earliest Jurassic geomagnetic polarity reversals. Outcrop exposure is, however, typically poor and discontinuous due to the low relief and urbanized setting of the basin. This difficulty was addressed by the National Science Foundation-sponsored Newark Basin Coring Project (NBCP) which resulted in the recovery of a virtually complete stratigraphic section through the thick continental rift basin sequence of central New Jersey from seven stratigraphically overlapping drill cores. The lithostratigraphy and cyclostratigraphy of the NBCP cores are described by Olsen et al. [1995] and Olsen and Kent [1995]. The paleomagnetism of the NBCP cores is reported here.
Journal of Geophysical Research, 1995
The Spences Bridge Group is a mid-Cretaceous (104 Ma) volcanic succession in the southern Intermontane Belt of the Canadian Cordillera (50.5øN,121øW). It comprises the Pimainus Formation (mafic to felsic lava, volcaniclastic and interbedded epiclastic rocks) and the overlying Spius Formation (andesitic lava flows). Including previous work, we have 55 sites distributed among 15 localities representing most of the > 3000 m thickness. Forty-seven sites (286 oriented cores, 457 specimens), mainly andesites, yielded acceptable data. The beds are gently to moderately tilted, partly due to synvolcanic deformation. Samples taken from a sequence of flows at any one locality have, with one exception, well-grouped magnetization directions. Polarities are all normal, as expected for rocks laid down in the Cretaceous Normal Superchron. Declinations always are clockwise of that expected of cratonic North America, indicating 60 ø rotation of the Spences Bridge Group as a whole. However, declinations differ from locality to locality, implying relative interlocality rotations about vertical axes. Hence inclination-only analysis has been used to estimate dispersion, mean inclination, and paleolatitude. Minimum dispersion for the Spius Formation (27 sites) was achieved after 80% untilting, but the changes between 80 and 100% untilting are insignificant, indicating that magnetization was acquired predominantly before tilting. By contrast, minimum dispersion for the Pimainus Formation (20 sites) was achieved after 50% untilting, indicating that magnetization was acquired after synvolcanic tilting when buried beneath the overlying Spius Formation. Polished thin section studies show that magnetite in the Pimainus Formation has undergone extensive low temperature hydrothermal alteration, whereas magnetite in the Spius Formation shows little alteration. Throughout the range of tilt correction, from 0% to 100%, the mean inclinations of both formations were less than expected from observations obtained from mid-Cretaceous rocks of cratonic North America. The best estimate of paleolatitude (from the Spius Formation) is 50.8 ø q-5.0 ø (P=0.05), which is 9.5ø-t-5.7 ø less than would be expected had the rocks had been rigidly attached to North America. This corresponds to displacement from the south of 1100 q-600 km. Displacement between the northern Intermontane Belt and craton probably was accommodated along major strike-slip faults (Northern Rocky Mountain Trench, Finlay, Pinchi etc.). In the south, our results require a major dextral fault (the Intra-Quesnellia fault) to be situated during Late Cretaceous or Paleocene time within or marginal to the Omineca Belt, along which about 1000 km of dextral motion occurred. This could be a southern extension of the Pinchi Fault whose trace is now obscured by Eocene extension and tectonic denudation. The results also indicate that the largest tectonic discontinuity in the Canadian Cordillera occurs not to the east of the Intermontane Belt, as commonly assumed, but to the west, because the displacements relative to cratonic North America observed from the Intermontane Belt are only about one third of those observed from the Coast Belt. Introduction The Canadian Cordillera is divisible into five morphotectonic belts [Wheeler et al., 1991]. The Foreland Belt comprises mainly Precambrian to Mesozoic miogeoclinal strata which were folded and thrust toward the continent in
Geological Society of America Bulletin, 1997
A magnetic polarity stratigraphy and a corresponding paleomagnetic pole position are reported from 113 sampling sites representing 3000 m of Upper Triassic continental sedimentary rocks that crop out in the Dan River-Danville basin of North Carolina and Virginia. Characteristic magnetizations isolated by thermal demagnetization for either the hematite-bearing red siltstones or the interbedded magnetite-bearing gray to black mudstones of the Leakesville Formation are indistinguishable in mean direction and pass reversal tests. The magnetic polarity sequence consists of 11 magnetozones that vary from ≈100 m to 800 m in thickness and can be uniquely correlated within biostratigraphic constraints to magnetochrons E9n to E14n of the Newark geomagnetic polarity time scale. According to this correlation, the sampled section is the age equivalent of the uppermost Stockton, the entire Lockatong, and the lowermost Passaic formations of the Newark basin, and represents ≈7.5 m.y. of deposition. The late Carnian Dan River-Danville paleopole is located at 55.4°N 100.1°E (A 95 = 1.9°), which is not significantly different from paleopoles reported from essentially coeval rocks in the Newark basin. Considering that the Dan River-Danville and Newark basins are ≈600 km apart, the close agreement of the coeval paleopoles argues strongly for the overall tectonic coherence of these rift basins with respect to each other and, most probably, with respect to cratonic North America. Discordant latest Triassic paleopoles from the southwestern United States, which have tended to be attributed to fast apparent polar wander for North America in the Late Triassic and predict anomalously high paleolatitudes for eastern North America, are best accounted for by a large net clockwise rotation of the Colorado Plateau.
The geomagnetic polarity timescale for the Triassic: linkage to stage boundary definitions
Geological Society, London, Special Publications, 2010
Studies of Triassic magnetostratigraphy began in the 1960s, with focus on poorly fossilferous nonmarine red-beds. Construction of the Triassic geomagnetic polarity timescale was not consolidated until the 1990s, when access to magnetometers of sufficient sensitivity became widely available to measure specimens from marine successions. The biostratigraphically-calibrated magnetostratigraphy for the Lower Triassic is currently largely based on ammonoid zonations from Boreal successions. Exceptions are the Permian–Triassic and Olenekian–Anisian boundaries, which have more extensive magnetostratigraphic studies calibrated by conodont zonations. Extensive magnetostratigraphic studies of nonmarine Lower Triassic successions allow a validation and cross-calibration of the marine-based ages into some nonmarine successions. The Middle Triassic magnetostratigraphic timescale is strongly age-constrained by conodont and ammonoid zonations from multiple Tethyan carbonate successions, the conclus...
Tectonophysics, 2000
The~190±5 Ma Big Creek hornblende-syenite and monzogabbro batholith has an outcrop area of~400 km2 within the Yukon-Tanana Terrane (YTT) in the west-central part of the Yukon Territory of Canada. Paleomagnetic analysis of 245 specimens from 21 sites isolates a characteristic remanent magnetization residing principally in magnetite and subordinately in hematite. The unit mean direction for the batholith from 16 normal polarity and two reverse polarity sites is D=305.6°, I=72.1°(a 95 =3.9°). Al-in-hornblende geothermobarometry at six locations yields emplacement depths of~16±2 km. Three arguments suggest that the characteristic remanent magnetization was acquired on exhumation at~180 Ma. More significantly, the pole position indicates no northward translation but counterclockwise rotation, implying that the YTT formed close to its present position on the Jurassic margin of the North American craton. This implies, in turn, that the allochthonous terranes of the Intermontane and Coast belts of the western Cordillera impacted onto, and overrode, the YTT upon accretion during Late Cretaceous to Middle Eocene time.