Late Triassic‐earliest Jurassic geomagnetic polarity sequence and paleolatitudes from drill cores in the Newark rift basin, eastern North America

Abstract

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 detailed 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° is recorded in the continental sediments and minor interbedded basaltic lavas in the basin, from 2.5° to 6.5° north paleolatitude in the Carnian and from 6.5° to 9.5° 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.

Magnetostratigraphy-based astronomical tuning of the early Pliocene lacustrine sediments of Ptolemais (NW Greece) and bed-to-bed correlation with the marine record

“…Lacustrine sediments in particular can give valuable information on the palaeoclimate and -environment, as demonstrated by Kent et al [9] and Olsen et al [10] in the Triassic Newark Basin. The sedimentary cycles they studied have frequencies similar to the present day values for astronomical variables.…”

A model of rift basin evolution constrained by first‐order stratigraphic observations

“…However, the northern North Sea graben exhibit a similar pattern: a succession of fluvial and shoreline sandstones overlain by deep marine turbiditic deposits followed by a sandier upward sequence deposited in shallower marine environments [Prosser, 1993]. Even in some basins with complex sedimentary histories, such as the Jeanne d'Arc whose sediments record marine incursions, it is possible to demonstrate by analysis of stratal patterns (and thus independent of lithofacies) high initial rates of subsidence in early phases of tectonic activity which give place to condensed sections followed by a shoaling upward trend [Driscoll and and Kent, 1996a], which has provided a paleomagnetic stratig-Faulting and Flexure Model raphy and most importantly a very accurate temporal reference frame for Late Triassic-Early Jurassic times [Kent et al, 1995]; and (5) this cyclicity also has allowed the calculation of sedimentation rates with a level of resolution of 104 years.…”

Climatically driven biogeographic provinces of Late Triassic tropical Pangea

“…Their mutually exclusive abundance patterns and similar trophic adaptations suggest they could be ecological equivalents. Paleomagnetic polarity correlations (8,11,30,31) and occurrences from multiple levels within several of these basins demonstrate that these disparate assemblages are broadly coeval, and that the traversodont-dominated assemblages occur in strata deposited within a few degrees of the equator, whereas procolophonid-dominated assemblages are found in higher tropical to subtropical latitudes. Thus, the differences between the assemblages suggest strong biotic provinciality, on a continent where an ambitious tetrapod could theoretically have walked from the Triassic location of Sydney to Vladivostok.…”