Extension of the Newark Geomagnetic Polarity Reference Sequence to Address Problems of the Carnian and the Middle Triassic

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ABSTRACTThe geomagnetic polarity time scale (GPTS) for the Late Triassic developed from the thick, continuous continental record from the Newark basin is based on cycle stratigraphy for 26 million years represented by the lacustrine Passaic, Lockatong and upper Stockton formations but on extrapolation of sedimentation rates for the fluvial lower Stockton Formation for which the single magnetostratigraphic record from a core hole has not been verified. Correlation of the Triassic-Jurassic boundary within the Newark succession seems secure but placements of the Norian-Rhaetian and especially the Carnian-Norian boundaries based largely on palynology have become highly problematical in attempts to merge the marine biostratigraphic and nonmarine lithostratigraphic records. Recently proposed correlations of the Carnian-Norian boundary in marine sections to the Newark sequence place this boundary in the middle of the Stockton Formation and would imply a boundary age of ~228 Ma. This is appreciably older than usually shown in geologic time scales although not precluded by available radiometric age data. If confirmed it would have major implications to our understanding of regional and global historical geology including the timing of evolution of major groups of land vertebrates like the dinosaurs and the rifting of Pangea. However, the correlation of the marine and nonmarine sequences depends strongly on the reliability of a reference polarity sequence, which needs to be validated and refined for the time represented by the lower Stockton Formation.We propose a two-pronged approach to resolving the ambiguities in the correlations between the marine Carnian and older strata and the Newark reference section: 1) paleomagnetic analysis and measurement of outcropping Stockton Formation to test and extend the polarity sequence delineated in the Princeton corehole and to link this record directly to the astronomically calibrated GPTS, and 2) paleomagnetic analysis and measurement of correlative outcropping strata of the Timesgadiouine Formation (Argana Basin, Morocco) for cycle stratigraphic control.Successful completion of this 2-year project will extend the astronomically calibrated GPTS to encompass more than 30 million years of the Late Triassic and possibly into the Middle Triassic. A precise geologic time scale has broad applicability and will, for example, provide a rare opportunity to resolve marine and nonmarine correlations over a significant and interesting interval of geologic time just prior to the breakup of Pangea, to correlate important land vertebrate faunal assemblages on a global scale, and to incorporate some of the few radiometric dates that are available for age control but which come from nonmarine sections.Our work includes collaboration with a Moroccan geologist and a significant in-kind logistical contribution from ONAREP, the Moroccan state oil company that in addition to being integral to the project itself will help build bridges between Arab and U.S. institutions during this difficult time. Finally, we will develop a web site that will include an Arabic version so that it can be used as an educational tool for both U.S. and Moroccan groups and revolve around the concept that the two areas (eastern U.S. and Morocco) are sister geological and biological provinces, now separated by an ocean, but were once part of the same vast land mass and directly adjacent to one another. U.S. undergraduates will be involved with several stages of this project in which they will get valuable experience in quantitative methods as well as exposure in the U.S. to Arab scientists and culture.