THE NEWARK BASIN CYCLOSTRATIGRAPHY IS NOT A DETERMINATIVE CHRONOSTRATIGRAPHY OF THE LATE TRIASSIC-EARLIEST JURASSIC

The Newark basin (New Jersey, USA) cyclostratigraphy has been identified as a floating astrochronology capable of providing a high resolution geochronometry for most of the Late Triassic and part of the Early Jurassic. Analyses of the cyclicity of Newark lithofacies from outcrops and cores has generated peak recurrence intervals, calibrated to sedimentation rates derived from varve counts in lacustrine mudstones, that yield cycles corresponding to orbital forcing at basic precession, eccentricity and long eccentricity frequencies. If these interpretations of the cycle durations are valid, the cyclostratigraphy of the Newark Basin is in effect a determinative chronostratigraphy.

The validity of cyclostratigraphy as chronostratigraphy requires, however, that the stratigraphic record is complete; i.e., no substantial erosional or depositional gaps can exist. Outcrop and core data demonstrate that portions of the Newark stratigraphy are non-cyclic, particularly in the Passaic Formation. Furthermore, seismic data of this structurally complex basin suggest that one or more unconformities may occur in the section. Correlation of the conchostracan biostratigraphy of the Newark Supergroup with the Germanic Triassic indicates that the uppermost Norian and most of the Rhaetian are missing in the Newark basin and elsewhere in the Newark Supergroup, which suggests that about 3-4 myr of Late Triassic time is not represented by the Newark cycles.

Disagreements about the numerical age of the base of the Norian highlight the limitations of using the Newark cyclostratigraphy as a determinative chronostratigraphy. Three biostratigraphic datasets (palynomorphs, conchostracans and tetrapods) identify the same position for the Norian base at the base of the Warford Member of the lower Passaic Formation in the Newark Basin. According to the Newark cyclostratigraphy, the biostratigraphically-determined Norian base is c. 217 Ma. A correlation between the Newark section and a marine section at Pizzo Mondelo in Italy based solely on magnetostratigraphy placed the Norian base much lower in the Newark Basin section, near the base of the Lockatong Formation, which is estimated by cyclostratigraphy at c. 228 Ma. Correlation to other isotopically-dated sections suggest that the actual age is between the two Newark dates.