What Do We Know about the Magnetostratigraphy across the Triassic-jurassic Boundary?

Rocks deposited across the Triassic-Jurassic boundary (TJB) are preserved in several areas, including eastern North America (Newark Supergroup), the United Kingdom (St. Audrie’s Bay), Morocco (central High Atlas), Paris Basin (Montcornet), Turkey (Oyuklu), Argentina (Neuquen Basin), parts of the Colorado Plateau and adjacent areas of western North America (e.g., Moenave Formation). Despite considerable analysis of these sections, including but not limited to biostratigraphy, geochemistry, and magnetostratigraphy, correlations among these stratigraphic sections continue to generate questions about the definition of the TJB, timing of extinction events, widespread volcanism associated with the Central Atlantic Magmatic Province (CAMP), and the state of the geomagnetic field during this time period. Parts of the global polarity time scale (GPTS) are calibrated to marine magnetic anomalies recorded in oceanic crust, yet the oldest oceanic plates are too young to provide data to attempt to calibrate the latest Triassic to earliest Jurassic GPTS. Strata from terrestrial and marine basins reflect variations in depositional environments, sedimentation rates, and biological preservation, and thus complicate efforts at universal correlation of all TJB sections. We present a review and evaluation of published magnetostratigraphic records that include, but do not necessarily span, the time period between (about) the Norian/Rhaetian (NR) boundary to near the Hettangian/Sinemurian (HS) boundary and use this review as a framework by which to analyze new magnetostratigraphic data currently being obtained (L. Donohoo-Hurley, PhD dissertation in progress, 2007) from previously unsampled sections of the Moneave Formation located both on and off the Colorado Plateau in southwestern Utah, and northern Arizona. In this discussion, we adhere to the nomenclature of Opdyke and Channell (1996), where a polarity zone is a magnetostratigraphic polarity unit with duration between 106 and 107 Ma; the geochronologic (time) equivalent is a chron, and the chronostratigraphic equivalent is a chronozone. Similarly, for shorter duration (105 to 106 Ma) features, the terms polarity subzone, subchron, and subchronozone, respectively, apply.