MAGNETIC POLARITY STRATIGRAPHY AND ROCK MAGNETISM OF THE CONTINUOUS CORES OF THE TRIASSIC MOENKOPI FORMATION STRATA RECOVERED FROM THE COLORADO PLATEAU CORING PROJECT (CPCP) PHASE 1

The Triassic and Jurassic periods have experienced several significant events in Earth history and the parts of the time interval are calibrated by the widely accepted Late Triassic-Early Jurassic Astrochronostratigraphic Polarity Timescale (APTS); mostly based on cores from the Newark Basin Coring Project (NBCP), which lacks in radioisotopic age dates and has significant gaps in biostratigraphically-based age controls. The interdisciplinary Colorado Plateau Coring Project (CPCP) phase-I, conducted in Fall, 2013, at Petrified Forest National Park, is providing high precision U-Pb zircon maximum depositional ages and a recoverable magnetic polarity stratigraphy for over 830 m of stratigraphically overlapping core material obtained from the Upper Triassic (Norian) Chinle and the Lower to Middle Triassic Moenkopi formations. This study concentrates on the Moenkopi Formation intersected in cores 1A (214 specimens) and 2B (320 specimens) from the ~87 m recovered Moenkopi strata in each core.

The red, fine-grained Moenkopi Fm rocks produced less variable NRM intensities (~2 – 8 mA/m) and bulk susceptibilities (~5.0 x 10 ^–5 – 3.0 x 10 ^–4 SI volume units), whereas the Chinle Fm have highly variable NRM intensities (0.07 – 128.7 mA/m) and bulk susceptibilities (~ 2 x 10^-2 - 5 x 10^-5 SI volume units). Our results show that well over 80% of the specimens yield unambiguous interpretable shallow northerly (normal) and shallow southerly (reverse) characteristic remanent magnetization (ChRM) with an average maximum angular deviation (MAD) values of 5°. Preliminary magnetic polarity stratigraphy model shows that the lower most part of the magnetic polarity stratigraphy correlates very well with the magnetic polarity study from the surface exposures of Moenkopi Fm in northeastern Arizona, a close proximity to the CPCP cores. Some core segments yield internally consistent, well-resolved magnetizations with unexpected declinations, which could be due to the orientation inaccuracies during coring. Core reorientation using CT-XRay data and bedding/core geometries should correct these results; and with additional sampling to fill the gaps in Moenkopi sequence in both cores should yield a very high resolution magnetic polarity stratigraphy and high-resolution timescale for this important time period.