Astronomical tuning, astronomical forcing and environmental conditions of the Lower Triassic Montney Formation, northeastern British Columbia, Canada

Abstract

Astronomical cyclicity calculated from a X-ray fluorescence (XRF) dataset from the biostratigraphically-constrained cyclic lithology of the distal Montney Formation at the c-65-F/94-B-8 core in northeastern British Columbia, generated a new astronomical time scale (ATS) for the entire Early Triassic. This ATS for the Lower Triassic Montney Formation provides dates for substages and stages (base-Dienerian at 251.1 Ma; base-Olenekian at 250.0 Ma; base-Spathian at 248.8 Ma; base-Anisian at 247.0 Ma) as well as an independent time calibration for the durations and rates of Early Triassic sedimentation and biotic recovery after the end-Permian mass extinction. This ATS compares closely with similar time-series analyses from South China demonstrating its potential for future global correlation. Moreover, two ecologically significant intervals (mid-late Dienerian and early Spathian), which show regular high frequency cyclicity in carbonate content, revealed a dominant obliquity signal that affected environmental and biotic changes. Lastly, this project has economic impact since the Montney Formation is a major natural gas play in Canada. A better understanding of environmental controls on cyclicity and of sedimentation rates will contribute to correlation and aspects of mechanical properties of the rocks.