COLVILLE BASIN RESPONSE TO ARCTIC TECTONICS AND CLIMATE: 3rd AND HIGHER ORDER APTIAN-ALBIAN DEPOSITIONAL SEQUENCES

The architecture of Brookian 2^nd order depositional sequences reflects tectonic forcing at timescales of 40-60 m.y. The relationship between higher order sequences and specific tectonic and/or climatic forcing at 10 m.y. to sub-m.y. timescales, however, has been obscured by imprecise chronostratigraphy, qualitative metrics, and the local extent of studies.

The 3^rd order Torok-Nanushuk sequence represents the world’s most voluminous (1.2 million km³), highest relief (>1 km thick), and longest (600 km west-east) foreland clinoform depositional sequence. This sequence filled relict Colville basin accommodation that had developed as a flexural response to earlier Brooks Range tectonic loading. We established chronostratigraphy for the sequence with detrital zircon U/Pb geochronology from 9 sites and intend to present new results from 9 additional sites. Maximum depositional ages defined by young detrital zircon U/Pb age populations, likely derived from coeval volcanism in Russian Chukotka, become progressively younger in the direction of eastward progradation. These data reveal a progradational surge between 115 and 106 Ma when the shelf margin prograded more than 450 km. Rapid progradation (~50 km/m.y.) and sediment flux (~111,000 km³/m.y.) were sustained for 9 m.y. and suggest a supply-dominated system. Progradation slowed after 106 Ma when seismic stratigraphy shows a shift from progradational to aggradational shelf-margin trajectories. The shelf margin prograded only another 125 km eastward before a retrogradation overlying the sequence boundary began at 95 Ma.

We estimate ~400 kyr cyclicity for the Brookian 4^th order clinoform sequences. This estimate is equivalent to the periodicity of Aptian-Albian sea-level fluctuations observed in the stable Arabian Peninsula as well as deep water sedimentation and carbon cyclicity. These observations have been attributed to the 405 kyr long eccentricity orbital signal that modulated insolation throughout the Mesozoic. We suggest that deposition of the 4^th order Brookian clinoform sequences was orbitally paced via insolation-driven fluctuations in sea-level and perhaps hydrology. If this hypothesis is validated by our new data, it may provide a predictive tool to tune sequence stratigraphy for petroliferous Arctic basins.