Seeing the Forest for the Trees Across North America’s Cordilleran Foreland Megasequence

Abstract

The North American Cordilleran foreland basin once formed a contiguous succession of sedimentary rocks that extended from the Gulf of Mexico to the Arctic Ocean. Much has been published on the structural character and evolution of the Cordilleran but little on the full breadth of the foreland sedimentary fill and hydrocarbon endowment. This is largely due to post-Cretaceous structural modification and fragmentation of the foreland and confusion related to variations in stratigraphic nomenclature. This paper is an attempt to reconstruct the continental scale of the foreland basin megasequence and demonstrate the continuity and reach of the basin fill and related petroleum systems.

The Cordilleran foreland basin formed during the Sevier orogeny in Late Jurassic through Early Cretaceous time. The combination of tectonic loading and a global sea level maximum resulted in a continuous basin and seaway that extended across North America. Toward the end of the Cretaceous a change in plate motion resulted in significant tectonic modification of the foreland into many 10’s of discrete basins that have experienced varying degrees of uplift, erosion, subsidence and burial. Evidence for the continuity of the Cretaceous foreland fill is represented by numerous transgressive and regressive units that extend for 100’s to 1000’s of miles across North America. Stacked reservoir and source intervals are present across the foreland megasequence making it one of the most productive and diverse petroleum provinces in the world. To date over 25 billion bbls of oil and 200 Tcf of gas have been produced. Current production across the megasequence is over 4 mmbopd and 14 bcfgpd with upwards of 200 billion bbls of oil and gas equivalent reserves yet to be produced.

The megasequence continues to be a focus of significant activity and investment. Since the early 2000’s oil production has grown significantly through development of heavy and tight oil resources across North America. Oil sands development in Canada through surface mining and in-situ steam recovery account for most of the heavy oil production increase. Tight oil developments, enabled through multi-stage fracture stimulation of horizontal wellbores, began at scale around 2010 and have since spread across the US and Canada. In addition, future potential is being realized in Alaska through successful exploration of the Nanushuk topset play and exploration and appraisal of additional tight oil reservoirs throughout the Rocky Mountain region.

Continued success in exploration and development will rely on pushing the boundaries of what is known and employing new approaches, methods and concepts. This can be facilitated by looking at the megasequence through a larger lens in order to see through local barriers that hinder deeper interrogation of analogues and the transfer of knowledge and best practices.

AAPG Datapages/Search and Discovery Article #90374 © 2020 AAPG Rocky Mountain Section Meeting, 2020 Vision: Turn Hindsight to Foresight, Grand Junction, Colorado, September 13-15, 2020 (CANCELLED)