--> --> Stratigraphic Framework of the Late Devonian (Frasnian) Duperow Formation in Western and Central Montana

AAPG Rocky Mountain Section Meeting

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Stratigraphic Framework of the Late Devonian (Frasnian) Duperow Formation in Western and Central Montana

Abstract

The Late Devonian Duperow Formation comprises shallow marine carbonate and minor evaporitic strata deposited on the western margin of North America. It is a prolific oil and gas reservoir in the Alberta and Williston basins where the depositional setting and sequence stratigraphic framework of these rocks is well-documented, primarily from subsurface data but also from rocks exposed on the western margin of the Alberta basin. Equivalent strata in western and central Montana remain comparatively understudied. This research focused on filling this gap by first documenting the facies relationships of this strata, and then interpreting the sequence stratigraphic architecture. Data sets including seven measured sections, three drill cores with associated well-logs, and forty-one thin sections were used to characterize facies, parasequences, and sequences of the Duperow; and to construct a sequence stratigraphic framework. Ten lithofacies are present and combine to form six lithofacies associations that correspond to six depositional environments. Discrete changes in relative sea level facilitated deposition of individual parasequences which stacked to form seven 3rd order and two 2nd order sequences. Each of these sequences are dominated by transgressive and highstand systems tract deposits with thin to no lowstand deposits preserved. Transgression across the Central Montana Uplift did not occur until middle Duperow as evidenced by an absence of lower Duperow in this region. Prior to this time, sequences lapped out on the slope of the Idaho Foredeep to the west of the platform. In addition to hosting large reserves of oil and gas, the Duperow Formation in north-central Montana hosts a giant accumulation of CO2 at Kevin Dome. This dome has been the focus of research concerning the longterm storage of CO2 in geologic reservoirs. This study is significant toward a better understanding of these subsurface reservoirs, those hosting oil and gas and CO2.