ASSESSING THE INTERACTION OF DISTAL FORELAND TECTONICS AND ICEHOUSE EUSTASY ON SEQUENCE ARCHITECTURE, UPPER DESMOINESIAN - LOWER MISSOURIAN, MID-CONTINENT, NA

The influence of foreland tectonics as a control on Pennsylvanian sediment thickness trends and gross facies distribution patterns across the greater Arkoma Basin has been recognized for decades. However, identifying specific foreland tectonic elements (foredeep, forebulge, back-bulge) and the evolution of these elements through the Middle and Upper Pennsylvanian has proven problematic. The goal of this study is to link the highly variable facies and stratal architecture of Upper Desmoinesian – Lower Misssourian high frequency sequences (HFS) to these evolving foreland basin elements.

Upper Desmoinesian HFSs within the lower Marmaton Group display a significant foredeep with no meaningful development of a forebulge/back-bulge pair. However, the overlying Holdenville and Seminole formations display subtle but distinctive facies and thickness variations indicative of a growing forebulge in northern Oklahoma. This includes partitioning of the HFS lowstands north and south of the forebulge in the incipient back-bulge and foredeep basins, respectively. Lower Missourian HFSs of the Coffeyville Formation show no evidence of the forebulge, as starved foredeep facies extend up-dip into aggradational shelf margins of the craton margin. The upper Coffeyville lowstand packages show some potential facies partitioning north and south of the incipient forebulge. This forebulge becomes very well developed in the overlying HFSs as portions of the LST and all of the TST and HST of the Dennis HFS are beveled beneath the Hogshooter HFS, yet are preserved north and south of the forebulge. The Hogshooter itself develops a thick carbonate mound complex atop the forebulge with the overlying Block/Cherryvale HFS draped directly atop the mound system. The overlying Nelly Bly LST of the Dewey HFS buries the forebulge, but displays a two – fold increase in thickness into the foredeep to the south. The overlying Dewey HST develops a thick algal mound complex in the same position as the Hogshooter mound, which then thins into the foredeep to the south.

While glacial eustasy is the dominant control on HFS development in the Pennsylvanian, it is clearly critical to identify the underlying subtle tectonic elements within the basin in order to fully interpret facies distribution and systems tract geometry within these sequences.