STATISTICAL COMPARISONS OF SUBMARINE FAN DEPOSITS DURING REMNANT OCEAN - FORELAND BASIN TRANSITION: EXAMPLES FROM THE OUACHITA MOUNTAINS, USA

Submarine fans at collisional continental margins record the interactions of deposition, tectonics, and paleogeography, but a comprehensive understanding of such systems is often limited by structural complexity and low preservation potential. This study interrogates an extensive outcrop dataset using a suite of statistical methods to characterize the influence of increasing tectonic confinement and structural complexity on submarine fan deposition. The Jackfork Group and Atoka Formation in the Ouachita Mountains, USA, recorded the submarine fan deposition from a late remnant ocean basin phase (Jackfork) to an early foreland basin phase (Atoka) during the Pennsylvanian Ouachita Orogeny. The Jackfork and the lower Atoka submarine fan systems are both laterally confined and primarily axially sourced from the east and seem quite similar at the system scale. However, detailed facies analysis using 119 measured sections (8702m) demonstrates many key differences related to the variable boundary conditions during deposition. For example, the downcurrent facies trend of the Jackfork is characteristic of classical submarine fan models, whereas the facies trends of the lower Atoka are more complex, with wedge-top being more stable and the foredeep being more variable. From remnant ocean to foreland phase, the statistical comparisons show that there is an increase in lobe deposits by 88%, an increase in the mud bypass and stratigraphic orderliness (using Markov Chains metrics) in more confined regions, and an increase in the strength of longer periodicities of sandstone recurrence. We interpret that the observed changes in stratigraphic architecture are related to more prominent allogenic (i.e., tectonic) controls on deposition during the basin transition, which is consistent with the regional tectonic and structural history. The methods and results established by this study quantify the stratigraphic record of a passive-active margin transition and can be used to improve the understanding of analogous submarine fan systems along the Appalachian-Ouachita Orogeny and in other structurally complex basins around the world.