--> Tectonic Subsidence Analysis and Evolution of the Pennsylvanian to Early Permian Oquirrh Basin, Utah

AAPG ACE 2018

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Tectonic Subsidence Analysis and Evolution of the Pennsylvanian to Early Permian Oquirrh Basin, Utah

Abstract

The Oquirrh Basin is a Pennsylvanian to Early Permian mixed clastic and carbonate basin exposed in northwestern Utah. The basin is the northwestern-most expression of the Ancestral Rocky Mountains orogeny, and locally contains up to 9 km of sediment. The subsidence history and tectonic drivers of the basin are poorly constrained. To better understand the subsidence and tectonic history of the Oquirrh Basin, tectonic subsidence analysis was performed on 12 published stratigraphic sections across the Oquirrh basin. This analysis allows for an estimation of subsidence due to tectonic activity where tectonic settings are reflected in subsidence curve shapes.

Curve profiles can be categorized into three main groups due to similarity in tectonic subsidence curves and geographical location. Within the basin, total subsidence decreases to the west, from 2500-3500 m in the eastern section, to 1900-2500 m in the central section, decreasing to 500-2000 m in the west. Though the highest total subsidence is in the east, the location of maximum subsidence rate changes through time. The highest subsidence rates occurred during the Desmoinesian and Missourian stages, focused in the east and central sections. Tectonic subsidence curves reflect proximity to crustal loading, with loading to the east resulting in highest subsidence rates in the east with less effect to the west along an identifiable subsidence gradient. During Virgilian time the gradient reversed, with the highest subsidence rates in the west, decreasing eastward.

We interpret at least two phases of tectonism based on the subsidence analysis. Rapid subsidence in the eastern and central Oquirrh basin during Desmoinesian to Missourian time is interpreted as flexural response to a fixed load on the eastern side of the Oquirrh Basin based on the convex-upward shape of the curves and the decrease in subsidence rates and magnitudes toward the west. Virgilian subsidence rate increases in the western Oquirrh Basin are interpreted as flexural loading from the west based on curve shape. This event may be part of the uplift and unconformity sequence documented in the Antler Overlap basins of northeastern Nevada. Therefore, subsidence in the Oquirrh Basin appears to be responding to tectonism on both the eastern and western margins through time.