Facies and flow regimes of sandstone-hosted columnar intrusions: Insights from the pipes of Kodachrome Basin State Park



Sandstone-hosted intrusions are found in a wide variety of environments, but remain poorly understood compared with their mudstone-hosted counterparts. In particular, they remain largely unrecognized in the subsurface, in part because they are problematic to image in seismic data. This study reports on the facies and fluid flow associated with a 20 000 km3 sandstone intrusion province in Utah, USA. Forming a small portion of this intrusion province, the intrusions cropping out in Kodachrome Basin State Park display a very wide array of facies and morphologies, factors which would make their identification in core a significant challenge. Remobilized sediment is shown to have been injected at least 200 m vertically from its source, with flow prolonged enough to concentrate heavy minerals in placer-style deposits at the pipe margins. Evidence for lateral pipe migration and for associated broader fluidization regions is also presented. A new approach to estimating flow parameters in injectites is implemented herein, and indicates that previous work has overestimated velocities and flow Reynolds numbers by up to two orders of magnitude. Flow modelling suggests turbulent flow in the pipes that is consistent with field observations of erosive margins and chaotic internal structures. Post-emplacement, these pipes remained as long-term fluid conduits, as revealed by their diagenetic history, focussing and facilitating flow of extraformational fluids, despite the relatively high porosity and permeability of the aeolian host strata.