77-2 Boxworks and streamers: Paleo-fluid flow features in the Navajo sandstone

Session: Boxwork and Fracture Halos: Changes in mineralogy and erosion resistance around fracture features on Earth, Mars, and across the Solar System

Presenting Author:

Basil Tikoff

Authors:

Tikoff, Basil¹, Bozikis, Grace Marie², Lee, Elizabeth Elene³, Reiners, Peter W.⁴, Hiett, Coleman⁵, McIntosh, Jennifer C.⁶, Guo, Tong⁷

(1) Geoscience, University of Wisconsin - Madison, Madison, Wisconsin, USA, (2) Geoscience, University of Wisconsin - Madison, Madison, Wisconsin, USA, (3) Geoscience, University of Wisconsin - Madison, Madison, Wisconsin, USA, (4) University of Arizona, Tucson, AZ, , (5) Barr Engineering Co., Durango, CO, , (6) University of Arizona, Tucson, AZ, , (7) University of Arizona, Tucson, AZ, ,

Abstract:

The Escalante River drainage is well-studied for the presence of iron-oxide/manganese-oxide cemented structures, including boxwork structures (boxworks).  Rapid incision of the Colorado River over the past few million years exposed evidence of past fluid-flow and fluid-rock reaction in a paleo-aquifer system.  Groundwater moved downgradient from the Aquarius Plateau in a SSE direction toward the Colorado River (a 2.3 km vertical drop).  Ongoing reactive transport modeling indicates that the groundwater, interacting with CH₄ and CO₂ from gas reservoir in the Escalante Anticline, reduced hematite grain coatings in the sandstone and transported Fe²⁺ downgradient.  Fe²⁺-enriched fluids migrated along the vertical joint, mixing with oxygenated groundwater, to reprecipitate Fe oxide cements.

As part of a larger effort to understand the subsurface microbe-rock-fluid systems, we have mapped out boxworks, streamers, and pipes in the Jurassic Navajo sandstone.  Boxworks are elongate structures with multiple joints within them, that range in length from m to 10s of m, with a width and high occurring on the m scale.  Boxworks are typically horizontal elongated.  We characterize boxworks as non-strataform or strataform.  Strataform boxwork structures occur along major stratigraphic bounding surfaces in the aeolian sandstone; non-strataform boxwork structures cut across bedding planes.  Interior cores of boxwork structures commonly contain calcite cement, low concentrations of transition metals, and concave-up REE patterns.  In contrast, exterior rinds are densely Fe-oxide cemented, display concave-up REE patterns, and have higher concentrations of REEs, U, V, and As.  The complexly patterned mantle regions of boxwork have intermediate compositions, but relatively high Cu.  One model for the origin of these features involves Fe-precipitation around large carbonate concretions, perhaps caused by migration of low-pH and/or -Eh water. Streamers are zones of yellow staining, which are associated with boxworks and pipes, but also exist independently of these features.  In specific locations, the streamers are constrained to be tunnel-shaped, with m-scale length and width dimensions and 10 m-scale length dimensions.  Critically, boxworks appear to form within streamers, such that streamers are observed both up-gradient (to the NNW) and down-gradient (to the SSE) of boxwork structures.  Our tentative conclusion is that the streamers appear to be channelized paleo-fluid flow that exerted a primary control on the formation of the boxworks.

 

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