RED WING IMPACT STRUCTURE
by: Charles O’Dale
- Type: Probable complex
- Age Ma: 200 ± 25 a
- Diameter: 9.1 km
- Location: N 47° 36’ W 103° 33’
a Estimates from stratigraphy. Red Wing Creek produces (oil) from disrupted Mississippian beds, the impact event there is not Mississippian in age but occurred later-in the Jurassic-Triassic in this case. Impact craters formed in middle and late Paleozoic time have been found elsewhere but are apparently absent in petroliferous regions, Donofrio 1998
The Red Wing Creek Field in the Williston Basin was discovered in 1972, and is one of a few well-known petroleum fields in the world to produce from a structure associated with a meteorite impact. Interpretation of a 3-D seismic dataset, covering 145 km2 over Red Wing Creek Field, shows that the crater has a diameter of 9.1 km and can be divided into three unique structural zones. First, the central uplift complex has a maximum diameter of 5.1 km, and consists of an uplifted central core, composed entirely of strata of the Mississippian Madison Group, and a flanking inner rim. The seismic reflectivity within the central core is poor, but well log data indicates extensive stratigraphic repetition. The central core is surrounded by an annular rim (1.7 km wide), which is structurally thickened by imbricate thrusts that dip towards the central core. This rim comprises eight distinct radial sectors, segmented by nine high-angle, reverse faults.
The second portion of the crater is a depressed annular trough with a maximum diameter of 1.5 km; its inner limit is bounded by antithetic normal faults and its outer limit by concentrically linked normal faults that dip toward the central part of the crater. This group of faults marks the edge of the third zone, the outer rim. The outer rim is slightly uplifted, relatively undisturbed, and its strata dip at a maximum angle of 8° away from the central crater.
Through detailed mapping of the stratigraphy and structural features within the Red Wing Creek seismic dataset, a multistep kinematic model of crater formation has been developed. The first step is the contact/compression stage that produced a shockwave, which propagated as deep as the Middle Devonian strata. The next stage was the excavation stage that removed the Upper Mississippian through Triassic/Jurassic section in the central crater. The final stage of formation is the modification stage, which produced most of the structural features, present in the crater’s final morphology (folding, outward directed thrusting, and radial faulting), due to the interaction of the inward collapsing crater walls and the outward collapsing central uplift complex (Herber 2010).
Earlier geophysical studies indicated that this subsurface structure has a central uplift, surrounded by an annular crater moat, and a raised rim. Breccias were encountered during drilling between ∼2000 and 2800 m depth in the central uplift area, and the presence of shatter cone fragments in drill core samples was suggested to indicate an impact origin of the Red Wing Creek structure. The petrographic and geochemical characteristics of samples of well cuttings from two boreholes at the center of the structure were studied. Planar deformation features (PDFs) in quartz with up to three sets of different crystallographic orientations were found in sandstone- and siltstone-dominated samples. The relative frequencies of the orientations indicate a shock pressure of at least 12–20 GPa. These results provide unambiguous evidence for shock metamorphism at Red Wing Creek and confirm that the structure was formed by impact (Koeberl et al 1996).
From Donofrio 1981:
The Red Wing structure is divided into three main provinces: a central uplift surrounded by a ring depression which in turn is surrounded by an outer rim. These are summarized below:
1. The central uplift is about 6.5km in diameter and consists of a chaotic arrangement of thrust faults, moderate- to steep-dipping beds, and overturned beds. Based on log correlations, the structural pattern is interpreted as having a 1.6km diameter inner zone of intense deformation and uplift, away from which deformation decreases in both horizontal and downward directions. Within this area of maximum deformation which has created a mega-breccia, Mississippian carbonates have been thrust as much as 915m above regional subsurface elevation. The main oil productive area of the structure is confined to this mega-breccia. The original 22X-28 “dry well”, however, is an exception; it was later recompleted as an oil well by another operator.
2. The ring depression is a syncline or graben which surrounds the central uplift. It is approximately 1.6km wide and is bounded by deformed rocks of the outer rim. The principal deformation evident in the ring depression is normal faulting, with fault blocks having moved inward towards the central uplift as well as downward. Displacements in the upper horizons range from 175 to 115m below expected regional elevations, and as much as 975m below equivalent formations in the central uplift.
3. The outer rim surrounds the ring depression and is composed of mildly-deformed rocks. Formations in this area are 90-185m structurally higher than their equivalents in the ring depression. A discontinuous narrow anticline with 45-60m of closure parallels the boundary between the rim and ring depression. Seismic investigation has shown that it has a width of less than 1.6km at its widest location.
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