Steen River - Hypervelocity Impact Crater

Alternate Names
Local Language
Coordinates 59° 29' 34" N; 117° 40' 8" W
Notes
  1. NW Alberta, 710 km NW of Edmonton.
Country Canada
Region Alberta
Date Confirmed 1968
Notes
  1. Confirmed by the presence of PDFs in nearly all quartz grains examined (Carrigy and Short, 1968).
Buried? Yes
Notes
  1. The structure has no surface expression, as it is buried beneath undisturbed Cretaceous strata.
Drilled? Yes
Notes
  1. Anomalously shallow basement rock was encountered during wildcat drilling for oil. A cross-section of the structure with drill hole locations is found in Carrigy and Short (1968).
Target Type Mixed
Notes
  1. The sediments in the rim syncline are Middle Devonian to Carboniferous in age and are structurally complex indicating that they were involved in the impact (Ogilvie et al., 1984). The central uplift is shocked Precambrian gneiss. Wells outside the structure yielded minimum pre-impact thickness for the target Devonian succession of 1.116-1.319km (avg. 1.228km) (Walton et al., 2019).
Sub-Type Gneiss, Sedimentary
Apparent Crater Diameter (km) 25 km
Age (Ma) 108 - 383
Notes :
  1. A Mid-Albian age of ~108 Ma for the Loon River Formation located ~100 m above crater-fill breccias constrains a minimum age. The maximum age is constrained by deformed Upper Devonian strata (MacLagan et al., 2018). Additional age constraints: Using a recalculated decay constant, (Walton et al. 2016) note the 95 Ma K-Ar age is closer to 91 ± 7 Ma. The pyrolcastic vesicular melt rock actually represents an impact-melt bearing polymict breccia (Walton et al., 2016). K-Ar dating of biotite from a plutonic rock provides an age of 560 Ma. K-Ar and Rb-Sr dating of whole rock samples of pyroclastic vesicular rock samples provides an age of 95 Ma. Most likely formed in early Cretaceous time (Carrigy and Short, 1968).

Method :
  1. Stratigraphy
Impactor Type Unknown

Advanced Data Fields

Notes

Erosion
3
  1. The upper part of the crater was partially eroded and weathered before being buried by marine Cretaceous sediments. A second period of erosion filled epirogenic uplift in the post-Cretaceous time. (Carrigy and Short, 1968).
Final Rim Diameter
Unknown
Apparent Rim Diameter
25 km
  1. Slightly elliptical structure at 25 x 20 km (Winzer, 1972). (Grieve, 1987)
Rim Reliability Index
1
  1. The outer boundary is defined by a rise in the crystalline basement followed by a sharp dropoff into a rim syncline that surrounds a central uplift (Winzer, 1972). Geophysics and drill cores indicate that the central uplift is ~8 km wide at the base. Precambrian basement is uplifted by up to 1.7 km above regional levels (MacLagan et al., 2018). The central uplift is completely covered by crater-fill impactites.
Crater Morphology
Complex
Central Uplift Diameter
8km
Central Uplift Height
760 m
Uplift Reliability Index
Structural Uplift
1.7 km
Thickness of Seds
1.116-1.319
Target Age
Precambrian Palaeozoic
Marine
No
Impactor Type
Other Shock Metamorphism
Maskelynite Kink bands Toasted quartz
  1. Winzer (1972) Kink banding of biotite is observed in the more intensely shocked rocks. Many quartz grains are "stained" by a diffuse substance that is orange-brown in plane polarized light; the term toasted quartz was not used here but description is similar to and references a similar observation from the Manson impact structure (Carrigy and Short, 1968)."
Shatter Cones
No
  1. Buried impact structure (Grieve, 2006).
Planar Fractures
No
Planar Deformation Features
Yes
  1. PDF in quartz grains and feldspars (Carrigy and Short, 1968) (Winzer, 1972). PDFs in quartz contain one to five sets in nearly every grain (Carrigy and Short, 1968). PDF is quartz and feldspar (Grieve, 2006).
Diaplectic Glass
No
Coesite
No
Stisovite
No
Crater Fill
LB, MB, M
  1. Sedimentary lithic breccias, melt-bearing breccias, and dark green glassy melt rock (vesicular pitchstone) are present in core samples (Carrigy and Short, 1968). The ST003 core from the central uplift contains ~164 m thick unit of polymict melt-bearing breccia, similar to Ries suevites (MacLagan et al., 2018).
Proximal Ejecta
Distal Ejecta
Dykes
Volume of Melt
Depth of Melting
~128 m thick unit of distinct green-coloured melt-bearing, clast-rich impact breccia has been identified in the ST003 core from the central uplift (Walton et al., 2017).

References

Spot a missing reference? Submit Reference

M A Carrigy, N M Short (1968) Evidence of shock metamorphism in rocks from the Steen River structure, Alberta, Shock Metamorphism of Natural Materials, p. 367-378, Baltimore: Mono Book Corporation

A R Hildebrand, M Pilkington, R A F Grieve, R R Stewart, M J Mazur, D W Hladiuk, D Sinnott (1997) The Steen river impact structure, Alberta, Canada, Large Meteorite Impacts and Planetary Evolution(1), p. 6090, pdf

M J Mazur (1999) The seismic characterization of meteorite impact structures, p. 179, pdf

M Niccoli, A R Hildebrand, D C Lawton (2004) Seismic velocity investigation of the Steen river impact structure, northern Alberta, CREWES Research Report 16, p. 1-19

E L Walton, A H Hughes, C D K Herd (2015) Previously unrecognized impactites from the Steen river impact structure, NW Alberta, Canada: A new variety of suevite?, 46th Lunar and Planetary Science Conference, p. Abstract 2592, Lunar and Planetary Science Conference, Houston, TX

E A MacLagan, C D K Herd, E L Walton (2016) Investigation of impact melt clasts in allochthonous crater-fill deposits of the Steen river impact structure, 47th Lunar and Planetary Science Conference, p. Abstract 1641, Lunar and Planetary Science Conference, Houston, TX

E L Walton, T G Sharp, J Hu (2016) Frictional melting processes and the generation of shock veins in terrestrial impact structures: Evidence from the Steen River impact structure, Alberta, Canada, Geochimica et Cosmochimica Acta 180, p. 256-270, Elsevier Ltd, doi:10.1016/j.gca.2016.02.024

E Walton, A Hughes, E MacLagan, C D K Herd, M R Dence (2017) A previously unrecognized high-temperature impactite from the Steen River impact structure, Alberta, Canada, Geology 45(4), p. 291-294, Geological Society of America, doi:10.1130/G38556.1

E L Walton, K Long (2017) A study of hydrothermal activity associated with the Steen river impact structure, NW Alberta, Canada, 80th Annual Meeting of the Meteoritical Society (LPI Contribution No., 1987)

E A MacLagan, E L Walton, C D K Herd, M R Dence (2018) Investigation of impact melt in allochthonous crater-fill deposits of the Steen river impact structure, Alberta, Canada, Meteoritics & Planetary Science 53(11), p. 2285-2305, University of Arkansas, doi:10.1111/maps.13122

E L Walton, T G Sharp, J Hu, O Tschauner (2018) Investigating the response of biotite to impact metamorphism: Examples from the Steen River impact structure, Canada, Meteoritics & Planetary Science 53(1), p. 75-92, University of Arkansas, doi:10.1111/maps.13011

E A MacLagan, E L Walton, C D K Herd, B Rivard (2019) Hyperspectral imaging of drill core from the Steen river impact structure, Canada: Implications for hydrothermal activity and formation of suevite-like breccias, Meteoritics & Planetary Science 55(7), p. 1564-1580, University of Arkansas, doi:10.1111/maps.13388

E L Walton, N E Timms, T E Hauck, E A MacLagan, C D K Herd (2019) Evidence of impact melting and post-impact decomposition of sedimentary target rocks from the Steen river impact structure, Alberta, Canada, Earth and Planetary Science Letters 515, p. 173-186, Elsevier B.V., doi:10.1016/j.epsl.2019.03.015

M McGregor, E L Walton, C R M McFarlane, J G Spray (2020) Multiphase U-Pb geochronology of sintered breccias from the Steen River impact structure, Canada: Mixed target considerations for a Jurassic-Cretaceous boundary event, Geochimica et Cosmochimica Acta 274, p. 136-156, url, doi:10.1016/j.gca.2020.01.052

D G Burtt, G A Henkes, E L Walton (2020) The effects of carbonate decomposition on clumped isotopes from heavily altered limestone clasts in the Steen river impact structure breccia, American Geophysical Union, p. Abstract #V019-0014, url

Daniel L. Sullivan, Alan D. Brandon, James Eldrett, Steven C. Bergman, Shawn Wright, Daniel Minisini (2020) High resolution osmium data record three distinct pulses of magmatic activity during cretaceous Oceanic Anoxic Event 2 (OAE-2), Geochimica et Cosmochimica Acta 285, doi:10.1016/j.gca.2020.04.002