The Late Holocene Whitecourt Meteorite Impact Crater: a Low-energy Hypervelocity Event

Introduction: Small impact events resulting in simple impact structures <100 m in diameter are common features recorded on the solid surfaces in our Solar System. Such structures are rare in Earth's impact cratering record and most are typically heavily modified by subsequent erosion or are found in remote locations. The recently discovered Whitecourt Meteorite Impact Crater (WMIC) provides significant contrast in that it is both well preserved and easily accessible. The level of preservation, age (<1.13 ka) [1] and associated meteorite fragments, scattered up to 70 m distance from the rim, suggest that this site will provide considerable data for the improvement of current models for similar structures. The Crater: The WMIC target material consists primarily of gently northeastward dipping Quaternary deglacial sediments deposited during the retreat of the Laurentide Ice Sheet. The crater formed along a narrow Holocene terrace immediately adjacent an ephemeral stream (Figure 1) [1]. The soil profile in the area is classified as an Orthic Grey Luvisol resulting from the weathering of the parent diamict [2] and extends to depths of at least 2 m. The crater shape is similar to other Barringer type (simple) structures. The bowl-shaped crater floor and crater walls do not appear to have undergone significant modification in recent history. A raised rim is only evident along the northeastern half of the crater where elevation is lowest. The southwest crater rim is 4 m higher than the northeast rim as a result of the local topography. The crater has a diameter of 36 m and a depth of 6 m as measured from a cross-section oriented parallel to the hill slope as obtained from a LiDAR-derived digital elevation model [1]. The subsurface stratigraphy at the center of the crater is presently constrained by two bore holes 4 m and 5.4 m deep. The local water table is below this depth. The stratigraphy consists of a 10 cm thick organic-rich silty soil sharply overlying a heterogeneous pebble diamict. The diamict includes clasts up to 10 cm in diameter in the upper 50 cm decreasing to 5 cm to a depth of ~2.9 m. At ~2.9 m there is a sharp transition to a clean medium sand, which continues uninterrupted to the base of the bore holes. A number of weathered meteorite fragments < 1 cm in diameter were recovered from a thin region immediately above the 2.9 m contact. No melt has been …